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  1. #151
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    Here's a video of a Segway driving up and down a steep slope. Note the Segway is moving at a constant velocity and is not accelerating. However the rider can be seen to lean forwards markedly. Why does she need to do this and why does she not fall forward. Does it make sense that a faster rider or a shorter rider of the same weight would need to lean forwards even more?
    Steep segway climb - YouTube

    There is clearly some leverage involved in stopping the rider from falling forwards.. Could this leverage be categorized as the class three? And could the leverage result from the torque reaction to the motor/gearbox?
    I'm not so good at the numbers side of all this, I seem to 'see' more complex mechanics problems in my mind or feel it on the bike but struggle to work through the actual maths in detail. So I can't put the sums together here without a headache and a few hours, if at all, but I think yes, surely you lean forwards due to the torque reaction? Like countering a rearward thrust you feel under acceleration. Maybe I'm simplifying this due to not fully grasping the problem though.
    When climbing over 25-30% in a low gear, despite the force on the crank and your fwd COG, your gearing must be so low that you can wheelie out easily if you move weight back a little. The force into the crank is bodyweight times 'x' (x is your strength adding to your weight) but the gearing multiplies the torque more than your strength or body position range on the bike multiplies your weight? (--edit to clarify - I mean when it gets limitingly steep. At that point you either can't pedal as you're trying so hard to balance your weight, or can't prevent loop-out if you can pedal hard enough). Is that not a torque reaction in the same way as the segway, the segway just simplifies it?

    All I do know is that when I've 'sessioned' steep climbs with friends, what stops us is the front wheel lifting over a bump and upseting balance, looping out, or stalling against uneven ground.. or fitness eventually / rapidly! My weight is at that point, it'll always be somewhere between the axles depending on what the wheels are going over and technique and skill count for all (ie weight in right place at right time) and the variance in bikes much less. Having said that, I'm talking about fairly conventional bikes, from std 26",29" to a Jones at the most extreme example. There's plenty of times when a really high BB, short cranks and short wheelbase would help keep the power going, but that same set up wouldn't be so good in other situations.

    I guess what I'm thinking is that good technique is always needed and a bike can't do all things well. It has to be biased well toward a riding style, but always needs a lot of dynamic input - that input is the beauty of a bicycle as well as what complicates these physics questions! You can make it easier for that input to effect the bike but much depends on the rider.

    Velobike - try Goldtec in the Uk, maybe via Tazzy on STW. Oval rings at a lower cost than Rotor. Not the most durable ime so far, mainly due to uneven pressure on the teeth and burring at the larger raduis area, but not bad at all, I like them. Great on the SS.
    Last edited by james-o; 09-30-2012 at 02:46 AM.

  2. #152
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    Quote Originally Posted by meltingfeather View Post
    The dragster example has a couple of key differences: weight as a critical design driver being primary.
    The dragster example was not intended to illustrate how forces behave in a bicycle. Just an example of how torque reaction and third class levers are used on other machines.

  3. #153
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    Aren't we talking about a couple of inches here? It seems to be a moot point.
    No, YOU don't understand. You're making an ass of yourself for all of eternity.

  4. #154
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    Quote Originally Posted by wmac View Post
    Aren't we talking about a couple of inches here? It seems to be a moot point.
    Yes and no!
    When it comes to the ideal positioning of the riders Center of Gravity we are talking about only making marginal gains. Which is only in the, impress your friends with your skill territory. But if you compare the steepness of the slope the Segway is climbing, described as 45 degrees (100%) but looks more like 80%. We are in the region of twice the incline that you can ride on a mountain bike. So making a bike that could climb as well as a Segway, would be a big step forwards.

    Imagine being able to do this on a mountain bike:
    Segway Steep hill with wipeout - YouTube

    Notice that the crash at the end happens because the motors don't have enough torque to counter the forward lean.
    Last edited by GrahamWallace; 09-30-2012 at 04:20 AM.

  5. #155
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    Wow, I am surprised that Cloxxki and David Copperfield have not chimed in on this one.

    Your style of riding is far too regionalized. Those bikes would suck in the dez and just about everywhere were you need to make time between features on even terrain.

    If you so want recognition for inventing 29" wheels you should nominate Geoff to the MTBOF (mtnbikehalloffame.com), stuff the ballot box with your band of merrymen, and then bring a few bikes to Vegas for the induction next year.

    They nominated a cigarette smoking non bike riding guy this year by that method so you stand a chance of getting him in to the club but I would wager no chance on the trails. Not saying you couldn't ride them but you won't be able to hang.
    A bike by any other name is still a bike.

