Left side drive brake options?

recumpence

recumpence

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Hey Guys,

In an attempt to keep from clogging up the drive system thread, I figured I would start a new thread about options for braking while using the disc brake flange as a sprocket mount.

Here is one possibility. I opened up my Avid caliper to the max and it fits (with room to spare) around this #25 sprocket! So, I could use a "Sprotor" (sprocket/rotor) arrangement if I am willing to run a #25 chain. I am not sure that small chain will be enough. But, if I go with a large enough sprocket, the chain loading will be lower and the "Rotor" will be larger for better braking. So, maybe a 8 inch Sprotor?

Any thoughts?

Matt
 

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This idea is exactly what I'm thinking of doing for a new frame build that I'm working on. Let's start finding caliper spec sheets and such to see what sort of clearances are available.

One potential issue is heat into the chain. There could be more warping, heat cycling fatigue, or the heat could accelerate the breakdown of the chain oil. Cooling could be a big deal.

The chain will have a lot of time to cool down as it travels the rest of the path, but the thermal inertia of the chain will have to be high in order for it to stay cool while in contact with the sprocket. A heavier / higher thermal inertia chain, heavier oil, or a bigger chain size, would be better for that, but the later will be limited by caliper clearance.
 
Can you run the chain through the caliper, or does it have to go around it, requiring that the caliper be relocated?
 
Does the chain fit through the caliper or does the caliper have to be located on the sprocket such that the chain goes around the caliper? Also, looking at all the fancy brake rotors with cutouts on the OD I bet the brake pads can ride on the sides of the teeth with no problems. (well except that the chain will have to go around the caliper.)

Marty
 
Chain lube... Most sprockets get messy.
 
The chain does have to go around the caliper.

Lube is not a big deal as you can use many different types of dry lube. Also, if minimal normal oil is used, it does not move from the teeth down the sprocket face.

The pads contact the disc just below the teeth. So, this would, in theory, work fine.

Oh, heat is not much of an issue on bike disc brakes unless high speed and long braking distances are encountered.

I think it could work. Again, I am concerned about #25 chain strangth.

I guess some testing is in order!

Matt
 
Excellent subject!

Matt,
That caliper is mechanical, right? It looks alot like my Avid. Is there a special relationship between the pad material and the type of metal used in the disks? Will that sproder be made of aluminum or steel? I don't see heat transfer to the chain to be an issue, most of the braking should be done in the front anywayz. Mounting the caliper will probably be the biggest hurdle to overcome, and then proper lube for the chain. I think the easiest, most universal system would be a seperate sprocket dished in toward the rim and stock brake bits intact. A sproder would be trick indeed though.
 
Yes, it is an Avid caliper.

I have been doing a little research into rotor material for production of my own rotors. I am sure there is a "Correct" material for a disc brake rotor. But, that is something I need to research.

Matt
 
A lot is being asked of the braking system on powered bicycles. Even though the rear brake has a 70% easier time, the potential for chain lubricant to contaminate the disc brake pads and seriously diminish brake performance on your rocket/sproder/sprisk is high. There is also the issue of heat, which on a reasonable descent can be high enough to make the chain lube on the teeth smoke. I would be inclined to use quality V brakes (Avid Ultimate or Shimano with paralell push like XT/XTR). It's only under the most extreme snow or mud conditions that discs offer any real benefits on the rear wheel. If you really want a rear disc, an option you may consider is the fitment of a 200mm rotor onto the hub, then 3mm or 4mm spacers, then the driven sprocket. I would also fabricate a small shield to prevent chain lube 'fly-off' from contaminating the pads and rotor.

I'm no expert, unless I'm on the internet.
 
Here's something I considered but have not pursued.

make a device that works on top of the stock brake disk, but reaches through the gaps. It would have a central hub that mounts on the six hole brake mount, then has five (i think) arms that reach through the gaps in the brake disk, and each of those is drilled and tapped for the sprocket.

So, on the mount, you would first install the brake disk, then the adapter would go over the top of that, but have arms that reach through (imagine grabbing the disk with your hands using your fingers to go through the disk slots) then you use longer bolts to mount both on the same mount.

If you use the larger disk brakes, the sprocket could be smaller allowing clearance for the caliper.

Potential problems:

The sprocket gets set too far back and gets close to the wheel, so that the chain cannot get to it.
The arms that the sprocket mounts to may not be strong enough.
Difficulty in manufacturing.
 
^^^ has potential ^^^

Similar, without spider: mount a chainring to the inboard side of the disk using standoffs. Less torque on the spider.
 

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what sort of size will the rear sprocket be (i know it will vary on gearing) roughly in inches?
i dont think combining is a good idea myself -if the chain goes around the caliper how much purchase will you lose? wouldn't it cause slippage?
im going to use sprocket mounted to disk with spacers (4mm or so) like tyler and hangdog suggest but have the sprocket on the outside of the disk just inside the frame - i figured the further to the outside the easier to get a reasonable chain line?
the point about contaminating the pads is valid too.
if you keep the sprocket size in check you can always go to 9" disks which would give plenty of clearence between the caliper and the sprocket? the idea about having a thin plastic disk between the sprocket and the disk is an excellent one which if you dont mind i'll use.


