18's on AUII..

[rayner22]

Okay this is just my mind thinking too much but you reckon puttin 18's (with 235 tyres) would put a AUII Forte speedo out??
You'd think that the rolling diameter would be the same huh

[blackers10]

it all depends on the profile matey
your local wheel and tyre shop knows whats best its all in a book they have)

goto this address and it has a calculator and you put your stock tyre in and your new tyre in and it shows the difference
http://www.miata.net/garage/tirecalc.html

i beleive 18" rims require a 40 profile tyre? with around 235 tyres?

thats what mine had from memory and i had no speedo dramas

[Racecraft]

4.6% difference

[rayner22]

Thanx boys, guess 4.6% difference isnt too bad. Least it wont mean any nasty speeding fines.....

[Smoked]

but the difference for speeding fines is 2-3%.

4.6% @ 60 km/H is 62.76km/h, which is in ticket zone.

[Racecraft]

Originally Posted by Smoked

but the difference for speeding fines is 2-3%.

4.6% @ 60 km/H is 62.76km/h, which is in ticket zone.

only in Victoria :P

[Smoked]

Yeah, thats true, i didnt see his location. Ohwell, guess im not getting 18" wheels anytime soon.

[HOTC2R]

I've had 18's on the wifes AU II for 3 years now. No probs.

[OZFORDAU]

Ok i've got 18" wheels on my AU1 Forte! What is this about my speedo been out?

Cheers

Simon

[XR6-VCT-2000]

Originally Posted by OZFORDAU

Ok i've got 18" wheels on my AU1 Forte! What is this about my speedo been out?

Cheers

Simon

eg .. Look at your old original rims with tyres ...measure the distance from top to bottom (top of the tyre to the bottom of the tyre) ..ok .. this is the wheel diameter...or measure the radius ..It's all just about keeping that same diameter or radius the same , to much bigger or smaller a radius and you will prolly put your speedo out a bit .. if u've gone a bigger rim , then by right you should of gone a lower profile tyre (wall height of the tyre is smaller) to compensate for the larger rim , to keep the diameter or radius roughly the same as the original setup ..

Not emplying anyone is dumb here ! - just explaing it to those who didnt understand ... thats if even my explination made sence ! ..lol ;)

[OZFORDAU]

LOL! I think it should be fine lol!

Cheers

Simon : ing_sm

PS: I really don't know if the speedo is out?

Example if i read that i was going 60km/h could i be going faster or slower? Is that what this means if the speedo is out? Can it do any damage or effect anything else?

[Smoked]

No damage, just possibly going faster, maybe get done for speeding, not that you've ever done that. ;)

[JC]

235/40/18 compared to a 235/45/17 (AU2/3 XR rim size), a speedo reading of 60km/h, means you are actually travelling 60.2 km/h.

If you got a 245/40/18 then at 60km/h on your speedo, you would be doing 60.9km/h.
If you got a 265/35/18 on the rear (9" rim), 60 on the speedo would be 59.9 in reality.

So either way you are fine.

[OZFORDAU]

Originally Posted by JC

235/40/18 compared to a 235/45/17 (AU2/3 XR rim size), a speedo reading of 60km/h, means you are actually travelling 60.2 km/h.

If you got a 245/40/18 then at 60km/h on your speedo, you would be doing 60.9km/h.
If you got a 265/35/18 on the rear (9" rim), 60 on the speedo would be 59.9 in reality.

So either way you are fine.

Ok i'll check tomrrow!

Makes sence now!

Cheers

Simon

[ronwest]

Did I read in these forums that Ford dealers could re-calibrate speedos to cater for different tyre/rim combinations?

[JC]

If you stick with the same rolling diameter, there is no need to recalibrate.

[rayner22]

Originally Posted by ronwest

Did I read in these forums that Ford dealers could re-calibrate speedos to cater for different tyre/rim combinations?

Well from a past experience the AU only has a listing of different tyre sizes etc in the ECU which are selected to recalibrate the speedo. Im gonna see my local dealer probly monday next week, I'll try and get a list of all the sizes that the ECU has stored in it.

But I think that with 235\40\R18's I should be okay.