tire question

the best way to get it accurate is to to an 'on the bike' roll-out on some sort of track that has the distance marked, and the longer the better. Then, when you get yours correct, you can tell your buddy that his is wrong :p

531Aussie said:

the best way to get it accurate is to to an 'on the bike' roll-out on some sort of track that has the distance marked, and the longer the better. Then, when you get yours correct, you can tell your buddy that his is wrong :p

Most computers suggest 2100mm. The roll out method is more accurate. make sure the tyre pressure is spot on and you sit in your normal riding position. I use cardboard on the hallway floor. 😉

^^ the hallway??? I do the whole 1km on the Carnegie Velodrome 🙂

Try staying on the white line for a whole km!!!! :p

Its a long hallway, we used to do 10m air rifle/pistol shooting in the hallway. 😄

[censored]!! :p

Yes, actually there is a standard circumference. It's 2 times the radius times pi.

Doing a roll out measurement, with you on the bike, is the most accurate way to go. The farther the distince over which you do the roll out, the lesser the error will be.

If you can't manage the roll out with your weight on the bike, you can do it with the bike unweighted. Then you subtract 4mm for every revolution of the tires. It's closer to correct than the "standard" values.

All I do is, line up the front tire valve stem vertically with the floor, mark this point, then roll forward one revolution until the valve stem is vertical again, mark this point and then measure the distance between the two points. Then I just input the reading in mm into the computer.

kleng said:

All I do is, line up the front tire valve stem vertically with the floor, mark this point, then roll forward one revolution until the valve stem is vertical again, mark this point and then measure the distance between the two points. Then I just input the reading in mm into the computer.

this is why people think they're doing 47kph when they're only doing 45 🙂

I'm just havin a crack at ya, but I reckon it's not accurate enough.
I've tried this way, then gone to the velodrome and found that my odo doesn't match with the 1000m mark when doing an 'on the bike' roll-out

531Aussie said:

I do the whole 1km on the Carnegie Velodrome

Being somewhat short on velodromes around here I've used a 100 m runners' track. Made quite a difference to the indoors roll-out and worked very well to calibrate two bikes against each other.

buy a gps comp like the edge 305

gawnfishin said:

Is there a standard circumference for a 23X700 tire? I just put on the new Continental Grand Prix 4000s tires. If there is not how do I find out the circumference? The reason I am asking is because one of my riding buddies always comes up with a different distance than I when we ride. The difference is about .25 mile every 20 miles. Is that normal or does one of us possibly have the wrong circumference entered in the computer?

The circumference VARIES from tire brand to tire brand for a specified size.

My observation is that a 700x23 Continental tire has a larger circumference than a Michelin 700x25 tire ... at least, that was the case for the two particular tire brands/models & sizes at the time.

If you've changed tire brands, you'll probably need to enter new data in your computer.

Thanks loads guys😠 . Now I'm going to have to take half a day and go find someplace that I can do a "proper rollout" so that I don't have erronious information showing up on my comp. 😄

Just messin' with you all. Thanks for the good info.🙂

531Aussie said:

this is why people think they're doing 47kph when they're only doing 45 🙂

I'm just havin a crack at ya, but I reckon it's not accurate enough.
I've tried this way, then gone to the velodrome and found that my odo doesn't match with the 1000m mark when doing an 'on the bike' roll-out

Hey!!! What happened to Aussie solidarity and the ANZAC spirit,
I thought we're supposed to 'flame' the other countries on the forum.😄

kleng said:

Hey!!! What happened to Aussie solidarity and the ANZAC spirit,
I thought we're supposed to 'flame' the other countries on the forum.😄

oops!! You're right, we are supposed to flame only O.S.ers.🙂

I didn't notice your "locale"