Can I replace the front front derailleur with chain guide?

Question

My front derailleur (Shimano LX T670 / 34.9mm) has been stuck on the highest gear for a couple of weeks now which has got me thinking about how little I use it. To save weight could I replace my front derailleur with some sort of static chain guard/stay to keep my chain on the same chain ring? Does such a thing exist for three speed chainsets (Shimano T780 48Ax36x26 with chainguard)?

I am not ready to completely convert my bike to a single speed just yet as I imagine I could install the front derailleur back on if I decide to go on a more adventurous journey compared to the daily commute where its not needed.

Update

While the FD is only 155 grams I do enjoy finding ways to save weight here and there, before you know it it's half a KG lighter. The problem with leaving it on is that the spring has rusted into place almost at mid shift, this causes the chain to rub the side of the chain guide which produces an annoying sound and causes it to occasionally jump to the middle chainset.

For now I have simply removed it but in the past on a different bike I suffered from chain jumping which is what I am trying to avoid by using a chain guide.

Thanks

Answer 1

The simple test is just to remove the derailleur. Some of them have a screw holding the bottom of the cage together, in which case it's easy - just undo the clamp holding the derailleur to the seat tube, the cable clamp, then once it's loose undo that screw and wiggle it off the chain.

Without that cage screw you'll have to break the chain which requires either a quick link that can be undo by hand, or a special tool. Putting it back on afterwards is slightly more complex but quite doable for most people. If that works, you can then remove the cable and outer, and possibly the shifter (these days likely to be built into the brake lever so not removable).

But as Batman pointed out, the front derailleur is not the heavy part of a multi-speed setup. Most of the weight loss from a single-speed conversion is in losing the extra chain, cassette and rear derailleur, and the maintenance benefits also come mostly from not having to adjust the rear derailleur. So the total benefit is likely to be low. You might also lose a little weight by removing one of both of the extra chainrings, but again not every much.

Answer 2

The product you want does exist, but it's not significantly lighter than a front derailleur, it just works better for single rings. The are much heavier and more robust chain keepers used for Downhill MTB.

Paul Chain keeper.

http://www.paulcomp.com/chainkeeper.html

Here's a whole page of similar devices.

http://www.jensonusa.com/Chain-Tensioners-and-Guides

Answer 3

Jump is when the chain stays on the gear but does not come off the gear - it skips. Off is when the chain comes off.

Chain tension is more to keep the chain from coming off. Yes chain tension would help jump but if you have badly worn gears / chain the tension is not going to save jump.

A chain jumps when the chain and or chainring are worn.

A keeper is not going to do much to stop jump. A keeper may help to prevent the chain from coming off.

If your gears, chain, and rear derailleur are in good shape your chain should not come off even without a font derailleur. When you look at you derailleur you may think it is there to keep the chain on but it is really just there to move the chain.

Chain rings are ramped to help them move up. You can get them that are not not ramped. Un-ramped chain ring should help a bit. Un-ramped leaves a little more metal on the chain ring so it should last longer. I went un-ramped when I converted my mountain bike to a single speed. Chainrings for single chain ring set up. RaceSingle SurlySingle
From Surly: If you are using a single front ring with multiple cogs out back, a chain guide is recommended to prevent the chain from jumping off the chainring.

The XC in this video is set up with single chainring (Race) and no guide. XCversusTrail