IS Mount Misalignment 160mm vs 203mm

Joined
Sep 8, 2019
Messages
452
Location
USA, CA, Bay Area
While I'm working on my torque arm extension, part of the setup is replicating the rear wheel IS Mount (aka I.S. Mount / International Standard Mount / ISO Mount / forum-search-term-stuffing) on the extension arm.

zoom-out.png

However, in both this design and the previous version, the mounts seem to work with 160mm adapters, but the 203mm adapter doesn't get the caliper in the right spot.

Above, with the 160 rotor and adapter, everything lines up very nicely:
160.png

However, when you go with the 203 adapter, it's completely misaligned:
203.png

I'm designing the mount points from this diagram, which I've found referenced quite a few places:

rear-is-mount-dimensions-diagram.png

And using a few models (caliper, 203 adapter, 160 adapter) for the 3d simulation.

What am I missing as to why this goes out of alignment?
 
Sometimes it ends up that a custom mount needs to be fabricated to fit the application.
Looks like your CAD skills will be able to work it out.

Edit :
If the swing arm is still in the design phase why not move the two brake mount holes to a more ideal place ?
 
chuyskywalker said:
While I'm working on my torque arm extension, part of the setup is replicating the rear wheel IS Mount (aka I.S. Mount / International Standard Mount / forum-search-term-stuffing) on the extension arm.
Add ISO mount to that term list; it's more commonly used by searchers. ;)



However, in both this design and the previous version, the mounts seem to work with 160mm adapters, but the 203mm adapter doesn't get the caliper in the right spot.
Sounds like the adapter is not designed correctly? I don't have enough experience with the adapters to know if this is a thing; I cant' really imagine how a correctly designed adapter could ever cause misplacement of the caliper vs the rotor, since it should be based on placing the caliper mounting bolts in a specific place vs the radius of where the caliper ends up with the larger rotor. Seems like a simple problem for the OEMs that make those to solve (though I have not actually attempted to do so :oops: ).

Is it possible that the adapters for one caliper have different caliper mounting hole spacing relative to ISO hole spacing, than a different caliper adapter? (I don't have enough experience with disc brakes to say).


I have not measured the ISO diagram vs the CAD you've done, but assume you've dimensioned everything correctly. Otherwise the only thing I can think of is that there is something in the placement of the ISO hole centers vs the axle center that is causing the radial displacement to be different from ISO standard?


If it is useful, I did an image search that finds various sites with diagrams and/or charts for ISO mount points and adapters:
https://www.google.com/search?newwindow=1&q=rear-is-mount-dimensions&tbm=isch&source=univ

which finds this site
http://www.peterverdone.com/disc-brake-mounting-systems/
that may be useful, including this diagram.
http://www.peterverdone.com/wp-content/uploads/2018/06/2018-06-04-PVD-2018IS.png
2018-06-04-PVD-2018IS[1].png
and there are futher links on the page to various manufacturer standards.

This site also has a fair bit of info
https://help.worldwidecyclery.com/hc/en-us/articles/4806280513943-What-brake-adapter-do-I-need-

If everything is correct dimension-wise, and it just can't be made to work, what I would do in designing the torque plate, if intending to always use larger rotors, is just design your mounting points to fit the standard mounting points on the "default" adapter, if those "always" come out right on various calipers vs the rotor size you will be using.

If you're making something universal (like the recent one in the Torque Arm Picture thread), then I don't know the solution to make "any" caliper/adapter vs rotor size work. :(
 
amberwolf said:
which finds this site
http://www.peterverdone.com/disc-brake-mounting-systems/
that may be useful, including this diagram.
http://www.peterverdone.com/wp-content/uploads/2018/06/2018-06-04-PVD-2018IS.png
2018-06-04-PVD-2018IS[1].png
and there are futher links on the page to various manufacturer standards.

Yeah, I did run across this site during my research on this, but I've had a very hard time making heads-n-tails of how to use these diagrams. (Which, I suppose, is part of what the fellow is championing.)

amberwolf said:
If you're making something universal (like the recent one in the Torque Arm Picture thread), then I don't know the solution to make "any" caliper/adapter vs rotor size work. :(

I was looking around for solutions and had a flash of, "Hey, wait a minute..." "Stealth bomber" type bikes had a weird thing going on:

2023-01-14 16_06_07-Newest Kickstand installed on the swing arm for stealth bomber. _ eBay.png

What if I just...

2023-01-14 16_05_01-Autodesk Fusion 360.png

So that...

2023-01-14 16_02_31-Autodesk Fusion 360.png

And if you just slide forward a bit...

2023-01-14 16_04_25-Autodesk Fusion 360.png

Well, the pad alignment gets a little bit off, but not much at all, really. (And, a single shim washer to the rear would likely completely fix that anyway.
 
