Future Road Track Racing Motorcycle (MotoGP) Wheelbases Will Be Far Longer

(c) Copyright 2011 David Dilworth

“Science is organized common sense where many a beautiful theory was killed by an ugly fact.” -Thomas Henry Huxley

Formula 1 Ferrari Inside Tyre Unloaded - Credit: F1-pics.com

Formula 1 Ferrari Inside Tyre Unloaded
Credit: F1-pics.com

When Elden Racing Cars owner Brian Hampsheir hired me as Designer-Engineer to recapture their glorious former racing car fortunes, I received the opportunity to interview their previous designer. He provided lots of good engineering history and perspective, but he claimed as fact one jaw-droppingly false physics/engineering idea.

He did not understand weight transfer for race cars. In fact he had it backwards. He believed that the more weight transfer side-to-side – the faster a car could corner. I believe he even bragged that Elden’s Formula cars were narrower than all of our competitors.

Weight Transfer Brief
Weight transfer occurs when during cornering, braking and accelerating – the weight (or load carried) on each tyre changes due to cornering, braking or accelerating.

The (weight transfer) load increases during cornering on the outside tyres, during acceleration on the back tyres, and during braking on the front tyres.

Conversely the load decreases (sometimes to zero) during cornering – on the inside tyres, during braking on the back tyres, and during acceleration on the front tyres.

You’ve probably seen a motorcycle or bicycle performing a “wheelie.” A wheelie is an extreme version of weight transfer where all the weight from the front tyre is transferred to the back tyre.

Formula 1 Ferrari Inside Tyre Unloaded

Formula 1 Ferrari Inside Tyre Unloaded – Credit: F1-pics.com

Another common example occurs during high-g cornering when racing cars sometimes lift one or both of their inner tyres off the ground.

Nose Stand (c) David Dilworth

Nose Stand / Stoppie (c) David Dilworth

A rarer type is when a racing motorcycle lifts its rear wheel off the ground during braking, called a “Stoppie.” Alarmingly, this can occur at any speed — even when exceeding 150 mph or more – though rarely as dramatic as this photo.

Somehow Elden’s former designer had acquired the backwards belief that for faster cornering more weight transfer is better.

In road racing reality (physics) the reverse is true. Less weight transfer means higher performance. The less sideways weight / mass load a tyre has – the better it can resist the load.

Wider Car = Less Weight Transfer = Faster Cornering

The wider a car is (its “track”, the sideward distance between wheels) the less weight transfer during cornering. This gives more traction and faster cornering.

The reason is that instead of just the outside tyre doing most or all of the work – the inside tyres are contributing traction more equally. More weight transfer makes the outside tyres take more load. Less weight transfer allows the inside tyres to help with the cornering. Similarly the longer the wheelbase, the less weight transfer during braking and accelerating.

I wonder if my design predecessor was confusing vertical tyre loads (or pressures) with sideways tyre loads.

Sideways loads are almost purely from weight-mass of the vehicle. We always want to minimize sideways loads (at least those loads towards the outside of a turn).

All cars and motorcycle tyres have vertical loads from the weight / mass of the vehicle. Non-mass vertical loads come from aerodynamics: wings, body shape and ground effects. Tyre traction does increase with increased non-mass (aerodynamic) vertical loads, but it generally decreases with increased weight-mass sideways loads.

This is why we always want to maximize non-mass vertical loads and minimize mass loads.

  • Summary of Generalities
    Weight/Mass Transfer = Bad (or slow)
    Aerodynamic (vertical) downforce = Good (motorcycles don’t yet use aerodynamic downforce – but that’s for another article)

The result of this misunderstanding was the older Elden racing cars were too narrow. The short version is : wider car = faster around corners, narrow car = slower around corners.

Well, that made my first contribution to Elden easy. I increased the track of the cars by several inches and with no surprise (to me anyway) — the otherwise identical cars immediately went around corners faster and had faster laps times at Brands Hatch. (Same engine, tyres and driver in dry conditions.)

So what does that have to do with racing motorcycles?

The same misunderstanding or tradition appears to be going on in racing motorcycles, but in a different direction. With the Formula cars the problem was side-to-side weight transfer was too high. With racing bikes the problem is way too much back-to-front weight transfer.

It couldn’t be more obvious that there is far too much weight transfer – because it is so painfully easy to get a bike to do a wheelie – and lift the rear wheel during braking.

(Take a look at this video of Casey Stoner going off track at Laguna Seca in 2008 because his rear tyre “got light” while braking — and then ask him if he thinks eliminating nose stand dynamics might be worth investigating.)

Once I braked too hard going into Sears Point’s Turn Two slightly leaned over at maybe 105 mph. It hard to forget the odd feeling of the Kawasaki 350’s rear tyre trying to join me up front — without any sliding . . . :-( . . . Yes, I made it around the corner; a bit slow, eyes wide open, but otherwise just fine.

