Had some free time, did some math (1 Viewer)

[FC138fan]

If the goodyear tire is the weak link and the reason for not wanting the cars to go over 330, couldn't they just increase the diameter of the tire to reduce the stress on not only the rubber in the tire, but get the same bang (speed) for less RPM throughout the power train?

Some calcs, calculating the radial acceleration on a 3' tire at 330... then increasing the diameter by 1 inch I get the following speeds yielding the same radial acceleration at the tire -

+1" = 334
+2" = 338
+3" = 342
34" = 347

I realize the tire grows as it runs and so on, but the principle is the same. Bigger tire = less stress. Why hasn't this option been discussed to oblivion?

 

[Just Paul]

More tire, more weight, more centrifugal force on the tire. It's probably a trade off at best so why bother? Just my opinion.

 

[glofria]

There will be more stress on the driveline. Will need to change gear ratio and clutch setting.

 

[Muddy]

I'm not an engineer but I think that increased size equals more rotating mass and more stress along with increased centrifical force unless the tire is radically changed.

 

[d'kid]

Nick, I Understand it's because GoodYear said they won't... and anyone else that could, dosen't want to even mess with it....

 

[The Counterfeiter]

If the goodyear tire is the weak link and the reason for not wanting the cars to go over 330, couldn't they just increase the diameter of the tire to reduce the stress on not only the rubber in the tire, but get the same bang (speed) for less RPM throughout the power train?

Seem to remember that there was some brief experimentation with larger diameter wheels which would yield (I think) your desired result. We are fortunate that Goodyear continues to build tires for a VERY limited market - my estimate is about 7000 tires per year. The cost to engineer and then build moulds to see if a new concept works would only add more negative figures to what has to be a losing proposition. BTW . . . increasing the diameter of the tire on existing wheels would result in higher centrifugal forces.

 

[Nitrohelper]

Many years ago Goodyear informed NHRA that the current size tire was the maximum their molding equipment would handle,
because the cost of new machines was more than the return on investment for a limited market could support, they wouldn't change...

 

[Jimbo]

To me the whole debate is crazy fans want to see close racing and whether they run 300mph or 330mph what the hell is the difference as long as the racing is close.

We waste so much time on this one issue instead of making the racing better for everyone.

I sometimes wonder what would happen if they said anyone who runs over 300 mph will be DQ?

Concentrate on making the show better for the fans and not thinking about just the speeds.

Jim Hill
http://www.nostalgicracingdecals.com

 

[FC138fan]

Many years ago Goodyear informed NHRA that the current size tire was the maximum their molding equipment would handle,
because the cost of new machines was more than the return on investment for a limited market could support, they wouldn't change...

This would make the most sense to me. The other talks about more tire mass, more stress on driveline may be right, but on the surface for me and what I've learned I'm not convinced that those ideas are necessarily true for the following reasons (I could be wrong too).

More stress on driveline - the driveline is already handling astronomical amounts of stress ... at least 9000 hp worth. Adding a few lbs of rubber would increase the resistance in the drive system, but I suspect it would be minimal.
The centrifugal force being increased - the formula for force is

F=MA... Force = mass x acceleration. For a spinning tire, acceleration is radial acceleration which = (V*V) / R (V squared over R). The acceleration would only go down because R is getting bigger (although V would go up if the cars were going faster... so there is some number crunching there to look into

Also, if the mass of the tire on the contact surface were the same (the tires were not thicker) mass would remain the same... to the force on the tire depends only on A... and if A goes down, F goes down - which is shown in my basic calcs (to get the same force on the surface of the tire you have to go faster as you make the tire bigger).

Of course, I am looking only at the stress at the contact surface. The side wall stress would increase, and I don't even know where to begin to calculate that. But last I saw tires were "chunking" on the contact surface, which tells me that the highest stresses occur at the contact surface.

But Jerry's comment makes all those calcs irrelevant and makes complete sense to me.