Stevie boy

22 hours ago, Greydog said:

Hi Stephen

So your original tyres are probably Runflat's which combined with their stiff construction and low profile have a reputation for giving a stiff/harsh ride. I helped a friend who has a Merc 4matic transfer case was toast quote from Merc £3k. Before pulling the transfer box (it is better to practice on someone else's car) I put a chalk mark on the front tyre and ground and rear tyre and ground then rolled it forward until the front tyre chalk mark was bottom again the rears had travelled about 80mm further, doesn't sound much but travel a few miles and the strain on the transfer case is enormous. To much for his, we rebuilt it successfully and a new set of tyres he was back on the road costly lesson learned. From other forums dealing with AWD depending on the mechanical set up mis-matched tyres can kill transfer cases and/or diffs.

So some maths your original tyre/wheel combo 225 x 35 x 20 will have a circumference new of 203.1 cm front and rear. The trick now is whatever tyres you choose they need to be within a tiny percentage front to rear circumference to avoid transmission wind up and damage.

So here goes (make sure you check my sums as I am an old bloke) 

Say Front wheel tyre combo is 225 x 45 x 19 circumference would be 208.9 cm. So target for the rear has to be as close to that as possible. As an example 255 x 40 x 19 would give a circumference of 209.5 cm, so I think that should work as the sizes are so close a better match would be 235 x 45 x 19 front 212 cm circumference with 265 x 40 x 19 rear 212 cm circumference 

That's the maths, in practice if your tyre supplier is helpful maybe put a front and rear side by side and roll them forward to be sure before fitting. If they from the same maker you should be OK ( lucky mine is and I have done this several times) 

Bit "War and Peace" but I hope it helps and makes sense 

Dave

 

 

 

Hi Dave, again great advice and the the larger depth side wall of the tyre is the look I am after to fill the arches a little more and protect the alloy wheels a little more on pot hole Brisish roads !

21 hours ago, Greydog said:

Hi Stephen

So your original tyres are probably Runflat's which combined with their stiff construction and low profile have a reputation for giving a stiff/harsh ride. I helped a friend who has a Merc 4matic transfer case was toast quote from Merc £3k. Before pulling the transfer box (it is better to practice on someone else's car) I put a chalk mark on the front tyre and ground and rear tyre and ground then rolled it forward until the front tyre chalk mark was bottom again the rears had travelled about 80mm further, doesn't sound much but travel a few miles and the strain on the transfer case is enormous. To much for his, we rebuilt it successfully and a new set of tyres he was back on the road costly lesson learned. From other forums dealing with AWD depending on the mechanical set up mis-matched tyres can kill transfer cases and/or diffs.

So some maths your original tyre/wheel combo 225 x 35 x 20 will have a circumference new of 203.1 cm front and rear. The trick now is whatever tyres you choose they need to be within a tiny percentage front to rear circumference to avoid transmission wind up and damage.

So here goes (make sure you check my sums as I am an old bloke) 

Say Front wheel tyre combo is 225 x 45 x 19 circumference would be 208.9 cm. So target for the rear has to be as close to that as possible. As an example 255 x 40 x 19 would give a circumference of 209.5 cm, so I think that should work as the sizes are so close a better match would be 235 x 45 x 19 front 212 cm circumference with 265 x 40 x 19 rear 212 cm circumference 

That's the maths, in practice if your tyre supplier is helpful maybe put a front and rear side by side and roll them forward to be sure before fitting. If they from the same maker you should be OK ( lucky mine is and I have done this several times) 

Bit "War and Peace" but I hope it helps and makes sense 

Dave

 

 

 

On 5/10/2021 at 11:15 PM, Stevie boy said:

Hi Dave, cracking advice mate and you sure know your stuff fella ! It was a deeper wall I was after so am I stuck with what I have been quoted for tyre size front and back ? 

Many thanks again and await you reply with thanks Steve 👍

Hi Dave, cracking advice mate and you sure know your stuff fella ! It was a deeper wall I was after so am I stuck with what I have been quoted for tyre size front and back ? 

Many thanks again and await you reply with thanks Steve 👍

Hi sorry for late reply , bought them online from alloy specialist I have checked this out and they will fit as looked at other reputable sellers and 8.5front and 9.5 on rear is fine I just really wanted to know if I can get more tyre then 255 35 19 rear and 225 40 19 front . Wheels I have on at mo was an option same all round or staggered so opted for staggered but do see loads of BMW's do have larger wheels on the rear .

Many thanks 👍

Can anyone give me sound advice on what is the biggest tyre I can fit to rear 9.5 and front 8.5 . I've been quoted 255 35 19 fro the rest and 225 40 19 for the front but want as much tyre as poss and don't want them looking so low profile and stretched as I have 20" on at the mo running 225 35 20 all round 🤔 Many thanks Steve