Sponsored by The Tire Rack

[Evolved M3]

When choosing a new wheel over the factory 19's, how much weight actually needs to be added or removed for you to actual feel a difference in performance?

From doing some google searching...i've read multiple times that 1lb of rotational weight has the same effect as 10lbs off the car. But some people where debating the exact formula and if that was correct. Is this true? Also that for every 100lbs off the car, you gain 0.100 in the 1/4 mile.

This gets me to my point.Now i was planning on trying to stay on the affordable side on wheels. Im coming from an Evo X where the money per horsepower was A LOT differant. For the M3, most aftermarket performance parts are highly expensive and have minimal gains. But i would still like to get some extra power out of the M3 wherever i can. It might actually be well worth it to spend the extra money on light wheels and at the same time improve yours cars acceleration. Now all of sudden the expensive wheels seem to be a better trade off if they could knock off 0.100-0.200 in the 1/4.

So is it true that every 1lb of rotational mass equals to about 10lbs off the car?

If i stay on the affordable side for wheels, i have some in mind that i might choose from, and they are all within a couple pounds, more or less, than the stocks. So at least i wont hinder the cars performance.

If what i found is true than....

OEM BMW 19":

Front: 23lbs
Rear: 26.5lbs

Linea Corse 818:


19x8.5 +30 23.7lbs
19x10 +38 25.5lbs

Forgestar F14:

19x8.5 23.8lbs
19x10 25lbs

Breyton GRS-R:

19x8.5 22lbs
19x9.5 25lbs

VMR V710:

19x8.5 25lbs

Now on the lighter side...also the more expensive side:

Advan RZ:

19x8 18.8lbs
19x9 19.8lbs

Advan RZ-DF:

19x9 18.4lbs
19x10 19lbs

So put it this way:

- Most of the light wheels i posted are between the $1400-$1700 a set range.

-The Advan RZ are about $2,900.

-The Advan RZ saves about 24lbs of rotational weight in total from all 4 wheels (using 19x8 & 19x9). Which should equal to about the same as 240lbs off the car's weight.

-If my research is correct, it seems loosing 100lbs off the car is almost equivalent to gaining 10hp, which in return will net 0.100 off the 1/4 mile.

So basically for $1,200-$1,500 extra on the set of wheels, you get similar gains as to gaining 25hp. Not a bad trade-off. I do like some of the other designs better than the Advans though.

Again...this is only true if the orignal statement i read is true that 1lb of rotational mass equals to 10lbs off the car. Which i found alot of debate on.

Im new to the this forum, and don't even own an M3 yet, but doing alot of research, so excuse me if any of my information is wrong...plus its 3am here lol

Even if the equation would be lower than 10:1, it may still make a major improvement as the Advans save 24lbs total just on wheels. If the equation is proven to be extremely low, then i may stick with the affordable wheels.

[AMPowerJ]

The thing you are missing is that most people go with larger than OEM tire sizes with lighter aftermarket wheels. These tires weigh more and negate a large % of the weight savings.

I had a set of TE37s but after I put the proper size tire for a 10.5 inch rear wheel (295/30/19), the weight difference was negligible if any.

When I switched back to OEM my car felt more responsive.

If you run aftermarket 18s that are very light with close to OEM spec tires then yes you will feel a difference but it still isn't going to feel like a huge power bump.

[gthal]

Originally Posted by AMPowerJ

The thing you are missing is that most people go with larger than OEM tire sizes with lighter aftermarket wheels. These tires weigh more and negate a large % of the weight savings.

I had a set of TE37s but after I put the proper size tire for a 10.5 inch rear wheel (295/30/19), the weight difference was negligible if any.

When I switched back to OEM my car felt more responsive.

If you run aftermarket 18s that are very light with close to OEM spec tires then yes you will feel a difference but it still isn't going to feel like a huge power bump.

All good points. One thing I would also add though is that with 265 rears, the car breaks traction easily and DSC will often kick in. This has the effect of making the car feel slower. Going with a wider, stickier rear tire will improve the traction issue and also improve both the feeling of acceleration and actual acceleration. I would bet that the improved traction of a wider but heavier tire would outweigh the benefit of a lighter but thinner tire in real world acceleration. I have nothing to support that opinion but if I were a betting man that's where my money would be.