  6. #156
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    I am afraid that the style of voting for the MTBHOF is far too regionalized.

  7. #157
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    Quote Originally Posted by Bigwheel View Post
    ...Your style of riding is far too regionalized. Those bikes would suck in the dez and just about everywhere were you need to make time between features on even terrain.

    If you so want recognition for inventing 29" wheels you should nominate Geoff to the MTBOF (mtnbikehalloffame.com)....
    I very much doubt he needs to chase recognition. He already has that where it matters, except maybe in the small region called USA.

    As for the invention of big wheels, perhaps you could enlighten us as to who you believe had the first application of them to purpose built all terrain bicycles. (And the big wheeled fat tyred bikes of 100 years ago don't count because the geometry of those bikes was road oriented).
    As little bike as possible, as silent as possible.
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  8. #158
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    Segway video - it shows a guy leaning forward as he goes up the hill at constant speed. My understanding of the segway is that you signal it to move by leaning forward. Also, almost all the weight of the Segway is at the bottom, so the center of mass of the seqway plus rider is very low. He is leaning just barely forward, with center of mass still near the tire contact patch. The forward lean causes the Segway to tilt, but not enough to tip it forward. I don't thing there is any torque reaction involved in this.

    Leaning forward to me is similar to leaning forward on a skateboard. Going up hill, hitting a bump or decelleration causes a weight shift back, so you lean forward in anticipation of any deceleration.

    Conversely, when going downhill you lean back because a deceleration will cause a forward weight shift.

  9. #159
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    Dragster: I might be missing the whole concept of "torque reaction", but again I don't see it in this example.

    I don't think the front end of the dragster is long and weighted to counter a torque reaction. I think that front end lift comes from air lift and bumps in the road. In other words, on a perfectly smooth flat ideal track in a vacuum, the front end won't lift! (?)

    (The force of the engine is acting through the rear axle, which is higher than the front axle).
    Last edited by smilinsteve; 09-30-2012 at 11:11 AM.

  10. #160
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    Torque reaction - Torque reaction is the rotational equivalent of Newton's equal and opposite force reaction. Some good examples of this are a helicopter, where rotation of the blades tends to cause an opposite rotation of the helicopter body. Or a pneumatic nut driver, that causes a torque reaction that twists the tool in the operators hand.
    I don't see any torque reaction in the bike climbing a hill.

  11. #161
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    Quote Originally Posted by james-o View Post
    When climbing over 25-30% in a low gear, despite the force on the crank and your fwd COG, your gearing must be so low that you can wheelie out easily if you move weight back a little. The force into the crank is bodyweight times 'x' (x is your strength adding to your weight) but the gearing multiplies the torque more than your strength or body position range on the bike multiplies your weight? (--edit to clarify - I mean when it gets limitingly steep. At that point you either can't pedal as you're trying so hard to balance your weight, or can't prevent loop-out if you can pedal hard enough). Is that not a torque reaction in the same way as the segway, the segway just simplifies it?
    I still do not see any torque reaction coming into play in the bicycle hill climb. As the grade gets steeper, center of gravity moves back. The front wheel has less weight on it. That makes it more likely to lift if you pull on the handlebars, or hit a bump with the front tire.

  12. #162
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    Quote Originally Posted by smilinsteve View Post
    Segway video - it shows a guy leaning forward as he goes up the hill at constant speed. My understanding of the segway is that you signal it to move by leaning forward. Also, almost all the weight of the Segway is at the bottom, so the center of mass of the seqway plus rider is very low. He is leaning just barely forward, with center of mass still near the tire contact patch. The forward lean causes the Segway to tilt, but not enough to tip it forward. I don't thing there is any torque reaction involved in this.

    Leaning forward to me is similar to leaning forward on a skateboard. Going up hill, hitting a bump or decelleration causes a weight shift back, so you lean forward in anticipation of any deceleration.

    Conversely, when going downhill you lean back because a deceleration will cause a forward weight shift.
    Segway weight 83lbs

    Segway weight capacity: 260 pound (118 kg) rider and cargo.


    That would put the COG of rider and Segway around the top of the riders legs.

    HowStuffWorks "Segway: Car Replacement?"

  13. #163
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    Quote Originally Posted by smilinsteve View Post
    Dragster:
    I don't think the front end of the dragster is long and weighted to counter a torque reaction. I think that front end lift comes from air lift and bumps in the road. In other words, on a perfectly smooth flat ideal track in a vacuum, the front end won't lift! (?)
    Would then not the simple solution be to fit a short front end and suspension?

