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Need help with caliper/frame clearance issue please

Old 06-23-22, 08:21 PM
  #1  
kim791
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Need help with caliper/frame clearance issue please

My son has a Prevelo Zulu Two Heir and we upgraded his brakes to Magura Mt4s. However the rear caliper sat on the frame. We added a.washer between the caliper and adapter, that helped but it still hit. So we added a second washer to the right side only. Will this cause any problems? It barely clears the frame and my son is 45lbs. If it will, what are my options? Safety is my priority but the stock brakes were terrible (Radius). The other issue is it causes the caliper to sit higher so there's a tiny bit of unused pad at the top, but I assume that uneven pad wear would be the only consequence? I appreciate any and all feedback, thank you!
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Old 06-24-22, 07:05 AM
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Does the brake work?
Does it work the same as the front.
Push on the bike and apply the brake. Let it go see does it open cleanly
If it's good ride slow and try it.
Keep testing till your sure.
And then keep an eye on it.
A washer shouldn't make much of a difference so long as the bolt has good engagement.
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Old 06-24-22, 08:53 AM
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Originally Posted by blamester View Post
Does the brake work?
Does it work the same as the front.
Push on the bike and apply the brake. Let it go see does it open cleanly
If it's good ride slow and try it.
Keep testing till your sure.
And then keep an eye on it.
A washer shouldn't make much of a difference so long as the bolt has good engagement.
Everything seems to work as it should, front and back brake the same. But I just want to make sure I'm not creating an issue with 2 washers on one side and one on another. I did use a longer bolt to attached the side with 2 washers.
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Old 06-24-22, 09:16 AM
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When the pads start to wear you'll run into a situation where the pads have a small lip of material that's above the rotor. Eventually those 2 lips will touch and your kids brake will instantly stop working.
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Old 06-24-22, 09:20 AM
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Originally Posted by cxwrench View Post
When the pads start to wear you'll run into a situation where the pads have a small lip of material that's above the rotor. Eventually those 2 lips will touch and your kids brake will instantly stop working.
Thanks, We will definitely be keeping an eye on the pads and replace as necessary. I was talking to someone who had the exact same setup and he said he filed the frame after installing one set of washers rather than adding the 2nd washer. ...does that sound like a better route? I've never filed a frame before.
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Old 06-24-22, 10:33 AM
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Which caliper-to-frame adapter are you using? I've run into a similar issue recently that had me going into plenty of shenanigans that were costly and aggravating, what with hunting for 165mm rotors and playing with washers to get everything to fit... Turns out it was all completely unnecessary: All I had to do was buy and use an dapter of the same brand as the calipers (Shimano in this case) and everything just fit together nicely with the original 160mm rotor. So, if you've mounted the caliper to the original adapter that tye Radius caliper was on, you probably should get a Magura adapter and see if that gets things lined up.
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Old 06-24-22, 10:53 AM
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The problem is i cant seem to find one that fits a 140mm rotor from Magura. I think it's just a pain since it's a kids 16" bike and parts are not readily available, even though the brakes are listed as good for bikes up to 20".

Last edited by kim791; 06-24-22 at 10:58 AM.
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Old 06-24-22, 11:11 AM
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Originally Posted by kim791 View Post
the brakes are listed as good for bikes up to 20".
Not sure what that means, but some pictures of your actual setup might help..
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Old 06-24-22, 11:14 AM
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Originally Posted by sjanzeir View Post
Not sure what that means, but some pictures of your actual setup might help..
I was just saying the brakes I bought are designed for bikes with tires up to 20", yet they don't sell any adapter for a 140mm wheel. I would love to add pictures but I can't yet as new here.
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Old 06-24-22, 11:31 AM
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Originally Posted by kim791 View Post
I was just saying the brakes I bought are designed for bikes with tires up to 20", yet they don't sell any adapter for a 140mm wheel. I would love to add pictures but I can't yet as new here.
Unless you're talking about a different MT4 than the one listed on Magura's website, I don't see how the caliper has anything to do with the size of the wheel.

