tyre size worries me

[michaelb]

Hi All

I have just had new tyres put in

245 17” 40 at the rear and 225 17” 45 front

When I got home I noticed that the front ones where 45 and seemed a touch higher / bigger

I called the tyre fitter and he said that my old font ones were also 45 and any way it was ok to have them different

What does the 45 stands for and is it OK to drive like this?

Regards,

Michaelb

[johnnywas]

245is the width 17"wheel diameter 45 profile tyre hight http://www.tyresave.co.uk/tyresize.html heres a handy link

[J_T]

The fronts are 6mm bigger overall with approximately 3mm difference in tyre wall height.  Nothing to worry about.  The rears have more rubber on the road for greater grip and improved power delivery.

The 40 and 45 is the percentage of the large number (the tyre width - 225 and 245) that is in the side wall of the tyre.

Jon

[SiH]

The profile is the sidewall height a a percentage of the width. Soon a 225.45 the sidewall is 45% of 245 high. 255\'s are wider, so to keep the same rolling radius, you need a lower profile
HTH
Si

[J_T]

Or what johnny said (I used that link too, lol) link should be: http://www.tyresave.co.uk/tyresize.html

[johnnywas]

Or what johnny said (I used that link too, lol) link should be: http://www.tyresave.co.uk/tyresize.html[/URL]

i kept looking and i couldent see wat i did wrong lol but i got it,thanks:Thumbsup!

[michaelb]

Chaps

Many thanks for your informative replies

I actually see the front tyres as being bigger

Honestly, the front tyres look bigger then rear ones when looking at the car from the side

The question is do I change the back ones to 45 or front ones to 40

What would give me better handling?  What is the “done thing! For an fd with 245 at the rear and 225 at the front?

Regards,

Michaelb

[Brett]

It would depend on how much flex you want in the tyre.  The tyre is the last part of the suspension, the less give in the sidewall the firmer the ride etc...

[silverrexman]

Chaps

Many thanks for your informative replies

I actually see the front tyres as being bigger

Honestly, the front tyres look bigger then rear ones when looking at the car from the side

The question is do I change the back ones to 45 or front ones to 40

What would give me better handling?  What is the “done thing! For an fd with 245 at the rear and 225 at the front?

Regards,

Michaelb

I have 245/35/17 on the rear of mine and 225/40/17 on the front,its all about rolling circumference,stick with what you have got,if you went to a reputable tyre place,i am sure they would have looked it up,cheers

[probedb]

Yup as others have said, the 40/45 is a percentage.

I have 235/40/18 front and 265/35/18 rear.

[neil_jdmr]

I always thought the lower profile figure (percentage) should be on the rear so as to equalise the difference in tyre width\'s
 
Ill try to explain what i mean
 
Take michael\'s tyres
F 225/40 R 245/45
 
So 225 x 40 / 100 = 90
and 245 x 45 / 100 = 110.25
 
The a difference of 20.25
 
But take the higher profile on the rear and do the percentage again
 
F 225 x 45 / 100 = 101.25
R 245 x 40 /100 = 98
 
Only give a difference of 3.25 Thus equalising the pressure beween the 4 much more evenly
 
 
Happy to be corrected though if im talking out of my dish

[efiniste]

neiljdmr - The only thing you\'re working out there is the height of the sidewall. It\'s the circumference of the tyre that matters.

michaelb - Use the link above to work out how close to the oem tyre circumference your new ones are. Too far out and it\'ll affect your speedo reading. From memory, originals are either 225/50 16 all round or R 255/40 17 and F 235/45 17 (both of wich are very close in circumference to the original 16"s).

Steve


Steve

[michaelb]

It would depend on how much flex you want in the tyre.  The tyre is the last part of the suspension, the less give in the sidewall the firmer the ride etc...

I have my tain set up on almost the hardest setting as I like a firm ride so on that note which set up would give me the most firm ride?

Which tyre combinantion?

Regards,
Michaelb

[michaelb]

I always thought the lower profile figure (percentage) should be on the rear so as to equalise the difference in tyre width\'s
 
Ill try to explain what i mean
 
Take michael\'s tyres
F 225/40 R 245/45
 
So 225 x 40 / 100 = 90
and 245 x 45 / 100 = 110.25
 
The a difference of 20.25
 
But take the higher profile on the rear and do the percentage again
 
F 225 x 45 / 100 = 101.25
R 245 x 40 /100 = 98
 
Only give a difference of 3.25 Thus equalising the pressure beween the 4 much more evenly
 
 
Happy to be corrected though if im talking out of my dish

Thanks for all the figures so the more even spread across all fours the better the handling? So I should really have them all at 40, right? or am I missing a point here and it does not really matter?

Regards,
Michaelb

[michaelb]

neiljdmr - The only thing you\'re working out there is the height of the sidewall. It\'s the circumference of the tyre that matters.

michaelb - Use the link above to work out how close to the oem tyre circumference your new ones are. Too far out and it\'ll affect your speedo reading. From memory, originals are either 225/50 16 all round or R 255/40 17 and F 235/45 17 (both of wich are very close in circumference to the original 16"s).

Steve


Steve

My radar detector is already telling me that my speedo is showing more sspeed than I am doing and that was before the change ...

Regards,
Michaelb