Anyone DIY a R side brake caliper mount on susp fork

[John in CR]

I need more front brake force but don't want to go with moto brakes, so double front discs seems like the best route. I can easily mod the hub for dual discs, but my concern is the caliper mount.

I found this adapter at CustomMotoredBicycles.com , but it seem to flimsy for my needs.


I'm hoping someone has already done it, so I can borrow ideas. Welding on my titanium 888's is out. I can spread the braking force over enough of the fork lower to be comfortable, but the twisting force is the concern. The two options I see are:
1. Use longer bolts on the 20mm axle clamps to a bracket that connects there and wraps around to the caliper mount.
2. The hub is a moto hub, so I have to diy spacers that go from the inner race of the bearings to the fork to prevent lateral movement of the wheel on the axle. I could fab the right side spacer and caliper bracket into one unit.

Both approaches would include a curved cradle to mate with the backside of the fork and transfer braking force there. That would be lightly clamped to hold it in place. It's just the torsional rigidity that concerns me. If high temp wasn't an issue, I'd consider simply fabbing a caliper bracket to a few inch long piece of tubing split in half and use light clamping along with DP460 epoxy to create a permanent right side disc mount.

How about other ideas?

John

 

[cal3thousand]

That's the only 'out-of-the-box' solution that I know exists. There's always the DNM dual disc forks, but that's throwing money at the problem and I know that's not what you are looking to do.

Good luck, I hope you do find a good solution for those that may look afterwards.

 

[amberwolf]

It's probably not as simple as it sounds, but I would just create a plate that mates evenly to the surface shape of teh rear of the fork on that side, that can be clamped/bolted on however you need to, and then weld the brake mount to that.

To align it before welding, you shoudl be able to bolt the caliper to it, clamp teh caliper onto the disc, then align the mounting tab to the plate that's already clamped/bolted to the fork, and tack weld. Maybe fully weld it if your parts can handle the heat or you can keep it from gettin ginto them. Othewise take the tackweled part off and fully weld it.


I've alredy done this to directly weld one on a leftside steel fork, and have planned to do it with the curved plate for an alloy fork but never got around to it.

 

[Punx0r]

If high temp wasn't an issue, I'd consider simply fabbing a caliper bracket to a few inch long piece of tubing split in half and use light clamping along with DP460 epoxy to create a permanent right side disc mount.

How hot are you expecting the fork stanchion to get? A high-temp epoxy might do you.

Or, an adaption of your split-tube mount, just gently (overlapping spots) weld the two halves in place. Either use a another section of tube below the joint to act as a heat shield, or welded flanges to the joint to physically move the weld away from the stanchion. You could probably get a decent shrink-fit from the welding.

 

[John in CR]

It's probably not as simple as it sounds, but I would just create a plate that mates evenly to the surface shape of teh rear of the fork on that side, that can be clamped/bolted on however you need to, and then weld the brake mount to that.

To align it before welding, you shoudl be able to bolt the caliper to it, clamp teh caliper onto the disc, then align the mounting tab to the plate that's already clamped/bolted to the fork, and tack weld. Maybe fully weld it if your parts can handle the heat or you can keep it from gettin ginto them. Othewise take the tackweled part off and fully weld it.


I've alredy done this to directly weld one on a leftside steel fork, and have planned to do it with the curved plate for an alloy fork but never got around to it.

I've welded caliper mounts on steel too, but I'm not getting any type of welding or brazing near my 888-Ti's. I can do a 2 piece bolt together easily, and probably wouldn't even need to go with epoxy, just use a high temp silicone. That's what I did with slip over straight tubed MC forks to accept a hubmotor like Punx0r mentioned.

Maybe I'm over-thinking regarding forces making the sleeve try to twist around the fork. I keep imagining the catastrophic failure that would occur if the caliper and mount get pulled around into the spokes. At this point I'm leaning toward a thick piece on the axle, that doubles as the spacer. Then that would swing up to the form fitting part to mate with the back of the fork lower like you mentioned, and clamp and glue in place.

First I'm going to the MC part store and bring my scale. Maybe there's a light enough drum brake hub that is little or no weight penalty. That will give me more braking surface than dual bike discs. Drums aren't good due to poor heat dissipation for racing or heavy stop and go, but that's not how I use them, since regen bears most of the braking load. My needs are more for an emergency stop from high speed. I need to get a braking distance from over 100mph reasonably short.

