Do lighter wheels change much?

[Gideon911]

I’ve taken about 200 pounds out of my 911. Changed the bumpers, seats, removed spare, etc.

I’ve realized my rims are quite heavy, about 28 pounds a piece (I believe). I have a set of Fuchs that weigh 17 pounds a piece (I believe). Seems this is an obvious choice to lose 44 pounds, being that my goal has been to have a lighter/quicker ride. Will this be a big change? Or not so much since it’s weight in the wheels?

Just curious what experiences you guys have had.

[icarp]

There have been many papers written on the subject of rotating mass .
It is the most important weight to reduce . PERIOD.
I have 15x7 and 8's on my RS clone, 205/60/15 front and 225/60/15 rear
I run V rated mini van tires , They are light , and handle better than most drivers will ever drive to.
39.5 pounds for the rear tires , and 32.5 for the front , complete .
Ian

[Cals911]

Always heard removing 10lbs of wheel weight is like 100lbs off the car

[TimT]

Yes, this exercise applies to lightweight flywheels.. but is applicable to wheels

Rotating Mass calculation

[Hx911]

so apart from all the advantages of actually reducing the weight, reducing rotating mass you also get better handling and compliance over bumps.

sounds like win-win-win

[Evan Fullerton]

And lighter steering!

[icarp]

Engine rotating mass has a 15 to 1 ratio, all the way to the ring and pinion , then axle to and including wheels 3 to 1 ratio
The pound saved x multiplier = performance weight saved

[PCA7GGR]

Can you say “unsprung weight”?

[Gideon911]

Originally Posted by icarp

There have been many papers written on the subject of rotating mass .
It is the most important weight to reduce . PERIOD.
I have 15x7 and 8's on my RS clone, 205/60/15 front and 225/60/15 rear
I run V rated mini van tires , They are light , and handle better than most drivers will ever drive to.
39.5 pounds for the rear tires , and 32.5 for the front , complete .
Ian

This is exciting news! I’m throwing these Fuchs on tomorrow. Not only will I be saving weight in the wheels, but also in the tires. I’m (stupidly) running Huge tires on my car. I didn’t want to have to re index my t bars. PO had 17’s with 245’s in the rear and 225’s in the front. I went down to a 16 and have been running 245/50/r16’s rear, and 225 for the fronts. What a mistake that was. The tires are g force Michelin’s with a ton of life left. So I’ll probably keep them for at least another 5k miles. I know it should be a huge difference when I go down in diameter.

Appreciate all of your responses. Currently the steering is really heavy..which I do enjoy . My other 911 has Fuchs with 15’s (7’s and 8’s). Steering is so much lighter, but it’s also a longhood. The car I was originally referring to is an 88 cerrera.

[Gideon911]

Originally Posted by TimT

Yes, this exercise applies to lightweight flywheels.. but is applicable to wheels

Rotating Mass calculation

Awesome info, thanks so much

[GH85Carrera]

No doubt smaller lighter wheels are a great advantage for rotating mass. My 85 came with 15 inch 7 & 8 inch Fuchs. They are light. The only issue is there is not quality performance tire that will handle rain on long drives. If you drive only in town on clear days and can avoid rain there are lots of sticky tires but they are scary deadly in rain or cold weather.

Since I drive my car on long road trips and I have driven in lots of rain, and in 16 degree mornings and 118 degree days I need tires that can handle all that and still perform as a modern tire can. I had to get some 17 inch wheels.

I can indeed tell there is a hit to acceleration speed. I can stop much faster as the traction is much higher, and the cornering is way higher then the best of the old tires I can find for 15s for rain and long drives.

I wish one manufacturer would make the 15s in a performance tire that can handle rain and long distance drives. I can't find that tire, so I went to the heavy 17s.

[icarp]

The tires that I am running on my Rs Clone are made by Nankang, they handle the rain they handle the track , they drift predictably at 90 miles an hour through turns. They really are about the best deal that you can purchase in tires in a 60 series for sevens and eights on a standard Carrera Fender
If you want to hear more about them just ask , I don’t want to go on and on and bore anyone

[Gideon911]

Originally Posted by icarp

The tires that I am running on my Rs Clone are made by Nankang, they handle the rain they handle the track , they drift predictably at 90 miles an hour through turns. They really are about the best deal that you can purchase in tires in a 60 series for sevens and eights on a standard Carrera Fender
If you want to hear more about them just ask , I don’t want to go on and on and bore anyone

I’d like to hear more! Thanks for your input. I have a set of 16’s (Fuchs- 7 and 8) for my Carrera. I’m going to be shopping for a tire here soon.

