Threads Gone On Trialtech Cranks

[psycholist]

In my experience all the threaded trials cranks I've used have failed at the threads - I would say half of those have been my own fault, but I did a lot less maintenance on cranks while I ran Middleburns and had no failures whatsoever in at leas 4 years using them. I've done for a couple of Echo CNC cranks, and 2 trialtech cranks in the last 2.25 years for comparison. I will say I'm slightly heavier than I was 5 or 6 years ago, and riding harder, but I'm not that much heavier and am not riding that much harder.

Firstly all the screw-on cranks I've used feel like tightening the pedals hard will pull the threads out of them (I have a proper pedal spanner, but I tighten pedals into Shimano and Middleburn cranks a lot harder than I'm wiling to risk tightening into trials cranks because they're just plain soft), secondly the natural tightening action usually seen in pedals on bikes ridden long distances due to pedalling forward all the time doesn't occur as much in trials, leading to the pedals loosening because all they see is massive force for a small portion of the pedal stroke as well as enormous peak loads from landings, and thirdly the threaded interface for the freewheel to sit on is badly compromised by having two manufactured thread diameters for the cranks available and having certain cranks (Especially the Trialtechs) which don't have clearance to run a bashguard with a wider rim than it's base without a spacer or an angle grinding job on the bashguard. It's the spacer put between the crank and bashguard in my last bike build that lead the threads to strip off my current trialtech crank. Thanks to the post taking well over a week to get from the UK to Ireland at the moment I'm into my third week of having no working trials bike even though the crank was returned in the post the first working day after it failed all because of a poorly thought out crank design.

The only good thing about the softness of trials cranks is that it tends to allow them to fail by bending rather than snapping, but my experience has been that the threads crap themselves long before either type of failure occurs. At least thread failures don't usually cause very nasty crashes, but it's not like Middleburns are failing all over the place and they don't get the thread failures either.

[Mark W]

There are a fair few bashrings you can buy that work on the TT cranks with no problems at all. I haven't had to do anything to the few different ones I've put on, at any rate.

If memory serves, you're (Psycolist) running an Eno too which doesn't really help things at all? I'm pretty sure if, with your Middleburns, you were running pedals that were slightly undersized they'd probably do a number on your cranks too. I know it's not the same thread, but you're effectively using a part for your bike that isn't made to the same standards as all FFW cranks out there, and then blaming the majority on the minority? Any 'normal' freewheel such as the Echo TR or SL will be fine, and if you swap up your bash (or just mod your current one) you'd have a reliable setup that will last you fine.

[Filo]

if the enos arent correct for trials cranks why do some shops sell them?

they shouldnt be avaliable from a trials shop unless they fit correctly,it would reduce the warrenty claims.

Edited April 15, 2010 by Filo

[monkeyseemonkeydo]

if the enos arent correct for trials cranks why do some shops sell them?

Because they were made for trials? The question is why have they got a slightly oversized thread? Not that it makes that much difference of course- as said I've been running my Eno on various cranks for over two years with zero problems.

[psycholist]

I'm running an Echo SL on my current bike based on Tarty's recommendation and it's absolutely excellent . The ENO was on my previous bike. The undersized pedal axles were a set DMR V8's, but I only assumed they were undersized based on the crank threads failing a little too often, I've never heard of this problem before. Replacing the pedals on the previous bike does seem to have fixed it as it has lasted for longer than it ever did before, but the guy I sold it on to weighs probably 20-30 kg less than I do, so it'll be a quite a while before he has similar problems.

[Mark W]

Cool, glad you like the SL - they really are awesome freewheels

[Filo]

i know there a trials freewheel,ive ran on with TT cranks for a year trouble free,i bought the same set up and the cranks stripped within 4 hours.

i think i got a bad set of cranks personally.

the reason the threads oversize is because they use a US standard not the ISO standard,Dam Americans making non conforming parts since 1880.

Edited April 15, 2010 by Filo