Mileage limit for autocross car?

Some wiseguy once said 'nothing says triumph of enthusiasm over physics like FWD racecar', and i'm beginning to see the light.

So let's say i'm looking for a RWD car that might do double duty as DD and autocrosser, like in STS or STR. Assume that wheel bearings and suspension bushings will get changed out, what's left is the stiffness of the chassis. Does chassis stiffness change with mileage? 700# springs can only do so much to control wheel position if the chassis droops around corners.

Short way of asking the same is : does a 225k mi NA miata (without major corrosion issues, i'm western US) handle about the same as a 135k mi NA miata, given equal setup?

<waves out of a north facing window>

I don't know if the tub gets softer over time to the extent that it would be noticeable or measurable in Auto-X times. Both will need suspension work but that's likely to fall under "equal setup". The highest mileage Miata I've owned and used on the track had something like 170k-180k on it and didn't feel that much different from the 130k one I have now.

Not sure if STS/STR allows chassis stiffening like frame rails, that would likely make a big difference for any NA regardless of mileage.

My experience around here suggests that you might have to pick up a car "across the border" (in CA) as the Miata market around here seems to be a bit non-existent.

Gosh i sure hope not, as i'm currently building on a chassis that has just under 300k miles.

Checking in with 165k mile STS / daily driver here.

(however, my engine has 130k fewer miles then the chassis)

I think most of the national level cars have well over 100k on them.

I'd worry a lot more about previous collision damage than I would mileage. I think it all depends on the car though. It's not something I've personally worried about in the past.

I think it would have a lot more to do with usage than mileage. If it's 225k miles of smooth highway driving in Arizona, that's one thing. If it's 225k miles of driving on (insert state name here) roads with tons of potholes and bumps and whatnot, and a state with snow/salt on the roads that may be different. I'd think repeated impacts over bumps or anything that caused the chassis to flex repeatedly, plus lots of exposure to cancer causing salt would weaken rigidity over a long time period.

100 miles of Pennsylvania roads equals 100,000 of Nevada roads.

pinchvalve wrote: 100 miles of Pennsylvania roads equals 100,000 of Nevada roads.

... as long as you don't stray across the border into CA. That accelerates wear .

Corrosion would definitely have an effect - rust in the sill in front of the rear wheels will loosen up the chassis of a Miata. The looser feel of a higher mileage car is often worn bushings, I think. I've read some reports that going through the car and re-torquing every bolt will stiffen it up, but I believe that to be a very high effort placebo effect.

Autox doesn't seem to place a high importance on chassis stiffness - light weight is more important. If I had a high mileage car and it was allowed by the rules, I'd seam weld it.

Deja Vu all over again?

I've never autocrossed a car with under 100k miles, and a couple over 200k

My 'rolla just went over 200k and it's not too flexy, and it's been pummeled by E36 M3ty roads since it rolled off the lot.

All I can contibute would be the firewall cracks that radiate out from the tunnel in first gen Neons, and the difference between a ministock car with 5 seasons on it vs. its replacement following a wall/nose interface issue.

I don't think mileage is as much concern as prior useage.

278k on my track car, chassis, engine and tranny. Still going strong. It does have all new bushings, suspension and a cage which helps

I was gonna mention something about the rally guys... but as Keith touched on, They seam weld and cage 'em up.

These, so some extent, are options if you see problems...