I am looking to fit 4 new tyres and been advised to fit 235 40/18 ....at the moment the tyres I have now are 225 40/18.

I was told that the 235 40/18 bulk up the tyre a little bit so protects the rims and also to put 36 air pressure in for a smoother ride?

Any one got any thoughts about this. Only just got my Superb elegance so trying to find the best tyre and best prices in Gloucestershire area.

Any advice would be much appreciated.

I am looking to fit 4 new tyres and been advised to fit 235 40/18 ....at the moment the tyres I have now are 225 40/18.

I was told that the 235 40/18 bulk up the tyre a little bit so protects the rims and also to put 36 air pressure in for a smoother ride?

Any one got any thoughts about this. Only just got my Superb elegance so trying to find the best tyre and best prices in Gloucestershire area.

Any advice would be much appreciated.

I am not sure about the advice to fit 235 40/18 tyres. Someone else may be able to advise if they have the same or a larger rolling radius.

There are several threads in the forum talking about choice of tyres which you might like to look at, and during September the Autoexpress did a test of 225 40/R18 92Y tyres on Octavias that I found particularly interesting.

Re tyre pressures: I am still running the original Conti Sport Contact 2s on my Superb 2 hatch.

I was unhappy with the pressures indicated on the fuel flap which, when converted, give about 30/31 lbs/sq inch front and 34 lbs/sq inch rear. I found that with the soft front, the handling was not as responsive as it could be, with the front end for example taking time to settle into the chosen line in sharper corners. I was advised by the dealer to use 32 lbs/sq inch front and rear.

After some experiment, I settled on 32 lbs/ sq inch in the front. I found 32 a bit soft for the rear, but did reduced the rear pressures to 33 lbs/sq inch, with the boot empty to discourage a tendency to bounce without making the rear end too soft.

IMHO that has provided a very satisfactory handling balance without upsetting the grip or the ride quality. When I drove to Northumberland some time ago with two up and several cases in the boot, I raised the rear pressure to 24 lbs/sq inch, and that seemed to be very satisfactory for motorway cruising.

OOPS!! I should have said 34 for the rears not 24.

They will have a larger rolling radius... 40% of 235mm as opposed to 40% of 225mm. It's only a marginal difference, but it will affect your speedo reading.

When I borrowed a demonstrator, I noticed in the maxidot menu that there appeared to be a setting to adjust the speedo in increments of maybe 5 mph. This may be sufficient to overcome the increased rolling radius. I guessed it was for when winter tyres are fitted

One option is to look for tyres with "rim protector" or "rim protection" built in. There are lots available and it ensures that the tyre actually sticks out past the rim a small amount.

Hope this helps

They will have a larger rolling radius... 40% of 235mm as opposed to 40% of 225mm. It's only a marginal difference, but it will affect your speedo reading.

When I borrowed a demonstrator, I noticed in the maxidot menu that there appeared to be a setting to adjust the speedo in increments of maybe 5 mph. This may be sufficient to overcome the increased rolling radius. I guessed it was for when winter tyres are fitted

One option is to look for tyres with "rim protector" or "rim protection" built in. There are lots available and it ensures that the tyre actually sticks out past the rim a small amount.

Hope this helps

You sure that wasnt the speed limiter/warning ?? I dont have a speedo adjustment feature on mine

Also bear in mind any change in tyre size will need to be told to your insurers , i dont see the point myself

Further to my original post, I checked with a tyre size change calculator on www.etyres.co.uk/tyre-size-calculator.htm .

According to their table:

225 40/R18 has a rolling diameter of 637 mm. (25.09 inches)

235 40/R18 has a rolling diamenter of 645 mm. (25.4 inches)

Thats 8 mm difference, or an increase of 1.26% in rolling diameter.

Their table recommends a maximum difference of +/- 2.5%.

If you are really worried about damaging your wheels then you could always try something like 'Alloygator' rim protectors, though I am unsure how effective they are.

You sure that wasnt the speed limiter/warning ?? I dont have a speedo adjustment feature on mine

Also bear in mind any change in tyre size will need to be told to your insurers , i dont see the point myself

Ah, perhaps it was, I was just messing with the system whilst I had the car for a few days