I recently purchased, from e-bay, a full set of rims and two 18" Conti tires for my x-fire. I was thinking of mounting the Contis to the 18" rims and keeping one at home and one at my office for when the inevitable flat tire occurs (so far always in bad weather or late at night). I have put the tireless 18" rim on the rear hub and the bolt pattern matched. My question is this: Will the 18" tire/rim 'work' on the rear axel? Will it clear the rotor? Etc.

 

The great unanswered (by anyone official) question. See/search intenseblu's notes on this. Also, HDDP (Derek) uses 18 rears for racing only.

 

if you've already mounted it 'tireless' and found out the bolt pattern is the same, isn't it obvious that it will clear the rotor? if it wouldn't clear the rotor, it wouldn't have fit on so you could check the bolt pattern... or did i read that wrong.

the bigger concern is that it sounds like you want to run one 18" rear wheel and one 19" rear wheel (in a situation where you had a flat). i would highly discourage this! running your rear wheels with different diameters will toast your differential.

 

I mounted the rim on the hub, and it looked like it cleared the rotor. But I was unable to turn the axle to see if it would rub against the suspension.

 

the 18" will fit so long as the tire is sized correctly, heed the advice you where given above and make sure you do not run two different size tires in the rear... the traction control will go berserk thinking you are going out of control...

the bigger worry is, make sure that the new wheels you have will work with the stock bolts on the crossfire... pop one in the new wheel and make sure you have 19mm of bolt exposed on the back side... definitely no more and not much less... could lead to plenty of damage...

 

Will it be okay to drive (for a short period) if the traction control is switched off?

I'm using stock Crossfire rims.

 

NO. not unless you're going to change the 18" tire to something taller (maybe a 45 or 50 sidewall... i didn't do the math, just guessing).

 

If the 18" tire is the same diameter as the 19" then it would be fine, correct?

 

225/40/18 = 803.84 revolutions/mile.

255/35/19 = 774.88 revolutions/mile.

Not a huge difference.

Handy calculator for tire sizes...

http://www.csgnetwork.com/tireinfo4calc.html

 

18" wheels on the rear work fine (preferred by me). Though I wouldn't be driving very far on one 18 and one 19. Good to get you to the tire shop after a blowout, but not for cruising down the highway.