[w00tw00t]

APEX ARC-8 18x10 Square Setup with 275/35/18 FTW!! (19lb ~)

Strong, great looking and reasonably priced wheels - I got my set a couple of weeks ago and its going to be my summer / track setup!

http://www.m3post.com/forums/showthr...highlight=APEX

[GregW / Oregon]

Originally Posted by Evolved M3

So is it true that every 1lb of rotational mass equals to about 10lbs off the car?

The thing about rotational weight is that the effect varies with the moment arm (distance from hub center). So, simplistically, saving weight in the tire has a greater effect than the same savings in the wheel. And for two wheels of the same weight, those with the lightest rim vs. center would have the most positive effect. Note that this is talking about acceleration only, not suspension responsiveness, where either place has a similar effect.

A brief check of data on The Tire Rack site shows, for size 265/35-19:

Michelin Pilot Sport PS2 - 25 lbs.
Continental ContiSportContact2 - 26 lbs.
Pirelli PZero - 28 lbs.
Bridgestone Potenza RE-11 - 29 lbs.

So, you can save at least 4 lbs. in tire weight, which would equate to something larger like 6 lbs. in wheel weight. Obviously, there is a lot more to tire selection than weight, but it should be a factor. And it should be noted the RE-11s are classified as in the Extreme Performance category whle the PS2s are Maximum Performance.

That being said, wheel lightness is important, but the effect on acceleration will be dificult to quantify except in track comparisons. The effect on suspension action is a little easier to perceive. The 1 lb. = 10 lb. rule of thumb has too many variables to confirm.

[JCtx]

Originally Posted by Evolved M3

Also that for every 100lbs off the car, you gain 0.100 in the 1/4 mile.

By that measure if you take 3,600 lbs off the car, you'd gain 3.6 sec in the 1/4... but you'd be walking, so something wrong with your logic man . So yes, it's a lot more complicated to calculate than that.

The effect of unsprung weight, however, sounds about right, with weight shaved on the outside (tires, for instance), making the biggest difference. I just can't understand why people plunk thousands of dollars for heavier wheels than stock... on a performance car . And not only performance and braking is affected, but fuel economy, ride, and often not noted, wheel bearing life and suspension bushings (depending on offset). But to each his own, I guess.

[Evolved M3]

Well its been said 100lbs is 0.100 off the 1/4. And I looked on some online calculators and when I dropped the weight 100lbs, 200lbs it made the 1/4 mile quicker by 0.100, 0.200. Obviously I'm logically speaking here, and I only tried it with up to 300lbs and it had that effect. A normal daily driven car is gonna be very hard to shed more than that, if that, anyway. So it probably is correct or close to that if used in a realistic situation.

[Evolved M3]

And yes you are correct about all the other benefits, that its not only acceleration. I'm still wondering how much lighter per wheel would you have to go to actually start feeling these benefits.

[MonteCarloM3]

Originally Posted by Evolved M3

OEM BMW 19":

Front: 23lbs
Rear: 26.5lbs

Time for some calculations...:

Ok, so stock PS2 tires are the following: (tire rack specs)
265/35/19 = 25 lbs
245/35/19 = 24 lbs

OEM Continental Contisports
265/35/19 = 26 lbs
245/35/19 = 23 lbs

OEM 19" Forged rims:
Front: 23lbs
Rear: 26.5lbs

Total weight Rear Wheels each corner:
With PS2 = 51.5lbs
Continental = 52.5lbs

Total weight Front wheels each corner:
With PS2 = 47.0lbs
Continental = 46.0lbs

Total weight all 4 wheels PS2 = 197lbs
Total weight all 4 wheels Continental = 197lbs

Okay, so VMR weights of the 710's 10" front, 11" rear
Front: 26.0lbs
Rear : 27.0lbs

Recommended Rubber (by EAS)
Hankook Ventus V12 evo K110
Rear 295/30/19 = 30lbs
Front 265/30/19 = 26lbs

Yokohama ADVAN Neova AD08
Rear 295/30/19 = 30lbs
Front 265/30/19 = 26lbs

Total weight Rear with Hankooks/Yokohama = 57lbs

Total weight all 4 wheels with either = 218 lbs.