Cornering Wheelie - Hayden Laguna Seca 2011

Cornering Wheelie – Hayden Laguna Seca 2011

Here’s a photo I took of Nicky Hayden on his MotoGP bike at Laguna Seca this weekend. His front tyre is off the ground – while he is still cornering hard. That means his bike has all its weight transfered to the rear tyre.

While this does not hinder his acceleration much (because the front tyre doesn’t provide any propulsion) this does mean all cornering power from the front wheel is lost; and because he is accelerating this also reduced the cornering power of his rear tyre.

Cornering Wheelie (Tyre off ground) Closeup

Cornering Wheelie (Tyre off ground) Closeup

Because a longer wheelbase would lessen weight transfer with the same acceleration – the front tyre could still be on the ground providing (more than zero) cornering power. Within limits, the longer the wheelbase – the more the front tyre adds cornering power while accelerating.

Faster Acceleration and Braking
Consider for a moment — What is the limit to how hard a racing bike can brake? Because 2011 racing tyres are so sticky and disk brake systems are now adequate, it no longer has anything to do with tyre friction or effective brakes.

Answer: The limit is when the rear tyre lifts off the ground and bike control is sharply decreased. As noted above braking too hard with the current short wheelbase MotoGP bikes and the rear tyre lifts off the ground – even at speeds above 150 mph. I’m guessing that even makes Kenny Roberts a bit squeamish.

Same thing for acceleration – what is the limit to MotoGP acceleration? Answer: The point at which the bike wheelies and steering control is lost.

Both of these limits can be removed by increasing the bike’s wheelbase; and the improvement will be noticeable and measurable.

Part of the reason a longer wheelbase works is it lowers the front to back “dynamic center of gravity.”(2)

The “dynamic center of gravity” is different than, and somewhat independent of, the standard center of gravity. The dynamic center of gravity is the standard center of gravity related to the horizontal distance to where the tyres touch the ground. This means that by lengthening the wheelbase you can have the same standard center of gravity height, yet have a lower “dynamic center of gravity.”

The lower the center of gravity in any direction – the less weight transfers – and the more friction the tyres can deliver.

While a short wheelbase may help street bikes’ walking speed maneuverability, and let you park in smaller spaces, a longer wheelbase will allow MotoGP bikes to lap notably faster by accelerating out of corners faster and braking harder into corners.

Of course if you make the wheelbase (or track width for cars) too large other problems may show up. However, I don’t believe we are anywhere near that limit for racing bike wheelbases.

I suspect MotoGP bikes could increase their wheelbase by 20% to 30% to 50% and maybe more without any significant side effects. There could be other benefits because there will be more room to put components. (Does a larger fuel tank attract anyone? or bigger, but lighter batteries for electric racing bikes.)

Brock's Long Wheelbase BMW S 1000 RR

Brock’s Long Wheelbase BMW S 1000 RR

Take a look at this long wheelbase bike which was called the “quickest and fastest stock bike in the world” improving upon the otherwise identical short-wheelbase version which was merely quick.

I realize this BMW in the photo is intended for drag racing, not road racing, but you might pause and consider – why do drag bikes and cars (dragsters) need long wheelbases?

The main reason is outlined in this article – weight transfer. Imagine a car dragster with 2,000+ horsepower — on the short wheelbase of a street car. How would it handle that power? It would be difficult to prevent a wheelie, just like on a motoGP bike. In any case the driver would not be able to use the full amount of power available to the wheels – just as MotoGP riders cannot always use full throttle or full braking – even when not cornering.

Longer Bike = Less Weight Transfer = Faster Accelerating, Braking and Cornering
There is no doubt in my mind that significantly lengthening MotoGP wheelbases would provide notably stronger braking, faster acceleration and slightly better cornering.

More subtle benefits should be improved control (and rider confidence) when combining braking and cornering, and when accelerating during cornering.

Update: After Colin Edwards tested a longer wheelbase: “I’ve gone back to a longer wheelbase setting … the longer wheelbase has made it probably the best bike I’ve ever been on for the last part of this track.” (1)

Update: I’ve been thinking about how to test whether a wheelbase is long enough. My first guess/hypothesis is – if a bike can easily do either a nose stand or a wheelie – the wheelbase is too short.

Sweden's Ghost Rider has Wheelie Record of 180 mph

Sweden’s Ghost Rider has Wheelie Record of 180 mph

My reasoning is that – a nose stand and a wheelie are overwhelming proof of total weight transfer – which is the opposite of what we want.

Formula 1 cars don’t wheelie or nose-stand and they have about the same power-to-weight ratio as MotoGP bikes ~ 1.4 pounds per horsepower. The big differences are wheelbase (and polar moment of inertia which is closely related) and center of gravity height. While center of gravity height has some bike racing tradeoffs, a mildly longer wheelbase does not.

I look forward to when we can all race bikes where we can brake and accelerate as hard as possible and both tyres stay on the ground – especially during cornering. We’ll leave today’s short wheelbase bikes in our dust.

