Rim/Frame flex causing brakes to grab? Muni

Okay so I have a Nimbus 26" muni with a KH26 frame and Echo rim brake.
While riding up hill or putting any kind of force onto my pedals while riding the brakes grip something wicked… no matter how far out I put them… which is very frustrating as I prefer my brakes very touchy.

Btw Im running a Duro 3" tubeless tyre… If that helps? Also 165 Ventures.
I mainly ride down hill and xc on this uni. With DH I love the brake really responsive but cant have it like this during xc or even on a small gradient uphill.

I have tried just flexing the rims with my hands and just by pushing on the wheel, the rim flexes right out to the pads.
So this makes me think its the rim right?
BUT I dont remember this happening with my nimbus frame on…
Confused indeed.

so how do I go about solving this issue?
Any advice and help would be great Cheers!

How’s the spoke tension? Maybe a tighter lacing would reduce rim deflection. Sounds like time to get some new skills wheel building or a trip to the LBS.

I don’t use my brakes much but when I need them…


When I moved from a KH 24 with nimbus wheel build to my custom KH26 I had break rub which I hadn’t had before, the fix was to put the maguras further out.

My guess is its to do with more flex in the bad? wheelbuild and the increased flex from the switch in frames. You shouldn’t have to tighten your spokes as often as you do…

Good luck Boffy :slight_smile:

Spoke tension doesn’t really affect wheel flex, unless the spokes are flopping around completely loose. Thinner spokes, longer spokes, fewer spokes all make for a flexier wheel.

Slop in the bearings could do it, if they are worn, or somehow able to move in the bearing holders.

When I used maguras on a 36 I had to remove them for off road use but a 36er has more leverage and a longer flexier frame than a 26.

The KH frame probably isn’t as stiff as the Nimbus frame but it should still be plenty stiff enough. I second Mr. Impossible’s suggestion that you check your bearing and bearing holders. If the connection between wheel and frame is not solid it doesn’t take a lot of movement there to make a rim contact a brake pad.

The wide double-walled rims we use for MUni won’t be flexing much even with a poor wheelbuild, so I doubt it is the wheel itself.

I would check the tension on the bearing holder bolts. You may be able to tighten them up–but there is a limit. You do not want the bearings themselves to bind.

I have one of Bryce’s Franken-brakes on my 36", which allows me to set the pads out far enough to avoid rubbing. My other unis do not have significant brake rub, but I have tightened bearings and worked on the wheel build to minimize flex.