Viewing 38 posts - 1 through 38 (of 38 total)
  • Motorcycle design (NOT OT)
  • druidh
    Free Member

    We quite often get the, err, older gents in the shoppe and they'll comment about the amount of technology on modern mountain bikes – hydraulic disk brakes, front and rear suspension, massive knobbly tyres. Quite often, they'll compare todays cycles to older motorbikes and it's evident that there's been a fair amount of crossover.

    How come it's only really one-way though? As cyclists, we tend to accept that most of these changes are primarily applicable off road, but where are the hardtail (or even rigid) road motorbikes?

    mboy
    Free Member

    One hardtail motorbike…

    The reason you don't see hardtail, or rigid motorbikes in the mainstream is quite simply, you want the tyres in contact with the ground as much as possible. On a mountain bike, the kinds of speeds you're seeing on an XC ride will not necessitate full suspension, but certainly in DH racing having long travel full sus makes a lot of difference in terms of keeping the wheels in contact with the ground for much longer, hence providing more control.

    Ride a motorbike above 30mph or so and you'll begin to see just how bumpy most roads are, hence the need for suspension, and relatively high sidewalled tyres (compared to cars anyway) to help with grip and absorb the bumps on the roads etc.

    Hardtails are the preserve of the custom motorbike makers, mainly they do it for the looks. They're not concerned with high speed handling or stability, only the way the thing looks.

    gab344
    Free Member

    Plenty of hard tail motorcycles around, normally with comedy forks and giant oversize rear tyres, almost exclusively used in boutique custom chops see "American chopper" on discovery chan (But don't say I didn't warn you first)

    andrewh
    Free Member

    No doubt someone will correct me but it has always struck me as to how primitive motorbike design is. Are all the rear susspension designs basic single-pivot jobs or are there fancier linkage ones around?
    Was racing against a (brand new) moped the other day, looked down and he had cable-operated drum brakes!

    gab344
    Free Member

    BMW paralever suspension is the first to "spring" to mind,(see what i did there 🙂 )the telelever at the front works well too.

    Edric64
    Free Member

    single-pivot jobs

    They used to be twin shocks, some still are

    gab344
    Free Member

    TBO the rear suspension on motorbikes has never been considered the limiting factor, some designers in the fringes of the industry, do however spend a lot of time trying to find an alternative to tele-forks.

    Mainly to in an effort to separate the "diving" action from the front brake.

    ..waits for a picture of a whyte to show up.. 🙂

    mboy
    Free Member

    Are all the rear susspension designs basic single-pivot jobs or are there fancier linkage ones around?

    Mostly they're single pivot, but with a linkage actuated shock… Think Orange ST4, Commencal Meta, Cannondale RZ140 etc. This is so that the manufacturer can create a progressive rate to the shock, so it's more supple to start but the spring and damping rate ramps up through its travel. This is desirable to create a supple initial action, but to help with bottom out resistance, which when you bear in mind most sports bikes have 120mm of travel or so both ends on the bike, but can hit up to 180mph or so and are ridden over BIG bumps etc. (think about what they go through on the TT races etc.), then you'll realise it's a lot to deal with. Different suspension designs (think 4 bar etc.) wouldn't really work on a motorbike, mainly due to packaging, but also it's to do with the engine. A single pivot MTB can be susceptible to pedal bob because a rider might not pedal very smoothly. A motorbike engine delivers its power in a smooth circular motion, so bob will never be an issue!

    As far as the front suspension goes, then there have been quite a few different attempts at improving its action, notably on the road the BMW setup which is rather like the front end of a Whyte PRST-1 in that it has telescopic forks that actuate a shock mounted to the frame of the bike. But there have been quite a few attempts on the leading swingarm, hub centre steering bikes, like the Honda pictured above…

    Here's another version of the same idea, the Bimota Tesi…

    aracer
    Free Member

    hence the need for … relatively high sidewalled tyres (compared to cars anyway) to help with grip and absorb the bumps on the roads etc.

