Dyno Runs - The effects of wheel/tire weights on wheel horsepower
 

Test:
Davenport Motorsports (www.davenportmotorsports.com) of Canada, wanted to see the dyno effects of running different wheels on cars. They took a factory 2012 Camaro SS and ran 3 dyno runs. They ran the first run with a set of aftermarket wheels, the 2nd run with a set of stock factory wheels and the 3rd run with a set of HRE P45S wheels, all in 20” sizes.

These results highlight the effects of rotational inertia on drive-train losses (the hp lost between the engine crank and the ground). Wheels and tires contribute to drive-train losses as energy is used to spin up the wheels (and decelerate the wheels under braking). From the dyno chart you can see the effect of replacing factory wheels with lighter HRE wheels and see the negative effects of installing heavier aftermarket wheels.

Results:
1. (Blue curve) Factory wheels: 20”x9.0” with Pirelli 275/40-20 tires weighing 68 lbs combined per rear wheel. – Max hp: 371 hp, Max Torque: 375 ftlbs - (Baseline)
2. (Red curve) Aftermarket wheels: 20”x9.0” with Pirelli 275/40-20 tires weighing 72 lbs combined per rear wheel – Max hp: 369 hp, Max Torque: 373 ftlbs - (A [-] loss of 2 hp and 2 ftlbs)
3. (Green curve) HRE wheels: 20”x11.0” with Nitto 315/35-20 tires weighing 60 lbs combined per rear wheel – Max hp: 380hp, Max Torque: 384 ftlbs - (A [+] gain of 8 hp and 9 ftlbs and that is running a 2” wider wheel/tire combo)

Conclusion:
The engine obviously still cranks out the same amount of hp and torque, the lighter HREs simply waste less of it before it gets to the ground. Also interesting to note is that the gains are not just peak gains, but gains across the entire rev range. If they had done a braking test, we would have seen similar results as the rotational inertia effects also have a significant effect on how much energy is used to stop the wheel/tire combo vs. stopping the car. We talk about these effects all the time and focus on designing lightweight wheels with low rotational inertia, but it isn’t every day that you get to see real hard data showing the true effects.

http://www.flickr.com/photos/hrewheels/6757639011/http://www.flickr.com/photos/hrewheels/6757639011/ by http://www.flickr.com/people/hrewheels/, on Flickr

This is a really tough comparison in my opinion...Since you did not use the same tires on the last run, although they are larger, still doesn't prove much...Tires vary dramatically in weight depending on brands...It would be nice to know the actual weight of each rim and tire to have a fair comparison...

The HREs were 2" wider, and had a heavier tire on them, the 315 is probably 2-3lbs heavier than the 275 on the other wheels, and they were still considerably lighter.

Figure a 315/35/20 probably weighs about 38lbs...thats putting the wheels at 22lbs...for a 20x11 that is really light.

Nice work.

Nice to see empirical data to support what some would one to expect.

Sorry Lon, game over:

http://youtu.be/HPh90yNX-mY

:)

That is an excellent Video! Thanks Neil!

excellent test and very true...

Even you you install lighter brake rotors you can gain power. And wheels and even more tires are more important since you are removing weight from the furthest point of the axle...

Don't forget that the stickier the tire the less the RWHP. I.e my GTO made less RWHP on drag radials and even less on full slicks, although, it ran faster ETs with the stickier rubber due to better traction from the dig and faster 60ft times.

Lon, Nice work. I always wondered.

Neil, That's just awesome. hilarious

Nice thread...Years and years now I always choose the lightest wheels for my car...Finally someone had the chance to prove the effect of less rotational weight...good job...

Now imagine if you stuck with a 19" wheel and tire combo that weighed a total of <50# per rear corner

That video was phenomenal... I need 3 people to loan me their donuts so we can test the true handling of a C4S!!

Nice to see data match up with theory. Good job.

The car does not make power. It is just that the parasitic losses are lessened, hence more power available at the wheels.

Enzo Ferrari was famous for enforcing his chassis/suspension designers to use narrow tires in order to get the best mechanical grip possible. From there they used scale up the tire widths to get the final result. It's a great way to force the issue.

I am up for testing the C4 or the Turbo with donuts. If anything, it should be a blast.