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 Post subject: Re:
PostPosted: Fri Nov 02, 2018 9:51 am 
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Joined: Tue Aug 21, 2018 3:43 pm
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Location: Cambridgeshire - flatlands (the horror, the horror)
Rick you need I think to consider crank length. For the retrogrom’s hyperlight first bikes I made sure that he had 150 and then 155 cranks. Even 160 is a bit long for young ones, according to the latest understanding of the physiology of cycle motion. For the DH I went even shorter, cutting down some zee cranks to 142; highpath eng do this exceptionally well. But zees are heavy devils, and fine on DH but not Xc. So for a really nice set up I went for thorn cranks from sjs - 150s, and then 155s - and used a hope ti square taper B.B. and of course ti bolts - the cranks really are not that expensive from sjs and you get a nice choice of chain line using the highly adjustable line on the hope and the double ring setup on the thorn. We ran these 1x9 and then 1x10 which is fine for a young one.


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PostPosted: Fri Nov 02, 2018 10:54 am 
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I'm in total agreement with you, lots of options at 170mm, a few in the 150-160 area, but I'm working on something more like 120-130mm as my target.

Info I have seen recommends to aim for crank length 10% of the childs height so that should be about right for a 6-8 year old, perhaps even shorter than that if she fails to grow properly :D


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 Post subject: Re:
PostPosted: Sat Nov 03, 2018 12:30 am 
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Location: Cambridgeshire - flatlands (the horror, the horror)
Rick that crank length sounds really sensible. Have you seen this?

http://forums.mtbr.com/families-riding- ... 32945.html

interesting even if you aren't into doing it. I used RS SIDs in 63mm format - then used discs so that I could run it with a 24 inch wheel. You could push them further and run with 20 inch wheels actually. White did a 24 inch air fork - wonderful thing - and you'd need to mortgage a small South American country to buy them...cost a fortune.

The Zokky Bombers which you have look v nice - fettled or original short format?


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 Post subject: Re:
PostPosted: Sun Nov 04, 2018 5:56 pm 
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Have seen similar but don't think I'd seen that particular one. Some great info there.

Wrt modding forks, thought about it but decided against. I figured the difference from 26 to 24 is not worth the bother, and if using disc brakes it's not a problem for brakes. Lazy perhaps.

For 20inch wheel I could see the problem. Not for this project but I have a 20" kona makena that the boy used so intend to give that a once over. The forks were soft enough for kiddy weight so should be OK still but always handy to have a plan b.


Last edited by RickTheUncivil on Wed Jan 02, 2019 2:08 pm, edited 2 times in total.

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PostPosted: Sat Nov 10, 2018 11:33 pm 
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RickTheUncivil wrote:
Impulsive and possibly ill-thought-out buying has happened :D details to follow once they arrive but for now let’s say we are using 32H rims which won’t support a rim brake


Not 100% on these, heck I'm barely 50%, but hey, sometimes you just got to roll with it.

Not super light but lighter than many. Colour is, well, colourful and plays nicely with the pink frame. And they were a fricking steal.


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 Post subject: Re:
PostPosted: Sun Nov 11, 2018 12:59 am 
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Nice.


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PostPosted: Wed Nov 14, 2018 2:26 pm 
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progress update.

Some rims in the box now and a choice of hubs so making good progress in the wheel department.
Or is it?
Black hubs because nice and tidy plus black forks, green rims because why not. Can’t decide whether to use silver spokes or whether I should go for black there too. Hmmm, that’s such a little problem I can barely type it out.

Moving on from colour onto patterns and numbers of spokes, I have seen some interesting threads around the web about lacing 32H hubs / rims with 16 spokes. Certainly for the front wheel there seems to be a reasonable case for saving a bit of weight by dropping the spoke count. It’s a small diameter wheel and the rim is strong so don’t have to worry too much about flexing all over the place, and no rim brake to worry about even if it is a little flexy. Plus remember we are talking about a kids bike here so light weight rider, light use.

couple of examples stolen from the web:

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Advice seems to be that a crossed pattern rather than radial is essential but beyond that theres lots of guesswork and reckoning.

Never done it before but I’d be interested to hear any experiences along these lines.


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PostPosted: Wed Jan 02, 2019 2:22 pm 
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thinking about this again.

say 6g per spoke x16 spokes is around 100g of weight from the front wheel. That's not bad.
Doing this with the front wheel should be fine but advice (chatter on the web) for doing so with the rear wheel is a bit less convincing.

Anyone here tried this?


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PostPosted: Fri Jan 04, 2019 9:58 am 
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photo is nicked from the web but I bagged a pair of these lightweight Novatec hubs for a good price.

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They certainly tick the weight box but I got them in white, so not quite ticking the optional 'black' box. Given the intended use I can't imagine that these won't be up to the job strength or durability wise.

~400g for the pair is pretty weenie for disc hubs, even lighter than Hope Pro 2's and a fraction of the cost. I'll give them a once over when they finally arrive but thats now a fourth option in the bag - these (398g), Ringle Disc Jockey (644g), Shimano XT 756 (663g) or Hope XC (590g).

I reckon the Novatec hubs and Spank rims (maybe with 16 spokes, still thinking on that one) should bring the bare wheelset in around 1.5kg, so some lightweight tyres should allow a sub-3kg wheelset, maybe a bit over once a cassette is added.


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PostPosted: Thu Jan 10, 2019 4:53 pm 
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And like busses, the options come rolling in all at once...

Just got my hands on Plan B in the shape of a pair of Sturmey Archer 8 speed drum brake hubs.

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Well, I say got my hands on, just sorting out delivery now :?

the spanner in the works being these are currently laced to 700C rims with 36 spokes and I want to pop them on 24" rims using 32 spokes :facepalm: guess Plan B would be involving a change of rim too then.

But before all that I want to try them out and see if they work, and establish whether what looks like a fair weight penalty is the way to go.


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