talk to me about 40 spoke wheels

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reohn2
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Re: talk to me about 40 spoke wheels

Post by reohn2 »

.....I built this years ago; these days I expect I'd just buy an XT disc hub, much easier


Just what I thought when I saw the first photo,though it wouldn't work for the front.............




........but I nice Suzue one would :)
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Brucey
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Re: talk to me about 40 spoke wheels

Post by Brucey »

531colin wrote:
Brucey wrote:
531colin wrote: Yes, its 8mm less dish....-4mm left, +4mm right.....and the brake is 4mm off if you fit a "normal" wheel.....think about it!! :wink:


it does rather depend on how you define dish; I have always used the definition of the rim plane distance from the midpoint between the flanges, in which case it is surely 4mm less dish, not 8mm?...........


Nobody could argue with that!......I guess I must think of it as the difference in spoke angle/tension.....which relates to the difference in the flange to centreline distance.....doesn't it? getting late for me!


I was thinking about this; when you use a dishing tool, dish errors appear to be x2 because of the way the tool works. I wonder if that is it?

cheers
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531colin
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Re: talk to me about 40 spoke wheels

Post by 531colin »

Yes, the dishing stick compares the 2 sides (so a centering error shows double)

I think what I'm doing is comparing the spokes' bracing angles (ie the angle between the spoke and vertical)....
so if you move the rim or the dropouts to change one sides bracing angle by say 2 deg, you inevitably change the other one 2 deg in the opposite direction. (Unless you move just one set of spoke holes in the rim, I guess)

What about if you take a 130mm hub, and put in a 135mm axle, with all the extra spacers on the left.
You move both flanges 2.5mm to the right....to me thats 5mm less dish, but you have centred the rim between the flanges by only 2.5mm.

......I think your way might be easier!!

and now my head hurts!
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531colin
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Re: talk to me about 40 spoke wheels

Post by 531colin »

Ambler wrote:Does rim width make any difference to all these factors?
(apologies for novice question)


A big strong (stiff) rim builds a wheel that is quite obviously stronger at resisting side loads when you stress the wheel as part of the building process.http://forum.ctc.org.uk/viewtopic.php?f=5&t=49702&hilit=spokes&start=30
It should also "share out" imposed loads between more spokes, so spoke fatigue is delayed....this is much harder to demonstrate!

Modern rims made for fewer spokes are impressively stiff.
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531colin
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Re: talk to me about 40 spoke wheels

Post by 531colin »

moonsafari wrote:http://www.chainreactioncycles.com/Models.aspx?ModelID=86123


Am I missing it, or is information a bit thin on the ground?
They say the MTB hub is 135mm OLN, and the tandem one is 145. I didn't find anything about spoke drillings....?

OK, its somewhere else...40 holes...for the tandem 145mm hub...?
reohn2
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Re: talk to me about 40 spoke wheels

Post by reohn2 »

moonsafari wrote:http://www.chainreactioncycles.com/Models.aspx?ModelID=86123


Looking at the tech docs:- http://whiteind.com/images/REAR_HUB_ADJUSTMENT.pdf
WI M16 seems to suffer(if that's the right word) from the same problems as DT Swiss rear hubs,which is that the supporting hub bearings (not freehub bearings,they only support the freehub) are too far inboard of the driveside dropout.
The WI does have a 15mm CroMo axle though.

Edit:- I've been looking through a few reviews and they seem to get the thumbs up from the MTB crowd :)
Edit II:- The ones in the CR link are really cheap too for tandem hubs :)
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teh

Re: talk to me about 40 spoke wheels

Post by teh »

My bike has a Shimano XT tandem hub, 40 spokes, and a FiR tandem rim. The hub was originally 145mm spacing, but it was a simple job to remove some washers and saw off some axle.

I weigh a lot, and my touring kit is heavy. This wheel gives me no problems.
Ribblehead
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Re: talk to me about 40 spoke wheels

Post by Ribblehead »

531colin wrote:Very interesting book. My copy is currently out on loan, so I can't refer to it just now, but I don't remember him actually quoting numbers for the extent to which Hi-Lo hubs reduced the tension difference?
Tony Oliver made his own roughstuff tourer with an offset back end and dishless wheel, which is what triggered me to get one built maybe twenty years ago.
I also used his preferred head angle/fork offset combination on that bike....it is the sweetest handling bike, and those numbers are still used for a certain titanium tourer.
However, there are some anomalies in the book....a whole chapter on steering geometry that doesn't mention the word "trail" ....?


It would appear that 'trail' is labelled in Figure 3 on page 13. I don't think he actually discusses 'trail' in the text, but trail is a function of head angle and fork offset, so I think Figure 5 on page 15 more than makes up for the fact that he doesn't discuss 'trail'. For those who haven't read this excellent book, Figure 5 is a plot of Fork Offset versus Head Angle, on which the author plots the 'trail' of various different types of bikes (time trial, road racing, touring, tandem) and offers his opinion on the range of combinations which will result in a stable front end.

531colin wrote:Jobst Brandt says that Hi-Lo hubs can reduce the tension difference by about 5%, but only if the spokes are fully radial. Edit....I think that should be radial driveside, left side tangential


Although the Tony Oliver book includes a picture of a radially laced drive-side on a hi-lo hub (Figure 104 on page 115), the only tension values he includes are for a combination of 2-cross and 4-cross on drive-side and non-drive-side respectively. The tension values also show there is a benefit in differential lacing even when a hi-lo hub is not used. I have an old screw-on hub (not a hi-lo design) I intend to build into a wheel soon, so I may do some calculations to see if differential lacing would be advantageous.
teh

Re: talk to me about 40 spoke wheels

Post by teh »

Unless a hub has been specifically designed for radial lacing, I wouldn't do it. If we are talking about heavy touring wheels, then it's a really bad idea.
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531colin
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Re: talk to me about 40 spoke wheels

Post by 531colin »

teh wrote:My bike has a Shimano XT tandem hub, 40 spokes, and a FiR tandem rim. The hub was originally 145mm spacing, but it was a simple job to remove some washers and saw off some axle.

