Offset mount for IS disc caliper

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jason701802   10 µW

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Offset mount for IS disc caliper

Post by jason701802 » May 03 2019 11:37am

I'm building a rear hub motor bike and I'm not sure how to mount the rear brake caliper. The disc is much further out than it was on the original wheel. This presents 2 problems: the caliper no longer lines up with the disc with the original adapter and the adapter doesn't fit between the disc and the frame. I'm also planning on spacing the disc out another 0.5-1mm as the current clearance between the hub and caliper is a little close for comfort.
Are there any offset adapters for IS mount calipers? I would think this would be a common issue but my searching hasn't come up with any solutions
20190502_184627_small.jpg
20190502_075622_small.jpg
P.S. is there a way to display an image as a thumbnail?

billvon   100 MW

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Re: Offset mount for IS disc caliper

Post by billvon » May 03 2019 11:41am

1) There are much thinner calipers out there. Ebikes.ca used to carry one; not sure if they still do.
2) A 203mm disk might move the problem away from the hub a little.
--bill von

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E-HP   10 kW

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Re: Offset mount for IS disc caliper

Post by E-HP » May 03 2019 11:42am

Looking at your first pic, the clearance between the hub and caliper is pretty generous, a lot more than i have. What is the concern, as long as there is clearance?

For the outer clearance, you can add a washer between the axle and inside of the dropout.

jason701802   10 µW

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Re: Offset mount for IS disc caliper

Post by jason701802 » May 03 2019 12:38pm

The issue isn't the clearance between the hub and the disc, the issue is mounting the caliper to the frame. The adapter that came with the bike doesn't fit, and even if it did, the caliper wouldn't align with the disc. In the first picture, you can see a few mm of overlap between the frame and the adapter.
This picture shows approximately where the adapter wants to live.
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furcifer   10 kW

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Re: Offset mount for IS disc caliper

Post by furcifer » May 03 2019 12:47pm

It's hard to see but your IS->post adapter looks a little fat. You can get slightly thinner ones (maybe a couple mm)

How is your frame spacing on the drive side?

eta: the more narrow one I have is 9.8mm wide

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E-HP   10 kW

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Re: Offset mount for IS disc caliper

Post by E-HP » May 03 2019 12:56pm

jason701802 wrote:
May 03 2019 12:38pm
The issue isn't the clearance between the hub and the disc, the issue is mounting the caliper to the frame. The adapter that came with the bike doesn't fit, and even if it did, the caliper wouldn't align with the disc. In the first picture, you can see a few mm of overlap between the frame and the adapter.
This picture shows approximately where the adapter wants to live.
Sorry, I responded to your second comment first "I'm also planning on spacing the disc out another 0.5-1mm as the current clearance between the hub and caliper is a little close for comfort."

and your first comment second, which is, it looks like you don't have an axle washer inboard of the dropouts:

http://www.ebikeschool.com/install-hub-motor-washers/

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Re: Offset mount for IS disc caliper

Post by jason701802 » May 03 2019 1:21pm

furcifer wrote:
May 03 2019 12:47pm
It's hard to see but your IS->post adapter looks a little fat. You can get slightly thinner ones (maybe a couple mm)

How is your frame spacing on the drive side?

eta: the more narrow one I have is 9.8mm wide
I'll measure the width of my adapter when I get home tonight.
E-HP wrote:
May 03 2019 12:56pm
Sorry, I responded to your second comment first "I'm also planning on spacing the disc out another 0.5-1mm as the current clearance between the hub and caliper is a little close for comfort."
There isn't as much clearance between the hub and caliper as the second image implies. The caliper isn't all the way on the disc in that image, so it's clearing around the rounded part of the hub cover. The point of the image was to show the overlap between the frame and adapter. The caliper just grazes the motor cover when it's fully on the disc.
E-HP wrote:
May 03 2019 12:56pm
and your first comment second, which is, it looks like you don't have an axle washer inboard of the dropouts:

http://www.ebikeschool.com/install-hub-motor-washers/
My frame perfectly matches the length of the axle without any washers on the inside. I have one of migueralliart's torque arms on order so I wasn't planning on using the torque washers. I'd rather not stretch the frame if I don't have to.

furcifer   10 kW

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Re: Offset mount for IS disc caliper

Post by furcifer » May 03 2019 1:33pm

jason701802 wrote:
May 03 2019 1:21pm
My frame perfectly matches the length of the axle without any washers on the inside. I have one of migueralliart's torque arms on order so I wasn't planning on using the torque washers. I'd rather not stretch the frame if I don't have to.
Yah, that's the fine print on these 135mm hubs I'm finding. The axle is 135mm, but the spacing needed to fit a 7spd and a disc is about 142mm.
I got this 1500W Voilamart hub used, but it came with a 7spd freewheel that sticks out further than the axle. I have to add spacers to get the ~142mm it actually needs. PITA.

