Tyre radius
Please note
Whilst the above is mathermatically correct - it is not entirely accurate when a motor vehicle tire is being discussed.
Tire pressure, vehicle weight & rpm can affect the "effective radius" - I'm sure you've seen the way a tire "balloons" at the bottom when the weight of the vehicle is on it, and you know that the greater the load of the vehicle, or the lower the pressure in the tire, the more it will balloon - what many people don't realize is that as the tire spins it expands due to the centrifugal force - on large soft tires, this can be a significant change in radius.
Good point
Yeah I wasn't too sure about how the mathematics would relate to the real world (hence the tie down strap measurement).
I was assuming that Fielies was talking about the spare tyre... I guess pressure would make slight differences, but as long as you take the measurements at the pressure that it will be at most of the time then it should be ok. There's probably a bit of guestimation involved with all of this stuff, but real world measurements will be a lot closer than anything you get from online calculators etc.
Wrong idea about radius
Guys, thanks for the feedback but im thinking outside the box. In RSA we dont get a huge variety of off road tyres so im improvising abit. As you get the snow chain in country's where its required, im busy looking at something similar (not chains) but for mud. Then you have road tyres (cheaper) for normal driving and fit the "thing" on and instant mud machine.....
"Vehicle designers should
"Vehicle designers should bear in mind the maximum values for tyre outer diameter and width when planning the wheel space of a vehicle, if all standard approved tyres are to fit without any restrictions"
is what it says in the Conti handbook
http://www.conti.nl/wp-content/uploads/2014/10/Technical-Databook-car-4x...
as mentioned in http://www.pajerio.com/forum/tyre-data-calulator-rolling-radius-letterin... .
Easy way to measure circumference (rolling)
Radius is the measurement from the centre of the wheel to the outer edge of the tyre. The Mitsubishi logo in the centrecap comes to a point right in the center of the wheel. Put a tape measure on it and it should be easy to find the radius. Diameter is the distance across the whole wheel, going through this centre point. Double the radius and there you go. Circumference is the measurement around the tyre - how far it travels in one revolution. I'd say the best way to find this would be to use a strap or tie-down and run it all the way around the tyre and then mark it and take a measurement from that. Or you could multiply the diameter by Pi. Hope that helps.
Chalk mark your tyre and the road surface, roll your car forward one revolution of the tyre and mark the road again, then using a tape measure, measure between the two lines on the road. Bingo....rolling circumference.
Fab.
Syndicate
Circle geometry
Radius is the measurement from the centre of the wheel to the outer edge of the tyre. The Mitsubishi logo in the centrecap comes to a point right in the center of the wheel. Put a tape measure on it and it should be easy to find the radius.
Diameter is the distance across the whole wheel, going through this centre point. Double the radius and there you go.
Circumference is the measurement around the tyre - how far it travels in one revolution. I'd say the best way to find this would be to use a strap or tie-down and run it all the way around the tyre and then mark it and take a measurement from that. Or you could multiply the diameter by Pi.
Hope that helps.
Size is not important; it's how you use it that matters!