Wheel Size

[F6 RAPID]

  chrislak said:

Thanks guys for your responses they have helped, so do I read this correctly are XR6's with 18 inch wheels actualy slower at take off than one fitted with 17 inch wheels, I suppose the proper way of installing very large diameter wheels is to change the diff ratio to composate for the extra diameter and possibly a step down/up gear for the back of the speedo.

One other point how would the wheel bearings react to 20 inch wheels.

Woudn't car would look at of this world with 20"s.

:lol:

Mrmods, you are completely correct!

You are NOT changing the rolling diameter of the tyre, it is simply a lower profile tyre with a higher profile wheel. Nothing else changes (diff ratio) because there is NO NEED for it to change. The rolling diameter of the wheel remains constant. Geez.

Why do you think you put lower profile tyres of an 18inch wheel as opposed to the 17incher?? TO KEEP THE ROLLING DIAMETER THE SAME.

[chrislak]

Ok, so the XR'S with 18 inch wheels have a lower profile therefore rolling diameter id the same.

[F6 RAPID]

Completely correct!

[Guest Mr Walker]

Mr Plow,

Your diameters are based on theoretical calculations - I'm sure you realise that two different brands of say, 235/45/17's aren't the same and from my experience can be 5 - 8 mm different even though they're labelled the same. I haven't checked with Ford but if the 18's are almost 10mm bigger than the 17's then there will be some speedo error. My car has arrived at the dealer with 17" wheels and they are now swapping over to the 18's. If there is a difference then the speedo would need to be recalibrated. I doubt there is a different speedo set up for 17 and 18" wheels. If there is can someone tell me in a hurry so I can get it sorted out before I pick up the car.

And mrmods, for those that don't understand, why don't you explain things to people rather than just pay out on 'em?

[CJF077]

MrWalker i have heard from people at FOMOCO that you do need to have your speedo recalibrated for the 18" wheels. I suggest you check this with your dealer.

[turbo_nick]

Mr Walker

Oh yeah, very theoretical. Every tyre is different.

As with 17" and 18" tyre size difference, you don't need to get the speedo recalibrated because you'll still be within the allowable limit.

My car was doing roughly 105kmh @ 110kmh with 15s and 17s, and it's just over 110kmh at the moment with 19s. Most cars are overcalibrated when they come out of the factory.

[chrislak]

Ok so here we go again the 18 inch wheels are actually larger in diameter, so that must mean I slight decrease in take off power.

[Guest DZ.]

  chrislak said:

Ok so here we go again the 18 inch wheels are actually larger in diameter, so that must mean I slight decrease in take off power.

No, that's not correct. You get larger wheels with the 18 inchs but lower profile tyres. It's the tyre diameter that determines whether or not you're acceleration is affected and that will stay roughly the same (within prescribed tolerances) such that it's unlikely to make a difference.

[F6 RAPID]

  DZ. said:

No, that's not correct. You get larger wheels with the 18 inchs but lower profile tyres. It's the tyre diameter that determines whether or not you're acceleration is affected and that will stay roughly the same (within prescribed tolerances) such that it's unlikely to make a difference.

Right on DZ.