Gretch

OK i finally found the 18 inch cup 2 wheels I have been looking for. They have track slicks on them, so I want to get a set of street tires. What is the right size tire for a 10 x 18 inch wheel (proper offset). is 275 30 the right one? I want to get close to the current wheel diameter including the tire. I am currently running 255 40 on a 17 inch rim. By my calculations I would be a bit less than a half an inch off on the total diameter.

On top of that I want to be sure 275 will fit under the fender. Advice?

Lagavulin

Here ya go, bruh':

http://www.miata.net/garage/tirecalc.html

Gretch

Cool. Now to try and balance my desire for wide meats with my desire to keep the speedo accurate.......

Plus I need to know just how much meat I can get under the fenderwells. I am gonna test fit the rims with the hoosiers on them and see how it goes, (plus prolly take her for a short 'vette hunt while wearing the slicks.....just for sihts and gigles......

Garth S

To stay close, here are two alternates in Pilot Sports ('NO' Porsche spec) - each brand varies a little in size.
TIRE DIAMETER SECTION Rev/Mile
255/40R17 25.1 10.2 (on a 9.0) 827

265/35R18 25.3 10.5 (on a 9.5) 819

285/30R18 25.0 11.3 (on a 10) 832

Will they fit? - a lot depends on the clearance you have now weighed against any width and ET differences between the 17 & 18" wheels: eg., if they were 17x9, then the 265s would fit a 18x10 identically if the ET were +13mm MORE than the 17s, and the fender lip would accomodate the 1/2 of the + 0.3" extra section width - all depends where it is now.

Tim Murphy

I run Michilin Pilot Sport PS2
295/30-18 with 10" on the back
255/35-18 with 8.5" on the front

Great tires!!

BTW, I dyno'd the car this weekend, check out my updated sig.

Gretch

Murph, what is the rear wheel offset? are you running with spacers? Did you get my pictures of the fan install?

Tim Murphy

Got the pics and they look great!!

56 front
54 rear

Lagavulin

Gretch, you know the rules by now, yet you did not state your offsets; BAD boy!

Gretch

Yeah, I had to run down the auction url to get the number, I didn't want to quote the wrong ones. the new wheel offsets are: fronts 52, rears 47.

I knew you guys were just being kind to me, and I hoped to get the numbs before I got whacked for being a lamo........I ran the offsets through the calculator before and I know they will fit with some combo of spacer. I also tried out my curent rears on the nose and, except for a deep knee bend, the will run on the front. gonna look like a steam roller though.

I don't need the 4 hoosiers nor do I need the 8.5 x 18 rims (cup 2). I am gonna see if I can get some of my capital back.........

stuartph

Tim


That is some mean rwhp you have there, cooooooooooool


Stuart

GT UK

Mattman928

Send me an email at matt.friedman@accelare.com and I will be happy to forward anyone a copy of the spreadsheet.

mark kibort

best tires to run on a 928 are going to be MAX 30s on the rear and 40s on the front. (ie 305x30x18 or 275x35x18) and lower aspect ratio and you will have a way to harsh of a ride, and the tire will not perform right if you go smaller than the 305 on the rear tire. on a street tire ive raced on 275x34x18 fronts and 285x35x18 rears in the speed gt series on the spec Toyo T1S tire. Ive also tried a 285x30 and there was really not enough sidewall for this tire to work well. certainly going to a 30 series tire would be a step in the wrong direction. However if you run 335x30x18's as I do in the rear now for the spec tire for SpeedGT, it works as well as a 315x35x17 and has about the same dimensions.(close anyway on an 11" rear rim)

as far as rolling diameters, they are all so close, its not really a factor, especially for the street. i just had a cop friend of mine radar me at 60mph, and my radar trap speed was 61mph. (thats with 335s on the rear vs stock 245x45x16 as a 928 spec tire) 25.5 " or 25" who the heck cares????

275s or the 285s are probably the best size tires for the rear of the 928. even 255s are a little small when you look at the size and weight of the car!
Up front 245 to 275 all can work with the right rims and proper back spacing (offset)

mk

Lagavulin

Gretch, according to my calcs, you're going to be really lucky if you can stick those 10 x 47's in the back, and that's without a spacer.

Gretch

Its gonna be close......Andy is running 265s on the same wheel, though I want more rubber. Mattman928's spreadsheet says 285 35 will work, With no spacer, you are correct there Lag. The 89 spacer is 20mm, the CS wheel has a 60 offset and the OEM Cup2 has a 55mm offset. that says the non spacer offset should be between 40 and 45. We will see..................what 2 mm does to the equation.....worse comes to worse, I will take 5mm off the tread width.......

Blown Beast

MK, Did you ever drive on the street with the 285/30/18's on the front? If so how did the car track ,corner,and stop in a straight line? Did it want to wander all over the place?
I have 335/30/18's on the rear and had 275/35/18 (25.7diameter) in front but they rubed so I now have 255/35/18's(25.2diam) up front. but would like to go to the 285(25 diam) which is the closest to the factory's (24.9) and would give me the largest foot print for stopping/cornering.
Thanks Rob