While this article is copyrighted, there is no patent on this concept. This concept of longer wheelbases is free for anyone to use. Free, as in free beer ! Which I’ll be buying for everyone at the finish line when the first road racing bike using this concept wins a major race. For real.

_______________________

References:
1. Full quote from Colin Edwards:

“It was a reasonable day without being spectacular. I’ve gone back to a longer wheelbase setting I haven’t run since winter testing and it’s similar to what Valentino (Rossi) and Jorge (Lorenzo) have been running. There are some advantages and some disadvantages but I’ve still got a small issue on the front like I had during the last race in Catalunya. I’m not able to turn into the corner as quickly as I’d like, and it feels like I’m waiting on the front before I can go through the corner. But the longer wheelbase has made it probably the best bike I’ve ever been on for the last part of this track. It’s so stable in the fast sections and I’m able to make up a lot of time, so there’s some good and some bad with it.”

2. There is not yet an official engineering term “Dynamic Center of Gravity (DCoG).” This is a term I developed to relate the center of mass to the width and length of a vehicle. While there may be a better term such as “Overturning Moment“, this term has the advantage that it is easy to remember (and makes some sense as it is related to a lower CoG). The lower the DCoG, the more effective a road racing car’s or motorcycle’s tyres are for turning and braking.

Additional reading:
Weight Transfer — A good overview from the perspective of Formula 1 racing cars. (There’s only one tiny error – that has no bearing on bike dynamics.)

Note:
Street Bikes Too: I remember getting surprised with a road bike cornering wheelie – when I upshifted a bit too sharply with a passenger on the back. (One slight difference between my cornering wheelie and Hayden’s is — I wasn’t sliding the rear tyre on asphalt – the fraction of a second previous to my wheelie. ;-)

This entry was posted in Dynamics, Education, Engineering, Physics, Racing, Simple Solutions Ignored, Vehicles and tagged , , , , , , , , , , , , . Bookmark the permalink.

19 Responses to Future Road Track Racing Motorcycle (MotoGP) Wheelbases Will Be Far Longer

  1. Pingback: "Stretched" MotoGP Bikes?!?

  2. Pingback: Replace Car Batteries Instantly – No Charging | Design: Leading Edge

  3. Lothar says:

    Yeah.
    That makes a lot of sense.
    Funny how I never thought about that. I expected that racing bike wheelbases were already optimized. But now that I think about how easy it is to wheelie, and how limiting that is. Wish I was still racing. I’d love to test a long wheelbase motogp bike.

    • David says:

      Thank you for your note Lothar.
      I’ll email you and everyone who writes in when I learn someone is testing this concept.

  4. Eddie says:

    You are wrong about the motorcycles, the shorter wheel base is needed for agility and corner speed. If the track was a simple oval with only two turns then the bikes might be longer. Motogp corner speeds are faster than ever and wheelies are now controlled with electronics but as you should know everything is a compromise. The bikes have been getting smaller and smaller.

    • David says:

      Thank you for your several thoughtful opinions.

      It is not widely understood except by those of us who have done the experiments that agility is not affected in the least by wheelbase length. Seriously. In a moment I’ll describe a demonstration you can do at home so you demonstrate it for yourself.

      Similarly, different wheelbase lengths make no difference to maximum steady-speed cornering speeds.

      However, when you add braking or accelerating during cornering — wheelbase length instantly turns very important !

      Agility is Independent of Wheelbase Length

      The primary phenomena affecting “agility” – or the ability to “flop” a bike from one lean or cornering direction to the other is — the height of its center of gravity-mass above the ground.

      (Secondary concerns are the total mass of the bike and separately the mass of the wheels. Wheels can give serious gyroscopic forces strongly resisting you leaning a bike over.)

      The higher the center of mass is above the ground – the less “agile” a bike is.

      The lower the mass the easier it is to lean from side to side; flip from one turn direction to the other – which is important for Laguna Seca’s “Corkscrew.”

      You can demonstrate this counterintuitive effect (Called Polar Moment of Inertia) at home by comparing how hard it is to balance a broomstick and a pencil straight up from your hand.

      Most people expect the shorter pencil is easier to balance, but are surprised to find that the longer broomstick is amazingly easy – and balancing the (lower center of mass) pencil is extremely difficult because it can lean over faster than you can move your hand to correct it. (Here’s a video showing how easy it is to balance things with a high center of gravity)

      The short version is —
      Low center of Gravity = High Agility and Low Stability
      High center of Gravity = Low Agility and High Stability

      No matter whether your wheelbase is short or long you can design a high or a low center of gravity. However, when you have a longer wheelbase – there is inherently more 3-D space/volume between the wheels that is closer to the ground where you can put components lower (like fuel, batteries, engines). This can allow a designer to give the longer wheelbase bike a lower center of gravity making it . . . gasp !!! — More Agile than an otherwise identical short wheelbase bike.

