Tire size

[Craig234]

So, a passenger car had '65' diameter tires.

One went flat and was destroyed, towed to local garage.

They only had one '75' diameter tire to put on, and sold it (Goodyear) for $140 including the labor installed.

They said 'it's fine to drive some with the mismatch, next week buy another 75 for the other side since it's worn and needing replacement' (it is).

How bad is it to drive at all with the mismatch - the corner of the car noticably sticks up higher - and is there generally any reason not to buy that second 75 and switch to that?

 

[Jimzz]

Need more information. You are only giving half the tire size. The 65 or 75 is percent of width. So I can't tell how much difference it is.

But you should not have different size tires on the same axle.

 

[nerp]

Don't do it.

 

[KDKPSJ]

65 or 75, doesn't matter. You need to let us know the first number, so we can suggest you whether it's ok or not.

If the first numbers are same, but only 65 vs 75 (ie. 225/65 vs 225/75), that's really bad.
If the first numbers are different and overall diameter remains same (ie. 225/65 vs 195/75), while still not suggested, but it's at least better than bad.

 

[Craig234]

It looks like the old ones are 215/65 and the new one is 215/75.

Question is what is best to do now, the second tire should be replaced soon.

Is this a case of 'go back to the shop and yell at them for doing something inappropriate' or just buy a second 215/75 on the front?

 

[EagleKeeper]

Get both of the same on the same axle.

And ensure that your spare is the same size also.
Even if the spare is a $30 semi-bald tire.

 

[Craig234]

Get both of the same on the same axle.

And ensure that your spare is the same size also.
Even if the spare is a $30 semi-bald tire.

No question they're going ot be matched. Question is whether this was an error by the shop and i should go back to 4x215/65, or just get a second 215/75 for the front.

 

[exdeath]

Depends on the vehicle.

I know someone who is out of a vehicle right now and unable to pay the $2000+ for a transfer unit/center diff repair/replacement in their AWD SUV for running mismatched tire/wheel sizes while taking an cross state trip.

 

[Zenmervolt]

It looks like the old ones are 215/65 and the new one is 215/75.

If the car is supposed to use 215/65 tires, you need to get rid of the 215/75 and put the proper tire on the car. Basically, if the car is supposed to use 215/65 tires, then you've just wasted $140 because of a very incompetent shop.

If you have the two mismatched tires on the drive axle, you will increase wear on the differential and potentially the traction control system since the wheels will always be spinning at different speeds, which a traction control system might interpret as wheelspin. Moving to two 215/75 tires on the drive axle when 215/65 tires are recommended will also make your speedometer inaccurate since the reading for the speedometer depends on you using the correct size tires for the car. In this case, if 215/65 is the correct size and you replace both front tires with 215/75 tires, your speedometer will read slower than your actual speed and your odometer will record mileage slower too.

You will also screw with the car's alignment by having a mismatched tire, which will increase the wear on the remaining tires over the long term.

ZV

 

[sgrinavi]

Might be OK for a little while - after all they put those little donuts in the trunk of cars there days. You're only talking about 6% difference in diameter (depending on the size)

What kind of car, what's the wheel diameter and which axle?

 

[Zenmervolt]

Might be OK for a little while - after all they put those little donuts in the trunk of cars there days. You're only talking about 6% difference in diameter (depending on the size)

You mean the temporary spares that have gigantic yellow warnings on them not to exceed 50 mph and to replace them as soon as possible? Those are intended only to allow you to limp to a repair shop and should not be operated at highway speeds nor should they be used for any appreciable length of time for exactly the reasons I mentioned in my previous post.

ZV

 

[sgrinavi]

You mean the temporary spares that have gigantic yellow warnings on them not to exceed 50 mph and to replace them as soon as possible? Those are intended only to allow you to limp to a repair shop and should not be operated at highway speeds nor should they be used for any appreciable length of time for exactly the reasons I mentioned in my previous post.

ZV

The tiny tire and rim are not rated for speed and they are about 50% of the size of a real tire. My point was that if it were as big of a deal as everyone is making of it then you wouldn't see the donuts in the trunk for any speed and or distance.

OP is running a tire that has a 6% different diameter- if it was on a posi-traction axle or complicated AWD system it could be a problem, In the case of the latter he would probably have some sort of TC that would be barking at him by now.

If the car has LSD or the tire is on a non-drive tire - especially on the rear of a FWD car, then there's not going to be any catastrophic results in a weeks time for a couple hundred miles.

 

[phucheneh]

You mean the temporary spares that have gigantic yellow warnings on them not to exceed 50 mph and to replace them as soon as possible? Those are intended only to allow you to limp to a repair shop and should not be operated at highway speeds nor should they be used for any appreciable length of time for exactly the reasons I mentioned in my previous post.

