Tyre Size Question

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Lord Tyrion

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I know I could do this on a car forum, left the last one due to casual racism becoming quite common :oops:, but I don't want to have to join one just for one question.

I changed my car a few months ago, 2nd hand car.

It came on tyres 225/55/R17

When looking for replacements, 2 will need doing soon, I put the reg into tyre sites and it tells me the appropriate size for the car is 245/45/R17

It is running fine, they clearly fit the alloys so I presume no issue, other than maybe the speedo is out by 0.75mph?

Is there a reason the previous owner would have done this? It is a Merc E Class, not a sporty version, so it not a boy racer car

The key question though, I have winter tyres from my previous car that are barely used. The size is 215/55/R17. Any reason that these will not be suitable? Again, I understand the speedo may be out by minor margins but I don't drive on the edge so it doesn't bother me. I only want to know if the tyre will fit the rim and there will be no rubbing or problems. Advice please.
 

RichA

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The original owner may have specced different alloy wheels to the standard ones or changed them at some point.
Best checking with your garage.
 

Twire

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The first figure 225 is the width of the rim (mm) so I'm surprised those two figures are different. The second figure 55 (mm) is the profile so this can change depending on how low a profile tyre you require. The third R19 (inches) is the wheel size.

The tyre width should match the rim width so I'd definitely get your wheel rim measured.
 

GreiginFife

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I know I could do this on a car forum, left the last one due to casual racism becoming quite common :oops:, but I don't want to have to join one just for one question.

I changed my car a few months ago, 2nd hand car.

It came on tyres 225/55/R17

When looking for replacements, 2 will need doing soon, I put the reg into tyre sites and it tells me the appropriate size for the car is 245/45/R17

It is running fine, they clearly fit the alloys so I presume no issue, other than maybe the speedo is out by 0.75mph?

Is there a reason the previous owner would have done this? It is a Merc E Class, not a sporty version, so it not a boy racer car

The key question though, I have winter tyres from my previous car that are barely used. The size is 215/55/R17. Any reason that these will not be suitable? Again, I understand the speedo may be out by minor margins but I don't drive on the edge so it doesn't bother me. I only want to know if the tyre will fit the rim and there will be no rubbing or problems. Advice please.
It may be that the tyres were fitted incorrectly (it happens) unless, as Rich says the alloys were changed although it’s usually not the profile that increases.

the section width, in this case 225 or 245 is the overall tread width and on many German cars the rear tyres are usually wider by 20/30mm than the front so just make sure it wasn’t saying that the front/rear is being selected as required.

Although a 17” alloy will always be 17” for the diameter, the rim width can differ (8 or 8.5J etc) and I’d be surprised if a 215 fit on a rim comfortably for a 225 or even 245.

Best to check if the alloys were changed then probably best to stick with the currently fitted sizes.
 

pauljames87

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Check your manual about what size your car should have. Online auto checkers can be wrong or have options

Was there more than one option?
 
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Lord Tyrion

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Check your manual about what size your car should have. Online auto checkers can be wrong or have options

Was there more than one option?
I put the reg into a few sites and they all came back with the same size, one size, not two

Annoyingly, check the manual is not as simple as it sounds now that one manual can cover a range of models within a range. Trying to decipher which one applies to your car is less simple than it should be.
 
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Lord Tyrion

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It may be that the tyres were fitted incorrectly (it happens) unless, as Rich says the alloys were changed although it’s usually not the profile that increases.

the section width, in this case 225 or 245 is the overall tread width and on many German cars the rear tyres are usually wider by 20/30mm than the front so just make sure it wasn’t saying that the front/rear is being selected as required.

Although a 17” alloy will always be 17” for the diameter, the rim width can differ (8 or 8.5J etc) and I’d be surprised if a 215 fit on a rim comfortably for a 225 or even 245.

Best to check if the alloys were changed then probably best to stick with the currently fitted sizes.
That is the answer i was hoping not to get, but knew was a strong option. My 4 x winter tyres only got used for about 4k last year due to covid restrictions and they were newly bought. I know that I can sell them on but they wont go for much and i would far rather have kept them for this car.

I'll get the alloys measured and see where I go from there.
 

GreiginFife

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That is the answer i was hoping not to get, but knew was a strong option. My 4 x winter tyres only got used for about 4k last year due to covid restrictions and they were newly bought. I know that I can sell them on but they wont go for much and i would far rather have kept them for this car.

I'll get the alloys measured and see where I go from there.
It all depends on the rim itself. The profile width (225 etc) is NOT the rim width. Rim widths are measured in inches (8J = 8 inches or c. 205mm) And rims have ranges of tyre sizes that they can accommodate (some stretch the tyre wall and some compress it) for different ride characteristics as the tyre wall will almost always be level with or overhang the outer rim on either side.

If the rim is 8J then it can take 215 (narrowest) to 245 (widest) so would be in your ball park to take the 215's with possibly a little stretch. If the rim is a 7.5J with the 225's fitted then you would get away with 215s.

However, and it's a big however, if your car has wider rear tyres then you most likely cannot use the 215's all round (apart from drastically changing the ride and handling they probably wouldn't fit on the rim itself).
 
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Lord Tyrion

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They will be fine, go down to your local tyre shop and give the guy 20 quid and he'll make them fit. they can stretch tyres, its quite common.

https://tyrestretch.com/

A bit extreme, but perfectly fine.
I've never heard of that before. Every day is a learning day 😄.

Another interesting option to explore 👍. It would certainly be the easiest solution.
 
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Lord Tyrion

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I'd do this ... Least then you could swap them yourself pretty easy
Swap them myself 😲. Doubtful I could remove the current wheels, doubtful I could balance them right, doubtful I could put the next ones on correctly and safely. A job for a proper person, not me 😄. I've got so much more I want to do in life.
 

jim8flog

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If you are having tyres fitted the tyre fitter can check the rim size it is usually stamped on the inside of the rim. Look for figure like 5 or 6 I recently bought a spare rim and a different size was delivered. Each rim will fit a a range of tyre widths according to the fitters who fitted the tyre to it ( I was using a tyre I already had).

good guide here

https://www.tyresizecalculator.com/charts/tire-width-for-a-wheel-rim-size-chart
 

harpo_72

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Right read enough of this, there is a tyre size and then another number which is the load index followed by xl or sl. This indicates the tyres load capability at 2.9 bar for xl and 2.5 bar for sl. There will be another letter and that will be the speed rating. These are the key numbers.. the rest is just size and Grieg has explained that.
Depending on the age of the car there should be a pressure placard. This is a black and white label ( merc usually puts them in the fuel filler cap if you cannot find it on the door pillar) This will tell you your tyre size and actually gives you an indication of rim ( rims usually noted like this 17 x 7.5j et 45 .. 17 is OD, 7.5 is width, et is offset)
Just pop the car spec on and I can guide you to what you need if that helps
 

chico

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The first figure 225 is the width of the rim (mm) so I'm surprised those two figures are different. The second figure 55 (mm) is the profile so this can change depending on how low a profile tyre you require. The third R19 (inches) is the wheel size.

The tyre width should match the rim width so I'd definitely get your wheel rim measured.
Not quite, the first figure is the width of the tyre not the rim. A few different width tyres can go on the same rim. It's a long time since I worked in the tyre game and there's that much electronics on a car I would check with the manufacturer before you changed anything.
 
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