Belt drive. It may be time to admit defeat.

Home Forum Bike Forum Belt drive. It may be time to admit defeat.

Viewing 45 posts - 46 through 90 (of 159 total)
  • Belt drive. It may be time to admit defeat.
  • Premier Icon molgrips
    Subscriber

    It’s the weight which has the biggest impact on drivetrain stress, not how “powerful” somebody is, as however weak you might be, the force through the belt/chain is the same for the same rider weight given the same gearing

    You have that the wrong way round. A stronger rider will put more power through the chain regardless of weight. A heavier rider will simply be going slower for the same power. What you said would only be true if everyone rode at the same speed which is clearly not the case.

    emanuel
    Member

    must get to that museum.

    I don’t even have a car, and I don’t even know how many bikes I have, so I can relate.

    I’m doing a belt drive soon, with the new conti belt, I’ll let you know.

    Premier Icon aracer
    Subscriber

    molgrips wrote:

    It’s the weight which has the biggest impact on drivetrain stress, not how “powerful” somebody is, as however weak you might be, the force through the belt/chain is the same for the same rider weight given the same gearing

    You have that the wrong way round. A stronger rider will put more power through the chain regardless of weight. A heavier rider will simply be going slower for the same power. What you said would only be true if everyone rode at the same speed which is clearly not the case.
    [/quote]

    Nope. Think about it – I’m sure you’ve done levers and stuff. Two riders both the same weight going up a hill (which is where you’ll see the peak loadings)at a steady speed. Both using the same gearing, one is simply pedalling slower than the other. What is the force required at the rear tyre contact point? What is the force required at the rear sprocket (let’s assume single speed with no Rohloff)? What’s the force in the chain/belt? Which of those is dependent on the pedalling speed?

    Premier Icon molgrips
    Subscriber

    I’m sure you’ve done levers and stuff.

    Yeah that’s covered on the way to a Physics degree πŸ™‚

    Rider weight has nothing to do with the force through the chain. That comes from your legs. The harder you pedal, the more torque you are generating, so the more pressure on the belt teeth – which is where the wear comes from.

    However, if you pedal with half the torque but twice as fast (to generate the same power), even though each tooth gets half the pressure it goes round twice as often. Rider weight has nothing to do with this – you could be 60kg or 100kg but if there’s 500N in the belt then there’s 500N in the belt.

    I can’t make head nor tail of your counterpoint, sorry.

    emanuel
    Member

    The integral of power over time defines the work performed. Because this integral depends on the trajectory of the point of application of the force and torque, this calculation of work is said to be path dependent.

    The same amount of work is done when carrying a load up a flight of stairs whether the person carrying it walks or runs, but more power is needed for running because the work is done in a shorter amount of time. The output power of an electric motor is the product of the torque that the motor generates and the angular velocity of its output shaft. The power involved in moving a vehicle is the product of the traction force of the wheels and the velocity of the vehicle. The rate at which a light bulb converts electrical energy into light and heat is measured in wattsβ€”the higher the wattage, the more power, or equivalently the more electrical energy is used per unit time.[1][2]
    from wikipedia.

    to me that means a masher will break more things than a spinner, even if they both ride at the same speed.

    And the broken chainstays / unstuck carbon rear triangles I see are from mashers.

    emanuel
    Member

    **** the quote thing.

    MTG – appreciate anyone who destroys things and heating about it. Keep posting.

    Premier Icon bedmaker
    Subscriber

    MTG – appreciate anyone who destroys things and heating about it. Keep posting.

    Agreed!
    If I had stuff to test, I’d send it FOC to MTG or for non bikey camping stuff to Tracksterman

    Lots of broken/ worn out stuff. It would appear not through outright abuse, but by sustained hard use at the limits of what it is designed for.

    Suggsey
    Member

    I think from my point of view being an 18 stone rider that weight (inertia) is an issue combined with poor pedalling technique and that is what trashing your kit along with a bit of bad luck and really muddy riding conditions!
    Try to ride for your next test period spinning circles, that’s why you’ve been snapping pedal axles. Ride light, it is possible to use more arm and leg flex ion to take out the sting from the cranks on rough sections etc. touch wood I’ve only ruined wheels and bearings in wheels ie cup and cone are a joke, one ride crushed a brand new set!
    I am quite sure that the natural oils within the rubber are probably being compromised by the UK off road riding too leading to belts becoming brittle. Think tyres left stood on concrete, is your main off road riding done in a high limestone area? Just a thought?

