Air

[Joloke]

Deflated

[gordonbennet]

Some Mercs and BMW's (and probably other German autobahn stormers) have similar size differences front/rear.

 

Just run your sizes through the carbibles tyre calculator, if you put the 35 aspect on the front then the fronts will have a rolling circumference difference of 42 mm with the fronts obviously smaller.

with 40 aspect on those fronts would be 35mm larger than the rears in rolling circ.

 

Not a massive difference, though the difference in size is smaller with the current fitment.

 

No sizes in the handbook? nothing on the door pillars or inside the fuel cap or boot?

 

By the way, that tyre with the screw in it, have a look yourself when the screw comes out or the tyre comes off, if the screw hasn't ripped the inside casing to shreds it can be repaired by a professional tyre repair workshops such as Tyre Revivers at Islip near Thrapston, Northants, other tyre repair pros are available but rare now.

[dieselnutjob]

255/40/18 has a diameter of 661mm

 

255/35/18 has a diameter of 636mm which is 3.8% less

 

275/35/18 has a diameter of 650mm which is pretty much in the middle

 

if your objective is to have a front with the same diameter as the back then I would say that there's not much in it

 

I thought that there is a rule that the fronts are not supposed to be bigger than the back, but maybe that's only width

 

You can expect a harsher ride with the 35 section tyre though

[JayW]

If the screw hasn't ripped the inside casing to shreds it can be repaired by a professional tyre repair workshops such as Tyre Revivers at Islip near Thrapston, Northants, other tyre repair pros are available but rare now.

It's not so much a question of skill, more legality.

[gordonbennet]

It's not so much a question of skill, more legality.

 

Major repair is quite legal depending on the extent of damage (but tyre fitters at fitting joints will not have the quals or the equipment) , we're not talking a glorified cycle repair kit, but damage cut out and the tyre carcass in the vicinity examined, if ok the outer side is filled with uncured rubber, and a suitable patch which might well be 6" x 4" with radial re-inforcements bonded to the inside, then the whole caboodle vulcanised and the outside refinished and any grooves/sipes that got filled recut.

[jon928se]

If it doesn't have ABS there is no real issue having slightly different diameters between front and rear. Lots of pre ABS performance cars had differing sizes / diameters of tyre between front and rear. ABS and / or permanent 4wd means you need to have same diameter (within about 1% or less) front and rear. 

IIRC some 70s/80s performance cars (Lambo and poss Ferrari and more obscure stuff) not only had different width wheels but also different diameter wheels. 

[tooSavvy]

Major repair is quite legal depending on the extent of damage (but tyre fitters at fitting joints will not have the quals or the equipment) , we're not talking a glorified cycle repair kit, but damage cut out and the tyre carcass in the vicinity examined, if ok the outer side is filled with uncured rubber, and a suitable patch which might well be 6" x 4" with radial re-inforcements bonded to the inside, then the whole caboodle vulcanised and the outside refinished and any grooves/sipes that got filled recut.

 

http://www.maaslandbanden.com/com/truck-tyres/repair-vulcanising

 

 

TS

[Snipes]

If it doesn't have ABS there is no real issue having slightly different diameters between front and rear. Lots of pre ABS performance cars had differing sizes / diameters of tyre between front and rear. ABS and / or permanent 4wd means you need to have same diameter (within about 1% or less) front and rear.

IIRC some 70s/80s performance cars (Lambo and poss Ferrari and more obscure stuff) not only had different width wheels but also different diameter wheels.

I can't recall many classic Ferraris having different wheel diameter sizes. Lotus tend to do that kind of thing.