Sram shifters with shimano f/r mechs

bjl

Has anyone tried Sram Force shifters with Shimano front /rear mechs?

the_jackalcp

my red shifters work just fine with my da front mech. the rear mech is a different story, it simply doesn't work unless you use a jtek shiftmate (or at least as far as I know)

andy_wrx

Agreed.

Front shifting is the same across Shimano Campag & SRAM, but rear shifting is totally different pull ratio.

You could use the shifters with a SRAM rear mech and Shimano front, Shimano or SRAM cassette

bjl

Thanks for replies,so, basically I only need SRAM shifters and rear mech cos shimano cassette and front mech will be ok,

andy_wrx

Yes

flasher

andy_wrx wrote:

Agreed.

Front shifting is the same across Shimano Campag & SRAM, but rear shifting is totally different pull ratio.

You could use the shifters with a SRAM rear mech and Shimano front, Shimano or SRAM cassette

I know nothing about this, so can someone explain why it wouldn't work, surely as long as the shifters and the cassette are all 10 speed the rear mech would work as the spacing on the cassette is the same between Shimano/SRAM, so surely the pull ratio has to be the same?

andy_wrx

No, the pull ratio is different

Each click of the shifter pulls/releases an amount of cable.
The amount of cable pulled/released causes the dérailleur to move sideways the right amount for the gap between the cogs

You're right, the gap between cogs on a Shimano cassette is the same as SRAM (assuming both 10sp, or both 9sp, or both 8sp)
But the amount of cable Shimano uses (the pull ratio) is different to SRAM
The amount of cable a Shimano shifter pulls/releases is correct for a Shimano dérailleur
And the amount of cable a SRAM shifter pulls/releases is correct for a SRAM dérailleur
But a Shimano shifter will pull too little (IIRC) cable for a SRAM dérailleur so it won't move far enough, and a SRAM shifter will pull too much (IIRC) cable for a Shimano dérailleur so it will move too far

flasher

Thanks for replying, but I must be stupid as I still don't get it!

The rear mech is dumb, it only has high and low stops, between those 2 stops it will go where the shifters tell it to go, so as the spacing is the same between Shimano/SRAM cassette, one click = one gear change = one movement of the rear mech............

veryslowtwitch

I am stupid enough to have set up SRAM levers with Ultegra RD and have proven they are incompatible.

Yes, one click = one shift over nine stops. The movement at the RD is the same between cogs but the SRAM and Shimano RDs need different amounts of cable pull to achieve that movement. So the SRAM/Shim levers pull different amounts of cable. It is a lever thing. Different leverage to obtain the same final movement.

Someone will be along in a minute to tell us exactly what the difference is, it must be fractions of a mm.

Regards

Alan

flasher

Ok thanks, it's slowly sinking in, I think.......................probably the difference is the distance between where the cable enters the rear mech to where it's bolted.

I may have to buy a cheap SRAM rear to have a play!

andy_wrx

SRAM cable pull is 1:1 - each click pulls the same amount of cable as the rear mech needs to move sideways, i.e. for every 1mm of cable pulled/released, a SRAM rear mech will move sideways 1mm
The spacing between 10sp cassette sprockets is 3.95mm, so each cable click from the shifter pulls/releases 3.95mm of cable, which causes a SRAM rear mech to move sideways 3.95mm

But Shimano has a pull ratio of 1.7 - each 1mm of cable pulled/released by the shifter will cause a Shimano mech to move 1.7mm sideways.
Thus for that 3.95mm of movement at the mech, a Shimano 10sp shifter must be pulling/releasing 2.23mm of cable per click

So if a SRAM shifter is used with a Shimano rear mech, the SRAM 10sp shifter will pull/release 3.95mm of cable per click, but the Shimano mech will move sideways 6.715mm : too much

And if a Shimano shifter were used with a SRAM rear mech, then each click would move the mech only 2.23mm : too little

http://www.ctc.org.uk/desktopdefault.as ... Shiftratio