Advice Needed On Tyres

[H4AFY]

Can anyone advise me if i can do this at the moment on my p1 i have standard 0z alloys with pirrelli p zero assimetrico tyres the sizes are

205/45 r17 zr ww

can i put 215/45 r17 or 225/45 r17 tyres on the wheels and what difference will it make the only reason i ask is i can get the 215/45 s at a great offer price on either toyo tyres or pirelli p zero rosso tyres.

Edited September 18, 2007 by H4AFY

[dougster]

Pinch a copy of this months EVO mag and if the search function was working....................

[RA Dunk]

Pinch a copy of this months EVO mag and if the search function was working....................

hi sailor boy

[crispyduck]

Can anyone advise me if i can do this at the moment on my p1 i have standard 0z alloys with pirrelli p zero assimetrico tyres the sizes are

205/45 r17 zr ww

can i put 215/45 r17 or 225/45 r17 tyres on the wheels and what difference will it make the only reason i ask is i can get the 215/45 s at a great offer price on either toyo tyres or pirelli p zero rosso tyres.

H4AFY, you can adjust tyre sizes however you'll have to do some research. Note you can't simply change to sizes you mention above as you'll be changing the rolling circumference of the wheels thus making your speedo inaccurate. As a rule, if you increase the width of your tyre (e.g. 205) you'll need to reduce the profile (e.g. 45). Again seek advice from a trusted specialist as they can advice on handling issues also.

If you're interested I found a tyre conversion chart on the following web site that demonstrates what I've said above.

http://www.performancetyresdirect.co.uk/co.../converter.html

-Steve.

P.S: I have no connection with the above company.

[thewelsho]

H4AFY, you can adjust tyre sizes however you'll have to do some research. Note you can't simply change to sizes you mention above as you'll be changing the rolling circumference of the wheels thus making your speedo inaccurate. As a rule, if you increase the width of your tyre (e.g. 205) you'll need to reduce the profile (e.g. 45). Again seek advice from a trusted specialist as they can advice on handling issues also.

If you're interested I found a tyre conversion chart on the following web site that demonstrates what I've said above.

http://www.performancetyresdirect.co.uk/co.../converter.html

-Steve.

P.S: I have no connection with the above company.

That doesn't seem right to me. If you change the width of the tyre the roling circumference remains unaltered. However, if you replace your wheels and buy bigger rims, e.g. 17s to 18s then you are changing the rolling circumference and that is when you require a lower profile. I went from 17/215/45 to 18/225/40. Even with the profile change it still threw out the speedo by about 3mph (I compared before and after with GPS); which isn't that much, and to be honest the change was more accurate.

[iainc]

That doesn't seem right to me. If you change the width of the tyre the roling circumference remains unaltered. However, if you replace your wheels and buy bigger rims, e.g. 17s to 18s then you are changing the rolling circumference and that is when you require a lower profile. I went from 17/215/45 to 18/225/40. Even with the profile change it still threw out the speedo by about 3mph (I compared before and after with GPS); which isn't that much, and to be honest the change was more accurate.

Bear in mind that the 45 part is a percentage of the width, so if you increase the width from 215 to 225 then the 45% is larger (96.75 -> 101.25). Your example changed both the size of rim, width and percentage so it's not easy to see the change required.

[thewelsho]

Bear in mind that the 45 part is a percentage of the width, so if you increase the width from 215 to 225 then the 45% is larger (96.75 -> 101.25). Your example changed both the size of rim, width and percentage so it's not easy to see the change required.

Ahhhh! I see! I take back the ignorant commens previously posted! I thought that the profile was a standard size. See, you learn somethng new every day.

[AlanG]

Ahh... Good old mathematics. Knew something would be learned at school.

Right children pay attention! YOU at the back of the class! QUUIIEETT!!

C= {pie} x D

For a 215/45 x 17" tyre

C = 3.141592654....... x (17x25.4)+((215x(45/100))x2)

C = 3.141592654.... x 625.3mm

C = 1965mm

C = 77.36"

For a 225/45 x 17" tyre

C = 3.141592654..... x (17x25.4)+((225x(45/100))x2)

C = 3.141592654.... x 634.3mm

C = 1993mm

C = 78.46"

To work out road speeds for different tyre sizes, you need the formula:

Road speed = (60 x engine rpm) / (wheel revs/mile x diff ratio x gearbox ratio)

Say you run 215/40 x 17" tyres and you have a P1 gearbox with 0.738 5th gear ratio

You also need to know the revolutions / mile of your tyre circumference, so for 215/40x17" for example the rev/mile of that tyre size is done by the formula:

63,360 / circumference (of tyre)

{1 mile = 63,360" btw}

In the case of 215/40x17" tyres, the circumference is:

74.68"

Your MPH calculation would be:

MPH = (60 x 1000rpm) / (848.41 x 4.444 x 0.738)

MPH = 60000 / 2782.51

MPH = 21.56 in 5th gear per 1000rpm

Think i've got the calcs right. I've a spreadsheet with all the formula in it which makes life quicker and simpler than buggerin' about with calculators.

