I have a Nimbus 36". I put brakes on it once, but the force from my pedaling up hill made the frame flex. The brake pads would rub and I would fall off. So, what is the gap between rim and pad?
Whatever’s right for a bike is probably not enough for a Nimbus 36" frame. Probably the right answer is as little as you need to keep it from rubbing. Though this also may depend on the type of brakes being used, probably not as you still need it not to rub…
On a Nimbus 36, you’ll want to keep it pretty wide. Even on my KH36, I keep about a quarter inch between the rim and pad on each side, and that’s a stiff frame. On my nimbus, I had about 3/8 of an inch… kind of a lot. My frame would still bend enough to rub the pads when I was REALLY torquing hard, but it was infrequent enough that it was worth it.
Are you using Maguras, or did you drill your own hole to mount your own caliper brake? If you’re using Maguras, something to try might be mounting the brake pads farther out than you would normally, then bleeding more than enough fluid into the setup, or, rather, just adjusting the screw or knob so that the pads reside in a position a bit closer to the rim than they otherwise would. Like, if you adjust the knob in too far, the brake pads will be constantly pushed in toward the rim from their natural “off” positions. If you do this, then pushing in one brake pad will cause the other one to naturally push out the other way, because the volume of the fluid has to stay constant. If you mount the brake pads farther out from the rim, then adjust your brake handle way, way in - until the brake pads sit closer to the rim (where you’d want them) then you’ll have this little bit of “play” where the wheel can touch a brake pad without putting any real pressure on it (it’ll simply move the pad aside). You’ll lose some range of brake motion doing this, but if you can find a happy medium, it might be worth a try.
Yeah, I think John’s right. I always adjust (whether on bike or uni) until it doesn’t rub when the wheel spins. It takes a while to get it right, but it’s the only way. Trial and error, you know.
I’m using Magura HS-33s. Thanks for the help. I will try again and see how it goes.
As noted above, when the wheel spins is a start, but what he’s talking about is frame flex. So then you have to ride up and down some steep hills. Just bring the tools along and keep making adjustments until you either don’t notice any rubbing, or until it’s only a rare occurrence. The Nimbus frame is pretty flexy.
Want a less-flexy frame? Get the Coker V2. Very rigid, and claimed to be lighter than the Nimbus. Even on that one I’d get the occasional rub on steep MUni trails, just to give you an idea.
Redlinewaterboy, there is also the possibility that if your hub is a Schlumpf it might have some play in it. With my Schlumpf, if I give my rim even a light lateral push with my fingers the rim will move towards the frame/brake pads two millimeters or so. Definitely not enough force involved here to flex the frame. This is wobble in the hub due to a smidgen of space between the gears.
This, of course, is a problem when climbing hills. The last thing I want is my brake slowing me down on the uphill. On today’s ~2,500’ climb I adjusted my Echo hydraulic brake out a notch so that they wouldn’t rub at all, even with lots of torque and a little frame flex. The downside of this adjustment is that when I apply the brake they won’t slow the wheel down enough to be helpful. I have effectively disabled my brake. So before I headed back down I had to un-adjust the brake back to the way it was.
The way I see it, there are three possible problems and three possible solutions:
The first problem is that the hub is a Schlumpf and it has too much play in it. This wouldn’t apply to a standard solid one piece hub unless the bearings or bearing caps were loose. The solution to the play in the Schlumpf would be to somehow figure out a way to tighten things up and reduce this wobble/play. Anybody know how to do this? If your bearing caps are loose, then tighten them up. If the bearings are old and rattly, get new ones.
The second possible problem is that the brake pads just don’t have enough travel in them, like mine. My pads move in about 2mm on each side when they make contact with the rim. I’d be surprised if they could move more than 3mm if there wasn’t a rim in the way. They would never have even close to enough travel to close a 3/8" gap like Chuck rode with on his Nimbus. I keep my wheel well-trued and leave about a 2 mm gap between the rim and the pad. The solution is to find a brake that can cover a lot of distance with the pads when you pull on that brake lever. Chuck, what kind of brake did you have on your Nimbus that could close such a wide gap? Redlinewaterboy, get that brake. Other folks out there, how much clearance can you get your Magura brake pads to close and still give effective braking power?
The third possibility is that, in fact, the frame is flexing too much to overcome even the farthest traveling brake pads that have been set with a wide clearance. The solution is to toss that frame you just spent several hundred dollars on and take John Foss’s advice and get a Coker V2.
I’d be exploring brake options before I bought a new frame. In fact, that’s just what I’m doing. Anybody got any answers out there?
That’s what I meant by the “trial and error” part, although I didn’t make it very clear. The riding is always the time when you really learn if it’s adjusted correctly. I haven’t had experience with the Nimbus, but experience frame flex-induced brake rub with both my KH24 and KH29 when I’m really torquing on uphills and downhills.
The fourth possibility is not enough spoke tension.
Another thing to look at is the toe in of the pads. If the front of both pads are slightly closer to the rim than the rear of the pads then if there is a little bit of rub it won’t be so snatchy so you should be able to cope with it better.
Sorry for hijacking this thread but i have a magura question and I couldn’t find the info I was looking for.
I have just mounted my HS33’s in my new KH 29 and I was wondering about the proper setup of the pads on the rim.
What is the best orientation of the pads for them to work efficiently and not squeal? Do the pads need to toe-in or should they land flat on the rim? Does it matter whether the pad lands closer to the tire or closer to the spoke side of the braking surface?
Could someone give me a run down on how to correctly set them up on the rim or point me towards a tutorials somewhere?
If your brakes are squeeling the standard fix is to adjust the toe of the pad so that the front of the pad touches before the rear of the pad. The amount of toe-in is by trial and error. Too much, and the brakes will lose effectiveness (not necessariy bad on a uni), too little and they will still sqeel.
As for postition, some rims are designed to have the pads hit close to the inside diameter, but most are set up for the pad to hit somewhat central. If you have them close to the tire it can cause tire rub, especially on cantilevers as the pads wear.
Official magura advice is that you shouldn’t need any toe in, although lots of people do.
I don’t think anyone I know has maguras that consistently don’t squeal. Mine squeal sometimes and other times they’ll be silent for a whole ride. I think it has something to do with how wet it is or something.
I haven’t been able to kill the squeal on my Maggie’s. Maybe I just need to powder my brake pads. Or, maybe a little tri flow. The toe in doesn’t seem to matter as the brakes contact the rim they just flatten out, unlike a caliper brake.
I have V-brakes on my 29’er, and I can’t imagine why i would want anything else. Of course on a MUni the clearance around the tire is why Maggie’s are king, but for anything else V-brakes work really well. Another thing you can do with a cable brake is add an inline multiplier that pulls more cable than the lever. This allows the pads to be set really far from the rim, but the lever feel is as if they are much closer. You lose some mechanical advantage, but on a uni that isn’t a bad thing.