    Quote Originally Posted by smilinsteve View Post
    (The force of the engine is acting through the rear axle, which is higher than the front axle).
    The key distance is to have the COG at the same height as the rear axle as this would cancel out the tendency of the inertia focused at the COG to lift the front. But even then a mechanism is still required to cancel the torque reaction.

  14. #164
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    Quote Originally Posted by smilinsteve View Post
    Torque reaction - Torque reaction is the rotational equivalent of Newton's equal and opposite force reaction. Some good examples of this are a helicopter, where rotation of the blades tends to cause an opposite rotation of the helicopter body. Or a pneumatic nut driver, that causes a torque reaction that twists the tool in the operators hand.
    That's correct.

    Quote Originally Posted by smilinsteve View Post
    I don't see any torque reaction in the bike climbing a hill.
    Newton's Third Law: "To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions".

    This also applies to rotational leverage forces known as torque, where a clockwise torque will always produce an "equal and opposite" anti-clockwise reaction.

    If the rear wheel has torque, there must be an equal and opposite force transmitted to the rest of the bike. However, the exact magnitude of this force will depend on the distance away from the axle that you measure it.
    Last edited by GrahamWallace; 09-30-2012 at 12:02 PM.

  15. #165
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    smilinsteve + Graham - is a torque reaction part of how we start a wheelie? Partly deliberate weight shift, partly using a low-ish gear to initiate that weight shift from the torque at the rear wheel. And popping wheelies is one thing that stops us climbing steep hills seated - mix of COG change due to the hill and the gearing producing more torque.
    And the dragster has a long wheelbase partly to help it steer straight, I thought. They have wheelie-bars to help against the torque reaction. I'm not sure why they don't have more downforce up front via aerofoils, probably since teh torque is highest when speed is lowest. But I'm a bit lost as to the original point of all this anyway )

    If you make a great hill-climber for 40% + grades you probably have a bike that won't ride well on other trails. I saw a bike with a 20" wheel once in an off-road hill-climb event .. kept the COG in the right place as well as good pedalling position - a rubbish all-round MTB though! The bush-whacking do-all in a trials-style ethic of a Cleland is great, but I think it'd need to do so without comproming flow at higher speeds too much to gain popularity. Niche appeal is no bad thing, but marginalisation is a shame.

    Velobike, I think those old roadsters aren't that far off the geometry of a Jones in some areas, and closer again to many really early MTBs? Exact numbers are different but the basis is similar, long rake forks, slack angles, long wheelbases and grips close to in-line with the steerer etc. I rode a early 1900s roadster once, very briefly, but it felt pretty good. I think people pointing out that no-one really 'invented' 700c off-road bikes have a valid point, they evolved slowly. To me, the early days of the Tour de France was the starting point of off-road riding - big mountains, dirt and mud roads, solo riders vs the terrain - the TDR isn't much different now. Culturaly it took the Marin Co downhillers to grab popular attention,and also for road riding to be something established that there could be an alternative to. Sometimes things have to settle in one area for some people to see a real difference in something new, or react against it and forge ahead in a different direction. But some rider/designers were pretty influencial between the 'birth of MTB' and now, and would have been more so if things like tyres that need a lot of to make hadn't influenced MTB direction. I'm just waffling now, no real point to make, just my thoughts on why these bikes and Geoff's ideas are recognised.

    I remember seeing a Highpath MTB in a magazine in the 80s and thinking the go-anywhere ideas in its design were exciting. No less so than the clunkers from Marin Co, just a different appeal.
    Last edited by james-o; 09-30-2012 at 12:19 PM. Reason: typos as ever..

  16. #166
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    Quote Originally Posted by james-o View Post
    And popping wheelies is one thing that stops us climbing steep hills seated - mix of COG change due to the hill and the gearing producing more torque.
    Yes, that's why it's pointless to fit a 15 tooth grannyring. The torque produced would either spin out the back wheel or tip you over backwards.

    Quote Originally Posted by james-o View Post
    I thought. They have wheelie-bars to help against the torque reaction. I'm not sure why they don't have more downforce up front via aerofoils, probably since teh torque is highest when speed is lowest.
    Long nose dragsters don't need wheelie-bars, as there is no need to have two mechanisms that do similar things. Modern dragsters do have aerofoils, though unlike torque reaction arms they only create downforce when the dragster is moving fast.

    Quote Originally Posted by james-o View Post
    But I'm a bit lost as to the original point of all this anyway )
    This all started when I suggested that moving the COG further away from the rear axle would reduce the torque reaction and so reduce front wheel lift.