It appears that what you have is a common PM-to-IS (post mount to international standard) adapter:




What you should do is find a replacement that would work better as an interface between frame and caliper. A quick search didn't return any Magura branded 140mm adapters, but there's bound to be something out there that works better than ruining a perfectly good frame with a file..
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Old 06-24-22, 03:00 PM
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Originally Posted by kim791 View Post
I was just saying the brakes I bought are designed for bikes with tires up to 20", yet they don't sell any adapter for a 140mm wheel (you mean rotor?). I would love to add pictures but I can't yet as new here.
What size rotor is on the bike now?
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Old 06-25-22, 03:21 AM
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The photos show the problem: https://www.bikeforums.net/g/album/25438694
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Old 06-25-22, 04:30 AM
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Originally Posted by cobba View Post
The photos show the problem: https://www.bikeforums.net/g/album/25438694
I have a feeling that the adapter might be on backwards, but I could be wrong. Perhaps someone else could confirm this.
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Old 06-25-22, 05:02 AM
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Originally Posted by sjanzeir View Post
I have a feeling that the adapter might be on backwards, but I could be wrong. Perhaps someone else could confirm this.
I reinstalled the bracket the way it came off but I can definitely try flipping it
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Old 06-25-22, 05:06 AM
  #15  
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Originally Posted by kim791 View Post
I reinstalled the bracket the way it came off but I can definitely try flipping it
There should be an arrow etched on the adapter. Check it out, see where it's pointing (forward or reverse) and what rotor diameters are marked on the adapter and report back (again, pictures would help a great deal.)
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Old 06-25-22, 06:22 AM
  #16  
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Pad hanging over the edge is bot a huge problem. It will be a long time before a 45lb kid wears them down enough to touch, but even then, all you need to do is file off the tabs.

But this is really not optimal. You might try stepping up to a 160mm rotor with an adaptor from magura.

I donít know about the mt4s, but I have the mt7s and the caliper body hangs down a little farther than most, and my Shimano and Sram adaptors did not work (the caliper hit them. I needed Magura adaptors.

Also, Many maguras are designed to be used with 2.0mm thick rotors. Not sure about the mt4s.
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Old 06-25-22, 10:05 AM
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Originally Posted by Kapusta View Post
Pad hanging over the edge is bot a huge problem. It will be a long time before a 45lb kid wears them down enough to touch, but even then, all you need to do is file off the tabs.

But this is really not optimal. You might try stepping up to a 160mm rotor with an adaptor from magura.

I donít know about the mt4s, but I have the mt7s and the caliper body hangs down a little farther than most, and my Shimano and Sram adaptors did not work (the caliper hit them. I needed Magura adaptors.

Also, Many maguras are designed to be used with 2.0mm thick rotors. Not sure about the mt4s.
You are correct,, ugh.. I had just followed someone else recommendations with all of this. If i grab Magura storm hc 160s for front and back, will the qm 12 adapter be the correct one?
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Old 06-25-22, 11:07 AM
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Originally Posted by kim791 View Post
You are correct,, ugh.. I had just followed someone else recommendations with all of this. If i grab Magura storm hc 160s for front and back, will the qm 12 adapter be the correct one?
I donít know I am not clear what your frame and fork mounts are.
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Old 06-25-22, 11:34 AM
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Originally Posted by Kapusta View Post
I donít know I am not clear what your frame and fork mounts are.
The pictures in his gallery show a regular IS-to-PM adapter on the rear.

Originally Posted by kim791 View Post
You are correct,, ugh.. I had just followed someone else recommendations with all of this. If i grab Magura storm hc 160s for front and back, will the qm 12 adapter be the correct one?
The QM12 is a 180mm front/160mm rotor adapter. So if you want to go ahead and use this, you're going to need to get a 160mm rotor, too, and swap it in place of the 140mm one you have now.

