Whats the brake pad to rim gap?

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?


--
redlinewaterboy
------------------------------------------------------------------------
redlinewaterboy's Profile: http://www.unicyclist.com/profile/16901
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com

More.



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...


--
johnfoss

John Foss
Email: "jfoss" at "unicycling.com" -- www.unicycling.com
-----------------------------------------------

"False facts are frequently formed from figures fabricated from fear
fired fiction." -- Harper
------------------------------------------------------------------------
johnfoss's Profile: http://www.unicyclist.com/profile/832
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com

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.


--
chuckaeronut

Uni to work to eat to live to uni to work to...!
------------------------------------------------------------------------
chuckaeronut's Profile: http://www.unicyclist.com/profile/14677
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com

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.


--
pkittle

*==========================
Peter Kittle * Chico, CA
"The Revolution is just a t-shirt away."
--Billy Bragg
==========================*
------------------------------------------------------------------------
pkittle's Profile: http://www.unicyclist.com/profile/12111
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com

I'm using Magura HS-33s. Thanks for the help. I will try again and see
how it goes.


--
redlinewaterboy
------------------------------------------------------------------------
redlinewaterboy's Profile: http://www.unicyclist.com/profile/16901
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com

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?
Geoff


--
naturequack

monocycle monstrosity
------------------------------------------------------------------------
naturequack's Profile: http://www.unicyclist.com/profile/16649
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com

johnfoss;1132318 wrote:
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.



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.


--
pkittle

*==========================
Peter Kittle * Chico, CA
"The Revolution is just a t-shirt away."
--Billy Bragg
==========================*
------------------------------------------------------------------------
pkittle's Profile: http://www.unicyclist.com/profile/12111
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com

naturequack;1132436 wrote:
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?
Geoff



The fourth possibility is not enough spoke tension.


--
goldenchickenIV
------------------------------------------------------------------------
goldenchickenIV's Profile: http://www.unicyclist.com/profile/16391
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com

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.

STM


--
semach.the.monkey
------------------------------------------------------------------------
semach.the.monkey's Profile: http://www.unicyclist.com/profile/12078
View this thread: http://www.unicyclist.com/thread/74303


Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
http://www.usenet.com