    Premier Icon njee20
    Subscriber

    My understanding was as per Molgrips – a light rider can exert a high force (and torque) or a heavy rider can spin. The weight isn’t the significant factor unless you assume all other variables to be equal, which of course they’re not.

    beeds
    Member

    MTG wish you had posted the pictures of your bike in use, would not have bothered posting.
    Your taking the belt to extremes and your weight and admitted pedalling technique are a factor that some people are totally ignoring.
    Doesn’t matter, keep testing and keep posting with updates dude!

    kudos
    b

    Suggsey
    Member

    I will repeat the main variable is inertia caused by (weight) gravity and drag ( increase in tyre footprint if same pressure run in the tyres) it stands to reason that an 18 stone rider will require more energy to be transmitted through the drivetrain into the floor to move at the same speed as a 10 stone racing snake!

    MTG, I’ve always enjoyed your determined attempts to ride something different for what you hope are good engineering reasons (incidentally I can see an engineering benefit to the Jones truss fork).

    A thought on pedalling better – drop your heels at the top of the stroke and push forwards and then downwards. Focus on starting the push as early as possible, and that will naturally cause the other leg’s power stroke to end at the right time (you don’t want to be pushing down on a pedal that’s trying to come back up).

    If your power stroke is concentrated in one small segment then your peak torque could be many times higher than that of someone with equal power and smoother technique. Very tough on your drivetrain!

    It may be that your pedalling approach isn’t any slower than smoother pedalling because your legs are pushing harder for short periods but resting for longer periods – I doubt it would work so well if you were racing DH, 4X, BMX, track, where you need bursts of very high power but you’re riding much longer races!

    I will repeat the main variable is inertia caused by (weight) gravity and drag ( increase in tyre footprint if same pressure run in the tyres) it stands to reason that an 18 stone rider will require more energy to be transmitted through the drivetrain into the floor to move at the same speed as a 10 stone racing snake!

    This is very true! And especially in mud.

    Does it take twice as much force to set a train of twice as much mass moving? I think not. Does it take twice as much force to pull twice as heavy a plough through a field? I suspect so…

    Premier Icon aracer
    Subscriber

    molgrips wrote:

    I can’t make head nor tail of your counterpoint, sorry.

    With a physics degree? All I’m doing is working back from the force at the contact point of the tyre on the ground.

    If it’s really so difficult, let me do a worked example with some numbers.

    100kg total bike and rider mass. Let’s assume g is 10m/s/s to make the numbers easier, so weight of rider/bike is 1000N. We’ll assume no wind or rolling resistance, riding up a 30 degree gradient hill so force parallel to surface at tyre contact point is 500N (I presume you don’t need calcs for that?) 2.5″ 650B tyres (just to be fashionable), rolling diameter 28″ or 711mm, so torque in rear wheel is 177.75Nm. 16 tooth rear sprocket conventional 1/2″ pitch chain drive, diameter at chain centre 2.546″ or 64.68mm. Force in chain 5.5kN.

    Where in that calc should I include the pedalling speed?

    Premier Icon njee20
    Subscriber

    So how do power meters give you a torque figure if it’s a pure function of speed and weight? Serious question. Why is it not the same if you do repeat a ride at the same speed? Why is my highest torque when I accelerate hard from a stand, rather than when I’m at my fastest?

    Surely you can achieve 200w by spinning a small gear fast (low torque) or mashing a big gear (high torque).

    Premier Icon aracer
    Subscriber

    Strain gauges, which for example measure the deflection in the crank arms.

    asterix
    Member

    Why is my highest torque when I accelerate hard from a stand, rather than when I’m at my fastest?

    because acceleration requires a force, but no force is required (other than to overcome frictional losses) to maintain a constant velocity – Newton’s first law init

    Premier Icon molgrips
    Subscriber

    With a physics degree? All I’m doing is working back from the force at the contact point of the tyre on the ground.

    Rest assured, I will be able to understand your point (if you’re not talking bollocks) as soon as you can put it into words that make sense.

    Just gone through your post again and you’ve calculated the force in his belt/chain if he were trackstanding. He’s going uphill at a certain vertical climb rate, so you need to add that on.

    Anyway – pedalling speed is important. Assume that the pulley is what, 20T, so ten teeth are in contact at once. The wear occurs when a belt tooth slides over a pulley tooth. The more force the belt is under, the more it wears. However, the faster the belt is moving the more times per minute it happens.

