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Where to start? First of all at the F1 level cars go way, way, faster than the GP bikes, as much as 20 seconds a lap on some circuits. Consider that the acceleration, and top speeds of these vehicles are about the same, in fact this year the staightaway speeds at some tracks have actually been higher on the bikes. That means the cars are way better on the brakes and carry some frighteningly high corner speeds. Because the bike has no aerodynamics working to increase download, the riders are dealing with much greater speed differentials in terms of acceleration/deceleration, I believe their job is much harder.

Secondly - the car stays essentially in a flat plane, the dynamics of the chassis load remain linear regardless of the speed. When the bike is at full lean the centrifugal forces is actually helping it more than a car, (if that car had no downforce assistance). Here comes the problem, at full lean, gravity is also acting vertically on the chassis, not inline with the direction of the centrifugal force, or the direction of the suspension (hence what happens with surface irregularity at full lean, this also includes the problem of torsional load, the chassis winding up and unwinding like a spring) Ever watch the continual head shake of the GP bikes,both under braking and acceleration? You can actually watch these guys exit a high speed corner, and watch the bike slide, shake its head and aviate the front end all at the same time!!!. This is why the idea of controlled frame flex is so critical in racing motorcycle design.

Third - trail is shortend and stability decreased on the bike exactly when stability is needed most, under heavy braking (hence everyone trying to figure out how to make the front fork obsolete & still do a good job of steering and suspending the motorcyle).

Fourth - there has to be some slip angle in the front tire for the bike to turn at all! Of all these engineering problems the aerodynamic issue is the biggest, if that can be figured out and applied to function in the multiple plane environment of the motorcyle, the speeds would at least be dramatically closer! It's all about traction and stability!

You gotta strong muscles, big huevos, quick reflexes and a sensitive ass to ride at the GP level!
 
Re: Stick to insurance pal

Woah woah....

I'm not sure i'm reading Kpaul correctly, but I want to go on record as saying that my post is a guess at what may be the physics of the situation, because the topic post asked about the physics.

As far as the practical realities of riding a bike, and the engineering of race bike design, I make no claims whatsoever as I'm a cruiser guy and I know exactly jack about riding and racing at high speed.

So if I read the post the way I think I did, I'm not sure why the two posts must be at odds. But except for a couple minor points I don't see why my post and the above poster's view must be at odds. It seems mine was about some science issues, and the other was about the nitty gritty of the realities of sportbike riding.

Or perhaps I'm an ass and I'm reading this all wrong.
 
Re: Stick to insurance pal

Thank you ~ You spoke of the physics involved, I didn't see the contradiction either. It still comes down to traction and stability. Racecars with download can turn in quicker, brake later, and carry more g-load in the turn. I think you probably described quite accurately the issues.
 
Lap Times at Daytona

To give you guys an idea of the difference in speed, Eric Bostrom had a pole time of 1:46.835 at Daytona this year. In happy hour this year at the Rolex 24 at Daytona, Tony Stewart ran a 1:49.422. To put it in another perspective, Marco Andretti ran a fastest lap of 2:11:542 at Daytona in a Skip Barber car (open wheel, wings, 150 HP, 1250 lbs fully fueled). Crappy (i.e. guys that are still way better than us) were running near 2:00.00 lap times at the Daytona 200 on superbike GSX-R1000s. And in the last perspective, the best SCCA raced prepared Mazda Miata (SSB class) at Daytona ran a 2:29.004. That is a huge difference to even the "****ty" superbike riders. Regardless of what is "faster" both cars and motorcycles are fun when driving at full speed. And believe me, a stock motorcycle goes through corners WAY faster than a stock car. There is one corner near where I live that my car (Camaro SS ~ .86 Gs on a skid pad) right before it starts to break away can manage maybe 102 mph. My bike, which I am not fully maxed out on, goes through the same corner over 130 mph. Mind you the bikes speedometer is off a good bit, but still. And this is a good comparison because I race cars and I know how to drive. Just thought I'd shoot my opinion.
 
One of the British bike press did a comparo where they put an R6 against a Subaru Imprezza Turbo (The non restricted European version) On the track, they were similar, with the R6 bing slightly faster.. However, on the road, with imperfect surfaces and no run off zones, the subaru was beating the R6, especially since it became hairy trying to ride at 10/10ths on the road on an R6. The main difference was the greater corner speed of the car.



Not my data, but thought I'd throw it into the pot.
 
The June 2004, British Supersport Qualifying Thruxton Round had Karl Harris qualifying his CBR 600RR on pole at 1:17.614 (flying lap). The 911 in the video did a standing start lap in a quoted 1:35.33. It is pretty clear that it wouldn't take 17 seconds for the bike to get from the start line to the first corner, so I think this test was BS. Mackenzie is a pretty damned fast rider, by the way...
 
