I have a friend who has an old mountain bike she wanted to use. I did some work on it - adjusted the derailers, tuned the brakes, trued the wheels etc - and managed to turn it from an unsafe mess to at least something that is rideable without fearing for your life all the time. However, the brakes are still far from ideal. They're cheap cantilevers, and even after I set them so the pads are a hair's width from the rims they still don't have enough braking power to be called safe. I suggested replacing them, but the friend in question doesn't have much cash available, so she said the cantis would have to do.

However, DealExtreme just put these Promax V-brakes on sale. At about €10, I should be able to convince her to buy them. Question is, would it be a worthwhile upgrade? I've had the displeasure to work with Promax disc brakes and they were junk, but then V-brakes are considerably less complicated, and even cheap V-brakes should be better than cheap cantis.

Your opinion? Do keep in mind that I'm looking for extremely low prices here.

The amount of cable pull between a canti and a v brake is not the same. You would need new levers as well.

It could be that the bike is set up with v-brake levers and cantilever brakes. Due to the longer cable pull of v-brake levers, the force at the brake will be reduced.

Right. Don't know how I didn't think of that. I guess I'll need to scrounge up the levers from somewhere... if, that is, the bike isn't set up as Monster Pete says. In that case just replacing the brakes with Vs would make a big difference...

What I often do on cheap bikes with poor brakes is to swap out the brake pads. I just did that on a Huffy rebuild. The cheap little pads on the Huffy's canti-brake would hardly slow me down, much less stop the bike. I put on some Jagwire Basics pads, and the difference was night and day. The Basics cost me $15, and the kids like that they come in different colors. Kool Stop Salmon pads are another excellent choice, probably even better in stopping power than the Jagwire pads.

There are other factors needed to be considered when setting up cantilever brakes besides how close they are to the rim. If you neglect the straddle cable height during setup the brakes have a 90% chance of feeling or working like carp.

LarDasse74 has probably hit the nail on the head. I have found that with cati brakes, the strength is often determined by the length of the straddle cable. To maximise mechanical advantage of a cati brake system it is normally better to have a shorter straddle cable. This will make the brake setup look like an equilateral triangle. Another VERY important point is to attach the brake pads properly. The brake arm face should be parallel to the rim when the brake is fully applied. With peg type brakepads it can be tricky to set up. Many people back the pad up to the brake arm face, which is normally incorrect. With bolt on pads, rearranging the spacers will do the trick. On my touring bike I have the canti brakes set up so that they are really strong, but the straddle cable is too tight to disengage when removing the wheel, I need to loosen the whole brake cable.
Also, someone else on this thread suggested changing the brake pads. This has worked for me in the past.
I think if you change the whole brake system with v brakes then you will be throwing away time and money. Once canti brakes are properly set up, they are far better than v brakes.

I didn't consider the length of the straddle cable. I'll have a go at shortening it, and I'll get proper pads. Live and learn

That said: "far better than v brakes"? From everything I've read or heard, good Vs are best rim-brakes money can buy and can only be threatened by discs. Is this not true?

I have a bicycle with Promax V-brakes. They're certainly adequate and work well. For whatever reason, when I installed Shimano Deore brake levers I found on sale, they seem to brake better. Or, maybe it's just the way they feel, I don't know.

Anyway, if I wanted to go with Shimano Deore brakes it would only be because they look easier to adjust. I read the Shimano XT ones can squeal and some people say they can't adjust them to get rid of the squeal. And as for Kool Stop Salmon pads, I read if you don't ride your bike during the winter (that's understandable), they can get hard which makes them extremely slippery the first or couple of times you use them again. So, I think the dual compound Kool Stop pads are a good idea.

Interesting that someone here said Jagwire works well. Because just to be a materialistic oddballl, I bought some yellow Jagwire pads to replace the pads on Shimano Deore brakes that I bought just to have the yellow color on my bike. But, I read somewhere that the Shimano Deore pads work well but apparently wear out faster in mud. Of course, this was bought for a project that's not finished yet. lol, I still don't have all the parts yet to complete a touring bike, oh well...(but I just ordered a dynamo hub, hehe)

I want to add though that for a cheaper bike, I would just go with Shimano Altus (or whatever) brake levers and brakes. (If I remember correctly, the Shimano website listed the Altus/Acera/Alivio V-brakes in the same quality level. And for brake pads, well for winter biking I'd prefer Kool Stop dual compound pads and if not, the Jagwire.

V brakes can easily be made to be very very good brakes. Cantilever brakes are difficult to adjust and can provide power anywhere from crap-ola to awesome. However, Cantilever brakes don't have the linear feel of Vs -- the further our lever pulls and the higher the straddle cable goes during braking the less mechanical advantage you have. This effect becomes more pronounced as the pads wear and the straddle cable rises higher to actuate the brakes. Cantilever brakes also have more clearance for fat tires, fenders and mud.

I think this may be the reason cantilever brakes tend to use unthreaded brake pads. While with v brakes you can roughly adjust the spacing by rearranging washers, relying on the cable to do the rest, cantilevers are a bit more picky. Smooth stud pads allow you to move the pads inwards on the brake arms to compensate for wear. My commuter bike came with v-brakes originally, but there wasn't enough clearance for my 2" tyres and fenders. I switched to cantilevers and the problem disappeared. Additionally, I think they simply look better than v-brakes. If I was building a bike from scratch, I would probably only use v-brakes with suspension forks.

Thanks. Been thinking about ordering them anyway and trying them out on my main bike. It currently has Shimano Vs that work very well, but try as I might I cannot get the front ones to stop squealing (I've tried toe-in, reversed toe-in, different pads and more adjusting than I want to remember... nothing). Might as well see if the Promax arms stop the noise - even if they don't, I still have spare brakes in case I need them.