    Isn't that more to keep lots of rubber in contact with the road when you lean over? I can't see car style lo pro tyres giving much cornering grip.

    mboy
    Free Member

    Isn't that more to keep lots of rubber in contact with the road when you lean over?

    Yeah, but also a higher sidewall tyre will be able to deform more, hence keeping more of the tyre in contact with the ground for more of the time. It's why MotoGP bikes run smaller 16" rims than road bikes (which use 17" rims) in combination with higher profile tyres.

    tinsy
    Free Member

    Most single shock motorcycle suspension systems work on a rising rate linkage system, weirdly when they were twin shocks its was the laying down, or angle of the shock that first allowed longer travel and a rising rate.

    Its no good looking at the Jingaling_lawnmower_deadly_toy companies latest offering and wondering where the tech is, you need to look at a modern MX'r or sportsbike.

    Remember Fox came from motorcycles background, Fox air shocks came about in the late 70's.

    The BMW telelever etc, is just a modern interpretation of stuff found in the 50's on bikes like Vincents.

    Similarly the old USE sub fork is just another version of a leading link (50's & 60's design), still commonplace on sidecars MX and road racers, because of its anti diveing nature.

    gusamc
    Free Member

    crossover – ? I'd say mountain bikes have completely pigged back on motorbike design, I personally can't think of anything that's gone the other way (stands by to be corrected) – however suspect thta given the massive change in bike money (upwards) suspect it might happen one day …)

    increasing suspension travel
    discs
    suspensions – twin, single then linkage
    http://www.promecha.com.au/leverage_linkages.htm

    re primitive – derailleur, and try cost vs required function equation

    awaiting, the first decent battery offroader

    tinsy
    Free Member

    gusamac, I cant remember the name but have seen some promo footage of a battery MX'r looked flipping great… will have a google.

    here you go.

    http://www.zeromotorcycles.com/dirt/

    HA HA HA, and here is the trickleback to motorbikes from MTB, looks a lot like a hope 4 pot caliper on the back of this!!
    http://www.racerxonline.com/video/zero-electric-motorcycle-intro.aspx

    ahwiles
    Free Member

    single pivot designs are affected by brake-jack; apply the rear brake whilst riding along, and the rear suspension is compressed.

    this is usefull: as compressing the rear suspension will negate some of the front-brake-dive, keeping the bike more level and controlled during hard braking.

    mert lawill liked brake-jack so much that he even included a little linkage on his 4-bar motorbike design which put the brake-jack back in after the 4-bar thing took it out.

    so, he'd made a 4-bar, which worked like a single-pivot. it's very clever, but i'm not why he did it…

    thisisnotaspoon
    Free Member

    Honda RN-01?

    Wasn't that designed in order to test out how lightweight you could go with an MX chasis?

    A few of the lightweight/electric motorbikes have used DH bits to save weight (zocchi shivers, hope 6 pots etc). But yea, we're unlikley to see much unique technology being developed for bikes finding a use in the wider world, unless you count the fact hat motorbikes were originaly just push bikes with engines! Even the most 'advanced' mountainbike suspension is just good car suspension turned through 90deg.

    epicyclo
    Full Member

    Probably find he did it to keep the belt tension steady.

    Nice example of how to do single speed on suspension with belt drive – wonder if that will trickle down to bikes 🙂

    jackthedog
    Free Member

    so, he'd made a 4-bar, which worked like a single-pivot. it's very clever, but i'm not why he did it..

    Vertical axle path, I assumed.

    Nice example of how to do single speed on suspension with belt drive – wonder if that will trickle down to bikes

    That Lawwill rear end has been finding its way onto bikes since the Fisher RS1 in the early 90s right up to this years Rotec RL9. Not singlespeedable though.

