GB4 Brake Booster - comments?


I was looking for comments about the GB4 Brake booster. The side clearance between the mounting holes and the tire seems really close to the tire sidewall. Does this create any problems?


Rod, I’m thinking you have a Hunter frame you’d be using this on?

If so, I can recommend it as being a significant improvement over not having one. It takes some messing around to get the adjustment right, but overall it works fine, helps keep the maguras from getting knocked out of whack, and definitely adds some strength to the braking power.

Tire clearance really hasn’t been an issue at all. I’ve never had gravel get caught up in it, and if you’re riding in enough mud to cause it to get gunked up, the problem will hit first at your brake pads anyway.

I’ve been told that Rick Hunter is now making his frames with two bosses on each side, eliminating the need for the booster. If you’re not lucky enough to have one of those new frames or the KH, then the booster is definitely worth its low purchase price.

here’s the scoop on brake boosters (if someone doesn’t know what they are actually for)

when the brake pads push against the rim, some of that force may be reduced by the frame flexing outwards. The booster prevents the frame from flexing, thus allowing all power to be used for braking.

Since your original question was around clearance, I should have also mentioned that I’m using the booster on a Hunter frame with standard 24X3 Gazz tire.

My 26X3 Gazz rubbed at the sidewall. This is with a 26" Hunter frame. When set up, the inside edge of the elongated sections at the mounting slots of the booster were so close to the fattest point of the sidewall that even slight tire roll would cause the brace to rub. It was every bit as close as it looks in the photo.
I remedied this by cutting the brace just above the elongated holes and redrilling new ones.
It has worked as it should since. But to answer your original question, yes, I did have problems with it.

  • Frank

although i’m pretty ignorant about all things magura, it would stike me that these things are only usefull if you have “standard” brake bosses, not the magura brake bosses, that you get on kh 24 frames for example.
i’ve got two sets of magura brakes that i scavenged a while back, but i havent bought a 24" frame yet, so they just sit in a plastic bag in the corner of my room. awaiting the day that i actualy have a few hundred quid burning a hole in my pocket.
the “evolution adapter” thing that they use to fit standard brake bosses looks quite unsatisfactory, when i get a 24 frame i’ll definatly want real magura bosses.

If you’re getting a frame custom made get the two bolt Magura mounts like what’s on the KH muni. With the two bolt style you don’t need a brake booster. Rick Hunter has put the two bolt mounts on some Coker frames, I assume he can now do the same with his muni frames.

The brake booster does two things. It stiffens up the frame to keep the frame from bowing when the brake is applied. And with the single bolt Magura mount it keeps the brake from rotating on the post when you rub it with your leg. The two bolt Magura mount won’t rotate so the brake booster isn’t necessary unless your frame flexes too much when the brake is applied.