So that's a 21lb increase in unsprung weight due mostly to increased rubber weight. (7lbs due to wheels, 14 lb increase due to rubber)

So if 100lbs loss gives you 10HP (someone's estimate) then you should lose the acceleration related to 10hp by adding 100lbs.
21lb increase in weight = ~ 2HP decrease. I doubt even my sensitive butt dyno could tell the diff.

[calintexas]

.... for the effect of upsized wheels. Here's the article: http://www.caranddriver.com/features...sted-tech_dept

[Evolved M3]

If your using the calculation above (which again I don't know how true it is), then 21lbs unsrpung would be 210lbs added to the car which equals to about 20hp, or 0.200 slower in the 1/4. You forgot to multiply the 21lbs of unsprung weight.

[Tim B.]

Originally Posted by Evolved M3

When choosing a new wheel over the factory 19's, how much weight actually needs to be added or removed for you to actual feel a difference in performance?

From doing some google searching...i've read multiple times that 1lb of rotational weight has the same effect as 10lbs off the car. But some people where debating the exact formula and if that was correct. Is this true? Also that for every 100lbs off the car, you gain 0.100 in the 1/4 mile.

This gets me to my point.Now i was planning on trying to stay on the affordable side on wheels. Im coming from an Evo X where the money per horsepower was A LOT differant. For the M3, most aftermarket performance parts are highly expensive and have minimal gains. But i would still like to get some extra power out of the M3 wherever i can. It might actually be well worth it to spend the extra money on light wheels and at the same time improve yours cars acceleration. Now all of sudden the expensive wheels seem to be a better trade off if they could knock off 0.100-0.200 in the 1/4.

So is it true that every 1lb of rotational mass equals to about 10lbs off the car?

If i stay on the affordable side for wheels, i have some in mind that i might choose from, and they are all within a couple pounds, more or less, than the stocks. So at least i wont hinder the cars performance.


-If my research is correct, it seems loosing 100lbs off the car is almost equivalent to gaining 10hp, which in return will net 0.100 off the 1/4 mile

Im new to the this forum, and don't even own an M3 yet, but doing alot of research, so excuse me if any of my information is wrong...plus its 3am here lol

Even if the equation would be lower than 10:1, it may still make a major improvement as the Advans save 24lbs total just on wheels. If the equation is proven to be extremely low, then i may stick with the affordable wheels.

I'm not knocking your post, as i'm always looking for added performance/weight savings and am considering lighter wheels too. But, seriously, unless you're racing for a National championship and/or some serious cash, is 0.1-0.2s in a 1/4 mile REALLY that important ??

[Evolved M3]

Originally Posted by Tim B.

I'm not knocking your post, as i'm always looking for added performance/weight savings and am considering lighter wheels too. But, seriously, unless you're racing for a National championship and/or some serious cash, is 0.1-0.2s in a 1/4 mile REALLY that important ??

Everyones different. I enjoy making cars go fast, I'm coming from an Evo with over 470whp and 400wtq. This time around though, I don't wanna go crazy like I did with my Evo. I wanna actually keep the warranty incase I need it, but at the same time, get some extra power wherever I can. And since most performance parts are very expensive for the M and don't put that much power down, I'm thinking of other ways to get some performance. To me 0.1-0.2 off the 1/4 is very good. Like I said everyone is different and some will agree that 0.2 is a substantial difference in the 1/4.

Main thing is I don't want to hinder the cars performance by getting a heavier wheel/tire combo. I may just stick with something of similair weight to the stock set-up at an affordable price.

[swamp2]

Have a look at these threads.

http://www.m3post.com/forums/showthr...27#post7113627
http://www.m3post.com/forums/showthread.php?p=8908395

[MonteCarloM3]

Originally Posted by Evolved M3

If your using the calculation above (which again I don't know how true it is), then 21lbs unsrpung would be 210lbs added to the car which equals to about 20hp, or 0.200 slower in the 1/4. You forgot to multiply the 21lbs of unsprung weight.

where do you get that calculation from? 10X unsprung weight

[Tim B.]

