# Need drivetrain suggestions for gravel bike build



## angelo1100 (Aug 24, 2012)

Assembling a gravel bike. Frame is a Soma Double cross disc. Not sure what gearing I want. My gut wants a compact 50/34 in the front and some kind of mountain bike cassette in the rear. Maybe an 11/34. Looking to go with 105 and or SLX. Will the GS derailleurs work with a 34 or do I need a mountain bike derailleur?


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## Lelandjt (Sep 11, 2008)

With 105 10spd shifters and a 10spd 11-34 cassette you need a MTB 9spd Shimano derailleur. This is you cheapest option. 1:1 is a super low gear that would suitable for trail riding a CX bike but probably never used on roads that a car could drive. If you do 11spd Ultegra you can get an 11-32 cassette with an Ultegra rear derailleur. Even better for dirt use you could get electric shifting and hydro disc brakes. That's a pretty weather and dirt proof gravel grinder, for double the price.


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## angelo1100 (Aug 24, 2012)

Excuse my ignorance but why a 9sp mtb derailleur with road 10spd shifters.


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## Lelandjt (Sep 11, 2008)

Because they have the same cable pull. 10spd Shimano mountain has a unique cable pull that isn't compatible with anything else. Except if you wanna get really techy and are into MTB, Shimano 10spd MTN derailleurs have almost the same cable pull as 8&9spd Sram MTN (1.21:1 vs 1:1). On all my MTBs I run Sram 8 or 9spd shifters (the older generation with indicators that wrap around the bar) with Shimano 10spd derailleurs with the cable on the opposite side of the bolt. This gets me a clutch derailleur pared with my favorite ratios and shifters and thicker, stronger chains and cogs.

For road purposes just remember: 10spd Shimano road derailleurs are only designed to go up to a 28t cog. If you wanna run something bigger use a Shimano 9spd MTN derailleur. With the advent of 11spd this has been simplified since our new fleet of Roubaixs came with 32t cassettes and long cage Ultegra derailleurs. Sram addressed this long ago with their Wifli long cage road derailleurs that go up to 32t.


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## headloss (Mar 3, 2013)

Lelandjt said:


> Except if you wanna get really techy and are into MTB, Shimano 10spd MTN derailleurs have almost the same cable pull as 8&9spd Sram MTN (1.21:1 vs 1:1).


Those are ratios for cassette sprocket-pitch/cable-pull. They are not values for cable pull. But, yes, at 1.16 (3.95mm/3.4mm ; cog spacing over average cable pull) the Shimano Dynasys (ten speed and up) for mtb is closer to SRAM.

@OP, as Lelandjt said, you will need a 9-speed (or earlier) Shimano mtb RD for the same ratio as the road bike stuff.

That gearing seems extreme for gravel, to me... especially with a compact double in the front. I don't think I've ever needed anything less than a 42t up front with a 11-32 in back. I don't race though, and have no idea what you'd see on a gravel course... I do ride on a lot of gravel roads. I guess it depends on where you plan to ride. If in the midwest, I'd definitely go with a tighter cluster and just stick with a straight road group.


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## tednugent (Apr 26, 2010)

Lelandjt said:


> For road purposes just remember: 10spd Shimano road derailleurs are only designed to go up to a 28t cog.


Tiagra 4600 is designed to go up to 30T
105-5700A, also 30T
Ultegra-6700A, also 30T


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## crossracer (Jun 21, 2004)

I run a xt rear der with a 12-34 nine spd and a compact up front. I ride mtn trails with this in addition to all the fire roads I can find. 

Plus my biggest tires are 700x 42 knobbies. 

I've never felt like it was too little gearing . Id rather be a bit under geared then over geared. Walking hills suck. 

Bill


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## junior1210 (May 2, 2013)

Microshift also makes a road rear derailleur that will go up to 34T, works with Shimano road stuff.


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## jmess (Aug 24, 2006)

For my gravel bike I run an Ultegra 6603 triple with 11x28 or 12x30 cassette. Nice having the 52 front ring to kick it up on the long fast down hill stuff. For the really steep stuff the 30x30 works well. With my frame (Bianchi CX) the 6603 RD works fine with both cassettes.


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## RRRoubaix (Aug 27, 2008)

tednugent said:


> Tiagra 4600 is designed to go up to 30T
> 105-5700A, also 30T
> Ultegra-6700A, also 30T


Hmm- I've got a 11-32t w/ my Ultegra 6700. Works great!


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