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I can't stop!(7 posts)

I can't stop!mt_biker
Apr 21, 2003 6:09 AM
Holy crap, I just put Radius canti's on my bike. They don't stop! I replaced ultegra road brakes because I needed more clearance. I followed all the advise about a high stradle cable, brake pad alignment, etc. to no avail.
Next step is to try Ritchey red pads.

Would less/no toe-in help?

Any other suggestions?

If the new pads don't work, I'm going to steal some v-brakes off my mountain bike.
re: I can't stop!Gripped
Apr 21, 2003 7:54 AM
I've got Radius cantis on my bike and the original pads didn't stop worth crap. I put on a set of Avid cartridge pads (replacable pads) and they stop much better. They still don't stop as well as my 15 year old 105 side pulls with generic brand pads.

Hasta banana ...
Ditto...(long)Steve_O
Apr 21, 2003 10:43 AM
I recently made the switch from Avid Shortys to Radius brakes. My Avids gave excellent power but the squeal was just too much. After a year of fooling around with pad adjustments, different brake pads, and even trying different rims I threw in the towel...

I got the Radius brakes off eBay and have been using them for several months. I too had heard BAD things about their stock pads so I picked up some cheapy TOPO brand (Performance) post mount brake assemblies and ditched the TOPO pads for Ritchey Extreme condition pads (the red ones). The Ritchey pads helped but I still wasn't getting as much power as I wanted.

The next step was to play around with the straddle cable. I kept moving the straddle cable up higher and each time gaining more power. I now have it set up with the hanger probably a good 5" above the tire. I am still getting SLIGHTLY less power then my Avids but I'll take it in exchange for the quietness of the Radius brakes.

If you want an interesting read check out Sheldon Brown's discussion on Cantilever brakes (Specifically "Wide Profile" Cantis!).

http://www.sheldonbrown.com/cantilever-geometry.html

Based on this Sheldon seems to think that Mafacs and similar designs (ala Radius, Spookys, Neo-Retros, etc.) are obsolete due to their low mechanical advantage design. I usually put pretty good faith in what I read from Sheldon but this would seem like sacrilege to most 'crossers.

The other thought I've had to improve power on the Radius brakes would be to get a wider hanger for the straddle cable. There was recently some discussion on this.

Steve_O "Braking Issues" 4/9/03 11:04am

The real question for me would be how much the Salsa hanger would actually increase power? I'm probably getting 90% of the power that I had with the old Avids so I'll probably never test this hanger theory.... Unless I can get some cheap ;-)
Ditto...and a question.hummu
Apr 22, 2003 7:52 AM
The way I understood the Sheldon Brown article was that you had to match the brake lever to the cantilever brake. Low mechanical advantage cantis need a high mechanical advantage lever, and vica versa. This is the reason that you "had" to change your levers on your MTB when Shimano V brakes were introduced, and why Marinovator Cheap Tricks were so finicky to set up (no V brake levers at the time).

Everybody tells me my brakes are too mushy when they do the brake squeeze test when not moving. But I think my cantilever brakes (Shimano wide profile, Shimano narrow profile, MAFAC, Paul Neo Retro) feel as good and give me as good braking power as my Avid "V" brakes. I just have to experiment with the set up.

Here's a question. When Dieter Runkle won his world championship with the now famous Runkle levers, was he using Ergo or STI? I find that when I brake from the hoods with my index and middle finger, and my ring finger and pinkie around the handle bar (hanging on for dear life) the ergo shifter blades hit my fingers and braking performance goes down the tubes. If I brake from the drops, it is a one finger affair with plenty of power. Same from my top mount levers, 'cept I seem to like two fingers up there on the tops. Any thoughts on this?
Some theory... Not sure if it is right though....Steve_O
Apr 22, 2003 10:00 AM
I don't have the Runkles (or other top mount levers) but I experience the same loss of power braking from the hoods vs. from the drops that you do.

I think difference is simply caused by leverage. From the drops you tend to be closer to the end of the brake lever. This means a longer lever arm which can exert more force to activate the brakes. When you brake from the hoods you have a shorter effective lever arm which leads to less power. To put it in Sheldon terminology, you have more "mechanical advantage" when you are out near the end of the brake levers (while in the drops) then you do when you are braking from the hoods.

MAYBE the design of the top mount levers gives you a similar mechanical advantage to what you are seeing with your road brake levers... Sheldon has a few tidbits on this too!

The lever's mechanical advantage is determined by the distance from the lever's pivot to the cable end, and by the effective length of the brake lever from its pivot to where the rider's fingers grip it. Typical mountain-bike type brake levers give a mechanical advantage of around 3 1/2, old-style drop-bar levers around 4, and "æro" drop-bar levers around 4 1/2. Levers for direct-pull ("V-type") brakes are around 2.

Here's a section of Sheldon's discussion that also seems to ring home...

A brake with high mechanical advantage will apply a lot of force to the brake shoe for a small amount of finger pressure on the lever; the other side of the coin is that a system with high mechanical advantage will require the hand lever to move a long way to move the brake shoes a short distance toward the rim. If you have too much mechanical advantage, the brake lever will bump up against the handlebars before the brake shoe has moved far enough to engage the rim. If you tighten such a brake up enough to avoid bottoming out the lever, the brake shoes may not retract far enough when the brake is released, and may still drag on the rim.

The way I see it more mechanical advantage (whether at the brake OR at the lever) means more stopping power. Based on Sheldon's numbers above. Road levers give you good mechanical advantage. Combined with low profile cantis they should be a good combination. When road levers are combined with VERY high mechanical advantage brakes like V-Brakes the problem becomes that very little cable pull is needed to create strong braking. Now the issue is that little cable pull means that the brake pads sit too close to the rim when at rest. This causes brake rub. The other problem is that your brakes have very little modulation. It looks like cam devices on V-Brakes actually serve to reduce the mechanical advantage to help these issues.

Or.... I could be completely wrong..... But it is interesting theories right?
most is....atpjunkie
Apr 22, 2003 7:17 PM
your 'mechanical advantage' from the hoods is absolutely spot on. try to lift someone on a teeter totter from the middle vs the opposite end. it's simple engineering, the further from the pivot the more leverage you have, thus the less force is needed to actuate the lever. road calipers function the same when compared hoods to drops. I'm not sure about the vee theory but it looks right by me.
Update - I Can Stop!mt_biker
Apr 25, 2003 10:03 AM
All is well now. I replaced the pads with v-brake cartridges and pads. I can lock up the rear and endo the front. Who could ask for anything more?

Thanks for all the suggestions.