With that said, I haven't found a Magura 140mm IS-to-PM adapter. If you want to keep the 140mm rotor, you could try your luck with a 160mm F/140mm R adapter from Shimano, Formula or Noah&Theo. But first, do check whether or not the existing adapter has been flipped around and report back.
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Old 06-25-22, 12:02 PM
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Originally Posted by sjanzeir View Post
The pictures in his gallery show a regular IS-to-PM adapter on the rear.



The QM12 is a 180mm front/160mm rotor adapter. So if you want to go ahead and use this, you're going to need to get a 160mm rotor, too, and swap it in place of the 140mm one you have now.

With that said, I haven't found a Magura 140mm IS-to-PM adapter. If you want to keep the 140mm rotor, you could try your luck with a 160mm F/140mm R adapter from Shimano, Formula or Noah&Theo. But first, do check whether or not the existing adapter has been flipped around and report back.

Yes, we will check the adapter although it appears to look the same on each side. I'm figuring if the rotors I have are not thick enough, I need new ones so may as well go 160. I should be able to solve all my issues using their 160 adapter, assuming it fits. Is there any downfall to having 160s in front and back? I'd love to post pics here but I'm a new member and haven't met my requirements yet.
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Old 06-25-22, 12:26 PM
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Originally Posted by kim791 View Post
although it appears to look the same on each side.
The front and rear adapters may look the same but they won't fit the same way. If yours are indeed the same, then check if they both say "160 F/140 R" on them. You really need to look this over before you spend any more money. Otherwise, just put the Radius back on the rear wheel the way it was and use better pads. (What was wrong with them, anyway?)

Originally Posted by kim791 View Post
I'm figuring if the rotors I have are not thick enough, I need new ones so may as well go 160.
And by that I assume you mean "not large enough in diameter," because rotor "thickness" refers to something else.

Originally Posted by kim791 View Post
Is there any downfall to having 160s in front and back?
Not really, especially on a bike this small and this light. All it really needs to do is just work.
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Old 06-25-22, 12:32 PM
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I see the brake mount on the frame allows for some adjustment of the location of the caliper. Have you tried messing around with that? Or is there simply no way for that caliper to clear the frame without the pads hanging over a 140mm rotor.

Last edited by Kapusta; 06-25-22 at 12:36 PM.
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Old 06-25-22, 12:35 PM
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Originally Posted by sjanzeir View Post
The front and rear adapters may look the same but they won't fit the same way. If yours are indeed the same, then check if they both say "160 F/140 R" on them. You really need to look this over before you spend any more money. Otherwise, just put the Radius back on the rear wheel the way it was and use better pads. (What was wrong with them, anyway?)



And by that I assume you mean "not large enough in diameter," because rotor "thickness" refers to something else.



Not really, especially on a bike this small and this light. All it really needs to do is just work.
As another poster pointed out to me and i verified in the Magura Mt4 manual, they have a wear limit of 1.8mm so they recommend 2.0mm rotors. These are 1.8mm to start with. So im assuming, that will be an issue?

i meant that the adapter on the rear looks to be mirror itself when flipped, so i dont "think" that will solve it. The Radius brakes were inconsistent and spongy. There are no marking at all on the stock adapter.

Last edited by kim791; 06-25-22 at 12:38 PM.
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Old 06-25-22, 12:42 PM
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Originally Posted by Kapusta View Post
I see the brake mount on the frame allows for some adjustment of the location of the caliper. Have you tried messing around with that? Or is there simply no way for that caliper to clear the frame without the pads hanging over a 140mm rotor.
There is no way for it to clear the frame without the washers, we tried sliding it all around.
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Old 06-25-22, 12:47 PM
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Go ahead and order a QM12 adapter and any 160mm/2mm six-bolt rotor. You'll find quite a few 2mm thick rotors on eBay and elsewhere. The rotor neither needs to be Magura nor does it need to be pricy. Just take care of the issue once and for all.
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