      Corner Speed is Independent of Wheelbase Length

      Because Motogp bikes have such a tiny amount of tyre on the ground (compared to racing cars), their pure steady-state cornering speed is primarily limited by tyre friction (assuming a bike can lean far enough to reach that limit without scraping). When cornering at a steady speed with no throttle or braking — wheelbase length has absolutely zero effect on cornering speed.

      Shorter Wheelbase Means Less Power and Braking During Cornering

      However, the moment you add in braking or accelerating while cornering the tyres’ cornering power is instantly reduced. If you add enough braking or accelerating you can lift a tyre off the ground – eliminating all its cornering power and reducing the cornering power of the remaining tyre – because one tyre is now carrying all the (not trivial) weight of the bike and you.

      A longer wheelbase bike will reduce that weight transfer, and reduce the ability of a bike to lift a tyre off the ground – thus giving a longer wheelbase bike more cornering power.

      You are arguing for my side and even underline it by saying “wheelies are now controlled with electronics” which should tell you that bikes can go faster if engine designers didn’t have to limit a bike’s silly tendency to wheelie by reducing engine power.

      Motogp corner speeds and Tyre Stickiness

      If indeed “Motogp corner speeds are faster than ever” it is certainly due to the constantly stickier tyres – not shorter wheelbases.

      If anyone believes they have any experimental evidence that MotoGP corner speeds are faster with short wheelbases, while I am skeptical, I’m also an empiricist (I believe physically testing things is superior to theorizing) so I’d be happy to look at it.

      If Motogp wheelbases are getting shorter – then the opportunity to leave current motogp bikes in the dust for a designer who actually understands physics is growing faster than I thought.

  5. Jack Russell says:

    I concur with your assessment of the pure physics and how this relates to the poor performance of current racing motorcycles, particularly braking and accelerating. I guess that manufacturers and riders are a fairly conservative lot.

    Being the first to bring out a 70 plus inch wheelbase, low c of g machine would be a big gamble and would probably be laughed at by the knee dragging, wheelie popping, endoing motorcycle fraternity. Maybe people are so used to riding “circus trick cycles”, they don’t want to consider going faster in safety.

    Problem is that racing dictates that longer wheelbased low c of g (Feet Forward) designs are not allowed in mainstream racing – until the FIM and ACU realise this – we will never see vehicles with any longer wheelbase than a Kids BMX.
    Colin R

    • David says:

      Thank you for your thoughts Colin.

      Could you please point me to where the FIM rules limit wheelbases ?
      I’d like to read about that.

  6. Raymond says:

    The wheel base for a Moto GP bike is ALREADY much longer than what you would find on a conventional street bike. 1000cc street bike wheel bases are considerably longer than 600cc bikes. You can only lengthen a motorcycle’s wheel base so much before it begins to negatively affect lap times, you are a bit unrealistic in believing we can achieve way better lap times by having a longer and longer wheel bases. There is a point of diminishing returns. A motorcycle with a long wheel base cannot turn in and corner as well as one with a shorter wheel base, handling is negatively affected and corner speed will suffer as a result.

    • David says:

      Thank you for your thoughts Raymond.

      Every new idea goes through these phases by the few who aren’t comfortable with change. They:

      1. Ignore it.
      2. Ridicule it
      3. Attack it.

      Then they —

      4. Adopt it, and ultimately
      5. Claim it was their idea all along.

      Let me try to respond to each of your opinions.

      Raymond: “The wheel base for a Moto GP bike is ALREADY much longer than what you would find on a conventional street bike. 1000cc street bike wheel bases are considerably longer than 600cc bikes.”

      dd: Unfortunately, that’s irrelevant. It doesn’t matter if a Moto GP bike’s wheel base is twice as long as a street bike. If they are doing wheelies while leaned over in a corner — the wheelbase is not long enough. Or if they are lifting the rear wheel during braking into a corner – the wheelbase is not long enough.

      Raymond: “You can only lengthen a motorcycle’s wheel base so much before it begins to negatively affect lap times

      dd: While this is true at some point, please feel welcome to show that we are anywhere near that point. While someone may feel this is correct, no one has cited any study or evidence whatsoever so far.

      Raymond: “You are a bit unrealistic in believing we can achieve way better lap times by having a longer and longer wheel bases.

      dd: My proposal is clearly presented, consistent with all known physics, easy and fairly affordable to build and test. (Not to mention free. As in I’m not charging a penny for the concept to allow race bikes to lap notably faster for virtually no increase in construction cost. I did not patent the idea. I have given it away to the bike racing world for free.). I’ve also shown pretty clearly how each concern raised so far is based on incorrect understanding of dynamics.

      Raymond: “There is a point of diminishing returns.

      dd: I agree there will be diminishing returns at some point, but it is my opinion based on race bikes currently doing wheelies while cornering and lifting their rear tyres while braking into corners that racing bikes are nowhere near such a point.

