skid stop
 

I recently had a disc brake mount added to the rear of our tandem. I installed a road bb7 with a 203mm rotor. We have Shimano brifters. We run a 32mm tire at ~90psi, and our gross weight is ~440lb. Using both brakes, I am unable to make the rear wheel skid. Should I be able to skid with this setup?

The brakes need to be run in and after this the braking will improve but have to ask how fast the new system is stopping you ?

Ideally, a bicycle will come to a fast / hard stop without the rear brake skidding with the front brake doing the bulk of the work... it is harder to skid a loaded tandem due to the extra weighting in the rear and you really don't want to be skidding as it is less effective and could cause control issues.

I'm fairly sure they're worn in. The brakes are satisfactory, as in they stop the bike, but if the tire doesn't skid that means I could potentially be stopping faster. I'm just using the skid stop as a metric for brake performance. Also note that the California vehicle code says
21201. (a) No person shall operate a bicycle on a roadway unless it is equipped with a brake which will enable the operator to make one braked wheel skid on dry, level, clean pavement.

That's in vehicle laws of more than a few states and makes no sense at all. Anyone aware of actual enforcement of this absurd law?

My experience with (unplanned) skidding is that it wears away tread.

A couple thoughts...

1. With regard to, "We run a 32mm tire at ~90psi, and our gross weight is ~440lb. Using both brakes, I am unable to make the rear wheel skid. Should I be able to skid with this setup?". Too hard to know without knowing what the front to back weight distribution is but, in general... probably not. I could conceive of some scenarios whereby we could probably get the rear wheel to skid and therein lies the falacy of the "brake test" developed for single rider bikes with coaster brakes decades ago.

2. Were you able to skid the rear wheel using just rim brakes under the same conditions? I'm guessing, probably not. If you were, then your rear disc is not delivering its full stopping power, i.e., too much elasticity in the brake cable/housing, brake pads aren't set close enough, or the pads and rotor truly aren't bedded-in.

3. Ignoring the rear brake skid test, what's your overall impression of the change in rear brake performance compared to your rim brakes? Better, worse, or about the same in terms of lever effort and stopping power?

1) Fair enough. I know the test is flawed, but I think it is a useful metric in some ways. I've never heard of anyone enforcing this.
2) You are correct. On this topic, I've considered upgrading to a fancier cable/housing. Right now I'm using Jagwire L3 housing w/ Jagwire SS cables. I've taken the time to bench grind the ends and run housing the full length. Is this a worthwhile upgrade?
3) Definitely better than the cantilevers, especially in the rain.

The law that says you have to be able to skid a rear wheel is ridiculous... a rear wheel skid by itself requires almost twice the stopping distance of a well applied front brake.

It is a good gauge to tell how well tuned your brakes are and can see how their wet performance is much better than the cantis... ideally one would run the canti and the disc so you could use the disc as a drag brake on descents.

Filing or otherwise finishing cable housing ends is always a good idea, as are using ferules that allow housing to fully seat.

As for running full-length cable housing, it's not a bad idea for off-road applications as it can keep grit and grime out of that end-segment of housing, but is probably overkill for road applications unless you spend an awful lot of time riding on wet or gritty roads and route your cables on the underside of the down and boom tube. If you have your brake cable running along the top tube and then down the left seat stay to the caliper, full-length cable is definitely not needed or of any benefit.

My question was misunderstood. What I meant to ask is "is it worthwhile to upgrade to a fancier 'compression-less' brake housing?" such as Jagwire Ripcord.

Not really. Just running cable housings with as little excess length and getting the housing ends finished-off and cleanly seated in ferrules and the cable stops is more important. I also recommend using a compression spring on the reaction arm, fitted between the Avid's cable stop and arm. More info here: http://www.bikeforums.net/showthread...=1#post8021962

About the only way to "super-charge" the rear disc is to use an in-line cable booster like a BPB (Brake Power Booster) or an in-line Travel Agent (kind of a kluggy-approach, but it does work), unless you have the newer Shimano Ultegra (6700) and DuraAce (7900) model STI levers with what they call “Super SLR”. The Super SLR’s increase brake lever purchase.

I don't believe that the law implies that a skidding tire is optimal braking but rather that a braking system should have the capability to completely stop a wheel, hence creating a skid. i.e you shouldn't "run out of pedal".

