Friction gears?

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Bike-Rich
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Friction gears?

Postby Bike-Rich » 21 Dec 2013, 9:39pm

Hi,

Can anyone please explain the term 'on-friction' or friction gearing and what advantages does this have?

Thanks

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cycleruk
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Re: Friction gears?

Postby cycleruk » 21 Dec 2013, 10:04pm

"Friction gears" refers to the changer which just stays in the position it is left in.
This is opposed to "indexed" gears where the changer has distinct ratchet positions matching the gear spacing.
A friction changer can work with any gear system whereas indexed gears can only work with a specific set number. ie: A 9 speed changer can only work with a 9 speed cassette.
(There are some anomalies to this such as a 10 speed "indexed" Campagnolo rear changer will match a Shimano 8 speed derailleur & cassette.)
A friction changer will operate Shimano or Campagnolo systems.
You'll never know if you don't try it.

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531colin
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Re: Friction gears?

Postby 531colin » 21 Dec 2013, 10:46pm

If your bike gets damaged far from home you can often bodge it up "on friction" to get at least some gears working.
For index shifting to work reliably the drivetrain needs to be in reasonable condition.

Bike-Rich
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Re: Friction gears?

Postby Bike-Rich » 22 Dec 2013, 10:02am

Thanks, think I understand,

With friction, is it common for gears to 'cross' at all? For example with index having set 'areas' there is not normally any grinding.
Although thinking about it, if there is a grinding noise when using friction, I could add slightly more pressure to the changer? Is that how it works,

Finally, I think i read somewhere it's possible to have index gears with a back-up friction shifter?

james01
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Re: Friction gears?

Postby james01 » 22 Dec 2013, 10:37am

Bike-Rich wrote:Thanks, think I understand,

With friction, is it common for gears to 'cross' at all? For example with index having set 'areas' there is not normally any grinding.
Although thinking about it, if there is a grinding noise when using friction, I could add slightly more pressure to the changer? Is that how it works,

Finally, I think i read somewhere it's possible to have index gears with a back-up friction shifter?


On friction mode the lever's positions are infinitely variable so you have to align the chain by feel. This is much easier than it sounds unless you one of those unfortunates who have no mechanical sympathy. And yes, many index gears have a selectable friction mode. This is extremely useful if faults develop on a journey. Unfortunately many modern designs omit this optional friction feature.

thirdcrank
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Re: Friction gears?

Postby thirdcrank » 22 Dec 2013, 11:04am

Friction is the last survivor of older technology. (There were others, such as twin wires pulling in opposite directions, and rods rather than cables.) Its main advantage in comparison with indexed equipment is its flexiblity, eg, as others have noted if something gets out of kilter. Since a mech doesn't know what sort of lever is pulling the cable, mix'n'match is generally easy, although the change to parallelogram gears meant that the newer levers didn't pull enough cable for earlier mechs.

When working properly, indexed gears are a doddle compared with friction. Some of the accompanying innovations, such as STI/Ergo levers (combined with the brake levers) enable changes to be made riding hard uphill, when downtube friction levers are not so easy to use. Modern profiled sprockets facilitate smooth changing. With friction levers and older sprockets, it's normal to overchange slightly, and then trim back. As well as speeding up the change, this avoids a tendency in some set-ups for the chain to ride along the tops of the sprocket teeth.

Presumably for commercial reasons, some manufacturers seem determined to minimise or eliminate compatibility with anything else. There are ways of getting around some of this and if you search on Shimergo, you will find all sorts of ingenious getarounds to thwart manufacturers' intentions. Apart from the need to have everything finely tuned to get the sweet running we've become accustomed to, this reduction in user choice is probably the main disadvantage. Whether it's a big one depends on how much you like to be in charge.

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meic
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Re: Friction gears?

Postby meic » 22 Dec 2013, 11:05am

Bike-Rich wrote:Thanks, think I understand,

With friction, is it common for gears to 'cross' at all? For example with index having set 'areas' there is not normally any grinding.
Although thinking about it, if there is a grinding noise when using friction, I could add slightly more pressure to the changer? Is that how it works,

Finally, I think i read somewhere it's possible to have index gears with a back-up friction shifter?



While I am not sure that I understand what you mean and whether it is the front or rear that is grinding.

It is quite possible that your gear cable just needs adjusting, there is a little adjuster* on the rear derailleur where the outer cable meets it. This should enable you to get the indexing realigned with the sprockets.

*almost certain on a bike using indexed shifters that still have a friction function.
Yma o Hyd

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cycleruk
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Re: Friction gears?

Postby cycleruk » 22 Dec 2013, 11:18am

Basically it is the down-tube shifters that have the changeable friction/index choice. Although there are one or two that fit on the bars.
There are though some that don't have any indexing and are just friction, especially old ones.

On the down-tube changers it is usually the right (rear derailleur) that has the indexing. There is normally a toggle that you turn to select friction or index mode.

The left shifter is normally just friction as you are only selecting 3 chainrings at most. This friction shifter also allows " trimming" of the front derailleur to overcome chain rub as the chain angles across the rear cassette.

