Rear brake largely ineffective?
 

So, I was on a ride with a couple of friends when the one in front of me stopped harder than necessary, causing me to need to stop harder than necessary, and the yoke/straddle wire on my front cantilever broke. Clearly, it must have been about to go, and would have gone sooner or later anyway. I was looking for a picture of the style of cantilevers, but haven't been having much luck. They are Shimano, aluminum, and of a type that was completely common 25 years ago. I don't think the precise type is important, though. I ordered replacement cables, and replaced the front *and* back, and have 8 more which should last me :-)

My question is this: after losing the front brake, I noticed that the rear was pretty darned ineffective. Note that the lever was *not* bottoming out against the handlebars or anything. I thought perhaps it was the pads, so I replaced those. With the new pads, it felt *exactly* the same. To give you an idea, doing down a modest downhill, the rear brake alone couldn't keep me from accelerating. Now, I will grant you that I am not small (225 lb), but this was unexpected to me. And of course, I don't know if it's *always* been like that, or if it's been like that recently, or what.

Anyone have any good theories? Or are my expectations just too high for a rear brake (I sure hope not)?

Rear brakes are by their very nature close to useless in emergency stops.

As you increase the braking forces there's a "weight" transfer to the front, and the rear wheel becomes unweighted and slides easily. It's the nature of the beast, and why auto brakes are proportioned with the front wheels getting half again as much brake effort as the rear and yet, despite that rear wheels lock first.

Rear brake only is fine for a child riding a BMX bike in a parking lot, but totally inadequate for the real world. If you have only one brake, it wants to be the front.

I had a similar problem with a more recent-gen bike where I had close to zero effective slowing on any downhills with the rear brake.

Even at 225, you should have significant braking power with the rear brake; it may take more distance, but it should be able to stop you with enough room (which will be a LOT more than the front brake!)

Things to check if it's not the pads:
- Brake rim clean/damaged? If you clean them, clean them with alcohol - don't use Simplegreen or other residue-leaving substances. The alcohol will evaporate with zero residue.
- Brake cables kinked at all? Even small kinks, particularly mildly angulated bends at the angle of ferrules or entry into the brake, can cause loss of a LOT of brake power. I had one ferrule that made a slight angle with the brake cable that accounted for nearly 50% of that brake power loss. (I used longer brake cable housing to improve the curve.)
- If all fails, don't hesitate to replace the entire brake setup. A good road brake (ultegra grade) costs like $60 - well worth it for the excellent quality and reliable hardware. I just bought this for my rear road brake with very effective stopping.

I agree that you should be able to stop the bike with the rear brake alone. You mentioned the brakes are cantilevers -- is the geometry setup the same between the front and rear? Could you post a picture of the way your rear brake is setup? I'm NOT a cantilever expert, though I recently did find a lot of success in setting up a set of basic Shimano low-profile cantilevers last weekend on one of my older mountain bikes. It has cheap (but new) Shimano BR-CT91 shoes on front and rear and they both work well, and much better than they did before I set them up anew last weekend.

I found that lengthening the straddle wire and lowering the yoke added a tremendous amount of braking power to the system (and also extending the brake pad out from the brake arm). I previously had the yoke quite a bit higher, and the pads set closer to the brake arm, and I think I was pulling the arm up and rotating it so I was close to losing all of the mechanical advantage. Lowering the straddle cable, and effectively laying the brake arms out to the side a little further dramatically improved their mechanical advantage when pulled.

That is not OK. Something is wrong there.

Rear brakes provide way less stopping power than front brakes, but by all means, they should be able to stop you. You should be able to lock the wheel up, which isn't ideal, but it will bring you to a stop.

^ +1

If you understand what is being said is that the rear wheel slides, that is it locks up and doesn't turn and the tire slides on the pavement. Because it slides on the pavement it won't stop as well. I recall as kids we would call it a brodie. Even though you are not trying to skid the tire the principle is the same.

If the rear wheel won't lock up, you might have a brake issue.

John

The other factor with the rear brake is the cable and housing. The multiple curves absorb a significant amount of the energy applied at the lever. This is especially true if the housing is much too long.

Try different pads. I'll just quote my post from another thread to save time:

I started out with Kool Stop Eagle 2 pads on a bike with Cantilever brakes and Araya PX-45 rims, which have a concave braking surface. Good pads, easy to toe-in (the plow tip is self aligning), but tricky to align perfectly to clear the tire while maximizing contact. The pads were just a bit wider than I'd like for the Araya PX-45 rims. And too thick to clear the fork enough to easily drop the wheel with slightly oversized tires.

