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Car is darty with heavy steering effort... cause?

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I switched on some new shoes, a set of 15x7 et20 with 205/50R15 kumho's, and the car is now very darty on the freeway with a heavy steering effort. When I switch back to the 14x6 et30 w/ 195/60R14, problem goes away. I can still feel the car tramlining, but it's not pulling like with the bigger setup. What is the biggest contributor? Offset, tire size, camber/caster, toe? The car was recently aligned, and it looks like camber is very low (0.2deg) and caster is different between the two sides (3.5 and 2.6deg). The toe looks good, and on flat, level pavement car does not pull or wander

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you mainly answered and solved your own question

by switching back the the 14" narrower rim/tires

your Caster MUST match on both sides

no matter what tire is on the car!

Same for Camber - both sides

must have same reading

Toe-in ZERO ....to 2mm-in on each side

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The biggest difference is the sidewall height. The shorter, stiffer sidewall will not deflect as much and cushion the tram effect, if you put a set of 185/70/13" on it it will get even better. This is a big problem with light cars with wide, short sidewall tires. Remember the car was designed to run on a 165/13 (80 series sidewall) The steering effort was much less on those tires, and even less with the original 16.5" steering wheel

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I was amazed at the difference between driving my car with 14" wheels with 60-series tires and 15" wheels with 50-series tires.

Excellent for Autocross with a slightly firmer ride on the highway.

Should ride like a older Cadillac with 13" wheels with 70-series tires (the 02 not a Caddy).

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...and if you REALLY want to poop your pants, put the 13's in back

and the 15's in front...

I did that once, and... did.

The practical solution is to check your toe- in. It SHOULD be heavier to

steer, and follow ruts more, but it shouldn't be 'darty'.

If you're not toed- in maybe 1/16 to 3/32nds, try adding just a bit more toe- in.

It's FREAKY what a quarter- turn of each adjuster can do when you're right

around zero toe with short tires-

as Byron says, with taller tires, the 'twitch point' is less noticable and wider.

If that's not it, might be worth having the suspension measured,

to make sure nothing's bent,

but first check everything, especially the trailing and front arm bushings

and the rear subframe mounts.

A shorter sidewall also amplifies any unwanted motion anywhere in the

suspension...

hth

t

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