      Raymond: A motorcycle with a long wheel base cannot turn in and corner as well as one with a shorter wheel base. Handling is negatively affected and corner speed will suffer as a result.

      dd: Both of these were solidly disproven above. They are simply wrong.

      dd: Wheelbase length is independent of roll stability and instability. Roll stability is almost entirely dictated by a bike’s vertical center of gravity:

      High center of gravity = high roll stability and difficult to lean a bike over.
      Low center of gravity = low roll stability and easy to lean a bike over.

      Interestingly enough, a long wheelbase bike is easier to make with a low center of gravity because it has more room down low to put necessary components. A longer wheelbase with a lower center of gravity would make it easier to turn into a corner.

      PS I’ve waited in vain for someone to point out that a longer wheelbase bike has a slightly higher Yaw polar moment of inertia. (Yaw is when the nose of a bike changes from straight ahead to pointing to the left or right. Pitch is when the bike does a wheelie. Roll is leaning the bike to the side.) One could reasonable argue that the larger yaw energy needed might make it harder to get a bike started turning.

      The counter argument is that a longer wheelbase needs less tyre force / friction to get the turning (yaw) motion started, so a long wheelbase may still actually begin a turn easier. I eagerly look forward to testing this.

  7. Lee Parks says:

    David, you have two fatal flaws with your idea of longer wheelbases and lower CoGs decreasing lap times. The problems are that the center of gravity becomes too low and the centralization of mass becomes too stretched out.

    The first problem was clearly demonstrated with Freddie Spencer and the first Honda four-cylinder NSR500GP bike that had the gas tank under the bike and the much lighter expansion chambers under a fake “tank” cover. The super-low-center-of-gravity bike would lean over really quickly but little turning was actually being done. This is why roadracers hang off their bikes: the higher the center of gravity in a straight line, the less lean angle the bike needs in a corner to do a particular amount of turning. Otherwise you run out of tire surface before doing an adequate amount of turning. I experienced this myself while riding the Gurney Alligator recumbent motorcycle. It had a very long wheelbase and a super low center of gravity. The bike would lean way over in turns but ran out of ground clearance in corners without achieving much actual cornering speed. It’s true that the bike was very good at not doing wheelies or stoppies so it could accelerate and decelerate better than a “standard” motorcycle, but it lost too much time in the turns being leaned too far over at too low of a speed. This higher center of gravity principal is partially what allowed the original 1990s-era Ducati superbikes to go so fast in competition. Achieving high lean angles is useless when it results in slower directional changes and corner speeds. And the higher the lean angle, the more dangerous it is to change your speed or direction.

    Additionally the longer the wheelbase is, the more difficult it is to change the direction of the bike. You can see this with figure skaters when they centralize their mass by pulling their arms in close, their “directional” speed increases. Long wheelbases are like figure skaters with super long outstretched arms that cannot be shortened. None of them could “turn” very fast in that state.

    Your analysis is a perfect example of why no one, including Honda which spent over $10 million trying before it gave up, has ever been able to create a realistic full-motion motorcycle simulator. It’s much more complicated than it looks. Effective car and aircraft simulators both exist, but no two-wheeled version. I’ve tested the best $160,000 motorcycle simulators available that are used on military bases, and they aren’t even close to realistic. When I did some consulting for the company that manufacturers them, they were horrified when I explained what they would need to do to make it even somewhat realistic as it was so far beyond their current capabilities. Surely you can’t believe the manufacturers are so stupid that they haven’t tried longer wheelbases as a possible way to win more races, with all the money that is on the line.

    I recently completed a dirt bike project where I added 5 inches to the wheelbase of a CRF15oR to make it more usable for adults (2.5 inches longer swignarm and 2.5 inches longer location of the steering head). The initial results are that the bike is way more stable over the large double jumps for an adult, achieving my main goal of not looping out or endoing my smaller dirt bike. But it has come at the expense of significantly less ability to change its line mid-corner. Unfortunately you don’t generally get something for nothing. In fact, when Edwards was raving about the longer wheelbase, he was talking about a measurement of less than two inches, not anywhere near a foot. Based on my experiences listed above–that would be crazy!

    Of course, you could prove us all wrong by building a long wheelbase bike of your own. Hell, even I did it, without a ton of money.

    I do agree with you about many new ideas, and how they are hard to accept for many people. For instance, everyone knew the universe revolved around the earth, until we realized that it didn’t. Everyone knew witches were evil and shouldn’t be suffered to live, then we discovered there was no such thing as witches. Even now, look at how many people just “know” that there is such a thing as talking snakes, virgin births, people coming back from the dead (zombies), million of species fitting on a boat with 100% effective animal husbandry, the human population twice being the result of incest from a single family, unicorns, and other glow-in-the-dark action figures. And that’s just the silliness of one book with over a billion followers. Yeowe, how did we get here in a conversation about wheelbases? Somebody stop me…

    • David says:

      Hello Lee,

      Thank you for your most thoughtful note and sharing the benefits and insights of history related to this – and your own experiments. Really appreciated.