    As moving the COG forwards would also reduce the weight on the rear wheel, it might to be more useful to move the COG upwards. And that this might explain why Clelands ridden out of the saddle climb so well.

  17. #167
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    Quote Originally Posted by james-o View Post
    ...If you make a great hill-climber for 40% + grades you probably have a bike that won't ride well on other trails...

    The bush-whacking do-all in a trials-style ethic of a Cleland is great, but I think it'd need to do so without comproming flow at higher speeds too much to gain popularity. Niche appeal is no bad thing, but marginalisation is a shame...
    I share that reservation, but I won't know for sure until I've tried a bike like that. Hill climbing is quite a specialised niche but there are quite a few people who really enjoy it. For example, I place a bike's climbing ability above its descending ability. Tests I have done to improve my lap times showed me that setting the bike up for climbing could save me 3 minutes in a lap, but only cost 1 minute on the descent (obviously that's very subjective and on one course, but it did work for me). The Cleland style bike is just as much a horse for its course as a downhill bike is for its. Maybe we need an uphill riding greasy hill championship



    Quote Originally Posted by james-o View Post
    ...Velobike, I think those old roadsters aren't that far off the geometry of a Jones in some areas, and closer again to many really early MTBs?...
    All the old roadsters I have ridden are great on the road, but truly horrible on technical terrain, but naturally I haven't ridden everything. The problem with the old roadsters mainly lies in the front fork rather than the frame geometry, so it's fixable.

    Here's some vintage pics of bikes with big wheels:

    A design for the future, P437 Cycling 1931

    [IMG]



    Racing and record breakers:


    Coolgardie 1896


    Francis Birtles, Warren & Robert Lennie, at Eucla WA, 1907. Lennies attempting Perth-Sydney record

    (The last 2 pictures are from the 1980 book,"The Bicycle and the Bush" by Jim Fitzpatrick, which is basically about the use of the bicycle in Australia from the 1880s to early 1900s)
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  18. #168
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    Quote Originally Posted by GrahamWallace View Post
    Segway weight 83lbs

    Segway weight capacity: 260 pound (118 kg) rider and cargo.


    That would put the COG of rider and Segway around the top of the riders legs.

    HowStuffWorks "Segway: Car Replacement?"
    Ok and I think the top of the riders legs are pretty much over the tire contact patch.

  19. #169
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    Quote Originally Posted by Bigwheel View Post
    Wow, I am surprised that Cloxxki and David Copperfield have not chimed in on this one.

    .
    Yes it would be fun to hear from other physics nerds

  20. #170
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    Quote Originally Posted by GrahamWallace View Post
    Would then not the simple solution be to fit a short front end and suspension?
    Well, there have been short dragsters. I tried to find more info on the length of dragsters but admit I'm not really clear on the reason for the length, but I think it has to do with lateral stability. Since they don't have to corner, there is no limiting length in that respect. Shorter dragsters could have the same downward force on the front (more of the engine weight with less moment arm).



    The key distance is to have the COG at the same height as the rear axle as this would cancel out the tendency of the inertia focused at the COG to lift the front. But even then a mechanism is still required to cancel the torque reaction.
    You may be right about the force needing to be at the cog to avoid any moment, but if it was, then surely there would be no need to cancel a torque reaction since a force at the COG could cause no rotation at the COG?

  21. #171
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    Quote Originally Posted by Velobike View Post
    I very much doubt he needs to chase recognition. He already has that where it matters, except maybe in the small region called USA.

    Then why are you guys always coming here to toot you horn? If the us is such a small region then what does it matter what we think?

    As for the invention of big wheels, perhaps you could enlighten us as to who you believe had the first application of them to purpose built all terrain bicycles. (And the big wheeled fat tyred bikes of 100 years ago don't count because the geometry of those bikes was road oriented).
    To me there was not a true fat tire available for 700c rims until the advent of the "tire" in 1999. Until the you were doing your wandering about on 28" wheels which is not a bad thing, just not what developed in to the real thing.

    As I keep trying to point out mtb's are more than about plonking around in the glen. They are an efficient tool that should be able to handle a variety of terrain. Your bikes don't strike me as such but I am glad you all are having fun with them.
    A bike by any other name is still a bike.

  22. #172
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    Quote Originally Posted by GrahamWallace View Post
    That's correct.



    Newton's Third Law: "To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions".

    This also applies to rotational leverage forces known as torque, where a clockwise torque will always produce an "equal and opposite" anti-clockwise reaction.

