Is this even possible?
 

A Shimano Claris 8 speed brifter (Right side) throwing an 8 speed chain over a sun race 8 speed mtb cassette (11-40) employing a long cage derailleur with a single chainring up front (undecided, but shooting for 48 or 50 tooth) any derailleur advice (thinking deore)...
8 speed cassettes are same width road to mtb, and have the same click spacing so it should work in theory.... Bike is currently all Claris (triple)

? why not try it, ?

first people use these https://www.wolftoothcomponents.com/...r-optimization

moves whole RD down, so May Be a better option than just putting in a longer B screw
to rotate the RD further away .. which will be cheaper..

Single plate in front is so fashionable.

1. Make sure the rear derailleur has capacity for a 40 tooth large cog.
2. Forget about 48+ chainrings. With only 8 speeds it's a waste to have a downhill only 48-11. Even if you limit your top crank revs to 100rpm on a 26" tire you're at 32mph (35mph on a 29r). Even the 48-13 is questionable on a mountain bike.

I am planning on a long cage derailleur to cover the 40 tooth cog.
This is on a 700c road bike. My mtb has a 32-11 top gear and that's just fine for that bike.

A long cage is for taking up chain slack on a wide range gear system. Although a long cage derailleur typically can handle larger cogs it does not necessarily mean the top pulley is low enough to handle a 40 tooth cog. Example - Deore XT long cage cog capacity is 34t. Deore XT specs. You may be able to use a hanger extender to increase large cog capacity by 4 teeth or so: Wolf tooth hanger extender review

What does a 32-11 on the MTB have to do with a 48-11 on the road bike?

The issue is that no Shimano compatible 8 (or 9 speed) speed derailleurs have an official rated capacity for a 40t. Also they actually have longer than necessary cages than needed for 1x. The best bet is something like an M3000 derailleur (rated for 36t) and possibly a longer B tension screw if necessary or a Wolftooth Goatlink.

You can also use a Jtek Shiftmate 6 to pair your 8 speed Shimano road shifters with a 10sp Shimano MTB rear derailleur, which will let you use a clutch derailleur; I'd probably recommend RD-M6000-GS in this case; Microshift also makes some offerings for this.

He thought I was talking about a 26" mtb is what I thought?


QUOTE=cny-bikeman;20568295]A long cage is for taking up chain slack on a wide range gear system. Although a long cage derailleur typically can handle larger cogs it does not necessarily mean the top pulley is low enough to handle a 40 tooth cog. Example - Deore XT long cage cog capacity is 34t. Deore XT specs. You may be able to use a hanger extender to increase large cog capacity by 4 teeth or so: Wolf tooth hanger extender review

What does a 32-11 on the MTB have to do with a 48-11 on the road bike?[/QUOTE]

This is what I was after, thanks!!!



Thanks!