      I’m in middle of a pressing project right now, but look forward to going over each of your carefully explained thoughts within the next week.

      Update: Sept 24 – Haven’t forgotten your comment, however still not done with my project, but do hope to respond soon.

      Cheers,
      David

      PS Let me clarify one point. If the article seemed to be advocating for lower center of gravity it wasn’t supposed to. I apologize. The only point I wanted to get across is about longer wheelbases (that doesn’t mean I wasn’t distracted and maybe diverged from my goal ;-) )

    • David says:

      (LP) Lee Parks said on July 24, 2013:

      “David, you have two fatal flaws with your idea of longer wheelbases and lower CoGs decreasing lap times. The problems are that the center of gravity becomes too low and the centralization of mass becomes too stretched out.”

      My responses are prefaced with “Dd:”

      Dd: Thank you Lee for your ideas and insight from some of your experience and experiments. Let me apologize for the long delay in my responding to your thoughtful comments — due to two large projects.

      However, neither of the concepts you’ve described are even close to being fatal flaws, and one has nothing to do with, is entirely independent of, a longer wheelbase. Nevertheless, you do raise a very useful observation near the end of your comments.

      Myth: The claim is that with a longer wheelbase the “center of gravity becomes too low.”

      Truth: Wheelbase length and center-of-gravity height are independent of each other.

      Dd: While a longer wheelbase allows a lower center of gravity because of the extra volume at lower height due to stretching, a longer wheelbase certainly does not require a lower center of gravity. In fact, in a design context, a longer wheelbase gives you more freedom to arrange the center of gravity height up or down to adjust other dynamics.

      This means you can keep the exact same center of gravity height as a shorter wheelbase version of the same bike – or you can even raise it if you wish.

      This also means you can also keep the exact same ground clearance, as opposed to how Dan Gurney’s Alligator recumbent motorcycle was designed.

      Claim: “centralization of mass becomes too stretched out.”

      Truth: While a longer wheelbase does make a larger bike Yaw polar moment of inertia (the phenomena where figure skaters’ turn slower when their arms are out – that I raised myself in a comment 8 months before yours, as I described it then – at most it may be a small disadvantage (even that is not certain) to be reduced to acceptable, not a deal-killer, and it may be at least partially offset by the greater torque of the longer distance from the front wheel to the center of gravity.

      LP: The first problem was clearly demonstrated with Freddie Spencer and the first Honda four-cylinder NSR500GP bike that had the gas tank under the bike and the much lighter expansion chambers under a fake “tank” cover. The super-low-center-of-gravity bike would lean over really quickly but little turning was actually being done.

      Dd: While this is an entertaining story about a bike with a “super-low-center-of-gravity” this has nothing to do with a longer wheelbase. Remember wheelbase length (or at least a longer wheelbase) and center-of-gravity are independent of each other AND Lean Angle has nothing to do with wheelbase length. In this case the Honda design was intended to have super-low-center-of-gravity – and it just didn’t work out.

      LP: This is why roadracers hang off their bikes: the higher the center of gravity in a straight line, the less lean angle the bike needs in a corner to do a particular amount of turning. Otherwise you run out of tire surface before doing an adequate amount of turning. I experienced this myself while riding the Gurney Alligator recumbent motorcycle. It had a very long wheelbase and a super low center of gravity. The bike would lean way over in turns but ran out of ground clearance in corners without achieving much actual cornering speed. It’s true that the bike was very good at not doing wheelies or stoppies so it could accelerate and decelerate better than a “standard” motorcycle, but it lost too much time in the turns being leaned too far over at too low of a speed.

      Dd: While this is another entertaining story about a bike with a low-center-of-gravity, again this has nothing to do with a longer wheelbase. Wheelbase length and center-of-gravity are independent of each other. In this case the Gurney design was intended to have a lower center-of-gravity – and as clever as it was, it was too low and “scraped its pegs” too easily.

      LP: This higher center of gravity principal is partially what allowed the original 1990s-era Ducati superbikes to go so fast in competition.

      Dd: There is absolutely nothing preventing a long wheelbase bike from having a high center of gravity like the successful Ducatis.

      LP: Achieving high lean angles is useless when it results in slower directional changes and corner speeds. And the higher the lean angle, the more dangerous it is to change your speed or direction.

      Dd: Achieving high lean angles, again has nothing to do with a longer wheelbase. Remember a longer wheelbase allows a designer more freedom to raise or lower the center of gravity.

      Yaw Polar Moment of Inertia

      LP: Additionally the longer the wheelbase is, the more difficult it is to change the direction of the bike. You can see this with figure skaters when they centralize their mass by pulling their arms in close, their “directional” speed increases. Long wheelbases are like figure skaters with super long outstretched arms that cannot be shortened. None of them could “turn” very fast in that state.

