Tyre v wheel size

Rjw76

Registered User
Good morning all,

I've searched the forum, but can't find an answer to this question, so hopefully someone can help - my car currently has 225 width tyres fitted (which seem to be standard). Having a look at tyre options online (I intend changing all 4 at once), I'm often being asked if I have 225 or 235 tyres. So the question is, how do I check if my particular wheels can take 235 tyres? (I've seen a few wheel size websites linked in other threads, but they don't give the detail of the actual wheel size for my car) - short of removing the tyre and measuring the wheel, I don't know what width my wheels are, so I can't check if they can take the wider tyre or not.

The other question is, what do people think about getting a wider tyre (if I can (without changing the wheel)) - is it worth doing - i.e. what is the advantage - will it actually give better grip?? Will it have a negative affect on acceleration/speed/fuel consumption?

I'd be interested to hear what people think about this.

Thanks all!
 

george forbes

Registered User
I have oe 18" alloys that are 225 but my winters from my first car are 235 they have fitted no problem to my s3 and the merc I had before it which was also 225

Sent from my SM-G950F using Tapatalk
 

Potterswheel

Active Member
Gold Supporter
Most O.E. wheels have the width and offset marked inside the spokes, generally the first place you will run into problems is when you put your steering onto full lock, the outside shoulder might catch on the arch liner, many things can influence this depending on model, springs fitted, ride height etc. etc. and it does not always follow that if they fit one car they will fit another, hopefully someone on here has already done this and to be honest you should get away with 10mm if everything else is standard.
BUT, your speedo will be out and will read slow, you will use more fuel as the rolling resistance will probably be higher, you will have less grip in the snow and wet and your gearing will be slightly higher, yes causing a slight (on paper) reduction in acceleration.
Try putting the steering on full lock and running your hand round the outside edge, then imagine the suspension travelling up and how close the tyre will go, If you have a friendly tyre dealer, you may be able to get the fronts fitted up and try them on the ramp and do the same test.
 

Bigjase88

Registered User
All 235 wide tyres will give you is a higher purchase price

the extra grip over 10mm will be negligible. Stick with the 225’s as they will be cheaper
 

AlS3BE

Registered User
There’s a difference between the hatch/sport back and the saloon/cab.
If I remember right the saloon/cab has 8in wide wheels and the hatch/sport back has 7.5in. Offset is also different, hatch/sport ET53 and saloon/cab ET43 I think.
18in had 225/40/18 and 19in wheels had 235/35/19.
So at the extremes with a 235 tyre on a 7.5in wheel will look a bit stretched, not the euro stretch look but opposite, and not offer much or any benefit other than maybe some extra rim protection.
 

Rjw76

Registered User
Most O.E. wheels have the width and offset marked inside the spokes, generally the first place you will run into problems is when you put your steering onto full lock, the outside shoulder might catch on the arch liner, many things can influence this depending on model, springs fitted, ride height etc. etc. and it does not always follow that if they fit one car they will fit another, hopefully someone on here has already done this and to be honest you should get away with 10mm if everything else is standard.
BUT, your speedo will be out and will read slow, you will use more fuel as the rolling resistance will probably be higher, you will have less grip in the snow and wet and your gearing will be slightly higher, yes causing a slight (on paper) reduction in acceleration.
Try putting the steering on full lock and running your hand round the outside edge, then imagine the suspension travelling up and how close the tyre will go, If you have a friendly tyre dealer, you may be able to get the fronts fitted up and try them on the ramp and do the same test.
I might be missing something obvious here, but why would the speedo be out? Surely the circumference is not altered I'm just adding wider (but with the same profile) tyres?
 

Rjw76

Registered User
Thanks for the replies and advise.. . all good stuff, and I think you are right - 10mm benefits are probably negligible versus the downsides (including the tyre cost!)
 

Bigjase88

Registered User
I might be missing something obvious here, but why would the speedo be out? Surely the circumference is not altered I'm just adding wider (but with the same profile) tyres?
Profile is not in mm it is a percentage of the tyre width

so 225/40/18 the height of the tyre is 40% of the width of 225 so 90mm

235/40/18 is 40% of 235mm so 94mm

Have a look at this website and input the information and it will give you how much the speedo will be out

 
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