AWD and tire sizes

[Melon]

I believe I know the answer, but want to verify with the knowledgeable folks

2000 AWD, had a flat tire a few months ago, replaced the tire and went about. Fast forward a few months and time for tire rotation. There has been a small vibration when slowing down from 70 and now after the rotation, it's worse.

My question here - do the tires need to be the same size and tread depth? Or will 3 older tires and 1 new one cause an issue? Is it a time bomb for the transfer case or trans? I'm guessing atleast 2, if not all 4, should be the same size and tread depth.

Thank you!

 

[Dono]

The slightly off tire needs to be on the front if you have limited slip on the back.
I'd keep the tires very close to the same (Don't use the same 3 new tires with 1 bald one).

The vibration you are talking about doesn't sound like its a tire size miss match issue. I'm sure others will chime in with their opinions/experiences.

 

[Melon]

The other 3 are no where close to bald. I believe they are 6 or 7/32? I'd have to look again.

My gut says the vibration is driveline and I've been leaning towards a U joint. Or maybe a wheel bearing? Since it seems to be speed related and not RPM? But after the tire rotation, tires came to mind.

 

[koda2000]

For AWD Ford says w/in 1/32 of an inch on all four tires. That's one reason I didn't want an AWD. I've always rotated mine to keep them equal and replaced all four at one time. Even installing a new tire of the same size can cause problems because it may not be the exact same diameter as a different brand and 1/32 of an inch isn't much.

 

[J_C]

While I also doubt it's the tire, there might be a tire shop near you that will shave the tire down to a matching diameter for ~ $20.

Vibration slowing down seems like it could be a warped (ambiguous term, as likely means raised hard spots on) rotor to me. If there's only one raised area it'll happen once per tire revolution but if more than one, can become rapid enough to seem like a vibration. Do any of the pads or rotors look like they have dissimilar wear to the rest, side-to-side at least?

 

[koda2000]

While I also doubt it's the tire, there might be a tire shop near you that will shave the tire down to a matching diameter for ~ $20.

Vibration slowing down seems like it could be a warped (ambiguous term, as likely means raised hard spots on) rotor to me. If there's only one raised area it'll happen once per tire revolution but if more than one, can become rapid enough to seem like a vibration. Do any of the pads or rotors look like they have dissimilar wear to the rest, side-to-side at least?

Oh they definitely can warp too. I used to turn rotors and they have a max runout.

 

[CDW6212R]

The tire sizes need to match between the front and back pairs. Ideally they should all four be identical, but it is possible to have a slight variance if the pairs result in a close match.

I mention this because lots of people may notice that certain tires wear faster than the others. If you are watching closely and can be aware, you can mix a more worn tire of the four, with the least worn, on one end, and result in an equal front/rear diameter.

I managed to do that with my mail truck, which is very hard on front tires. With mine the only way to maintain the size balance was to swap one front and rear tire, and swap the tires left to right. My transfer case when I got the truck had dark fluid in it, and has slowly become less "dirty."

You should change the ATF in your TC, and hope it's not dark, full of wear material from mismatched tires. With a good TC you should be able to feel the roughness that comes with mismatched tires.

I could the one time I tried to use two different pairs of snow tires, which had about a 1/4" difference. I drove about two miles and turned around to correct the issue(I had two sets of snow tires, one new and one time to retire/sell. I was going to use the new set but discovered during, that the old wheels(Sport Trac) would not fit over my big brakes). I had to use my old set one more time, for the snow that came that night. I sold those snow tires a few weeks later to a customer with a Ranger who lived on a steep hill.

 

[koda2000]

As an extreme example of tire mismatch, when my daughter had her 2000 Mountaineer AWD, she had a flat and never bothered to get it replaced/fixed. Then she had another flat and was stranded on the way home from work. The closest family member to her location had a donut spare that fit the bolt pattern, but was a smaller diameter tire. After installing the donut the truck would barely move due to the tire mismatch. Fortunately she was only 1/2 mile from her house.

 

[Melon]

The tire was replaced with the same tire, just brand new.

All 4 brakes and rotors are new and replaced at the same time.

Next time I'm home, it looks like I'll be checking trans fluid. It's probably due for a change anyway. It has almost 160k on it.

Thanks guys!

 

[CDW6212R]

If you think you have any tire size difference, look at them hard and try to place the most worn tire, and the least worn tire, together on the same end of the truck. That should get the two end pairs as close to a match as possible. I've done that with my mail truck, as it eats the front tires faster than the back.