      Dd: This is a valid concern (technically called an increased Yaw Polar Moment of Inertia) that I described earlier, but in my opinion, a minor one that might be offset in part by the higher torque arm of the greater distance from the front wheel patch to the center of gravity. We won’t know with much confidence if this is more than a trivial problem, or if it is offset, until someone does some well designed experiments.

      LP: Your analysis is a perfect example of why no one, including Honda which spent over $10 million trying before it gave up, has ever been able to create a realistic full-motion motorcycle simulator. It’s much more complicated than it looks.

      Dd: I agree that many motorcycle dynamics are incompletely understood and some are easily misunderstood, recently illustrated by a mistaken assumption that a longer wheelbase forces a lower center of gravity.

      LP: Surely you can’t believe the manufacturers are so stupid that they haven’t tried longer wheelbases as a possible way to win more races, with all the money that is on the line.

      Dd: That is essentially the same claim as the head of the US Patent office wrote in 1843 absurdly asserting that – soon, there will be no more inventions.

      In an 1843 report to Congress Patent Office Commissioner, Henry Ellsworth stated, “The advancement of the arts, from year to year, taxes our credulity and seems to presage the arrival of that period when human improvement must end.”

      Dd: It would be relatively impossible to try every reasonable experiment to improve racing bikes. Typically the few experiments that are funded and tested are by a tiny handful of designers who are given extra money and time.

      LP: I recently completed a dirt bike project where I added 5 inches to the wheelbase of a CRF15oR to make it more usable for adults (2.5 inches longer swignarm and 2.5 inches longer location of the steering head). The initial results are that the bike is way more stable over the large double jumps for an adult, achieving my main goal of not looping out or endoing my smaller dirt bike. But it has come at the expense of significantly less ability to change its line mid-corner.

      Dd: That’s a very useful experiment and observation. A more complete description of how you found less ability to change its line mid-corner would be even more valuable.

      LP: Unfortunately you don’t generally get something for nothing. In fact, when Edwards was raving about the longer wheelbase, he was talking about a measurement of less than two inches, not anywhere near a foot. Based on my experiences listed above–that would be crazy!

      Dd: My own guideline is along the lines of Formula 1 cars (which have a similar power to weight ratio) – if the bike is doing wheelies and stoppies – the wheelbase is too short. Formula 1 cars do not do wheelies and stoppies.

      LP: Of course, you could prove us all wrong by building a long wheelbase bike of your own.

      Dd: Due to allowing more power upon acceleration and stronger braking I have no doubt longer wheelbases will allow significantly faster lap times for otherwise identical road racing bikes and make them safer under braking as well. If a bike racing team seriously wants to do the experiments, I will be happy to help them plan a test method and oversee the tests.

      Steam Ship Defeats Napoleon

  8. Nick says:

    Very interesting discussion. I’m currently working on the design of a Feet Forward motorcycle and am struggling to get everything in between a ‘normal’ wheelbase (wanting to make the bike as ‘flickable’ as possible.

    I’m slightly less hung up about achieving a sports-bike wheelbase now, having read the discussion, however it’s true that the longer the wheelbase, the further over you have to lean for any given cornering speed. How long a does a wheelbase have to be before other factors make cornering slower?

    • David says:

      Lean Angle is Independent of Wheelbase Length

      Thank you for your note Nick.

      You ask a wonderful question that helps illuminate a myth.
      The myth is that a longer wheelbase needs to lean more for a given cornering speed. The corollary is also false – a shorter wheelbase needs to lean less.

      If either were true, the shortest wheelbase bike, a unicycle (wheelbase = zero) shouldn’t have to lean at all to turn. But it does need to lean — for a given speed — exactly the same lean angle as any bike or motorcycle.

      Conversely, if a longer wheelbase bike needed to lean more (for the same cornering speed), then a 30 foot long wheelbase motorcycle (hard to imagine) probably could barely turn at all. Which is not true either.

      The reality of the physics is that the amount of lean a bike needs to turn at a given speed has absolutely nothing to do with wheelbase length. Lean and wheelbase length are independent of each other.

      The degree of a bike’s lean is directly related only to how sharply you wish the bike to turn. The sharper you want to turn, the more a bike must lean to balance the sideways (centrifugal) force on the bike’s centre of gravity.

      Bike Lean Angle Independent of Centre of Gravity Height

      To the surprise of many, the height of a bike’s centre of gravity (mass) height has no influence on the degree of lean either. Most racing bike riders make this appear a bit confusing because they rarely sit over a bike’s centreline while cornering; they typically hang off the bike towards the centre of the turn. This allows their bike to stand up straighter so that (among other benefits) it is less likely to drag pegs on the asphalt.

      To help illustrate (and exaggerate) this last point, imagine leaning way off the left side of a bicycle while continuing to ride in a straight line. The bike is leaned over to the right, yet it isn’t turning. Then when you do turn the bike to the left (still hanging way off the left side), the bike can be straight up, with zero lean, yet turning left !

