belizelittle39439

iTrader: (4)

So I've been trying to figure out how changing my tires and wheels is going to affect the vehicles straight line acceleration / stopping. I know that these changes will affect the gyroscopic effect of the wheels as well when turning but I've not yet figured out how to go about calculating that. I'm not a math whiz by any means--but this seems logical to me. If I'm wrong anywhere please let me know.

Anyway...here are the specs:

Stock/HPDE: Forged BBS rims = 17.7lbs
Street: Cast Rota Boost rims = 20lbs (18-20lb range, so I went with highest)

Stock: Yokohama A046 tires = 25lbs (235/45/17)
Street: Bridgestone RE050A pole position = 25lbs (235/45/17)
HPDE's: Bridgestone RE01R = 26lbs (245/40/17)

General rules of thumb:
10lbs of static mass lost = gain of 1hp / 10lbs of static mass gained = loss of 1hp
1lb of rotational mass = 2lbs of static mass

Using the rules and weight above, and using the BBS/A046 as the control weight; I got these numbers:

--------------------------------------------------------------------------------------------------------
0. BBS/AO46 = 42.7
1. BBS/RE01R = 43.7 (+1lb per corner)
2. Rota/RE050APP = 45 (+2.3 per corner)
--------------------------------------------------------------------------------------------------------

1. 1lb of rotational mass = 2lbs of static mass x 4 corners = 8lbs ~ -0.8hp
2. 2.3lbs of rotational mass = 4.6lbs of static mass x 4 corners = 18.4lbs ~ -1.8 hp

Conclusions:

Since I plan on using my stock BBS rims w/ the RE01R's as my HPDE setup, the loss of just under one horsepower is a good compromise to me considering the overall higher performance of this tire compared to the Yokohama A046.

The Rota Boost / RE050APP combo is going to be a street setup...done mainly for style purposes--keeping that in mind I still didn't want to inhibit the car to any extremes. So the loss of less than 2hp to me can be considered negligible at best given that is not even noticeable while sitting in the driver's seat.

Warrtalon

iTrader: (6)

I wouldn't expect an increase in performance going from A046s to RE01Rs. The extra 10mm is good, but the shorter sidewall isn't.

Jasil

iTrader: (22)

Sounds about right glad your not using the crazy multiples on the net for sprung and unsprung weight.

FWIW, went to BBS rims, lightweight brakes, 21lb tires and noticed no difference in acceleration.

belizelittle39439

iTrader: (4)

Really? From what I understand the RE01R's are a great tire! The only negatives being that (of course) the sidewalls aren't as stiff as the A046 and that the tire is hypersensitive to air pressures.

I was also under the impression that a smaller aspect ratio was a good thing in terms of better responsiveness and less sidewall deformation. According to the Tire Rack website "Some performance improvements of a shorter sidewall include quicker steering response and better lateral stability."

Can you elaborate further on your opinion?

Pure EvoIX

iTrader: (7)

bump for answer.

Shaun@AWDMotorsports

iTrader: (56)

lol yea this is crazy

belizelittle39439

iTrader: (4)

^^ Glad you're amused.

I don't think Warralton is going to elaborate in this case because he's pretty much wrong in this instance if he's saying what I think he's saying. Shorter sidewall is better in terms of responsiveness and stiffness--there is no downside [in my opinion] except that you're more likely to screw up the wheel on sharp impacts. The effect is similar to when you shave off some tread.

mxpop

You gotta remember that the weight may not be evenly distributed on the wheel. For instance, a 2lb lighter wheel may have just as much rotational energy if it carries it's weight closer to the circumference rather than the hub area.

As for sidewall heights: All else being equal, shorter will give you quicker response to steering imputs but will usually not give you as much potential for out right lateral traction, esp on real-world roads/tracks that aren't butter smooth.

belizelittle39439

iTrader: (4)

^of course. The weight on the circumfrence of the wheel/tire is going to play more of a role with rotational mass. Ironic how a lot of people pay attention to the weight of the wheels but forget about the tires, which are on the outermost area of the rotational mass.

Thanks for the input!

Warrtalon

iTrader: (6)

Yes, the RE-01R is a great tire, but the A046 is, too. Just because one tire is great, it doesn't mean it's going to be automatically better. The shorter sidewall will negatively affect your gearing.

belizelittle39439

iTrader: (4)

^^^AHHHH thank you!!! I figured that you'd reply if I said what I said. Sorry about that!

But I completely understand you on the gearing! But do you think it will affect the car all that much? I measured out the overall diameter of the 235/45/17 vs the 245/40/17 and we're talking like .6 inches here.

Warrtalon

iTrader: (6)

The combined effect will be negligible - that's what I'm saying.

belizelittle39439

iTrader: (4)

Gotcha...thank you.

It's always good to hear from someone who actually drives their car.