Another Shimergo option

[GRAVELBIKE]

da Vinci's custom SRAM derailleur:

http://www.gravelbike.com/?p=706

[don compton]

I can't wait for their "Shimergo" fix for 10spd.

[mvrider]

I was under the impression that Campy 10-sp shifters already worked with SRAM 10-sp RDs?

This doesn't specifically mention it, but I was assuming that Apex wide-range derailleurs would work as well:
http://velonews.competitor.com/2008/03/bikes-and-tech/can-you-run-campy-shifters-with-a-sram-drivetrain-sure-why-not_73404

[thegunner]

I was under the impression that Campy 10-sp shifters already worked with SRAM 10-sp RDs?

This doesn't specifically mention it, but I was assuming that Apex wide-range derailleurs would work as well:
http://velonews.competitor.com/2008/03/bikes-and-tech/can-you-run-campy-shifters-with-a-sram-drivetrain-sure-why-not_73404

yessir, this is how i roll.

[don compton]

yessir, this is how i roll.
Are you guys telling me that the Sram derailleurs work perfectly with Campy 10sp. shifters and Shimano 10sp. cassettes?

[thegunner]

Are you guys telling me that the Sram derailleurs work perfectly with Campy 10sp. shifters and Shimano 10sp. cassettes?

perfectly? maybe not, but it's close enough where i can hit 10 gears without grinding and any oddities are more likely to be caused by my mechanical ineptness and not incompatibility.

[Kontact]

Are you guys telling me that the Sram derailleurs work perfectly with Campy 10sp. shifters and Shimano 10sp. cassettes?
Campy rear derailleurs don't have quite as much actuation as a SRAM derailleur, but a Campy 10 cassette is wider, so extra cable is needed. The two are apparently a wash, and shift pretty well.

Campy 10 will shift Shimano 8 for similar reasons.

[Dave]

Here's what should happen. Campy 10 shifters pull only 2.5mm of cable, five times, 3mm twice and 3.5mm twice. A SRAM RD requires uniform cable pulls of 3mm for every shift. That means that the SRAM actuation ratio is 3.95/3 = 1.32.

Each of those first five pulls will only move the RD 2.5 x 1.32 = 3.3mm. The correct movement is 3.95mm. After five pulls, that's 16.5mm from the start point, but the cog that the RD supposed to be centered over is 19.75mm from the start point. That's 82% off location - much closer to the fifth cog than the intended sixth.

The next two pulls are the correct 3mm, so the same misalignment would prevail. Only on the last two pulls would the alignment improve a little.

Of course, there are ways to cheat the system. Start with the RD aligned a little too far to the left, with the limit screw and apply more than normal cable tension to get the RD further to the left, after those five short cable pulls.

Other mismatched setups are much closer. For example, if a Shimano 10 cassette is used with a Campy drivetrain, the RD would be positioned at 20.6mm from the start point, after five shifts, but a Shimano cog would be located at 19.75mm. That's only .85mm or 21% off location.

Since both Campy and Shimano shifters use nonuniform pulls that increase toward the larger cogs, there are some coincidental close matches, like the average cable pull of a Campy 10 shifter matching that of a Shimano 8 speed and Campy 11 shifters matching Shimano 9.

[thegunner]

Here's what should happen. Campy 10 shifters pull only 2.5mm of cable, five times, 3mm twice and 3.5mm twice. A SRAM RD requires uniform cable pulls of 3mm for every shift. That means that the SRAM actuation ratio is 3.95/3 = 1.32.

Each of those first five pulls will only move the RD 2.5 x 1.32 = 3.3mm. The correct movement is 3.95mm. After five pulls, that's 16.5mm from the start point, but the cog that the RD supposed to be centered over is 19.75mm from the start point. That's 82% off location - much closer to the fifth cog than the intended sixth.

The next two pulls are the correct 3mm, so the same misalignment would prevail. Only on the last two pulls would the alignment improve a little.

Of course, there are ways to cheat the system. Start with the RD aligned a little too far to the left, with the limit screw and apply more than normal cable tension to get the RD further to the left, after those five short cable pulls.

Other mismatched setups are much closer. For example, if a Shimano 10 cassette is used with a Campy drivetrain, the RD would be positioned at 20.6mm from the start point, after five shifts, but a Shimano cog would be located at 19.75mm. That's only .85mm or 21% off location.