      So to answer your question Nick, you may make your bike’s wheelbase as long as you need and not worry that it will limit your cornering speeds. However, just as others have discovered, a feet forward bike bike tends to have more stuff (technical term) down low that can scrape the ground while leaning. If you design it properly so that all the pegs etc. are inboard and up from the deep V lean avoidance zone your bike should corner just fine.

      The genuine trade-off you will need to deal with is related to “flicability” by which I take it you mean ability to roll a bike from side to side rapidly. The physics is the lower your centre of gravity the more rapidly you can flip a bike from side to side. The drawbacks are less directional stability and more dragging. The lower the centre of gravity the more likely you will have stuff (pegs, engine parts, etc. ) in the deep V lean avoidance zone.

  9. Sabine says:

    I was working on a project motorcycle and came to similar thinking as yourself, mind you im not a motorcycle engineer or anything, I come from aerospace. However it seems logical to lower the second moment of inertia in pitch, roll, and yaw, and limit weight transfer when cornering for greater agility and more consistent tire loading.

    I’ve read through several books on motorcycle dynamics and the wheelbase rules are pretty ingrained it seems, but Cossalter (Motorcycle Dynamics, Second Edition) just notes a greater torque is required for longer wheebases and increased min turning radius. None of these would be of great importance on a grand prix track and mechanical advantage systems can exist to compensate for the extra torque needed.

    I keep thinking I’m missing something though, camber thrust wouldn’t be effected either. My analysis only shows that chassis tends to be heavier and larger min turning radius. I am glad to see I’m not the only engineer who came to a similar conclusion. If you would like me to keep you informed of my research drop me a email.

  10. Luke says:

    Wow. Lots of opinions here, some more informed than others.

    Everyone seems to be forgetting one thing, that is vital to any two wheeled machine; gyroscopes.

    When cornering on a motorcycle, you use gyroscopic progression to lean over, and the wheels (gyros) resist changes in angle to their direction of rotation, Including the initial lean over. This is why on a racing bike, the lighter the wheel the better; less gyroscopic inertia.

    To overcome this inertia, you need torque. This why as previously mention low centre of gravity isn’t so good on a bike. If you hang a weight on the end of a pole, the longer the pole. The more difficult it is to hold it out straight from the other end; the same weight has more torque. It’s not as simple as that though, as higher c of g makes the problem of wheelies / endos worse, so you have to compromise.

    Back to gyros. And poles with things on the end. This time, put a gyro on each end in line with the pole. Try turning that pole from the centre. Making the pole longer (longer wheelbase)will make it harder to turn, requiring either more mass with the same c of g (bad for accel and braking, and also bad for flickability) or a higher centre of g with the same mass to provide more cornering torque when leant over (making wheelies ect easier and therefore longer wheelbase pointless)

    So, in order to allow for the same cornering speed with a longer wheelbase, you need ever increasing weight and c of g height to compensate. And weight is bad for everything in racing.

    So, therefore the perfect motorcycle doesn’t exist, it’s all about compromises: long enough not to flip over either way at the ends of a straight, high enough c of g to provide cornering torque, but not so high that the bike is slower to lean over into bends, and so on, ad infinitum.

    • David says:

      Thank you for your note Luke.

      I’m also not sure I understand all your rationale.
      I’ll try to summarize it, but let me invite you to elaborate.

      We agree that the lighter the wheel, the smaller the gyroscopic effects. Then it seems you are agreeing that a larger polar moment makes it hard to lean a bike over due to gyroscopic resistance.

      But it also seems that a key idea I call “HandleBar / Gyroscopic Steer-Lean Effect” is slightly misunderstood.

      A bike does not lean into a turn by itself. For a left turn a bike must be “pushed” over by turning the wheel to the right so the bike “falls” to the left. When it has reached its desired angle of lean, the handlebars are returned slightly to the left of center and the bike keeps that angle. Some call this phenomenon “Countersteering.”

      I really can’t figure out what you mean by “cornering torque.” I hope you aren’t suggesting that a higher center of gravity provides a bike more sideways force, more cornering Gs because that is as clearly false as astrology – as in there is absolutely no evidence for it. If it were true, then we could build bikes 50 feet high and they would corner far better.

      The truth is center of gravity height has essentially nothing to do with how far a bike needs to lean over to corner at a given speed. High center of gravity or low center of gravity – the bike leans essentially exactly the same amount.

      (The only slight deviation from this is whether a bike has wide (say 4 inches or more) or narrow tyres (like a 10-speed). A bike with wider tyres does need to lean over slightly more for a given cornering speed, because the wider tyre moves the tyre point of contact slightly towards the centre of the turn.)

      PS In case anyone hasn’t seen it – I’ve recently added a new article specifically on bike gyroscopic effects —

      Motorcycle / Bicycle Gyroscopic Effects

Leave a Reply

Your email address will not be published. Required fields are marked *