ZV

Another thing that I've noticed- a lot of cars come without spares anymore. Often the kind of stuff that would've used to have a full-size spare...which always made me say, 'really, you cheap bastards? Full spare to nothing?'

But I realized it's pretty much exclusively RWD cars with a limited slip diff at least available as option, if not standard. So they probably just want the weight/cost savings of no full size tire (in the case of something like a new Camaro, it probably wouldn't even fit in the trunk), but are unwilling to give you a donut for fear of having to warranty out diffs.

Probably not a concern to OP, but worth noting that there's an extra reason to avoid extended (or even any) donut use, in addition to simply the poor traction and lack of durability. Also, I'd wager that if you went around and check peoples' spares [edit: of the 60psi space-saver variety], you'd find maybe 10% of cars more than a few years old with the proper pressure. I commonly find those things down to 30-40psi or less.

 

[unokitty]

How bad is it to drive at all with the mismatch - the corner of the car noticably sticks up higher - and is there generally any reason not to buy that second 75 and switch to that?

Without further information, your question can't be answered definitively.

For example, if you have a Subaru, or other 4WD vehicle, you would need to change to a matched set as soon as possible.

On the other hand, if you have a conventional FWD car and the mismatch is on the rear set of tires, I would still change to a matched set -- But whether I change to it on Monday or Tuesday or Friday, I wouldn't be concerned ...

For more info:
Tire mismatch - Car Talk

Using mixed or mismatched tires

Whether or not putting that new tire on your car was a mistake depends on what your other options were at that time.

If it were me, I would probably just buy another tire to match the new one.

Best of luck,
Uno

 

[Zenmervolt]

If the car has LSD or the tire is on a non-drive tire - especially on the rear of a FWD car, then there's not going to be any catastrophic results in a weeks time for a couple hundred miles.

If the car has an LSD it's worse, not better. Having mismatched tires on a drive axle with an LSD will either cause scrubbing (in the case of a gear type LSD), excessive heat buildup (in the case of a viscous LSD), or accelerated clutch wear (in the case of a clutch type LSD).

Two weeks for me is 600-900 miles. I would not ever recommend running mismatched tire sizes for that long. For 50 miles at low speeds, sure. But not for daily use.

ZV

 

[OGOC]

Would help to know the full info of what kind of car.

As for the car sticking up higher part, if you put the same taller tire on the other side, that side will stick up too. Maybe it actually looks better that way, or not.

You can generally put any size tire you want on a car as long as they fit and as long as they match. Taller or shorter can mess with your speedometer calibration, though.

 

[Craig234]

That idea of 'supposed to be' tire size was pretty new to me, so did some checking, and it looks like the car is 'supposed' to have 205/70.

If that's the case, the old 215/65's were equally off as the new 215/75.

It's a front wheel drive car. This is the left front tire.

It 'feels' like more than 6% change, but I'll assume that's what it is.

I was still just trying to find out the next step:

- the shop ripped me off by selling an inappropriate tire because it's the only one they had, andI should demand they replace the tire with a more appropriate one.

- it's fine, just buy a second 215/175 to match.

- it's fine, buy 3 more 215/175 to match.

- these are all bad options, buy four 205/170 like I'm supposed to have.

Keeping the new tire on the car, demanding the shop replace it, or using it as a spare are all options.

 

[Craig234]

Whether or not putting that new tire on your car was a mistake depends on what your other options were at that time.

I had the tow driver wait while I asked the shop if they could replace the tire.

When they said yes, I had him drop the car and leave. I could have gone another shop.

Only after they were working on it did they say they'd put the 215/75 on and it was the only one they had.

It's normally been a pretty good shop, and he insisted it's 'no problem for a few days'. At that point, I wanted it fixed 'enough' rather than calling for another tow.

If it were me, I would probably just buy another tire to match the new one.

Best of luck,
Uno

Thanks.

That is an option, even if it seems to make the car higher in the front than the back. I do need to see if the rears need replacing too, I assume they likely do.

 

[Zenmervolt]

That idea of 'supposed to be' tire size was pretty new to me, so did some checking, and it looks like the car is 'supposed' to have 205/70.

If that's the case, the old 205/65's were equally off as the new 205/75

OK, now you really just need to tell us the year, make, and model of the car here. You've switching things around a lot.

First you said the tires on the car were 215/65 and the new one was a 215/75.

Now you're changing things up on us. The difference in rolling diameter between a 205/70 and a 215/65 is actually very small (the second number is a ratio describing sidewall height as a percentage of tire width) while the difference in rolling diameter between a 205/70 and a 215/75 is much larger.

A 205/70 tire has a sidewall height of 143.5 mm.
A 215/65 tire has a sidewall height of 139.75 mm.
A 215/75 tire has a sidewall height of 161.25 mm.
A 205/75 tire has a sidewall height of 153.75 mm.

Notice how the difference in sidewall height is more than twice as large for the 205/75 as it is for the 215/65.

