# Rohloff and Post Mount : Discuss



## fokof (Apr 24, 2006)

Just got a new rohloff , I want to instal it on a 700c / SS bike.
One problem is that it's a post mount brake.

Anybody found a solution ?

An Idea I had but I don't have access to a machine shop:
(photo)
I have IS brake with a post mount adaptor but if there is a post mount calliper right on the tabs , we could fit an adaptor on top of the calliper (longer nuts) that would act like the "Speedbone" provided by Rohloff
(2nd photo)

3rd photo would be what it could be,
Sorry for my poor Photoshop knowledge


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## genefruit (Feb 24, 2011)

Maybe this? - Monkey Bone Post-Mount Brake Adapter for Rohloff SPEEDHUB - Cycle Monkey


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## fokof (Apr 24, 2006)

Thanx but that is the opposite of my situation , I have a post mount frame.


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## SimpleJon (Mar 28, 2011)

Can you not just use the OEM plate and torque arm that ships with the hub? Looks a lot less hassle and expense than machining stuff to me.


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## ladljon (Nov 30, 2011)

Monkey Bone....


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## fokof (Apr 24, 2006)

Thanx for the reply guys but my frame has *Post mount* tabs.
It's not the same thing as IS tabs.

Post mount screw itself from the top , IS screws itself from the sides.

The Monkey bone works with an IS tabs frame , it doesn't work with Post mount tabs.
Here's a link that explains the difference between both:
Disc Brake Mounting Standards

SimpleJon:
Yes I could use the torque arm , but it is not as convenient and practical.
I will use that until Cyclemonkey come up with a solution 

Sharing ideas here might accelerate the processus!


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## TraxFactory (Sep 10, 1999)

I would recommend a custom torque arm. I've seen some frame cracking issues on what you are trying to do. The leverage of the longer TA puts much less stress in a non critical area (ie; welds).

See this post: http://forums.mtbr.com/turner/sultan-rohloff-583416.html


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## fokof (Apr 24, 2006)

Thanx for that

My thinking is to make an adaptor that would be on top of post mount calliper and would act as a Speedbone. Brake area of a frame being strong , should not be an issue.

Like on the thread you linked , I also have some welds in the way of the OEM2 plate , placing it like on my 1st photo (towards the back) clears the welds. 
I think that it might be the same for a lot of Postmount frames too.


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## TraxFactory (Sep 10, 1999)

fokof said:


> Thanx for that
> 
> My thinking is to make an adaptor that would be on top of post mount calliper and would act as a Speedbone. Brake area of a frame being strong , should not be an issue.
> 
> ...


I mocked up a wooden bone, something similar to what you are describing but it would have been huge in my situation and opted for a cleaner torque arm in the end.

In lower gears ( i think 1 - 10) the torque is opposite your breaking force, so the leverage is a back and forth situation. My friend broke 2 stays using the Bone, that is why I think using the TA is always best.

All that said, all frames are different in design so you may be good to go....but it sucks finding out the hard way.

Best of luck! Post some pics..


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## SimpleJon (Mar 28, 2011)

How much torque does the hub generate at axle plate and surely a lot of that will transferred to the frame through the dropouts? 
I would be very surprised if it is anywhere near the loads that a disc brake generates at the caliper mounts - I think that any stays designed for disc brakes should be more than capable of handling a Rohloff


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## TraxFactory (Sep 10, 1999)

No idea on the amount of torque. What I am trying to convey is, the torque from the Rohloff in lower gears is clockwise and the brake is counter-clockwise so you have a back forth lever situation on the same mounting area. To me that is a recipe for crackola if you don't have enough beef in that area and I have seen it first hand. I would not assume anything and finding out the hard way (crackola) is not fun.

Since the torque from Rohloff is counter-clockwise its actually trying to be ripped out of the dropout not up into it like brake torque would.

The longer torque arm puts the leverage point in a different location and the longer lever also reduces the amount of torque on the connection point, that we know for sure. Don't take my word, you should call Niel at Cycle Monkey.

Edit: After looking at that 3rd picture again, if your set on using the SpeedBone or similar I would just have someone weld some material onto the alxe plate ( it is just mild steel), drill a hole in the proper position (speedbone pin) and then grind in and opening.
Other possible issue you may have is getting the wheel out of the dropout. Wheel goes down and out of dropout but cant because speedbone pin needs to go up and out.........


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## gatouille (Aug 17, 2009)

Hi fokof,

Max hub torque (Rohloff data) : 100 N.m
1st gear (R 0,279), clockwise, torque on plate (for max hub torque) : 260 N.m
14 gear (R 1,467), unclockwise, torque on plate (for max hub torque) : (-)32 N.m

I have the same opinion that RipRoar.
Apply torque on seatstay will only bend this tube, not the chainstay. On aluminium frame it can break after the weld between dropout and chainstay (after that, frame = dead). A lot of alu frame broke like this.

Your have your solution : machining a thick plate like a "long" speedbone.

The best solution is Torque Arm. It's not pretty but it works.


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## TraxFactory (Sep 10, 1999)

Custom torque arm, visually better than Rohloffs OEM setup.


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## SimpleJon (Mar 28, 2011)

Makes sense thinking about it, a bike drive train sees 2 load unload cycles per revolution of the crank unlike an electrical motor or flywheel driven arrangement. Even though the forces are much less than disc brakes - at 80RPM thats 160 cycles per minute. If the frame designer doesn't consider local stresses in the stays from a high torque IGH and minimise them by design so that they are at or below the fatigue threshold, fatigue failure is pretty likely. Aluminium has pretty low fatigue threshold and the extrusion process allows for weird geometries, easy to see how failures can occur in a relatively short space of time.


