Effect of light weight wheels and tires on acceleration

[cahouston]

You're getting entirely too caught up in magazine numbers.

C&D numbers, or any magazine, should be taken with a grain of salt but it was just about the only test of that nature I could find. Everything else is mathematical calculations, theory, "feel", and tribal "knowledge". I'm also not interested in dyno numbers.

I may have to invest in doing this year myself at some point. Same tires/sizes across 2 sets of wheels. Run 1 set, swap, run next set, compare data.

Sponsored

 

[shogun32]

you should be able to back into a HP loss for accellerating a rotational mass of X vs Y assuming frictionless bearings and assuming constant tire rolling resistance. And then extrapolate that HP difference into Elapsed time. But I suspect the effect is pretty damn small. It's when you do it 30 times a lap that the miniscule finally tally up to something meaningful.

 

[Schwerin]

You're getting entirely too caught up in magazine numbers.

My point is they make no sense.

 

[TeeLew]

C&D numbers, or any magazine, should be taken with a grain of salt but it was just about the only test of that nature I could find. Everything else is mathematical calculations, theory, "feel", and tribal "knowledge". I'm also not interested in dyno numbers.

I may have to invest in doing this year myself at some point. Same tires/sizes across 2 sets of wheels. Run 1 set, swap, run next set, compare data.

Go ahead, but it will be below the noise floor of your measurement. Trust the math. F=ma, you just can't get around that one.

 

[TeeLew]

My point is they make no sense.

Nor do you.

 

[cahouston]

Go ahead, but it will be below the noise floor of your measurement. Trust the math. F=ma, you just can't get around that one.

Yeah, that is another question I had was if the real world difference was enough to even account for normal variance. The last time I got 2 clean runs at the track back-to-back, 60' and 1/4 mile ET were within 1/100 of a sec and MPH difference was a few 1/10 of a MPH. Any change in that window of variance would not be enough to confirm benefit or not.

 

[sk47]

Yeah, that is another question I had was if the real world difference was enough to even account for normal variance. The last time I got 2 clean runs at the track back-to-back, 60' and 1/4 mile ET were within 1/100 of a sec and MPH difference was a few 1/10 of a MPH. Any change in that window of variance would not be enough to confirm benefit or not.

Hello; I am back to an earlier thought. The trade off is overcoming rotational inertia ( that may not be a proper term) and getting the most traction to the ground.
For one, traction, you want a large contact patch. You get that with more diameter and more width. I figure the reason pure drag cars are tubbed in the rear is to fit the biggest tire wheel combo possible or practical. By practical I mean what is capable of being manufactured which will withstand the forces applied. Tread compound and sidewall flex will also figure in to this.
I do have a question. Maybe you addressed this already. Are you planning to keep the car's body stock? Are you going to "tub" the body so the largest tire can be fitted in?

The rotational inertia would be more simple if traction was not a premium. Get a small diameter wheel tire combo with the greater mass close to the center and less mass to the outside. I do have a WAG (wild @ss guess). This may be why F1 cars have such small diameter wheels and brake rotors. My guess is the wheels will be more mass than the tire at the same diameter. Say a 20 inch wheel with a very low profile tire having an overall 26 inch diameter. Compare to a 13 inch wheel with a higher sidewall tire profile having the same 26 inch diameter. In my WAG the smaller diameter wheel/tire combo could be the better choice if the tire is a dedicated drag tire. Tire with thin flexible sidewalls and a sticky and also thin tread structure.

I think the F1 cars want to be able to both accelerate and brake very quickly. So any rotating mass will be picked to rev up and slow down quickly. My guess is they have the lightest and smallest diameter flywheel possible also. If you are chaseing the best ET's a look at the flywheel/ clutch might give rewards. If you do much drag racing you will be looking at them eventually.

Bear in mind these are guesses and not the documented sort of reference material you seek.

 

[deanm11]

Absolutely, weight at the center vs. the outside diameter is a large impact. My summer street setup is almost 50lbs. lighter than the factory base 18" setup. (275-40-17 Nittos on 17x9s, 245-40-18 on 18x9.5 front)
I have no hard data but I do believe it a material and measurable difference.