The difference between a 215/65 and a 205/70 would generally be considered negligible in terms of affect on speedometer/odometer readings and may even have been an optional size from the factory.

Basically, right now I'm not even sure what size tires are actually on the car right now since you've given us conflicting information.

ZV

 

[Craig234]

OK, now you really just need to tell us the year, make, and model of the car here. You've switching things around a lot.

First you said the tires on the car were 215/65 and the new one was a 215/75.

Now you're changing things up on us. The difference in rolling diameter between a 205/70 and a 215/65 is actually very small (the second number is a ratio describing sidewall height as a percentage of tire width) while the difference in rolling diameter between a 205/70 and a 215/75 is much larger.

A 205/70 tire has a sidewall height of 143.5 mm.
A 215/65 tire has a sidewall height of 139.75 mm.
A 215/75 tire has a sidewall height of 161.25 mm.
A 205/75 tire has a sidewall height of 153.75 mm.

Notice how the difference in sidewall height is more than twice as large for the 205/75 as it is for the 215/65.

The difference between a 215/65 and a 205/70 would generally be considered negligible in terms of affect on speedometer/odometer readings and may even have been an optional size from the factory.

Basically, right now I'm not even sure what size tires are actually on the car right now since you've given us conflicting information.

ZV

Shoot, my mistake. The first post was correct - they are 3x215/65 and 1x215/75.

After seeing the 'supposed ot be 205/70', I wrote 205 for all of them. I edited it.

See PM also.

So what we have looks worst case - 139 versus 161.

 

[Throckmorton]

Forget the math. It doesn't matter because any mismatch is bad. Go back to 215/65 all around or replace all your tires with 205/70 like it's "supposed" to have. But also, the front tires need to have the same amount of wear because wearing down decreases the diameter of a tire. There is also variation between brands.

That shop shouldn't have said they could fix it and then put the wrong tire on. At least they should have put the bigger one on the rear since it's FWD. Go to a different shop, get the problem fixed, then return the big one to the original shop.

 

[SpatiallyAware]

YEAR / MAKE / MODEL?? You come here for help, and have been asked this numerous times already. We can't appropriately help you without this info! This should be MANDATORY if you are in ATG asking for help!

Past that, it's hugely insulting that you intentionally ignore this important question while wanting accurate advice that NO ONE can give without it! Look at all of the replies and time you've wasted by not giving us the information we have repeatedly asked for!

Even with your edits this is ridiculously confusing.


Ok... with that out of the way...

We NEED year/make/model, and FACTORY suggested tire size.

We NEED for you to go outside, and write down EVERY tire size including this new tire. At this point do not assume anything, go look at it yourself.

 

[SpatiallyAware]

I had the tow driver wait while I asked the shop if they could replace the tire.

When they said yes, I had him drop the car and leave. I could have gone another shop.

Only after they were working on it did they say they'd put the 215/75 on and it was the only one they had.

It's normally been a pretty good shop, and he insisted it's 'no problem for a few days'. At that point, I wanted it fixed 'enough' rather than calling for another tow.



Thanks.

That is an option, even if it seems to make the car higher in the front than the back. I do need to see if the rears need replacing too, I assume they likely do.

It sounds to me like you gave them the go ahead to put that tire on. You're in a bit of a grey area if they told you they have the wrong size, but from a safety perspective it's ok, yet you gave them the go ahead to do the work. It's not their fault if they told you all this, you made a 'bad call', and are now having buyer's remorse.

I will say that a $140 goodyear in those sizes just sounds overpriced to me. I would've asked them for a loaner tire until the correct size is in stock, or install the spare.

 

[Craig234]

It sounds to me like you gave them the go ahead to put that tire on. You're in a bit of a grey area if they told you they have the wrong size, but from a safety perspective it's ok, yet you gave them the go ahead to do the work. It's not their fault if they told you all this, you made a 'bad call', and are now having buyer's remorse.

I will say that a $140 goodyear in those sizes just sounds overpriced to me. I would've asked them for a loaner tire until the correct size is in stock, or install the spare.

Well, I think they told me after they'd already put it on. The tire was $90, the rest was labor. Question is what to do now.

When they had got to that point, I did take it rather than saying 'no' and getting a whole new tow, not wanting to deal with that headache, it was Saturday afternoon already.

 

[SpatiallyAware]

Well, I think they told me after they'd already put it on. The tire was $90, the rest was labor. Question is what to do now.

When they had got to that point, I did take it rather than saying 'no' and getting a whole new tow, not wanting to deal with that headache, it was Saturday afternoon already.

You think they told you? I mean that's the crucial part of all this, in regards to liability.

$50 labor to install a tire you bought from them is borderline robbery.


What to do now is tell us year make model and factory tire size. No one here can accurately tell you a damn thing without that critical info.