rebuilding my wheel

a long time ago i asked on this forum what length of spokes i should use to rebuild my trials wheel, i got some varied answers. and when i look back at the thread its a bit confusing.

now my monty rim is starting to split at the spoke nipples and i`d prefer to replace it before it fails, because it may damage other parts in the process. being a cheap skate i intend to build the wheel myself and take it to an expert to tension it.

so, simply,
who built a trials wheel with a profile hub and an alex dx32 rim?
what size spokes did you use? (length and gauge)
and how many crosses.
and what make of spokes.

i cant use the spoke calculator from this computer for some reason. and besides i dont realy trust it.

thanks,

I’d still go with what I put down at the end of that thread:

here.

thanks u-turn,
unfortunatly im realy fussy for details when im embarking on something new.
so i`ve got a few more questions…

what you said was:

We at the Ordinary Bike Shop just built two of these. Profile >hub, Alex DX32 19" rim, 4-cross. The rim ERD was 376, the >spoke length was about 185mm, spokes were 14g of type DT >Swiss.

was that spoke length exactly 185mm?

i ve never bought spokes before so i don`t know if they come in 1mm increments or .5mm or whatever.

and did you use DT nipples?, i hear that these are a bit smaller than normal. and require the spokes to be 5mm longer.

i ned to know all the details so i can walk into francophone bike shop and walk out with the spokes and nipples and be sure they are the right size.

thanks

i realy need to know

I didn’t order those spokes but I’ll talk tomorrow to the fellow who did and get right back to you.

186mm, by my calculations… assuming I’ve managed to find the correct dimensions :slight_smile:

Spokes for mountain bikes tend to come in 2mm increments. Presumably for smaller wheels you get smaller increments…

I don’t think you need to alter the spoke length due to the nipples, and certainly not by as much as 5mm. I think the spokes should extend the same distance regardless, i.e. protrude just into the rim.

Adrian.

i found a guide to wheelbuilding here:


somebody else might find it usefull too. its from a bmx site.

also, does anybody know anything about this “interlace under the third” thing that he talks about
apparently to make the wheel more resistant to grinds,
if this works shurley it would be a good plan for trials wheels too.

I don’t see how that would make the wheel grind-resistant. Grabs and grinds abrade the spokes and catch crossings; this technique increases the number of crossings.

That last photo is pretty unconvincing, as far as whether the wheel is built well or not. There are large kinks in some of the spokes and there has been no spoke line correction at the nipples. There are huge curves in some spokes between crossings. Although he states that this is a finished wheel, it looks like a wheel that has not been tensioned yet. I think I’ll stick to the standard texts.

i think the wheel in the photo is untensioned,

the guy obviously knows what he`s doing though, look at the rest of the site.
he designs all sorts of bmx stuff. i spoke to him via email a while back when i bought one of his g.l.a.n.d. devices to protect my hub from grabs and grinds. he can ride a unicycle too aparently.

my current thinking is to build the wheel myself and get it tensioned by a pro. but first i`m going to find a decent wheel builder and ask him whats going to work out cheaper.

Ok, so with a alex dx32 3x profile 36º wheel, I used 176’s. that’s DT straight gauge. not problems at all, I however havent really gotten to test it yet. Just incase you havent figured it out yet, or for future reference.

How true does a unicycle wheel actually have to be? Assuming you’re not running brakes.

I’d’ve thought you could get away with quite a lot, assuming you can get the general tension approximately right, for strength purposes.

Well we don’t have the info (sorry), but I have never found Roger’s spoke calculator to be wrong, giving 186mm for a 4-cross. I personally wouldn’t hesitate to order spokes based on that information. I ignore the nipple length thing.

A unicycle wheel for a uni without brakes can get away with more radial and lateral wobble than one with brakes. However, in general, wheel strength is a function of:

  1. wheel geometry
  2. rim geometry and quality
  3. spoke quality
  4. average wheel tension
  5. max spoke tension
  6. min spoke tension

If one assumes that (1) is good, and that (2) and (3) are valid, then the wheel strength depends on average wheel tension (4)primarily, and max spoke tension (5) and min spoke tension (6) secondarily. (5) is important because if (4) is high, then the spoke with the highest tension is the one most likely to fail due to overstress. (6) is important because if (4) is too low, then the spoke with the lowest tension is going to fret most and fail (at the spoke head) soonest.

So not only is average tension important, but also keeping the max and min as close to the average as possible. Since by assumption (2) we have a “perfect” rim, basically excursions from average will show up as wobble.

Although this is a simplification, it is a useful one. Basically it says that with a good wheel design and good components, all the spokes should be nearly the same tension when the wheel is true. Conversely, if the wheel is not true, then the spokes have variations in tension that weaken the wheel.

