Tire size's could do with advice

[daviesbike]

i am currently running 245 45 18 bridgestone potenza

i would like a better ride from the car can i fit 245 55 18 or maybe 245 50 18 to the rs6 wheels i currently have
what will the side affects be ?
how much will it affect the speedo how many mph will it be out + or -

the car is tracking all over the place as in it feels like a real effort at times to steer the car because it seems to want to follow all the ruts in the road and chase the white lines

also how would it be with the firm ish ride set up i have at the moment

many thanks

[HPsauce]

The tyre calculator I use http://www.tyres-pneus-online.co.uk/...ce-advice.html
says 7.2% difference, i.e. speedo seriously underrepresents your speed.

There may also be wheel arch clearance issues.

[daviesbike]

Hmmm is there no way to recode the ecu to a new profile or is it all to do with abs sensors ect ..?

[daviesbike]

so if i Go to a 245 50 18 its only 3.4% out with speed of 62 mph its actual at 64 i could live with that if it makes a difference to the quality of the ride

[ainarssems]

There is a lot of difference in ride quality depending on manufacturer and load index. Higher load index = stiffer side-wall = harder ride.

I just changed from Avon ZZ3 to Michelin Primacy Alpin on A6 both with the same load index of 93 ( minimum is 91 for that car) and it feels like different suspension- a lot softer on bumps and potholes but the same or better stability in the corners.

As for the speedo -on some cars you can calibrate it, have not looked it up for A8 and all/most cars show higher speed on speedo then actual with standard tyres, check yourself comparing to SatNav.

Also you need to inform insurance company if you changing to non standard tyre size and it may attract additional premium.

the car is tracking all over the place as in it feels like a real effort at times to steer the car because it seems to want to follow all the ruts in the road and chase the white lines

You might want to check suspension bushes and wheel alignment for this- full alignment not just tracking.

[daviesbike]

when i say its tracking i mean its following the pattern in the road and im not sure if this is because of the lower profile of tyre to what was on there before but when it had a 55 profile on the 17" winter wheels it never did that, but if im buying tires i would prefer to spend on the 18" wheels rather than 17"s but at the same time fix the ride quality,

would it have an affect with this if the tracking was out at all ? or if the alignment was out ?

also would an increase from a 45 to a 50 profile be sufficient to feel a difference on the road comfort wise ?