Road Cycling - Roll-out distances

Does anyone know of a site with a chart with roll-out distances, or an accurate way of calculating them?

Anything will be better than trying to do roll-outs in my loungeroom.

Thankyou :D

I'm guessing that you're interested in the circumference of your wheels? I've measured these for the wheel and tyre combinations on my bikes, but that won't do you much good. Plus, when measuring the "roll-out" distance, it should be done with the rider mounted for greatest accuracy. The simplest way to arrive at a rough calculation of your wheel circumference is to measure the radius (or diameter), double the radius to get diameter then multiply by 3.1414 (pi). The accuracy of this method isn't particulary good. The formula's good, but most of us lack the neccessary equipment to make an error free measurement of our wheel diameter, and whatever that error might be, it's multiplied by 3.1414!

Does anyone know of a site with a chart with roll-out distances, or an accurate way of calculating them?

Anything will be better than trying to do roll-outs in my loungeroom.

Thankyou :D


If your trying to determine wheel size then a roll out is the best method. If you just measure the circumference or radius using a formula it won't take into account the deformation of the wheel (or change in circumfeence) when you sit on the bike.

This is what I do:

- find an area that you can roll the bike (with you on it) about 2-3 metres and that has something for you to balance against, or perhaps a friend can help support you. I use my basement and the wall. If you look along this wall you'll see little dabs of paint over the floor. :-)

- using some nail polish make a small dab of paint on the tire, I usually do this next to the valve so I know roughly where the dab of paint is. (no I don't wear nail polish, but my wife does, don't tell her I use it for this though). Make sure you do this for the correct tire. If you sensor is on the back, use the back tire.

- spin the wheel so the valve is just level with the ground with the valve top facing the rear. So it's just about to spin past the floor.

- roll the bike until the valve (or dab of paint) passes over the ground (or floor) twice.

- measure the distance betwen the paint marks.

- repeat as many times as you need to be confident, take the average of the readings.

Works great for me, and takes into account your weight. OH! Also make sure you have the correct tire pressure in the tire too.

Digger

A good estimate is available at the computer calibration section of Sheldon Brown's web site LINK (http://www.sheldonbrown.com/cyclecomputer_calibration.html) . (Sheldon Brown knows roughly as much about bicycles as the rest of us put together.)

I'm pretty persnickety about it though, and after I've got a good guess, I ride a series of measured distances on state highways (which have survey marks pressed into them) and adjust my computer to match those measurements.

I did what Digger did. Easy, accurate, takes about 30 seconds with a friend.

I'm guessing that you're interested in the circumference of your wheels? I've measured these for the wheel and tyre combinations on my bikes, but that won't do you much good. Plus, when measuring the "roll-out" distance, it should be done with the rider mounted for greatest accuracy. The simplest way to arrive at a rough calculation of your wheel circumference is to measure the radius (or diameter), double the radius to get diameter then multiply by 3.1414 (pi). The accuracy of this method isn't particulary good. The formula's good, but most of us lack the neccessary equipment to make an error free measurement of our wheel diameter, and whatever that error might be, it's multiplied by 3.1414!


pi to four decimal places is 3.1416...you round up from 5 to 6 because of the 9 that follows it. most people just use 3.14 for pi though, and that .0002 won't skew the data all that much anyway, i just like to point things out like that. carry on.

my TI-30X calculator says pi =3.141592654.

what is the purpose of this measuring "roll-out" distance?

Purpose = to set the bike computer so it will accurately measure distance traveled.

hmm....i use maps for that, if i NEED to know. usually i don't care, so i just ride. it's fun, you all should try it some time.

Thanks for the tip. And to think I wasn't having fun until I read your suggestion!

hey no problem!

eh, i'm just foolin' anyway. i sometimes i think people get too wrapped up in how many miles they go, how fast and what their cadence is. if you're racing, then that info can be helpful, but for the casual rider, i don't think it's necessary. it's nice to know all that stuff, i guess, but...eh. i think a computer on my bike would just be one more thing for me to be fooling with instead of paying attention to my surroundings.

hey no problem!

eh, i'm just foolin' anyway. i sometimes i think people get too wrapped up in how many miles they go, how fast and what their cadence is. if you're racing, then that info can be helpful, but for the casual rider, i don't think it's necessary. it's nice to know all that stuff, i guess, but...eh. i think a computer on my bike would just be one more thing for me to be fooling with instead of paying attention to my surroundings.

Amen.

The way I did it was to use a tape measure that I have that is about .5" wide so it's really flexible. Take the wheel off of the bike and just wrap it around the wheel and read the results.

Thank you all.

I'm trying to calculate cadences for any given speed for any given gear ratio without having to get out on the road and get up to 45mph, then try to guess my revs.
http://www.sheldonbrown.com/gears/ I think this will do me, but I'd like something that calculates the distance to more than one decimal point.

I'm arguing with a friend that he needs bigger gears.

The way I did it was to use a tape measure that I have that is about .5" wide so it's really flexible. Take the wheel off of the bike and just wrap it around the wheel and read the results.

The problem with that is when your weight is on the tire, it changes the circumfrence slightly.

hey no problem!

eh, i'm just foolin' anyway. i sometimes i think people get too wrapped up in how many miles they go, how fast and what their cadence is. if you're racing, then that info can be helpful, but for the casual rider, i don't think it's necessary. it's nice to know all that stuff, i guess, but...eh. i think a computer on my bike would just be one more thing for me to be fooling with instead of paying attention to my surroundings.

Guess it depends how and where you like to ride, but I don't care to ride without a computer. On my regular training route, I like knowing my average speed and HR readings. I track miles ridden daily, and roughly time spent above 85% HR, so I can figure weekly and monthly training efforts. Helps me know when to rest and recover.