Glenn, that’s the same reason I went with a 16 rather than a 15. It seems there are more options in 16’s.

[GH85Carrera]

Originally Posted by Gideon911

I’d like to hear more! Thanks for your input. I have a set of 16’s (Fuchs- 7 and 8) for my Carrera. I’m going to be shopping for a tire here soon.

Glenn, that’s the same reason I went with a 16 rather than a 15. It seems there are more options in 16’s.

Yea, I tried to find some 16 inch Fuchs and they are hard to find and tires are limited compared to 17s.



I do love the look of the 17s and this is at standard European ride height. Zero tire rub issues.

225/40-17 front and 255/40-17 rears.

[HarryD]

Originally Posted by Gideon911

I’d like to hear more! Thanks for your input. I have a set of 16’s (Fuchs- 7 and 8) for my Carrera. I’m going to be shopping for a tire here soon.

Glenn, that’s the same reason I went with a 16 rather than a 15. It seems there are more options in 16’s.

Depending on the level of performance your desire, for everyday driving and occasional Autocross/HPDE days, I am very happy with my Continental ExtremeContact Sport tires on my 16 inch Fuchs.

[icarp]

More info on the Nankang
https://simpletire.com/nankang-225-50r16-24365009-tires for the rears
https://simpletire.com/nankang-205-55r16-24460045-tires for the front

I prefer the smooth release of a good tire vs the quick release of a sticky tire
I have been teaching and coaching racing for 45 years. I have a pretty good understanding of cars and tires .

I do love the Continental ExtremeContact Sport , but for price and fun I bought the Nankang .
I have been on the track with other cars running the toyo R888 and drove around them on the outside of the turn
in a nice little drift . They were my friends and I was making a point

[Bill Verburg]

Originally Posted by Gideon911

I’ve taken about 200 pounds out of my 911. Changed the bumpers, seats, removed spare, etc.

I’ve realized my rims are quite heavy, about 28 pounds a piece (I believe). I have a set of Fuchs that weigh 17 pounds a piece (I believe). Seems this is an obvious choice to lose 44 pounds, being that my goal has been to have a lighter/quicker ride. Will this be a big change? Or not so much since it’s weight in the wheels?

Just curious what experiences you guys have had.

I'm curious, are the 15-52 the 28# wheels?

[Bill Verburg]

Originally Posted by icarp

There have been many papers written on the subject of rotating mass .
It is the most important weight to reduce . PERIOD.
I have 15x7 and 8's on my RS clone, 205/60/15 front and 225/60/15 rear
I run V rated mini van tires , They are light , and handle better than most drivers will ever drive to.
39.5 pounds for the rear tires , and 32.5 for the front , complete .
Ian

Yes reducing weight is in general a good thing but there are other factors that are in play that have a more significant effect on performance

Here's an example, 2 sets of tires are compared here, both on 7 & 8 x15 Fuchs, the second set has a ~41lb-ft advantage over the first set in first gear, the difference diminishes as you go up through the gears Both are 205/225, the first though is a 60 series tire and the second a 50 series.

The inertial cost difference for the tires alone is ~18lb-ft favoring the lighter and shorter 50 series tires, the rest is the gearing cost incurred buy the taller 60 series tires, So Here the gearing is far more significant than the weight

[Bill Verburg]

Originally Posted by Cals911

Always heard removing 10lbs of wheel weight is like 100lbs off the car

more like 50#, all else being =

100# of chassis is worth ~8lb-ft in 1st

10# of wheel = ~4lb-ft in 1st

[Bill Verburg]

Originally Posted by TimT

Yes, this exercise applies to lightweight flywheels.. but is applicable to wheels

Rotating Mass calculation

Only in general, the moment of inertia of a flywheel is fairly easy to calculate because the shape of the flywheel is pretty simple and the mass is fairly uniformly distributed, wheels and tires have much more complicated shapes and far less uniformly distributed mass.

The flywheels significance is greatly multiplied by the gearing in the car, the wheels are not affected except by the gearing imparted by various tires different loaded rolling radii