Wheel and tire weight is irrelevant (1.5% lap time difference for 2x the weight)???

[Duc Hunter]

I found this very interesting. Seems counter to everything I thought I knew. I thought moving from 20lb wheels to 52lb wheels would be a huge difference in performance, including 0-60, braking, lap time....and MPG. This test says no. Thoughts?

If this test is right, for 99% of us it seems to be irrelevant, except for feel....but not performance.

Wheel Weight Testing

[Racerbvd]

If I remember correctly, Ruf had a reason for making his wheels heavier than most on the market.

[mepstein]

I’m guessing it would depend on how much acceleration and deceleration occurs during the lap. There would be almost no difference during steady state driving but a course has a ton of speed changes, the difference would add up. 1.5% is actually a lot if you are racing.

[Kevin Stewart]

is the tire and wheel size different, tire compound?

[ted]

So the old story goes something like removing rotating weight is 3 times more effective than static weight.
Lighter rotating parts reduce inertia for better acceleration and braking too.

[GeorgeK]

1.5% is the difference between first and last in many races.

[jac1976]

Originally Posted by GeorgeK

1.5% is the difference between first and last in many races.

No doubt. This information is reassuring for those that drive on rallies or otherwise with spirit.

[85RedCarrera]

Could it have anything to do with the damper rebound settings no longer being suitable for such a reduction in unsprung weight?

[GH85Carrera]

My 85 Carrera came delivered with 15 inch Fuchs. It got to the point where I could not find any tires that fit except autocross gummies, or minivan tires. I drive cross country in rain and cold temps, and do autocross and track days, I needed a performance tire. I gave up and bought 17 inch Euromeisters. They are much heaver wheels, and the tires are a LOT bigger and have way more contact patch. I went from 205/50 15s front and 225/50/15 rear to 225/45-17 front and 255/40-17rear.

I could feel the slower acceleration right away. However the massive increase in tire patch made it corner MUCH better. I have done several track days and autocrosses and the cornering is way more now.

I know that is not quite what the OP was posting about, but in my case, yea way different acceleration and way better cornering.

The only real downside is steering effort in a parking lot is way higher as well. I am not sure my wife could drive it in a parking situation, but she never wants to drive it anyway.

[Duc Hunter]

Originally Posted by Kevin Stewart

is the tire and wheel size different, tire compound?

In his test they were the same.

As for some of the other comments.....

Yes 1.5% is the difference between first and last.....for top level drivers in series like F1. In lower series, like the ones 99% of us would be in, it's more like 20%. On a 2 min lap in a 20 minute session thats about 2.4 seconds per lap.

As for feeling the acceleration we feel, I agree. I seem to feel it too when I change wheel/tire weight significantly on a vehicle, like I recently did on my Jeep Wrangler Diesel. That said, his test says it's not that much of a difference. I do think part of his tests close numbers here are the turbo toque his car produces vs out 3.0'ish air-cooled cars with basically no torque. More torque probably hides the effect to my mind.

[shoooo32]

When my wife bought a new VW Alltrack (six speed wagons rule!) she wanted a better looking wheel and tire package. I gave her a half dozen options and she really wanted the VW Atlas Prismas. These are an SUV wheel that weigh 32lbs each, and considering the 18" tire weighed six lbs more than the stock 17s, the increase was substantial.

Now Jessie isn't Sebine Schmitz, but she can heel-toe better than most dudes. She immediately noticed, identifying that "I ruined her car". I found a set of VW CC wheels that were much lighter and sold the Prismas to a kid on marketplace. The story is obviously anecdotal, but Jessie was an unbiased test subject. She knew nothing of wheel weight, only that she did not like the handling characteristics. I'm guessing that a modern ///M car on a race track was less influenced by wheel weight than a VW running stock GTI struts on garbage midwest pavement.

[RarlyL8]

Bill V's having a stroke about now ...

[famoroso]

Originally Posted by RarlyL8

Bill V's having a stroke about now ...

I came back here for BV's take.

[917_Langheck]

Originally Posted by RarlyL8

Bill V's having a stroke about now ...

So are all the people who developed, and those who bought, magnesium or carbon fiber wheels.

[Bill Verburg]

Originally Posted by RarlyL8

Bill V's having a stroke about now ...

????

I've been telling everyone this for years, because I've seen it on dyno runs

The big drain comes from tire OD

[RarlyL8]

Just having some fun Bill, wheel/tire performance optimization and a 30 pound per wheel/tire differential are in no way compatible ideas, ha!

[Showdown]

I can only speak from the world of competitive cycling where I was a pro-am category 1 racer for 20 years… but there’s significant data in cycling showing that at speed during accelerations, the weight of the wheel/rim with is negligible but with repeated accelerations at lower speeds, the weight does in fact become a very large factor. So much so that using ultralight latex inner tubes was a thing to save grams, often at the cost of durability.

In watching the video, and then reading some of the comments, it seems that the fail point of the analysis is that the accelerations used were 31-87mph where the “cost” of the weight of the rim has already been paid or absorbed.




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[Kevin Stewart]

For years in motor sports people have controlled spin by weight. example i have friends that have put in heavier fly wheels to not lock up the rear tires when they lift on entry. I have friends that have also used heavier wheels to control traction, exiting corners. This is pre racing traction control at the armature level or where it is not allowed and teched. I might add usually compression or HP is involved.

[Bill Verburg]

Originally Posted by Showdown

I can only speak from the world of competitive cycling where I was a pro-am category 1 racer for 20 years… but there’s significant data in cycling showing that at speed during accelerations, the weight of the wheel/rim with is negligible but with repeated accelerations at lower speeds, the weight does in fact become a very large factor. So much so that using ultralight latex inner tubes was a thing to save grams, often at the cost of durability.

In watching the video, and then reading some of the comments, it seems that the fail point of the analysis is that the accelerations used were 31-87mph where the “cost” of the weight of the rim has already been paid or absorbed.




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That's true, the inertial loss is proportional to acceleration. There are 4 sorts of acceleration that the wheel/tire assembly is subjected to.

rotational, here the more mass and the further from the axle the more inertial cost
linear in X, the faster the car accelerates the more inertial cost

linear in Y, the rougher the pavement and the steeper the hill the more inertial cost, neither shoes up on a dyno

linear in Z, the faster the tun or yaw the more inertial cost

the 5th cause of torque loss is the gearing coast, which as w/ the inertial coast is greatest in the lower gears where it has the most leverage through drivetrain gearing.

here's a comparison of the thrust w/ 2 different tires, the 245 is heavier but shorter than the 225. But there is more thrust from the 245. This doesn't fully capture the acceleration effect as it is only from the effect of the rotational acceleration.


It's difficult to compare bicycles and cars except in the most general terms, as the bicycle powerplant is relatively torque limited and also has a very limited rpm range which which greatly hampers acceleration magnitude and duration. Many can ride all day at a steady speed on flat ground but the hills in particular separate the men from the boys.

[Showdown]

Originally Posted by Bill Verburg

Many can ride all
day at a steady speed on flat ground but the hills in particular separate the men from the boys.

Don’t I know it! I was a climber/breakaway artist. I loved the mountains.

That said, I recall many 100+ lap 8-corner 2km criterium courses and having raced the same course with both aluminum clinchers and carbon tubulars, the data was clear: faster acceleration, less power used and faster lap times with lighter wheels. And I’d wager that the analog to less power spent by the rider (wattage) would be better fuel economy for the car.

I suspect that wheel weight really comes into factor on tight courses with elevation and lots of speed changes.

On a nascar oval, outside of the first lap, it probably means very little.

Fun exercise!


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