chico1st

ok so i just want to make sure that im on the same page as everyone.
to keep my braking performance good with my caliper rim brakes I need to:
Keep wheel true
Use decent pads
and clean rim

thats it right?
I just made up a bike and the braking performance is horrible! The rim is clean, the wheel is true and the pads are the same pads that work on a different bike. They are sorta longish reach but not that long. Im very confused.

Crankycrank

What pads?
What brakes?
What Rim? Anodized or bare aluminum?
and what brakes and rim are you using on the other bike that stops better?

FBinNY 

You're on the right track, except that aligned wheels only help to the extent that they make adjusting the brakes closer possible. Bur since you depend on friction, clean quality pads on clean rims are the place to start. Good cables also help by reducing movement lost to housing compression, and lowering effort lost to friction.

The last part are your hands, if you don't have a strong grip hand exercises help.

DannoXYZ 

Don't get "braking power" as in deceleration force slowing you down, mixed up with "lever force" or the hand-squeeze required to generate that deceleration. Ultimately, any braking system will have a maximum deceleration based upon the traction of the front tyre. Some braking systems will require more and others will require less hand-squeezing force to generate that same deceleration rate.

So a poorly adjusted brake with cable-friction and hard old pads will still be able to stop you at the maximum-deceleration rate of about 0.85g, but it may require 5x the lever squeezing force of an optimally adjusted and tuned brake. Both brakes possess the exact same "braking power".

chico1st

The pads are SNG rubber pads, sorta crappy but they work on another bike just fine.
Brakes are semi-long reach calipers
The rims look like aluminum (they are) but i dont know if they are anodized or not... everything looks the same as my other brake

I can brake on the other bike so i know its not my hand strength

The way i judge strong enough AKA stop fast enough, is the ability to toss myself over my bars if I want to... which i cant do with this.

noglider 

Show us a picture.

I_bRAD

what kind of levers are you using?

chico1st

Tektro R200 levers, ok picture coming tomorrow sometime.

DannoXYZ 

Cable-friction is the single component that can rob 80+ of your hand force on the way to the caliper. I'd go with new cables, preferably ones with a rolled smooth outer surface for slick sliding action.

mkane77g

Give em a bit of toe-in

noglider 

That's what I was going to suggest, but I still want a picture.

Before assembling the cable, I rub grease on the inner wire, and I drop oil into the housing. I drop a lot of oil in. It takes patience.

z90

This post should be automatically inserted into any thread that has the key words "braking power" or "crummy brakes" or similar. Well said!

JohnDThompson 

Or -- perish the thought -- steel?

Steel rims have notoriously poor braking performance; changing to aluminum rims will both improve performance and lighten the bike considerably.

noglider 

DannoXYX, is that really true? On some bikes, I could squeeze and squeeze like hell but not increase the braking. I have very strong hands, and they're large, too.

chico1st

okay here we go:

It has new greasy cabling


The brakes are well aligned



and the calipers arent that long of a reach


I put on new dual compound koolstop pads after this but the braking wasnt any better... they havent worn in yet though.... if they need it.

I can redo the cabling if you think its necessary.

noglider 

It does look like you've done a good job. One thing you can do, to check that the cables have adequately low friction, is to unfasten the brake from the caliper. Play tug-of-war with yourself with two hands: pull the cable by squeezing the lever, then pull it with the other hand at the caliper end. Go back and forth and verify that it moves well.

Those steel calipers generally don't work well, because they're too flexible. Replacing the calipers could help, though I can't say for sure. But I hesitate to recommend you spend that kind of money, because those calipers come only on cheap bikes. Maybe you're better off replacing the bike. Or are you planning to resell the bike? If so, perhaps you've done the best that can be done.

And try using the front brake more heavily than the rear. It's the one that should be doing the most braking.

chico1st

I wanted to use it, I should be able to have a perfectly functional bike even if it is old :S

yeah the front is the only one im concerned about (no pictures of back brake)

JTGraphics

If you are serious about getting better performance from the brakes I'd really suggest replacing the calipers and pads with some double pull calipers and it will make a world of difference in stopping performance.

cyccommute 

There are a number of issues here. The calipers (they look aluminum not steel) that chico1st has don't do a very good job of translating the hand power to clamping power on the wheel. Part of it is flex and part of it is friction loss. The arms can flex in about 3 different directions...the arms twist, the pads bow outward as force is applied and the caliper arms bend backwards from the force of the wheel. This happens on all brakes but some are worse than others. Melt forged parts like these, with poor quality materials, bend and flex more than cold forged parts.

