How much does wheel weight affect performance?

[churchx]

Twinz: Best think of wheels (and brake rotors) as four flywheels. Going at constant speed/cruising engine will need same power with wheels of different weight. But you need to input more energy to spin them up to speed, and more energy to slow spinning due more stored rotational energy as with any flywheel. So car will accelerate slightly faster and will stop slightly sooner. Not by much, but with big weight differences it can be noticeable. More so vs removing same amount of weight elsewhere. Also in addition to that being rotational it's also unsprung weight. Lighter wheel/suspension can react better on road defects, as there is less mass inertia for springs to move wheel&brakes assembly&it's suspension arm alongside those bumps/roadholes, impacting slightly grip (wheel is more of a time and with better contact with road) and comfort. For many 'butt dyno' margin of detection error might be larger then slight weight difference, but if difference is much larger (eg. forged wheels and even more so + lightweight BBK), or in opposite to lightening direction (installing for sake of looks big heavy barrels for wheels of too big size, heavy weight and with heavier due width tires), then it can be felt subjectively by most. More so then with empty or full tank.

[Twinz]

I agree on the handling aspect but for acceleration sake, even if we think of the wheels as flywheel, the vast majority of resistance is from the mass of the car itself and the load it creates when the wheel tries to move it.

If the wheel was just spinning in the air, that would be one thing, but it's sandwiched between the earth and a 2700lb car.

[Lynxis]

While in theory, a lighter wheel will provide more response in both turning and accel/decel but the reality is that the strength of the wheel tends to provide a larger difference.

I remember reading an article where Enkei took 2 sets of the exact same wheel and shaved as much weight they could off one set. The set with weight removed negatively impacted rigidity although they were about 4 pounds lighter per wheel. Then they tested each set back to back on track with exact same tires on the exact same car and the heavier wheels were repeatedly faster. In the test data, the lighter wheels had slightly faster top speeds on the straights but lost time in the corners to the tune of half a second on a minute long lap. Enkei suggests this was due to improved steering feel and feedback to the driver with the stiffer wheels.

The take-away is that there are always compromises. At most, you are impacting performance by half a second per minute in a track situation. I'm a track rat so that is always a consideration for me but outside of that, I wouldn't worry about it and get what I think looks best within my budget.

[churchx]

Lynxis: point is to not go overboard with lightening wheels. In that experiment imho Enkei overdid cutting material out for lightening from regular wheel and maybe even at wrong places/amount, and wheel rigidity got below acceptable, it got too weak. Not sure if results of this experiment can be attributed to lighter wheel that is designed from ground up such and tested/certified for specific loads. Rest being same forged wheels can be lighter even while still as rigid as heavier cast ones. Also often oem wheels are too strong then it's really needed due manufacturer erring on safe side to lessen any possible warranty work even if car is abused way above reasonable, with owner driving it without any care over worst roads possible at high speeds. Mentioned some posts above as example RPF1 imho is reasonable compromise of strong enough but light wheels. Something like Kosei K4R (even lighter, with weight on par to forged wheels of that side, but seen them talked about as easy to bend wheels) might be lightened too much.
Well, however things end, if someone decides to change stock wheels to aftermarket ones (most probably for looks), it's worth to at least not go for heavier ones. If it can be afforded, then - lighter ones, that are still sufficiently strong.

[why?]

that is why it is worth spending too much money on good forged wheels. I have had Volk Ce28N wheels on my Yaris for a decade. I'll take $200 a year for a wheel that can survive anything and is lighter than anything else.

[nikitopo]

I was reading lately about the flow formed technique. A few manufacturers that use it is Rays, Enkei and Work.

A nice article related with cast, flow formed and forged wheels.
http://speed.academy/why-wheel-manuf...rating-matter/

A wheel I like is Work's M.C.O type CS, which is used in the 86/BRZ Gazoo races. Some wins here:
https://www.work-wheels.co.jp/en/top...ry/86brz_race/

[Lynxis]

