gman44116

iTrader: (1)

I just swapped out the 17" rims & Bridgestone Turanza's for:

18" 245/40/18's on the 18" A-Spec rims.

I am in a tight spot based on the odomoter which will be quite inaccurate now..

I heard the the Navi screen can adjust to the new tire & rim size to report the accurate mileage.

Has anyone done this? If so, how?

Any help would be greatly appreciated.

Thank You

GMan

cM3go

the Navi and the Odometer have no correlation as far as I know

3PUTT

i have the same wheel/tire size. the speedometer/odometer/navi do not need any adjustments. i even had the opportunity to check my spedometer against the radar stations they setup in the residential areas here in NJ. so far 25 on the meter was 25 on the radar.

245/45/18 is still pretty close to the same size as the stock. the difference is fractional if any.

gman44116

iTrader: (1)

I believe the 245/45's are much closer to standard than the 40's.

If I am correct, I am posting 100 miles when actually it is 97.

3% difference. this could add up.

Does anyone know if the Navi can adjust the dimensions??

cvajs

err,

235/45 is about the same as a 245/40

245/45 will be taller than a 235/45

3PUTT

it's really only about a 5mm difference....

Bareback

Have to tried: http://www.miata.net/garage/tirecalc.html

With the change from 245/45/17 to 245/40/18 the difference is only 0.1% too slow.

Your speedo shows 60 mph you are actually at 60.1mph.

cvajs

yes, but he moved from 17" rims to 18" rims.

235/45/17
[(23.5mm * 1in/2.54cm)*.45]*2 +17in = 25.32in tall

245/45/18
[(24.5mm * 1in/2.54cm)*.45]*2 +18in = 26.68in tall

245/40/18
[(24.5mm * 1in/2.54cm)*.4]*2 +18in = 25.71in tall

so to stay around oem height i would opt for 245/40/18, not a 245/45/18

gman44116 - the diff between bolded heights is not enough to throw your speedo off or affect Navi (Navi should use GPS sampling to know where you are, not by how many miles the car says it has gone. in other words, your Navi should work even if your car is on a flatbed).

3PUTT

That is right!! I was mistaken. I do have 245/40/18 on my SSRs.
My Fault....

that's right!! i was mistaken. my car

cvajs

a 245/45/18 may work good for those who dont want to drop the car. this size will fill the wheel-well more (approx 1/2" closer to well lip), but note they are also 1" taller than oem 17's.

tire sizing has always been a game of "try-it, try-another". i find that tires of same size from diff brands are not always the exact same size.

cheers.

and i have to correct my calcs, the answers are correct but the tread widths should have been in "cm" units as opposed to "mm".