Need new tyres, but is it ok to have the same profile???

P

peddy

Veteran
 London
I have the M wheels with the M tyres (so current profile is 40 on the fronts and 45 on the rears). I'll be needing new rear tyres soon-ish and I'd like to go to the standard profile tyres.

So question is do I need to change the fronts too or is ok to have a profile of '40' on the front and rear?

Thanks!
 
Won't changing the profiles play havoc with your speedo, mileometer and OBC?

Or did you already address that when putting the M wheels on?
 
The profile is the aspect ratio between height of tyre wall and width.

If you have a staggered set up of 8.5 on the rear and 8.0 on the front then the profile difference is how the tyres compensate for the wider tyre needed on the rears and keep the rolling radius the same.

If you go higher profile on a narrower tyre you won't get any issues mentioned by Tweed, but you'll be stretching a tyre marginally to a wider rim. It will look a little pinched, expose the rim and not look quite right.

why would you want to do it anyway?
 
cj10jeeper said:
why would you want to do it anyway?
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To save money (since there is a lot of life left in the front tyres), but if it's no advisable then i'll just change all four to have the correct profile.

EDIT: CJ just re-read your post... I'm not going to a higher profile. I currently have the original tyres on so still to the M spec. so the front is 40 and the rear is currently 45. I'd like to go back to non-M spec, so 35 on the front and 40 on the rear, but my front tyres currently have a lot of thread still left. if I change just the rears then i'll have a 40/40 setup... will that be an issue. if it will then i'll swap all four to have a 35/40 setup.
 
Peddy - sorry I'm utterly confused now. Talk of standard and ///M specs is too vague.

If your rims are the same width, the front and rear should have the same profile tyres
If the rears are wider then they should have a wider tyre and a lower profile to match and compensate.

Anything else is wrong.
 
cj10jeeper said:
Peddy - sorry I'm utterly confused now. Talk of standard and ///M specs is too vague.

If your rims are the same width, the front and rear should have the same profile tyres
If the rears are wider then they should have a wider tyre and a lower profile to match and compensate.

Anything else is wrong.
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x2

Looking to save some money by playing with the profiles? now that's being cheap! Sorry, had to say it...
 
ok sorry i got a little mixed up. ignore all I've said and let's start again...

current tyres:
rear: 255/40R18
front: 225/45R18

now i need to change my rear tyres and would like to go to the standard non-M profiles for 18" wheels. i.e. 40 on the front and 35 on the rear, but I don't need to change the front tyres yet so is it ok to change just the rears and have...

rear: 255/35R18
front: 225/45R18

or is this not a good idea and therefore I should change all four?

Am I making sense now? :)

powerontap, not trying to mess with profiles but if it's not an issue with what i've suggested above then why the need to change all four? that's what i'm trying to find out...
 
Try it and find out - it may upset the balance but it won't be inherently unsafe (your contact patch siz eon the road is going to be the same, but your front end will be ever so slightly higher than normal - yes, this is obvious I know!). If it feels odd, change the others too.

Personally - I would just change them all.
 
This is what i wanna do with my M wheel's on my 3.0 to give me more clearance on the rear... Wanna go on the rears to a 35 pro and front to a 40..But the rears are gonig bald in a few 1000 miles so gonna do them first..Should be ok ? Don't think it should upset the handling too much.

Also diemension wise 35/40 profile tyres should be dine as size wise there's standard fitment 18's on z4's the same witdth at 18inch? So shouldn't be too much of a problem.

Migth make the ride a bit ruffer tho?
 
If the brand of tire and tread pattern are the same, why worry about changing 4? Are you also changing the wheels when you change tires? As Tweed said, when you change ratios, you change speedo, etc IF the wheels are the same size and you keep the width the same.
 
Smokin said:
If the brand of tire and tread pattern are the same, why worry about changing 4? Are you also changing the wheels when you change tires? As Tweed said, when you change ratios, you change speedo, etc IF the wheels are the same size and you keep the width the same.
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Wheels are staying the same. just need to change the rear tyres.
 
peddy said:
Smokin said:
If the brand of tire and tread pattern are the same, why worry about changing 4? Are you also changing the wheels when you change tires? As Tweed said, when you change ratios, you change speedo, etc IF the wheels are the same size and you keep the width the same.
Click to expand...

Wheels are staying the same. just need to change the rear tyres.
Click to expand...

So why don't you just buy the "M spec" rears? I'm confused...... :?
 
Because of the different offset it once in while rubs the tip of arches (i think "fenders" is the proper term for it??) when I go over a bump.
 
Here are the differences between the ///M and 3.0i 18" Rears:
ts.png


3.9% (3.6% from the fronts) circumference difference is pretty significant! This will potentially play havoc with the ABS/Stability control systems.

Also the car will look wonky with a 1.3cm Sidewall height difference.

Id either get one more set of 255/40 rears to last till the fronts run down. Or bite the bullet and change the lot.
 
Thanks Ed. The exact info I was after. :thumbsup: I'll do one of the two options you've suggested.

Thanks all for the help. :thumbsup:
 
Having now posted exactly what you are considering and with the clear input from Ed, then walk away from the car.....Don't be tempted to screw up things.

Buy a full set and sell off whatever you have left.

As an aside you're already out on a few things running oversided tyres, so you already have speedo errors and all that stuff. Just need to correct it and in so doing will likely also stop the rubbing

EDIT - sorry - you posted a response while I was doing real work...lol
 
I don't blame you CJ... I barely understood what I was talking about myself! :)

I think I'll probably end up changing all four as I currently have Continental Sport Contact (not sure if it's 2 or 3 though??). Two of those for the rear would be around £355. F1's all round are about £510, which are probably better than the Continental's?
 
Im taking delivery of a full set of M alloys with continental tyres in the next week. Im hoping to get my current Toyos stuck on them so will have the Contis to sell. Not sure how much tread they have but it looks like theres quite a bit from the photos.
 
Dreamer said:
Im taking delivery of a full set of M alloys with continental tyres in the next week. Im hoping to get my current Toyos stuck on them so will have the Contis to sell. Not sure how much tread they have but it looks like theres quite a bit from the photos.
Click to expand...

Will this be another one of your freebies? :D :P
 
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