For club rides, an accurate odometer reading on the bike really helps when trying to follow a route cue sheet. When the next instruction says "turn left at the unmarked road at 22.4 miles", it helps a whole lot to know about where that turn should be.

Every time I change tires I re measure and re calibrate my computer.. some tires say 23c but they are really 22 or even 21 (Conti supersonic)...
So here is what I do to make sure the measurement is accurate.. I use duct tape to tape to the tire a small piece of paper towel soaked with a bit of oil. then I ride in a straight line on the sidewalk in front of my house, and measure the distance between 2 stains.. you can do it with chalk too but oil stains are easier to see.. this method takes into account the compression of the tire etc. etc..

Every time I change tires I re measure and re calibrate my computer.. some tires say 23c but they are really 22 or even 21 (Conti supersonic)...
So here is what I do to make sure the measurement is accurate.. I use duct tape to tape to the tire a small piece of paper towel soaked with a bit of oil. then I ride in a straight line on the sidewalk in front of my house, and measure the distance between 2 stains.. you can do it with chalk too but oil stains are easier to see.. this method takes into account the compression of the tire etc. etc..

I do the same thing at the local velodrome which, for some reason, is an odd 363 metres. This gives you a larger distance over which to test the accuracy. If I veer off the line I simply start again. We have another strange velodrome that is 501 metres!

I'm obsessed with my odometer; I run a second computer for back-up (and as an extra trip meter), and I replace the batteries every new years eve, then reset to zero :)

I find the recommended wheel sizes on the Cateye instructions slightly inaccurate.

I've gotta get a life!

Anyway, Fat Hack's queery was cadence calculation. I've done one with the help of Sheldon Brown's site (in metric):

If you're riding a 700x23 wheel, with 172.5mm cranks, on a 53/12 gear, you produce a 9.3 meter roll-out. So, if you're doing 60kmh (37.3mph) you'll be doing 107.5 rpm. A 53/11 produces a 10.1 meter roll-out.

53/12........(60,000/9.3) /60 = 107.53 rpm
53/11........(60,000/10.1)/60 = 99.00 rpm

This makes me think that an 11 tooth cog is preferable for racing.

I used to measure roll-out everytime I changed tires/wheels. Now I'm too lazy so I just measure the actual width of the tire (not always the same as the advertised width) and use that to calculate the circumference.

circumference = (bead_diameter + 2*tire_width)*pi

Example: 700x23C - bead diameter is 622mm so circumference = (622 + 2*23)*3.1416 = 2099mm
If you were to measure the roll-out for this, you'd probably get a slightly smaller number - maybe 2096mm or 2097mm.

oooo, I found one:
http://www.analyticcycling.com/PowerMeasAnalyGear_Disc.html



Gear Development (aka: Roll-out distance for 1 pedal revolution)

.........39......42.....52......53
11...7.474 8.049 9.965 10.157
12...6.851 7.378 9.135 9.310
13...6.324 6.810 8.432 8.594
14...5.872 6.324 7.830 7.980
15...5.481 5.902 7.308 7.448
16...5.138 5.534 6.851 6.983
17...4.836 5.208 6.448 6.572
18...4.567 4.919 6.090 6.207
19...4.327 4.660 5.769 5.880
20...4.111 4.427 5.481 5.586
21...3.915 4.216 5.220 5.320
22...3.737 4.024 4.983 5.078
23...3.574 3.849 4.766 4.858
24...3.426 3.689 4.567 4.655
25...3.288 3.541 4.385 4.469
26...3.162 3.405 4.216 4.297
27...3.045 3.279 4.060 4.138
28...2.936 3.162 3.915 3.990

The formula's good, but most of us lack the neccessary equipment to make an error free measurement of our wheel diameter, and whatever that error might be, it's multiplied by 3.1414 Or the error could be due to the fact that pi is 3.1416, not 3.1414 ;)

i think a computer on my bike would just be one more thing for me to be fooling with instead of paying attention to my surroundingsThough I understand, for me the miles are vital. It's what keeps me going. If I was "just riding" I don't think I'd get out that much. But when I know my goal for the year is 2000 miles, that keeps me on the bike. On the other hand, I'm only in my 2nd year as a roadie. At some point, I'm sure I'll need goals less since it'll just become a part of life. Then again, knowing that last year I rode the equivalent of going from Dallas to Miami was cool. This year, it'll be Dallas to Columbia! :D (Next year it's 3000 which is all the way to Bolivia!)

http://www.sheldonbrown.com/gears/
HOLY CRAP! Look at that guy's BEARD! :D

The problem with that is when your weight is on the tire, it changes the circumfrence slightly.

True, but how anal do we need to get here. You could also say that the circum. is going to change depending on the air pressure in the tire. It will also change depending on your riding position which will change the weight distribution from front to rear.

Does it really matter?

True, but how anal do we need to get here. You could also say that the circum. is going to change depending on the air pressure in the tire. It will also change depending on your riding position which will change the weight distribution from front to rear.

Does it really matter?


Nope! I did a "roll-out" and found it to be exactly the same reading as the number in the computer's owner manual. The charts will give you a number that's close enough!

Thank you all.

I'm trying to calculate cadences for any given speed for any given gear ratio without having to get out on the road and get up to 45mph, then try to guess my revs.
http://www.sheldonbrown.com/gears/ I think this will do me, but I'd like something that calculates the distance to more than one decimal point.

I'm arguing with a friend that he needs bigger gears.

Why didn't you say so? Here's all you'll ever need in playing with gear ratios and cadences.