Disc Brake Conversion
 

Hello everyone, this is my first post here and this forum looks to be extremely friendly and helpful.

I have a lot of experience with cars/trucks and am in school for engineering so I know how everything works just fine, but I have no idea about brands, whats popular, some of the terminology, good components, etc.

On to my question. I have a 2007 giant boulder se, which works very well for my needs, that is soon in need of new brake pads. It has the traditional V-style brakes. This bike is pretty heavy, probably about 20-30 pounds and I weigh about 270 pounds, so basically there is 300 pounds of moving weight - no wonder the pads are gone in less than a year, right? As you can imagine trying to stop so much weight in a hurry is not easy with v brakes so I am looking to upgrade to a front-disc setup instead of replacing the pads and still not braking that great. I constantly adjusted the pads so I could get the maximum braking force.

The front fork has mounting tabs for a disc caliper which is good as I can reuse the stock fork, but my wheel (26") does not have mounting holes on the hub for a rotor. So beyond knowing I either need a new wheel or some sort of adapter, a caliper, rotor, and possible wire, I am lost. I would like to stay with a mechanical setup since I dont have any need for hydro, nor do I want to spend that much. I would like to keep the whole conversion under $100, but I want something that is decent. It doesnt have to be the best, but I dont believe in cheaping out with safety devices. After some searches I see the avid mechanical setup mentioned often, but I dont know if that will work for me...

I am currently in college and use my bike to get around campus which isnt particularly taxing, but I also use my bike to exercise and a couple times a week I will ride 15-20 miles at a time. This is my first real bike and I love it. Some things I have done to it are put in a slightly wider and 35mm rise handlebar (last one was bent after a wreck...tore my achilles from that which put me out of commision for a couple months, not pretty) since I have broad shoulders, replaced the stock cassette with a higher 28-13 set, and replaced the stock plastic pedals with some metal ones since I literally tore the plastic ones in half the second day I owned the bike. I also switched the brakes from right-rear, left-front to right-front, left-rear since my right hand has a much better grip.

I have also done away with the quick-release rear axle because I have completely sheared two in half in the course of a few months. The biggest jump I go off is a curb or step, so it was getting a bit ridiculous. I finally had the hollow quick release axle replaced with a solid steel bolt-on axle, and since I never used the quick release feature it wasnt a hard decision. If I break this one then I have real problems.

If anyone could steer me the right direction with how to go about putting a disc brake on my front wheel I would be grateful!

Thanks

Unfortunately you probably won't be able to do it for under $100.

As you mentioned, you will need a rotor, caliper, mounting bracket, and cable (inner + outer).

In regards to the hub, you will need to buy a new, disc-compatible hub.

I, and many others, will recommend an Avid BB7 brake.

Would it be better to buy a new hub and have the wheel re-spoked, or just buy another complete wheel with the proper hub?

How much over $100 do you suppose it would be?

thanks

The Avid BB5 or BB7 disc brake will come with the rotor, caliper, and mounting bracket. You will need the cable and housing and a disc compatible front wheel.

The BB5 brake will help keep you closer to your budget at $31:
http://www.speedgoat.com/product.asp...at=26&brand=16

New cable and housing for $1.99:
http://www.niagaracycle.com/product_...oducts_id=2238

And a front wheel for $45:
http://www.niagaracycle.com/product_...ducts_id=20793

Under $100 with shipping. I'd recommend having that wheel retensioned at a compentent LBS though.

A cheaper alternative is to get some Avid V-brakes,
http://www.jensonusa.com/store/produ...ull+Brake.aspx

Should give you better braking than the no-name ones that came stock. While you're buying them, get some spare kool-stop pads for when the stock wear out.

Discs are definitely better, but getting it under $100 is difficult. don't try to get it cheaper by buying a lesser known brand.

Im guessing the most important part is the caliper which also means I need to spend the most on it?

What would a decent setup cost?

For $30 more, you can get a Hayes hydraulic setup (comes with caliper, levers, prebled hoses, disc, but you may need an adapter for the fork mount).
http://www.blueskycycling.com/produc...s_HFX_9_XC.htm

I would go for a single BB7; the BB5 is more difficult to adjust for not much savings. The mechanical BB7 will provide plenty of fine control and way more stopping power than you will ever use unless you start downhilling. Don't mess with hydraulic brakes for this use.

