SL to the rescue !

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Merc220cls

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Feb 14, 2018
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628
Location
Ayrshire
Car
220 CLS Shooting Brake & 350 SL
A couple of months back and just days after a puncture repair I was losing air on one of the rear tyres on my CLS. After a visit to the tyre shop it was found that the tyre wasn’t sealing against the wheel rim so a new tyre would be required. As they didn’t have one in stock I had no option but to get the tyre re fitted to allow me to drive home.
With the car at 15k and the tyres only half worn before fitting new tyres I tried that horrible stuff out of a can and to my surprise it worked. Just last week the same tyre began losing air again and today it was completely flat. This hadn’t happened before so I tried another can in the tyre to no avail.
On removing the wheel I’ve found that I have obviously hit a pothole (just my luck) as there is a bulge on the inner side of the tyre and the air was just going straight out.
Thinking i’m off the road ( no spare ) so unable to even drive to get two new tyres on Monday I thought why not try one off the SL just for the trip and it fits perfectly so having the SL helped out. It’s sitting on SORN at the moment so no problem there.
The CLS has now done 17k and the tyres still have 4.5mm left so I will hold onto the remaining good tyre just in case “lightning” strikes a third time. I’m keeping the car on the standard Pirelli P Zeros as I’ve never had any complaints with them.
 
Got two new Pirelli P Zeros fitted today @ £206 each. I’ve retained the one good tyre with 4.5mm tread left in case I require it in the future.
Out of interest I measured the circumference of the 17” wheel I had fitted temporarily from my SL against the 19” on my CLS. The difference is less than 10mm with the SL wheel being the larger circumference.
Just goes to show what you “gain” with low profile tyres !
 
Got two new Pirelli P Zeros fitted today @ £206 each. I’ve retained the one good tyre with 4.5mm tread left in case I require it in the future.
Out of interest I measured the circumference of the 17” wheel I had fitted temporarily from my SL against the 19” on my CLS. The difference is less than 10mm with the SL wheel being the larger circumference.
Just goes to show what you “gain” with low profile tyres !

I'm sure you know but just in case I'll mention it - The rolling diameter is pretty much set as it affects gearing/speedo/ABS etc so with an increase in wheel size the profile is also smaller to maintain this.
I suppose fitting a different size wheel is OK for that short trip as it is only like fitting a space saver.
Does your not have a spare?
 
what would be the impact on the diff of running different rolling circumference tyres at either end of the axle?
 
The 10mm difference in circumference mentioned here is trivial IMHO ... tyres vary by more than that as the tread wears. Many cars have a spare that's a different diameter to the standard road wheels, but this wheel/tyre combination will be sized so the rolling radius is close enough not to cause a problem with ABS/ESP. etc.

However it's only legal to use tyres of a different size on the same axle temporarily (normally interpreted as 50 miles e.g. to drive the car somewhere that a proper replacement can be fitted) and at reduced speed (generally 50 mph or less).
 

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