Made this using aluminum flat bar 1/8 inch thick 1/2 in wide. Twisted the upper end so it could be attached to lower brake boss. Lower end attached to the outside D-brake bracket.
I would have thought it would bend under load over such a great length.
It’s simply an auxiliary support to help buttress the D-brake. It would not bend since there is no evident movement of the D-brake during braking. The braking forces originally stressing the bottom arm are now partly shared by the added strut. The added reinforcement makes it less likely that the D-brake arm will fail. If this were to happen, then and only then, would the strut be likely to bend under the stress of the breakage.
Sure, but in order to perform as a strut, a member must resist bending. It will make some contribution to strength but not much.
The main problem with dBrakes isn’t so much bending (although that does happen) but chatter and vibration. The strut should help with that.
By the way Terry, if you’re worried about bending there is a newer version of the dBrake which is a bit more beefy than the one you have.
Very cool, thanks for letting me know!
Terry, do you have problems with disk brake chatter on steep downhills? I do, and had to add a bracket to support the D-brake adapter.
I’m just curious about when other people have issues with chatter. For me, I’m riding a KH 29" with a 203-mm disk and TRP 4-piston calipers with steel pads. If I’m on a hill that is >22 degree grade, this setup chatters really bad. So far, my little bracket has fixed the problem. But, what a hassle.
It makes me think that there is room for KH or UDC to develop a better out-of-the-box production solution.
By the way, I have the newer D-brake bracket. I think it looks even beefier than the “new D-brake” in the picture above. Plus, my D-brake bracket is 7075 aluminum which has a slightly higher Young’s Modulus than 6061AL.
Actually, the higher modulus makes the 7075 bracket stiffer. There is a chance that this may make the chattering worse (don’t remember my vibrations class that well). Are there any mechanical engineers out there that would know if chatter would be worse with a D-brake made from 7075 AL vs 6061 AL?
could you please post a link to that newest dbrake?
UDC shows the 6061 version but in the description it says 7075 aluminum. Can you post a pic of your 7075 d-brake?
I don’t use a d-brake bracket but I wonder if this would help. On my bearing caps I add carefully selected washers/shims so that the bolts can be tightened without deforming the bearings. Maybe using shims on both bolts that hold the d-brake and bearing cap on would help. With the correct shims the bolts can be fully tightened and maybe would help reduce any vibrations or looseness in the d-brake.
I was just about to order a new 7075 version D brake when I discovered that I already had one! It was buried in a drawer and covered with swirl dip from an old paint job. So I cleaned it up. Here it is next to the original 6061 version.
And here is a more direct method for reinforcing the D brake, with no attachment to the frame required.
There are lots of reports of chatter (and pictures of braces) in this thread.
Nimbus has switched to welded mounts in their current gen.
I wish KH frames came with disc tabs on the left side as well for those who want to run an external system.
The Mad4One frames have double disc mounts. Not sure that they do a 36" though :(.
Yeah, I knew about the mad4one frames but the largest they have will only fit a 29er wheel.
yeah, unfortunately they don’t make any frame larger then 29er.
Actually, their L size can accommodate up to 32"!
It does exist, it’s called buying a frame with welded on disk tabs.
A D-Brake adapter is really always going to be flawed, since there are only two bolts available on all frames, the bearing bolts (they happen to be in an unfortunate position for brake mounting). Any clamping solution would have to be pretty specific for each tube profile, since the forces can be pretty high, so you need rather a lot of surface area.
Side question: Does anyone know why we aren’t using post mounts? IS2000 seems like the worse standard when it comes to handling the forces to me. Pretty much all failures on Muni frames I’ve seen are close to the brake mounts.