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So I had a blowout on my front tire after hitting a fairly large pothole and immediately pulled into a side street and proceeded to change the front tire and put on the spare. The manual specifically states not to mount the spare on the front as the diameter of the wheel is smaller than the stock tire. I was in a hurry and drove on it for ~3 miles, then switched the rear tire with the spare at home. Could this have caused any damage to my differential? BTW, the blowout was from a previously patched hole. Vehicle is a 17' Honda Civic.

  • Does your vehicle have a limited slip differential? Did you see any dash indicators highlighting that your traction control system was taking exception to the wheel speed difference? – Caius Jard May 6 at 6:11
  • similar Q & A exist, here is one : mechanics.stackexchange.com/q/43606/10976 – Solar Mike May 6 at 8:14
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    It is extremely unlikely that you caused any damage whatsoever in the three miles you drove. Basically, there are a couple little gears that don't normally spin except when you go around corners. When the tires are different sizes they spin all the time. However, three miles isn't enough to cause these gears abnormal wear, especially if you weren't driving it hard. – the_storyteller May 6 at 14:49
  • @CaiusJard Yes my vehicle was giving a TCS error on the dash, except it always gives this error when I mount the spare tire on any wheel. I did hear an abnormal noise like a bad wheel bearing – thediyer May 6 at 15:57
  • @the_storyteller Yeah wasn't driving it very hard, going very easy. I feel good now :) If you put your comment as an answer I will be happy to solve it, – thediyer May 6 at 15:59
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It is extremely unlikely that you caused any damage whatsoever in the three miles you drove.

Basically, there are a couple little gears that don't normally spin except when you go around corners. When the tires are different sizes they spin all the time.

Three miles isn't enough to cause these gears abnormal wear, especially if you weren't driving it hard.

For a detailed explanation of how a differential works, see the Wikipedia article

The gears which spin when you run different sized tires are called spider gears, and are tagged number 4 in this diagram.

differential_diagram_with_part_tags

The Traction Control System (TCS) error you saw displayed was caused by the tires spinning at different rates. Traction control detects differences in the rate of rotation of the wheels, and assumes that if they're spinning at different rates one or more of them has lost traction. In your case, one of the wheels was smaller, so it was always spinning at a different rate.

  • What does the TCS do when one wheel spins faster than the other? – Solar Mike May 6 at 19:38
  • It will decrease power, usually by cutting spark, to stop the tires from spinning. When it detects that the tires are no longer spinning, it will restore power. – the_storyteller May 6 at 20:17
  • Or by controlling fuel delivery - especially as diesels don't have a spark. – Solar Mike May 6 at 20:20
  • I was just wondering if the honda has a fancy diff (limited slip.. for example) which is why they give the warning not to put the small spare on the front. Missing a comment now? See torquenews.com/1574/… – Solar Mike May 6 at 20:24
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    If the outside diameter of both the worn and unworn tires match exactly, then yes. Otherwise, it's not recommended. Because it's almost impossible to match tire diameter, shops usually recommend that you just replace multiple tires. I've always run whatever tires I could on my old Civic and been fine, but if you have the new Civic Si with a limited slip differential, it might cause you issues. If you do choose to replace only the single tire, I'd rotate it to a rear tire where it shouldn't matter, and run the matched tires on the front. Just be sure the TCS light goes out and stays out. – the_storyteller May 7 at 13:40

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