Surface area may not affect the final measure of friction, but tires do not work only thru friction. The rubber has a certain amount of adhesion to the pavement and also micro deforms to conform to the pavement surface. That's why soft sticky race slicks give better traction than street tires even if the same size.
 
The problem is that friction itself, at the microscopic level, is a poorly understood phenomena. So those various values for the coefficient of maximum static friction and coefficient of dynamic friction between two surfaces are empirical values taken by measuring two samples of particular characteristic against each other (e.g. a flat piece of rubber against a smooth section of asphalt). As the rubber compound gets softer and larger in surface area, it gains better ability to deform to fit the surface beneath it. As such, the coefficient of maximum static friction of a particular racing slick against dry asphalt is likely to be higher than the coefficient of maximum static friction for a tire of the same compound and profile, but with tread grooves in it.
 
What a bunch of BS, first, the "race" did not happen at the Ring, It was at thruxton, both participants are very good at what they do, Plato and McKenzie are by no means ***** footers, but to be honest, McKenzie is the fastest one, he just did not want to get hit by the car, that is pretty clear, so the whole thing is irrelevant, since all he wants to do is "grow an avocado tree from a stone" And by the way Wambo, did you ever work out the nerve to scrub your tires? Or are you still sanding them in your living room? And last but not least, how does it feel to be close enough to the longnazi, to have him post your comment?
 
Hey guys, thanks for the input. I probably should have emphasized the comparison between stock 911 (or any sports car) and stock sportbikes in general. I didn't want to venture into the F1 world of open wheeled cars and F1 bikes. I wanted more of a comparison of what you and I (or someone with more money than me) could buy and set up for track days-both car and bike. 911's, Vipers, Corvette's vs R1's, GSXR1000's, CBR1000RR's, ZX10R's.



Thanks bboule, bdesmo, Andonyx, Abe for restoring my faith in this issue. Thanks to dp5 to point out the difference skill can confidence can have in the outcome. My belief in the sportbike having the greater potiential edge is vindicated, especially after finally seeing the video (thanks Abe!). To me, the whole thing seemed like a set up from the beginning. It looked like the R1 held off in the corners and on the final break for the finish, it could have easily passed the 911 in the distance left. I agree with Kpaul: the narrator is definately being biased.



Kpaul, by the way, if you only find flying to be 5% exciting (like a car), don't go any further. Save yourself the money and put it into something you like better. For me, flying will always be #1, but motorcycles are a close second.



obandoj, I'm not sure why the venom towards me and "longnazi" ( I guess you mean longride?). But to set you straight on one point, I don't and will never "sand a tire" to scrub it in. I remember the original post and my input. I was the one who mentioned to the poster using MEK or Acetone to remove the dry lubricant (mold release) and make the tire tacky, so I think you're a bit confused. I think you may wish to pursue what we used to jokingly refer to in Pharmacy school "as a better life through chemistry." That may smooth things out for you in the long run. But if you want to flame me some more, I do like Buells (and Triumphs, Ducatis, Suzukis, Yamahas, BSAs, ok, some Kawasakis, old british cars, homebuilt aircraft, etc.). Pick a topic and go from there.
 
Great post Andonyx. You made reading a physics lesson easy to understand and interesting. And, you related it very well to the topic. Thanks for taking the time to write it up.
 
Interesting post, but I have a few comments:

  • While your point of coefficient of friction being more important than tire surface area is important and well-made, the modeling of mu (the coefficient of friction) as a constant is only a first-order approximation. In reality, the graph of force of friction versus normal force (per unit surface area) is not linear; the effectiveness decreases as Fn becomes too great. Long story short, more surface area can help. That said, it's true that during hard turning in a car, the brunt of the normal force is borne by the outside tires.
  • I'm not convinced that extra tire friction is used to hold the bike leaned over. The lean is required to balance the horizontal force of friction between the tires and the road and the force of gravity acting on the center of gravity of the bike/rider combo. Bringing the CG farther inboard of the contact patches and closer to the ground allows greater force of friction, resulting in 'more' turning. That's why we (try to) hang off and scrape pegs to corner quickly! Note that the limiting factor on car cornering is the same interaction between car CG and friction of the tires on the outside of the turn. That's one reason why turning too abruptly can cause a rollover in a Ford Exploder.
 
This was interesting topic. Good work man. As for obandoj just having a bad day I think. Not that I have ever had one. :) He flamed me for thinking the rider was a wus. I would be a wus too if I might get hit by a car. I am sure he is a great rider without the car cutting him off.



On the flying thing, I guess I might think flying was more exciting if I was flying a jet but I had my chance at that and blew it... but thats a long story for another day. Flying 172s and 182s can be fun but I don't get the adreanline rush like I do on my bike.... Think I'll spend my money on track school and start doing some club racing.





 
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