Originally Posted by swamp2

Have a look at these threads.

http://www.m3post.com/forums/showthr...27#post7113627
http://www.m3post.com/forums/showthread.php?p=8908395

thanks Swamp

[Evolved M3]

Originally Posted by MonteCarloM3

where do you get that calculation from? 10X unsprung weight

I've read it a bunch of times while trying to research about wheel weight and such. A lot of different stuff came up about it but none had any concrete information to back it up.

Originally Posted by swamp2

Have a look at these threads.

http://www.m3post.com/forums/showthr...27#post7113627
http://www.m3post.com/forums/showthread.php?p=8908395

Thank you. I just skimmed through those and it seems its in fact only 1lb on the wheel equals to 2lbs off the car, correct?

If so, i will most likely stick with some affordable wheels and not spend a lot on light wheels to see minimal gains, if any. Cause like previously stated above, even if you get light wheels, the wider tires will just weigh more any way.

[pbonsalb]

I am going with Apex ARC 8 and Continental Extreme DW

18 x 10.5 = 20.5 lbs
285/35/18 = 28 lbs
Total new rear = 48.5 lbs

stock 18 x 9.5= 25 lbs?
stock 265/40/18 PS2 = 27 lbs
total stock weight = 52 lbs

18 x 9.5 = 19 lbs
265/35/18 = 25 lbs
Total front = 44 lbs

stock 18 x 8.5 = 25 lbs?
stock 245/40/18 PS2 = 24 lbs
total stock weight = 49 lbs

One inch wider wheels and 3/4 inch wider tires and still saving 17 lbs. While I would not pay thousands of dollars to save 17 lbs of unsprung weight, I put snows on my stock wheels so I needed new wheels anyway.

[aus]

I've always read it's about 4-5 lbs per pound of unsprung weight.

OP should also look into the MORR wheel. It's a great price to weight ratio and is forged. The TE-37 SL is around $2,900 shipped too the last time I asked around.

[swamp2]

Originally Posted by Evolved M3

I just skimmed through those and it seems its in fact only 1lb on the wheel equals to 2lbs off the car, correct?

Pretty much. With the approximations I described, which are rough but decent, 1 lb saved on ONE wheel is like the 1 lb off the total weight itself and an additional 1 lb due to rotational inertia. You can then multiply this by 4. So in some way (assuming 4 identical wheels) 1 lb of of "a" (i.e. each) wheel is like 8 lbs total (instead of just 4 total).

It applies to wheels or tires. Generally a tire will be slightly closer to this ideal approximation since a tire is much more like a thin annulus than a wheel is.

[swamp2]

Originally Posted by aus

I've always read it's about 4-5 lbs per pound of unsprung weight.

That is a myth and an overestimate (unless you include the natural redundancy of the set of 4 tires).

Reducing unsprung weight specifically has advantages but they are more handling related than making your car faster in a drag. Recall the additive benefits are simply for rotating weight, not unsprung weight. The simple reason is that such rotating items have to translate along with the car but they also take extra energy to spin them up. Thus the benefits are more than the weight lost for ANY rotating component in a car, crank, flywheel, tranny components, drive shaft, wheels, axles, tires, brakes, etc.

[Richbot]

5lbs per corner has been a very seat-of-the-pants noticeable difference on the several cars I've made that change to.

It's been touched on by swamp and others several times, but I'll mention a couple other things. Wider tires don't weigh nearly enough to offset the unsprung mass you lose from a good lightweight wheel, you're talking about 1-3lbs for the tire (to add 20-30mm of width within the same tire model anyway) against 5-7 for the wheel, so it's hardly a zero sum game you're playing. The suspension works better when the total mass that moves in response to road forces is lower. This translates to real-world performance every time the suspension moves.

The benefits in rotational inertia from a lighter wheel with heavier wider tires (beceause you're sticking more weight at the edge of the wheel/tire combo) are smaller and when you add the extra rolling resistance from wider tires the benefit of the change will be smaller still, but that has little effect on how the suspension reacts. The car accelerates better when the wheel/tire combo has lower inertia and less rolling resistance (assuming traction isn't lost). Separate and distinct concept from unpsrung mass.

There's no accurate rule of thumb for what one pound chopped from here or there is worth in terms of total vehicle weight with respect to performance. Hell, drop 100lbs from the left front corner of the car and it would probably go slower around a counterclockwise racetrack, so it's not like just reducing overall mass has a known effect all by itself without considering other variables.