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Front tires slight mismatch , '08 Civic

The trusted indep mechanic pointed it out, saying it was bad for the transaxle. I’m aware of the issue for AWD differentials. How bad is it for FWD?

Both front tires are 205/55/R16. Left is newer ContiProContract (sp?) 91H, tread depth ~1/4". Right side is older Goodyear Eagle 89H, tread depth ~3/16"; side wall looks a little bit worn, maybe with some surface cracks (??) near the bead. These tires came withthe car when I got it 14 months ago.

Rear tires have about 25% of tread left. Pretty clear that I should buy two new tires for front and shift the odd-pair to the rear. Question is whether I should do it right now, or if I can wait until the rears need replacing.

You have this backward. The good tires belong on the rear. If you can afford it, buy four new tires. If not, shift your rear tries to the front and buy two new tires for the back.

You could be OK, but there is a risk and that risk is expensive if you lose on this one. Differential repairs are expensive. If the Civic is an Si then it might have a limited slip differential, even riskier and yet more expensive.

I feel your mechanic must be concerned to point this out and he did a good job in giving you a heads up to potential trouble. If the rear tires are matching tires (same brand, size, tread design) and are worn to the same degree you might be best moving the rears to the front.

In all cases where you have two mismatched tires on opposite sides of the same end you’re causing extra wear of the differential. In FWD cars the differential is contained in the transaxle. The differential contains a gear setup that allows the opposing wheels to turn at varying different rates while still both transmitting power,

In normal driving the wear on the gears that allow this is minimized. Using the example below, when you’re traveling straight the engine turns the ring gear, which spins the differential case. The case causes the differential pinion gears to orbit the axle’s axis, pulling the differential side gears and their attached axles along. When you turn, the differential pinion gears and the side gears turn relative to one another, allowing a difference in axle speeds.

When you have two different sized wheels on the axles, the side gears and differential pinion gears have to spin constantly against one another, adding a lot of unnecessary wear. This can cause premature failure.

http://tijil.org/Scion_Docs/05_tC_Shop_Manuals/Repair%20Info/Repair%20Manual/Manual%20Transmission-Transaxle/Differential%20Case%20Assy%20(E350)/conponen.pdf

If you must maintain two different tires on a FWD car, you face a tradeoff. You’ll reduce wear on the differential by putting them on the rear, but you’ll also make the rear more prone to losing traction in bad weather in a turn, like an entrance or exit ramp.

I just knew you would say to put the good tires on the rear. That’s what I asked this mechanic to do when he replaced the front tires on my Camry a few weeks ago – but he put them on the front! A difference of opinion among experts?? Or maybe I should not trust him so much.

Sounds like F/R swap is the thing to do, unless I buy four new tires. (Anybody want a couple of good used tires? :>) )

Thanks.

Its a change of opinion. It used to be considered best to put the good tires on the front but now most people say to put the good ones on the back for better control. In your case, I would get the rear tires on the front for the time being, then just bite the bullet on four new tires that match. You’re going to have to do it eventually anyway so why wait so long?

There are different opinions on this issue but I prefer new on the front for the following reason. My main concern is traction on wet roadways, not dry ones.
When there is standing water I prefer that the new tires (which are much less prone to hydroplaning) be in the front and cutting a path, so to speak, for the worn rears which are more prone to hydroplaning.
Let the rears follow on the pavement where the fronts have momentarily pushed the water aside.

As an analogy, when it’s raining and I’m on the road I usually tuck in behind a semi and follow in the their tracks. It makes a very noticeable difference.

If a car has lost grip and is going sideways I don’t see that tread depth on the rear is going to mean much.
That’s just my 2 cents anyway and the practice has always served me well.

I agree with @ok4450 I have never really gotten the new tires on the rear of a FWD car thing…I get that the rear is less likley to want to swap direction with the front in an extream situation. However, I think for the day to day driving that most of us do… New on the front makes me feel better, and I think suits a FWD car better… AS a side note on a RWD car I would put the new tires on the rear… I think its the power wheels that need the better traction at the end of the day.

I waffle on the subject. I have a hard time getting my right brain and my left brain to agree on this. I’ve seen the videos, but still have doubts, especially in the winter.

I think Mountainbike is talking about this video:

I still don’t buy it though, maybe I’m just a stubborn mule (at least that is what my wife says)

Mismatched tires are NEVER a good idea…Your differential will absorb that SLIGHT size mismatch okay, but handling and emergency braking will suffer. Time for 4 new matched tires. You will think you are driving a new car…

The video I was thinking of was produced by Michelin, but I like this one.

I think the bottom line is that mismatching tires on the same axle is not a good idea. The OP really should consider 4 new tires.

Sorry for delay in thanking you all for the advice. I’ll check further, but I think the two tires currently on the front are matched closely enough for the rear. They have a lot of life left. I’ll get two new ones for the front.

If this car did not have TPMS, I’d get a salvage yard rim and use one of the two front tires as a full-size spare (and make the other into a table lamp???).

Can I trust a TPMS rim from a salvage yard? Can I operate thecar without the TPMS?

Re: trusting a salvage yard rim; you can if you check it out to see that it’s straight & true. You’ll want to change th pressure sensor if your car uses them, as that may be dead, but the rim itself should be no problem if it’s the correct rim.

Can you drive without TPMS? Yup.

The other thing that people are forgetting is that two tires from two different companies, even though they are listed as the same size (205/55-16 in this case), might actually be different in overall diameter, and tread depth, when brand new.

So, if one tire was slightly larger, and had more tread when new compared to the other, if its worn more, it might actually be closer to the same height.

What should be done is have the tires measured, and if available, have one shaved to match the size of the other.

BC.