Dynod today with 20 inch wheels -hp loss?

[Chriskm3]

Just a quick question. I dyned today and pulled 496.5 hp with 20 inch cv3. Vossen wheels.
How much loss -if any- would you say my 20 inch wheels contribute?
I would like to hit the 500 hp club. Thanks
If I switched to stock 19 inch Wheels would that help?

[1SICKM]

Yes...they rob you of power. I saw a significant difference on the dyno

[ABC99G]

I lost about 17kw (23HP) between 20" and 19"
Same dyno, different day. My car is stock except for exhaust.
That should give you an idea.

[Longboarder]

Originally Posted by Chriskm3

Just a quick question. I dyned today and pulled 496.5 hp with 20 inch cv3. Vossen wheels.
How much loss -if any- would you say my 20 inch wheels contribute?
I would like to hit the 500 hp club. Thanks
If I switched to stock 19 inch Wheels would that help?

Mustang dyno or Dynojet dyno? Which SC kit did you get? What are all your mods? Do you mind posting your dyno for us? sorry for all the questions but that way, maybe we can evaluate the gains you'd get by putting back the stock wheels.

[Andrew@ActiveAutowerke]

20-25 hp is a very good estimate of power loss.

[ROB_S2K]

To give you a little perspective using my car as an example.

All Stock - Dynos 362 whp on a DynoJet

Full Exhaust HFC's, tune and 20" wheels - The car dynoed 347 whp on a DynoJet

So there is a significant difference

[Chriskm3]

Thanks guys. In that Case I am a happy customer.

[Chriskm3]

Originally Posted by Longboarder

Mustang dyno or Dynojet dyno? Which SC kit did you get? What are all your mods? Do you mind posting your dyno for us? sorry for all the questions but that way, maybe we can evaluate the gains you'd get by putting back the stock wheels.

I have to thank you aswell. Your xpipe with hfc produces amazing hp

[Porschefile]

Does the trend continue on down, so 18's would gain noticeable dyno power versus 19's?

[Longboarder]

Originally Posted by Chriskm3

I have to thank you aswell. Your xpipe with hfc produces amazing hp

No worries. My x-pipe actually is catless. While it didn't produce a ton of HP up top, it produced a significant amount of torque in the mid-range which is what the car was lacking. Adding high octane takes care of the power at the top end. So the combo of the SC, catless x-pipe and higher octane is fantastic in daily driving and track conditions.

Good luck with your build.

[gatorfast]

Why would power be affected by wheel size assuming rolling diameter remains unchanged?

[CanAutM3]

Originally Posted by gatorfast

Why would power be affected by wheel size assuming rolling diameter remains unchanged?

Wheel diameter per se does not have a direct impact on inertial drivetrain loss. However, as a general rule, one can assume that a bigger wheel will have more mass and that mass will be distributed farther away from the centre of rotation. Both contribute to increasing the wheel rotational inertia, hence the power required to accelerate the wheel.

As an extreme example, a very light 20" wheel could have less inertia than a very heavy 19". In that case, the dyno would read better with the 20" wheels. However, this situation it is not very likely.

Without knowing the inertia difference between a specific 20" wheel/tire combination compared to a specific 19" or 18" wheel/tire combination, it is impossible to assess the relative loss (unless someone already ran back to back dynos of Vossen 20" vs stock 19" on the same car ).

[Carlos@MORR]

Originally Posted by CanAutM3

Wheel diameter does not have a direct impact on drivetrain loss. However, as a general rule, one can assume that a bigger wheel will have more mass and that mass will be distributed farther away from the centre of rotation. Both contribute to increasing the wheel inertia, hence the power required to accelerate the wheel.

As an extreme example, a very light 20" wheel could have less inertia than a very heavy 19". In that case, the dyno would read better with the 20" wheels. However, this situation it is not very likely.

Without knowing the inertia difference between a specific 20" wheel/tire combination compared to a specific 19" or 18" wheel/tire combination, it is impossible to assess the relative loss (unless someone already ran back to back dynos of Vossen 20" vs stock 19" on the same car ).

Correct.

Our 20" VS8.2 setup weighs less than the OEM 19" setup. You will not loose power with this setup. Wheel weight will have a deeper effect on performance than size will. Our M3s are a night and day difference betwen 18", 19" and 20" wheel/tire setups. Weight is the biggest weakness of the E9X M3. Any change to it cause a performance gain or loss.

[CanAutM3]

Originally Posted by Carlos@MORR

Correct.

Our 20" VS8.2 setup weighs less than the OEM 19" setup. You will not loose power with this setup. Wheel weight will have a deeper effect on performance.

I am not saying it is the case of your wheels, but simply looking at the wheel weight is not enough to assess if it will perform better on the dyno.

Rotational inertia (polar moment of inertia) varies with the square of the distance to which mass is located from the centre of rotation. So even if the wheel weighs less, if the mass is distributed farther from the centre, it could still have more rotational inertia.

[Parkanzky]

You can't just consider the wheel weight, but also the weight of the tires. 20" tires will tend to weigh significantly more than a 19" tire and a lot of that weight is at the worst possible place.

[Carlos@MORR]

Originally Posted by CanAutM3

I am not saying it is the case of your wheels, but simply looking at the wheel weight is not enough to assess if it will perform better on the dyno.

Rotational inertia (polar moment of inertia) varies with the square of the distance to which mass is located from the centre of rotation. So even if the wheel weighs less, if the mass is distributed farther from the centre, it could still have more rotational inertia.

I was agreeing with you , it is however a special relationship between unsprung weight and rotational inertia which after all both depend on the mass of the wheel.

[CanAutM3]

Originally Posted by Parkanzky

You can't just consider the wheel weight, but also the weight of the tires. 20" tires will tend to weigh significantly more than a 19" tire and a lot of that weight is at the worst possible place.

Why would the tires weigh more?

For a given rolling diameter, increasing the wheel diameter actually reduces required tire sidewall. This reduction in tire sidewall material is most likely offset by the material needed to compensate for the structure stiffness. But, in my opinion, not to a significant extent.

Comparing different sizes weights on Tire Rack could confirm this...

For example Michelin PSS: 265/40R18=27lb 265/35R19=25lb 265/30R20=26lb 275/35R19=27lb 275/30R20=27lb

[NFAM3]

I'm getting 15's

[aka_phox]

wow! i did not know 20s" made that big of difference in horse power.

[FogCityM3]

Time for the 17" wheeler dyno queen! Seriously, makes a very strong case for using a hub dyno only if one wants to get as close to reality (what hp the engine is actually producing pre/post mod) as possible.

[Chriskm3]

I will post dyno results soon with 18 inch Wheels.

[edwinm3]

Vossens are heavy as sh^*