Double with bash from triple

chrisga

Thinking of ditching my outer chain ring and going to a double with bash guard setup. I've also seen some people running these with a chain tensioning roller type device under but behind the chainset.
My question is how do these cater for the chain moving between two rings or do they only provide tension when the chain is on the larger (middle) ring position. Does the roller move? Are tere any diagrams anywhere to help me understand. What do these attach to. Do they just fit between the bottom bracket and frame, or do you need special mounts. Is this what the ISCG thingies are for? What if you dont have these.

Thanks in advance.

nicklouse

they dont do anything for the tension. that is the mech.

they are bb mount or iscg or iscg 05.

chrisga

What do the rollers do then if they arent for tension? They cant be guiding the chain can they, as the ones i've seen are on the bottom side of the chainset where the chain leaves the chainset not joins it.

peter413

They stop the chain falling off the the chainrings.

If you go to your bike and try to move the chain up and down with your hand, you can't on the top because that is under constant pressure but the bottom bit moves because the rear mech does, this is how the chain gets droped from the chain ring but the rollers you are describing stops the chain seperating itself from the ring.

Thats the best way I could explain it anyway

RupertCommunicator

The roller doesn't move on dual set ups. It's there to provide chain security mainly in the larger chainring. The front mech keeps the chain on, the roller stops the chain from slapping around, which is why you see them on DH and FR bikes.

The dual set up I have on my FR bike is dual and bash using a homemade chain guide consisting of an MRP System 3 chainguide cut in half mounted upside down with the slider plates removed. Works really well, but I'd recommend that you get something proper for the job like the Gamut, RaceFace or E13 offerings!

You can get them in BB mount if you don't have ISCG tabs but something you'll need to think about is chainring sizes. Normally using 44 32 22 if you ditch the big ring you'll be left with 32 22, which may be a bit slow for the downs. Going for 36 or 38 middle ring means that you'll still be able to pedal down as well as up! Also the dual chainguide bashrings come in 36 or 38 anyway.

If you're keen on only spending a couple of quid on ditching the big ring you can still run dual and bash without a guide and buy a 32 bashring, raising ground clearance, protecting your rings (ha!) at the cost of more rear shifting, chainslap and outpedalling on the downs.