Edited September 19, 2007 by AlanG

[andy]

C= {pie} x D

[frank c]

Ahh... Good old mathematics. Knew something would be learned at school.

Right children pay attention! YOU at the back of the class! QUUIIEETT!!

C= {pie} x D

For a 215/45 x 17" tyre

C = 3.141592654....... x (17x25.4)+((215x(45/100))x2)

C = 3.141592654.... x 625.3mm

C = 1965mm

C = 77.36"

For a 225/45 x 17" tyre

C = 3.141592654..... x (17x25.4)+((225x(45/100))x2)

C = 3.141592654.... x 634.3mm

C = 1993mm

C = 78.46"

To work out road speeds for different tyre sizes, you need the formula:

Road speed = (60 x engine rpm) / (wheel revs/mile x diff ratio x gearbox ratio)

Say you run 215/40 x 17" tyres and you have a P1 gearbox with 0.738 5th gear ratio

You also need to know the revolutions / mile of your tyre circumference, so for 215/40x17" for example the rev/mile of that tyre size is done by the formula:

63,360 / circumference (of tyre)

{1 mile = 63,360" btw}

In the case of 215/40x17" tyres, the circumference is:

74.68"

Your MPH calculation would be:

MPH = (60 x 1000rpm) / (848.41 x 4.444 x 0.738)

MPH = 60000 / 2782.51

MPH = 21.56 in 5th gear per 1000rpm

Think i've got the calcs right. I've a spreadsheet with all the formula in it which makes life quicker and simpler than buggerin' about with calculators.

A giraffes ar$e matey...........right over ma heid

[AlanG]

lol

Basically smaller diameter, lower gearing, bigger diameter, higher gearing.

{Marks Franks homework down as a fail.... }

Edited September 19, 2007 by AlanG

[RA Dunk]

A giraffes ar$e matey...........right over ma heid

same here, i wish i knew what that ment

but hey it looked good :D

[frank c]

Gotcha

The first explanation looks better though

{Too many distractions at the back of the class , either that or the teacher talks a funny language}

Edited September 19, 2007 by Frank C

[AlanG]

PMSL

i can get the 215/45 s at a great offer price on either toyo tyres or pirelli p zero rosso tyres.

You should be fine with 215/45x17"'s.

[AlanG]

Snapshot of spreadsheet used to calculate mph/1000rpm.

If anyone wants a copy to piss about with tyre/wheel/gearbox options, you can mail me.

Edited September 19, 2007 by AlanG

[RA Dunk]

ohh aye, like i know what that means lol

[AlanG]

Fair enough.

I'll edit the posts and stick to topic.

[RA Dunk]

some people might have had a better clue than me so no need to edit the post m8, im not really technically minded so that kind of stuff goes right over my head lol

[AlanG]

some people might have had a better clue than me so no need to edit the post m8, im not really technically minded so that kind of stuff goes right over my head lol

Oops! Too late!

Looked a bit nerdy after i put it all up, so disnae matter.

Edited September 19, 2007 by AlanG

[frank c]

It's alright I'll leave my explanation there

I would imagine both the 215/40 and the 215/45 would be fine. Not sure about the 225's though.

[AlanG]

Here's a strange one...

Trollin' about from one forum to another jist now 'n i clicked back on this thread 'n it's got the original posts in it again What's that all about? Normally it goes to the "latest" version.

Gie's a minute 'n i'll put the posts back.

[RA Dunk]

you hadnt refreshed yer screen since ya deleted it and moved across to 22b lol it so the original post will still be there untill you refresh

[AlanG]

you hadnt refreshed yer screen since ya deleted it and moved across to 22b lol it so the original post will still be there untill you refresh

PMSL!

I thought if you went from one page to another in the same browser it would automatically have refreshed the page?

I could see that if i had two browsers open but...

Need more PC lessons methinks!

[iainc]

PMSL

You should be fine with 215/45x17"'s.

TBH, I seem to remember that the UK94 I had before was 215 wide...

<suddenly remembered having some pics of it on this laptop>

... 215/40/17's is what I had on it the whole time. Fooks knows if the speedo was accurate or not as I didn't have GPS and was never caught by the police[1]

You could always ask the tyre dealer as they will no doubt know the main differences between them all but I would have thought that 205 wide on a P1 sounds wrong to me[2]

[1] - They got me the first month of owning the 06 STi on a day when I was taking it easy and happened to overtake <shock> on an overtaking lane and was done for 70mph on a 60mph road. :-(

[2] - But I'm wrong often enough that even *I* don't always listen to myself