Speed Variation With 17'' Rims????

[DoAwEe]

Hi all,

 

 

does anyone know of a link or have some information of the speedo variation from actual speed to the speed shown on the speedometre when upgrading your rim size?

 

i currently have 17'' rims on my 91 corolla and would like to know approximately how much the speedo is out by?

 

i think i speak for us all when i say, i do not want to be done by a speed camera.

 

any help would be great!

 

thanks in advance

[styler]

its not the inch size of the rim, doesnt count at all.

 

it the rolling diameter of the tyre which affects the speedo.

 

try kumho tyres website for a calculator that compares the rolling diameter

to your old one.

[RinconRolla98]

Here you are this link is a Tire Calculator...You put in what your car comes stock and it will tell you what tire to use for your 17....

 

 

CLICK>>>> http://www.miata.net/garage/tirecalc.html :lolcry:

[Hiro Protagonist]

Quick calculation

 

If you want to know the difference in speed as a percentage (which is what it will be, not a constant number), you use the ratio of the old rolling diameter to the new diameter

 

D = rim diameter (in inches) + 2 * (tyre width in mm * sidewall profile (in percent) / 100)

 

So if you have 17" rims with 205/40 tyres, you'll have a D of 596.8mm

 

Chances are your original wheel/tyre combo was something like 175/65 on 14" rims, or 165/75 on 13" rims

 

In that case you'd have an old D of 583.1mm for 14", or 577.7mm for 13"

 

Thus, your speed ratio is then 102.35% if you originally had 14s, or 103.3% for 13s

So it's around a 2 to 3% increase in speed, thus your speedometer will be reading low by 2 to 3% (which equals 102.35 or 103.3km/h at an indicated 100km/h)

[Beejae82]

Nice reply Hiro, simply and to the point, I gaurantee that those 2-3% would actually bring the actual speed at 100km/h to 100, because most cars are only doing around 95 at 100.

[love ke70]

http://www.carbibles.com/tyre_bible.html

 

about half way down.

 

or read the whole thing, its a good read :lolcry:

[DoAwEe]

Quick calculation

 

If you want to know the difference in speed as a percentage (which is what it will be, not a constant number), you use the ratio of the old rolling diameter to the new diameter

 

D = rim diameter (in inches) + 2 * (tyre width in mm * sidewall profile (in percent) / 100)

 

So if you have 17" rims with 205/40 tyres, you'll have a D of 596.8mm

 

Chances are your original wheel/tyre combo was something like 175/65 on 14" rims, or 165/75 on 13" rims

 

In that case you'd have an old D of 583.1mm for 14", or 577.7mm for 13"

 

Thus, your speed ratio is then 102.35% if you originally had 14s, or 103.3% for 13s

So it's around a 2 to 3% increase in speed, thus your speedometer will be reading low by 2 to 3% (which equals 102.35 or 103.3km/h at an indicated 100km/h)

 

 

your a legend buddy!

[styler]

just remember that the factory speedo buffer is there for wear and reading compensation,

its a bad idea to make it exact as it leaves no room for any slight error unfortunately.