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Discussion Starter #1
Question at work: What is the max G rating of a bike? We were talking about the Ariel Atom versus Motorcycle video from Top Gear. I know with most cars sans aero help maxed out it's around 1.5 or so with super sticky tires. But what about motorcycles? I searched the internet to no avail.
 

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Lotus Fury said:
Question at work: What is the max G rating of a bike? We were talking about the Ariel Atom versus Motorcycle video from Top Gear. I know with most cars sans aero help maxed out it's around 1.5 or so with super sticky tires. But what about motorcycles? I searched the internet to no avail.
Bikes have only 2 very small tire contact patches to work with, so they won't pull anywhere near what a car does. They also won't brake nearly as a well either for the same reason. However, they kick the crap out of cars for acceleration.
 

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Discussion Starter #3
That was the discussion - what tracks would a motorcycle have the advantage versus the cars? Any long straight tracks and the car would have to be very close in weight/HP. Curvier tracks would give a car with great handling/aero help the advantage. But it came down to the fact that even the motorcycles guys had no idea how many G's their bikes could pull.

Needless to say this wasn't one of our more productive workday discussions... :D
 

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For bikes, the tangent of the lean angle is the g's for that turn.

Earlier in the year during the MotoGP (top level of MC racing) TV broadcast, onscreen telemetry showed John Hopkins reaching 56 degrees of lean (from straight up). This equates to 1.48 g's. This past race, the winner Casey Stoner showed 63 degrees of lean going thru the corkscrew at Laguna Seca. 63 degrees equates to 1.96 g's. Banking in the corkscrew allowed for more lean than what could be achieved on a flat turn.

The 2007 Yamaha R6 is designed with a max of 57 degrees of lean. With a very good rider on the track, in a flat turn riding a current 600cc sportbike and using racing tires, I would expect a reasonable max lean to be about 55 degrees. 55 degrees of lean would be 1.43 g's.
 

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Cars without aero help max out ON A LEVEL FLAT SURFACE at very slightly over 1g - owing to some straightforward physics plus a bit of rubber chemistry. In a slightly banked corner, or compressing into the beginning of a hill etc. its easy to hit 1.4 to 1.5 g, but that's different to the level surface idea.

Now someone needs to explain why the same argument doesn't hold for bikes!
 

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chrisp993 said:
Cars without aero help max out ON A LEVEL FLAT SURFACE at very slightly over 1g - owing to some straightforward physics plus a bit of rubber chemistry. In a slightly banked corner, or compressing into the beginning of a hill etc. its easy to hit 1.4 to 1.5 g, but that's different to the level surface idea.

Now someone needs to explain why the same argument doesn't hold for bikes!
What argument? Those rules still apply to bikes. They just have less of that rubber chemistry biting the ground. The "bikes vs cars" thing has been done over and over. This is hijacking the thread a bit since the OP wanted a cornering g-force range for bikes, which I don't have. But cars with similarly equipped tires (R-compounds on bike vs R-compounds on car) will always out brake and out corner a bike, even sans aero.
 

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milcher said:
For bikes, the tangent of the lean angle is the g's for that turn.

Earlier in the year during the MotoGP (top level of MC racing) TV broadcast, onscreen telemetry showed John Hopkins reaching 56 degrees of lean (from straight up). This equates to 1.48 g's. This past race, the winner Casey Stoner showed 63 degrees of lean going thru the corkscrew at Laguna Seca. 63 degrees equates to 1.96 g's. Banking in the corkscrew allowed for more lean than what could be achieved on a flat turn.

The 2007 Yamaha R6 is designed with a max of 57 degrees of lean. With a very good rider on the track, in a flat turn riding a current 600cc sportbike and using racing tires, I would expect a reasonable max lean to be about 55 degrees. 55 degrees of lean would be 1.43 g's.
OK, so what you are stating is that my 06 harley ultra classic (getting a 08 in a few months) would be able to acheive -.8g's due to it not being able to lean at all :)

Seriously though, what would the R6 that does 1.43g on track tires do with some good street tires? Would it break 1g? Don't sport bikes do 60-0 in under 100ft?
 

