Thursday, October 4, 2012

More tension...

After writing that last piece on the various ways to tension cables after they stretch, I noticed something peculiar.  Everyone knows that disc brakes are coming to road, right?  And when I say road, I mean drop bar bikes with integrated shift/brake levers.  And lumped in "road" are cyclocross bikes which will be, by far, the bulk of road looking bikes with disc brakes.  Okay, to summarize, a lot of bikes will be on the market that combine road shift/brake levers and disc brakes.  Road levers do not have any method to tension cables.  That's the duty of the brake caliper on road bikes.  "So what," you say.  So, if there are new disc brake calipers coming from SRAM/Avid and Shimano that are designed to be used with road levers and SRAM and Shimano know that their levers have no means of tensioning cables, why did SRAM/Avid and Shimano forgo barrel adjusters on their disc brake calipers?  Good question and one that would have seemed easy to address by adding a barrel adjuster to the caliper.  I think this point is a fail on both SRAM/Avid and Shimano's parts.  Heck, Hayes was able to get a barrel adjuster on their CX5 caliper.  

Avid's BB7 Road SL caliper.  Nope, no barrel adjuster.

Shimano's CX-75 road caliper.  Like Avid, no barrel adjuster.

Hayes' CX-5 road caliper.  They got it right with that barrel adjuster there.  Nice touch, Hayes!

(What's playing:  Elvis Costello Chemistry Class)

9 comments:

Rob At Ocean Air Cycles said...

I really do hope it is a forest through the trees sort of issue for their designers. From reading the general info the manufacturers provide, one would be under the impression that you can solve the issue with the pad adjustment. In reality though that is no different then adding washers under the brake pads of a traditional pad and lever rim brake system. The question then begs, if industry design veterans like yourself, and engineers new to the industry like me, can clearly see such a basic omission, how do we bring about change? If the designers at the big component houses are missing the bus on a huge safety issue who hits the button to ask the driver to stop?

This is a safety issue far greater than users leaving the quick release open on their caliper brakes. Even a well set up installation per spec will need adjustment in short order. Average riders will have poor and/or limited stopping power in under 1000 miles of riding. The resulting required adjustment will need to have the cable re-set at the caliper end. The adjustment is not impossible, but the added effort will cause many to put it off. The bike will become less functional, and likely see less and less use.

Is this an clear example of poor design? A slow motion conspiracy to force riders back to their local mechanics if they have any hope of stopping at intersections?

I see some irony in the situation, reminiscent of what happened to center-pull brakes through the bike boom era of the 70's.

blackmountaincycles said...

I hear you, Rob. A few weeks ago, I had a touring cyclist come in for a derailleur adjustment. When I looked over her bike (Avid road disc equipped), I realized that she had no brakes. I could pull the road lever all the way to the bar and still push the bike forward by hand. I have no idea how she stopped when she pulled up to the shop.

With mechanical disc brakes that operate with ball bearings moving on a tapered ramp, you have to be careful how far the lever moves so the ball bearing doesn't run out of ramp and cease to function. Avid's instructions for the BB7 was always to make adjustments at the pad and not at the cable.

I think for sure there needs to be some more thought. It seems like the Shimano and Avid road disc calipers were designed more as a secondary thought without taking into consideration cable management. In-line cable adjusters work fine, but they are really for a case when there is no tension adjustment option - as in putting things together from road and mountain groups. A barrel adjuster on the disc caliper is much cleaner looking than in-line adjusters.

Rob At Ocean Air Cycles said...

We live in a popular launching point, West Ventura, for riders to park cars prior to their rides up into the coastal range. If I had a nickle for every front brake quick release I see open and help the rider close, I would not need to be working nearly as hard. I have no idea how these folks stop or even perceive what adequate stopping power and control should be.

I know that the inline style adjusters work, Having cobbled a few dirt drop systems together over the years. Are the inline type recommended by their own supplier for brakes or just shift system adjustment? Based on the info that Jagwire published I suspect we will not be seeing their inline adjusters on an OEM braking system any time soon. The answer is as simple as you have shown, but how do you get it into implementation outside of your own shop? Or do we sit back and let it unfold while designing/selling rim braked bikes and reference you opinion piece on brakes from a while back?

In reality any brake is only as good as its installation and setup, but to see OEM options hitting the street with an apparent design fail is sad. I am surprised that Zinn has not been more vocal on the issue, he seems to be a smart guy when it comes to issues like this.

blackmountaincycles said...

Avid does include in-line adjusters with their road BB7 calipers so they (SRAM) are aware of the situation. I think the adjusters are the same Jagwire ones that Jagwire says aren't compatible with brakes. However, they do work fine on brake systems. I would imagine that we'll see specific brake in-line adjusters out soon and manufacturers will likely incorporate an in-line adjuster or some other cable tension method into their frames.

Guitar Ted said...

Having set up several road tandems with mechanical disc brakes (Avid), I can say that the inline adjusters provided are working great for the customers we have. I also use these on my drop bar set ups as well.

Interestingly- Avid BB-5 calipers do have the adjusters as the Hayes example does in your post. I always figured Avid didn't provide them on the BB-7's so they could say they weighed less. :>)

My concern is that the housings used for mech disc brakes from OEM are not very good. It seems that it should be imperative to spec the stiffest, least compressive housing possible, no matter the price, but I know that's a pipe dream!

blackmountaincycles said...

GT - I think Avid's intention with why the BB5 has the adjuster where the BB7 does not is for the BB7 to use the outboard pad adjuster instead of a cable adjuster.

Seems like a no-brainer for compressionless housing to be specified at the OEM level. But then that would add another couple bucks to the landed cost of the bike.

jimmythefly said...

I've been telling everyone within earshot who is just getting into road disc breaks that they need to add in-line adjuster ASAP.

I personally like having them (even if the caliper has an adjuster) because I can locate them up near the bars where they are reachable on-the-fly.

brad said...

I have a set of Avid BB7's and they are designed to adjust with the inner and outer screws on the caliper. The instructions advise against adjusting the brakes with the a barrel adjuster, and they don't say why, but it's because the brake clamps from one side so you have to set the inner pad as close as you can first, and then set the outer. It works fine.

blackmountaincycles said...

That's true, Brad. However, Avid does include an in-line adjuster with their BB7 road calipers. Seems they do recognize the need to take out cable slack when used with road levers.