I just started autocrossing last year in a mazdaspeed 6 and going to start in the 8 in july. How big a difference are the 2 tires assuming a 45 sec. course? The re40 has less than 500 miles currently and seems like a waste to change the tire and leave it in the yard. If I was to get the 615 should I get 225 or 245? I'm still got a lot to learn about driving this car considering my two previous car before the speed6 had LS1 in them. Any input would be appreciate.

 

i dont know much about autoX so im just kinda thinking out loud but you might want to make sure upsizing the tire doesn't up-class you.

 

well, on a grip scale (1-10) the OEM 040 are like a 6, the 615's are like 9 .9.

HUGE diff. Just check your regional rules

EDIT

mac11 quoted FTMFW!!!!

 

It's not that much difference, I'd say the RE040's are like a 7 and the RT615's are like a 8.5 with the RE01R and AD07 being the 10's. If you're still fairly new to autocrossing the tire won't matter as much as your driving. A local fast guy brought his bone stock RX-8 on RE040's out and was within 2-3 seconds of B stock guys on a 100 second course.

 

+1
The 615's are better, but to me it's not good enough to worth spending the money and replacing perfectly good stock tires. Beside, what's better way to dispost them than burn them up on autox? Unless you're getting R Compound, you're still loosing time with the best street tires, so I wouldn't change them out yet.

2-3 seconds within the fully setup B Stock guys in R compound? That's almost like beating them...

 

Yep, I think he will be fast in the local B stock field. We have some very quick drivers already from DFW in the category so this should mix it up big time.

 

no offense, but if he was within 2-3 sec on OE tires they must not be that quick based on my experience there

 

OE tires, shocks, exhaust and alignment Baggy. It may be an anomoly but I ran that type of difference from the B-stock guys both days at a 2 day event. I don't think it means anything. We'll see what happens when I get the car setup for B-stock.

CSP is getting to rich for my blood at a national level (I'd pretty much have to buy a new MX-5) and I like to keep my autocross cars fairly streetable. I can't keep the Miata and not trailer it to events and expect it to be competitive. Besides, I'd venture to say that B-stock in DFW is the best/tightest competition in the area.