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-   -   "Half Moon" Fork Dropout Shims? (https://www.bikeforums.net/bicycle-mechanics/1025379-half-moon-fork-dropout-shims.html)

Dilberto 08-18-15 10:49 AM

"Half Moon" Fork Dropout Shims?
 
I only need 3-4mm of clearance in my disc fork. Front tire(700x33c) slightly rubs inside the crown, at steerer bottom(Cannondale Headshok fork). I use tires on a disc brake urban commuter with some dry packed dirt, so I need the comfort of 33mm width. Rear has plenty of clearance. I can manually set the wheel 3mm lower in the fork...but I really don't want to rely on my front skewer(Mavic internal cam) clamping force solely. I'm currently running 55psi on both tires(Clement LAS CX tires). I need something solid for the front axle to drop into, that I can remove fairly easily.

I have read people use cut spoke sections, ball bearings/BBs, solder, hard ABS plastic, drill/tap tiny screws....all I need is something that does not break the bank, requiring hours of fabrication. See I highlighted "hard ABS plastic" because it can be trimmed with a blade and affixed with double-stick tape. Can this possibly work, or will constant load-bearing deform it? Ideally, I'd love to tap a small Woodruff key inside the dropout....but do they make such small keys(4mm x 11mm)?

dsbrantjr 08-18-15 03:12 PM


Originally Posted by Dilberto (Post 18086112)
I can manually set the wheel 3mm lower in the fork...but I really don't want to rely on my front skewer(Mavic internal cam) clamping force solely.

You already are relying on it to keep the axle from coming out of the dropouts due to braking forces exerted by the disc brakes; having it slide up is a lesser problem.

I would advise against shimming the front axle on a disc brake-equipped bike, or anything else which keeps it from settling properly into the dropouts; the braking force tends to "eject" the axle. Many bikes have "lawyer lips" tabs to help mitigate this problem. If you shim the axle you may shim it past the tabs and negate this protection.

Tim_Iowa 08-18-15 03:38 PM


Originally Posted by dsbrantjr (Post 18087008)
You already are relying on it to keep the axle from coming out of the dropouts due to braking forces exerted by the disc brakes; having it slide up is a lesser problem.

I would advise against shimming the front axle on a disc brake-equipped bike, or anything else which keeps it from settling properly into the dropouts; the braking force tends to "eject" the axle. Many bikes have "lawyer lips" tabs to help mitigate this problem. If you shim the axle you may shim it past the tabs and negate this protection.

I agree, perfect advice. Dilberto, I can't imagine how you could get a shim to work on your fork with short dropouts and lawyer lips. An ancient steel fork with long dropouts, no "lawyer lips", and bolt-on axle? Still questionable, but possible.

However, since your fork has disc brakes, you could use a smaller diameter rim in order to gain clearance fit a wider tire. A 650b rim (aka 27.5, aka ISO 584) would give you 19 mm of extra tire clearance. You could probably fit a 38 or 42 mm tire with the smaller rim.

Is this a cheap solution? No, but it's not very difficult and totally safe. 27.5 is a popular mountain bike size now, so there are inexpensive disc-brake wheels available, and lots of tire choices.

dwmckee 08-18-15 09:52 PM

Try a short piece of a steel or brass tube fitted over the axle and to sit inside the drops, Just be sure the pieces are shorter than your fork thickness so the QR still bites on the fork. Be sure it does not affect rotor alignment with the pads.

HillRider 08-19-15 08:29 AM


Originally Posted by dwmckee (Post 18088129)
Try a short piece of a steel or brass tube fitted over the axle and to sit inside the drops, Just be sure the pieces are shorter than your fork thickness so the QR still bites on the fork. Be sure it does not affect rotor alignment with the pads.

If you do this, or any other shim, be certain the qr ends still sit above the lawyer's lips. As noted, these are essential to be sure your front wheel stays in place under disc braking loads. Don't rely on just the qr's clamping force.

wesmamyke 08-19-15 07:49 PM

Is it rubbing on the air valve in the bottom of the steerer? If so I would remove the cap, would buy you a few mm's.

Beyond that I would be way more inclined to modify the tire, shave it down, or maybe swap it with a rear tire that has some wear on it.

I made a half moon shaped shim out of some bit of metal one time, to position a single speed rear wheel. It worked but making sure it was in there just right and not losing it was a serious pain.

Dilberto 08-20-15 12:33 AM

Modified Lawyer Tabs did it....
 
I finally got the 4.7mm tire clearance I needed. The modified/trimmed tabs now face inside the dropout "U" just above the resting hub axle, secured by the clamped skewer ends(photo):
http://i276.photobucket.com/albums/k...psbwhrhbae.jpg

Here are the tabs, out of the fork:
http://i276.photobucket.com/albums/k...psriqx7dwf.jpg

Thanks to everyone's mention of "Lawyer lips"....I suddenly got the idea it would better suit this application. Instead of trying to bond or semi-permanently adhere the half-moon, Woodruff spacers to the fork dropouts - this solution works, simply because I can still mount the fork to my roof rack trays, without compromising structural integrity, or worrying about the bike flying-off at 80mph. Getting used to putting the front wheel back on quickly does still remain a challenge, as I have to make sure both tabs stay outside the fork...but between the skewer clamp ends. :thumb:

Net tire clearance, after grinding Headshok air valvecap release nub off(yes - dry conditions ONLY!):
http://i276.photobucket.com/albums/k...pskwz2gi20.jpg

Tim_Iowa 08-21-15 02:53 PM

No offense, but that seems terribly, horribly, and completely unsafe. I'm seriously horrified, and I work in a bike shop and see lots of kludges of questionable safety.

