uspspro

https://www.bikeradar.com/news/articl...sc-brake-30034

So who will be the first to have an adapter machined for 203mm rotors, and try these out

DubT

Will someone please explain the advantage of disc brakes on road bicycles? The caliper/rim brake is in effect a large diameter disc brake that applys force to the rotating member, the wheel. The small diameter disc is attached to the hub and puts tremendous loads through the spokes. I understand about wet/muddy conditions and carbon rims but why when you have good caliper brakes with true rims and machined braking surfaces.

Just curious, maybe I have been in a vacuum to long.

Wayne

joe@vwvortex

Any 203mm adaptor will work - that caliper is an standard 74mm post mount.

Have no idea why you would want the complexity of hydraulic lines with a cable works perfectly fine.

PMK

Caps for emphasis, not yelling.

PK

dfcas

[QUOTE=DubT;12568595]Will someone please explain the advantage of disc brakes on road bicycles? The caliper/rim brake is in effect a large diameter disc brake that applys force to the rotating member, the wheel. The small diameter disc is attached to the hub and puts tremendous loads through the spokes. I understand about wet/muddy conditions and carbon rims but why when you have good caliper brakes with true rims and machined braking surfaces.




Rim brakes on tandems may cause overheating issues, leading to tire blowoff and a bad crash. In non hilly riding rim brakes are not an issue, but downhills with switchbacks are the problem.

Chris_W

These are a long way from being rated for tandem use - at the moment they are only recommending them for use in cyclocross races because they aren't even sure if they can handle the heat build-up on long road descents on single bikes, let alone tandems. It sounds like the problem is more in the caliper than the rotor, so a completely different, less racey model is probably needed. Having said that, it looks like the beginning of something interesting and I'm looking forward to seeing ho it develops. Even so, I'm completely happy with the cable discs (Avid BB7) that I have on our tandem and my cyclocross bike, and I'm not sure what advantage the hydraulic line would add.

uspspro

I agree, I am mostly happy with the Avid BB7.

Also, I couldn't deal with that 20mm stack height, unless I could fit a -17 degree stem.

TandemGeek

The only thing I can think of that would make the system attractive would be for cyclo-cross racers who typically ride mountain bikes with hydraulic brakes and who are looking for the same lever feel and system responsiveness: hydraulics take very little hand lever pressure.

As for why (mechanical) discs vs. rim brakes on road tandems, as noted the #1 advantage is more heat capacity which is directly linked to #2, reduced risk of brake-heat-induced tire failures. Beyond that, discs offer more reliable brake performance and rim longevity for folks who ride in harsh weather conditions or climates where grit, snow, ice, mud or dust that collect on rim brake tracks can be problematic. The modulation is a bit more precise, which is nice... but nothing you'd notice if you never used discs.

DubT

So if you live on the prairie and only ride when the weather is nice there is no need for a disc brake.

Is the exploding tire thing real or is that an old wives tale? I know that at Caterpillar they put nitrogen in the big truck and earthmover tires to prevent explosions in the event of a fire.

rdtompki

Seems like the Nitrogen might be more of an attempt to extend the time between having to air up those gigantic tires. Unless your moving earth on the moon the earthmover is surround by the same air that is ordinarily in the tires. Marketing ploy maybe?? In terms of the tire exploding when it gets hot I'd think the Nitrogen would expand at approximately the same rate as "air" (which is mostly Nitrogen anyway).

DubT

I was told that nitrogen does not support combustion.

dfcas

You asked "why" for disc brakes and were given the answer, yet you seem to remain skeptical. Prior to disc brakes, the Arai drum/drag brake was used to take the heat stress off the rims/tires and tubes.

With rim brakes, I would not use a wire bead tire.

wheelspeed

When I looked into new tires, I heard of opposite suggestions in that the heat build-up may expand or warp Kevlar beads more than wire beads. The trade-off is that a wire bead could heat up and aid in melting the tube. I had found arguments on both sides, and ended up buying wire-bead tires even though it killed me to buy that old fashioned technology. (I haven't bought wire bead tires for 15 years until these.)

Anyway, I haven't had problems down the steep switch-back roads here, but I pace myself. I love speed and hate having to maintain lower speed descents because of the rim brakes, so I'll probably shop for disk brakes one day.

DKMcK 

Why?

DubT

That is my nature! I like to see empirical data. Many decisions that people make are based on what someone says without real data to back it up.

I see the benefit of disc brakes in certain situations, however does the stress on the hub and or spokes make a disc feasible when you have a large diameter disc in the form of the rim. Today's rims are very true and the braking surfaces are machined and the newer calipers are very stiff, some of the new brake pads are excellent.

The question that I ask is; has anyone actually had a tire heat up and explode because of the heat build up on a long descent. If so then I see the need for the disc or a drum brake to eliminate that issue.

waynesulak

My only experience with tandem disk brakes is the zing zing zing I her from most of them at rallies. I realize this is most likely a user maintenance issue but it seems that it is an issue for many folks. I would consider them if needed for wet or mountainous conditions otherwise keeping it simple and light with rim brakes seems like the best option.

mkane77g

We have blown a front tire from an overheated rim. Operator error, should have stopped, cooled the rims, then procede. Or, just go like the dickens and not use the brakes, but @ 50+mph down a 15% grade,

TandemGeek

We've seen a couple blow on other folks tandems over the years, and when I included a question on blow-off's due to overheating on a descent in a 2008 survey of tandem owners, 6% (17) responded in the affirmative.

BTW, 50k miles of kevlar beaded tire use... never any issues.

dfcas

I've read/heard about tandem tube failures with wire bead tires. My experience with wire bead tires has been that they are are built down to a price, ride crummy and are heavy. The last 2 I bought were out of round. I think a good quality wire bead tire is possible, but I don't know of one.

abikerider

Continental Gatorskins come in wire bead and are a very high quality tire. I have them on my road tandem and love them.

wheelspeed

Welcome abikerider!

Phantoj

I had Avid discs on a Giant OCR Touring (BBDB, predecessor to the BB7). Anyway, I didn't like the Road implementation of the Avid cable brake. Mushy feel and too much lever travel. I'm not the only one. Hydro discs are still preferred for MTB; I think they are an improvement.

I have seen a similar kludge for cable/hydro integration. It used hydraulic brakes mounted on the bar tops (like "cross" levers") drilled so that the STI brake levers cable pulled on the hydraulic levers and caused it to squeeze. Good idea!