At the rim joint there will almost always be tension excursions that are unavoidable.

166 2 cross
174 3 cross
183 4 cross

I’d go with 3 cross - 4 cross wont work unless you re-drill the rim holes at an angle.

Leo White

Quoting myself…

You can see what I mean about 4 cross not being a good idea on a small rim.

http://www.unicyclist.com/gallery/albun41/P1010017

The nip*les emerge at 90 deg but the spokes bend away towards the hub.

This makes it a pain to tension and introduces a weak spot.

If you use a larger flange hub like a suzue I’d use 2 cross.

Leo White

These are my pics and are placed in the gallery precisely for the opposite reason – to show that 4x on a trials uni is practical. There is not any additional work or trouble to tension this wheel. It does involve spoke path correction, but that’s normal for any wheel (you do spoke path correction, don’t you?). There is nothing weak about it; this wheel has done at least 3 foot drops and tons of stairs with no problem whatsoever – no loss of trueness or damage of any sort.

If you read the literature you will see that the angles between nipple and spoke are common and straightforward.

Redrilling the spoke holes would accomplish nothing because the seating for the nipple flange would not change.

2 cross in a trials wheel is not a good idea, however; the minimum I’d use is 3 cross.

thanks for the advice everbody,

basicly i know nothing about wheel building,

i can see however that i`m going to have to trade off the number off crosses against the angle of the spokes as they interface with the rim/nipples.

i can see that extra crosses give me laterral strength,
and that i don`t want to have too great a spoke angle because it will cause failure at the rim,

now i have to decide what my priority is,
on my current wheel the point of failure is the spoke nipples pulling through the rim. this would point to the spoke/rim interface as being more critical.
however the wheel is also bent. which i want to avoid too.
so i need plenty of lateral strength such as 4x would priovide.

since the wheel builders in the know seem to disagree about the order of priority between these two aspects,
i`m going to ask has anybody ever killed a profile/alex wheel? and if so what was the mode of failure?

in some ways though i suspect that my wheel is overspecified anyway, but i find that the quest for knolege is intersting sometimes.

Apologies for not attributing…

I still think that introducing an unnecessary kink in the spoke is a bad idea.

4 cross looks cool - I’ve got it on 2 20" unis, a 24" muni and a 29er but those are all 48 spokes so the spoke angle is exactly the same as 3 cross on 36.

I had to use 4 cross on my giraffe when I replaced the rim because I couldn’t remove the spokes due to the welded sprockets.

Leo White

evilewan – The Monty rim is notorious for pulling through the rim. The Alex is not.

leow – That’s cool that you figured out how to relace a giraffe wheel without unwelding. I’m expecting to build my first here soon. The advice I currently have is to build the wheel, then attach the sprocket and weld. Do you think it would be possible to build the wheel after welding?

do you really have to weld it to the hub? what we always did was weld the cog to a freewheel, weld the freewheel in place, and then loc-tite the frozen freewheel to the hub. we’ve never had one spin off after loc-tite and the apropiate drying time. however I think we’ve had a couple cog’s welds break on the freewheel… but those are easier to replace. and if that makes any sense.

I had the same trouble that Ewan had - spokes erupting through my Monty rim. My solution was to rebuild the wheel with a Profile hub and Alex DX32.
I just picked up my rebuilt trials unicycle wheel 1/2hr ago. The spoke calcuator on unicycle.uk.com was right on the money for spoke length (177.47mm predicted for 3-cross; 177mm actually used.)
The guy who rebuilt my wheel said that reason spokes were pulling through the rim was likely to be because of pedal grabs putting extra stress on the wheel. Has anyone else experienced the spoke nipples pulling thru their Monty rim problem without doing pedal grabs? If so then we know that it’s a problem with the Monty rim itself, rather than how the rider treats it.

Tony Melton

It seems to me a little thought shows that this is incorrect. What is a pedal grab?

  • A hop
  • an unloaded 90 degree rotation to get pedal in place
  • landing on platform with weight on pedal
  • side-to-side unloaded balance motions
  • unloaded 90 degree rotation to get foot on other pedal
  • pull on seat and hop up to rubber
  • landing on platform after ~ 1 foot unloaded hop
  • subsequent micro-hops for balance.

See, there is nothing here to stress the wheel any more than riding along the sidewalk or the height of the initial hop.

It seems to me that the Monty design is flawed. They should have used either eyelets or thicker material around the spoke holes. Since the Monty tire is infamous for not fitting the Monty rim well, we could surmise that the design process in general was not up to, say, the Alex design process in terms of quality.