There is also friction losses at the pivot of the brake, in the cable and in the levers. There is also a lack of friction at the pad themselves. The pads he has are pretty bad. Probably an old compound and they are small. A larger pad gets more friction at the rim with less hand force. Something from Koolstop would help. Changing calipers would be a huge step up too but more expensive.

DannoXYZ 

Well mostly, it's certainly possible on some really old crappy brakes, to squeeze as hard as you can, and get less than 5% of that force to the pads. In which case, it's possible to not develop enough friction on the rim+brake interface to get up to the front-tyre's limit. But it's very rare that I've encountered brake systems this bad. Although, I've seen rusty-cables inside unlined housing that eventually snapped when squeezed hard enough. So yeah, I'll add a disclaimer of "most of the time" on my initial statement, like 95-99%. There's always this device to help :


https://www.chelstondirect.com/images...-exerciser.jpg

DannoXYZ 

Those are most definitely steel chrome-plated calipers, possibly ChangStar, LeeChi or some of those generic OEM brands. You can certainly tell they are steel where they are bent at the top for the adjustment barrel. An aluminium part this thin bent that sharply (90-degrees! ), will most certainly snap. All is not lost though because it's possible to adjust these types of brakes for enough performance to throw you over the bars with 2-3 fingers on the lever. Do this test:

1. unbolt the brake-cable from the caliper

2. hold the loose end of cable with one hand and squeeze the brake-lever with the other hand. "Floss" the cable back and forth by alternating pulling on the loose-end and squeezing the lever. Does it feel smooth and effortless to squeeze the lever with minimal-tension from the other hand? I suspect so.

3. now squeeze the caliper together with your hands and feel how smooth the movement is. Better to remove the wheel to squeeze the caliper through a larger range. Does it spring back fully by itself? I suspect it will not.

Here's the problem (green):


The reflector SHOULD NOT be part of the brake-caliper assembly. At the front of the caliper, there should be an adjustment nut AND a locknut. These two determine the spacing and preload for the two caliper-arms and how tight they are sliding against each other. The adjustment nut should be set so that there's no axial-play between the two arms, but not too tight that causes excess friction that must be overcome by the return-spring:

https://www.parktool.com/images_inc/r...sidepull11.jpg

I recommend following this Park Tool site on sidepull caliper service and disassemble the brake-caliper assembly. REMOVE that reflector and make sure you have an adjustment nut AND a locknut. Grease the front & rear of the arms where they slide on each other and the centre-bolt. There should be a washer between the arms, if not, find a brass-washer to go in between to reduce friction. Nicer brakes actually have a bearing-assembly between the arms. Then, adjust preload for no play and smooth action. Make sure the adjustment nut and locknut are tightened into each other to lock the assembly together. THEN re-install the brake with the reflector in front of the fork and BEHIND the brake-caliper. Good luck!

BTW, the reach (red) of about 60mm is a little on the long side and reduces mechanical-leverage of the levers, but it's not that significantly long to be the cause of the issue here.

Also, adjusting the calipers so the pads are as close to the rim as possible does not give you more braking power, if any thing, less. The hand generates the most squeezing force when the fist is closed, not fully open. So you want to adjust the calipers so that the pads touch the rims when the lever is squeezed to about 1/2 way towards the bars. A more-closed hand gives you more squeezing power and also gives you more modulation-control at the limit of adhesion.

DannoXYZ 

Why thank you!

chico1st

wow thats awesome! like a nice analysis
I'm excited to test this, probably not until tomorrow though.... but im actually excited... its wierd.

cyccommute 

Look at chico1st third picture. The cable perch isn't bent. It's machined into the metal. Additionally, the arms are too thick for steel calipers and, in the picture you use, you can see prominent mold flashing left over from the melt forge (look at where you drew the top red line) as well as rough edges in the brake pad mount slot. A steel caliper with that kind of thickness would make for great...very, very heavy but great...brakes. They wouldn't flex at all. They'd also need one hell of a press to bend them into shape. Compare this steel caliper to chico1st's ChangStar

chico1st

hmmm I was considering putting this brake on the front

but i dont want to put on one of those cantilever cable housing stoppers.

and now im convinced that these calipers should have lots of power,

still havent done the adjustments yet