    I'd sell a kidney to get my hands on a Lawwill Street Tracker. In fact I wouldn't turn my nose up at an RL9…

    Dibbs
    Free Member

    Who asked for a Whyte photo? 😀

    tinsy
    Free Member

    I would love a go on one of those… compare the ride to a convetional full sus Dibbs… ??

    Amos
    Free Member

    AHHHHH My eyes, take it away! for the sake of the children!!!

    sam-r
    Free Member

    mboy[quote]A motorbike engine delivers its power in a smooth circular motion, so bob will never be an issue![/quote]
    nonsense, this is one of those myths that does the rounds here (and elsewhere). You're suggesting that power-delivery is smooth? Watch some moto-x or MotoGP & it should be apparent that the torque (rather than power) is being applied in very sharp bursts, far, far quicker than any puny human could even begin to deliver. As for someone else suggesting that motorcycle design is "primitive" – you're having a laugh, right?

    LoCo
    Free Member

    Check these out for current 'funny front end' motorcycles

    http://www.vyrus.it/index2.html

    and the dynamics of a motorcycle are a bit different to those of a bicycle.

    thisisnotaspoon
    Free Member

    yes, but at 6000rpm (which if your racing, your unlikely to drop below) a single cylinder is firing 50 times a second. So a superbike bike is firing 50 times a second, and a GP bike probably doesn't drop below 300. Thats pretty dam smooth. Compared to a push bike which manages 2.

    jackthedog
    Free Member

    Compared to a push bike which manages 2.

    Also, each power stroke is accompanied by a bouncing human that comprises about 75-80% of the combined mass of the vehicle, who might have his weight right back or all the way forward, and can be in any gear combination, which changes the angle of power transmission. I've always assumed getting mountain bike suspension right is really quite a tricky job, considering the frequently shifting location of the weight, the varied terrains and speeds, lumpy power delivery, light weight, compact size and rider-detectable feedback.

    Often I get the impression that when the comparative simplicity of motorbike suspension is noted on STW, a lot of motorbike fans (of which I'm one) feel the need to jump to the defence of the hardcore nature of engined machines. I don't think it's a slur on the good name of motorcycle design to suggest that a mountain bike suspension design might have a harder job to do?

    Comparing them directly is a bit daft – 0.2bhp vs 160bhp, 15mph vs 150bhp – it doesn't really matter. I suspect there are a few more considerations dictating the design of bicycle suspension than motorcycle suspension. And a whole lot of marketing nonsense clouding the issue.

    IainGillam
    Free Member

    The effect of the torque from the engine on the rear suspension can be advantagous, for example when landing a big jump or heading into a set of rollers application of the throttle will lessen the effect of the landing/ bumps on the rear suspension due to the resistance from the motor to the lengthening of the chain. Simmilarly braking on the face of a bump or kicker with the back brake will stop the rear wheel kicking up. On the more 2D surface of a tarmac race track it might not be so useful but I'm not even sure if the suspension causes a variable chain length on road bikes or not, however, due to the linkage driven single pivot on Japanese MX bikes and the single pivot on KTM's It does on Mx bikes.

    Iain

    mboy
    Free Member

    nonsense, this is one of those myths that does the rounds here (and elsewhere). You're suggesting that power-delivery is smooth? Watch some moto-x or MotoGP & it should be apparent that the torque (rather than power) is being applied in very sharp bursts, far, far quicker than any puny human could even begin to deliver. As for someone else suggesting that motorcycle design is "primitive" – you're having a laugh, right?

    Sorry, but PMSL right now…

    yes, but at 6000rpm (which if your racing, your unlikely to drop below) a single cylinder is firing 50 times a second. So a superbike bike is firing 50 times a second, and a GP bike probably doesn't drop below 300. Thats pretty dam smooth. Compared to a push bike which manages 2.

    Well put TINAS.

    The power pulses on an MTB are as written above, something approaching 2 per second. A 4 cylinder motorbike engine revving at a mere 6000rpm will have 200 power pulses per second (4 stroke engine each piston fires every 2nd revolution), which by all accounts is really rather smooth!

