Help with tyre's

[PHILGZ4]

Looking to get some help/advice. I have an E85 and the two front tyres are needing replaced. I was going to get the rear done at the same time so all done.
However a local garage said the front tyre's are bigger than the rear. The reading's are:
Front: 225 45R 17 91w
Rear: 255 40R 17 94W

My questions are as i don't know and now thinking i wont use this garage if he doesnt know!
1: should they all be the same size for all four or different. Cost wise if i get all front tyres they are cheaper
2: should front be bigger/smaller than the rear?

any help is much appreciated.
Thanks

 

[Haro]

Those are the correct sizes apart from the rears, they are 245 from the factory but you can fit 255's.

 

[enuff_zed]

45% of 225mm = 101.25mm
40% of 255mm = 102.00mm

So the rolling radius of front and rear is .75mm difference. With the rears being slightly bigger if you wanted to be pedantic about it.
Surely a garage should understand basic tyre sizing figures??

 

[PHILGZ4]

45% of 225mm = 101.25mm
40% of 255mm = 102.00mm

So the rolling radius of front and rear is .75mm difference. With the rears being slightly bigger if you wanted to be pedantic about it.
Surely a garage should understand basic tyre sizing figures??

So could you use the 225mm for all four tyres then?. is this allowed? advisable, terrible drive?. As i said i really dont know what is correct. thanks

 

[synthedup]

Those are the correct sizes apart from the rears, they are 245 from the factory but you can fit 255's.

No, 255 is correct for the rears and standard on 18” whee options.

 

[skelters]

Square set up would basically be the same size of tyres on all four wheels.

Staggered would be wider tyres and wheels on the rear.

Rear wheel drive cars usually have a staggered set up.

For the Z4 a square or staggered setup works.

Has someone swapped the wheels around from front to back and put the wider tyres on the front?

 

[Haro]

Those are the correct sizes apart from the rears, they are 245 from the factory but you can fit 255's.

No, 255 is correct for the rears and standard on 18” whee options.

You're right. I always thought 17s were 245 for some reason.

 

[enuff_zed]

I think a basic answer would be that the front and rear sizes you quote in your original post would be fine to go back on.

 

[ben g]

45% of 225mm = 101.25mm
40% of 255mm = 102.00mm

So the rolling radius of front and rear is .75mm difference. With the rears being slightly bigger if you wanted to be pedantic about it.
Surely a garage should understand basic tyre sizing figures??

So could you use the 225mm for all four tyres then?. is this allowed? advisable, terrible drive?. As i said i really dont know what is correct. thanks

It depends on the width of your rear wheels.

Are they standard wheels or aftermarket? Being 17's, I'd imagine they're the same width front and rear, therefore you would be fine to use the same size tyre on all 4 wheels. Won't know for sure until we know the wheel widths though.

 

[PHILGZ4]

Square set up would basically be the same size of tyres on all four wheels.

Staggered would be wider tyres and wheels on the rear.

Rear wheel drive cars usually have a staggered set up.

For the Z4 a square or staggered setup works.

Has someone swapped the wheels around from front to back and put the wider tyres on the front?

. Not too sure as these were the tyres on when i bought it 2nd hand so may have been swapped over. So it would be ok to go with 225 45r front and rear?. Big saving if i do but then dont want to do the wrong thing and then its horrendous to drive!.

 

[PHILGZ4]

45% of 225mm = 101.25mm
40% of 255mm = 102.00mm

So the rolling radius of front and rear is .75mm difference. With the rears being slightly bigger if you wanted to be pedantic about it.
Surely a garage should understand basic tyre sizing figures??

So could you use the 225mm for all four tyres then?. is this allowed? advisable, terrible drive?. As i said i really dont know what is correct. thanks

It depends on the width of your rear wheels.

Are they standard wheels or aftermarket? Being 17's, I'd imagine they're the same width front and rear, therefore you would be fine to use the same size tyre on all 4 wheels. Won't know for sure until we know the wheel widths though.

