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Larger tyres and speedo differences
Posted: Tue Oct 28, 2008 10:09 am
by Wozza244
There is prob a thread on here about this but i cant find it, does anyone have a table or formula of how much your speedo goes out per inch bigger your tyres are, for example i hav 35's and 37's but the speedo was right when it had 31's on it if ya get wat i mean.
Cheers
Posted: Tue Oct 28, 2008 11:02 am
by hilux79
Have emailed you one.
Don't know how to post it up here as it is a Excel program
Posted: Tue Oct 28, 2008 12:41 pm
by ISUZUROVER
It is quite simple.
Just work out the circumference of your existing tyre: Diameter x PI So for a 31" tyre it would be 31*3.14 = 97.4 (33" = 103.7 and 35" = 110).
work out the % increase. e.g. 31" to 33" = (103.7 - 97.4) / 97.4 *100 = 6.5%
31-35 is 13%
So if your speedo is 100% accurate with 31's, you would be doing 113 km/h on 35's when your speeds is on 100.
Posted: Tue Oct 28, 2008 2:58 pm
by dklyne454
That's all good........ as long as your tire is the size that is indicated. there is a lot of variance in stated size, and actual size.
Best bet,
Wrap a tape around your tyre to get the circumfrence and a more accurate measure.
as isuzurover said.
Circ / pi = diameter.
2760mm / 3.14 = 878.98 (mm x 0.39 = inches eg. 878.98 x .39 = 34.28 inches)
Now work out your difference between the 2 tires
or
borrow a GPS and get an accurate reading of what your new tires are at.
Posted: Tue Oct 28, 2008 6:55 pm
by Tomo_89
Get a mate who has standard tyres and an accurate speedo and have him drive at 100km/h and just follow him and see what your speedo reads.. to get a rough idea just how much bigger your tires are. say 10% and add 10% to your speed and thats what you will be doing. ie 100 = 110
hope this helps
Tomo
Posted: Tue Oct 28, 2008 7:37 pm
by frp88
when I had my 29' and went to 33 it has gone up 10km/h spot on.
Posted: Tue Oct 28, 2008 8:00 pm
by love ke70
10kph at 50?
or 10 kph at 100?
percentages work so much better than a kph difference
id go off what the tyre says it is, theyre gonna be a little smaller than they state normally, so then u drive just under the limits.
keeps you safe
Posted: Tue Oct 28, 2008 8:00 pm
by kruzen84
http://www.miata.net/garage/tirecalc.html
this should help ... as a guide only i would think.
Posted: Wed Oct 29, 2008 7:04 am
by frp88
love ke70 wrote:10kph at 50?
or 10 kph at 100?
percentages work so much better than a kph difference
id go off what the tyre says it is, theyre gonna be a little smaller than they state normally, so then u drive just under the limits.
keeps you safe
the diffrence is constance it is 10 kph
Posted: Wed Oct 29, 2008 8:44 am
by Wooders
frp88 wrote:love ke70 wrote:10kph at 50?
or 10 kph at 100?
percentages work so much better than a kph difference
id go off what the tyre says it is, theyre gonna be a little smaller than they state normally, so then u drive just under the limits.
keeps you safe
the diffrence is constance it is 10 kph
So when you are parked the Jeep is still doing 10km/h
Percentage is the right way to measure it.
Posted: Wed Oct 29, 2008 8:48 am
by blackmav
Posted: Wed Oct 29, 2008 11:07 am
by ISUZUROVER
Wooders wrote:frp88 wrote:love ke70 wrote:10kph at 50?
or 10 kph at 100?
percentages work so much better than a kph difference
id go off what the tyre says it is, theyre gonna be a little smaller than they state normally, so then u drive just under the limits.
keeps you safe
the diffrence is constance it is 10 kph
So when you are parked the Jeep is still doing 10km/h
Percentage is the right way to measure it.
Indeed - a constant 10kph difference is unpossible. I call BS.