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## fokof (Apr 24, 2006)

Brake tabs are designed to get a lot more stress than an IGH counterforce.

How many people with aluminium frames are using Rohloff's or Monkey cycle's monkey bone without issues ?

I had my OEM2 right on the IS tab on my Cannondale for 8 Years , frame is still OK.

Might get funky if you try somewhere else me thinks, that's why I prefer to find a solution involving the brake tabs.


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## TraxFactory (Sep 10, 1999)

fokof said:


> Brake tabs are designed to get a lot more stress than an IGH counterforce.
> 
> How many people with aluminium frames are using Rohloff's or Monkey cycle's monkey bone without issues ?
> 
> ...


Q1: Yes and No. They are designed to get the force in a COUNTER-CLOCKWISE direction.

Q2: Probably far more people running no problem compared to those with cracked frames.

Its just a call you need to make based what you have available to you. I am just pointing out my experience. We are all engineers in our own way.

When and if you do make that bone, keep in mind the part about getting your wheel out. I ran into that when I was mocking up what your describing.

Good luck and post back if your make a mutant bone or axle plate

Also check out this thread, see what 2X-pneu came up with, you may be able to do the same. Pretty clean, no idea if its held up.

http://forums.mtbr.com/turner/sultan-rohloff-583416-2.html


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## gatouille (Aug 17, 2009)

Q1 : Rohloff torque on plate is opposite than brake force. Brake tabs design is not a problem, it's strong. I think that it's the repeated inversion + variation of torque which causes crack on chainstay + the contrast between strong seatstay with brake reinforcement and "basic straight tube" chainstay. That's why we put a bridge between seatstay and chainstay.

Q2 : same answer that RipRoar. We just want to give you information about the risk of this solution, certainly low risk.


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## fokof (Apr 24, 2006)

Thanx for the heads up and for the link.

I'm hoping that this discussion will give ideas to people who actually have access to machinery. I don't.


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## Wombat (Jan 25, 2004)

If you do a google search for "post mount frame rohloff adapter" and look at the images you'll see the first image is this one.

There are quite a few other examples.

Tim


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## TraxFactory (Sep 10, 1999)

Wombat said:


> If you do a google search for "post mount frame rohloff adapter" and look at the images you'll see the first image is this one.
> 
> There are quite a few other examples.
> 
> Tim


Nice! its been awhile since I googled it. Makes sense by now other people would be coming up with other solutions. Still looks like custom solutions, and in my opinion the Torque arm is the safer route, I wouldn't want to use my frame to test that single bolt setup.

Now if Rohloff would only re-tool and make a 142x12 hub......


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## fokof (Apr 24, 2006)

Wombat said:


> If you do a google search for "post mount frame rohloff adapter" and look at the images you'll see the first image is this one.
> 
> There are quite a few other examples.
> 
> Tim


Wow !!!
That's exactly what I was thinking of , except maybe screwed on top of both tabs , not only one.


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## fokof (Apr 24, 2006)

Bingo !!!!!!!!
(from another thread)
Rohloff SPEEDHUB 500/14 - A12: Rohloff für Steckachse

(Rohloff PM Bone)

Waiting for this to be available on the market and I'll get my third Speedhub.


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## TraxFactory (Sep 10, 1999)

fokof said:


> Bingo !!!!!!!!
> (from another thread)
> Rohloff SPEEDHUB 500/14 - A12: Rohloff für Steckachse
> 
> ...


Nice find! Finally..


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## MonkeyWrench (Feb 7, 2006)

Here's the English version of the press release:



__ https://www.facebook.com/permalink.php?story_fbid=938215636220431&id=304605066248161



Note that you will have to bump your rotor up one size to use the Post Mount Bone.


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## fokof (Apr 24, 2006)

So to close that thread beautifully : the final solution !!

Thanx Rohloff


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## TraxFactory (Sep 10, 1999)

*Rohloff Fat Bone*

Finally!, it only took 7 years for a simple machined part. I guess Rohloff does nothing until a standard is well cemented in.

Here are some better pics


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## fokof (Apr 24, 2006)

Anybody had success installing a Rohloff with a PM disk "inside" the rear triangle ?

I was wondering if the PM Bone Extension would clear the seat stay.


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## MrBadger (Apr 4, 2010)

fokof said:


> Anybody had success installing a Rohloff with a PM disk "inside" the rear triangle ?
> 
> I was wondering if the PM Bone Extension would clear the seat stay.


I looked into this to Rohloff a Stooge frame with the brake mount in this position (although on the Stooge it's IS mount not PM) and from what I can gather the advice from Rohloff is not to use Speedbone/Monkeybone when the brake mount is forward of the axle.


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## fokof (Apr 24, 2006)

Strange ........ the torque arm is forward ......

The counterforce will always be the same no matter where the fix point is.


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## MrBadger (Apr 4, 2010)

fokof said:


> Strange ........ the torque arm is forward ......
> 
> The counterforce will always be the same no matter where the fix point is.


Good point. They say that if the brake mount and hence the bone are forward of the axle it could force the wheel out of the dropouts whereas in the rearward position it forces it in. I'm tempted to try it though. I'll let you know if I die trying.


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