Originally Posted by churchx

Lynxis: point is to not go overboard with lightening wheels. In that experiment imho Enkei overdid cutting material out for lightening from regular wheel and maybe even at wrong places/amount, and wheel rigidity got below acceptable, it got too weak. Not sure if results of this experiment can be attributed to lighter wheel that is designed from ground up such and tested/certified for specific loads. Rest being same forged wheels can be lighter even while still as rigid as heavier cast ones. Also often oem wheels are too strong then it's really needed due manufacturer erring on safe side to lessen any possible warranty work even if car is abused way above reasonable, with owner driving it without any care over worst roads possible at high speeds. Mentioned some posts above as example RPF1 imho is reasonable compromise of strong enough but light wheels. Something like Kosei K4R (even lighter, with weight on par to forged wheels of that side, but seen them talked about as easy to bend wheels) might be lightened too much.
Well, however things end, if someone decides to change stock wheels to aftermarket ones (most probably for looks), it's worth to at least not go for heavier ones. If it can be afforded, then - lighter ones, that are still sufficiently strong.

Yes, all things considered equal, a lighter wheel is preferable but as I mentioned, there are always compromises. All wheels are manufactured with certain price, weight, stiffness targets. Compare wheels in Enkeis Racing line to the RR line. Many lighter and cheaper wheels are available in the Racing line but for drivers who value feedback and require more durable wheels for bouncing off curbs and pulling 2+ gs around corners, the RR wheels are for them. Of course, if you want an exceptionally stiff and lightweight wheel, I hear carbon fibre is making the rounds these days... but expect to pay around $3000 per wheel right now...

[tennisfreak]

Feel the difference for yourself.

Take a 4lb weight in your hand and hold your arm straight out. Rotate the arm.

Then do it with an 8lb weight.

There is your answer.

[Tcoat]

Originally Posted by Twinz

I agree on the handling aspect but for acceleration sake, even if we think of the wheels as flywheel, the vast majority of resistance is from the mass of the car itself and the load it creates when the wheel tries to move it.

If the wheel was just spinning in the air, that would be one thing, but it's sandwiched between the earth and a 2700lb car.

OH god somebody get's it! I was beginning to wonder. This is the same concept as people that think they can feel an improvement in acceleration created by the 4 ounce weight difference in a light weight pulley.

[Tcoat]

Originally Posted by tennisfreak

Feel the difference for yourself.

Take a 4lb weight in your hand and hold your arm straight out. Rotate the arm.

Then do it with an 8lb weight.

There is your answer.

That is NOT the same thing.

[Twinz]

Originally Posted by tennisfreak

Feel the difference for yourself.

Take a 4lb weight in your hand and hold your arm straight out. Rotate the arm.

Then do it with an 8lb weight.

There is your answer.

That 2700lb car is what makes the engine work to rotate the wheels. Yes, technically, the mass of the wheels themselvs add to the work. But then, technically, standing next to a swimming pool and peeing in it raises the water level too.

[nikitopo]

Originally Posted by Twinz

I agree on the handling aspect but for acceleration sake, even if we think of the wheels as flywheel, the vast majority of resistance is from the mass of the car itself and the load it creates when the wheel tries to move it.

If the wheel was just spinning in the air, that would be one thing, but it's sandwiched between the earth and a 2700lb car.

Acceleration is different with a heavier or larger wheel. Many times it matters even if the weight is similar, but distributed far away from the center of the wheel. Check in last column timings where corner entry speed is larger and acceleration is smaller giving a smaller top speed:



Source: http://www.roadandtrack.com/car-cult...ransformation/

[Racecomp Engineering]

https://mbworld.org/forums/c63-amg-w...orsepower.html

Originally Posted by HRE Wheels

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.

- andrew

[Twinz]

Originally Posted by nikitopo

Acceleration is different with a heavier or larger wheel. Many times it matters even if the weight is similar, but distributed far away from the center of the wheel. Check in last column timings where corner entry speed is larger and acceleration is smaller giving a smaller top speed:



Source: http://www.roadandtrack.com/car-cult...ransformation/

For the FRS, you are comparing two different-diameter wheel/tire combos. You are changing not just the weight, but the length of the "lever".

Originally Posted by Racecomp Engineering

https://mbworld.org/forums/c63-amg-w...orsepower.html


- andrew

This test has two samples with the same outer diameter and the results of those two pulls fall within the "noise" of dyno pulls. My 350Z spent a good amount of time on different dynos and no two back-to-back runs ever matched....even when nothing was changed on the car between pulls.

I'm not saying that lighter isn't better. I personally think getting heavy rotating wheels to turn on the horizontal plane (left/right) is more likely to be felt by the driver than getting those same heavy wheels to move a much heavier vehicle forward.