[ommac]

So I have been thinking about this and haven't seen much talked about it in this forum.

I have an OEM 18x7" that weighs 26.8 lbs and stock dunlops that weigh 23 lbs total weight of 49.8 lbs. That gives a wheel/tire weight ratio of approx 1.16. The heavier wheel is closer to the center of rotation.

Now compare it with an aftermarket wheel of same diameter that weighs 18 lbs and performance tires e.g an 18" Michelin pilot sport that weighs 25 lbs total. Weight is now 43 lbs and the wheel/tire ratio drops to 0.72. Heavier part is now towards the edge of the rotational axis. However I have dropped almost 7 lbs in weight

Seems like the inertia (resistance to change in state) for the aftermarket pair will be more than the OEM since the heavier part is moved outwards. Does this have a negative effect on performance? i.e acceleration and handling?

 

[arathol]

Probably not as much as you think.
Lighter wheel weight has more effect on suspension efficiency than anything else.

 

[Brian.]

Pulling from part of my mechanic career where I did suspension for national race teams (motorcycles) ~ the wheel and tire is a combo, a unit, one. There is no "ratio" of wheel weight vs tire weight, it's all seen as one item when it comes to the physics of the matter. You can see this in the simple fact that no one makes "lightweight" tires, not anywhere or for any reason. This is despite the fact that you can buy carbon fiber rims that can weigh several pounds less than even the best of the best of forged wheels. Never mind that road racing has nearly unlimited budget and would Absolutely make a big deal out of tire weight if there was anything there.

As for the unit weight, it has 3 main areas of impact. It's un-sprung rotational weight (the worst kind for a vehicle) that directly impacts suspension function, turning, acceleration and deceleration. Less weight, easier to rotate/change the speed of rotation... lighter means less gyroscopic effect and easier to deflect one direction or another (bigger deal on motorcycles where you're changing the vertical orientation). And lighter weight means the suspension has less "work" to do (usually means that weak/undersprung OEM suspension gets closer to being properly functional).

Anyway, don't worry about tire weight, it's not important. Or rather it's as low as it can be for the type of tire you're buying IF you're buying performance tires. If you're not buying performance tires, there's no reason to worry about performance as the tire compound itself is the weak link.

 

[Z3MC3Mazda3Lover]

Your overall inertia will still be less most likely, due to the amount of weight reduced in the wheel vs weight gained in the tire.

 

[ommac]

Thanks guys for chiming in. It all makes sense.