Need help from you guys in deciding whether a 275 square setup is more beneficial compared to a 255 square setup I'm running now.

Current Setup:
255/40 17x9; wheel weight 19 lbs; tire weight 26 lbs

Proposed Setup
275/35 18x9.5; wheel weight 19.4 lbs; tire weight 30 lbs

Alignment: -4 front and -3 rear. 1/8 toe-in rear, 1/16 out in front.

Car weight 2700 w/o driver. AP2 stock motor & gearing. GTC300 wing and front splitter.

Running the Gendron 1-5/16 bar with Tein SRC (16k spring rates) on RA1's. Car will be used on road courses only (no autocross). I did a search and found several folks running a 275 setup for autocross. Seems to be pretty neutral, but unclear whether the added contact patch is effectively being used. I love my 255 square setup now, feels great and confident. Will I loose performance running a 275 or should I make the move?

-Arax

 

I think it's clear that the extra contact patch is being used for autocross.

Do you have a datalogger? Are you running consistent laps at your home track?

Why not run a faster compound (R6 / Eagle / V710) if you're looking for more performance?
Especially if you're not competing in a series and just running for fun.

To that end, then why the desire for faster tire? Totally get it if you want to pass more people at the HPDE, but it's not likely to make more than a second at the track. If that. And faster car doesn't mean better driver.

Personally speaking, I max compound before size. Sometimes there are additional factors to consider such as wanting more surface area if a particular tire is overheating (like R1Rs).

 

I'll +1 on Charles advice, and add the following:

With the disclaimer of "all other factors being equal" and "used effectively" i.e. proper temps, aligntment, pressure, no change in gearing etc., then more tire will absolutely give you more ultimate grip. It's physics, you can't change that. With more tire and bigger wheels comes more rotating, unsprung mass, and more tire means more drag on the straights. Still, your cornering speed will go up by a measurable amount. I would absolutely speculate that your lap times will drop with this in mind. Your tires will also take a lot longer to go off, another added bonus. If these are your goals, go for it.

 

I do not have a datalogger, but use a GPS receiver for lap timing. Am running consistent laps and would be able to do a comparison using 275's, if that's what I end up with. I'd love running a faster compound; however my car is also a daily and would like to stick to one set of wheels & tires.

The larger rotating mass is what kills me. I may have more ultimate grip, but will loose average speed around the course. Again, I cannot quantify this without trying myself or getting feedback from you folks. Another downer is the overall cost of larger tires.

 

Generally the car that carries more speed in the turns has faster lap times IMHO. But, if for no other reason, you should do it to find out if it really is faster.

 

If cost is an issue, then I would skip the larger tires. You're just competing with yourself and posting quicker lap times doesn't mean you've done anything better if the change is due to equipment.

I'd spend the money towards a datalogger / video setup and try to see where you're under / overdriving. That'll make you faster in every situation. Try to get a fast guy in your passenger seat to give you help.

The best track learning I had was in a stock Miata on 205 Star Specs. I like going fast(er) than other people on track, so I get that. But at the end of the day, being a better driver is way more satisfying. That's where I'd spend the money and effort.

 

What are your current tire temps? If they are high then you would probably benefit from a wider tire. But also a wider tire takes longer to warm up/get grip.


0.02

 

I would probably swap out your suspension first.

 

the car has stock power im assuming? no FI. I think most of the stock NA guys are funding that the 255 is more than enough unless you are extremely aggressive on the tires... in that case i would refer back to what billy asked about the tire temps.

 

Tires are not over-heating and within the required operating temperatures. Yes, the motor is NA and unmodified.

So far I have:

Pros:
More contact patch, faster corner speed
Faster lap times (unknown ?)

Cons:
More unsprung weight, slower turn-in & acceleration
Tires more expensive
Longer to heat tires to optimal temp