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 SWB trail, WB, handling?

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SpiderMonkey Posted - 09/29/2017 : 07:38:31
I am tinkering with a SWB design for my kiddo, which makes for some interesting challenges.

Currently, I've got something that *looks* workable in sketch, with a 37 inch wheelbase and 3 inches of trail on a 72 degree head tube angle. Weight distro would be (initially, with seat so far forward) closer to 50-50 than the 60-back, 40-front that seems more typical for long-legged dad on a SWB.

Does that seem within the realm of normal? Or is handling complete speculation until you actually get something built?

7   L A T E S T    R E P L I E S    (Newest First)
SpiderMonkey Posted - 09/29/2017 : 17:58:41
My first cut at an actual design sketch. Probably need to lift the return chain above the tire with a small idler, and just run the power side up the larger idler. Trying to avoid crank/tire interference, but no way to avoid foot interference given the sizes, unless I try a LWB.


SpiderMonkey Posted - 09/29/2017 : 14:03:58
I think warren's stickbike tubes were originally goin to be thinner wall, but he beefed them up. I remember he was originally looking at 2" tube about 1.5mm thick, but everyone said that was a bit light, so he got something else. Can't remember what it ended up being. Maybe I'm not reading straight.


The tube I saw is this (price has been bouncing around between "yeah, sure," and "no thanks.") (https://www.aliexpress.com/item/500mm-3k-Carbon-Fiber-Tube-50mm-60mm-Roll-Wrapped-Light-Weight-High-Strength-High-Corrosion-Resistance/32738916988.html

The not-too-far-along plan would be buy 3 of these, get rear chainstays, headtube, BB from chopped-up chromo donor bikes, throw on a cheap Chinese fork. I'd be better off learning to weld again, but I don't really have shop space for sparks and fire. I do OK with CF layup.

Speedbiker Posted - 09/29/2017 : 12:33:36
Wall thickness depends on the quality of the carbon and the layup schedule. Most of which is beyond my understanding. So someone else can advise better. But the carbon frames I've repaired were nowhere near 2mm wall thickness. But it can't hurt unless the tube is wider than your bb, which would cause problems with assembly.
SpiderMonkey Posted - 09/29/2017 : 10:56:26
Originally posted by Speedbiker

2.362" diameter tubing? How much does this kid weigh? How wide is the bottom bracket you are bonding in? Also, how tall is the youngster?

They've got 50mm tubing too, but the wall's not as thick. I'm just spitballing here, and I thought I remembered from prior discussions here that one would want about 2mm wall thickness for CF tubing about this diameter. I would be fine giving this another wrap if necessary.

She goes about 60 pounds with a 31.5" x-seam, currently, but of course, growing like a weed. She's got a nice little upright, but much prefers her recumbent trike, which is fine, but it weighs 30 pounds. That's why I'm constantly trying to figure out how to get a 2 wheel 'bent for her.

Speedbiker Posted - 09/29/2017 : 10:36:16
2.362" diameter tubing? How much does this kid weigh? How wide is the bottom bracket you are bonding in? Also, how tall is the youngster?
SpiderMonkey Posted - 09/29/2017 : 08:59:14
I need to review your stickbike/zbike process again. I found some 60mm CF tubes with 2mm wall thickness, 50 cm long each, that aren't *too* expensive. I mocked my sketch up with those, assuming mitering and then CF wrap at the join.

Since I don't/won't have capability to do this in metal, I'd be scaling up my small CF repair/fab skills to a larger scale, perhaps not the best idea...

Part of me just wants to cut 15cm out of the middle of the Giro 26 I just picked up cheap and CF that steel back together, then slap on a 20" fork, 20 inch wheels and be done with it. But the bike's too nice to chop up.

I need to find a real POS frame for that, I guess.

warren Posted - 09/29/2017 : 07:58:43
Sounds fine. Just make sure to design is so the riders head is in front of the rear axle and it should be rideable.

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