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single vs. dual pivot . . . i don't get it(14 posts)

single vs. dual pivot . . . i don't get itbm
Jun 15, 2003 7:54 PM
i searched roadbikereview for discussion about single pivot and dual pivot brake calipers. but i don't understand the arguments.

what are the advantages in each? (weight, power)

why are they only making duals now? (at least in shimano)

and are there serious disadvantages to single pivot?
(like a risk of crashing)

thanks
and why . . .bm
Jun 15, 2003 8:09 PM
and why do the campy's come with single rear and dual front?

should i set up my bike this way . . . with a dual front and a single rear?
and why . . .russw19
Jun 15, 2003 8:26 PM
Dual pivot brakes are heavier, but more powerful. That explains the reason Campy uses one of each. 80% of your braking power comes from your front brake. So if you put the stronger more powerful brake up front, you can use a light (but less powerful) brake on the rear. If you understand the dynamics of independent brakes on bikes or motorcycles, you should know you use your rear brake for speed control and modulation, but use your front brake to slow down or stop.

Single pivot brakes work well, but dual pivots work better. Dual pivots are heavier than modern single pivots, but at the expense of power... between the two, would you rather stop or have a bike that is 100 grams lighter? That's why Shimano only uses dual pivots and Campy uses it at least where it's needed more on the front.

Russ

If you take a look at mountain bike downhill brakes and motorcycle brakes, you will see that the front has a larger rotor than the rear for this same reason... then again, your car probably does too. It's all the same concept.
Actually, ...seyboro
Jun 16, 2003 4:30 AM
...Campagnolo's thinking, albeit with the same result, has a differrent reason. Their main concern was not weight savings, but to even out the difference in feel at the lever and to eliminate accidental rear brake lock up.
As both you and another poster below stated correctly, the front brake produces more power.
If both brakes are applied, the force to pull the levers differs with dual pivont calipers. Poperly tuned Campagnolo brakes eliminate the difference and give an 'even' feel. Switching back and forth between a Record-equipped bike and a dura-ace 'rain-ride' frequently, I actually notice the difference.
As for overall stopping power, the single/dual pivot issue has less of an impact than the design of the calipers and pads itself. Due to the groove in the caliper arms of a D/A brake, they are a bit more flexy, producing less power than a Record D/P brake. Also, the curved pads introduced in 2000, added significantly to the Campys' stopping power.
Here's a link to a full explanation:
Actually, ...divve
Jun 16, 2003 5:16 AM
That's strange because when set properly my front and rear DA feel the same.
True, but...seyboro
Jun 16, 2003 5:50 AM
As far as I know, the D/A rear and front calipers are identical (except for bolt length). If you can, try this some time: swtich from a Campy bike to a Dura-ace bike and back on the same ride. If you first use the front to stop from a certain speed to a stop, then the rear, you will notice that the front brake alone will stop you sooner. If you pull the rear to stop in the same place, you might well get a skid out of the D/A bike.
On a Campy-equipped bike, this does not happen. Can you still lock up a Campy rear brake brake? Yes, but in everyday riding, this should only happen if you want to, not by accident.
Of course, all this 'feel' might just be in my head, but that's what Campagnolo's engineers/designers aim for, anyways...
re: single vs. dual pivot . . . i don't get itAllUpHill
Jun 15, 2003 8:33 PM
There's no serious disadvantage to single pivots. With just a single pivot rear, you would probably not notice a big difference. With single pivot in front as well, you'll just have to get used to the feeling of less braking immediacy. If you're heavier and ride fast hills, you might need to get in the habit of beginning your slowdown a little sooner.

People rode single pivots for many decades and they worked just fine. Some still choose to ride singles front and rear for weight-weenie or retro purposes.
thanks . . . that helpsbm
Jun 15, 2003 10:17 PM
re: single vs. dual pivot . . . i don't get itxcandrew
Jun 15, 2003 11:19 PM
The overall leverage ratio on a single pivot sidepull brake is 4:1 (4:1 at the lever, 1:1 at the caliper). The leverage ratio on a dual pivot sidepull brake is 5.6:1 (4:1 at the lever, but 1.4:1 at the caliper). Thus, you need to pull 4 mm at the brake lever to move the brake pads of a SP 1 mm, and 5.6 mm at the lever of the DP for the same 1 mm movement at the pad, so the DP has a higher mechanical advantage. DP's require less force to brake than SP's.

