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[greenman]

Anyone know the correct tyre profile for 18" wheels so that the speedo is accurate?

[Martian]

Assuming the standard tyre size for your particular model is 225/55 16, and assuming you are not going to increase the width on the 18" rims, the closest match is a 225/45 18

[greenman]

Typical!
I,ve a set of 235.40,s. So how much would the speedo be off if
I fitted these?

[Martian]

The speedo will be off by 1.3%, so at an indicated 60mph you will actually be travelling at 59.2mph 

[i260]

Typical!
I,ve a set of 235.40,s. So how much would the speedo be off if
I fitted these?

I believe that this was the specified size for the 18 inch option from factory though!

225 on an 18 is deffo not right from VX even if it is the nearest match.

If you look at the difference in rolling radius between the 225/55/16 and 235/45/17 they are not exactly close, the 17 being somewhat smaller.

The 225 will offer better handling, particulaly if you are on the usual 7.5 inch aftermarket rim width but on the Irmy 8 inch widths you will be leaving yourself exposed to kerbing - your choice!!

[2woody]

ok - so here goes.....

your standard tyre gives a wheel revs per mile of 817 - indeed, this is the standard for Omega A and Omega B

if you're wanting to go to 18" wheels, you have the following options.....

215/40 x 18, giving 811 wrpm ( or 0.7% diffrerence )

235/40 x 18, giving 820 wrpm ( or 0.4% difference )

245/40 x 18, giving 811 wrpm ( or 0.7% difference )

the aforementioned 225/45 yields 804 wrpm, which is 1.6% different - a bit too much really.

my choice would be the 215/40, which will still give you some combat against tramlining and a bit of handling left.

[TheBoy]

ok - so here goes.....

your standard tyre gives a wheel revs per mile of 817 - indeed, this is the standard for Omega A and Omega B

if you're wanting to go to 18" wheels, you have the following options.....

215/40 x 18, giving 811 wrpm ( or 0.7% diffrerence )

235/40 x 18, giving 820 wrpm ( or 0.4% difference )

245/40 x 18, giving 811 wrpm ( or 0.7% difference )

the aforementioned 225/45 yields 804 wrpm, which is 1.6% different - a bit too much really.

my choice would be the 215/40, which will still give you some combat against tramlining and a bit of handling left.

Cars with 225/55/16 tyres have a different dash (pre 98) or config (post 98) to all other tyre sizes, guess that size is too far out of the standard Omega-A/B spec

[cube]

My 2001 2.2 petrol estate has got 205/50-16 tyres on, not really sure if right or wrong  
Not due for change for a while so will be sticking with unless completely wrong

 

[Sam Burton]

Not completely Wrong they are just a Smaller tyre Height wise if yours has the Facelift CD wheels on they should be 225/55/R16 but then again you may have a completely different style wheel e.g. early GLS spec wheels with the chrome style centre but im not familiar with that size?

[cube]

Not completely Wrong they are just a Smaller tyre Height wise if yours has the Facelift CD wheels on they should be 225/55/R16 but then again you may have a completely different style wheel e.g. early GLS spec wheels with the chrome style centre but im not familiar with that size?

Thanks Sam  , car drives ok with them lol, i'll have to keep them for a while and swap round when i need to. Change the back to 225/55-16 first lol  Ps no idea at all which model allow wheels are fitted ?

[Zippy2012]

My 2001 2.2 petrol estate has got 205/50-16 tyres on, not really sure if right or wrong  
Not due for change for a while so will be sticking with unless completely wrong

 

Not compleatly wrong but your speedo will be...
if the standard tyre size should be a 225 55 16 & you have fitted 205 50 16s
at 30mph on speedo you will be doing only 28mph
but at 60mph on speedo you will only be doing 56mph
90mph-84mph
120mph-112mph
Great if you dont want to be caught speeding in the local limits but over time you will put more miles on your car than its actually done 
if the standard size for you car was a 195 65 16 speedo would be out by..
30mph-27 actual
60mph-55 actual
90mph-83 actual
would be worth finding out the standard fitment to your car & soucing a set of replacements soon

i bet the 205 50 16s look tiny in the huge omega wheel arches!???