psycholist

The loading on the threads from the top cap and the location of the last engaged thread is almost totally irrelevant to the failure I'm talking about. What is relevant is the increase in the stress concentration at the root of the thread cut into the steerer caused by the geometry of the material. I'm not sure if you're familiar with threaded headsets, but the two most common failure locations on forks with threaded headsets was within the threaded area or within 20-30mm of the top of the fork crown as these are the highest stress areas in the fork (Peak bending is at the lower headset cup, but that's usually reinforced enough that peak stress occurs either at the root of the threads or just above the reinforced area near the fork crown - peak stress is where an overload failure will occur or where fatigue cracking will begin. Fatigue cracks need tensile stress, while overload failure stresses can be tensile or compressive). Fatigue type failure was most common at the threaded area, while overload or fatigue would cause the failure near the crown. The threads being cut on the inside rather than the outside of the steerer tube will reduce the stress somewhat (Peak strain (And stress) will always occur at the outside of a structure loaded in bending) compared to cutting them on the outside, but I wouldn't trust an internally threaded aluminium steerer unless the threaded area sees no bending stress - i.e. is well within the area clamped by the stem. The failures I've seen were all in steel as aluminium isn't hard enough to allow threaded headsets with standard threads to be reliable AFAIK. Steel has much better resistance to fatigue failure than Al in the first place too. And as for most joining methods between the fork and steerer being weaker than a steel/Al tube with a thread cut in it - that would be almost exactly wrong... Star nuts, while they create scratches in the steerer, will remove less material and unless you use a very long bolt, remain within the area clamped by the stem, which doesn't allow bending to be felt by the headtube the stem has clamped as well as superimposing compressive stress on the headtube, further reducing the peak tensile stress in that area. Headlock type systems create no extra stress anywhere on the steerer and are the best solution unless you're desperately worried about saving weight.

Provided the threads don't extend to anywhere on the steerer that's stressed in bending (If the threads end within the stem clamp, which appears to be the case with the forks being discussed) there's no issue. If they do then fatigue cracking is extremely likely at the root of the thread where the bending moment in the steerer is at its peak.

It's ok in the winter when there are no wasps out, but in the summer I'd expect the insect life (and various small furry animals) to be very interested in your bike if it smells of food...

20mm of thread kind of limits the amount you can cut the steerer down by then... Though trials frames probably have nothing like the headtube length range you see in XC/DH bikes, so it may not be a limiting factor, though 200mm seems a little long to be within 20mm of what most frames need...

If the thread is within the height of the stem clamp then it's not an issue - if it's threaded past the bottom of the stem, the bending between the stem and the headset will lead to fatigue cracking a lot quicker than with a constant cross section tube of the same material (Even if the thinnest point in both tubes is the same thickness). If the thread is rolled rather than cut or the surface is shot peened after cutting it will last better than if it's left smooth too. Only having the thread go 40mm ish down the fork steerer will cause people who want to cut the steerer shorter to fit their frames problems fitting the top cap though. As for a threaded top cap loading the headset better, once the stem has been clamped into position you can take the top cap off and it will have no effect on the load on the headset bearings as the stem does all the work in keeping the headset tight.

Does the top cap screw into the inside of the fork steerer? I'd expect a few nasty fatigue failures if this is the case - not as bad as externally threading the steerer of course...

Once it goes black it never grows back...

I bet Ryan Leech uses Maple Syrup... Given that honey is water soluble I'm guessing that at the first sign of wet the braking will disappear though, probably no worse that tar, but given a grind needs less minding and isn't as sensitive to the wet for the Irish/UK climate there is no other choice for me...

A friend of mine gave himself a nasty shinjury a few weeks back. There were two cops in a squad car watching and they came over and offered to take him to hospital. He declined, and they said they'd be passing back there in a half hour or so and if he changed his mind later the offer was still open... Can't get much cooler than that... The cops usually have better things to be doing than whinging at trials riders - rent a cops on the other hand can be a real pain...