    For what you are saying to stand true sam r, you'd be implying that the rider of a given motorbike would be stabbing the throttle open and shut at a massively high frequency! IT DOES NOT HAPPEN!

    MTB suspension designs have to get over the VERY un-smooth power delivery of human legs. A motorbike has a massive advantage in that it has an inherently smooth, relatively low torque (even in the case of a big single) engine, that doesn't cause any suspension induced bob. What it can do, and this is what you are confusing it for probably sam r, is cause extension and/or squat depending on what it has been designed to do. But this is also why they try to make the swingarms as long as possible on most bikes these days, and get the pivot placement as close to the output shaft of the gearbox as possible.

    Also, each power stroke is accompanied by a bouncing human that comprises about 75-80% of the combined mass of the vehicle, who might have his weight right back or all the way forward, and can be in any gear combination, which changes the angle of power transmission. I've always assumed getting mountain bike suspension right is really quite a tricky job, considering the frequently shifting location of the weight, the varied terrains and speeds, lumpy power delivery, light weight, compact size and rider-detectable feedback.

    Often I get the impression that when the comparative simplicity of motorbike suspension is noted on STW, a lot of motorbike fans (of which I'm one) feel the need to jump to the defence of the hardcore nature of engined machines. I don't think it's a slur on the good name of motorcycle design to suggest that a mountain bike suspension design might have a harder job to do?

    Another point well made.

    Strange as it might sound, it's probably a lot harder to design an MTB suspension setup to do exactly what you want it to do than it is for a motorbike. With a motorbike you'll already know what the engine is going to be (probably), and what the application is for. On an MTB you've not got a clue how smooth or powerful or heavy the engine is going to be, hence why some bikes suit some people but not others! Generally on a motorbike the suspension is having to deal with bumps in a higher frequency (anyone who doesn't recognise this, watch some super slow mo footage of a bike at 160mph or so on the TT course) mainly due to the speed, so the shocks have to be very supple and well controlled. On a mountain bike the emphasis with rear shocks is much more on controlling the slow speed compression damping (to combat pedal induced bob) and the high speed compression and rebound (which is more important on a motorbike) is nowhere near as important in general.

    Anyway, ask yourself this question if you don't believe what I'm on about with the MTB Vs Motorbike complexity argument… How many different variations of rear suspension design are there currently in use on the MotoGP circuit, or for that matter the World Superbike circuit either? The answer will be one… Single pivot with a linkage driven shock!

    Now how many different suspension designs are there being used in top flight DH or XC MTB racing? Dozens, and the main reason for that is that still nobody has been able to come to a general consensus that one suspension design is significantly better than another!

    Northwind
    Full Member

    There's an interview with the feller from Pace in MBR (I think) this month which makes some comparisons between dirtbikes and mtbs… Quite interesting reading though it just touches on the subject.

    lobby_dosser
    Free Member

    what about this?

    Single crown forks, stem…

    solamanda
    Free Member

    It's already been said by the posters above but one of the many reasons motorbikes get away with a single pivot, and more importantly why single pivot is perfect IS chain tension.

    On a motorbike bike chain tension is, on the whole, constant if the rider is holding the same throttle position. The slight chain growth allowed on a motorbike system means that throttling tensions the movement of the swingarm to stiffen up it's suspension. This is partly why it is so important to keep the throttle open around corners and why backing off mid corner can end in horrible consequences. This effect is so powerful that at high level riders use different amounts of chain tension free play to adjust how the suspension works!

    One thing that interests me is that Magura Gustavs are arguably the most powerful MTB brake, (I'd agree, I've had two sets), and one of the reasons is their floating caliper – similar to cars or motorbikes. However the most powerful of motorbike brakes do not use a floating brake caliper and are fixed like a 'normal' MTB disk brake.

    epicyclo
    Full Member

    lobby_dosser – Member
    what about this?

