Running different tire sizes

[ukrms6]

I bought a pair of used Kumho Ecsta ASX for $20 each but the size is slightly different then the two stock tires I am planning on keeping. Stock size is 215/45/18 and the Kumhos are 225/40/18. Could this in any way be harmful for the car, specifically the awd system since the fronts will be spinning a little bit fast then the rear?
Thanks.

 

[Zack]

on an awd car you wanna avoid using different tire sizes, tires of the same size but different brands/models or same size and brands but more than 1/4 inch different in treadwear

 

[ukrms6]

so running a pair on 40s in the front and 45s in the back is unacceptable?

 

[wannabe]

yeah, i wouldn't do it.

 

[Zack]

definitely dont wanna do that. the shorter tires will rotate at a faster speed and the 45s will try to catch up to that speed, putting strain on the AWD system. thats why even the same 4 tires at a 1/4 difference is not acceptable. some awd systems are that sensitve to the rotational speed

 

[illeztimportz]

i have a question similar to this. the 4 tires i have on my 06 MS6 are 'chopped up'. i have a pair of the same tires sitting in the garage and was wondering if it would be ok to put on? my current tires have about 7-8/32nds and the pair im wanting to put on are about 9-10/32nds. would it be ok to put them on? if so, front or rear? the 'chooping' of the tires is causing slight vibrations. thanks for any info!

 

[sunshineFC]

calculator says 812.1 revs per mile on the 215, and 829.3 revs per mile on the 225.

http://www.1010tires.com/TireSizeCalculator.asp?action=submit

 

[Guest20182]

In my experience, you can use the same size tire with different tread AS LONG AS the difference is no greater than 2/32" no more without any harm to AWD.

 

[illeztimportz]

Thanks for the reply ZoomZoom06. BTW, would it be best to put on rear or fronts? I would like for the newer pair to wear quicker, so wouldnt I put them on rear?

 

[batou079]

no, put them on the front.
Our cars are front wheel biased... meaning torque controlled by the ECU puts most of the power in the front during calm driving.

 

[BlackCherry06]

Put newer tires on the front of a FWD-biased AWD vehicle. This will cause the fronts to rotate slightly slower than the rears, which will cause the AWD system to remain neutral during normal driving. If you put the bald tires on the front, the system will detect a faster rotation up front than at the rear, and engage AWD to compensate.

 

[funkytuqe]

This is interesting. What about running the spare doughnut tire on the MS6in the event of a flat? What damage could be done? I would imagine Mazda would have thought this through though.

 

[batou079]

i believe the spare runs an overall smaller diameter, but its main purpose is SHORT runs to the local tire shop to get a new tire ASAP.
long term driving with the spare im sure would end up putting unnecessarily prolonged stress on the AWD system.

 

[funkytuqe]

Yah, that's right but i guess the question is how much stress will it put on the AWD system? The spare does you no good if you drive it for 10 miles to get a new tire and you end up screwing something.

 

[BlackCherry06]

Doesn't the differential bare the brunt of mismatched sizes from side to side? I wouldn't worry so much about the AWD as I would the LSD.

 

[Guest20182]

Doesn't the differential bare the brunt of mismatched sizes from side to side? I wouldn't worry so much about the AWD as I would the LSD.

^this. A differential allows for wheels to turn at different rates. Center diff would be taking the stress.

 

[vrspeedemon]

I just recently had the pleasure of using my donut spare on the speed, rode like absolute s*** and I had to turn off dsc as it was basically going nuts at any speed over 20....I don't see how some people can ride those donuts on the freeway awd or not!!!!
Trust me, the 20 miles I drove home on the side streets was scary enough for me to start my search for a full size spare

 

[batou079]

yup. trunk spare is scary stuff, lol.
glad you made it home safe.

I have an old bent stocker from a day at teh track, im gonna repair it, get a random cheap used tire mounted, and have it at home as a full size spare.