18" Tyre Profile - Is anyone running a 45 profile tyre?

[manganaj]

I've got a 184 Quattro on the standard 225/40 R18 Contis and will be looking to change them out between now and the end of summer depending how long they last.

I'm considering running a slightly higher profile tyre, so going up to a 45. I think this would have a few benefits:

- Bring the speedo and odo closer to the absolute number. I currently do 73 mph indicated on the speedo to get 70 by GPS and yes, I'm OCD enough for that to bother me.
- Slightly improved comfort and grip from a higher profile and what will be a slightly wider tyre.
- Increased fuel economy as the rolling diameter will be greater for one revolution, so although the car will require more energy to accelerate from a standstill, once underway and momentum takes over I will travel further for a given number of revolutions.

So, has anyone else done this and what are your experiences?

Thanks in advance...


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[GSB]

Going up in profile won't give you a wider tyre. A wider tyre dies not equal more grip.

If you're OCD enough for a tiny instrument error indication to bother you, you're definitely OCD enough to notice an extra 1/2 inch in the sidewall. Also, GPS is not the last word in accuracy.

Besides the aesthetics, There's also the greater unsprung wieght to consider, and the effect on gearing.

Have you considered instead the slightly smaller jump of moving to a 235/40-18? The rolling circumference is larger, but not as marked as the 45 profile tyre. You'll get greater comfort at the expense of slightly reduced steering response due to the wider tyre on the same width rim.

 

[GSB]

For reference, on a 6 speed manual S3, you get the following engine rpm changes;