Two questions:
Which do you recommend for a trials wheel and why: A 3 cross or a 4 cross?
When was the last year profile made silver cranks with a regular bold head instead of an alan wrench to tighten them on? (they have a spider as well)
Mark and I were trying to figure that out tonight. Thanks.
Seager…
I built my old trials wheel 3 cross. With 4 cross, the spokes may enter the rim at a weird angle, on such a small rim. But I could be wrong.
I have no idea when they were made. 
Mojoe
Yea, the spokes are actually digging into the hub flanges on a 4-cross I’ve got. It’s kind of crazy.
4 cross will give you a stronger wheel
I don’t think profile ever used a hex head bolt
I say forget about the 4x spoke pattern and go with 3x because they are the most comon and if you make a wheel with a lets say and alex dx 32 rim with stainless spokes you should bend any crank on the market before you ruin your wheel unless you land realy bad but then it will be a bone that breaks
Onetrack, I’ll post a picture if you want but they are standard bolt heads that you use a socket wrench on. I wasn’t able to get a clear story about their origin so I was just wondering how old they are. Just for the heck of it. I didn’t know they existed either. They also seem to be 140s…
Use 3 cross, it is plenty strong. 4 cross sometimes runs into a problem where the spokes are leaving the hub at too close to tangential.
I’m pretty sure profile doesn’t (and hasn’t) made 140s.
Is there a reason why you want the ones with the hex head?
well, I have the ones with the hex head, I’m just wondering what their history is. I don’t know that they are 140’s, but when held up next to KH140s they sure look the same length. I know they’ve gotten down to 145 in the past (and make some now)
Yeah, I just remembered that my friends profiles on his bike have the hex head. Dunno how old they are though. I think the shortest profile can make cranks is 145 for some reason having to do with their machines not going small enough or something.
I’d like to see a pic. there are quite a few profile look alikes floating around that use hex bolts (which would explain it being a 140mm crank). Also, it’s not like the allen bolt has to be used. A previous owner could have swaped it out for a hex bolt.
I would just like to note, that going 4 cross wont be any harder to build, or cost any more than 3 cross, but you will end up with a stronger wheel. And what if you do “land realy bad” wouldn’t you rather know that you are using the strongest lacing patern?
The fewer the crosses, the stiffer. the more crosses, the stronger. radial being the stiffest and weakest, and 4 cross being the strongest but having the most flex.
19" wheels are really stout, which is why 3 cross will hold up under abusive riding. but if you would like your wheel to be truer, longer, I’d go 4.
I haven’t seen evidence that wheels with fewer crossings are stiffer. I don’t see why they would be so, either; certainly radially spoked wheels would feel quite loose on a unicycle, due to wind-up.
I also don’t think four-cross is inherently stronger than three-cross; if four-cross causes weird spoke angles at the hub or rim, it will put stresses on the spokes which will be more likely to lead to spoke failure.
Re: spoke lacing and profile crank question
On Thu, 20 Oct 2005, tholub <> wrote:
>
> I haven’t seen evidence that wheels with fewer crossings are stiffer. I
> don’t see why they would be so, either; certainly radially spoked
> wheels would feel quite loose on a unicycle, due to wind-up.
Fewer crossings are radially stiffer.
Radial spokings are (as you note) tangentially much less stiff than a
tangential (or near-tangential) spoking.
The radial stiffness is almost purely a function of spoke length. As
to evidence, you can read Jobst Brandt ‘The Bicycle Wheel’ which
includes both experimental and theoretical examination. If you’re
prepared to accept purely theoretical work I have some analysis
results at http://www.astounding.org.uk/ian/wheel/patterns.html.
However, the stiffness of the ‘rigid’ parts of the wheel (hub,
spokes, rim) pale into insignificance compared to the behaviour of the
tyre. While the wheel may be stiffer, what you ‘feel’ radially will
be the behaviour of the tyre.
> I also don’t think four-cross is inherently stronger than three-cross;
I think it is, though only slightly - a good three three-cross will
probably be better than a merely average four-cross.
> if four-cross causes weird spoke angles at the hub or rim, it will put
> stresses on the spokes which will be more likely to lead to spoke
> failure.
No it won’t (or not directly) - spokes rotate at the hub and have a
spherical seating at the rim (on the nipple).