The trade-off is that the pads on the DP brakes need to be set closer to the rims. The levers are the same mechanical advantage for both (4:1). If the pads were set equally far apart for both, you would risk bottoming out the levers on the DP's. The DP brakes can be forced to be centered, and this allows them to run closer to the rims. Sidepulls sometimes lose their centering because of friction (dirt, etc.) on the spring contact points (but this has never been an issue with me with brakes from the last 15 years). The requirement for the pads to be closer to the rims is a disadvantage for DP's, and is perhaps the main reason (rather than weight) that Campagnolo went back to a SP for the rear brake. When climbing out of the saddle, some people find that the rims move enough laterally to rub the pads on DP's, and some pros were seen to ride with their rear QR's open. This is less of a problem with SP's. Even in cases of an out of true wheel, a SP will 'follow' the rim better than a dual pivot because it doesn't have fixed centering, though this is admittedly a minor advantage since you would open the QR in either case.

There is no serious disadvantage to SP's. They have less mechanical advantage, but this could arguably translate directly to better "modulation". They require 40% more force, but this is not necessarily a disadvantage unless your hands are weak - people have dramatically different grip strength. This is not an issue of braking "power". Anyone can brake hard enough with good SP's to lift the rear tire from the ground. On long downhills, the important issue is heat dissipation, which has more to do with the rims and brake pads. With good pads like Koolstop salmons, any advantage from mechanical advantage could be negated or made into a toss up anyway. The advantages of SP's are that they can be lighter, have better 'modulation', and they can run the pads farther from the rim, and don't need pad height adjustment with pad wear.

Another (perhaps minor) issue has to do with the offset pivot side of the DP calipers. If you trace the arc that the pad makes around this pivot, you will see that it traces an upwards path towards the top the the rim and tire. Thus, as the pad wears, it rises higher and higher on the rim and can reach the tire if unchecked. With SP's, you can use thicker brake pads and never have to adjust the pad height with wear because the pivot is centered directly over the rim. (The opposite problem of pad dive in cantilevers is also because of offset pivots - similar problems with centerpulls, U-brakes, rollercams, etc.)

I like my old SP's... they have done well for me in all situations. If you like DP's that's fine too... you just favor a different set of advantages and tradeoffs.
disadvantage is adjustability...C-40
Jun 16, 2003 4:22 AM
Single pivots don't have a convenient centering screw like double pivots. The only way to center the pads on the rim is by rotating the calipers with a (15mm wrench, and then tightening the mounting bolt. Field adjustment isn't easy.

I've had the single pivot rear for the last two seasons. Never been a problem.
disadvantage is adjustability...dave woof
Jun 16, 2003 7:34 AM
Actually field adjustment on SP calipers is easy. Take a small screwdriver or allen wrench and a small rock, user the screwdriver and small rock to tap the spring near the loop on the top. Just one or two taps will center the spring and center the calipers over the rim. Works every time.

Dave
Just wanted to clear up a misconception...brider
Jun 16, 2003 9:45 AM
...that somebody ALMOST got to, but didn't take it far enough.

Your brakes don't generate more braking power on the front wheel.

The brake doesn't really know the difference between the front and rear wheel. What you get is more effective braking on the front because of the weight transfer to the front wheel. This is also why it's much easier to lock up the rear wheel.

Static friction is directly proportional to the normal force (the force acting from ground to hub). At rest, this is 55-60% of the rider+bike weight on the front wheel. When you start braking, this goes to 75-80% (this is also the reason a car nose dips when braking). As the rear wheel unweights, the amount of possible braking force is reduced.

The actual advantage of a dual pivot brake is that it provides a better mechanical advantage in transferring cable tension into pressure on the rim. Less hand force is required to provide a given amount of pressure to the rim.
Disadvantage on steep hillsLC
Jun 16, 2003 11:09 AM
I got bikes with both kinds of brakes and I got to say it is pretty scarry with a single pivot front coming down a steep hill. If the hill is steep enough then about all it will do is slow me down, but not enough to actually stop till the hill flattens out. Maybe I got to start doing some hand workouts or something, but I don't quite find single pivot powerful enough where I ride.
re: single vs. dual pivot . . . i don't get itmapei boy
Jun 16, 2003 4:10 PM
My experience is the same as LC's. In the thirty years I've been rattling down the 14-20 percent, mile-mile and a half CalNeva Drive in the Santa Monica mountains, I've come to appreciate dual pivot brakes and the power they bring to bear. In the Seventies, with my Campy Nuovo Record single pivots, my hands would start to cramp by the time I was half way down. In the Eighties, with my Dura-Ace single pivots, they'd cramp at about 3/4 of the way down. In this brave new Century, my Campy Record dual pivots take me down CalNeva with no cramping at all. Ahh. Progress.