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 Post subject: Re: Re:
PostPosted: Fri Sep 14, 2018 7:05 pm 
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Location: Macclesfield, Cheshire
Timoth27 wrote:
What you could try is (if you have a wheel, disc and caliper) is trial fit the wheel and offer up the caliper against the mount and see how it looks


My next job :-)

well, my next job on this project, might be next week

Got an odd non disc frame hanging in the shed and a hope disc caliper still in the inbox, just need to dig a wheel out


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PostPosted: Fri Sep 14, 2018 9:55 pm 
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Joined: Tue Oct 23, 2012 10:52 am
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Location: Whelmington on Sea
The disc adapter you have there is a Onza disc mount, the hole on the face is for attaching it to the dropout (optional), there should be grub screw in the threaded hole on the rear edge & you need the extended skewer.

I've just bought a Sturmey XRD8 (W) for the princely sum of £15 :D , after it was trashed by the previous owner trying it on a tandem :shock: . Luckily the hub is not damaged, spares are available & the internals are a complete cartridge unit at £99.99 inc vat.


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 Post subject: Re:
PostPosted: Wed Sep 19, 2018 1:42 pm 
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So, tried the bracket of mystery. Couple of issues now.

1) the xmaxle fits the frame dropout, but obviously it does not extend the the bracket. This means the bracket is no braced against anything at this point and if it all moves the contact would be with the qr skewer. I guess the onza kit included some sort of spacer arrangement. Any clues?


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 Post subject: Re:
PostPosted: Wed Sep 19, 2018 1:44 pm 
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The bracket seems to place the caliper just so... which is good....


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 Post subject: Re:
PostPosted: Wed Sep 19, 2018 1:48 pm 
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.... But
2) the alignment between caliper and disc seems somewhat offset... (note the exposed thread on the bolt, say what, 6 to 8 mm?). This is just plain bizarre. What am I doing wrong here guys? More spacers required here too? Surely the bracket would be designed to get the mounting points closer than that!

I also started a separate thread to try to resolve this particular issue <here>, seems to make sense and having a sensible thread title might just get some answers in :(


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PostPosted: Tue Sep 25, 2018 1:13 pm 
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Weight Weenie? Not really....well, maybe just a bit….

So, weight. Given the light frame and forks and the general intention of making this a ‘better’ proposition than a shop-bought jobbie I’m keeping an eye on the numbers to make sure it doesn’t get unnecessarily lardy. I have already started considering weight in the previous chat about in-hub gears. So where from here? Well, let’s start with what we already have....

The parts supplied with the frame were tidy enough but nothing special, so I popped them on the scales and compared them to others I had in the spares bin:

:arrow: Stem – no-name silver alloy job, ~90mm reach, 236g. OK….. Azonic ORC ~90mm from the parts bin comes in at 180g. Ditch it, that’s minus 56g. This is easy.

:arrow: Bars – ‘XTX’ (?) black risers, alloy, 545mm wide, 292g. Some black Easton EA70 Syncros bars (karma’d from Alison) 500mm, come in at 114g. Ditch it, minus another 178g. That’s a good saving right there.

:arrow: Seatpost (31.6mm x 300mm) – black alloy logo might say ‘Most’ not sure. 394g. There’s definitely some room to improve there. Got plenty of spare posts and they tend to come in between 200-300g, and could lop a chunk off the bottom to save a bit more too since the saddles never going to be raised too far on a frame this size. There’s a cheapy alloy jobbie cut-down to about 150mm in there that weighs in at 218g, and a full length raceface XY unit at 292g. So a decent full length post or even a cutdown cheap post would cut the weight down considerably. Let’s split the difference and call it a projected 150g saving.

:arrow: Saddle is another 350g. It’s a basic saddle so didn’t expect it to be super light, and these ‘ladies’ comfort saddles are rather more generous than most. Got loads of saddles in the box and many are sub 300g, bet I can find one to suit that’s under 250g if I tried, but will have to leave that to m’lady to see what’s comfy when we get there I guess. But call that another projected 50g saving to be had.

:arrow: Forks (Bomber Z4 flylight air) – nice and work well. Book says 1780g, my scales say 1950g but that’s including bits of headset and a fancy SFN plug thing. Book also says my RST XMO are around 1500g so might be a few hundred grams saving to be found there. Could also explore the Pace route as I gather they come in about 1500g too. Need to be 24” wheel friendly so disc brake mounting is ideal. Hmmmm.