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Conan said:
What argument? Those rules still apply to bikes. They just have less of that rubber chemistry biting the ground. The "bikes vs cars" thing has been done over and over. This is hijacking the thread a bit since the OP wanted a cornering g-force range for bikes, which I don't have. But cars with similarly equipped tires (R-compounds on bike vs R-compounds on car) will always out brake and out corner a bike, even sans aero.
Let me add a few more axioms: Car is an equivalent version of the bike. ie: Yamaha R1 = Arial Atom/Ferrari F430/Z06 Corvette/ etc. I think an R1 is going to out brake and out corner a Yugo, for instance, because they aren't really comparable.
 

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chrisp993 said:
Cars without aero help max out ON A LEVEL FLAT SURFACE at very slightly over 1g - owing to some straightforward physics plus a bit of rubber chemistry. In a slightly banked corner, or compressing into the beginning of a hill etc. its easy to hit 1.4 to 1.5 g, but that's different to the level surface idea.

Now someone needs to explain why the same argument doesn't hold for bikes!
I can hit over 1.4 on a level flat surface, depending on type of tires I use.
 

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If the road is really smooth and flat, then the size of the contact patch doesn't make much difference. The maximum G level obtainable will be dependant upon:

#1. The coefficient of friction between the rubber and the road.

#2. The suspension's (including tire sidewall) ability to keep the contact patch in a stable and usable condition while subject to the forces of that maximum loading.

Now assuming you were willing to pay for a new set of very expensive tires every ten miles, I'm sure one of the companies could produce a sticky enough compound to get a suitably suspensioned car up into the 3G range sans aero. Same goes for a motorcycle if it was physically designed to lean over at 72deg and retain a stable contact patch.

I don't think the lean angles mentioned by milcher take into consideration the fact that the rider is shifting the CG by hanging his body off. So the G-forces mentioned are actually calculated a bit lower than really achieved.

xtn
 

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For a nice simplified overview, see Gaetano Cocco's books.

I've lost track of the physicist's name that consults with a lot of Italian manufacturers, but he used to have an excellent site with lots of formulas and resources on it. An older gentleman who has spent most of his life figuring out how motorcycles work as systems (not all the questions have been adequately answered).

And there's always Tony Foale's work.
;)
 

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Ummm, Randy, no you can't - unless there is some banking to the corner. I've got plenty of data logged at 1.4g to 1.5 g but always at the bottom of a hill or on some slope.

Witness all the magazine skid pad tests that never really go over 0.95g to 1.05 g for a practical evidence, but the real theory is that as xtn said, the maximum g is proportional to the coefficient of friction - and that is always less than 1. Put another way, absent any actual molecular level sticking to the ground - which is never going to be more than a small amount - simple friction can't resist more sideways force than the weight pressing down.
 

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Flat surfaces. Testing between different tires. Put fresh slicks on the data logger's accelerometers report 1.4gs. No elevation. No banking. Skid pad.

:shrug:
 

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chrisp993 said:
Ummm, Randy, no you can't - unless there is some banking to the corner. I've got plenty of data logged at 1.4g to 1.5 g but always at the bottom of a hill or on some slope.

Witness all the magazine skid pad tests that never really go over 0.95g to 1.05 g for a practical evidence, but the real theory is that as xtn said, the maximum g is proportional to the coefficient of friction - and that is always less than 1. Put another way, absent any actual molecular level sticking to the ground - which is never going to be more than a small amount - simple friction can't resist more sideways force than the weight pressing down.
You're quite wrong.

Those tests you're discussing are on OEM tires or other DOT street legal tires at least. You put some good racing slicks on, and equip the suspension to keep the contact patches usefull under the higher loads, and those same cars will run 1.3 to 1.4 Gs all day long. Under the most optimum conditions the stickier tires have coefficients in the neighborhood of 1.7 against good concrete.
 

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xtn said:
I don't think the lean angles mentioned by milcher take into consideration the fact that the rider is shifting the CG by hanging his body off. So the G-forces mentioned are actually calculated a bit lower than really achieved.

xtn
That is exactly correct! The lean angle method is accurate only if the driver is centered on the motorcycle, otherwise it is an underestimate. BTW, I still remember the first time my knee puck touched pavement... sizzle... panic... realization... awe... :D

Thomas
 

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codymac said:
And there's always Tony Foale's work.
;)
Tony F! Yes, he's a good guy. I corresponded w/ him after a motorcycle accident in 2000. Good texts, too.