    I said that the rider power was important, not pedalling speed, because more sliding events per minute cancels out with lower torque, for a lower gear and same power.

    Premier Icon aracer
    Subscriber

    Nick Evans wrote:

    Surely you can achieve 200w by spinning a small gear fast (low torque) or mashing a big gear (high torque).

    Given we’re talking belts I’m discussing a singlespeed (for the time being I’m ignoring the Rohloff).

    Premier Icon njee20
    Subscriber

    Strain gauges, which for example measure the deflection in the crank arms.

    I still don’t get it. Are you saying that’s entirely irrelevant for the purpose of drivetrain forces/wear?

    Edit:

    Given we’re talking belts I’m discussing a singlespeed (for the time being I’m ignoring the Rohloff).

    Ah ok, makes more sense.

    Premier Icon molgrips
    Subscriber

    So how do power meters give you a torque figure if it’s a pure function of speed and weight? Serious question

    They actually read force, using strain gagues. But the designers know how far the strain gagues are from the centre of the axle, so they know torque. They multiply this by the speed of rotation to give power.

    Surely you can achieve 200w by spinning a small gear fast (low torque) or mashing a big gear (high torque).

    Correct.

    Why is my highest torque when I accelerate hard from a stand, rather than when I’m at my fastest?

    Because when the pedals are stationary or moving slowly, as you set off, it’s easier for you to put a lot of force onto the pedals. The faster you pedal, the faster the pedal is moving away from your foot so you have to accelerate your foot to meet it. If it’s moving fast enough this is really hard, which is partly why you can only pedal so fast.

    Premier Icon aracer
    Subscriber

    molgrips wrote:

    Just gone through your post again and you’ve calculated the force in his belt/chain if he were trackstanding.

    Nope – it’s for a constant speed, so there is no acceleration force. Given I’ve also mentioned I’m neglecting air and rolling resistance, the only force the rider is working against is gravity, no matter how fast he’s going.

    He’s going uphill at a certain vertical climb rate, so you need to add that on.

    What force does the constant speed result in? Where do I include it in my calcs?

    Anyway – pedalling speed is important. Assume that the pulley is what, 20T, so ten teeth are in contact at once. The wear occurs when a belt tooth slides over a pulley tooth. The more force the belt is under, the more it wears. However, the faster the belt is moving the more times per minute it happens.

    True. In a traditional XC race where you’re covering a set distance or going for a ride where you’re covering a route it would be irrelevant as it would happen more times per minute for the more powerful rider, but that rider would be riding for less time so would have exactly the same number of slides. Of course Graham is talking about doing timed events, but the suggestion seems to be that a more powerful rider ought to result in a higher wear rate – I’ve seen no mention of a rider doing more events resulting in the same thing, and I think it’s accepted that Graham does quite a large volume of riding. To come back to the start, all of these breakages are being measured against the distance covered, and in that case there have been exactly the same number of sliding events no matter how powerful the rider.

    emanuel
    Member

    what about rolling resistance?
    You’re going to put more force into a drivetrain in snow or thick mud than on tarmac.
    Though on the other hand you’re going to put more torque on the drivetrain on a standing start on tarmac than on snow,mud.

    Plus the fact that calculating pedal force as linear is not realistic, less so with pro level technique pedal stroke (track mostly) more so with normal riders.

    emanuel
    Member

    edit, they said that while I was writing it.

    Premier Icon molgrips
    Subscriber

    What force does the constant speed result in? Where do I include it in my calcs?

    In a traditional XC race

    We weren’t talking about XC racing, but distance travelled is the other variable yes. If you assume a fitter stronger rider is riding the same number of miles on their bike as a weaker one, then you have a point, but that’s a) unlikely and b) you should’ve specified.

    What force does the constant speed result in? Where do I include it in my calcs?

    If riding uphill didn’t require extra force in the belt, we wouldn’t need to pedal harder, would we?

    You have to do X amount of work to get up the hill. The chain has to go round Y times depending on how far it is and what gear you’re in/have fitted, and as you will know work = force x distance moved. So the extra force is X/(Y * belt length or whatever it works out to)

    Premier Icon aracer
    Subscriber

    molgrips wrote:

    We weren’t talking about XC racing, but distance travelled is the other variable yes. If you assume a fitter stronger rider is riding the same number of miles on their bike as a weaker one, then you have a point, but that’s a) unlikely and b) you should’ve specified.