For a new front wheel (it will likely be more expensive to rebuild your current wheel, and not as robust a product), make sure you get one with a good quality hub (Deore at a minimum, I'd look for XT), a nice robust rim like a Sun RhynoLite, and good quality name brand spokes such as DT
stainless steel. This is biking season, so prices are much higher than during the winter.

Given in-season pricing, I'd look at this one: http://www.niagaracycle.com/product_...ducts_id=13483

+1 on all of the above. Get the BB7, worth every penny over the BB5.

I went to my local bike shop and they were looking at at least $150 for parts for a decent setup. They recommended I go with a new wheel instead of trying to replace the hub. They also said I could reuse the lever and cables I have now, and if I cant its only like $8.

So the sun rhyno wheel with the BB7. What size rotor should I be looking at? I see 160mm, 185mm, and 203mm. Is there any difference between the '07, '08, and '09 versions?

Thanks for all the help guys.

A 160mm rotor should be sufficient.

I would imagine that the current cable (and housing) would be much too short, but as your mentioned, cheap and easy fix.

Yep, 160mm. There are some packaging difference between the different model years IIRC, involving which adapters are included. Whatever you get, make sure you've got the correct adapter for your fork's mount type (IS vs post mount).

I've been thinking of the same myself, just for the extra braking carrying/pulling the kids. To keep the wife happy I need to make sure the front wheel looks like the original, i.e. matches the rear wheel. I found out that in 08 my cypress DX came with discs and my 09 didn't. So I'm going to look up the 08 specs to see what exactly it had.

In case anyone thinks my post is a "this is the best way to do a disc brake conversion" post, please understand that it is not. My post details how to do a disc brake conversion for under $100 which is what the OP asked for advice on. If he's willing to spend more, as pointed out there are several better disc brake options available and certainly better wheels.

How do I tell what kind of mount type I have?

There are a lot of tandems weighing (team + bike) in excess of your 300 lbs using v-brakes even on challenging terrain. It doesn't appear you're doing long, steep descents so a good set of v-brakes with good pads should stop your and your ride quickly. I would think a good setup would be able to lock your front wheel.

Try some better brake-pads first. KoolStops work pretty well. Perhaps some new brake-cables too.

If you have thru holes going perpendicular to the frame then you have tab mounts. If you have blind, tapped holes facing towards you, then you have post mounts.

While we are on the subject, I suppose I should ask how much a good V-style brake setup would be? I already have everything for that except the actual clamp so I imagine a bit cheaper. Any suggestions?

Didn't you mention that you already had V-brakes? New Cool-stop salman pads for those will run $12 per pair plus or minus.

Yes, already have the V-style. This conversion is adding up to be a little more than I want to spend unfortunetlly. The pads you mentioned are the best ones for my needs?

Kool Stop Salmon ( colored ) are generally considered the best in all weathers. They should cost, $7? for a replacement pad. Someone want to confirm that? I think that you could also get an improvement by getting some Avid V-brakes, not their crazy expensive CNC machined ones, but maybe the single digit 7s?

Say $39 at the LBS. Less on-line.

What is the difference between a decent and a great set of v-brakes? I ask because mechanically its a very simple device, and I have plenty of grip strength to close the lever. How much do cables typically stretch under load?

Are pads pretty much a universal size?

The differences has to do with design, materials and manufacturing tolerances. Nicer V-brakes have better materials & finish and will typically last longer. They'll be easier to adjust and service. However, braking-power may not be that different since ultimately, it's the friction between the pads and rims that translates into friction between the front-tyre and ground that determines your deceleration.

Cables have negligible stretch under load, it's the brake's arms that bend. Better designs are stiffer. Another cause of flex is the fork itself where the mounting posts are forced apart. A brake-bridge brace will stiffen that up nicely. Also cable-friction can rob A TONNE of braking-power, make sure your cables slide easily in their housings. I like the cables that have the inner-wire drawn through a die so that the outer surface is perfectly smooth.

Another cause of V-brake issues is that the levers aren't matched to the brakes. However, in your case, if you have non-compatible levers (non linear-pull), you'll actually end up with MORE mechanical leverage and single-finger lock-up power from the brakes.

I'd go with the KoolStop pads first and replace the cables if necessary.

I thank you and everyone else who has contributed to this thread. I bookmarked some of the stuff given here if I eventually do want to go ahead and do discs, but for now I will try better pads.

Is there anywhere in particular you like you buy your stuff from? Also, the pad size is universal?