THIS is why you need to be able to skid your rear wheel: YouTube (low quality, but fun)

IMO: yes you should /// I have the exact same brakes and 203 rotors. Our gross weight is 390 so a little less but I can skid my 38 mm tire on demand.
I have full-length cable housing with metal ferrules...
Also make sure you don't ever get any oil on the pads or rotors... if you do toss those and buy new. I clean my rotors with acetone after handling as just the oils from you skin will make a difference in braking power.
The red screw on the levers moves the leverage point... screw it out for less power and in will increase you leverage.
Lots of steep roads here in NW AR... and I only use 1 finger on my brakes.

Can you skid on a flat road or going down a grade? If a grade how steep? A difficult question but what is the captain-stoker weight distribution?

As noted earlier, there are a lot of variables that can factor into whether or not -- and if so how easily -- a wheel and tire can be induced into a skid on a tandem.

- Brake set-up is one, inclusive of cable routing, pad & rotor condition, which model brake levers are being used, boosters, etc.
- Tires are wild cards: How hard or soft is the compound, and is it a slick, herringbone or have a tread pattern? What PSI?
- Environmental: What type of road surface, flat or on a grade, what speed, and never forget about the temperature of the road, tire and brake system.
- Weight & Weight Distribution: 280#, 390# and 440# are vastly different, but even more important is the weight over the rear wheel: are we talking a 60/40, 50/50 or even a 40/60 split?
- Braking Technique: If, how and when you apply the front brake coupled with the bike's weight distribution is what will ultimately determine if you can skid a tandem's rear tire.

Like I said, I could easily conceive of some scenarios whereby I can get just about any tandem to skid it's rear wheel. But, the reverse is also true. What really matters is how well a given team can safely stop their tandem and if you can do something to a tandem that can improve the stopping performance (to include rider training and improved technique), that's always a good thing. Frankly, I depend more on my situational awareness to keep me out of trouble more so than maximum braking efforts.

I can skid my rear tire on any road surface rather it's flat, uphill, or downhill... 2010 Cannondale tandem
weight is 55% on front so pretty close to being even
Running around 45-50 psi... so tire is really soft and easy on my stoker :)
I'm really impressed by the BB7's performance coupled with a 203 Cleansweep G2 '07' model I borrowed from one of my old downhill bikes.

Over 230,000 miles of tandeming.
Have never skidded . . . and there is no need to.
Stopping is all that is required. Skidding presents it's own issues . . .

I agree partially with this.

Yes clean is important.

I disagree with the idea of discarding the brake pads once contaminated, especially the Avid BB7's. The oem pads are metalic and clean easily and well with brake cleaner.

I also will wipe the discs to remove residue.

FWIW, brake dust or road dust, even residue of soap from washing will decrease how crisp the brakes feel. I recently inspected our brake pads for minimum thickness. While removed they were again cleaned. Typically the road tandem will go about 800 to 1000 miles (about each rear tire change) between brake pad removal and cleaning.

Clean your disc, ride normally for a bit and see if the brake performance doesn't get better. It does take a bit to bed in the brakes for full performance.

PK

Every few hundred miles I clean the rotor and sometimes the brake pads with isopropyl alcohol. It improves the braking of the disc brake. Have never tried to skid a tire since I was a kid. Seems to me it would be hard on the tire and the wheel. Antilock brakes on a car are a safety feature.

Funny, just a few days after I read this post, we wound up having to make two very quick stops on our tandem. Both times locking up the rear wheel.

I was surprised at how easily the rear locked up. As soon as I felt it lock, I eased off the brake.

I do use both brakes. I am especially heavy on my front brake. That's where all of the stopping power is. In an emergency situation, I do grab all I can of both brakes. Still, I was surprised of the power of the back brake. I really didn't think it would grab so well.

For the record: We are a 260lb team. I use Sram red levers, Dura Ace 7900 brakes with Dura Ace brake pads. Nokon cables. Very solid set up.

I switched out my cable housing, and boy did that make a difference. It's possible that it's just a coincidence; perhaps I simply did a better job of aligning the caliper, but they feel like whole new brakes. No problem skidding now.

Previously, in the 3 places that the cable bent (handlebar to top tube, then around the captains seatpost, then down the seat stay), there was significant movement of the housing when the lever was squeezed, but now it stays put. I haven't done the math, but it must be saving me a few mm of cable pull.

I'm guessing that law dates back to the old coaster brakes. If you stood up on the pedal and the back tire didn't skid, there was something awry with the brakes. Hand brakes are a whole different game.

You need to be able to skid. It is important to maximize stopping power. This is the principle that ABS brakes work on. In an emergency you should be braking hard enough to just barely not skid.