Generally the worst that can happen to friction changers is they loose their friction and slip round under tension from the derailleur.
This is usually easy to overcome by tightening a screw or in need of cleaning.
Obviously the cable can break but it is no problem to carry a spare cable.

In index mode, if you get a slight mismatch then an adjustment of the rear derailleur is all that is needed.
In friction mode, as you say, just alter fractionally the changer.

If I was putting together a real touring bike then down-tube changers would be the most simple and reliable ones.
You'll never know if you don't try it.

Brucey
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Re: Friction gears?

Postby Brucey » 22 Dec 2013, 2:40pm

Bike-Rich wrote:....Finally, I think i read somewhere it's possible to have index gears with a back-up friction shifter?


Yes indeed. As well as the downtube levers with a friction mode, there are/were thumbshifters and bar end levers which also have a switchable friction mode.

The thumbshifters like this made by Shimano (for midrange and upwards groupsets) were a very reliable product indeed. They even worked better as friction levers than most friction levers did. It is a great shame that they stopped making really good quality thumbshifters that worked like this.

The only potential flaw with these is that the friction mode is not readily adjustable, but since I've only ever seen one or two sets that needed adjustment, this isn't a big deal. The parts that might wear in friction shifting are not loaded when the levers are in index mode; thus it takes prolonged use in friction mode to cause any appreciable wear, I think.

cheers
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andymiller
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Re: Friction gears?

Postby andymiller » 22 Dec 2013, 2:54pm

Brucey wrote:The thumbshifters like this made by Shimano (for midrange and upwards groupsets) were a very reliable product indeed. They even worked better as friction levers than most friction levers did. It is a great shame that they stopped making really good quality thumbshifters that worked like this.


You can produce something that achieves the same result by using a set of bar-end shifters with a pair of 'thumbies' from Paul Engineering. IIRC these (or a copy of them) are available from SJS cycles.

There are bits that can break (or at least there are on the shimano bar-end shifters I don't know about other brands) - so they're not completely bombproof, but you don't have to adjust for cable stretch, so they do reduce day-to-day maintenance a lot.

Bike-Rich
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Re: Friction gears?

Postby Bike-Rich » 22 Dec 2013, 5:15pm

Many thanks guys, that's made it much clearer, i'm re-reading the above posts but think I can see the plus & negatives on both systems,

With friction, 'down tube' seems to be a popular choice (bar-end and thumbie being the other choices?), is the only difference the position? Presumably with the levers being on the tube this minimizes movement/stretch compared to being on the bars and possible reduce daily-maintenance?

Brucey
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Re: Friction gears?

Postby Brucey » 22 Dec 2013, 5:45pm

I've never been a big fan of bar end shifters for the following reasons;

- except on frames that are quite large and/or on which the bars are set quite high there is little or no reach advantage vs DT shifters if you ride mostly on the tops or hoods.

- bar end shifters are far from being immune to accidental damage in a crash or if the bike just falls over.

- the extra cable run can be another place for the cable to get draggy and cause trouble. Not as bad as under-bar-tape STI's /ergos though.

- some recent models of Shimano bar-end shifters have proven to be unreliable, with internal parts prone to failure.

I believe that shimano DT levers are not made the same way and therefore are not similarly vulnerable to failure. Since you can get a bracket to accept these on the handlebars, (or the stem) I'd look into that as a route for having handlebar mounted shifters.

cheers
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andymiller
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Re: Friction gears?

Postby andymiller » 22 Dec 2013, 6:16pm

Bike-Rich wrote:With friction, 'down tube' seems to be a popular choice (bar-end and thumbie being the other choices?), is the only difference the position? Presumably with the levers being on the tube this minimizes movement/stretch compared to being on the bars and possible reduce daily-maintenance?


Yes.

No (or at least not so mach that it would be a practical issue - just take up the slack every so often: a 5-minute job).
Last edited by andymiller on 22 Dec 2013, 6:37pm, edited 1 time in total.

LollyKat
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Re: Friction gears?

Postby LollyKat » 22 Dec 2013, 6:26pm

With some riders/riding styles there is a risk of gouging the knees on the bar-end shifters when honking up a hill. I've occasionally brushed the bar end like this and been glad that I have down tube levers instead.

Another advantage to friction shifters is that it is very easy to shift several - i.e.four or five - sprockets at once. I've used friction shifters for 40 years and know exactly where each gear is by the position of the lever. There is no need to look, I simply do it by feel. Very useful when riding with a cape, too, as it is easy to avoid cross chaining.

I'm not a Luddite and enjoy the STIs on another bike, but I do like the simplicity of friction levers, especially when they are nice ratchet ones like Suntour Powershifts or Simplex Retro-friction. :D

Bike-Rich
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Re: Friction gears?

Postby Bike-Rich » 22 Dec 2013, 7:20pm

Many thanks, I understand now :)

For down-tube shifting, is it required for the frame to have provision for the fitting or is it braze-on type?