    If the rear wheel has torque, there must be an equal and opposite force transmitted to the rest of the bike. However, the exact magnitude of this force will depend on the distance away from the axle that you measure it.
    I don't get why you are splitting the force out of the torque or what the justification for doing so. Equal and opposite means the torque reaction is the same as the applied torque... whether it is made of a small force and a large arm or vice versa is inconsequential (unless you are building a dragster and the combination of short and heavier is a detriment to acceleration, among other things).
    Again, in your own example of COG at infinity the bike tips immediately upon input and you acknowledge this. How is that not a direct contradiction to your argument?
    It started for me when you said that raising COG equalizes weight distribution between the wheels, something I still dispute and which is very easily proven false.
    I don't think we're going to get anywhere, but it's been a pleasure.
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    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  23. #173
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    Quote Originally Posted by Bigwheel View Post
    To me there was not a true fat tire available for 700c rims until the advent of the "tire" in 1999. Until the you were doing your wandering about on 28" wheels which is not a bad thing, just not what developed in to the real thing.

    As I keep trying to point out mtb's are more than about plonking around in the glen. They are an efficient tool that should be able to handle a variety of terrain. Your bikes don't strike me as such but I am glad you all are having fun with them.
    I think I get what you're saying, if your mtb riding is centred around fast descents then you're right. I don't know about Graham but my riding is on all sorts of terrain, not just "plonking around the glen". Frequently I'll ride 20 or so miles just to get to the trail, come out somewhere on the other side of a mountain and then ride home. Often there will be stretches with no actual trail, just sheep pads or deer tracks, or a scramble over some scree carrying the bike.

    For your interest, the 28" wheels with a 2" tyre are the same size as a 29er with a 2.35", but most mountain riding in the UK prior to the mtb era was done on 27" rims, often fitted with 1*1/2" tyres. If you're interested in knowing more about traditional UK offroad riding, look at the the Rough Stuff Fellowship which has been going since 1955.
    As little bike as possible, as silent as possible.
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  24. #174
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    Graham,
    I'm starting to see some of what I had missed earlier. I think the term "torque reaction" was throwing me off, but if a force acts away from the center of gravity, it creates a moment.
    In my drawing, the front wheel is just starting to lift, so it has a normal force of zero. The rear tire contact patch is the fulcrum around which the COG is rotating.
    B is the vertical distance from the COg to the fulcrum and A is the horizontal distance to the fulcrum.
    F is the forward driving force from the tire/ground force, which we can say is acting at the COG.
    Mg is gravitation force acting on the center of mass, which I have broken into Mgx and Mgy (rather than throwing around sines and cosines )


    The sum of moments around the tire contact patch are zero at the time right before front tire lift, so
    M clockwise = M counterclockwise

    The clockwise moment is:

    Mgy (A)

    The counterclockwise moment is the sum of the moment caused by the drive force and that of gravity pulling the weight at the COG backward:

    Mgx (B) + F(B)

    The point of all this is to see what happens if you move the COG upward. distance A stays the same and distance B becomes greater at COG 2. So the counterclockwise moment becomes greater, and the wheel is more likely to lift.

    The only way to counter that lift from the higher COG is to also move it forward, so that the clockwise moment again balances the counterclockwise moment.
    Attached Thumbnails Attached Thumbnails Cleland: The original big wheeled off-road bicycle?-bicycle-free-body-diagram.jpg  

    Attached Files Attached Files

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    Quote Originally Posted by Bigwheel View Post
    To me there was not a true fat tire available for 700c rims until the advent of the "tire" in 1999. Until the you were doing your wandering about on 28" wheels which is not a bad thing, just not what developed in to the real thing.
    1999 WTB Nanoraptor dimensions: Otherwise known as "the tire"

    700x52c (marked size)
    A 700c rim diameter is 622mm add 52mm x 2 for the additional diameter of the tire to get an overall diameter of 726mm or 28.5826771653852 inches.

    So it appears that the worlds first 29er tire only measures 29inches when rounded up to the next integer.

    In Comparison:
    Nokia Hakkapeliitta snow tire dimensions
    (The tire used by Geoff Apps on his 1981 700c rimmed Cleland)

    700x47c (marked size)
    A 700c rim diameter is 622mm add 47mm x 2 for the additional diameter of the tire to get an overall diameter of 716mm or 28.188976377983202 inches.

    That makes the Nokia 10mm or 1.4% smaller in diameter

    A crucial difference?

    From the Cleland viewpoint it means 5mm more mud clearance.
    Last edited by GrahamWallace; 10-01-2012 at 09:21 AM. Reason: Typos

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