205/50R15 on an MN-12, really?
I realize that you probably have several hundred pounds out of the car as part of the race prep, but before you worry about the engine, find yourself some beat up 17" Jag / Volvo / Lincoln LS wheels or something that you can at least jam some 245/45R17 rubber on to.
I used to track my SC at lapping days, of the various wheels and tire combos I had over the years, the narrowest section width was 255 ... I can't imagine what the car would have been like with even narrower rubber, even if it was down on weight.
Sounds like you are gaining experience and having fun out there, nice to see some MN-12 representation.
* Yes, really.
* Our car, race ready (full cage, w/o trunklid and lights, full tank) but without driver, is exactly 3000LBs acording to the corner scale
* While wheels are budget exempt from Lemons, they aren't budget exempt out of my wallet. I bought this car with 4 stock 15" fanblades. I found 4 more for <$100. Even beat-up 17" wheels for another car with the tbird bolt pattern would cost more.
* Smaller tires look stupid but help with acceleration and we needed all the help we can get given our engine power deficit. Using my smartphone, I did some quartermile testing using both the stock 215/70R15s and the first tires 225/50R15s. The quarter mile dropped from 17.96sec to 17.05sec.
* Direzza Star Specs are THE recommended tire for Lemons... even with heavy cars. Plenty of other folks with heavier vehicles (Jaguar V12s, Crown Vics, etc) go with the clown car look and rock these wheels. There are rules about minimum tire wear ratings (must be 190 or greater) and these Spec Miata tires wear well and just plain work in the dry and wet.
* I defied conventional reasoning and went with Toyo Proxies 4 in 225/50R15 for our first race. The logic was that a TW rating of 300 would help with wear and these tires had a larger cross sectional width (and therefore larger contact patch) than the stock profile. The result? Severe chunking after 2 days of racing. They cooked themselves. We still have a pair as emergency spares but the other two I just ended up selling to someone for $10 total (they were just going to use them to hold a car up). For the second race, we went with Direzzas.
* Star Specs are ~$100-115/tire in 15" and $168 in 17". Even though the Star Specs can last another race day, why would I screw with something that works? Of course, had I won the lottery on Fri, I'd probably spring for the new shoes.
* We have the suspension thing dialed in. As stated above, we did awesomely in the wet. Most cars in this series have really bad handling and we could out corner and out brake them handily. I'm not going to mess with a single component in this department (and this includes tires) except for stocking up on spares.
Would fatter tires help us? Sure. Is it worth the $$$ out of pocket and the additional scrutiny? IMO, nope.