Slightly different tyre sizes on front and rear (205 vs 215)?

DubDani

I saw that my wife's car needed new tires, as the outside was running "bald", and accordingly ordered 2 new tires online to get them fitted today.

The size that I ordered, and which is the correct size, is 205/55/17. When I went to the Tyre fitter today to get them fitted they advised me that somehow my car was currently fitted with the wrong size, 215/55/17. So my dilemma is now what to do?

Do I just replace the two front ones, and run two slightly different sizes until the rear ones need changing, or do I change all 4, even though the two rear ones are perfectly fine.

Does anyone have any knowledge on the possible impact of running two slightly different sizes on front and rear? The tyre fitter thought the cars sensors won't agree with it and might throw some alarms.

two wheels good

I don't think you need be concerned. Just fit a matched pair on the same axle.
The 10mm difference in width is negligible. Even on a motorbike wheel that would be nothing.

The difference in wheel diameter is the only issue. And I can't see 11mm diameter difference upsetting the sensors. Between manufacturing tolerances and inflation variations it's probably not significant.

Sidewall height:
215x55% = 118.25mm
2015X55% =112.75mm
5.5mm difference in sidewall height.
Mult by 2 to for difference in tyre diameter : 11mm
17in = 432mm wheel diameter

It will alter your speedo accuracy of course. The inaccuracy will be ... Oh, is that the door bell ... sorry, gotta dash.

rex-x

It will be fine to drive and for nct etc but could your ocd live with it

colm_mcm

Stick the bigger ones on the back. It’ll look wrong otherwise.

GSBellew

The different rolling radius of the tyres will mean the front / rear wheels will report different speeds to each other.

If it's smaller on the front the car will see higher reported front wheel speed relative to rear, hence assume wheel spin and intervene earlier, this is vastly exaggerated whilst driving around a bend.

khaldrogo

What car is it?

FishOnABike

The difference in overall tyre diameter is 10mm or 1.5% (658mm vs 668mm), slightly less than the difference between a new tyre and a tyre that's still got approx. 3mm of thread depth left.

With the new tyres on the front and the part worn tyres on the back the difference would be less than 1.5%, how much less would depend on how much thread there is on the rere tyres. If the rere 215/55R17s are worn down to 3mm thread depth they would be the same diameter as the new 205/55R17 front tyres.

put the bigger ones on the drivers side front and back.
Makes cornering easier ( to the left)

FishOnABike

BrownFinger wrote: »

put the bigger ones on the drivers side front and back.
Makes cornering easier ( to the left)

Wouldn't the passenger side be better? It would make going around roundabouts easier ;-))

CJhaughey

Tyres are not always the same size either for a nominal diameter there can be a big variance between Brand A 205-55/16 to Brand B 205-55/16.
I wouldn't worry about it too much just fit the new set to the rear and see what happens.
There probably won't be much of a difference in real terms, even TPMS that report different rolling diameters won't usually be that sensitive.