I ran into the same problem when I upgraded my ebike's rotors to 203mm:
https://a.co/d/i2iHDkJ

The 203mm adapter I bought from Amazon wouldn't work and the brakes bumped against the rotor:
https://a.co/d/foiL6py

I had to stack my old adapter on top of the new one until things fit:
PXL_20221026_123348053.jpg

Never figured out why either.
 
Product page for the brakes does, interestingly, have a vertical IS mount and an angled one of the same size:
Screenshot_20230114-162443.png

And below that it has flat adapters and wavy adapters. So maybe I needed the wavy adapter of the same size instead of the straight.
 
Ok, how about reversing the engineering process:

In the same "model", place the 203mm adapter (and be sure it's for 203, not 200, as there are both!) and the 180mm adapter, and for good measure a 160mm adapter if the calipers support that, such that the calipers all intersect but all correctly line up their calipers with the rotor.

Rotate that set about the axle center until their frame mounting ISO holes line up with each other--because there *has* to be some point at which they do...unless I simply don't understand how this stuff works (which is always possible).

Then you have the point where you can place the ISO mounting holes in the plate.
 
The standard size rear rotor for IS is 140mm, not 160mm.
The older IS adapters for 185mm and 203mm were specific for rotor size and position. The newer ones for 180mm,200mm and 220mm use an offset in 20mm increnets. So a +40mm IS bracket would be 200mm in front and 180mm in the rear. If you use the 140mm rotor as a standard, and the newer 20mm increments maYbe it will come together for you..
 
I just made my own . Cut my own, took 1 hour, works great. Ihave been thinking about making this on a machine in ten or so and selling them.

It is a Unicorn... Very rare in the wild... 180 ISo to 203 post mount adapter. I just decided to cut my own.

I would post pictures if I knew how to shrink them.
 
Here's some modeling up I did to get to the bottom of this; tl;dr: It seems the adapter I have (both on my bike, and the one I found online) are both just bogus.

  • Setup the basic IS mount dimensions and a dummy "fork".
  • Setup all the various brake rotor sizes (usually they are more like 15-20mm thick, for this exercise I left them 10 just to save myself some headache.)
  • Brought in the 160 & 180 adapter that lined up well, programmatically aligned everything to be A+ on point. (couldn't find a 140)
  • Projected the working mount locations, extrapolated where the next incremental version (technically 200mm) should be and created a mount based on that
  • Lined up the caliper to this "should be in the right place" mount and magic, it's dead on.

So:

a) I used the wrong model in my CAD; apparently the 203 front is very different from the 203 rear (as I've no learned one of the major failings of the IS system is that front/rear are very much not interchangeable) and
b) the Shimano SM-MA-R203P/S looks pretty much like what I modeled up and should need....

....which is what I have on my bike and does not align correctly. I guess everything is a lie and shims are life.

1.png2.png160.png160-through.png180.png180-through.pngextrapolation.pngtheorhetical-mount.png203-through.pngmount-comparison.png

And yet:

still-needed-washers.png
 
Heres mine I cut.
 

Attachments

  • IMG_20220915_165041780.png
    IMG_20220915_165041780.png
    209 KB · Views: 234
  • IMG_20220915_173816431.png
    IMG_20220915_173816431.png
    250.6 KB · Views: 234
  • IMG_20220915_181804434.png
    IMG_20220915_181804434.png
    255.8 KB · Views: 234
The rear IS mount would require a +60mm adapter to fit the modern 200mm rotor in the rear. It would be for the newest 220mm size in the front. To get 203mm you might need an extra washer to line it up.
 
DogDipstick said:
I would post pictures if I knew how to shrink them.
You don't have to--the forum will do that for you.
 
Ultimately I think that 1) I picked the wrong model for CAD and 2) the "Shimano SM-MA-R203P/S " maybe fits some weird shimano caliper which comes with special stand-offs or some other dimension that makes it work for those, but not most calipers.

Looking around it seems SRAM and Hope make 203mm IS rear adapters that look much closer to my theoretical model, so I've gone ahead and picked those up to see if reality matches up.
 
Quick follow up: the bike industry spits all over the term "standard" in "International Standard"

I picked up both the Hope and SRAM 203 adapters for IS rear: all three of them are different sizes/shapes/angles

2023-01-20 20.08.57.jpg
2023-01-20 20.08.38.jpg
2023-01-20 20.08.26.jpg

I'm not crazy, they're crazy!
 
chuyskywalker said:
Quick follow up: the bike industry spits all over the term "standard" in "International Standard"

I picked up both the Hope and SRAM 203 adapters for IS rear: all three of them are different sizes/shapes/angles

2023-01-20 20.08.57.jpg
2023-01-20 20.08.38.jpg
2023-01-20 20.08.26.jpg

I'm not crazy, they're crazy!
Do you have links to the three adapters? That second one looks like it might work for my bike. The caliper/pads sitting too high, especially on the leading side, so not just the depth by the angle of the adapter is wrong. I removed about 1/8" from the adapter before the pads would make full contact.
 
