Why stagger wheel sizes?

[SingleCamSam]

I've heard, and it seems logical, that keeping wheel/tire sizes uniform from front to rear will produce more neutral handling. If this is so, why would manufacturers stagger wheels from the factory on obviously front heavy cars like the 300zx, supra, mustang etc. Is it:

a. because it improves handling somehow? (though it would seem a wider size in the rear would promote under-steer)

b. Because it looks cool?

c. To handle the power these motors put to the rear wheels?

d. Some evil plot the OEM's have with tire manufacturers to make people spend more on bigger tires?:pface

[Exar-Kun]

little bit of A< little bit of C.

in,s ay, the twin turbo Z, it understeers and plows like a mofo until the turbos wind up, then it can snap oversteer.

think about how bad it would be if they had smaller tires on the rear...

when you think about it, some of the worst under-steering cars..the Z32 and supra, has stagered setups, and a more neutral car, the Rx-7 had a universal(same f/r) setup, it makes sense logically.

now for some cars, with high torque bands, snap oversteer is a very real problem, and necessitates the use of a wider/stickier rear tire...like nils SR20 powered car for example...given the output it runs, (like chris may, also..) the wider tires in the back may make it understeer off bost, but for daily controllability and diriving, you actually want a bit of understeer....its safer than the opposite.

make sense?-chet

[SingleCamSam]

Quote »make sense?[/quote]

Yup. Kind of like an insurance policy on cars like the Z etc. to keep it under-steering on boost rather than the opposite, which, like you said, is bad news on the street.

I think i'll be sticking with a uniform setup. Cheaper, easier, and on a near 50/50 car like the 240 i think it'll be the best bet.

Thanks again Exar!:bearchug

[Q45tech]

Sideways tire sliding friction [stickson].......the Wider patch has the same AREA [WxL] as a narrow patch [at the same psi] but more rubber in the sideways [fishtailing] directions. More probability that the rubber will find something rough in road [at the molecular level] to bond too. More chances per sideways inch.

The problem is that non active suspensions have pretty much the same rates with roll and the suspension doesn't know when it's raining.......When the coefficient of friction drops from 0.9 down to 0.4...............when you lose more than half of rear grip.

To set up powerful RWD for rain you would really need more than 2 times the rear tire width........the 10-15% extra that factory uses is just a tiny band aid.

The BMW 745 has a rain sensing ACTIVE rear sway bar, that decouples when the wipers are on fast!.......reducing the rear roll stiffness by 30%...........not enough but with wider rear tires it suffices for the expert driver.

Rear sway bars actually decrease the rear PEAK grip because that is necessary to decrease understeer. Understeer by definition is when the front is doing more work [the slip angles are higher in the front than rear].

[SingleCamSam]

I always thought a narrower tire was more advantageous in the rain?

[C-Kwik]

It can be when you are referring to hydroplaning. But hydroplaning is a lot different than driving on a thin layer of water where traction is just decreased, not lost completely.

[Q45tech]

I was speaking of the tire moving sideways perdendicular to the plane of forward motion..........skidding sideways.

Think of pushing the rear when on ice, the width isn't much help but it is all you can do - adding width.........assuming you have already chosen the stickiest tread compound all around [for the temperature range of the road].

[Grant@tirerack]

For what it's worth, most of the serious M3 track guys run the same size all the way around for better handling.