They all show as 17's but the front tyre's are 225 45R & Rear 255 40R which is what is confusing me as i would have thought they should all be the same.

 

[mmm-five]

Square set up would basically be the same size of tyres on all four wheels.

Staggered would be wider tyres and wheels on the rear.

Rear wheel drive cars usually have a staggered set up.

For the Z4 a square or staggered setup works.

Has someone swapped the wheels around from front to back and put the wider tyres on the front?

. Not too sure as these were the tyres on when i bought it 2nd hand so may have been swapped over. So it would be ok to go with 225 45r front and rear?. Big saving if i do but then dont want to do the wrong thing and then its horrendous to drive!.

It’s one of the standard configurations, so there nothing inherently dangerous about it...just be aware that you’ll have slightly less grip at the rear when you’re driving ‘enthusiastically’.

 

[mmm-five]

They all show as 17's but the front tyre's are 225 45R & Rear 255 40R which is what is confusing me as i would have thought they should all be the same.

Is this your first rear wheel drive car? If so, that may be what’s worrying you about the “different sizes” of the tyres.

Overall the only difference between front & back is the rears are an inch wider...to help with grip/looks. However the sidewall has been reduced by 5% to make the overall diameter of the wheel/tyre almost identical to the front.

If the tyre place does not understand this then I’d be taking it somewhere else, as it’s a fairly basic/regular occurrence.

 

[PHILGZ4]

They all show as 17's but the front tyre's are 225 45R & Rear 255 40R which is what is confusing me as i would have thought they should all be the same.

Is this your first rear wheel drive car? If so, that may be what’s worrying you about the “different sizes” of the tyres.

Overall the only difference between front & back is the rears are an inch wider...to help with grip/looks. However the sidewall has been reduced by 5% to make the overall diameter of the wheel/tyre almost identical to the front.

If the tyre place does not understand this then I’d be taking it somewhere else, as it’s a fairly basic/regular occurrence.

Yes it is so now makes sense that you point it out re the bigger rear tyre. Think I would rather have more grip on these Scottish roads!. Thank's for that.

 

[Jl-c]

However a local garage said the front tyre's are bigger than the rear. The reading's are:
Front: 225 45R 17 91w
Rear: 255 40R 17 94W

this confuses me, OP says front are bigger than the rear but then says front =225 rear =255 so rear is bigger? Unless they have been put on the wrong rims ie 8J as against 9J or whatever they are?

 

[ronk]

I would go to a garage that knows what they are talking about - the tyre width and aspect ratio is basic stuff!

 

[mmm-five]

However a local garage said the front tyre's are bigger than the rear. The reading's are:
Front: 225 45R 17 91w
Rear: 255 40R 17 94W

this confuses me, OP says front are bigger than the rear but then says front =225 rear =255 so rear is bigger? Unless they have been put on the wrong rims ie 8J as against 9J or whatever they are?

Garage might have meant the PROFILE is bigger on the front - which it is, but has to be read with the width to make proper sense.

 

[ronk]

However a local garage said the front tyre's are bigger than the rear. The reading's are:
Front: 225 45R 17 91w
Rear: 255 40R 17 94W

this confuses me, OP says front are bigger than the rear but then says front =225 rear =255 so rear is bigger? Unless they have been put on the wrong rims ie 8J as against 9J or whatever they are?

Garage might have meant the PROFILE is bigger on the front - which it is, but has to be read with the width to make proper sense.

It would seem they don’t understand the fundamentals!

 

[eddiemunster]

It would seem they don’t understand the fundamentals!

Most people don't know the difference between their and there, or the possessive plural, or Oxford 'and' (!), but it doesn't mean they can't speak English or don't understand the fundamentals.

 

[MrPT]

I think a basic answer would be that the front and rear sizes you quote in your original post would be fine to go back on.

This.

Sounds like something’s gotten lost in translation, but I wouldn’t write off the garage just yet.