Tire Diameter And Circumference

[TrailerRider]

ok so I have 23.5x8.00-11 and come up with a circumference of 3708 from a post I read somewhere but when I use the calculator on this page I get 35.022. I am lost. Which is correct? I tested my speed and it seems pretty close to what I would think.. Any help would be most appericiated!

EDIT: My wife figured out the need figures. It is dead on now.
Info: X = multiplication

X inches WH (Wheel Height) by 25.4 (25.4 mm = 1 inch) X 3.14 (pi)
23.5x25.4=596.9 X 3.14(pi)=1874.266 (But .266 is ignored) so your final answer is.................. 1874

So if you have a stock 1984 200x with a front wheel of 23.5 inches and you have a sigma bc506 Bike computer your answer is 1874. Wife likes the bouce emoicon and sence she figured it out...

[Thorpe]

Are you including the tire tread depth in your calculation?

[Coaltrain]

you need to use the "loaded radius" in your calculation. Unless you are running crazy high pressure in your tires there will be some inherint "squat" or "sidewall flex" to them. measure from the center of the axle to the ground.

[cr480r]

you need to use the "loaded radius" in your calculation. Unless you are running crazy high pressure in your tires there will be some inherint "squat" or "sidewall flex" to them. measure from the center of the axle to the ground.

i disagree... rather squated or flexed the rollout remains the same. rollout varies with air presure so use a string or soft tape to measure the true rollout(circumference)

[TrailerRider]

ok so if you just use straight math to convert it which one is right? NOT worrying about the tire pressure. Just straight size is this and (circumference) = this. I am not worried about it being exact but close would be good.

[cr480r]

ok so I have 23.5x8.00-11 and come up with a circumference of 3708 from a post I read somewhere but when I use the calculator on this page I get 35.022. I am lost. Which is correct? I tested my speed and it seems pretty close to what I would think.. Any help would be most appericiated!

tires seldom measure as advertised. and true measurements vary trememdously from brand to brand in a given size. if the tire had a true diameter of 23.5 the circumference would be 73.79.. diameter x pi= circumference

[Coaltrain]

i disagree... rather squated or flexed the rollout remains the same. rollout varies with air presure so use a string or soft tape to measure the true rollout(circumference)

Good point, never thought about or tested for that.

[bigred44]

Don't forget that tires expand during acceleration. This can throw your calculations off too.

[TrailerRider]

Dam, so many variables. How the hell are you suppose to ever know your exact speed??? lol I am going to drive down the road with my wife behind me and I will compare her speed with mine and if need be I will recalculate after. I mainly want the speed and trip to work as acurate as possible. I ride trails and like to know how far we went so I can map it correctly and for fishing spots I find too

[bigred44]

The most accurate reading you will be able to get is from an up to date radar gun. A GPS should be really close also. I have been told that even automobiles spedo's are off a couple mph to keep you from speeding so that might not even be as accurate of a reading as you're trying to acheive. In my truck my spedo says im doing 2-3 mph slower than what the GPS says.

[TrailerRider]

Interesting info. My little digital speedometer thing uses magnets so I would guess it has to be pretty close being that it is mounted to the front wheel. Again pretty close as the front wheel bounces off the ground on trails. Hey look there is another variable. If the wheel comes off the ground that would change it up also..lol.

[TrailerRider]

...See 1st post for final equation + answer...