    What is it? Looks "interesting"

    One theory of bike geometry I have is that within a reasonable range of head angles, trail, etc, a rider can compensate for the differences because we move our weight around so much and it is a greater proportion of the total than on a motorbike.

    brant
    Free Member

    One theory of bike geometry I have is that within a reasonable range of head angles, trail, etc, a rider can compensate for the differences because we move our weight around so much

    That's fine until you're pointing down something steep and going over the bars.

    solamanda
    Free Member

    That's fine until you're pointing down something steep and going over the bars.

    Sportsbikes can be abit scary on steep downhill corners with their steep angles.

    lobby_dosser
    Free Member

    it's a KTM 'Freeride' concept bike

    adeward
    Free Member

    chain tension is used on Motorbikes as anti squat, on gp and bikes the pivot position is adjustable to change the anti squat,

    you also have to remeber that most gp bikes have fully floating rear brakes, not in terms of disc rotors but tha caliper is mounted on a bearing concentric to the rear axle then a torque arm is located to the frame the postion on the frame dictates what the brake reaction does squat, rise or something neutral

    back to mountain bikes,, the whyte bike was designed as an alternative to telescopic forks,, it had a few advantages almost constant trail throughout the suspension travel ,, j shaped axle path to help the forks to move when hitting a bump ,,
    there were no telescopic parts of it unlike the bmw system,, (actualy designed by norman hossack i think)
    i still think they were great ( i may be slightly biased )

    adeward
    Free Member

    one more thing unless the output sprocket on a motorbike is concentric to the Swinging arm pivot then the chain tension is not constant

    I did work for a bimota british superbike team who ran a tesi and I think that had concentric pivot,, and a hub center steering system which meant you could adjust most front end angles indipendantly ,, shame the rider had no feel for it

    mboy
    Free Member

    It's already been said by the posters above but one of the many reasons motorbikes get away with a single pivot, and more importantly why single pivot is perfect IS chain tension.

    On a motorbike bike chain tension is, on the whole, constant if the rider is holding the same throttle position. The slight chain growth allowed on a motorbike system means that throttling tensions the movement of the swingarm to stiffen up it's suspension. This is partly why it is so important to keep the throttle open around corners and why backing off mid corner can end in horrible consequences. This effect is so powerful that at high level riders use different amounts of chain tension free play to adjust how the suspension works!

    Spot on, all achieved by a relatively smooth power delivery that's not trying to make the whole bike bob up and down constantly. And yes, you definitely don't want to just shut the throttle off going round corners, as you well know it just unloads the rear suspension, which unloads the rear tyre causing a lack of grip, and either a low side (if you're lucky) or a highside is likely to happen!

    One thing that interests me is that Magura Gustavs are arguably the most powerful MTB brake, (I'd agree, I've had two sets), and one of the reasons is their floating caliper – similar to cars or motorbikes. However the most powerful of motorbike brakes do not use a floating brake caliper and are fixed like a 'normal' MTB disk brake.

    More to do with caliper design, piston area, pad size, leverage ratio between master and slave cylinders, and a few other reasons than it is to do with whether the brake is a sliding caliper or not. In fact one of the first things they do on a lot of performance cars when improving the brakes, particularly for track work, is remove the single piston sliding caliper brakes and replace them with multi piston fixed caliper brake calipers.

    Here is an article that explains some way why generally sliding caliper brakes are less desirable in performance applications

    epicyclo
    Full Member

    brant – Member
    'One theory of bike geometry I have is that within a reasonable range of head angles, trail, etc, a rider can compensate for the differences because we move our weight around so much'
    That's fine until you're pointing down something steep and going over the bars.

    I agree. That's when you discover what really works.

    There are some things you can't compensate for 🙂

    MrKmkII
    Free Member

    i remember rob warner commentating for some FMX about a year ago and he was asked where it should all go. he suggested single crown forks for whips and bar spins!

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