There are 2 standards for attaching calipers. The cross bolted IS 51mm, and the Post mount 74mm.
Many calipers such as AVID/ SRAM and TRP/ Techtro have the 74mm PM pattern on the calipers. I've interchanged those. But not all calipers follow that standard.
Here is a page of SRAM adapters that follow the 2 standards. IDK if this will help with the particular caliper you're using. But these are the standard sizes.
https://www.universalcycles.com/shopping/product_details.php?id=60011&category=5543
 
E-HP said:
Do you have links to the three adapters? That second one looks like it might work for my bike. The caliper/pads sitting too high, especially on the leading side, so not just the depth by the angle of the adapter is wrong. I removed about 1/8" from the adapter before the pads would make full contact.

Hope: https://thelostco.com/products/hope-rear-is-to-203mm-post-mount-adaptor

SRAM: https://www.worldwidecyclery.com/products/avid-sram-disc-60mm-is-adaptor-fits-200mm-rear-rotors

I suspect the SRAM will work best for me, but need to test it out later.
 
Retrorockit said:
There are 2 standards for attaching calipers. The cross bolted IS 51mm, and the Post mount 74mm.
Many calipers such as AVID/ SRAM and TRP/ Techtro have the 74mm PM pattern on the calipers. I've interchanged those. But not all calipers follow that standard.

All of these pictured claim to follow the IS mounting system (51mm axle-parallel holes on frame as in my original post with dimensional diagram) for a 203 rotor. (Ok, to be fair, the SRAM is technically for a 200mm, but the difference between 200/203 should be very minimal, not nearly as pronounced as these exhibit.)
 
It's the holes where the caliper mounts that are not following the Post mount 74mm standard. The Original Avid/ SRAM calipers used the 74mm Post mount at the caliper. The brackets were an adapter to mount them on IS bikes.
On the page I listed you will see 51mm IS to 74mm Post adapters, and 74mm Post to 74mm Post adapters for various sized rotors. if your calipers have holes 74mm center to center they should work. If the calipers are not that size then you will need brackets to fit that specific caliper. The brackets you show are obviously not all 74mm at the caliper. Maybe none of them are.
They probably all follow the IS standard at the frame holes. But they may or may not follow the 74mm post mount standard at the caliper holes. obviously some do not. The IS standard is not the problem. The caliper side st where you need to figure out what you need to match your caliper. If it is 74mm Post mount then the SRAM brackets should work. If it isn't then you need special brackets for those calipers
 
Do they match your caliper? I guess the brackets looked different in the first photo.
All I can do to try and help is explain the new system of 140,160,180,200,220mm rotors
A 0mm offset bracket will fit 160mmF, 140mm R
20mm offset will fit 180mmF,160mmR
40mm offest will fit 200mmF, 180mmR
60mm offset will fit 220mmF,200mmR
So there is a 20mm diameter difference between Front and rear
. Since 185mm, and 203mm weren't 20mm increments those require individual brackets for each size, and each end.
You should be able to shim up to 203mm.
i see from the photo in your avatar a scooter.. Scooter brakes may not be the same as bicycle brakes. The rotor may be thicker. Bicycles inherited flexible 1.8mm thick rotors from the cable brake days. TRP has some newer systems that use 2.3mmm rotors that don't flex. It's possible they made the parts not interchange intentionally to prevent using bicycle parts on a scooter.
Another thing is some calipers like AVID BB7 used spherical washers on the caliper bolts, above and below the caliper tabs. The TRP calipers bolt solid to the same bracket with no washers. So even following the standard the tabs are quite different due to the hardware used.
 
Avid BB7 You can see the washers.
https://imgs.search.brave.com/Gkt60x-wq7aDAnEMA5PKhYu5-oRjDHOpR_WKT1tngD0/rs:fit:640:578:1/g:ce/aHR0cHM6Ly9pLmVi/YXlpbWcuY29tL2lt/YWdlcy9nLy1xd0FB/T1N3S09KWUlPSk0v/cy1sNjQwLmpwZw

TRP Spyke bolted straight to the bracket.
https://imgs.search.brave.com/BD_0KMZ3CZ22PSS0HXbUf3zvDpblXZ8UMgcfXFMTI20/rs:fit:1200:1200:1/g:ce/aHR0cHM6Ly9pLmZy/b2cuaW5rL3ZOY3dF/VG9EL2RzYzAxNDY1/LmpwZw

These switch back and forth on the same brackets.
 
Back
Top