Chain Guide, ala PVD
The need for a chain guide
By running a single front ring on my six speed MTB, I have to have a way of keeping the chain on the ring. Without a guide, the chain will fall off several times a ride.
Since I ride trails, I wanted a nice solid chain guide that didn't mount in a heavy way to a bash guard. Chainrings are the only bash guard a singletrack rider needs.
What's wrong with bash rings?
Bash rings are great things for trials riders and downhill racers. For the rest of us, they are just heavy clutter on the bike.
Most people running bash rings have a fantasy as to how hard they ride. They are usually unscratched and never used.
Almost all singletrack trail riding will not need a bash ring, even with large obsticles.
Why not a front derailure?
While a front derailure is probably capable of reasonably holding the chain in place, I chose not to go this route for two reasons:
- I wanted the most rugged and solid solution. A front derailure has two jobs, to hold the chain in place and to derail it. I figure that something committed to just one of those tasks is going to work far better at that task.
- Using a deraillure as a tensioner or a guide while not using it for derailling looks amature and hack. I hate that look.
The consumable parts
The Truvative Boxguide box is available as a spare part for about $20. It's a good idea to design around cheap and commonly available consumables.
This is the stock configuration of the part.
The parts included in the spares.
The custom clamp
The print for making the clamp and mount bracket. It's not a production drawing, so it's a little sloppy with some details left for other prints.
I machined a custom bracket to mount the box to my frame from the seat tube. Locating the proper position of the guide was the most difficult part, but a little math helped.
It's a super solid set-up.
139 grams. Not the lightest, but tougher than anything you can find.
Fitment on the bike
With the guide installed, the chain has no place to go but the right way. It is rock solid on the trails.