ShawnC32

Is it true that our C32's will take a performance hit if fitted with larger wheels? I'm reading some posts that sorta hint and suggest that, and some posts that suggest 'no hit' if the turning radius is unchanged.

Haven't been able to find a thread thru search that specifically addresses this with a consensus. Found a guy in my area trying to unload wheels from a C55. They look identical to the wheels from the C32, but are 18's instead of 17's, and I'm assuming will be a perfect fit.

Thanks!

boohooramblers

Yes, but not by much using the C55 18"s. If the wheel is increased in diameter, the gearing will be slightly changed. Also, the bigger AMG rim will most likely be heavier than our stock 17". The increased weight will contribute.
How much will it decrease rwhp? - hard to say, but maybe a decrease of 5 rwhp, going by what Vadim sees in his thread on the 211 AMG section - he has the effects of larger wheels documented nicely on the dyno:
https://mbworld.org/forums/w211-amg/202131-amg-63-r-d-1-a.html).

Fifth Ring

The performance hit is all related to unsprung weight (the weight of the car that is between the road and the springs (tire, wheel, control arms). Heavier means that the suspension will react more slowly to bumps. This adversely affects handling (the suspension's ability to keep the tread on the pavement.)

Heavier wheel/tire setup will also require more HP to rotate/accelerate and more braking power to stop. Basically, wheels diameter weighs more than tire diameter.

If done right, the outside diameter should not change signficantly. If it does then it affects gearing.

In the end, I believe the effect is minimal, unless you're rollin' on dubs. (PS: 20" wheels on the 6.3 liter AMG ate up 20 HP. That's not trivial.)

e1000

not true. depending on tire size, the overall diameter of tire+wheel can be smaller with 18's versus the stock 17's.

neihouma

from 17" to 18" expect to loose anywhere from 5 to 10rwhp,
of course that's with the propriete size tires.

Example:

Stock C32 17X8.5 with 245 40ZR17

to 18X8.5 with 245 35ZR17 you'll loose anywhere from 5 to 10hp

Josh K

I haven't seen anyone mention the performance decrease associated with increased weight of larger wheels (if they are in fact heavier than the ones you're replacing). Unsprung, rolling weight affects acceleration, braking, and handling response .

boohooramblers

Agreed - I was assuming that all proportions would be maintained going from 17" to 18" wheels + tires. But yes, the 18"s can be fitted to yield an overall smaller diameter.

Fifth Ring

Read ^up^there^. We say it a couple of times.

ShawnC32

Ok, I think I understand now. So larger wheels are strickly cosmetics with a controllable performance cost. Depending on how much care you put into the mod. Got it! Goes to show how much you can learn in here. I originally thought larger wheel/tire combo's mean better performance... more rubber on the road. And that ain't it! Thanks guys!

Soooo! I think I'll re-focus my attention and research back to engine mods packages like EvoSport, Renntech & Kleeman. I got +/- 5k I wanna spend on my C32 before summer's end, and I don't think I'll be throwing any of it at wheels/tires now. Maybe over the cooler months. I'd rather get a WOW! from the sensors in my butt, than to turn the heads of pedestrians with blinding shinny wheels.

Someone is turning me on to a independent shop in my area who will install a Stage I EvoSport & a Limit Slip Differential within my budget. How's that sound? Fair? Cheap? Too much?

amgmark

Hey.. maybe I should have gone to smaller wheels.. LOL.. cmon guys.. if you go to a lighter wheel +1 inch you should not be losing much if any power.. It's more about the extra weight than anything else..

You will get better handling out of a wider larger low profile tire.

Hey.. maybe this is why the C55 has a few more ponies.. to account for the larger wheels.. LOL

Just put in green filters.. doesn't that add 5hp.. LOL

dkflipse

Yeah - I don't think you'll see too many 17" wheels at NASCAR or Formula?

Vadim @ FD

Shawn: Figure for every extra 1 lb. of wheel/tire weight going up 1-2'' in diameter expect 1 RWHP loss. I have tested numerous other FWD and RWD cars this rule of thumb is right on.

What city are you in?

Fifth Ring

Think again. Look at the tire profiles in those series. They are MUCH taller profile than what you see on street cars.



Some series like European DTM and GTR use lower profile rubber.

But for performance, there is a point where a shorter sidewall stops offering improvements.

Vadim @ FD

The reason for 15'' tires in F1 has to do with rules, not with taller sidewall offering better traction.

In the end it is the weight and where it is on the wheel/tire combo.

e1000

Formula1 regulations stipulate the size of both the wheels and tires. I've seen an interview with a bridgestone engineer who said that if F1 could go to an 18" wheel, the car would vastly exceed the limits of human reaction time and cause very dangerous accidents.

How much more do the 18's weigh over the 17's anyway? For some reason I thought both were on the heavy side.

ShawnC32

I'm in the Baltimore/Washington metro area Vadim.

And yes, I'm not lost to the fact that moving from 17 to 18 inflicts a nominal hit, especially if you take care to keep the rolling diameter near stock as possible. I'm just thinking that at this point (my very 1st mods on this car) my budget would be better spent improving performance than improving cosmetics. Like I said, originally (before reading many of these posts) I thought that larger & wider wheel/tire combo's would significantly improve performance. Then I started reading that in fact it may introduce a performance hit. This discussion has brought me up to speed on the topic. I now know that both could happen depending on your approach,... and in either case, the movement is nominal.

Fifth Ring

Oh, I know why. I was just commenting on the post suggesting that we'd never see 17" wheels in F1 (implying we'd only see larger diameter wheels); when in fact, we may never see wheels as large as 17".

Fifth Ring

My tendency is to favor performance over appearance; and that's why I elected to stick with the OEM wheels, but to buy a set of rear wheels for use on the front. With 245/40/17s on rear wheels, I get no interference, and I put more rubber on the road. In a perfect world, I'd find 17" forged wheels, or even 18" forged wheels that are lighter than OEM.

AKnight55

18 inch renntech monolites are pretty light. lighter than the stock 17s?

rbaker

Here's another issue I didn't notice anybody touching on... tires play a big part in the spring rate of the suspension, in a way that alters the effective spring rate/wheel rate. And I don't mean unsprung mass. In F1, they are the primary spring as the suspension is almost immovable and doesn't give until the tires has flexed severely. As the Bridgestone engineer mentions, the reaction time & breakaway warning is reduced as the sidewall becomes shorter. So, you can achieve faster turn in & sharper response from reduced flex of a short sidewall tire/wheel combo, but when you're at the limit & the tire's slip angle is about to "give" from the road you get less warning. Big sidewalls give you a nice gentle knee if you were to plot the breakaway curve and short sidewalls = sharp knee.

dkflipse

Does anybody know what stock 17" doublespokes weigh? I see on Tirerack some SSR's in 18" that weigh 24.7 lbs.

ScottW911

Nice analysis. Although we are getting off topic here, I thoroughly enjoyed your explanation of "sharp knee" vs. "gentle knee".

I am thinking I'll stick with my 17's now.

hkycoldrct

Come on guys! This isn't the Winternationals here. If you like 18" put them on and enjoy 'em. I would be really suprised in anyone could really notice the difference in performance going from 18" down to 17" wheels.

amgmark

I believe stock is somewhere around 27lbs. A nice 19 or 18 inch forged wheel should be lighter or close to stock weight.

I believe my 19" iforged are around 25lbs.

c32AMG-DTM

lol - I saw the same thing... your post was only 3 posts up from his