bobolysza

Hi Everyone,

I have just bought a Tribeca, and the front two tyres are 225/55/18s while the rear ones are 255/55/18s
The first tyres were changed 2 weeks (before I bought it) ago and the car has run 40 miles since than.
I know it can demage the transmission and transfer case so I called the garage. It was told that they always fit the same size so it must be 225s before they change them.
The dealer does not remember, and I did not find the previous owner either. He moved out from his address.
So basically we don't know if the car has run 40 or maybe 400 miles on 225s on the front and 255s on the back the same time.

I called an official subaru serivce and they said if I don't feel or hear anything and there is no warning lights on the dashboard than it should be fine.
I called an independent subaru mechanic after that who said if it was running more than a couple of hundred miles on these tyres than the transfercase and transmission were already demaged.

I was just wondering if any of you have had in the same situation or do you have any experience with cars running on different tyres for a while.

Thank you so much!

markjmd

iTrader: (11)

I could be wrong, but I'm pretty sure the most important dimensions so far as transmission damage on an AWD car is concerned are the rim and profile sizes, which in your case appear to be the same (18 and 55). This should mean the rolling radius front and back are the same (except for any possible minor difference resulting from variance in the side-wall flex), so in theory, you should be OK.

djandyg

iTrader: (2)

I didn’t think think different widths of tire would have any impact on diffs, esp if in same axle? Granted if you had different profile or diameter on the same axle then it could cause damage but all you have are slightly wider tires? Plenty of cars run wider wheels on the back than the front? Correct me if I’m wrong...

1509joe

iTrader: (2)

The profile of a tyre is not 40mm high for a 235/40/18 the 40 is a percentage of tyre width so it would be 94mm not 40mm if I've got the sums right.

Your tyres are 140.25 and 123.75mm sidewall heights they need changed.

bobolysza

Thank you Guys,

Yes 1509joe is right unfortunately.
The 255/55 18 tyre diameter is 737mm while the 225/55 is 704. It means more than 30 more revs on the smaller tyre in every mile.
That kills the transmission and the differential as well.

I found this very good site, they explain perfectly why mismatched tyres are a big big problem on AWD cars:

https://www.souzastireservice.com/Ti...tching-AWD-4WD

All wheel drive vehicles are different from four wheel drives in that all four tires are engaged at all times. These range from the extremely tightly toleranced to the more forgiving. Again, the owner's manual is always a good place to start. Some good examples of these are as follows:

Subarus: Subarus have, to our knowledge, the tightest tolerance of any AWD system. Since we see so many, we can tell you what the tolerance is. It can be stated in two ways: The first is 2/32nds tread depth across all four tires. The problem with this is that actual tire dimensions can vary from brand to brand and even from model to model. Therefore the 2/32nds rule is only good if you have the exact same size, brand, and model tire. The other way to check is to measure the tire around the circumference and then the tolerance is 1/4". That was circumference, not diameter, so you have to have a flexible tape ruler and measure around the tread of the tire. Also, having air in the tire affects the circumference. Though the change due to having air in it is only about 1/8", it's pretty critical since the tolerance is only 1/4". Therefore, to get an accurate measurement, it's necessary to let the air out before you measure (since the prospective replacement probably won't be aired up). This second method allows you to check compatibility with any make or model of tire.

Don Clark

Tribeca OEM tyre size is 255/55/R18




The autobox will have struggled to deal with this difference, particularly the transfer clutch

bobolysza

I bought 4 brand new Bridgestone 255/55s and replaced all tyres yesterday. I decided to not take any risk and replace the old 255s in the rear as well.
I took the wheels off from the car and took them to the tyre shop to prevent any further demage.
After I put the wheels back, by myself I went for a short ride and felt everything perfect.
I booked the car for a differential and transmission check, flush and fluid replacement to Monday and will not drive it till than.
If eveything is okay I'll take it back to the tyre shop for an alignment check just to make sure everything is okay.

Fingers Crossed

P.S.:
The shop who fit the wrong tyres did the MOT and a full service as well 40 miles (two weeks ago). The car went through on MOT with NO ADVISORIES!!!

- They changed and overfilled the engine oil. The level on the stick is an inch higher than the full mark.
- They changed the brake pads, but the discs are so worn, than the pads are almost disappear in the hollow. It also has a loud squeaky noise as well.
- They fit the wrong tyres
- The exhaust is leaking (you can hear and also see it)

Both the exhaust and the brake discs were advisories on the last MOT a year ago! But these *******s found nothing and the car went through on MOT with no advisories.
On the meantime they fit wrong tyres on the car and overfilled the oil. If I wouldn't have recognized these issues than basically the engine, the transmission and the AWD system (the whole car actually) would be killed in a months time.

The dealer says it's the garage's fault, but the garage said they fit the same tyre size what was already on the car (impossible because after a couple of hundred miles the mismatched tyres kill the transmission).
I assume these guys (the dealer and the garage) know each other very well. All cars in the dealership has fresh MOT with no advisories.
I think they know nothing about AWD cars so asked the garage to fit the cheapest chineese tyre whatever the size is.

Both of them should be jailed.

You can f**k the RAC guarantee ot rhe dealership responsibility. Of course I could sue them but I'm sure nothing would be happened for ages...

Anyways I hope everything will be okay on Monday and I can forget this nightmare quicky.

1509joe

iTrader: (2)

Now Don your cheating I did mine with a calculator

Don Clark

A pictorial presentation is always more dramatic

1509joe

iTrader: (2)

Have to agree