What is a "reverse pull" front derailler?
 

What is a "reverse pull" front derailler? I saw that terminology written on an old ad for a Suntour front derailler. Anyone knows what this means? thanks.

As you are aware, most front derailleurs pull the chain up onto the big chainring and rely on spring pressure to return the chain to the small chainring.

Old time Suntour front derailleurs worked the opposite. They used spring pressure to lift the chain up onto the big ring. The only advantage of that system that I could see was that it made the shifters work the same on both ends of the bike. You would push either shifter forward to go faster and pull either shift backward to find an easier gear.

A quick googleing told me that such an FD has a reversed action. Instead of using the cable pull to shift to the larger chainring, it shifts to the smaller. I hope I got it right.

whoa! That is really weird. I don't know if I could deal with the backwardness of the front shifting. thanks for the info guys.

Some people prefer it, since it is a positive shift to a lower gear.

Down tube shifters (friction shifters) used to move in opposite directions. This front derailleur allows for shifting in the same direction as the back one.

My old bike has an FD that moves to the large ring when the cable's slack. As others have said, it means that the levers (downtube) are both moved back for a downshift, forwards for up.

Tony S

The modern application of this idea is Shimano's "Rapid Rise" low normal rear derailleurs that work in the opposite direction from conventional ones. The spring pushes the chain toward the larger cogs instead of the smaller. Again, one effect is that both shift levers work in the same direction to achieve the same gearing direction change.

It makes sense to use the cable tension to drag the chain off of higher gears to lower gears in high torque situations. The Suntour front derailer solved a lot of problems with trying to drop to a low chainwheel while in the middle of a climb. Remember this was before profiled, ramped and pinned chainwheels. One of the sounds you didn't want to hear when you just had to have that granny was the clatter of a too weak return spring not being able to move the chain over. The reverse acting Suntour worked like a dream in those situations.

That's the major problem I have with RapidRise. In high torque situations, you are relying on a spring to move the chain over instead of the much stronger cable pull. If you have time for the shift to happen when you ease off pedaling, that's great but if you can't wait you are sunk...and usually walking:rolleyes:

I agree that relying on the spring to move a derailleur in high stress situations is less certain that the solid connection a cable provides. I certainly remember waaaaaiiiiiting for a front shift in the middle of a hill because the fd's spring couldn't quite overcome the chain tension and the old-style flat chainrings did nothing to help. Benefits notwithstanding, Sun Tour's reverse action fd never became standard and was never adopted by any other maker.

I have no experience with Rapid Rise rear derailleurs but Sheldon Brown was a strong advocate of them. As he noted, rear shifting isn't done on the high tension part of the chain so it's less sluggish under load. It's easier on the drivetrain since the Rapid Rise allows the shift to occur when the release teeth are positioned properly since the spring won't force the shift the way a hard cable pull will.

Regarding Rapid Rise, a lot of it depends on your riding style, technique, etc. I like Rapid Rise for mountain biking for the very reason Shimano introduced it, I guess because I don't seem to have a problem easing up on the pedaling torque for an instant or two when shifting, even when in urgent downshift situations off road. Overall, for XC mountain biking, I like Rapid Rise better. But different strokes for different folks. I will say I'm glad Shimano offers mtb rear derailleurs in both configurations-

Mine relies on cable outer (housing) to push the derailleur. The inner wire is clamped to a non-moving point on the mech, and the outer buts onto the moving lever below that. So increased cable tension causes the outer to push that lever up. Once frame makers changed to a bare cable running under the BB this mechanism wouldn't be usable, which could have been a factor in its demise.

Intersting how they did that.

I have a '93 Trek MTB that has toptube and seat tube front derailleur cable routing but uses a standard low-normal (LX) front derailleur that works in the standard fashion.

There is a cable housing stop bolted to the the fd's normal cable anchor point. The housing enters from above and stops on it but the cable passed through and is anchored to a screw in the seat tube just above the bb shell. Operating the shift lever pushes down on the housing and pivots the fd's operating arm down just as if the cable was pulling from below.