How much do rims affect my spedo on my V6?

[Juans_93_MX3]

I am taking the car to get the tranny rebuild
I got 18 inch rims in the back and the 14inch stock wheels in the front (I think its 15inch stock wheels, dont remember)

Anyway, I know bigger rims affect the speedometer but by how much is it going to affect my MX3?


by the way, yes I do got two more 18inch rims for the front, its just the tires are dead, need to replace

[mxmaz]

depends on the size of the rubber

[georgechicken]

Give us the size of the TIRES going on the front, and we can give you an exact figure... it doesnt matter if you had 35" mudgrips on the rear, that wouldnt' throw off the speedo a hair... .well, except for the fact that you'd be riding on the front bumper instead of the tires..
Speedo error is calculated by comparing the circumference of the original equipment tire to the circumference of the new tire.

Daniel

[johnnyb]

the rims really dont affect your speedo unless they're bigger then your stock wheel. You will have no affext at all as long as you keep the diameter of the tire the same.

[J0HN_R1]

I am taking the car to get the tranny rebuild
I got 18 inch rims in the back and the 14inch stock wheels in the front (I think its 15inch stock wheels, dont remember)

Anyway, I know bigger rims affect the speedometer but by how much is it going to affect my MX3?


by the way, yes I do got two more 18inch rims for the front, its just the tires are dead, need to replace

the wheels in the front are gonna be smaller, and the speedo takes its reading from the tranny anyway...

:

[Juans_93_MX3]

I am taking the car to get the tranny rebuild
I got 18 inch rims in the back and the 14inch stock wheels in the front (I think its 15inch stock wheels, dont remember)

Anyway, I know bigger rims affect the speedometer but by how much is it going to affect my MX3?


by the way, yes I do got two more 18inch rims for the front, its just the tires are dead, need to replace

1st, the wheels in the front are gonna be smaller, and the speedo takes its reading from the tranny anyway...

2nd, WTF are you doin with 18's in the back & 14's in the front...? Going for the RWD "muscle-car" look...? Please tell us they're different style rims cause one/both of the 18's are being replaced...?

No, its just that the front tires need to be replaced

[RoundTop]

ok, so you are in a GS..

so that means your front tire are 15" rims, with either 205/55/R15 or 195/60/R15 tires on them. That is normal.

Now if you go to 17s, you will need to go to around a 205/40/R17 (depending on width of tire you want. But that is a difference of 1.256" around the tire. So, a difference of -1.5% on your speedo. ((new circumference-old circumference/old circumference) * 100).

I used http://www.s-series.org/htm/calc/tiresizeconv.htm to convert the diameter from the tire sizes. and the old stanby of PiD for the circumference.

Rear tires do not matter as the front ones are the ones that are the drive tires, and hense where the speed is coming from. The rear tires, if larger, will simply spin slower, if small, will spin faster.

[D323]

our friends over at miata.net have done most of the leg work for us....

their garage section has many handly tools such as this one:

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

[Spinkx79]

our friends over at miata.net have done most of the leg work for us....

their garage section has many handly tools such as this one:

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

That is a cool little tool.

Didn't know i was going 2k slower than the gauge. I thought i was a bit faster.