If I can't find a decent wheel/hub/drum brake combo, then I'll come up with something. It may be a bit Frankenstein-ish like my first clamping dropouts and torque arms, but hopefully as useful to the community.

John

 

[John in CR]

If high temp wasn't an issue, I'd consider simply fabbing a caliper bracket to a few inch long piece of tubing split in half and use light clamping along with DP460 epoxy to create a permanent right side disc mount.

How hot are you expecting the fork stanchion to get? A high-temp epoxy might do you.

I was thinking about the heat coming from the brakes. Discs get scorching hot, but I don't know about the caliper and heat moving through the bracket. Maybe I can find enough stainless scraps at my friend's machine shop to fab the bracket out of. That might be enough to bring epoxy into play, since stainless has much lower thermal conductivity than carbon steel. That's why eating utensil handles don't get hot.

 

[Punx0r]

I think the stanchion will act as a good heatsink for the caliper mount. You make a good point about ensuring there's no way the brake can end up in the spokes. It shouldn't happen because the braking force should pull it straight, but I wouldn't bet my life on it. The drum brake also sounds like a good idea. I'm sure you'll come up with a good solution

 

[John in CR]

False alarm. I found the complete wheel with drum brake that weighs the same as my unmodded wheel before counting discs and calipers. The double disc front will have to wait for my trail bike mid-drive bike build. 20kw of high efficiency geared down to a top speed of only 60mph on the high speed pulley set and 40mph on an 85-90lb ebike including everything but the battery should be a monster. With the 21" moto wheels I have think of something along the lines of Drunkskunk's big red beast with some components even heavier duty.

 

[mat h physics]

I need to get a braking distance from over 100mph reasonably short.

Right off the bat, my though was you need to go full blown moto, bicycle brakes won't be enough. Glad to see you found an alt, though keep in mind drum brakes have an inherent flaw of locking up easy. And while you may not even be using brake fluid, if you should get some brake fluid on the shoe material they will lock up VERY easily. Just want to make sure you know, as I remember you getting dumped by patch of sand a few years back.

I've been wondering how much stopping power a regen can recover on the front wheel, surly it won't lock? The purpose of inquiry is to find a practical use for this: https://youtu.be/MfEroyS6Ix0
Being you like to fabricate, why not a fast charging power sink?
Tried to get informed opinions here: http://endless-sphere.com/forums/viewtopic.php?f=3&t=68715
but didn't have much feedback.

Best of engineering skill to you my friend, stay safe.

 

[John in CR]

mat h physics,

Moto vs motorized bicycle is just a legal definition, and either should be built to withstand its use without failure. Mine are legally treated as bicycles regardless of the power, but I'm certainly not putting myself at risk of any of my bikes falling apart or having an important mechanical failure. While I've some have been a bit long on braking distance, I ride in a manner where emergency stops occur a very low speeds. I use distance between myself and other vehicles as my route to safe riding at traffic speeds and greater.

Yes, I know not to get brake fluids on pads.

I would call drum brakes inherently flawed, though the do require tome touch to modulate well. FWIW these are leading/trailing type brake shoe alignment, so the "self-energizing" effect is lessened. I'll get plenty of practice on the track prior to the top speed attempt, so I'll know where I have to start braking and add a bit of cushion. I have a fast bike, but I'm not crazy. It's been capable of over 100mph for a year and a half, but I've only done it twice. Neither video turned out well, which is why I'm giving it another go with proper preparation and planning. Except on the highway I don't ride any faster that I did for the year and a half it was at 74V and capable of only 67mph.

Regen braking by it's nature cannot lock up the wheel, though it can skip and skid, but I have no interest in having a front motor on this bike. At speed my controllers combine for a max regen braking of about 5kw. That's the max going into the battery, and with my high efficiency motor I think I can safely assume what goes back into the battery is a decent measure.

 

[riba2233]

Regen braking by it's nature cannot lock up the wheel, though it can skip and skid, but I have no interest in having a front motor on this bike.

Are you sure :lol: It happened to me a few times on a rainy day and bad, slippery asphalt. It's with kelly controller which can regen down to almost zero, and mid drive on my moped.