Looking at the above, weight matters. Just by switching a few parts out I have saved nearly half a kilo for zero spend, and can save a dollop more by looking carefully at forks. I think I will keep a keen eye on weight, not going crazy but it will be a consideration. The Boys’ build he chose a chunky frame and his emphasis was all about bulletproof so it came out a bit on the heavy side, I mean we didn't even consider weight. This one I fancy being a bit more careful with.


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PostPosted: Tue Sep 25, 2018 6:50 pm 
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You had me at weight weenie :)

Wheels & tyres. Wheels & tyres. Wheels & tyres. SO much weight to be saved, and in the most important area too.

Go 1x8, 1x9 or 1x10, tons of weight to be saved, and kids just won't use all the gears.

Cranks, brakes and shifters, not so easy (or cheap) and functionality can suffer. A lot.

Best of luck.


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PostPosted: Wed Sep 26, 2018 8:35 am 
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My_Teenage_Self wrote:
You had me at weight weenie :)
Go 1x8, 1x9 or 1x10, tons of weight to be saved, and kids just won't use all the gears.


I want to give her a decent range of gears, particularly low range, so I’m looking towards a triple set with smaller rings, probably 3x9 as that what I have lots of, but you’re right, maybe I could go all modern and put a whacking great cassette on and run a single at the front. I think I’d like to fit a double or triple crankset even if I run a single ring since the frame can take a front mech so adding a mech later would be a simple enough task.

Weight wise, single ring means save a couple of chainrings (say ~100g) a front mech (XT 750 is 125g) and a LH shifter (XT 750 is 125g). So call that a 350g saving by not running a front mech. Not bad.

So, what’s in the magic box? Well:

SRAM (PG970 I think) 9sp at 412g
Shimano (LX?) drilled out 9sp says 324g
XT M750 9sp at 294g
XTR M970 9sp comes in at 244g.
(and the cheaty) KCNC Sc/Al/Ti jobbie at ~160g :D

Careful choice of cassette then and ~100g can be avoided without too much bother. That 970 is a bit bling for a kids bike but its certainly light and has a good range. I'll use the M750s reasonable ~300g for the benchmark though for any future comparisons.

I have also been contemplating the step towards in-hub gears which would mean spending (see previous on this) but I can see some benefits on the maintenance side, but perhaps a penalty on the weight side. I’m leaning away from that plan at the moment but maybe I’ll revisit it if I can get my hand on a cheap, good setup.


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 Post subject: Re:
PostPosted: Sat Sep 29, 2018 11:42 pm 
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Joined: Tue Aug 21, 2018 3:43 pm
Posts: 181
Location: Cambridgeshire - flatlands (the horror, the horror)
Hi Rick - read your comment on the Kona which I built for Alex (retrogrom) - thanks for the compliment - and can see the hassle which you are having with the rear brakes. There is a simple solution. If you can remove the brake posts - which I think you can, then you can bolt on two alloy plates, one each side, with a large M6 bolt. The plates will need a lower hole reamed in them to take the brake posts, moving them down to the location needed on the 24 inch wheel. This could also be an arch-shaped plate instead of two small plates. The plates, or better, arch will need to be machined for you. I have seen this done when people have converted front forks from 26 to 24. Also if you run 150 cranks ground strikes will be unlikely. I can send through some drawings if you need them. Getting this machined will not cost very much and is a very simple solution, which will add little weight to the build. I ran 24 on a 26 P7 for Alex and with 155 cranks there was absolutely no problem.

See

http://forums.mtbr.com/27-5/26-v-brake- ... 84165.html


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PostPosted: Mon Oct 01, 2018 8:56 am 
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thanks, yeah I have seen a few examples of these but they dont seem to be a common solution, as in they are pretty darn hard to find in shops. So making one would be the way forwards.

If you have a design I can work off that would be great, please do send it over. Good to have a few options. I tend to lean towards disc brakes just so I don't need to worry about the rims staying true so thats why I'm looking at that one mostly.

But with weight in mind there does appear to be a weight penalty with disc brakes. Theres a bit more in the hub I guess, and compare a BB7 caliper and rotor at 350g to an XT m750 V at more like 230g . Maybe disc rims can be a bit lighter than rim brake rims, not really thought about that but can't see it being a massive difference.

More research!


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