Fat bike vs Road bike (bad) science

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  • Fat bike vs Road bike (bad) science
  • Premier Icon cynic-al
    Subscriber

    I rode my hill rep loop this am on my On One fat bike. I’ve previously taken my road bike up it.

    Road bike (18lb, 23/25mm tyres @ 85psi) 3m 15s; fat bike (35lb, 3.8″ tyres super hard at 20psi) 4m 15s – 31% slower.

    My weight is ~80kg, meaning the fat bike and I are around 9% heavier than the road combo, and so the fat bike rolling resistance is 22% greater* – interesting!

    *the bad science bit: Assuming the same power. I’ve not got my powercal yet, so I can’t verify this, and I’ve not been riding so much since I did that time a few weeks ago, but my HR was in the same area for the climb, and I’ll re-do it once I have the meter.

    ton
    Member

    is this all you have to do with your time?
    no wonder bike shops get a bad name, with lazy layabout staff like you doing sod all work……….. 🙄

    Premier Icon cynic-al
    Subscriber

    Love how you assume I was skiving, says something about you!

    It was before work you moron.

    ton
    Member

    bit harsh that Al………. 😆

    dpfr
    Member

    I suspect the difference in rolling resistance is probably greater. At the higher speed of the road bike you’ll be expending more energy to overcome air resistance, and that’s not lineraly related to speed.

    taxi25
    Member

    Not sure if the 22% is only rolling resistance. I’d bet the road bike transfers power much better as well.

    Powercal ain’t going to tell you anything more than your HR monitor.

    kayla1
    Member

    Do you have fun on both bikes?

    edit- I meant that if the fat bike is out of its element it may not be as much fun as the road bike.

    edit again- although that might be part of the enjoyment.

    You’ll be more aero on the road bike…probably counts for a fair bit.

    Premier Icon wwaswas
    Subscriber

    road bike riding position may allow more efficient pedalling.

    Premier Icon rickmeister
    Subscriber

    Try another lap of a similar distance with both bikes, but this time take them off road and post your times…

    Premier Icon cookeaa
    Subscriber

    Seems like a moderate, reasonable, scientific Approach IMO.

    You’ve conducted the same test on two bikes, using the same rider and treating time taken as your measure, you’ve calculated the differences in mass, I’d say Aero is negligible for a climb (discuss) and you say you’ve maintained a similar HR for both (as good a measure of the work done as possible)…

    I’d buy that 22% figure, applied to climbing, accepting an appropriate margin for error…

    I supposed you could try to verify it by conducting a similar set of tests rolling along on a flat level surface, and coasting down, from a standing start. Both would probably require calculating the difference in frontal area to reconcile the aero differences…

    Premier Icon igm
    Subscriber

    Better riding position for power / efficiency on one of the bikes?

    Huge Wallace-like grin on the fat bike causing aero-drag?

    Perhaps try putting the fat bike wheels on the road bike to compensate for the different riding position and see if that affects rolling resistance?

    Let us know how you get on with that last one. And if any spoons were harmed.

    Perhaps try putting the fat bike wheels on the road bike…

    Al, has your road bike got clearance for 3″ tyres?

    I’d bet the road bike transfers power much better as well.

    If the bike doesn’t transfer the power, where is the power going??

    TooTall
    Member

    bit harsh that Al.

    Classic ton. Troll in hard then back away with ‘I didn’t mean that 😉 ‘ when someone calls you on it.

    fisha
    Member

    When you say rolling resistance, are you meaning frictional tyre to Tarmac resistance, or inertial resistance of trying to get a heavier tyre rolling going uphill.
    U
    I really doubt that the first would make 22% difference, where as the latter would.

    Edric 64
    Member

    Only 85 psi in road tyres ? they must be nearly on the rim !

    umop3pisdn
    Member

    Sounds about right. Most people run far too high pressures in road tyres. Or are you a fat bastard?

    fisha
    Member

    I’m a fat bastard … 90 to 100psi

    Premier Icon cynic-al
    Subscriber

    ton – Member

    bit harsh that Al……….

    You clown.

    taxi25 – Member

    Not sure if the 22% is only rolling resistance. I’d bet the road bike transfers power much better as well.

    Despite what mfrs say, I doubt it. It’s a 2.5kg alu fat frame vs a 1kg carbon.

    Speed is such that aero is irrelevant IMO (10mph av)

    fisha – Member

    When you say rolling resistance, are you meaning frictional tyre to Tarmac resistance, or inertial resistance of trying to get a heavier tyre rolling going uphill.

    I mean the energy lost to tyre deformation at the contact patch with the road. As the speed is relatively constant the losses due to your latter affect are IMO small, though greater with the fat tyre.

    I’m surprised this could be 22% but of course it would be way smaller given the errors involved.

    ahwiles
    Member

    i’m surprised it’s only 22%…

    nice test, you’ve done the best you can with the tools at your diposal, and identified the uncertainties associated with them = good science!

    Premier Icon andytherocketeer
    Subscriber

    now go and repeat the test on a beach, to cross-calibrate the results

    Premier Icon boxelder
    Subscriber

    You clown.

    Takes all sorts

    [video]http://www.youtube.com/watch?v=Fzu-YFHqfMc[/video]

    ndthornton
    Member

    Add 17lb of ballast to the road bike
    time the loop again
    See if you are 9% slower

    Shaun20
    Member

    If you ride a fat bike I doubt you are that worried about power transfer.

    Premier Icon winstonsmith
    Subscriber

    I thought you had a girlfriend now al?

    Premier Icon Paceman
    Subscriber

    Find a nice techy singletrack downhill and compare the two bikes on that, I suspect you’d find the fat bike was at least 22% faster (if you lived to tell the tale on the road bike 😉 ).

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