Street riding on moto trials bikes is awesome though - have a look for a biking film called 'Out of Section' - It's pretty much all street riding on mototrials bikes. They were even going for 180 drop offs pivoting on the front wheel on motorbikes... I reckon you'd get arrested very fast trying that in Ireland - they filmed Out of Section in France mostly I think...

That's still only a slight modification to the overall gap distance though - weight shifting on the bike including pushing the bike forward will add a foot or two onto a gap, but regardless of what happens at the landing, the flight remains parabolic...

Stretching the bike out to a landing increases your gapping distance over the theoretical distance suggested by your takeoff velocity. This will add to the gap length, but by the same amount for each gap. Because the bike and rider are separate masses which can be moved relative to each other, a more complex model (Based on exactly the same equations as before) is needed if you want to account for movement between the bike and rider. Regarding the difference in gapping range where there's a drop from the takeoff to landing all that extra calculation will tell you nothing new though as for almost all of the flight the bike and rider still follow a parabolic path.

Once you have the flight time you should be able to solve for the parabolic path. If you're to land balanced, the centre of gravity of the bike + rider must end up above the contact patch of the tyre. If there's a change in the height of the combined centre of gravity this should be added to the gap height change in the equations, but I don't think it needs to be to affect the usefulness of these equations as a guideline. Also given that most people extend the bike into the landing, pretty much everyone will gap further than their initial takeoff velocity would suggest (But that's a fixed offset and won't be affected too badly by the length of the gap unless your technique changes drastically depending on the gap you're doing). Once the bike and rider are in the air gravity is the only force acting on them (Gyroscopic forces from the wheels spinning will play a very small part if there's spin involved in the hop, but can safely be ignored at trials speeds), just because it doesn't look like an obvious parabola doesn't mean that's not what's happening though. If the centre of gravity of the bike and the centre of gravity of the rider are averaged you'll find the average following a perfect parabola every time (Unless outside forces such as wind are also acting on the system).

Look up ballistics calculations - anything flying through the air with only gravity acting on it will follow a parabolic path. The combined centre of gravity of you and the bike will follow a parabola as you fly through the air during a gap. The usual way to solve for distance is to solve for the time of flight in the vertical direction - initial vertical velocity component u, acceleration due to gravity, -g (Negative for coordinate system with vertical direction positive), time of flight t, and height change between takeoff and landing, s, using the equation: s = ut - 1/2 gt^2. The value of s will be negative if the landing is below the take off height, zero if they're level or positive if the landing is higher. Rearrange the equation to the standard quadratic form ax^2 + bx + c = 0 and solve using the quadratic solving formula to get the time of flight, t. To find the distance take the horizontal component of the take off velocity and multiply it by the time of flight - say 4 m/s * 0.5 s = 2 m... The problem with this is it's hard to measure the initial take off velocity, the peak height of the parabola (Given it's the average of the centre of gravity of the bike and rider this is hard to measure even on video) or the flight time and one of these is needed (Along with the dimensions of the gap) to define the shape of the parabola. Flight time measured off a decent frame rate video is your best chance of getting data to put in to the equations... Here's what NASA says about the whole subject: http://exploration.grc.nasa.gov/education/.../ballflght.html

Head for your local petrol station and use their air compressor to blow air through the brake - this will evaporate the water out, leaving the internals dry and ready for oil... I was thinking about water bleeding my brakes, but then I realised they were working fine as they were. Having tried water bleeds on other people's bikes, they do feel better (less lever drag). I'd change to water bleed if the brake leaked or I was bored some day...

Duel trials would lead to a lot of 'trackstand offs' as both riders get to the entrance to a line they both want at about the same time... There'd have to be judges calls on who should give way and stuff - could be a bit of a nightmare... Alternating races and standard sections could work though - definitely looks class in indoor mototrials - but then trials motorbikes have a selection of gears, while trials bike racing would still be pretty slow unless you just point everyone down a hill, and I'm pretty sure racing bike down hills is covered in other disciplines...