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E-HP   10 kW

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Re: Offset mount for IS disc caliper

Post by E-HP » May 03 2019 1:40pm

jason701802 wrote:
May 03 2019 1:21pm
E-HP wrote:
May 03 2019 12:56pm
and your first comment second, which is, it looks like you don't have an axle washer inboard of the dropouts:

http://www.ebikeschool.com/install-hub-motor-washers/
My frame perfectly matches the length of the axle without any washers on the inside. I have one of migueralliart's torque arms on order so I wasn't planning on using the torque washers. I'd rather not stretch the frame if I don't have to.
OK, I'm sure you'll figure something out then. :thumb:

(you may want to be careful tightening down your axle bolts, since there's no inside washer and the axle shoulder doesn't provide much surface to spread that load)

jason701802   10 µW

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Re: Offset mount for IS disc caliper

Post by jason701802 » May 03 2019 8:49pm

The IS adapter I have is just under 10mm thick, so I don't think I'm going to get very far with a thinner adapter. It looks like I'll have to stretch the frame out ¯\_(ツ)_/¯

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E-HP   10 kW

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Re: Offset mount for IS disc caliper

Post by E-HP » May 03 2019 9:09pm

jason701802 wrote:
May 03 2019 8:49pm
The IS adapter I have is just under 10mm thick, so I don't think I'm going to get very far with a thinner adapter. It looks like I'll have to stretch the frame out ¯\_(ツ)_/¯
mine was like that and i just turned the bike upside down, position the wheel so the washers are kind of angled (like a V) and axle is just started, then grabbed the frame on each side, near each dropout, and pulled apart until the axle dropped in.

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MadRhino   100 GW

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Re: Offset mount for IS disc caliper

Post by MadRhino » May 03 2019 9:33pm

Stretching the frame with one or two washers is a common solution. Using a larger rotor is a good solution to gain some space between the rotor and the motor. It does also make some distance from the IS mount, making it possible to fabricate an offset adapter. It is easier to fit a post mount caliper in that situation. There is a solution that is very simple but expansive: Magura Gustav M caliper with 6’’ IS to 9’’ Post mount adapter, and a Hope 225mm vented rotor. No mod, no spacing required, best brake modulation and heat dissipation, but hard to find. My solution is custom dropout plates with integrated brake mount, so they can be whatever width, height and length required to match the motor, brake, and desired geometry.
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jason701802   10 µW

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Re: Offset mount for IS disc caliper

Post by jason701802 » May 09 2019 12:32pm

Stretching it was much less eventful than I expected. It easily stretched to fit around the washers and now I've got more than enough clearance for the brake caliper. Unfortunately it doesn't leave many threads for the nut after putting the torque arm on. Maybe I'll build an extra protector for the cable at some point (since it can't go out the side with the nut on), but I'm fine with it as is for now.
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E-HP   10 kW

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Re: Offset mount for IS disc caliper

Post by E-HP » May 09 2019 12:36pm

jason701802 wrote:
May 09 2019 12:32pm
Stretching it was much less eventful than I expected. It easily stretched to fit around the washers and now I've got more than enough clearance for the brake caliper. Unfortunately it doesn't leave many threads for the nut after putting the torque arm on. Maybe I'll build an extra protector for the cable at some point (since it can't go out the side with the nut on), but I'm fine with it as is for now.
Glad it worked out. That's a really beefy torque arm, so I don't think the nut has to do much work, as long as you can get it on.

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Re: Offset mount for IS disc caliper

Post by amberwolf » May 09 2019 5:46pm

jason701802 wrote:
May 09 2019 12:32pm
Unfortunately it doesn't leave many threads for the nut after putting the torque arm on.
Maybe use the torque arm *as* the inboard spacer?

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E-HP   10 kW

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Re: Offset mount for IS disc caliper

Post by E-HP » May 09 2019 5:53pm

amberwolf wrote:
May 09 2019 5:46pm
jason701802 wrote:
May 09 2019 12:32pm
Unfortunately it doesn't leave many threads for the nut after putting the torque arm on.
Maybe use the torque arm *as* the inboard spacer?
Ya but that torque arm look like it's 3/8" thick, so a lot more stretching of the chain stays than the washer.

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