    I was talking about Graham (sorry, Graham), because the original assertion was that he would put less stress on the drivetrain than a more powerful, faster rider, so wasn’t sure I needed to specify anything else as the data is all there. If that assertion was because the more powerful rider was riding more miles than Graham, maybe that should have been mentioned, though we’ve already established that Graham is actually putting in lots of miles, so it seems fairly likely that the weaker rider (Graham) is actually putting in more miles than the stronger one.

    If riding uphill didn’t require extra force in the belt, we wouldn’t need to pedal harder, would we?

    Agreed, but that’s because you’re riding up hill, not because you’re riding at a particular speed and is the same for all riders no matter ow powerful.

    You have to do X amount of work to get up the hill. The chain has to go round Y times depending on how far it is and what gear you’re in/have fitted, and as you will know work = force x distance moved. So the extra force is X/(Y * belt length or whatever it works out to)

    Yep. That has the same result as what I wrote before (doing the calc with work is a nice elegant way of doing the same thing), and doesn’t have a speed term in.

    Using the same bike and rider as before:
    rider/bike weight = 1000N
    hill height = 100m
    work done = 100 x 1000 = 100kJ
    distance along the ground on 30 degree hill = 200m
    2.5″ 650B tyre diameter 711mm, circumference = 2234mm
    number of rotations of wheel = 200 / 2.234 = 89.54
    16 tooth 1/2″ pitch sprocket circumference = 8″ = 203.2mm
    distance moved by chain = 89.54 * 0.2032 = 18.19m
    force in chain = work done / distance moved = 100000 / 18.19 = 5.5kN

    Premier Icon molgrips
    Subscriber

    It doesn’t have a speed term, but it is not the same as you wrote – you were wrong. And your explanations made no sense.

    However now I have figured out what you meant, you were right – over the same course, rider weight is the factor. I was thinking in terms of riding a set amount of time.

    And to be fair, the OP’s preferred event is fixed time not distance.

    Premier Icon aracer
    Subscriber

    molgrips wrote:

    It doesn’t have a speed term, but it is not the same as you wrote – you were wrong. And your explanations made no sense.

    Nope. I’ve run the numbers for your calc above in my edit and got the same result as I did just from calculating forces and torques before. I’ve also reread my previous explanations and see no problem with them from a science perspective – I was simply explaining that the speed makes no difference to the force when riding up a hill at a steady speed. The only reason you’re confused is that you were assuming a non-existent speed factor.

    And to be fair, the OP’s preferred event is fixed time not distance.

    It is, but I covered above that the suggestion didn’t seem to be that the more powerful rider was wearing the drivetrain more because of higher mileage.

    Well, this has gone off at a tangent, hasn’t it ? πŸ˜•

    I’m off to Hay Cycling Festival now for a three and a half hour orienteering event.
    I’ll be logging the ride, to keep track of wear on the new belt & pulley, and I’ll be thinking more about how I pedal. πŸ˜›

    Premier Icon molgrips
    Subscriber

    Pedaling nicely is important for lots of reasons!

    If the relationship between tooth pressure and wear is non linear, you could end up saving your belts too.

    Premier Icon biff
    Subscriber

    I wouldn’t buy a Jones truss fork or a Lynskey helix frame because they just look to me like they are just different for the sake of it.

    I don’t know about Lynskey, but Jones, not ‘different for the sake of it’ at all.

    I’m not convinced about the Jones fork.
    The triangulation, albeit with curved tubes, is fore and aft, which looks like it would make it very rigid in that plane.
    Two thin tubes are not as strong as one thick one, so it looks like it would flex sideways more than a more conventional fork.
    The whole thing looks to me like it’s the complete opposite of what you’d want.

    Anyway, a bit of musing about power outputs and I had a look on Strava at Battle on the Beach.
    I was 40th out of the 98 who uploaded a full lap to Strava.
    I’m about 10 minutes a lap, or 30%, slower than the front runners, but I’ve got a power output that wouldn’t look out of place in the top 3.

    If I could lose 30kg, I’d be a champion. πŸ˜›

    Premier Icon epicyclo
    Subscriber

    One problem with belts is that to maintain alignment, they require more lateral stiffness than you get in an average chainstay.

    Another problem is when the belt tensioning system allows the end user to misalign the wheel in relation to the BB, then the belt tries to rid off the pulley, and basically the only way to avoid this is with an EBB.

    In other words belts need bicycles designed from the start for belts, not modified or tweaked.