Some research/reading:

https://www.civicx.com/forum/thread...much-of-a-difference-do-they-make.7569/page-2

https://grassrootsmotorsports.com/articles/are-lighter-wheels-really-better/

 

[Macwest]

 

[cahouston]

Hello; I am back to an earlier thought. The trade off is overcoming rotational inertia ( that may not be a proper term) and getting the most traction to the ground.
For one, traction, you want a large contact patch. You get that with more diameter and more width. I figure the reason pure drag cars are tubbed in the rear is to fit the biggest tire wheel combo possible or practical. By practical I mean what is capable of being manufactured which will withstand the forces applied. Tread compound and sidewall flex will also figure in to this.
I do have a question. Maybe you addressed this already. Are you planning to keep the car's body stock? Are you going to "tub" the body so the largest tire can be fitted in?

The rotational inertia would be more simple if traction was not a premium. Get a small diameter wheel tire combo with the greater mass close to the center and less mass to the outside. I do have a WAG (wild @ss guess). This may be why F1 cars have such small diameter wheels and brake rotors. My guess is the wheels will be more mass than the tire at the same diameter. Say a 20 inch wheel with a very low profile tire having an overall 26 inch diameter. Compare to a 13 inch wheel with a higher sidewall tire profile having the same 26 inch diameter. In my WAG the smaller diameter wheel/tire combo could be the better choice if the tire is a dedicated drag tire. Tire with thin flexible sidewalls and a sticky and also thin tread structure.

I think the F1 cars want to be able to both accelerate and brake very quickly. So any rotating mass will be picked to rev up and slow down quickly. My guess is they have the lightest and smallest diameter flywheel possible also. If you are chaseing the best ET's a look at the flywheel/ clutch might give rewards. If you do much drag racing you will be looking at them eventually.

Bear in mind these are guesses and not the documented sort of reference material you seek.

To answer your question, yes, I plan to keep the body stock. At the track, I run a 26" tall bias ply DR on a 17x9 wheel and at stock power level, they hook well (1.79 60' on stock tune).

 

[Norm Peterson]

I found one mathematical discussion involving rotational inertia and mass which concluded you get 2:1 benefit for tire weight reduction versus sprung weight reduction and 1.6:1 benefit for wheel weight reduction.

Those numbers sound about right.


Norm

 

[Norm Peterson]

you should be able to back into a HP loss for accellerating a rotational mass of X vs Y assuming frictionless bearings and assuming constant tire rolling resistance. And then extrapolate that HP difference into Elapsed time. But I suspect the effect is pretty damn small. It's when you do it 30 times a lap that the miniscule finally tally up to something meaningful.

Trust me, it's far easier to work with torque than HP. Rotational inertias amount to parasitic torque losses that remain essentially constant over any rpm range.


Norm

 

[Norm Peterson]

Wait. So, they dropped 0.4sec off 0-60 but only 0.3 from the full 1/4 mile? What did the car get slower on the top end with lighter wheels or something?

Aerodynamic resistance is a bigger factor, and rotational acceleration slows down as speed rises just like forward acceleration drops off (I suspect that the lighter weight isn't buying you as much of a rotational inertia x rotational acceleration benefit).


Norm

 

[Schwerin]

Aerodynamic resistance is a bigger factor, and rotational acceleration slows down as speed rises just like forward acceleration drops off (I suspect that the lighter weight isn't buying you as much of a rotational inertia x rotational acceleration benefit).


Norm

Yes but if you have a .4 faster 0-60 I'd expect at least a .4 faster 1/4 time.

 

[Norm Peterson]

Yes but if you have a .4 faster 0-60 I'd expect at least a .4 faster 1/4 time.

Apples and oranges.

0-60 times are measured on a speed basis (time = speed divided by acceleration). Quarter mile ETs are distance-based (time = a sqrt function of distance divided by acceleration). So the comparison isn't a direct one.

Not only does acceleration drop off as you grab the next gear - the difference in acceleration between the light wheel case and the heavy wheel case also gets narrower. IOW, the amount of benefit you get below 60 mph / 2nd gear does not hold true for 60 and up and 3rd/4th gears.


Norm

Sponsored