Since both Campy and Shimano shifters use nonuniform pulls that increase toward the larger cogs, there are some coincidental close matches, like the average cable pull of a Campy 10 shifter matching that of a Shimano 8 speed and Campy 11 shifters matching Shimano 9.

dave speaks the truth, but this is all assuming that RDs and shifters are all built with tolerance levels of 0% error. there is a slight amount of lateral play in SRAM RD jockey wheels (even more evident if you use the 3rd party KCNC ones) that i'm pretty sure mutes the effect of such exact calculations.

[Dave]

Jockey pulley play is typically .5mm. The first shift error would eat that up.

J-tek makes a shiftmate that attempts to improve the shifting by increasing the average cable pull, but anything that increases the cable pull should improve those first five shifts and make the other four worse, unless it's a more sophisticated cam shape that only works on those first five pulls.

[thegunner]

Jockey pulley play is typically .5mm. The first shift error would eat that up.

J-tek makes a shiftmate that attempts to improve the shifting by increasing the average cable pull, but anything that increases the cable pull should improve those first five shifts and make the other four worse, unless it's a more sophisticated cam shape that only works on those first five pulls.

even so, that still doesn't entirely negate the fact that bicycle components aren't built to the same tolerances as a spaceship. i don't think sram is seriously losing sleep if some of their RD's move 3.3mm on a single pull vs 3.4mm etc.

[tylerbick]

I like this DaVinci design because, to me, it's the kind of tinkering/rigineering I enjoy dreaming about, and it's a great example of someone taking something that usually is only practical for a smaller number of people and making more options and more importantly, more practical options for more riders of different types, getting more people riding more! (Pedal) Power to the people!

I think Grant Petersen would be proud...

Go DaVinci!

[hankchong]

Are the cogs on the cassettes spaced commensurate with the cable pulls (i.e., more closely, then wider), or are the cogs spaced uniformly along the cassette body? Does the RD translate the non-uniform cable pulls into uniform translations across the cassette?

Here's what should happen. Campy 10 shifters pull only 2.5mm of cable, five times, 3mm twice and 3.5mm twice. A SRAM RD requires uniform cable pulls of 3mm for every shift. That means that the SRAM actuation ratio is 3.95/3 = 1.32.

Each of those first five pulls will only move the RD 2.5 x 1.32 = 3.3mm. The correct movement is 3.95mm. After five pulls, that's 16.5mm from the start point, but the cog that the RD supposed to be centered over is 19.75mm from the start point. That's 82% off location - much closer to the fifth cog than the intended sixth.

The next two pulls are the correct 3mm, so the same misalignment would prevail. Only on the last two pulls would the alignment improve a little.

Of course, there are ways to cheat the system. Start with the RD aligned a little too far to the left, with the limit screw and apply more than normal cable tension to get the RD further to the left, after those five short cable pulls.

Other mismatched setups are much closer. For example, if a Shimano 10 cassette is used with a Campy drivetrain, the RD would be positioned at 20.6mm from the start point, after five shifts, but a Shimano cog would be located at 19.75mm. That's only .85mm or 21% off location.

Since both Campy and Shimano shifters use nonuniform pulls that increase toward the larger cogs, there are some coincidental close matches, like the average cable pull of a Campy 10 shifter matching that of a Shimano 8 speed and Campy 11 shifters matching Shimano 9.

[Dave]

Shimano/SRAM cogs are uniformly spaced at 3.95mm and Campy's are uniformly spaced at 4.12mm. The idea is for the RD to have uniform movements. SRAM is the only brand using uniform cable pulls to do that. Campy and Shimano both use pulls that increase toward the larger cogs.

Mixing the two styles of RDs and shifters isn't wise, IMO.

[hankchong]

Just edited my question to ask, additionally, if the RD translates non-uniform cable pulls into uniform translations across the cassette body... trying to get a better handle on what's going on, out of idle curiosity. Thanks.

Shimano/SRAM cogs are uniformly spaced at 3.95mm and Campy's are uniformly spaced at 4.12mm.

[Dave]

even so, that still doesn't entirely negate the fact that bicycle components aren't built to the same tolerances as a spaceship. i don't think sram is seriously losing sleep if some of their RD's move 3.3mm on a single pull vs 3.4mm etc.


That's not the point. The positioning error is huge in comparison to the minor contribution of the jockey pulley.

I worked in the manufacture of nuclear weapons components for 22 years. I'm familiar with tolerances. You'd be surprised to find out how close the tolerances are held.

[GRAVELBIKE]

One reason I went the da Vinci route for my latest bike was that all my other bikes/wheels are 9-speed/Shimano compatible. The chains/cogs last longer than 10-speed units, and 9-speed chains/cassettes are plentiful.