tire sizes affecting acceleration
 

I have been trying to decide wether its all in my head or an actual problem - when i originally had the car with the 13's on it, it felt like 1st and 2nd gear pulled harder than they do now with my racing beat carb and header and all the other mods I have. I switched to some 15" rims with a way bigger tire in the back its a few inches taller than the stock tire, I am about to buy new tires and will go smaller just wondering if it could be possible that I messed with the ratio by changing the tire size and smaller tires will bring my acceleration back. Any info would be appreciated. - getting a little tired of getting pulled on until 3rd gear by my brothers jetta, its sad.

The amount of torque you put to the ground is absolutely affected by the overall diameter of your wheel/tire combo.

In addition, you probably increased the rotational inertia, so that's going to further suck power.

There are a lot of "tire calculators" oon the Net that will let you plug in the stock tire size and the new tire size and see the difference in diameter.

thats what i figured the front tires have lower profile tires so they arent much bigger than the 13's with regular tires. I'll get the same size tire for the back and take off the ones that came with the rims.

Thats acool program but i have no idea what the info/stats im pulling out mean. All i figured out is that my new tires will turn more times that old ones.....

I'm surprised you noticed a huge difference. You must really be in tuen with your car.

What is the overrall diameter difference between your two set ups?

that was a good program - you wouldnt have to be a car whiz i dont think to notice the difference. with the original tires it was def. quicker. when you put the stock rims/tires next to the new ones that are on the back they are about 5 or 6 inches taller. Everyones been telling me it would take more to spin such large rims and tires I just wanted to see what others thought.

5 or six inches taller!! Holy shit!

I would not have the clearance in my wheel wells for that!!

That is a BIG difference from stock. You basically changed your rear end gear from a 4.11 to like a 3.11. You would really notice it. Not to mention the difference in your speedo. It would read like 30MPH too slow.

I use the www.miata.net tire size calculator. http://www.miata.net/garage/tirecalc.html

According to this, you are probably running a 235/70R15 or 215/80R15 tire. I would like to know how this would even fit! The widest tire you can go with is a 215 with stock fenders. But I don't know how you could get such a tall tire in there.

instead of eyballing - i got out the ruler and its around 4 inches - they are I think 195 - 65 they fit in the wheel well fine until you hit a decent bump then they rub on the inside. I bought the rims and tires from someone who had a first gen so i figured worked for them work for me, the front tires wouldnt turn with that tire on so I got 195 - 50's I was holding off on back tires until i decided if i was gonna keep these rims - but they'll be off in the next week or so.

5-6" talller, post pics I gotta see it.
I'd say that's more than enough to notice a difference.

Pics would be cool to see.

What your saying doesn't add up. The tire size you say you have is only two inches higher than original. If it is a 195, then the height would have to be 80 or higher.
I don't think they even make a tire like that, so they must be wider too.

Just get 205/50/15's they are what I got on my gf's 7 and they fit and look fine, never rub when turning full lock or when hitting big bumps... I got Pirelli P700Z's or something they were like $56 each from tirerack ;) hehe