I would never ride a bike with the wheel attached that way, and I'm honestly afraid for your safety if you if you do.

Disc wheels are notorious for ejecting the wheel under hard braking, because of the high clamping force and short lever arm. Proper wheel retention is very important, especially with discs.

1) The clamping action is less secure because there is now a tab (acting as a washer) between the textured skewer cap and the fork end. The textured skewer cap now grips the washer, which does not grip the dropout very well.

2) The tab/washer pushes the skewer ends outside of the recesses/lawyer lips on the fork end, so there is absolutely no backup retention if the skewer opens. Which, it is more likely to do because it isn't gripping the fork end as securely.

Your solution gains you a larger tire, but loses you both primary and secondary wheel retention security. Seems like a bad trade, with the risks involved. Looks like a nice tread on that tire, though. Continental Cyclocross Speed?

It's unfortunate that this bike doesn't do what you'd like (fit a wider tire), but now you've put it at risk of functioning properly at all.

cobba 08-21-15 06:59 PM

2 Attachment(s)
Another problem with this dodgy setup is the disc brake caliper alignment with the rotor.

If the changed position of the caliper makes the pads overhang the outer edge of the rotor, the pads will get a step worn into them, overhanging pads will have less stopping power because there's less pad to rotor contact, a setup like this could also lead to brake failure if the overhanging unworn parts of the pads touch.

http://bikeforums.net/attachment.php...hmentid=472418

http://bikeforums.net/attachment.php...hmentid=472419

reshp1 08-21-15 07:39 PM

This is a bad idea especially with disc brakes. Think about the force the brakes are exerting on the wheel and which way your axle wants to go. Yes, your weight is counteracting that, but all it takes is a second of unweighting the front wheel for your wheel to pop out, which would be very very painful.

reshp1 08-21-15 07:43 PM


Originally Posted by Tim_Iowa (Post 18097747)
Looks like a nice tread on that tire, though. Continental Cyclocross Speed?

99% sure they're Clement LAS. They also look to be installed backwards.

Dilberto 08-21-15 10:03 PM


Originally Posted by reshp1 (Post 18098463)
99% sure they're Clement LAS. They also look to be installed backwards.

There is no directional arrow, indicating which way is which. Guys, I understand your concerns - the wheels never leave terra firma and there is weight loading at all times. Cobba, I am installing an older, Avid 165mm rotor....

reshp1 08-22-15 10:27 AM


Originally Posted by Dilberto (Post 18098750)
There is no directional arrow, indicating which way is which.

FAQ | Clement Cycling, Cyclocross Tires, Adventure Tires, Mountain Bike Tires, Road Bike Tires

"
Q: Which direction should I install the tires?
A: We prefer to install all our tires so any arrow-shaped knobs or chevrons face forward when viewed from the top. Typically, the most prominent knobs will have a sloped or ramped leading edge and a more abrupt or steep trailing edge, when viewed from above. This is true for both front and rear tires. On the PDX, the center arrow-shaped knobs face forward. The LAS side knobs form arrows facing forward too. Some riders may install them differently to get different traction characteristics and that’s perfectly OK!"

Some people (including myself) flip the rear for better traction under acceleration for climbing, but it doesn't make any sense to do it for the front since it's only ever going to see braking force, never accelerating force.



Guys, I understand your concerns - the wheels never leave terra firma and there is weight loading at all times.
That's only true if you ride on perfectly flat and smooth pavement, any bumps and all bets are off. Besides, completely lifting off the ground is ok since there's no braking force exerted anymore, the worst case is when you slightly unweight the front but the tire contact patch is still trying to pivot the wheel out. Believe me, that happens A LOT.

Dilberto 08-22-15 02:16 PM

Corrections Made...
 
Observe more closely(scroll above) the way I originally modified the Lawyer tab "washers." There really is no way the wide outer radius of the washer can slip past the narrow fork dropout opening, since it first has to clear the 2mm recess of the machined, dropout Lawyer lips. The only direction the Lawyer tab washers clear this recess, is by being pulled away outwards(after skewer is loosened). Also notice I left the lower tabs intact. Once the QR skewer is sufficiently loosened - I simply reach under and pop the lower tabs away from the dropout, then the wheel finally comes down. Install is reverse of removal....albeit a bit more finicky. Another thing is I don't need Gorilla-grip skewer tension, to keep the washers in the dropouts...but just enough, to keep the Lawyer tab washer always firmly faced to the dropout. Basically, to get the tire clearance desired - I stayed within limits of where the front axle should be, inside both ends of the dropout. The fork dropout has a wide flare at the bottom, to facilitate ease of wheel install. If in any way the axle final position were at or near the flared portion of the dropout....I would have gone with 650b wheels, hands-down. Thanks to the narrow "wiggle room" of the Cannondale Headshok fork - I did the bikes' shakedown run on a smooth, hard-packed XC race trail(Bonelli Park - Covina, CA)...and the bike performed without incident. Furthermore, I filed-down the IS brake mounting tab holes inward, so I could set the caliper correctly, with full pad contact restored. The vintage, Avid BBDB 165mm rotors would strike inside caliper body, by 0.51mm:

http://i276.photobucket.com/albums/k...psiyscxmhs.jpg


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