Different tyre heights on same vehicle

cormie

Hi,
I had a blowout yesterday and went straight to get a new tyre. I have 195 r14's on and the guy said he only had 185's and said that it was ok as long as I had two of the same on the one axle. I wasn't too sure about that and he didn't have 2 of the same tyre anyway so I thought I'd wait and try somewhere else.

I got to another place and they had 195's so I got one and asked the guy about using 2 different heights on the one vehicle and he said absolutely not, that all 4 should be the same.

So what's the story does anyone know? Should they all be the same and was the first guy just trying to pull a quicky and sell me 2 tyres? I need new tyres anyway, the new one I got is now the spare so I haven't even used it yet so I'm just wondering, is it best to buy 3 more of the exact same tyre or will 3 more of any 195 r14 do?

Any feedback appreciated:)

Guy:Incognito

Can you not put this in th eright forum www.boards.ie/Cormiessuperdeluxetransitvanforum

Anyhoo, short answer I would have thought no.

MarkR

AFAIK, as long as they are both on the same axle it's fine. A lot of modified car owners might have slightly lower profile tyres in the front. I think that some high performance cars have this as standard actually.

Seth Brundle

You didn't mention what the height difference would be but:
Keep the one bought from yesterday as the spare - it will get you out of a hole and stick with the 195/?/14.
Most cars sold now have those spacesaver tyres which are both narrower and shorter than standard tyres - but they are to be used at low speeds.
You are driving a van and possibly under pressure so don't start messing with the settings.

cormie

Oh no, I didn't buy the 185, I went to another place and got the 195. So I now have 4 old 195's and a new 195 as the spare. But I want to put 4 new tyres on anyway, so would it be best to get 4 new tyres that are all the same, or would 3 and the new spare do or would the fact it has different thread design matter?

The height difference would be 10mm I think? 185 to 195.

Seth Brundle

I see.
On a 196/65/14" tyre the 195 is the width not the height.
The 65 means that the sidewall height is 65% of the width(195).
The 14 is the diameter of the wheel.

cormie

Really? That's mad, so your man pitching the first two tyres didn't even know that himself as he was saying it's the height difference

So what would and wouldn't be ok when it comes to getting new ones?

peasant

errr ...

Commercial tyres (C rated) arent usually "low profile" (i.e. /75 or /70 or /65 even) They're xxx R14 or XXX R15 or R whatever.

The height ratio on a commercial tyre is roughly 82 ...so your'e getting 195/82R14 or 185/82 R14.

As the 82 signifies percentage of width (either 82 % of 195 or 82 % of 185 mm as flank heigt )...you do indeed get a height difference between a 185 and a 195. google "Tyre calculator" and see for yourself.

As for getting new tyres:
Im a firm believer in having "four of the same" as tyre performance can vary wildly between differnt threads. With four of the same at least it doesn't vary between wheels then.

cormie

Yeah, I've read here before that it's suggested to get 4 of the same and always replace all if replacing any. It would of course be ideal to get 5 of the same, 1 for a spare and just trade the dunlop one I got for a new one that's the same. Wonder would anywhere do that? Is a new tyre a new tyre, could they sell it as new?

bushy...

Not a great idea having one odd tyre anyway, different grip and so on.
Having a way different height tyre would be a bad idea as among other things you'd end up with a situation like a chair with one slightly short leg , two diagonally opposite tyres would be taking more weight then the other two . It'd be more of an issue on cars with stiff suspension though.

Savman

Personally I wouldn't go near different sizes. I have 4 of the same on my van, but the spare is slightly larger and when I had a blow out and stuck it on the ABS and "Stop" lights kept coming on.

Vans + tyres seems to be a delicate combo

cormie

yeah, might try my luck at exchanging the new one I got for 5 new ones of the same type.

bushy...

Not a great idea having one odd tyre anyway, different grip and so on.
Having a way different height tyre would be a bad idea as among other things you'd end up with a situation like a chair with one slightly short leg , two diagonally opposite tyres would be taking more weight then the other two . It'd be more of an issue on cars with stiff suspension though.

Can be serious , guy i know collected his car after getting a wheel bearing done in it , and it spun out on the way home ( wet , normal bit of acceleration , no oil/crap on road etc). The next day we went looking and found the mechanic had turned the magic bolt on that side that sets the ride height.
Sad thing is it could have wiped out him and people in an oncoming car.Its far from the reason for every crash , but the logical conclusion in that one would've been car with a bit of power, wet road , can't drive .

bkehoe

On some vehicles with DSC/ESP/whatever then having an odd size tyre with a different rolling radius can cause all sorts of wierd things to start happening as the traction control system thinks that the wheel is spinning slower, or faster, than the other 3 and tries to sort it out! Auto gearboxes may refuse to change up gears on more modern cars as well.

Seth Brundle

peasant wrote:

As for getting new tyres:
Im a firm believer in having "four of the same" as tyre performance can vary wildly between differnt threads. With four of the same at least it doesn't vary between wheels then.

My car has 235/40/17 on the front and 255/35/17 on the back (OEM setting) - in theory it shouldn't make too much of a difference as long as each axel has the same type of tyre.

CJhaughey

Don't do it on a permanent 4wd vehicle like the toyota landcruisers, you will end up with transmission windup, the end result of this over a period of time apart from weird handling will be a broken differential.

Mr.Diagnostic

kbannon wrote:

My car has 235/40/17 on the front and 255/35/17 on the back (OEM setting) - in theory it shouldn't make too much of a difference as long as each axel has the same type of tyre.

Hi KB,

True, but your car is set that way, ie the ABS/traction/ETC etc are programmed to read the wheel speed signals and compensate for the difference.

I doubt Cormie has traction but maybe ABS? Even if not, it is still not a good idea.

Mr. Presentable

cormie wrote:

Really? That's mad, so your man pitching the first two tyres didn't even know that himself as he was saying it's the height difference

So what would and wouldn't be ok when it comes to getting new ones?

Of course, given that he stores them lying flat, his definition of height would differ

peasant

kbannon wrote:

My car has 235/40/17 on the front and 255/35/17 on the back (OEM setting) - in theory it shouldn't make too much of a difference as long as each axel has the same type of tyre.

According to the tyre calculator thats a difference of 1.61 % in circumference in favour of your fronts.:D

Your OEM setting specifies smaller tyres on the driven axle

(well ...in real life 1.61% is nudd'n ...so your still driving equal sizes back and front, just the rear ones are wider)

Glanza V

Well first off, if they are both the same with (the first part 195, 205 etc is the width of the tyre in mm) they will be ok but it does depend on the car, for example front wheel drive, rear wheel drive, 4 wheel drive.

And my take on it is: I would never put smaller in width than 195mm because in a breaking condition the extra 10mm in enough to decide between life and death. A lot of people laugh and are very ignorant when it comes to tyres imo.

sundodger5

keep the tyres the same size. even if different brands.
a smaller tyre will effect a whole pile of things. also it will have a lower load carrying capacity. that is the often forgotten 2 numbers. normally after the rim size and before the speed rating i.e 185/60R14 82H
the first guy was an idiot the second gut is on the right track. make sure all the markings match.

crosstownk

Keep the tyre sizes as per manufacturers spec. Some cars have different tyre size on the front axle vs rear axle - more common with RWD. If you choose to put larger wheels then make sure you go with a size within the spec allowed.

I've seen ABS warning lights come on because of different tyre sizes across the same axle. An ABS sensor simply counts wheel rotations - if the tyre size is different then there will be a difference in the rolling circumference of the tyre.