    Much as I love the silence and cleanliness of a belt, for a lifetime drive system, nothing beats an oilbath chaincase with a decent ?” chain and hardened steel chainring and rear cog. There’s enough old bikes still getting around with their original components. Sunbeams being the best example.

    Premier Icon biff
    Subscriber

    The whole thing looks to me like it’s the complete opposite of what you’d I’d want.

    Edited. Different wants. Where’s Jennifer Aniston when I need her?

    People talk about watts/kg when referring to road cyclists. I’ve heard it a few times (most in depth in Tyler hamilton’s book) that to win the TdF you need a power output of 6.5watts/kg body weight. He reckons the easiest way to achieve this is simply to lose weight.

    Interestingly, and perhaps pertinent to molgrips/aracer’s discussion, two riders could have the same winning specific power output (6.5watts/kg) but if one was 80kg, they’d put more force through their bike/ drivetrain than a 70kg rider.

    ndthornton
    Member

    Does anyone know when the new 108 and 111 tooth Gates belts are coming out?
    I want to get in the game but need a shorter belt. Come on Gates!

    Premier Icon veedubba
    Subscriber

    CBA to read most of pages 2 & 3… but, IME of belts (4 years and perhaps 4000km, so not up there with some of the distances discussed earlier) I’m on my second belt on a singlespeed commuter. It’s geared so that hills are a pain but the torque I’m putting through the drivetrain on steeper stuff must be quite high (and I don’t meant that I’m ace, just that in those situations, to move the bike along the rider needs to really get some leverage on the cranks).

    I too have experienced the increased frequency of replacing BBs (perhaps one every 6-8 months).

    My main reason for purchase was the low maintenance aspect. Apart from whole bike cleaning I never touch the belt in normal service – no oiling, degreasing or anything.

    When the belt failed I actually thought my rear cog was stripping the splines off the freehub so I tested it by riding up a steep hill one evening and ended up stripping half the teeth off the belt. On inspection the remaining ones were worn to a triangular profile, and the creaking noise I thought was my freehub was actually the teeth shearing at their base.

    I love my belt drive but I can see that in conditions where there’s debris getting into it, or where its being loaded from the side, then a belt would fail a lot more quickly than I’ve experienced.

    Premier Icon epicyclo
    Subscriber

    Just to veer slightly OT (this is STW after all). One of the advantages of a belt is its lightness.

    If we had a fully enclosed chain, how light could that be made? Maybe smaller pitch, etc. Didn’t Shimano have a crack at a 10mm pitch a few years back?

    avdave2
    Member

    One of the advantages of a belt is its lightness.

    That’s one of the things that first got me interested but now Gates have had to change the rear carrier to steel, they want you ideally to fit a snubber and you need a stiffer rear triangle that can be split which again adds weight. I’m not sure the weight savings are that great.

    Premier Icon epicyclo
    Subscriber

    avdave2 – Member
    That’s one of the things that first got me interested but now Gates have had to change the rear carrier to steel, they want you ideally to fit a snubber and you need a stiffer rear triangle that can be split which again adds weight. I’m not sure the weight savings are that great.

    Good point. My experiments have all been on the ordinary belt and cogs. The stiffer rear triangle and split need not add more than a few grams of weight. If they do, it’s bad design.

    However a rear cog made of steel is going to be considerably heavier than the same thing in aluminium and also than its equivalent for a chain. As for a snubber, that’s tantamount to admitting the system doesn’t work without a bodge… πŸ™‚

    wilko1999
    Member

    A somewhat trivial point after all the heavy-hitting physics going on, someone earlier on mentioned the motorbike industry had given up on belt drive. Harley Davidson however didn’t and have it taped.

    jackthedog
    Member

    someone earlier on mentioned the motorbike industry had given up on belt drive. Harley Davidson however didn’t

    BMW still use belts too.

    Physics arguments aside, this is a very insightful thread. Thanks for sharing, OP.

    Premier Icon epicyclo
    Subscriber

    wilko1999 – Member
    A somewhat trivial point after all the heavy-hitting physics going on, someone earlier on mentioned the motorbike industry had given up on belt drive. Harley Davidson however didn’t and have it taped.

    It was the thousands of miles I did on my HD in outback Queensland on dirt roads that convinced me belt drives were more than up to the job.

    cynic-al
    Member

    Is anyone else disappointed this thread is not about turntables?

Viewing 45 posts - 46 through 90 (of 159 total)

The topic ‘Belt drive. It may be time to admit defeat.’ is closed to new replies.