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02-19-2011, 01:54 AM | #1 |
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Wheel weight and acceleration...expensive, light wheels may be worth it.
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. |
02-19-2011, 07:46 AM | #2 |
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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.
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02-19-2011, 08:08 AM | #3 | |
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02-19-2011, 09:06 AM | #4 |
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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 |
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02-19-2011, 11:05 AM | #5 | |
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Rotational mass and acceleration
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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.
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Greg Lake Oswego, Oregon, USA 2023 M2 Coupe - Brooklyn Grey/Cognac/CF, 6MT; 2020 MB GLE 450 Last edited by GregW / Oregon; 02-19-2011 at 11:19 AM.. |
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02-19-2011, 12:31 PM | #6 | |
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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. |
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02-19-2011, 12:47 PM | #7 |
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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.
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02-19-2011, 12:49 PM | #8 |
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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.
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02-19-2011, 01:05 PM | #9 |
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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. |
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02-19-2011, 01:19 PM | #10 |
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Car & Driver Has Actually Tested....
.... for the effect of upsized wheels. Here's the article: http://www.caranddriver.com/features...sted-tech_dept
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02-19-2011, 01:23 PM | #11 |
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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.
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02-19-2011, 02:41 PM | #12 | |
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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 ?? |
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02-19-2011, 03:29 PM | #13 | |
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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. |
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02-19-2011, 05:02 PM | #14 |
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Have a look at these threads.
http://www.m3post.com/forums/showthr...27#post7113627 http://www.m3post.com/forums/showthread.php?p=8908395
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02-19-2011, 05:20 PM | #15 |
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where do you get that calculation from? 10X unsprung weight
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02-19-2011, 05:45 PM | #16 | |
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thanks Swamp |
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02-19-2011, 06:51 PM | #17 | ||
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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. |
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02-19-2011, 07:34 PM | #18 |
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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. |
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02-19-2011, 11:16 PM | #19 |
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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.
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Let me get this straight... You are swapping out parts designed by some of the top engineers in the world because some guys sponsored by a company told you it's "better??" But when you ask the same guy about tracking, "oh no, I have a kid now" or "I just detailed my car." or "i just got new tires."
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02-20-2011, 05:48 AM | #20 | |
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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.
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02-20-2011, 05:55 AM | #21 |
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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.
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02-20-2011, 11:58 AM | #22 |
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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.
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Last edited by Richbot; 02-20-2011 at 12:15 PM.. |
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