Low Profile Tyres?

[T3inthebitout]

guys i wanna know whether or not i will require low profile tyres for the new 17" alloys i am gettin....any help

[Theorist]

yes if going from a smaller size wheel . what size wheel you going from?

[LAA69]

205/45/17 i believe is the recommended size to keep the speedo near standard ....

[T3inthebitout]

yes if going from a smaller size wheel . what size wheel you going from?

Just a standard set of 15" unfortunately...i desperatly need a set...any suggestions on the tyres i may need

[Theorist]

oh ok 15" . is this an E11 carolla?

[Theorist]

this should help . http://www.etyres.co.uk/tyre-size-calculator.htm

[jonnnnnnnnnnnno]

Ha keep the 15" then i wont look so bad!!! jokes

[T3inthebitout]

oh ok 15" . is this an E11 carolla?

Nah its on a T3

[cfc1]

Ok.. 17" on the Compressors is 215/45x17.

[T3inthebitout]

Ok.. 17" on the Compressors is 215/45x17.

shes an 06 mate

[-T- Sport]

What's the plate got to do with it? :P

I think he's just suggesting what the best tyre size would be as that's what they use on the compressor.

Btw, When it comes to Tyres.. cfc1 is the chap in the know. ;)

[cfc1]

My compressor is a 56 plate, standard fitment is 215/45x17 Pirelli P Zero Nero.

As for the reasoning behind stating the year.. I originally asked what year his Corolla was, but after posting I noticed he made a new post stating that the car was a T3.. thus telling me whatI needed to know, maybe he quoted me before noticing I had edited my post.

Having said that, The T3 standard size is 195/60x15, so.....

195/60x15

Rolling Radius : 307.5mm

circumference : 1932.08mm

Now the options...

205/50x16

Rolling Radius : 305.7mm

Circumference : 1920.77mm

Difference in Circumferance = -11.31mm or -0.59%

So when your speedo reads 70mph, you're actually travelling at 69.59mph

As you can see these are slightly lower and it drops the speedo very very slightly.

215/40x17

Rolling Radius : 301.9mm

Circumference : 1896.89mm

Difference in Circumferance = -35.19mm or -1.82%

So when your speedo reads 70mph, you're actually travelling at 68.73mph

These are lower again and drop the speedo by a little more.

215/45x17

Rolling Radius : 312.65mm

Circumference : 1964.44mm

Difference in Circumferance = 32.36mm or 1.67%

So when your speedo reads 70mph, you're actually travelling at 71.17mph

This time the new tyre is slightly higher than the standard 195/60x15 and the speedo will read slightly higher than your actual speed.

215/35x18

Rolling Radius : 303.85mm

Circumference : 1909.14mm

Difference in Circumferance = -22.94mm or -1.19%

So when your speedo reads 70mph, you're actually travelling at 69.17mph

With 18" we return to a slightly lower tyre again and once more the speedo will read slightly less than your actual speed.

205/45x17

Rolling Radius : 308.15mm

Circumference : 1936.16mm

Difference in Circumferance = 4.08mm or 0.21%

So when your speedo reads 70mph, you're actually travelling at 70.15mph

As stated above, closest match to keep the speedo reading as close to stock as possible with only 0.21% of a difference in circumference

I would probably fit the 215/40x17, this being slightly lower would make it easier to lower the car by around 30mm in the future without any serious issues with rubbing should I deceide to do so (this obviously depends on wheel width and offset) also the extra width (over the 205/45x17) makes the car ever so slightly more stable, although under normal driving conditions this wouldn't really be noticeable.

Hope that helps ;)

Edited December 1, 2009 by cfc1
To add the option of 205/45x17

[aaronjp1990]

that info should be made a sticky.

[Sagitar]

My compressor is a 56 plate, standard fitment is 215/45x17 Pirelli P Zero Nero.

As for the reasoning behind stating the year.. I originally asked what year his Corolla was, but after posting I noticed he made a new post stating that the car was a T3.. thus telling me whatI needed to know, maybe he quoted me before noticing I had edited my post.

Having said that, The T3 standard size is 195/60x15, so.....

195/60x15

Rolling Radius : 307.5mm

circumference : 1932.08mm

Now the options...

205/50x16

Rolling Radius : 305.7mm

Circumference : 1920.77mm

Difference in Circumferance = -11.31mm or -0.59%

So when your speedo reads 70mph, you're actually travelling at 69.59mph

As you can see these are slightly lower and it drops the speedo very very slightly.

215/40x17

Rolling Radius : 301.9mm

Circumference : 1896.89mm

Difference in Circumferance = -35.19mm or -1.82%

So when your speedo reads 70mph, you're actually travelling at 68.73mph

These are lower again and drop the speedo by a little more.

215/45x17

Rolling Radius : 312.65mm

Circumference : 1964.44mm

Difference in Circumferance = 32.36mm or 1.67%

So when your speedo reads 70mph, you're actually travelling at 71.17mph

This time the new tyre is slightly higher than the standard 195/60x15 and the speedo will read slightly higher than your actual speed.

215/35x18

Rolling Radius : 303.85mm

Circumference : 1909.14mm

Difference in Circumferance = -22.94mm or -1.19%

So when your speedo reads 70mph, you're actually travelling at 69.17mph

With 18" we return to a slightly lower tyre again and once more the speedo will read slightly less than your actual speed.

205/45x17

Rolling Radius : 308.15mm

Circumference : 1936.16mm

Difference in Circumferance = 4.08mm or 0.21%

So when your speedo reads 70mph, you're actually travelling at 70.15mph

As stated above, closest match to keep the speedo reading as close to stock as possible with only 0.21% of a difference in circumference

I would probably fit the 215/40x17, this being slightly lower would make it easier to lower the car by around 30mm in the future without any serious issues with rubbing should I deceide to do so (this obviously depends on wheel width and offset) also the extra width (over the 205/45x17) makes the car ever so slightly more stable, although under normal driving conditions this wouldn't really be noticeable.

Hope that helps ;)

I don't have any argument with the figures as such, nor with the general conclusion that is drawn. I haven't actually checked the calculations, but all things being equal they should be right. However, they do imply a level of precision that may not be justified. Every dimension has a tolerance and a tyre in use is not a static object. In use, several factors modify its idealised rolling radius and circumference.

Wheel rim conformation, inflation pressure and temperature, tyre carcass construction, tyre wear, road surface roughness and vehicle speed, manouevering patterns - all contribute to changing the actual rolling radius away from the idealised rolling radius by larger percentages than are implicit in the tyre size changes described. This is one of the reasons why speedometer readings have such a large tolerance on them and why it is always stipulated in such a way as to give a reading higher than the speed that is actually being achieved.

[cfc1]

I would think that the data given for circumference etc will be for each tyre on it's own, not fitted to a car or under any stress what so ever.

Every dimension has a tolerance and a tyre in use is not a static object. In use, several factors modify its idealised rolling radius and circumference.

Of course it does, after all we do not drive in laboratory conditions, we drive in the real world, however if each tyre size was tested in the real world under the exact same circumstances (wheel size, pressure, road surface etc etc etc) then perhaps the differences between each different size would be equal (or damn close to it) to the differences between each tyre tested in a lab.

There are far to many variables in tyres for every single piece of info to be factually 100% correct for every size of tyre on every make of car used in the many different situations we my find ourselves in, as such the info given must only be used as a guide... a guide that is as accurate as can possibly be given within reason.