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Gravel vs road gearing… less force to pedal?

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  • March 14, 2018 at 5:55 pm #28252
    kvert

    Completely unscientific question…

    I have a 42 front 10-42 rear setup on my gravel bike… for the last couple years I’m trying to convince myself to pull the trigger on a road bike with 52/36 front 11-30 rear setup.

    For a recreational and never will be competitive rider, is there any reason to let this stupid thought win out?

    It would certainly give me more top-end but would the gearing be any easier/more efficient to pedal? I have absolutely no mathematic principles to apply to it but I just feel like having more teeth up front (52 vs 42) would be more efficient since that force is pretty direct compared to having less in the back (11 vs 10) which takes more indirect force to spin.

    To answer the obvious–no I will not change my gravel bike gearing and no I won’t want to sell it to switch over–I’d want to keep both bikes. It actually came stock with a 50/34 11/36 setup but there’s something in my head that wanted to stick with a simple single ring setup.

    There’s also something in my head that really wants to go with a di2 setup and is trying to win over the other half of my brain that reasonably doesn’t want to drop 4 grand to get me there to do essentially the same type of riding anyway (I primarily use my gravel bike as a road bike).

    Thoughts?

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  • March 15, 2018 at 1:10 pm #914511
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    Daveyraveygravey

    My road bike has 52/36 and 11

    My road bike has 52/36 and 11-32, I use all the gears.  If I lived in the Alps I would be tempted to go proper compact at the front but other wise I think you want a big chainset.

    I am old school though, until 3 years ago I rode a 53/39 with 12-28.  I could get up the Sussex hills with that, but I would be painfully slow and out of the saddle to do it.  My friends on compacts would sit and spin and ease away from me.

     

    March 15, 2018 at 12:18 pm #914509
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    Canyon48

    Short answer, bigger gear up

    Short answer, bigger gear up front and smaller gear out back is more mathematically efficient.

    Drivetrain efficiency improves as mechanical advantage increases. When you are using the 42 front ring with the 42 cassette, you have no mechanical advantage, therefore, the drivetrain loses are significant.

    If you could have a gearing with infinite mechanical advantage (i.e. infinitely large front gear) it will be 100% efficient.

    Obviously, you can’t have an infinitely large gear ratio.

    Chain line is important too, the straighter the chain line, the lower the drivetrain losses. With a 42 tooth, you’ll spend more time using the small cogs on the cassette, so the chain line will be better.

    By far the most important thing is if the range of gears is suited to your type of riding. You could have the most efficient drivetrain, but if the gear range is wrong, you won’t be able to use the gears efficiently.

    Your gear choice should be influenced by the speeds you ride at, hence why the gravel bike has lower gearing. My road bike, Canyon Ultimate, has 52/36 with 11-28 – absolutely great for fast road riding, as I use the whole spread of gears over a ride. My commute/winter road bike has 50/34 with 11-32, I don’t need such top-end gears as I don’t hit really high speeds on commutes and I need to lower gears when I taking it easy up hills (with a full rucksack).

     

    March 15, 2018 at 9:17 am #914507
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    kil0ran

    I did the Di2 thing – great

    I did the Di2 thing – great for commuting as it guarantees reliable shifting in all weathers, although the buttons are harder to use in winter gloves than mechanical.

    I think if you can find a used 6870 Ultegra Di2 group then that’s the best option, at worst you’ll need to replace the battery.

    I’ve now gone back to a mix of Tiagra and 105 (chainset & front mech) on both my bikes as that’s definitely the sweet spot in terms of performance/weight/functionality/price. Unless you’re racing you really don’t need 11-speed, a 10-speed Tiagra wide-range cassette will do the job.  You do need to know how to set up and service your drivetrain, or be willing to pay your LBS to do it for you (that soon gets old, and drivetrain tuning is pretty easy once you’ve done it a few times – certainly easier than wheel building, or diagnosing Di2 issuess).

    To get back to your question, it doesn’t matter what size the rings are, if the development is the same then the same amount of effort will be required. Crank arm length can make a difference to efficiency but that’s one for an advanced bike fit to determine.

    March 15, 2018 at 8:48 am #914505
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    hawkinspeter

    I don’t think the gearing

    I don’t think the gearing will make as much difference as the difference in tyres and aerodynamics on a road bike vs a gravel bike. In general, drivetrain losses/inefficiencies are tiny, so recreational riders are unlikely to notice any real difference beyond which gear ratio you are using.

    Di2 is lovely to use, but in my mind is more of a luxury thing. If you’ve got the money, then go for it but if you have to dress your children in sackcloth in order to afford it, then maybe a mechanical 105 groupset would be a better spend.

    Since upgrading to a Di2 road bike, the biggest difference that I found was hydraulic disc brakes vs calipers. I’d assume that your 4k road bike would be equipped with hydraulics.

    March 15, 2018 at 7:21 am #914503
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    ChetManley

    I use my gravel bike for all
    I use my gravel bike for all sorts, flirted with 1x but not that into it. I use a 46/34 double for everything now, it’s plenty of top end for non racers who aren’t putting down a load of watts.

    It was also good enough for the guy who won the TCR last year.

    March 15, 2018 at 6:29 am #914501
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    Boatsie

    Mathematics of powering a
    Mathematics of powering a bike is fairly simple.
    If your mate peddling along with you at the same pedalling rpm. If you were to double the force on your pedals you would double your power output.
    Likewise if you were to remain with consistent force on the pedals, by doubling your rpm you would double your power output.

    We are mere mortals. We have a limit of force we can comfortably apply to the pedals. Pros know this better than I hence to improve horse power they lower their ratio and increase their rpm at the crank.
    Just common cyclists like me don’t bother exerting large efforts knowing knees/cranks/peddles will wear faster and increasing rpm at crank is slower at first yet brings thirst to eat properly and use slightly different muscle group coordination.
    Per example. If you’re riding into the wind and peddling gets harder. A drop of a couple of cogs might result in slightly less effort (about the same) yet twice as fast rpm at peddles. Hence twice horse power.
    Therefore, a speed that is about 30% faster!!!!

    Big ratios might tend towards downhill sprinting with us non pros.
    50/34-11/36 covers a lot of ratios. Already set up hence no need to configure chain length.
    Reads awesome bro. (Better than walking up the steep hills. Lol)

    March 15, 2018 at 12:36 am #914499
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    Boatsie

    I ain’t a strong rider. Tall
    I ain’t a strong rider. Tall leverage is on the bike primarily to bolt downhill and downwind. 52-10 is heaps tall.
    Here I’m waiting on a chain breaker to finish my bike. Tall is 53-13 which I’m guessing will be rarely used. Usage intended is coming down 5-7% grades and long flats with 20+ knots on the back.
    But aye, if you can get good pedal rpm on tall cogs,, let me admire your tree stumps. Been commuting solid 2 months, getting more speed with pedal rpm rather than heat on knees.
    On an aero 8kg fixed drive 50-16 I find sprints of 40kmph, cruising of less than an hour at 30kmph and all day at 20kmph.
    With my tall ratio bike I built that above my strength because our local conditions are a continual downhill road of 25 km and dominant winds that blow me home and blow me along flats and downhill of distances about 30-40km.
    With only 10 teeth on rear, a compact 50-34 would be heaps tall!

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