Staggered tires and handling

[RustyBucket]

Does anyone on here have experience with running a staggered tire setup on their G50?

I just switched off my winter tires and onto a staggered setup, running 235/60R15 in the rear and 215/65R15 in the front on stock BBS rims. The handling of the car now seems off; the vehicle feels kind of "high strung". It seems to be mostly bump steer; going over bumpy road surfaces, I can feel the rear stepping to one side or the other a little bit. It's a little unnerving to see the slip light come on under acceleration at 90KM/H when going over a few little pavement patches. I've been playing around with rear tire pressures, wondering at first if it was sidewall flex, but I didn't notice much of a difference between 42 psi and 33 psi (max pressure for the tire is 44). It definitely does not feel like tramlining, which I've read can happen with staggered setups.

My current theory is that the wider tires are causing toe changes in the rear which then cause bump steer. What's the best place to start attaching this problem? Is my rear tire pressure still too high at 33 psi? Should I take it in for an alignment? Inspect/replace suspension components?

[maxnix]

So are we talking about a fully restored suspension here.

Are the tires the same manufacturer and the same series from that manufacturer?

Pressures and tread depth front and rear?

[RustyBucket]

The suspension has not been restored... As far as I can tell, the most recent suspension work has been Tokico blues a couple years ago.

The tires are not the same manufacturer front and rear; the rears actually have a 98 load rating with 44 psi max and the fronts have 95 with 35 psi max. Both front and rear all-seasons. I didn't measure the tread depth, but both front and rear are well above the wear bars. Currently, the fronts are about 32 psi and the rears are about 35 psi. I think I'm going to take the rears down a bit in pressure to see if it helps, as reducing them to where they are now seemed to help a bit.

[Q45tech]

Normally one would have the widest strongest tires on the front to reduce understeer and improve braking. Just as one uses a stiffer rear sway bar to reduce rear traction from having equal size tires.

I have run 235 front 215 rear a few times.

[maxnix]

I'd go 35 psi or higher in front.

With an aged suspension and different tire manufacturers you are gaining an education of what not to do by experience.

[Q45tech]

A 95V tire =1521 pounds of support with 44 psi of inflation.Depending on driver weight the left front can have 1130>1240 pounds sitting still.

Starting inflation: Pick driver weight first then find tire load sitting still say 1200# so 1200/1521 = 0.788 x 44 [or 51 psi tires] = 34.7 or [40 psi].

Then add inflation to correct for turning [g load] or braking or panic braking load shift.

Anyway 200 pounds of load shift is reasonable since it is short term peak not continuous [UNLESS you race, slalom, etc].............say 34.5 pounds per addition psi ABOVE standing still so 5-6 extra psi to adjust for aggressive driving.

Tires are a little self adjusting to stress as the casing temperature rises from friction heat so does PSI ~ 1 psi per 10F.................a 1>3 second panic stop has little reaction time to raise internal psi nor does a sudden swerve.

A 1620 vs 1560 vs 1521 will obviously have different static PSI [6.5% or 2>3 psi].

Lots of difference with a rear 950 pounds and a front with 1160 pounds, same problem with 150 pounds of gasoline or near empty.

Inflation sets hydroplane speed so the higher the psi the higher the possible speed before hydroplanning. Remember tires cool down in rain so pressure drops almost immediately [2>3>4 psi].