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SpiderMonkey
recumbent guru

USA
690 Posts

Posted - 06/03/2019 :  19:15:01  Show Profile  Reply with Quote
I've been fine tuning the Chinese carbon-fiber fork for the kid bike, and I didn't like the looks of the "lawyer lips." They don't protrude very far, and using a 20mm flat Dremel disc to bring in the outside edge of the fork ends to make the lips deeper didn't give me much confidence either. Maybe I read too many of those scary web pages about disc brakes spitting out wheels, but I think if it were going to happen, this would be the fork for it. Before I started modding it, if you just undid the QR and pulled the wheel (no turns) it would pull free no problem.

I'm not sure how easy it is to spit a 406 wheel with a 160mm disc out of the fork ends with the downward force generated by disc braking but I decided I didn't want to find out. After pondering it for a few days and considering stuff like trying to jerry rig a Schwinn clip or similar, or drilling a 2mm hole below the axle ends and inserting a spoke with a nipple for a threaded nut, I noticed that the front axle ends really only take up about half the thickness of the fork ends, I decided to do several layers of CF over the bottom of the fork ends, simultaneously building up the lips toward the outside so they'll catch the skewer ends better, but also closing off the bottom of the fork end (on the outside) so that the axles will still slide in, but only if the QR is completely removed. I don't mind having to remove a QR to drop a wheel, since we tend to run touring tires that don't flat too often anyway.

The NoCom's front fork has holes, not slots, I would have thought for similar reasons, except the force of stopping that wheel would push the fork straight forward, since the brake is rotated 90 degrees clockwise from the more normal, vertical.

Anyone out there have experience with fork ejection or near misses (or no problems at all with forks that shoulda had problems?)

--SpiderMonkey

Edited by - SpiderMonkey on 06/03/2019 19:17:50

warren
human power expert

USA
6528 Posts

Posted - 06/04/2019 :  07:51:49  Show Profile  Visit warren's Homepage  Reply with Quote
I have never had an issue with that, even with a loose skewer. I always remove the lawyers lips on my bikes.

Edited by - warren on 06/04/2019 07:53:41
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SpiderMonkey
recumbent guru

USA
690 Posts

Posted - 06/04/2019 :  07:56:29  Show Profile  Reply with Quote
Good to know. The stuff I've seen is all either hypothetical vector drawings, youtube videos of people popping wheels out with no skewer, or message board claims. Usually mt bikers too. I checked that one you just modded and saw there were pretty substantial lips in one of the photos. I'd wondered because my stickbike fork came without lips.

--SpiderMonkey

Edited by - SpiderMonkey on 06/04/2019 07:59:22
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warren
human power expert

USA
6528 Posts

Posted - 06/04/2019 :  13:24:45  Show Profile  Visit warren's Homepage  Reply with Quote
LOL, I can imagine MTBers jumping over a log and having their suspension fork ejecting the front wheel. Whee!
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SpiderMonkey
recumbent guru

USA
690 Posts

Posted - 06/04/2019 :  14:59:03  Show Profile  Reply with Quote
There are a few scary-ish stories out there. The guy who raised the first fuss (famously) was using a custom fork on a tandem and many people said "dude, that fork was too flimsy and it bent." Read another thread where a dude's friend ejected his wheel while touring. Brand new custom upright, no lawyer lips, was hitting the brakes hard before corners coming down mountain switchback, threw out the front wheel but right outside a bike shop, no one hurt. Fork was toasted of course.

I just put some tow scraps on across the bottom of the fork ends, trimmed open toward the inside to allow the axle ends to slot right in. What I've got now is a combo of deeper lips and I left the closed bottom on the outside of the fork too. The wheel slides right in w/o the skewer. Can't come out with the skewer in place unless it breaks through a couple mm of CF cable across the bottom. I'll leave it like that since it will give me peace of mind, and it was about 6-8g worth of material.















--SpiderMonkey

Edited by - SpiderMonkey on 06/04/2019 14:59:47
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Larry Lem
human power expert

South Sandwich Islands
2541 Posts

Posted - 06/04/2019 :  16:44:02  Show Profile  Reply with Quote
I had a steel 700c fork with slotted dropouts that I converted to disk brake. The axle and QR lever would like to slip in the dropout under hard braking but it always stayed in (fortunately). I would stop, release the lever, shove the wheel back in properly and tighten it.

I scored the dropout surfaces with a grinder but the problem remained, still too slippery for the hub and QR and braking forces.

I got rid of the fork.

Larry Lem
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SpiderMonkey
recumbent guru

USA
690 Posts

Posted - 06/04/2019 :  17:04:36  Show Profile  Reply with Quote
Also good to know.

I did a second little campaign of CF on this fork just before I went for my run this afternoon, since I had a little scrap tow still out on the work bench. This time I left the hub and QR on (masked off with electrical tape) and added a little more to the lips/retention bridge.

The explanations of the phenomenon say its worse for a bigger wheel with that small disc. I'm not enough of a student of physics to comprehend that. I'll just do what I'm doing and I think it'll be a good backup.

From other threads I've read on MTB forums, the quick release skewer can make a big difference. Everyone swears by the big, heavy Shimano ones. Since I'm building all these bikes on XT hubs, that's what I've got on hand.

--SpiderMonkey
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