TCS & Drag Racing

[Sig]

While much of what NSXtasy's response is accurate, there is a point at which theory and reality deviate.

Next time you visit a drag strip, where traction from a stop is critical, I challenge you to find a single tier-one car running tires smaller than 245.

Gerry's statement is a reflection of the reality side of my comment.

Another more accurate measurement of traction differential between skinny and fat tires, is to compare traction with the same size wheel but different tire widths. While running 245 OEM Yokes on 17 inch rims, I could spin my tires through 2nd gear. Now, sitll on 17's using 265 rubber, I can only spin in 1st..... and that's only achieved by dumping the clutch.

There is a very good reason why the big boys in straightline racing are running around on big-fatty tires instead of choosing 245's for their shoes. If the skinnier tires provided equal traction, by God everyone would use them! Not to mention the weight savings in the unsprung category that lighter tires provide. But they don't use them and skinny tires do not provide equal traction to fat tires.

 

[apapada]

On the dry pavement under the neon lights, I could see my tire tracks. The 275 rear end tire tracks were DEFINETLY wider than the entire 245 tire is!!! So I'm going to stand by my belief that wider tires touch more ground than narrower ones unless you can explain to me what my own eyes saw...i might be missing something.

what you are missing is that the shape of the footprint is very important for the performance you are considering. If the performance we are discussing is longitudinal traction, then the width of your contact patch is not as important as its length. (The opposite is true for cornering, hence Ken's point about wider tires). What you saw was the width of the footprint as you couldn't have seen its length unless you would lift the car right up. When studying the stress in the contact patch, its the front of the footprint which transmits most of the forces during acceleration and the rear during braking.

A very big factor that Ken omitted to mention is that the tire's construction (belt angles, cords size,...) is also very important as it actually dictates the shape of the footprint under load at a given inflation pressure.

 

[apapada]

There is a very good reason why the big boys in straightline racing are running around on big-fatty tires instead of choosing 245's for their shoes. If the skinnier tires provided equal traction, by God everyone would use them! Not to mention the weight savings in the unsprung category that lighter tires provide. But they don't use them and skinny tires do not provide equal traction to fat tires.

If you take your example to the extreme and look at Top Fuel Drag Racers in slow motion during launch, you will notice that the BIAS ply tires they use become half the width under centrifugation forces when under full acceleration. The shape of their footprint goes from | to ---. Under full torque the tires are already at the best footprint shape they can be (--), plus the aerodynamic drag becomes 4x less as they are half their initial width.

 

[apapada]

Another misconception people have is that a 245 has a rolling tread width (RTW) of 245mm. Depending on load and tire inflation pressure the tire actually has about 80% of this under normal load and inflation pressure. This said however, all 245 are not "equal" as there is this little thing called the Tire and Rim Association Window which allows for tire to be fluctuating quite enough. Hence you may get in some sizes 245 which are not wider than 225s for instance.

 

[apapada]

I've got two sets of wheels and tires and as soon as my car gets out of the paint shop I will do a test. Say, 3 runs on my 245's and 3 on my 275's at the same tire pressure, on the same day, on the same car, at the same track and I will even use my rev limiter to keep the launch rpms the exact same. I can gaurantee a lower time with the 275's. How do I know---BECAUSE I ALREADY DID IT!!!! My quater mile times improved by 3 10th's consistently, but what do I know?

you probably know quite a few things but not everything about tires...

If you used the same pressure on your 245 than on your 275, I can guarantee you then that your footprint shape was way different. Even if you mounted the tires at the track on the same wheels or even had another exact same set of wheels, then you again had a different footprint shape. Even if the tires where the same brand, their construction is different, and probably so is the compounds the manufacturer used.

You may believe all you did was change the width of the tires in the overall equation, but you changed many more things than one would think...

 

[Macster]

There is a very good reason why the big boys in straightline racing are running around on big-fatty tires instead of choosing 245's for their shoes.

Yes, those drag racing tires are big but that is because they need to carry high loads from weight transfer (almost the entire weight of the vehicle) and downforce. But they are relatively tall and skinny.

A smaller diameter tire tends to have a wider contact patch, while a larger diameter tire tends to have a longer contact patch. The wide contact patch is optimal for side loads (i.e. cornering) and the long contact patch is optimal for longitudinal loads (i.e. acceleration and braking).

Thus dragsters run large-diameter, relatively skinny tires for maximum traction under acceleration. And road racing cars tend to run smaller diameter, wider tires for better traction when cornering.

The problem with the 245 vs 275 width traction test has to do with tire construction. The sidewalls are stiff and the design makes the tire resist 'getting out of round' or shall I say prevent from laying long. Ignoring changes in gearing, if you got the 245's in high profile 30" diameter tires, you'd probably have about the same traction as the 275's.

 

[Macster]

And apparently the head of Bridgestone Motorsport tire development agrees with you too.

quote:
What performance advantage would be gained by increasing the contact patch of the tyres? An increased contact patch gives increased grip because there is more rubber in contact with the track surface.

I read the article. I believe they are talking about slicks vs. grooved tires, not tire width. Going from grooved tires to slicks will definitely increase the contact patch.

"Perhaps we should also look at the history behind this issue and remember that originally Formula One used slick tyres. As speeds increased, however, the FIA decided to try to slow the cars down and consequently introduced grooved dry tyres in 1998."

http://www.firestone.co.nz/default.asp?action=abo.longnews&NewsID=71

 

[tochigidream]

I can say with the stock 92 rear wheels on my car I can have the car in third gear @ 60-70mph get into boost and burn the tires like I just left a stop sign, but with my 275/30/19's I can only do this in second. Wider tire = more traction.

Could it be that those bigger wheels you have, weigh considerably more than stock? Could we also make the assumption that there is more unsprung weight for the engine to fight with in regards to the heavier wheels? With these arguments, could we also assume the wider tires are not the only reason you can't burn out above second?

Please go easy on me with the flamethrower, Gerry!

Dave