What is the maximum lateral G's a bike can do? - BMW S1000RR Forums: BMW Sportbike Forum
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Old 11-22-2012, 12:37 AM   #1 (permalink)
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Default What is the maximum lateral G's a bike can do?

I have a general question I can't seem to find the answer to.
I believe that the max lateral g's is in the end lited not by traction but by lean angle and the distance a human can hang off the bike towards the inside of the turn.

Anyone have any input? Perhaps a number and an explanation?


Thanks.
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Old 11-22-2012, 01:18 AM   #2 (permalink)
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The simple theoretical limit is 1.0G and occurs with the bike at a 45-deg lean angle. It assumes the tire's coefficient of friction with the ground is 1. It's the same for all bikes, even Harleys. It's also 1.0G for cars.

In reality, things get a lot more complicated. Super sticky tires can interlock with the pavement and have coefficients of friction higher than one and in this case, you can go over 45-deg and corner at somewhat more than 1.0G. OTOH, pavement isn't perfect and there are other loads on the tire which reduce maximum cornering G's. So the answer is that "it depends".

Regardless, the maximum cornering G IS limited by the tire's traction. The reason F1 cars can develop in excess of 5G of cornering load is because they have wings that push the tires into the ground letting them develop huge amounts of traction. If you could have the same on a bike, you could corner way over 1G, but putting aero downforce on a leaning bike is obviously fraught with problems.

Hanging off affects the bike's hardware lean angle, but not the lean angle of the combined bike/rider mass. It's a method of having the rider closer to the ground so that the bike can be less close and have more clearance between parts that might drag. But the overall lean angle of the bike/rider system is not changed by hanging off.

- Mark

Last edited by markjenn; 11-22-2012 at 01:31 AM.
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Old 11-22-2012, 10:57 PM   #3 (permalink)
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You can achieve greater than 1g just by accelerating, let alone experiencing centrifugal force in a banked corner.

There are a lot of a factors but I'm welling to bet its closer to 1.4-1.7g's
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Old 11-23-2012, 02:21 PM   #4 (permalink)
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Quote:
Originally Posted by Zed03 View Post
There are a lot of a factors but I'm welling to bet its closer to 1.4-1.7g's
Notwithstanding drag bikes and the like, no motorcycle develops significantly more than 1.1G or so in any direction, acceleration or cornering.

- Mark
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Old 11-23-2012, 03:34 PM   #5 (permalink)
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Originally Posted by markjenn View Post
Notwithstanding drag bikes and the like, no motorcycle develops significantly more than 1.1G or so in any direction, acceleration or cornering.

- Mark
Very right. Lacking either more mechanical grip (much larger contact patches) or aerodynamic grip from wings,ducts, v gen, etc. motorcycles run into a physics wall.

So basically either a bigger tire or more pressure pushing down on the present tires. Neither of which seems to evident in any tech info I have seen to date. Seems like a great opportunity.

But at the same time it is this very limitation and the feeling that it gives you when riding that makes motorcycles so very much fun. Just enjoy that electronics are at least making it safer for us less talented mortals to enjoy that 'on the edge' feeling.
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Old 11-23-2012, 04:04 PM   #6 (permalink)
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Originally Posted by Jaxian View Post
Very right. Lacking either more mechanical grip (much larger contact patches) or aerodynamic grip from wings,ducts, v gen, etc. motorcycles run into a physics wall.
Even larger tires run into very diminishing returns. Doubling the contact patch doesn't double grip as the loading on the tire per unit of area is halved.

As you say, motorcycles run into very hard physics walls that make getting G loads over 1G very, very difficult and the amount you can get over 1G is relatively small, even with huge tires and slicks. 1.1G is a good ballpark number for the practical upper limit. Our street bikes with street tires don't come close to this.

- Mark
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Old 11-24-2012, 12:57 PM   #7 (permalink)
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A modern sport bike can easily exceed 1g cornering loads especially with a little camber thrown in. In this article a Ducati 1098 went as high as 1.56 against a Ferrari 458's 1.41: Ferrari 458 Italia vs. Ducati 1198 S - Motor Trend
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Old 11-24-2012, 01:46 PM   #8 (permalink)
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A modern sport bike can easily exceed 1g cornering loads especially with a little camber thrown in. In this article a Ducati 1098 went as high as 1.56 against a Ferrari 458's 1.41: Ferrari 458 Italia vs. Ducati 1198 S - Motor Trend
First off, cool article. I've seen it referenced, but I figured it would contain a bunch of test to try to justify why the car is better; like luggage space.

That said, magazines don't routinely test lateral g's because you test for it by spinning 'til failure. That's a bad idea on a bike.
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Old 11-24-2012, 02:21 PM   #9 (permalink)
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Quote:
Originally Posted by bidwell View Post
A modern sport bike can easily exceed 1g cornering loads especially with a little camber thrown in. In this article a Ducati 1098 went as high as 1.56 against a Ferrari 458's 1.41: Ferrari 458 Italia vs. Ducati 1198 S - Motor Trend
Yes, camber throws everything off. A vehicle can do an arbitrary number of G's with enough camber.

- Mark
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Old 11-24-2012, 02:27 PM   #10 (permalink)
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What about the wall of death or is that cheating? :-)


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