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Oversized tyres

pillow

Active Member
Joined
Feb 19, 2019
Messages
274
Location
Hampshire
Car
C216 CL600
Hi all,

My alloys have been cracked several times and welded up. I'm currently looking into getting a new set. I'm of the opinion the tyre profile is too small.

I was wondering what the feasibility was over putting on oversized tyres. By bumping up the profile by 5 I gain a little over half an inch of sidewall which I think will help significantly. It would be equivalent to moving down to 19" alloys while retaining the 20" look.

I believe I can correct the speedometer discrepancy (the larger tyres have a circumference increase of about 3.5%) using DAS.

Are there any other reasons why this might not be a good idea?
 
What is the current rim size?

And what is the current tyre size?

What rim and tyre size combinations are permitted for your car in the owners manual?
 
Currently on 20 inch rims. 255/35 front and 275/35 rear.

The manual has the above tyre sizes listed for 20 inch rims. So the car is stock at the moment.
 
Today's UK roads are patently nothing like the ground-glass surfaces that exist only in the minds of car stylists. Or should I say Marketing Men?

This is unlikely to change in the present "looks are everything" culture, so take your own action and put fit tyres you actually can drive on real roads.

If the speedo error can be corrected, so much the better, but even if it can't, it's worth living with.

Just keep it in the back of your mind when plod is around or if one of those average-speed road sections is approaching.

Changing my 255/40x19" to 285/50x18" was the best move I ever made.
 
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Today's UK roads are patently nothing like the ground-glass surfaces that exist only in the minds of car stylists. Or should I say Marketing Men?

This is unlikely to change in the present "looks are everything" culture, so take your own action and put fit tyres you actually can drive on real roads.

If the speedo error can be corrected, so much the better, but even if it can't, it's worth living with.

Just keep it in the back of your mind when plod is around or if one of those average-speed road sections is approaching.

Changing my 255/40x19" to 285/50x18" was the best move I ever made.
That is a huge change in size! Do you have any pictures before/after?

Other than the speedo being out did you notice or have any other issues?

Thanks
 
According to willtheyfit.com it's only 4% speedo error.

I can live with that, bearing in mind the upsides..

I should have some pictures somewhere, I'll see if I can find them.
 
4% speedo difference may be within original tolerances for overreading. Why not check your current set-up against GPS?
 
Are there any other reasons why this might not be a good idea?
Clearance issues, regarding suspension/struts?
Insurance issues, what does your insurer say about deviating from the manufacturer's recommendations?
Geometry issues, might need to be realigned/adjusted to avoid uneven tyre wear?
 
and expect better dry grip and worse wet grip and worse aquaplaning resistance with the same brand of tyre. this can be offset by replacing the current tyre with a better tyre if one is available
also expect different cornering feel etc. sometimes better , sometimes worse
 
Tire Size Comparison

I've found this useful.
I've fitted larger with 6% extra circumference, now the speedo is spot on.

This week I've re fitted standard wheels / tyres for diagnosis of a vibration, I'm glad to be back on the oversized, the ride is preferable.
 
I'm now in my 6th year of running 'oversize' tyres on ML and GLE 20" rims. Up from 265 to 275. It's not a massive change, (much the same as new to worn tyres!) but it does have the following benefits:
  • Better rim protection from kerb scuffs
  • The correction of the speedo from very optimistic to spot on
  • Small increase in ride comfort
  • Slightly more relaxed higher gearing.
  • More common 275/45/20 size means much keener prices in that size than the 265. (Like up to £140 on a set of 4!)
No disadvantages that I have found in both the Michelin and Avon Tyres used...including economy.
 
Well the rear wheel had ample space. The front wheel is hampered by the upper ball joint. The little blue thing I've put on the top of my current wheel corresponds to a tyre size of 255.40.20 instead of the current 255.35.20.

Looks like I will need to cut off the exposed threads on the ball joint to avoid it running and even then it's cutting it quite close!
 

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................ The front wheel is hampered by the upper ball joint. The little blue thing I've put on the top of my current wheel corresponds to a tyre size of 255.40.20 instead of the current 255.35.20.

Looks like I will need to cut off the exposed threads on the ball joint to avoid it running and even then it's cutting it quite close!

Or get smaller rims ...... and avoid all the hassles - 1/2" of radius is not going to make a huge difference in appearance.
 
My Typo, sorry.....standard size on my W164 is 255/50x19, NOT 255/40x19.
Which explains why I settled on the 285/50x18 wheels/tyres. the rolling radius is within a knat's of identical.
Next time, I might go for 285/55x18 to give me a slightly smoother ride, the difference represents only 4% speedo error.
Obviously, I 'd like to go wider but it was so much aggravation getting hold of 18" alloys for the ML, that I think I'm probably stuck with them and their skinny 8" width..
 

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