So I switched the front set to Jagwire Mountain Sport 70mm pads for cantilever brakes. Perfect. Thinner, to fit the rim perfectly, snugged into the concave surface. Curved to match the rim. Longer than the Kool Stops. Overall more effective brakes than Kool Stops for this particular rim. I kept the Kool Stops on the rear wheel.

But if I needed stronger braking on the rear I'd ditch the Kool Stops and put on another set of Jagwire Mountain Sport 70mm pads for cantilever brakes. They're cheaper than Kool Stops too.

Agree as well that you should also make sure you're using GOOD pads. There really is a big range in pad performance, and it is surprisingly easy to get really, really bad pads.

I recently upgraded a Sora/2200 entry level bike circa 2010 to Tiagra 10sp, and I was hoping to save money on the brakes (dumb) while trying something new. I bought some decent looking brake on Amazon near-randomly which had the typical decent reviews for a bike brake (not many), it was an Origin8 branded brake.

The brake pads were TERRIBLE. I learned this the hard way as I mounted it on my FB and then burned through literally 1/3rd of the brand new brake pad in a single 6 mile descent of avg 6% decline. The braking power was truly awful - it was really dangerous.

I swapped the pads to some well used Kool-stop salmon pads that my racing bike retired, and braking power was mostly back. At that point though I was fed up enough to just toss the Origin8 brake completely and buy the ultegra brake (which was a mere $25 more) - the new ultegra brake and its native brake pads are outstanding.

Don't cheap out on the brakes - they're not an expensive part, even for ultegra-level, and the small price difference between cheaping out (which will still cost you $30-$40 for a crappy brake like the Origin8 one) and ultegra is a huge difference in safety on steep descents.

Thanks for all the thoughts -- just to clarify the rear wheel is *not* locking up; just not stopping me. The brakes are squeezing the rim, but somehow not really giving me good stopping power. Here is a picture:
https://farm5.staticflickr.com/4341/...32cae5_z_d.jpg

And as I was trying to figure out how to take a second picture, with the brake engaged, I was looking at the back brake while squeezing the lever, and figured out what the problem is. The yoke carrier is hitting the cable stop, so the way it's currently configured, it simply can't pull any tighter.

Funny that there was enough slack to make contact with the rim, and provide a teeny bit of friction, but not enough to really brake.

Now I feel a bit silly for having posted, but the conversation here made me look at it more carefully, so thanks for listening and all the thoughtful replies!

Newtonian physics is at work, and that is why the front brake is more effective.

I'm glad you noticed that when you took the picture! I was going to comment that your yoke looked pretty high. In general, the lower you can get the yoke, the more mechanical advantage you have on the brakes. Here's my rear brake:

https://farm5.staticflickr.com/4367/...fbfa2083_h.jpg

And my front:

https://farm5.staticflickr.com/4341/...31cc1e53_h.jpg

Getting the yoke down low, and keeping the straddle cable as flat as I can reasonably make it, has helped my cantilever setup on this bike tremendously. In your case, that means a shorter straddle cable and a longer main cable. If you're going to take it apart and re-configure it, I'd probably want to get the yoke down about as close to the fender as I could get it -- within a couple centimeters or so anyway. My yokes sit a few millimeters above the reflector mounts. I could remove the mounts and go lower, but then the risk exists (small as it may be) of popping the main cable and catching a tire tread with the straddle cable.

https://farm5.staticflickr.com/4396/...893591f3_h.jpg

Your brake pads are also way too high on the rim. They will likely need to be filed flat, then re-centered on the brake track.

ditto.... maybe it's just the view angle, but the pads do look like they are hitting high on the rims brake surface.

OK, I will look at that as well when adjusting things. Note that in the pic the brakes are *not* applied, and when applied, they do come down noticeably. Which is to say, if you think they're hitting the very top of the rim and the tire, they're not. But they *may* be high on the rim. I confess I'm not familiar with the term "brake track" -- can I assume that the pads should end up centered on the rim when they make contact? Or is there more to it than that?

My question wasn't about front vs. rear. I am comfortable getting most of my braking with the front, and I understand the physics (well enough...) behind it. My question (which has been well answered now) was about whether my terrible stopping power with the back was expected or not. It is not, and now I understand the problem.

Thanks, @hokiefyd, I will work to lower the straddle cable and (obviously! :-) ) lengthen the main cable.

Shortened the straddle cable; replaced the main brake cable. Pain in the butt working in that area with the rear rack, but didn't feel like moving the rack. Took a quick test ride, and can now skid. Will try not to abuse my new power :-)