Wheel weight.. does it Matter?

[Superhatch]

On my Mini Cooper S I went from 17" heavy wheels and run flats to 15" RPF1's and I saved 20lbs per corner. The difference was literally night and day.

With this car I went from the OEM wheel and tire to a 17x9 RPF1 with a 245/40 D2. While the weight in each corner is the same (40lbs) the gains in grip are vast and I added no weight to get it. The Direzza in 245/40 is 26 lbs which is 6lbs per corner heaver than the 215/45 Primacy HPs. Now add another 4lbs per wheel (say going with an 18 vs a light 17) and you're at 10lbs per wheel heavier.

You will notice that.

[fatoni]

Originally Posted by Anaxilus

This is because you need to calculate for contact patch and traction versus polar moment if you want to determine the fastest way around a track. Larger wheels have bigger contact patches. Adding weight increases the psi on each contact patch. So that's traction.

Polar inertia is something independent of traction, and far more relevant to the street than to track. Track cars maintain more high speed even in deceleration than street cars, so they have less work to do to spin the wheels back up. Plus they tend to have much more power/torque than street cars and move less mass overall.

It's a question of balance versus your driving environment. In terms of absolute timed track performance, you always go with the most rubber you can put on the road (unless the weather is bad). Street is different and will depend on user preferences and driving style. The ideal track car above will absolutely suck to drive in street conditions.

the test was done on the same tire on the same width rim at the same psi on the same car iirc. the contact patches should be as close to identical as you can get in the real world. it was a miata at an autox so it was much closer to a street car than a track car. im not using this data to prove anything. im just throwing it out there to kinda reel in a lot of the crazy that this forum is all about.

[ZDan]

Originally Posted by R3d

where did you get 1.7 from?

From 3D tire and wheel CAD models I made which simulate the mass distribution of the wheel and tire.

Because all the research I come up with say that there is no number and that the gain is proportional to the part, its location

Yes, it is dependent on the form of the part and its location.

and how soon it breaks inertia.

??? What are you talking about here? There is no 'how soon it "breaks" inertia'! The body's inertial properties are what they are, they don't change with speed.

For example the tire and wheel have a bigger impact then [than!] the brakes and pads would.

On acceleration, yes.

Apparently the real life gains after removing 1lbs from a wheel ``are`` greater then [than!] removing 1lbs of non rotating sprung mass ( something that doesn't spin and is after the suspension) but nowhere can I find any kind of value for sprung vs un-sprung.

That's because *it depends*, as you already suggested.
For a rotating wheel, the effective mass reduction is ~1.5x. For a rotating tire, it's ~1.9x. Actual figures will vary depending on the specific wheel or tire, but these are good ballpark numbers for changes.

Also I read that removing 20lbs from your wheels would be more of a direct improvement on acceleration and breaking [braking!] compared to shaving 100lbs from the body even tough loosing 100 lbs will help more ``over all``!?!?

Utter B.S. Losing 20 lb. from your *wheels* only is going to be roughly equivalent to losing 30 lb. as far as acceleration is concerned. Braking is limited only by the tires, assuming you have enough leg and pedal travel.

[R3d]

Originally Posted by ZDan

From 3D tire and wheel CAD models I made which simulate the mass distribution of the wheel and tire.

so then 1.7 is a reference based on one of the applications you happen to have done in the past and not a rule of thumbs for all applications then ?

[continuecrushing]

Most people on here won't notice the difference in handling (other than steering feeling heavier/lighter).

@ZionsWrath is right on the money...are you really gonna notice that 1/10th of a second on the street? Most likely not. If you're competing, than sure, give yourself every advantage, but otherwise you just won't drive your car so hard that wheel weight is affecting your speed on street/canyon/track.

If you can afford lightweight wheels, go for it, but don't break the bank thinking its gonna be like adding a turbo to your car or something.

Keep wheel weight under 22 or 23lbs, and just enjoy the car and its awesome looks.

[ZDan]

Originally Posted by R3d

so then 1.7 is a reference based on one of the applications you happen to have done in the past and not a rule of thumbs for all applications then ?

1.7 is a rule of thumb for wheel/tire combined weight
1.5 is a rule of thumb for wheel weight
1.9 is a rule of thumb for tire weight

[Anaxilus]

Originally Posted by fatoni

the test was done on the same tire on the same width rim at the same psi on the same car iirc. the contact patches should be as close to identical as you can get in the real world. it was a miata at an autox so it was much closer to a street car than a track car. im not using this data to prove anything. im just throwing it out there to kinda reel in a lot of the crazy that this forum is all about.

No, the increased weight increases psi on the contact patch, nothing to do w/ psi inside the tire. Since the psi is the same in the tire, even the contact patch could increase in size.

[fatoni]

Originally Posted by Anaxilus

No, the increased weight increases psi on the contact patch, nothing to do w/ psi inside the tire. Since the psi is the same in the tire, even the contact patch could increase in size.

im pretty sure the psi in the tire is the same as it is on the outside of the tire. otherwise, why would people change the tire pressure if it had nothing to do with contact patch? i dont think you dont know what youre talking about.

[Anaxilus]

Originally Posted by fatoni

im pretty sure the psi in the tire is the same as it is on the outside of the tire. otherwise, why would people change the tire pressure if it had nothing to do with contact patch? i dont think you dont know what youre talking about.

Bravo, I see your problem. ^

So a wheel and tire package that weighs 40lbs @30psi weighs the same as a 43lbs package @30psi. Got it. No, YOU don't what you are talking about again, as usual.

I'm outta here, the usual experts have arrived.

[fatoni]

Originally Posted by Anaxilus

Bravo, I see your problem. ^

So a wheel and tire package that weighs 40lbs @30psi weighs the same as a 43lbs package @30psi. Got it. No, YOU don't what you are talking about again, as usual.

I'm outta here, the usual experts have arrived.

haha editing aside, if there was more pressure on one side of the tire than the other, the tire would be rising or sinking. its kinda how everything else in the universe works. i would love for you to explain how that isnt the case.

[Anaxilus]

Originally Posted by fatoni

haha editing aside, if there was more pressure on one side of the tire than the other, the tire would be rising or sinking. its kinda how everything else in the universe works. i would love for you to explain how that isnt the case.

O-M-G...try going back and rereading w/ better comprehension of the topic at hand and carefully wrt the terms used.

I can't believe your mind took what I said to mean adding weight to a wheel turns your car into a hovercraft and violates the gravitational constant of the universe. That is a shockingly amazing interpretation. Please don't quote me anymore.

[Draco-REX]

Originally Posted by Anaxilus

No, the increased weight increases psi on the contact patch, nothing to do w/ psi inside the tire. Since the psi is the same in the tire, even the contact patch could increase in size.

The increase in size would be so small as to be non-existent. Remember, each contact patch holds up the corner of the car. So on a Miata, that's about 600lbs per tire. Adding 3lbs or even 10lbs per tire isn't going to increase the contact patch much at all. In a perfect world, on a 35psi tire, you'd have to increase the corner weight by 35lbs just to gain 1 square inch of contact patch. But there's a lot of other factors involved in the real world(tire resiliency for example), so the increase would be even less.

[etherealfall]

Lol. So, how much faster will 18x9.5 +30-34 Varrstoens affect the bearing in terms of 'wearing' them out?

[boarder1995]

Originally Posted by ZionsWrath

Need a +35 offset at stock height. Can go higher offset and run camber with coils

For 17x9 on stock suspension, 42 will work, just a bit close. Plenty of people and shops are saying this. But, 35 would certainly be a safer bet. I've got 42 17x9 coming in soon and will mount 245 Conti tires - will advise once installed.