urbamworm

Anyone know for sure if running different size wheels (say stock 18s to say my 20s) will cause negative results on horsepower numbers? My 20s are pretty much the same weight as the last SL63 AMG 19s I had on the car but not sure about the weight of the stock wheels and if they are less and if there would be more power to be had with lighter and smaller diameter wheels like on the street where the car will be faster.

For example, on the streets larger diameter wheels create more rotational inertia away from the hub causing more work to make it spin, now how about on the dyno? I have did a little internet search and found someone say how it can affect an inertia dyno (dynojet) which is what I use, but not a loaded dyno (like a mustang or dyno dynamics).

Anyone ever happen to dyno with different size wheels (stock to larger aftermarket wheels) without changing mods?

99lightning

it will dyno higher with lighter wheels

urbamworm

Found this confirming it as well Click here

Here I am thinking my car sucks, but it is probably just my big damn wheels.

Anyone happen to know what the stock 18s with tires weight? I didn't weight the front but weighted the rear (20x10.5 Vossen CV7) with 285/25/20 Pilot Super Sport tires and they were 56lbs and my rear SL63 AMG wheels (19x9.5) with 275/30/19 tire size weighted the same.

berti_00

really wow... so if we dyno with 18s we'd be able to get more higher numbers?? hmmm

typhoon43

You also want to air your tires up for a little extra help.

lowprofile

Don't get caught playing the numbers game and comparing other people's dyno reading to your own. Aside from showing that your a/f is safe, your own delta is the only important #.
Quick story, the last time I dyno'd my car was when I had the 178mm on. A few cars after me was another 55k running a larger pulley with similar mods. He put up about 30 more peak hp on his best pull and a bunch more torque. In contrast, I made less power, but I had three pulls which were nearly identical. Anyway, a few weeks go by and we line them up on a closed roadway, I'm on the Hankooks and he has a sticky Nitto street tire.
Long story short, I took him surprisingly easy on every pass.

RedBullJnky

Don't get caught up in numbers David. Your car is as fast as mine is. And you have the video.

urbamworm

Haha, not quite man, that was a race tune (my car) vs you on pump! That was also when I had the 180 pulley and around 45whp more

I think I need to lose these 20s though and get some 16s lol.

AKnight55

Stock wheels weigh around 26-27 lbs. add the tire and your looking at 53-56 lbs. My rear wheel and tire set up now is about 45 lbs.

Manuyc

dang I dyno'd 482whp and 502 trq with 20x10 rears with 285 tires I could of gotten more to put down with lighter rims...

urbamworm

Yeah mine are 20x10.5 with 285s.

AKnight, I would like to know a confirmed number and not just estimates, because your estimate has them weighing the same as my rear 19x9.5" SL63 wheel with a 275 width weighted and I doubt the narrower and smaller diameter also with narrower tire E55 wheel weights the same as that at 56lbs.

19" SL63 AMG wheel

AKnight55

If you dont believe me...

https://mbworld.org/forums/w211-amg/...-amg-rims.html

https://mbworld.org/forums/w211-amg/...ew-pounds.html

urbamworm

I would have never guessed. Hard to say though with the weight since one guy said ~27lbs but said he had 9.5" in the rear and not the 9" And the other had chrome ones which chrome weights more right?

Either way if the wheel is 27lbs and a tire is 26lbs that is 53lbs so 3lbs lighter in the rear than my SL63 wheel or my 20s. If the non chrome wheels are say 26lbs then it could be a 4lbs difference. I guess every little bit helps though. Then obviously going to a light 18" wheel would be better where there could be some big savings.

Did you have a noticable change going to the light wheels you have on the street since you stayed same diameter so no gearing change from a different rolling circumference, just less rotational mass?

BlownV8

Yes, you can have wheels that weigh the exact same and the one with smaller diameter wheels will produce more power. It's how the weight is distributed on the wheel. The larger rims have more weight toward the furthest point from center. It takes more force to spin when the weight is further out from the hub.

slownrusty

Timely thread as I just removed my wheels on the weekend to clean my inner fenders

Fronts with tires: 50lbs +/-:


Rear with tires: 55lbs +/-:


Hope that helps.

dre5373

This!

To me, it sounds like you are factoring in 3 different variables into your question. Dyno #s, wheel/tire combination weight and rolling diameter.

Like lowprofile and RBJ said, comparing your dyno #'s to others is pretty much useless. Unless you are swapping to different radius and/or weight wheels/tires at the same dyno at the same time, I wouldn't put too much emphasis on comparing dyno numbers.

As far as your total wheel/tire weight: what is MOST important of the 3 variables is the moment of inertia of the combination. BlownV8 is right on the money about weight distribution in your wheel/tire combo. Got a baseball bat or sledge hammer handy? Grab it from the grip/handle and twirl it around. Then switch ends and twirl it around again. The closer to the rotational axis the center of gravity is, the easier it is to spin around. There's some decent info here...
http://www.sportrider.com/gear/146_0...n/viewall.html
They may be motorcycle wheels, but the laws of physics don't discriminate. If you compare, there are wheels of similar weights that have large differences in MOI, and wheels of different weights that have similar MOIs. It's all about weight distribution. Sadly, this info is not available unless you want to waste wads of cash to do your own tests, so the rule of thumb is lighter for a given diameter or smaller diameter for a given weight=lower MOI.

As for differences in rolling diameter of your wheel/tire combo, that's just a change in your final drive ratio, just like a gear swap although the change is to a smaller degree.

However you acheive it, lower MOI=faster acceleration/braking and better handling