Different tyres on front and back of ML320

[mrjamjam]

Can anyone shed any light why my ML320 has different spec tyres on the front and back:

Fronts 255/50 19s
Rears 285/45 19s

I bought the car like this and whilst I understand that the diameters are near enough the same, why would you have different width sizes on a 4X4? (can understand on a RWD but not 4X4?)

 

[paulyV6]

What are your wheel specs?

 

[mrjamjam]

Bought the car second hand (it's an '05) 2 years ago with the current set-up and noticed the difference when I started to search for replacements. I spoke with the independent garage that last serviced the car and they siad that there were many variations of wheel and tyre combos's available fron the option list but I still don'y get why the width difference. Anyway, how do find out what the wheel specs are?

 

[A-AvantGarde]

Bought the car second hand (it's an '05) 2 years ago with the current set-up and noticed the difference when I started to search for replacements. I spoke with the independent garage that last serviced the car and they siad that there were many variations of wheel and tyre combos's available fron the option list but I still don'y get why the width difference. Anyway, how do find out what the wheel specs are?

The only sure fire way is to remove the wheels and check what's stamped on the inside of them.

It's most likely that you have a staggered setup (which is quite common on Mercedes & BMW) where the rear wheels are wider than the front. My W203 has wider rears as does my dads BMW and the S Class before that.

If you can post some pictures of the wheels on your car other members may be able to assist further.

Assuming the wheels are original (at time of build) then you could get something called a 'datacard' print which should also indicate which tyres would have been originally specified too. A local dealer would be able to get you a datacard print out, otherwise some members on here can (you'd need to provide the VIN number to get one though).

Finally, at the back of your service book / owners manual it should also have a printed sticker with lots of 3 digit numbers (this is the data card).

 

[paulyV6]

The wheel specs will be stamped inside the wheel somewhere.

There will be something like 19 x 9J, where 19 is the diameter and the 9 is the width (both in inches). Tyre sizes in Inches for diameter, but mm for width and profile. So a 235/45/19 tyre is 235mm wide with 45mm profile to fit a 19" wheel.

You can see how various tyre sizes look when placed on specific wheel sizes at Tyrestretch.com - Image Library

 

[mrjamjam]

Ok, thanks got soem work to do and I'll try and get some pics

 

[renault12ts]

The wheel specs will be stamped inside the wheel somewhere.

There will be something like 19 x 9J, where 19 is the diameter and the 9 is the width (both in inches). Tyre sizes in Inches for diameter, but mm for width and profile. So a 235/45/19 tyre is 235mm wide with 45mm profile to fit a 19" wheel.

You can see how various tyre sizes look when placed on specific wheel sizes at Tyrestretch.com - Image Library

Oops...this is entirely wrong.

The profile of a tyre is not expressed in millimeters but as a percentage of the width.

So, a 235/45 tyre has a profile (ie a tyre wall depth) of 45% of 235...which is nowhere near 45mm but is in fact 105.75mm.

Although both your tyres are different sizes , they are the correct ones for a staggered set up on 19s. However both tyres will be almost exactly the same diameter, or rolling radius or circumference. If they were not...then nothing would work, particularly on a four wheel drive.

255/50 = 127.5mm tyre wall, and 285/45 = 128.25mm tyre wall. This is only 0.75mm difference between them. Less than the difference between worn and new tyres. So...you have nothing to worry about.

Sometimes a post has to be put down...because the info is so completely wrong. Sorry.

 

[paulyV6]

Oops...this is entirely wrong.

The profile of a tyre is not expressed in millimeters but as a percentage of the width.

So, a 235/45 tyre has a profile (ie a tyre wall depth) of 45% of 235...which is nowhere near 45mm but is in fact 105.75mm.

Although both your tyres are different sizes , they are the correct ones for a staggered set up on 19s. However both tyres will be almost exactly the same diameter, or rolling radius or circumference. If they were not...then nothing would work, particularly on a four wheel drive.

255/50 = 127.5mm tyre wall, and 285/45 = 128.25mm tyre wall. This is only 0.75mm difference between them. Less than the difference between worn and new tyres. So...you have nothing to worry about.

Sometimes a post has to be put down...because the info is so completely wrong. Sorry.

Haha - it wasn't completely wrong. Just the profile bit!