Where there is a problem is that the spokes shouldn’t be beyond
truly tangential at the hub (ie, shouldn’t be tipped over more than 90
degrees from radial). The limiting pattern is a function of rim
inside diameter and hub spoke-hole pitch circle diameter, but for
reasonably foreseeable unicycle geometry, 4 cross doesn’t work.
For example, if the inner diameter if the rim is 490mm, and the hub
ends of the spokes are on a 60mm diameter circle (values taken from my
20" Sem), then 4X would have spokes at 87 degrees from radial - just
acceptable.
If it were built with high flange hub, however, at say 100mm, the
spokes would be at 92 degrees from radial, and that’s generally not
such a good idea.
Admittedly, two degrees, you might get away with it. In fact, for
both these cases, it’s so close to tangential at the hub that the
actual practical issue of whether it will be OK is a function of the
height of the spoke head (because it’s a bad interference between
spoke and the head of the adjacent spoke that’s actually the problem
with going past true tangential).
(The preceding may actually be what you meant by ‘weird spoke angles’,
in which case take my disagreement as an agreement.)
In practice, 3X works for most geometries. 4X sometimes doesn’t.
4X may be very slightly stronger, but it’s a theoretical rather than a
practically useful increase in strength. Similarly, the different
stiffnesses of spoke patterns are not actually likely to be detected
in practice, on a wheel with a tyre fitted.
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The story behind the bolts is that the Hex head bolts that you see on lots of BMX bikes are the standard profile bolts. Buy a profile crank/bottombracket set and it should ship with those regular hex bolts. The allen bolts we use are known as the profile “bitchin’ bolts” and can be bought at extra cost. For some reason the profile unicycle hub has always shipped with the bitchin bolts standard.
4 cross isn’t neccessarily stronger on a 19" wheel because opf the odd angles and stresses the spokes are exposed to. Also, a 19" wheel doesn’t really need that extra strength, since it’s so small. On top of all of this, it depends what kind of strength you’re wondering about. For axial flex during pedaling, the more crosses, generally the stronger, however for lateral flex during hops, there’s not nearly as much difference between 3 cross and four, since the spacing of the spokes isn’t really changing.
Both my trials and muni wheels are 3 cross and I’ve never had problems with flex or tacoing. I think that the quality of the wheel build plays a far bigger part in the wheel strength than the soke pattern.
Regarding radial stiffness, you note yourself on your page that “it should be apparent that the answer is that different spoking makes very little difference to the stiffness.” The difference between three-cross and four-cross in your example is .0028mm maximal deflection; that is four orders of magnitude less than the tire deflection of a MUni or trials tire, well below any level of human perception.
Spokes do rotate at the hub, but depending on the hub and the degree of tangentiality, it can be difficult to seat the spoke head properly so that the elbow is not under stress. The spoke can be under stress where it enters the nipple, as well. These stresses can be reduced with good wheelbuilding, but it’s easier to do with less tangential spoking patterns. And as you note, at some point your spoke line will run into the next nipple over, since unicycle hubs generally have wide flanges.
The strength of a wheel is largely a function of the spoke tension. One effect of different crossing patterns is that tangentiality increases the amount of spoke tension the wheel can hold, as tangential spoke patterns stress the hub flange less. (I once had a two-cross wheel pull out a big chunk of the hub flange). But this effect should be fairly small when comparing three-cross and four-cross wheels.
Re: spoke lacing and profile crank question
On Thu, 20 Oct, tholub <> wrote:
> Ian Smith wrote:
> >
> > However, the stiffness of the ‘rigid’ parts of the wheel (hub,
> > spokes, rim) pale into insignificance compared to the behaviour of the
> > tyre. While the wheel may be stiffer, what you ‘feel’ radially will
> > be the behaviour of the tyre.
> >
> > I think it is, though only slightly - a good three three-cross will
> > probably be better than a merely average four-cross.
>
>
> Regarding radial stiffness, you note yourself on your page that “it
> should be apparent that the answer is that different spoking makes very
> little difference to the stiffness.” The difference between
> three-cross and four-cross in your example is .0028mm maximal
> deflection; that is four orders of magnitude less than the tire
> deflection of a MUni or trials tire, well below any level of human
> perception.
Yes, that’s what I said above, too.
> The strength of a wheel is largely a function of the spoke tension.
Yes, that’s what I said above, too (although indirectly, referring to
“good three-cross”, and “merely average four-cross”).
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