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Awesome, can't wait to see this come together.

Superted does that sort of thing, doesn't he?

Contact details supposedly here, but I'm getting 509's:
http://www.tedjamesdesign.com/

I am indescribably excited by this thread on three or four totally separate levels.

Oh yeah, very very beautiful.

Just Hammerite, innit?

It won't kill you dead or make you drop a chain unless you've got mega low chain tension, but it will increase wear and noise. You could always use a Miche Primato BB (and I happen to have a 107mm one...). They're not the best BBs and take some effort to set up right, but they do give you a lot of adjustability.

Check whether the headset is (false-)brinelled, or if it's adjusted properly.

I believe (might be wrong) that the seatpost clamp ears are a cast part of the lug. You could have them ground off and new one brazed on, but if you can get it acceptably straight again, the least destructive way of fixing it might be to braze a washer into the ear, replacing the bit which has been ripped out. The best (and probably most expensive way) would be to have someone replace the whole seat cluster lug.

So yes, definitely fixable, but not nicely fixable without a bit of effort / money...

I see, yeah.

A few reasons for the long head tube, none of them super good, so I may change it now someone's noticed. Need to give it some thought:

1. Ceeway sell headtubes in 160mm lengths so it would save me the hassle of having to cut it down exactly straight and face it. And yes I know you should face it anyway ;)
   
2. A longer headtube means I don't need to use stem spacers (got the stem the wrong way around on the drawing as well, would be vertical for normal use and facing up as shown for longer more relaxed rides) but still not have an enormous seat-bar drop.
   
3. Having a short headtube is all very well and good but puts more strain on the joints (or so I've heard but when you think about it, it's just reducing the size of the lever, so maybe it reduces the stress ... who knows.) and means that only someone with a correspondingly short headtube will be able to use your fork in future.
   
4. I'm going to experiment with thinner bamboo tubes than is normal; usually 40-45mm tubes are used for the main triangle; I'm going to try more like 35. I'm 80% sure this will be stiff enough if the joints are good (my slightly noodly thick-framed bamboo bike has taught me that the joints are the big deal). But no-one (that I can find) has done that before; I guess it doesn't have the margin of error for commercial builders and there aren't that many hobby builders. If it turns out to be awful a longer headtube would let me graft in a second TT like on some of the bigger Rivendell frames. It would still end up weighing a respectable amount, though more than I plan at the moment.
   
   

How do you mean, almost a polo bike? Is it the lack of trail and the fat tyres? I think fat tyres are great; wish that I could get some of the Rivendell or Grand Bois gucci ones, but I'm happy with the Specialized Infinity ones I've got at the moment, apart from the weight. On thinner tyres I'm just rattling around the whole time and the placebo effect of feeling sportier is not enough to convince me that I'm going faster ;) as for the lack of trail I don't know whether I should play it safer. I've read some very convincing arguments in favour of low trail bikes, though many of them have been from the point of view of tourers using handlebar bags and 650 wheels. High speed stability is not an enormous issue, but the question is whether it would be too twitchy at normal speeds. I could lengthen the chainstays, but the rear triangle is quite difficult when you're building with bamboo...

Thanks for your replies.

I suppose the fact that no-one has commented means I've not done anything heinously wrong ;)

FWIW, I think I've decided to go for the Kinesis DC37, or maybe the DC19 if I can find one...

By the way, the marked 19mm half way down the ST is the distance between the ST and the tyre; the mudguards are mounted 7mm away from the tyre which I've always found just about fine, but there's room for them to go a bit further out.

Hi all,

I'm planning my second bamboo bike, and I'd like a sanity check on the geometry. Note that I've only very roughly sized it using the rider height function on bikecad, so that might change a little once I've taken more measurements, worked out my centre of gravity, decided what cranks I'll be using, etc. ... the geometry should stay pretty much the same though.

I was unhappy with the bendiness of the rear triangle on my last bike so I'm going for 420mm chainstays, which is about as short as I reckon I can get them with room for 35c tyres and mudguards.

The BB drop is 65 which is quite a lot on the safe side 'specially considering I like very short cranks (I've got 140s at the moment but may get some nicer 155s because no-one makes decent shorter cranks), but having a high CoG is good despite what you might think (recumbent wisdom).

I've gone for a quite short trail of 45mm, on the basis that though I flatter myself, most of my riding is done at low (>20mph) speeds, so stability on quick descents isn't much of an issue, whereas low-speed maneuverability without wheel flop is. The idea is that with the steep front end and short(ish) rear triangle it should handle quite quickly, while the unique compliance of bamboo should mean it isn't too rough a ride. Might slacken the seat tube a little for some more comfort but I need to do some CoG sums first ...

Here are some pictures: (by the way, ignore the handlebars. I'll probably use Nitto moustache bars - I got as close as I could on bikecad but they're not as low as that really.

'cept the axle-crown is about 6cm too long on suspension-corrected 29er forks, and it doesn't have eyelets ;)

Oh really? OK, the site I saw probably just had the details of different models muddled up, thanks for letting me know. It did seem like a pretty stupidly small size for an 'XL'.

