SLK Wheels

[dan f]

Hi.

I have noticed that the wheels on my wifes SLK are all the same size.

They are 18" wheels and they all have 225/40-18 tyres on.

I have read that the wheels on the back should be wider or at least have wider tyres on, is this correct? Will it cause any problems if the wheels are all the same width?

The rear wheels don't fill the arches as much as the front ones which leads me to believe that someone bought 4 identical wheels for the car instead of front and rears with different widths as they should have.

Is it a good idea to replace just the rear ones or would it be better to sell the current wheels and buy a new set?

Cheers,
Dan.

 

[SLinKyjoe]

no problem with what you have there.....

a problem may occur is you had 245's on the rear and 225's on the front and you wanted to swap back to front.....the back's wont fit in the front's then.

the R171 standard size is 225's all round...i think.....

 

[mlc]

You dont say if the car is the new model or old, but I assume its the old (170) series.

Factory standard was 20mm wider on the rear, but it was also 16 inch not 18. We have 225 all round on 17 inch and they run perfectly. I assume (but dont know as a fact) that the original format was wider on the back for more grip, narrower on the front for less tramlining, but I suspect someone will give us the definative answer.

mark.

 

[pascal]

Factory 17s for the 170 were

front: 7.5J x 17 ET 37 with 225/45 tyres
back: 8.5J x 17 ET 30 with 245/40 tyres

With you 18s, you may be able to fit slightly wider tyres on the back, depending on the rim width (J size)

 

[dan f]

Thanks for your replies.

So it is OK with the same width on all 4 tyres, however it would probably be beneficial to fit wider tyres on the back.

I will wait until 2 of them have worn out and then fit 245s on the back.

Cheers,
Dan.

 

[pascal]

Dependson your rim width. What is the J (rim width) number


245/35s would mean your rolling circum would be 27mm less than front, and top show a 1.33% higher speed on the speedo than you were actually traveling at.

245/40s would have the oppisite effect, by some 2.5 % and could cause problems with your ASR/EPS/ABS and cruise control

If your rim with is 8.5" or more 255/35 would be a near perfect match

 

[dan f]

Hi.

Not sure about the rim width, I will endeavour to check tonight.

However at a guess I would say they are 8J or 8.5J

I have 225/40-18s on all the wheels at the moment. Which wheels does the speedo take its reading from, or is it from the gearbox?

There is always going to be a slight variance in rolling radius, however that same thing can happen as the tread wears anyway.

Dan.

 

[pascal]

Sure dan,

The manufacturers allow for tyre wear in the software of the ASR/ESP/ABS which takes readings from all four wheels.

But if you put on new 245/40 on the back, and new 225/40 on the front, the difference in circumference will be 50.27mm (2 inches) (2001.82 v 2052.09). And if the fronts have less thread than the back (which is inevitable at some stage) this difference will be increased further.

If it turns out your rims are 8" the widest recomended wheel is 245, and 245/35 the closest to the fronts

If you have 8.5" 255/35 are almost the exact match

 

[dan f]

Thanks for the reply.

As I think they are 8J then the tyre I had reckoned on (245/35-18) will be the best one to use anyway. They are also a fair bit cheaper than 255/35s.

Cheers,
Dan.