Techie bike question

I've got a turbo and I'm trying to calibrate it so that I can compare my workouts.

I've been told that you can calibrate the turbo by:

1. pumping the rear tyre to 100psi

2. riding at 25 mph at usual cadence (100) then stopping and measuring time taken for rear wheel to stop spinning

3. adjusting the resistance (by either the resistance setting or by adjusting the roller)so that the time taken for wheel to stop spinning is 10 seconds.

On my usual (uncalibrated) setting the wheel stopped turning after only about 3-4 seconds. I found that to keep the wheel turning for 10 seconds required the resistance to be very very light so much so that I was having to ease off to bring the speed to 25mph. This clearly can't be right. Has anybody tried calibrating their turbo in this way?

I'm tempted to get a table of gears and speed and adjust the resistance based on say 52/17 - although I've no idea if this will give me the right readings in other gears. Anyone any thoughts?


  • Its not so important how long it takes the wheel to stop after the spin- so long as you keep it the same kind of time for your workouts. And thats only really necessary if you want to compare between sessions.

    Turbo is not the same as the road, so it won't be the same.

    Clearly if you're having to ease up to get down to 25mph, then its not hard enough though, so add some resistance until it feels pretty sensible. Then keep it like that.

    A cadence of 100 is pretty rapid.
  • I think whoever told you that was pulling you leg.

  • Ey Up Punchie ! Where you been then ?
  • I do want to compare between some sessions. I agree that as long as the run down time is the set up will be the same. I suppose what I was trying to do is recreate as closely as possible the resistance you get on a calm day outside.

  • That's OK then - but I wouldn't try and use the turbo the same as you would outside - so use it for short sessions of up to an hour or so steady, or interval sessions to really stretch you.
  • You measure turbo setting in litres per minute. If you have to wade out the room after an hour then it's probably about right.
  • how about "megavolks"?

    the number of brain cells (in millions) that voluntarily kill themselves per second rather than endure any more of the mind numbing boredom
  • or, if your calculator has fewer than 10 digits, gigavolks
  • i have an abacus
  • megavolks - very funny. i've discovered the simpsons helps with turbo sessions.
  • Donuts as refuelling ? You could loop them round the tribars ?

    I bought some Krispy Kreme doughnuts in London last week - they're nice, but nothing special ?
  • Thanks

    Re the other tips: I've never ridden for more than 70 minutes on the turbo. Most are 30-60 min sessions and pretty hard. I find that boredom is not really the main issue above 85%HRR.

    Also just in case you thought I was a total anorak, I do 100+pw outside.

    I know there is an army of protestors waiting to leap into action on this forum if anybody mentions those two dirty words: turbo & treadmill.

  • JRM - I assume you have a bike computer for the turbo? If so, that will give you the wheel speed directly - never mind the table of gears & cadences.

    I've heard about the spin-down method of calibrating, and from respectable sources too (er, well, respectable *forum* sources), though I can't remember the details. But the cadence you ride with and the gear you do it in have no relevance whatsoever once your wheel is spinning freely.

    How about putting on your HRM and trying maybe 20 minutes steady on the road (on the flat, on a still day), then trying the same nominal speed on the turbo - if your heart rate isn't the same, the resistance isn't right.
  • Not sure I follow you on the first part Swerve.

    Yes I have computer.

    Altering the resistance will have a direct bearing on what speed I can do for a given effort. If the resistance is light I could hold 25mph+ without breaking sweat. If the resistance is high I might struggle to hold 18mph in the same gear and cadence.

    The gear ratio speed tables work outside really well (on a calm day), for example I can ride at 24.0 mph in 52/17 at a 100 cadence which is what the tables say. My idea was to adjust the resistance on the turbo so that I reproduce these figures.

    The HR method sounds like a sensible idea.
  • >>You measure turbo setting in litres per minute. If you have to wade out the room after an hour then it's probably about right.

    LOL :-)

    Top of my Santa list is one of those towelling thingies that catch the sweat :-)
  • JRM - what I mean is that you have to adjust the resistance to give the right amount of retardation at (say) 26mph. The turbo and the wheel neither know nor care what gear ratio you're using. If you calibrate it to give the proper amount of effort at 26mph at 100 cadence in 52/17, you will get exactly the same result as if you'd calibrated it to give the right effort at 26mph at 80 cadence in 52/12 (or whatever the appropriate raio/cadence is). In a nutshell, the resistance needed only depends on the speed of the wheel (and in an idealised turbo, not even on that).

    By the way, speed = gear ratio x cadence x 2 x Pi x wheel radius. Not dependent on effort, wind, slope or anything else.
  • Swerve

    I think we are in agreement but as it is a fairly complicated point I've set out how I understand it and what I am trying to do.

    If you cycle in a particular gear at a particular cadence then the wheel will turn at a given speed which will be equal to the speed the bike moves forward. This is true whether you are cycling indoors or outdoors providing you are not going downhill.

    Wind resistance and cycling uphill won't make the speed any less if you can maintain the cadence at the given gear. The only effect will be the difference in effort required to maintaining the speed. Similarly on the turbo, increasing the resistance will not affect the speed if you can maintain the gear and cadence.

    So what I am trying to do on my turbo is (as a starting point) match the effort required to turn a gear at a particular cadence with that required to turn the same gear at the same cadence on a flat road outside without any wind resistance (this is my reason for using the gear/speed tables). Then maybe I can tweak the resistance a little bit higher to factor in the wind resistance on a still day.
  • You can't do that because drag and all that will increase with speed on the road, but will not increase with speed on the turbo. Because of that all you can really do is try and get it more or less the same for a given speed...I think.
  • Why not make the effort harder...then you'll be pleasantly suprised when back on the road.
  • I wouldn't even try to compare the turbo with the road, just keep it as a time/heart rate tool. Thats what its best for.
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