By the way, I swore off riding motorcycles then... "but I'm getting a Lotus!" :)

Thomas
 

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I have read a few articles in the past with street bike and street car comparos (ZX-7R vs. Ferrari F40 or something similar, I can't remember exactly). They were both the high performance versions of bike and car for the street, and both using street tires. I always remember the outcome being the same. The car would pull away from the bike on the corners, and the bike would pull away from the car on the straights; I don't remember the braking distances. If it was a curvy tight track, the car would win; if it had a lot of straights, the bike would win. I think I probably read at least 3 articles like this with the same results.

I also seem to remember one article that actually had the G forces. The car was somewhere in the high .90's and I seem to remember the bike being somewhere in the .70's. They always said that four flat contact patches was better than two curved ones with the ability to lean.

My guess is that this still holds true as long as you keep the machines and their relevant parts equal, i.e. if one uses racing slicks, then both should; or if one is a "real" sports car, then the other needs to be a sport bike.

In my personal street experiences (I have never raced against a bike on a track), there have been times where I am on the highway and have a long sweeper or just a little canyon run and it is at a time when it is safe to push the car to 8/10's because of no traffic close to me. And occasionally I have had a car or bike behind me trying to keep up (this has happened with me driving my Fiero, my Focus SVT, my Boxster/Cayman/911, or my Elise/Exige). When it was another car, I would leave them in the dust in cornering 95% of the time (this is due to many factors), but occasionally I would get the guy or gal who is also an enthusiast and they had an idea of what their car could do and they would keep up very well. But in all the cases involving bikes; they never came close. When it came time to take a corner, especially a long sweeper like I-25 Southbound to I-40 Eastbound, they would turn into a little dot, but then catch up in no time on the straight.

And for those of you who do not condone street racing; I do not approve of it either and will only do a friendly game of chase when I really feel it is safe and reasonable to do so. I would never do a side by side race on the street with cornering and weaving between cars. It basically has to be me and the other vehicle, and we are playing follow the leader with a good distance between us. And if it is a bike, it needs to be a guy in full leathers and a helmet, or I will not do it either. I don't want a kid who thinks he knows what he is doing try to keep up and then wreck their bike; I would feel very responsible if I knew they were trying to keep up.

Anyway, my point is that my own personal experiences in 20 + years of driving support the magazine tests that I have read. Cars win in the corners, bikes win on the straights.
 

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Stephen said:
In my personal street experiences (I have never raced against a bike on a track), there have been times where I am on the highway and have a long sweeper or just a little canyon run and it is at a time when it is safe to push the car to 8/10's because of no traffic close to me. And occasionally I have had a car or bike behind me trying to keep up (this has happened with me driving my Fiero, my Focus SVT, my Boxster/Cayman/911, or my Elise/Exige). When it was another car, I would leave them in the dust in cornering 95% of the time (this is due to many factors), but occasionally I would get the guy or gal who is also an enthusiast and they had an idea of what their car could do and they would keep up very well. But in all the cases involving bikes; they never came close. When it came time to take a corner, especially a long sweeper like I-25 Southbound to I-40 Eastbound, they would turn into a little dot, but then catch up in no time on the straight.
My experiences, on bikes, with car drivers has generally been the opposite. Most drivers and riders have no idea what their vehicles are capable of - and most street riders are painfully slow. I know i certainly treat a track bike/race bike differently than I do one of my "babies."
:)
 

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Not to thread jack but...

What is the coefficient of drag for a sport bike used in say, MotoGP?

And another thing i have been pondering lately is....

There is going to be a limit as to how streamlined something can be moving through the air. So what is the lowest Cd of drag that has been achieved and by what???

I konw that the koenigsegg has a Cd of something like a fish.... So what is the Cd of a shark then?? Would it be the same as the fish?

I've tried tons of searches for this kind of stuff but rarely do i find anything substantial. Someone really needs to make a motorcycle sight in the same style that Ultimatecarpage.com is designed.
 
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