Cheers,

D
 
TPA,

That sounds very complex and different for every disk. Are you wanting to mount on the other side of the disk because the extra material from the sprocket would cause alignment issues between the disk and the caliper? ...breath... If so, it would seem easier to just shave down the disk mount to the proper fitting, and just use some sort of dished adapter to bolt the sprocket to. I am going through the same thing here, so if we figure out a solution, it should be universal to everybody. I also think the aussie is right in trying to seperate the braking from the chain because of dirt and oil. I am lucky in that my cheapo bike happens to have V-brake mounts and disk brakes. :p
 
Hi etard,

well for me i was under the impression that the matts reduction box that i want to use will have a drive sprocket of limited adjustability for the chain line so i thought have the sprocket furthest out and smaller than my rotor. adjusting the caliper postion is easy enough to align with the rotor wherever it is but for me my rotor could only be adjusted inwards as its quite close to the frame as is.

Cheers,

D
 
Seems like a hub like this would have enough metal to turn down the mount and install a sprocket adapter, then the disk.
red_large.jpg

or maybe an adapter that just slides over the hub...
sprohAdap1.jpg
 
For mine, I'd leave all the meat on the hub and get the sprocket as close to the brake rotor as I could and make sure the bolt holes are as tight as I can get 'em. There's a lot of forces going both directions and most MTB hubs aint that strong in that particular area. I like Phil Wood's hubs in that area, they're STRONG.
31071275.jpg
 
That adapter should be perfect TD. The mount on that hub seems to be very similar to mine, I bet it is universal, I will ask my LBS tommorrow. Could you just slip the adapter over the hub, and then secure it laterally by mounting it with spacers to the disk? I wonder how strong that would be.
 
Another thing you may want to consider is using an internally geared hub like the Shimano Alfine 8 speed.
I say Shimano because I believe they make the best hub this side of the Rohloff.

Two reasons. First, the forces on the wheel with these powerful motors are going to be significant. Normal 9 speed bicycle hubs are weaker because of the way the cassette side spokes are closer to vertical on that side. On an internally geared hub the right side spokes are the same as the left side. Wheels built (properly) with these hubs are dramatically stronger than cassette hub wheels.

Secondly, the alfine hub uses a splined disc mount for which there are a number of adapters as the design lends it self to adapters. The gearing is quite wide in practice and removes the need for multiple front chainrings. It also lends itself to quite high gearing for the legs to take advantage of the higher speeds/lower effort made possible by the motor.

alfine.jpg

Above, Alfine hub showing greater spoke flange width
Below, normal hub showing weaker and narrower triangle
2x_3x_theory.gif

Shimano splined disc rotor flange shown
shimano_xtr_wheels_06_p.jpg
 
Spacer rings that attach to the disk and an adapter plate would handle torque better than standoffs. The spacers could be drilled to fit a variety of disks.
 

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Tyler,

In your previous design, I meant that if you slipped the adapter over that "petal" pattern in the red anodized 8) hub, wouldn't most of the stresses be transfered here? Then just use some spacers and bolt the chainring to the disk and adapter for proper alignment.

Hangdog,

Glad to have you here! Those internal hubs are very heavy aren't they? I see your points about triangulation, and gearing for actual pedalling. Also, the splines on the disk mount are steel?
 
etard

The hubs are heavier than the stock derailleur set-up for sure. The Shimano Alfine is better than most (bang for buck). The benefits outweigh the weight disadvantages in my view. Stronger wheel, protected from the elements, reliable shifting and wide ratio gearing are a few. The downside is more unsprung weight but in my experience handling isn't affected much on the road. I used a Rohloff rear wheel in MTB Downhill competition and there was a difference in handling for sure. I have a non-suspension cargo bike we developed for postal delivery with a the Shimano Nexus hub and the handling difference is undetectable, and we tried very hard to detect it. They're extremely reliable and after about 6 months the trick is to open it up, pull out the mechanism and wash all the grease out then dunk it in light gear oil, sit to allow the excess to oil run off and then re-install. It's a 10 minute job and you won't believe the performance after that. Repeat every 6 months. Another downside is that it is a bit of a pain to change a tire.

The spline is aluminium. Yes, could be a problem.
 
etard said:
Tyler, In your previous design, I meant that if you slipped the adapter over that "petal" pattern in the red anodized 8) hub, wouldn't most of the stresses be transfered here? Then just use some spacers and bolt the chainring to the disk and adapter for proper alignment.
Click to expand...
Ja, that was my thought, but it seems too dependent on the specific hub... needs a close fit for good transfer of force.

Mounting to the disk or the disk flange might be more universal. The spacer rings will also help prevent the torque from flexing the disk.
 
Tyler, I like your rendering of the adapter/spacer plate. That seems to me like the right direction to move forward. (scratch my shimano spline suggestion :| )
 
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