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Discussion Starter · #1 ·
After a couple of replacements for bulging sidewalls on the efficientgrips I changed to some Michelin Crossclimate 2's yesterday. (I do quite a few trips up north and the Midlands)
I opted for 215 45 17's to try and lessen the harshness on the front suspension and since I got stopped recently for being a little too brisk down the A3, I am planning to drive with a little less enthusiasm for a while.
I have to say I am happy with the result having straight away done a trip up to Birmingham. Upsides are a softer and more compliant ride, much quieter, even the concrete bit between J10 and J11 on the M25 was nice. They fill the arches very nicely and do clear the struts, (Something I was a bit concerned about) Only downside so far is on the very abrupt speed humps it does skim the little arch extension screws coming down from them. I will adjust my speed to suit.
On the last one I switched to 205 40 17's and it was an improvement but that was on Vredsteins. That was also a noticeable improvement.
The speedometer does now over read by 3mph but as long as I am aware of that it is not an issue for me. Also at 70mph the rev counter now reads around 2700 which is slightly lower than before.
Obviously I have not explored the limits of traction but I thought this might be useful for those who are fed up with the fragility feeling caused by the Goodyears, the bulging sidewalls and the poor grip in the wet. It does look a little more Tonka Toy with the bigger wheels but I kinda like that. I may have a little less acceleration to 60 but I am enjoying getting there a little more than I was before.
I have to say as an aside that the car is now 18 months old, has just been for its' 30k service and the rear Goodyears were still 6mm tread. They do last if you drive on perfect roads, Shame they are so nasty in other respects.
 

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I think your speedometer will ‘under-read’ and not ‘over-read’ like you said, i.e the speed displayed will be under the real speed.

Changing from standard 195/40R17 to 215/45R17 is a relatively big change in wheel circumference of +6.5%, so even if the speed was reading a few % higher than real on the original it will now be reading under the real speed.

For comparison changing to 205/40R17 (as is popular and I have done) is only a change of around +1.5%.
 

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Discussion Starter · #4 ·
Yes you are of course correct. Yesterday it would read 73mph at 70, today it reads 67mph at 70. It is that Friday feeling.
 

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Yeah, that's a massive difference. Also illegal to have underreading speedo and so has voided your insurance :(
 

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I'm running slightly oversized tyres myself (195/50 16) but they still give v slight overread.
 

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so yours also voids your insurance then ????
 

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No. Why do people struggle to understand this ?
An underreading speedo is a breach of the construction and use regs. Manufacturers build in a margin to avoid any risk of being sued by drivers. The margin is usually around 2 to 3 mph at 30 to 60 mph. With a very slight circumference increase you will still be traveling slower than the speedo indicates, so not in breach. But the OP (by his own GPS measurements) is traveling faster than the speedo indicates, so in breach.
 

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type approval insists on Manufacturers original tyre size.

so your sweeping statement is wrong then ???

Ha ha
 
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