 

[John in CR]

Regen braking by it's nature cannot lock up the wheel, though it can skip and skid, but I have no interest in having a front motor on this bike.

Are you sure :lol: It happened to me a few times on a rainy day and bad, slippery asphalt. It's with kelly controller which can regen down to almost zero, and mid drive on my moped.

Of course I'm sure. The wheel must turn for regen to occur, so "locking up" isn't possible. That doesn't mean it can't skip or skid with the wheel turning slower than the bike is moving.

 

[riba2233]

Well enough to make you drift lol, not pleasant when you're not expecting it :lol:

 

[MadRhino]

A dual brake is not necessary to shorten your braking distance. You can use a better brake and a larger rotor, that are available in bicycle components. Magura Gustav, MT 7, Hope M6, Shimano Saint... Fitted with performance pads and a 225mm rotor, can bring your braking distance shorter than any motorcycle. The difference is in heat dissipation, that is why motorcycles are fitted with dual brakes, and most are just for aesthetics and fashion because their performance doesn't require that.

Slow brakers are making a lot of heat, I mean those who are starting to brake long before they need to stop. Aggressive braking is much cooler.

 

[Punx0r]

I don't think that is correct: the more slowly you brake the more energy is lost to aerodynamic drag and there is more time for thermal energy to be dissipated from the brake.

John, the drum brake sounds ideal as a mechanical backup, should be nice and reliable

 

[Hillhater]

Which ever way you go, dual disc, drum, etc, you will be increasing the braking forces and consequently the loading on the forks, fork head tube, frame headstock welds etc etc,
You are stopping a lot of weight from high speed and whilst I'm sure you have a quality set up, are you comfortable with these unknown loads on those "bicycle" design components ?

 

[Punx0r]

Braking forces through the front end are limited by either traction of the front tyre or lifting or up-ending the bike. Therefore these forces should be independent of speed. They would be proportional to the weight of the bike, but as long as the frame can bear that weight, the speed should not matter.

Of course, hitting a bump/pothole the speed does make a difference and travelling at greater speed may warrant an increased factor of safety for the frame.

I have a feeling John will not be easily deterred from high-speed riding

 

[MadRhino]

I don't think that is correct: the more slowly you brake the more energy is lost to aerodynamic drag and there is more time for thermal energy to be dissipated from the brake.

Try and measure temp of your brakes.

Hard braking is heating the tire, slow braking is heating the brake

 

[Punx0r]

True, hard braking will increase tyre flex which must increase tyre heating to some degree, but I cannot believe that it's significant compared to the heat put into the actual brake. My experience with cars bears this out: a rapid stop from high speed produces hot brakes, gentle braking from the same speed does not. Reductio ad absurdum: no braking results in a complete stop with zero brake heating. Infinitesimal braking results in infinitesimal brake heating.

 

[MadRhino]

Using the same logic: Locking the wheel makes no heat in the brake

 

[Punx0r]

Can't argue with that! Tricky for a front wheel on a bicycle, though

 

[amberwolf]

Not if the bike is long enough and/or weighted rear-end enough, so you don't do a stoppie but instead just skid.

 

[MadRhino]

My experience is downhill. Braking aggressive short bursts saves your brakes and seconds on the chrono, while the brake draggers always have trouble with their brakes and never win a race..

 

[jansevr]

upgrading to a larger rotor or a better caliper might not be the best option. recumpence might be someone to talk to. he has experience with these on one of his recent builds: "20 inch full suspension street build" http://endless-sphere.com/forums/viewtopic.php?f=28&t=65549&start=150

the rotor is Hayes V9 and the calipers are Hope Tech 4

however this is what he says about the rotor and caliper:

You can see the front rotor blued from heat. The caliper got hot enough that I could not touch it (after 8 full throttle, full brake sessions back to back).

considering the higher speeds that your bike is capable of im not sure this will work as well as you would like, but without welding or buying a dual disc fork this might be your only option.

 

[MadRhino]

The problem here is a brake that is not big enough to shed the heat. I said HOPE M6, that is almost twice the V4.
Then, "hot enough not to touch it" is not unusual. Overheated means the rotor turning to blue and the braking distance starting to lenghten.