I weigh a lot, and my touring kit is heavy. This wheel gives me no problems.


I don't think anybody is suggesting that you can't build a serviceable 40 spoke wheel.
However, I know of more than one 20 stone man riding around on 36 spoke LX/Sputnik wheels which Spa currently have for £157 for the pair, compared to £150 for just the rear XT tandem hub from SJSC.
I don't know how much the OP weighs, but in the general run of events, 36 spokes is OK.
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531colin
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Re: talk to me about 40 spoke wheels

Post by 531colin »

Ribblehead wrote:
It would appear that 'trail' is labelled in Figure 3 on page 13. I don't think he actually discusses 'trail' in the text, but trail is a function of head angle and fork offset, so I think Figure 5 on page 15 more than makes up for the fact that he doesn't discuss 'trail'. For those who haven't read this excellent book, Figure 5 is a plot of Fork Offset versus Head Angle, on which the author plots the 'trail' of various different types of bikes (time trial, road racing, touring, tandem) and offers his opinion on the range of combinations which will result in a stable front end.


I struggle with figure 5.(got my book back).71 deg. 2 1/4 inch offset for touring....spot on, I think. But then he has less than about 1 1/2 inch offset 71 deg as "steering too quick", whereas his own fig 3 shows reducing offset gives more trail, (therefore more stability?). Same on page 16 in the text "If the rake is too short, the steering will be so sensitive...."

Anyway, back on topic....

Ribblehead wrote:Although the Tony Oliver book includes a picture of a radially laced drive-side on a hi-lo hub (Figure 104 on page 115), the only tension values he includes are for a combination of 2-cross and 4-cross on drive-side and non-drive-side respectively. The tension values also show there is a benefit in differential lacing even when a hi-lo hub is not used. I have an old screw-on hub (not a hi-lo design) I intend to build into a wheel soon, so I may do some calculations to see if differential lacing would be advantageous.


You may have to help me here......my maths. is crap...... Page 114, fig 103(b)
Lots of examples, I'm going to take the 130mm OLN, as its the most up to date.
lacing 4x both sides, tension ratio 1: 0.879, whatever hub flanges.
Lacing 2x drive side, 4x left side. tension ratio 1:0.931 for small flange, 1:0.955 for large flange, 1: 0.962 for Hi-Lo
I make that about 6% better for the differential crossings on small flange.....about 2.5% extra benefit of L/F over small flange, and Hi-Lo offer less than 1% advantage over L/F.

Hardly a ringing endorsement of Hi-los, unless I mis-understand.
Brucey
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Re: talk to me about 40 spoke wheels

Post by Brucey »

531colin wrote: Hardly a ringing endorsement of Hi-los, unless I mis-understand.


I think your assessment is correct, and tallies well with what I have understood to be the case.

cheers
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Ribblehead
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Re: talk to me about 40 spoke wheels

Post by Ribblehead »

531colin wrote:I struggle with figure 5.(got my book back).71 deg. 2 1/4 inch offset for touring....spot on, I think. But then he has less than about 1 1/2 inch offset 71 deg as "steering too quick", whereas his own fig 3 shows reducing offset gives more trail, (therefore more stability?). Same on page 16 in the text "If the rake is too short, the steering will be so sensitive...."


There's more than one way of measuring 'trail'.

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

Would that explain it?

531colin wrote:You may have to help me here......my maths. is crap...... Page 114, fig 103(b)
Lots of examples, I'm going to take the 130mm OLN, as its the most up to date.
lacing 4x both sides, tension ratio 1: 0.879, whatever hub flanges.
Lacing 2x drive side, 4x left side. tension ratio 1:0.931 for small flange, 1:0.955 for large flange, 1: 0.962 for Hi-Lo
I make that about 6% better for the differential crossings on small flange.....about 2.5% extra benefit of L/F over small flange, and Hi-Lo offer less than 1% advantage over L/F.

Hardly a ringing endorsement of Hi-los, unless I mis-understand.


I agree, the additional benefit gained from a hi-lo is fairly small, but I'm glad this topic has come up, as it has reminded me that differential lacing may be worth looking into for a rear wheel I am building.
Ribblehead
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Re: talk to me about 40 spoke wheels

Post by Ribblehead »

reohn2 wrote:With huge gaps and dodgy reliability issues.


I think the Alfine 8 is generally considered fairly reliable now. Anything that can withstand MTB use is good for me. :D

reohn2 wrote:Deraileurs can more often than not be rigged for SS if necessaryin any gear until it can be repaired.


Hardly anyone has the horizontal drop outs to do this anymore. Also, you can't just choose any sprocket, without a rear derailleur or precise chain tensioning to keep it all in order, you will need to choose a sensible chain line, or you could end up with an accidental shift onto a larger sprocket, especially with todays profiled sprockets.

reohn2 wrote:Hub failure can = stranded.


I took a bit of a flyer on mine. The night I fitted and adjusted it, I rode it half a mile up and down the rode outside my house to check all the gears worked, and up a steep road close by to check it wouldn't slip in first gear. The next morning I rode it on a 120 miles loop, high into the Dales. :lol:
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