Dockhead

Disk mounts? Jury rig discs to a frame? I don't understand what you mean with this at all. Disks don't mount to the frame at all -- they mount to the hubs.

CALIPERS mount to the front fork and to the rear triangle, and I have mounting bosses for these already -- the German A suspension was designed for disk brakes, and the next year of my bike, with the same suspension, already came standard with Avid Juicy hydraulic disk brakes.

My hubs -- American Classic front and SRAM Dual Drive II rear -- are disk brake hubs with flanges for mounting the rotors.

I believe adding disk brakes is a simple bolt up operation -- what am I missing?

Dockhead

I'll post photos this weekend when I'm near the bike, but there are definitely welded on bosses on the German A Kilo front fork, and on the suspension arm of the rear suspension. With two holes each for mounting disk brake calipers.

Concerning rotor size -- this would be determined by the mounting position of the caliper bosses, wouldn't it? Or do you use and adapter to move the caliper further out for bigger rotors?

I have zero experience with disk brakes on bikes, so I don't know how it works, and would be grateful for any advice.

That does not mean zero experience with bikes, however -- built my first road bike in 1979, custom Reynolds 531 frame, mostly Dura Ace and Campy components, even built up the wheels myself (still have a box of double-butted spokes somewhere).

I never liked rim brakes. They work better, in my experience, if the caliper is not too far from the rim -- NOT the case when your frame is designed for 27" wheels but your using 700C :banghead:. I've had center-pull brakes on mountain bikes which worked better. But I just don't like them. I don't like the feel of them, I don't like how they tend to drag, and I don't feel good -- ESPECIALLY on a 20" wheel bike -- about heating up the rims on a long downhill with a heavy load of something or a trailer. I really want disk brakes.

Dockhead

This is my fork:

kilofork.jpg

You can clearly see the caliper boss on the left leg. According to the specs it's for "Brakemount: IS 2000 Disc Only (max. 160mm Disc Rotor)"

The P.O.G. German:A Kilo Air Force Paralellogram Fork Folding Bike 20"

This is a catalogue photo of my bike:

jetstreamEX2009.jpg

It has rim brakes, but you can clearly see the bosses for disk brake calipers.

bargainguy

From your pix, we now know that your frame is equipped with disc tabs. Good.

Your wanting discs is fine. I'm wondering if that particular suspension fork doesn't mate well with V-brakes (or cantis), and maybe that is causing your issues, rather than any inherent weakness in rim caliper design and function.

Thor stated that he once ran a folder with a 200mm front rotor. Makes sense to put the larger rotor up front, as the front brake tends to do most of the braking work compared to the rear. He also stated it was probably overkill. I'd start with a 160mm front and then increase rotor size if you really felt it were inadequate, as the fork is already set up for that size. You could always get an adapter and a bigger rotor at nominal cost.

Dockhead

Yes, I think that is very likely the case. I never liked V-brakes on any bike, but these are worse than usual. Maybe cantilever brakes would be better, but I just don't want to mess with them. All rim brakes are toys compared to disks, in my opinion.


I don't understand how we are able to choose disk sizes. Isn't the rotor diameter determined by the distance of the caliper from the skewer? The German-A materials say "maximum" 160mm -- huh? That means it's possible to use a smaller one? How?

I would like to at least guess about the right size, so I can order the rotors at the same time as the calipers. It will save me a lot of time compared to ordering and receiving the calipers, measuring, only then ordering the rotors. If it's 160mm, great -- I'll order 160mm.

bargainguy

The "160mm maximum" spec on the fork may represent the biggest size you can run unmodified. So 160mm if you don't use an adapter, and perhaps larger if you can. We know the fork will take a 160, so if you want to order now, I'd get a couple 160's and call it a day. Perhaps Thor will chime in as to whether this fork will accommodate a larger rotor with an adapter.

Dockhead

This excellent video answered a lot of questions:


Looks like 160mm is default standard. But I need to figure out whether the hubs are centerlock or six bolt. I think they're centerlock.

ThorUSA

160 mm rotor as the fork might be to weak for 200 mm rotor

Joe Remi

Well yeah, I've been around long enough to know the difference between a pad, a disc and a caliper. I was obviously under the impression your frame didn't have tabs for disc CALIPERS. It clearly does, so you're good to go for hydros.

Trevtassie

This.... use the money you save for beer.

V brakes can pull 95kg me up on a 50kg bike from 70km/h on a 10% slope no worries with good pads. Before I spent hundreds of bucks sorting out discs I'd try getting the V brakes to work properly. Good pads set up on the rims properly, good cables with good outers will make a huge difference. The Jagwire kits out of China on Ebay for $10 are good, stainless inner cables too. I'm not a particular fan of BB7s the ones with stock pads on my bike squeal when they get wet and need more adjustment than V brakes.