Having used platfom pedals and V8's I'd say your chances of shin carnage are significantly less with the V8's for two reasons; firstly, you're a lot less likely to slip off in the first place (A lot of platform pedals are high enough off he pedal axle that they can roll out from under your feet) and pedal pins don't seems to do as much damage as beartrap pedal cages when they do hit.

Presumably every time you view the topic to read the replies it adds another view to the tally...

Having used the Hope XC hub for XC I'd stay well away from them as they're not even strong enough for that. Freehub bearings went draggy in months, shoulder on the axle to space the freehub and hub bearings deforming, damage on the freehub from the flex in the hub axle allowing the ratchet ring to gouge the freehub, visible deformation in the freehub spline (The cassette had to be hammered off - this was a steel freehub body BTW!!) and the ratchet pawls were also deformed... Hope informed me that the hub wasn't suitable for trials when I contacted them about the hub damage (Even though I'd never used it for trials), presumably if you ride these hubs heavily they fail the same way as trials riding makes them fail.

Possibly a fun/sport class might be a plan to get new people in. For XC races there are usually two starts - the sport class races first, does about 2 laps of the course and then when they've finished the expert/masters/elite (At least 2 or 3 times the sport race) etc. are started, so a sport rider can get a bit of (Not too serious) racing in, though there is still the odd twat who takes racing the sport class seriously. The great thing is that you can then watch (Or help with marshalling) the elite race afterwards. Fitness is a big issue for competitive trials riding though - I'll quite happily pedal a mountain bike up 1000m of altitude in 1.5 hours (Did it last week - had to climb the same mountain twice, once from each side), ride street for hours hitting stuff over and over again, but put me on a line of rocks 5 or 6 bike lengths long with no flat surfaces and awkward hops and gaps between them and I'm ruined before I've done the line once... A difficulty a lot of people probably have, certainly I see it, is that all the photos I see from trials competitions show people on obstacles that I will never be confident enough to risk or skilled enough to get away with. The natural tendency is of course to photograph the elite riders as they're the most impressive photographs, but it means I have no idea what level the non-elite sections are like and what level of riding is expected. A few videos of people doing the easier sections would be very good to help with this. I know it's already been said that you can pick your class on the day, but I still don't know if there's a class low enough for the level I'm at with natural riding - If I was to go to a trials competition I'd have to travel from the west of Ireland, so I'd want to be pretty sure there was something I could do before committing to traveling.

Next question is does anyone brake with their middle finger rather than index finger? I discovered that with 4 finger levers on cantis on the 1989 Specialized I bought recently, middle finger braking is better - still frightening how little power cantis have though, but on anything else it doesn't work as well as index finger braking. Does everyone have a big gap between the grips and the brake lever clamp so the lever only just reaches their finger and won't catch your other fingers when it's pulled to the bar?

I could use one in gold... ...and a bong and a blitz... or crepe and a pipe...

The Deng freehubs seem to be a bit variable in terms of reliability - they look to be pretty well made though. Awkward to build into a wheel compared to most hubs as the spoke holes are a very tight fit, but that should mean less fatigue failures in the built wheel. A lot of people on this forum complain about them being unreliable and a friend of mine (The only person I know who runs one) had his freehub start to spin foward under power - the ratchet ring was moving in the hub body, replaced within a week under warranty, but if it had broken loose on the edge of something it'd have been very nasty... Chris King and Pro II's are the only back hubs that seem very well regarded for trials - nothing in the price range you're looking in is that trusted. I run a fixed Deng hub with an ENO freewheel on the cranks and prefer it to freehub style hubs though.

Since Wellgo make the DMR pedals that might not be a big surprise... I love the greaseport on the V8 though - I got 5000 miles of XC riding from one set before I had to tighten the bearings...

DMR V8's because anything else I've tried is nowhere near as good to grip on and V12's develop play in the crank side bushing pretty quickly from new - and I don't really care about the weight saving.