[Yahoo]

I am getting some new tyres for my e92. I can get the original size 225/35/19 for the fronts in the make I want, but can only get 265/30/19 for the rear (instead of the original 255/30/19).

I know this will alter the rolling radius of the wheels but don't know if this is likely to have any negative implications.

I quite like the idea of having a wider tyre on the rear, but does this mean that I ought to go with wider tyre on the front to keep them proportionally the same?

[NFS]

Originally Posted by Yahoo

I am getting some new tyres for my e92. I can get the original size 225/35/19 for the fronts in the make I want, but can only get 265/30/19 for the rear (instead of the original 255/30/19).

I know this will alter the rolling radius of the wheels but don't know if this is likely to have any negative implications.

I quite like the idea of having a wider tyre on the rear, but does this mean that I ought to go with wider tyre on the front to keep them proportionally the same?

Wider tyres at the back means better grip at the rear and potentially increases bias towards understeer. I don't know if a change this small will have a noticeable effect though.

[SoYank]

A larger diameter tyre will increase your actual speed over your speedometer reading because a larger diameter translates to a larger circumference giving an increase in distance travelled per revolution. But since the speedo is biased high anyway, a small increase shouldn't be a problem. It also depends on how the speedometer pickup is taken, whether it is from the drivetrain, i.e., transmission, propeller shaft, or differential, or from a sensor on the front axle.

Tire Rack has a calculator that will display what the change in the speedometer would be between two different tyres. It's interesting to see the differences between manufacturers, or even the same manufacturer, with the same "tyre sizes".

[CD]

why cant you get the 255 ? ...

i run the same 225/35 19 255/30 19 setup with continental contact 3 tyres.

when i was enquiring about tyres the only make of tyre with that combination available was either continental or toyo ( and i tried loads of places for prices )

and would rubbing be an issue with 265 tyres ? that is quite wide !

[Yahoo]

Rubbing shouldn't be an issue. The new Alpina D3 coupe run on 265 on the rear and 245 on the front.

I couldn't get 255 for the rear because I specifically want to go for Vredestein Ultrac Sessantas - the company that I was looking to buy from didn't have 255 available. I guess I could have sourced them from elsewhere, but the price is right with the company I have ordered with.

[330cdsport]

Excuse my ignorance but if you go from 255 to 265 wide tyres (keeping diameter and profile the same - 19"/30 ) then surely this only affects the width and not the rolling circumference ????

[G33]

profile is the percentage of the width if u know what i mean... so if its a larger width (265 as opposed to 255) and same profile (30) of course the profile will be higher..increasing the overall diameter. throws yours speedo out my 1mph or so, however the speedo isnt 100% accurate anyway. check on the wheels and tyre forum calculator at the top of the page. if youre going 265s on rear id get 235s on front to suit, but i wudnt say its crucial nor am i an expert on these things

diameter of 255s = 635.5079999999999
diameter of 265s = 641.604mm

difference of 5.9944mm or 0.935%

@60mph speedo will read 61mph...if u can notice it!!!

[M3-FAST]

Originally Posted by G33

difference of 5.9944mm or 0.935%

which is 3mm wear off a new tyre!!!

you will never notice the difference Ben

[Yahoo]

Thanks for your responses - much as a thought really.

33cdsport - I have only just learned that the second number in a tyre size is a %age proportion of the tyre width. Seems odd to me, but I'm sure there are good enough reasons for it.

[330cdsport]

You learn something new every day...... as they say.

I always thought that the profile represented millimetres - as in '35' mm's for the tyre wall height.

OOpps!!!