P clips are a bit messy plus it's not much fun clamping things to CF, though they're an option if I get totally stuck. Raceblades are no good for me, I need the option of running fat tyres and even the XL ones only go up to 23 (?).

Ah good catch on the weight. I'm a bit (irrationally?) afraid of carbon steerers, maybe I just need to read up more on them to put my mind at rest, plus get a torque wrench. What's the deal with the tapered steerer? Find it hard to believe that there's much of a benefit... tapered tubes should be stiffer and weigh less, but I bet you have to make the taper section thicker than it would be otherwise...

Another option is a Bontrager Satellite Elite fork, but I can't find anywhere that still sells them. Not mega light either I expect. Also, I've realised that the Trigon fork I mentioned doesn't have eyelets, which is a shame cos someone's selling one for £60...

Alternatively there's always something like this, aluminium but pretty light considering the price (if you believe the manufacturer's specs, haven't checked them out). Expect there's probably loads of options if I drop the carbon plan: http://www.ebay.co.uk/itm/Mosso-26-MTB-Aluminium-Disc-Brake-Rigid-Straight-Blade-Fork-Black-Only-/110989447430?pt=UK_sportsleisure_cycling_bikeparts_SR&hash=item19d77c9106

Cheers for the tipoff - my German google-fu has failed me but on the bright side I found another potential option:

http://www.mob-bikes.de/quantec-cross-gabel/1280-quantec-carbon-crossgabel-fur-scheibenbremse.html

It says it's designed for integrated headsets, which confuse me. Am I right in thinking that that's just a styling matter (ie. it has a larger top to make a smooth transition into a larger headtube), and a normal non-integrated 1 1/8in headset would do as well?

No-one got any bright ideas?

tl;dr because that was all a bit long-winded -

I want a lightweight but not flimsy 1 1/8in steerer fork, axle-crown probably no more than 410mm, with mudguard eyelets, room for a 35c tyre, and ideally disc brake fittings.

I've had another look at the Exotic / carboncycles.cc forks and they don't have eyelets as I thought they did, so they're out. So far the nearest I've got are these, having relaxed my distaste for monocoque forks...

Kinesis DC37, £120ish: http://www.winstanleysbikes.co.uk/product/51770/Kinesis_DC37_Carbon_Forks
Trigon MC01 (loads on ebay), £110ish, ugly as sin and big A-C.
Spot carbon fork: http://spotbrand.com/bikes/product-page/forks/. Can't find them in the UK but they are lovely looking, bit dear though. [ah bugger, sidewayscycles sell them but they're £199]

So, essentially, after about two years on my current bamboo bike, I fancy making a new lighter stiffer shinier generally whizzier one. Before I design the frame geometry, I'm trying to decide what fork to use. I have some funny requirements so it's a bit tricky just to use google, but it's the kind of thing where human intelligence should sort it pretty quickly. [edit - long and boring post, see my next one for the tl;dr summary]

At the moment, I fancy carbon fibre, but I still don't know whether this is a good idea. I use the bike for everything, but realistically use it most of the time commuting and getting around town, with occasional light off-road stuff. Maybe a lightweight metal one of some description would be nearly as good and cheaper.

Because I'm building the frame from scratch, axle-crown distance and rake is not such a big deal because I can adjust the headtube height and angle to get the trail I want. Though nothing stupid that will limit my choice in future.

I use a front hub brake at the moment but can see myself switching to disc to save a bit more weight, so a disc specific fork is best (even if I'm still using the hub brake, I don't trust a non-disc fork not to do horrid things when I brake sharply).

I don't like the look of forks where the crown is u-shaped and blends into the legs (whatever that's called); something that has a flatter top (like classic steel road forks, or most MTB forks), or v-shaped (like most carbon road forks) is more my kind of thing. Also I must be able to run a full mudguard, with clearance for 35mm slicks.

Lastly, cheapness is of the essence. Say £150 max, cheaper would be much better, though that limits me greatly on the carbon front. I'm considering the 26in carboncycles.cc MTB forks, though they still have quite a long A-C length which will limit my choices in future...

Anyone got any ideas? I'll post things that I find as I come up with them.

Cheers :)
Ben

Bumpp, £12 posted

Bump

Miche Primato for sale.

Really nice little BB, selling only because there's no way I'm making my chainring fit with a 107mm spindle. Consequently it's been round the block once and had brand new cranks put on and off twice, so there is a tiny bit of scuffing on the square taper bits and probably some grease residue on the threads but otherwise new. I can take some photos if you like. Uses a Campagnolo tool to fit, bit of a knack to it but really very easy, and lets you adjust your chainline by probably +/- 10mm or so.

Bought it for £17 or something like that, say £14 posted ONO? I live in Oxford so can't bring it to London drinks, but you can have it for 10 in cash if you're nearby.

Dibs followed by PMs please.