Dockhead

Thanks. I've ridden many tens of thousands of miles on bikes with rim brakes. Good ones (Dura Ace, Campy) with short enough distance from the cross-bar, good pads, teflon-lined cables are somewhat OK.

But the brakes on my Jetstream simply suck -- there is too much distance, so the levers flex; the caliper arms stick a little so they drag -- it's not a problem with pads.

The rest of the bike is SO good -- the frame is so stiff and rock solid; the suspension is so plush; the drive train works so well -- it really deserves brakes which are up to the rest of the bike.

Trevtassie

Sounds a bit like the outers might be stretching and sticking? (I'm assuming you cranked up the arm tension) there are some pretty average quality ones around. Even some of the linear strand ones can have issues, I had the inner cable bulging out between the strands on one outer (I think it was a Clarkes one) and on another one the linear strands were being forced down the inside of the ferrule because the cable hole was too big. Both things made the brakes feel so flexy. But anyway, I'd say forget cable discs, they need constant adjustment and the need for decent outers and inners is just as critical as V brakes, if not more so.

jur

Linear outers are dangerous for brake use. The outer can explode outwards leaving you with no brakes. Spiral outers are for brakes, linear outers for gears. Safety critical issue. You do get combination ones, or those link ones.

Trevtassie

Some manufacturers are a bit skimpy on the braid that's supposed to hold the strands together. Nice concept if done right but not something you'd want to cheap out on as a manufacturer, but they still do, as I found out.

Dockhead

Thanks for this -- I hadn't thought of that.

I'll be with my bike this evening -- I'll have a look.

Dockhead

Bit of a necropost, but I never managed to figure out any way to convert the brakes, and just left them. Then -- this summer I had my bike serviced professionally for the first time in all these years, and the mechanic changed the brake cables. Now it's like different brakes completely!! I realize disks would be better, but I am no longer in the market to convert the brakes on my 13 year old bike.

Dockhead

And this experience fully vindicated what Jur and Trevtassie were saying!!! If I had followed their suggestions at the time, I would have solved this problem much earlier!!!

Pinigis 

I have a kinked hydraulic line on one of my folders that’s been kinked for about five or six years now. It still works perfectly fine. If that were a cable with a kink in it, it would not work at all.

bargainguy

Wait a minute. You think it's safe to run hydraulic brakes with a kinked line, just because yours hasn't blown yet?

For someone involved with bike manufacturing, I'm a little surprised by that statement.

Brakes are critical safety items. Full stop.

Any kinked, bent or otherwise compromised lines should be replaced immediately. Full stop.

Anyone who thinks otherwise, please remember if your brakes fail for any reason, you are at risk of serious injury or death.

That means keeping your brakes maintained to the highest order.

I don't recommend riding any bike with any compromises in the braking system.

Pinigis 

I will get to it. But, there is no leakage, no impairment, etc. Is it ideal to have a kinked line, no, but the point was that it still functions just fine and a cable would not.

Duragrouch

I see old thread, with new entries.

I'll have to look into that fork, I'm seeking a 20" fork to mount a disc. Long downhills heat up the rims enough to pop spokes.

In case not covered above, a couple things:

- For the same size disc rotor, larger wheels have more leverage. That means, if a rotor and caliper are designed for 26"/700c wheels, then put on 20" wheels, they are more prone to lockup, if they are powerful. The Dahon Formula 18 (discs) I test rode was very prone to lockup, especially the rear on a good downhill. Thus, good modulation is key. Hydraulics are best, but more complex maintenance issues. Maybe there's a sensitive mechanical caliper out there, or road discs have less grab. But a recent innovation is cable actuated hydraulic brakes, the cable pulls a hydraulic piston at the caliper, that sounds best of both words.

- There is considerable documentation online, regarding the risk of front disc brakes with conventional quick release axles, the brake torque will overcome friction and pull the axle out of the dropouts. They fixed this in back by mounting the rear caliper above the dropout, or inside the rear triangle; That is impossible in front, and you can't just swivel the caliper to the front of the fork (the disc slot will be on the wrong side); You could rotate it to the front, but then the cable would exit on the bottom. This is the impetus for thru-axles, that's why they were invented. Trek uses a "thru-skewer" (at least on their 520), requiring only a small mod to the fork. Some sort of tabs or rim at the dropout may help. Nutted axles may help. 20" wheels may help, as for the same ground-thrust, they are imparting less torque to the wheel system.