Over tiring vehicle
 

I autocross my FRS. I'm currently on MPSS 235/40/18 with a +35 offset. Would going 245/45/18(firestone indy 500) slow me down by going that much wider?

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It (245/45/18) will slow you down because it's too tall and heavy.

245/35/18 is the proper size. It should weigh the same or less as the 235/40/18 (of the same model/brand of tire), but have a larger contact patch.

Can't comment on the firestone tires compared to the MPSS. I have only used the Michelins.

What size wheels do you have?

Dude what mediocre tire choices for autox.
If you are autoxing more than once a month consider getting separate tires just for that. Trying to get find a tire that would do both will only lead to faster ware. Unless you hardly drive your car outside autoxing. Ever noticed why most people switch out tires at autox?

Road and Track went *slower* on the same make/model tire (Dunlop Z1 StarSpec) in 235/40-18 vs. 215/45-17 size.
http://www.roadandtrack.com/car-cult...ransformation/
245/40-18 would be another step in the same direction of wider, taller, and heavier.
245/35-18 would work but no Extreme Perf tires available in that size.
For street/autoX, and you want to go faster, I would be running "Extreme Performance" rather than "Max Performance" category tires like the PSS (which I wasn't too impressed with when I ran on my RX-7).

Honestly you'd be better off on 17" wheels, but with the wheels you have you might actually be quicker on 225/40-18s rather than 235/40 or 245/40.

I'm saving for a separate pair of wheels, preferably 17s. Spent all my money on suspension and bolt ons.

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18x8.75

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Indy 500 is a decent street tire choice, horrible for autox. If you're okay with being really noncompetitive and slow, then it doesn't much matter. The MPSS/S-04's of the world aren't even competitive tires.

there is no such thing as over tiring your car for autocross

The only real answer in this thread.

But possibly a point of diminishing returns. As the patch gets bigger it would also reduce tire temps which could reduce grip. At which point this happens I have no F-ing clue. Hahaha.

When it comes to tires it's the tire structure/compound that has the biggest impact. I have been autoxing off and on since 1996 and I learned real quick what impact tires have. From that point on I have only owned xtreme perf tires. I wasn't as active autoxing at one point and decided I would cheap out a little and also gain some mileage and dropped to max perf for one set. Man did that suck... next set I was back to xtreme perf. I just got my FRS a few months ago and it came with some 500tw Falkins and I want to slit my wrists but also don't look forward to buying new tires.

Long story short... buy xtreme perf and not stress out as much about 235 vs 245. An RE71A in a 225 would probably smoke a MPSS in a 245.

I think you should use a 245/35R18 for that size wheel. Same size wheel as me and that’s what size tire I’m using. It’s only 4 revs difference than stock size so my speedo is exactly the same. More responsive than a 40 or 45 also.

I agree the 245/35 is the correct street tire size.


But, OP is into AUTOX, and needs some R Compound tires like the RS3 and a set of 17's to run them on.


I would just keep the 235/40s on the 18s and save for the extra set of wheels and tires for AUTOX.

Taller tires and heavier wheels will definitely slow you down.

235/40-18 is taller than stock. 245/45 is WAY taller. very few tires are actually made in 245/35-18

stock 215/45-17 is 24.7"
235/40-18 is 25.4"
245/45-18 is 26.7

IMO if you wan to use a 245, it should be a good 245/40-17 on a nice, light 8.5-9" wide wheel (enkei rpf1, 949 6ul, etc). Same diameter as stock, pretty common size, and probably cheaper than an 18.