chriswoody
Legendary Member
- Location
- Northern Germany
The Problem with 1x Drivetrains.
SRAM released their Rival 1, 11 speed groupset back in 2015, the first commercially available groupset aimed squarely at gravel bikes. Given the off road capability of these bikes, the groupset mirrored mountain bike groupsets with a single narrow/wide chainring and a clutched derailleur. Unfortunately though, they then chose to make the derailleur a medium cage with a maximum capacity of 42 teeth, giving an overall range of just 420% when used with a 10 - 42 cassette. With the standard 40 tooth chainset this gave a groupset that was far too highly geared and this is a trend that continues today on gravel groupsets, whether it's Shimano or SRAM.
So why is this a problem? Well for gravel racers or folk who ride compacted, almost smooth gravel roads, this is undoubtedly fine, but for those of us that like to seek more adventurous off road trails, or even go bikepacking, these gears are far too high for serious off-road use. So no doubt many are now laughing and thinking what on earth is wrong with a good old double chainset, well let's have a look at that.
Shimano’s GRX groupset is aimed squarely at gravel bikes as well and as we can see below, it has a whopping 502% range, so already much better. Look closer though at the ratios and we can see again, it’s heavily leaning towards the top end, with the lowest gear being only 23 inches, far too high again and this isn’t just Shimano, but an industry wide trend.
Introducing the Mullet.
So what’s the solution? Looking across at mountain bikes and specifically SRAM GX Eagle 10 - 52, we can see it has 520% of range and more importantly a lovely low 18 inch gear when paired to a 34 tooth chainring, perfect for steep ascents loaded up. Yes we are losing some of the top end, but really if you're not racing this isn’t a problem.
This notion of sticking mountain bike gears on a drop bar bike is known as the Mullet drivetrain and it’s not a new concept, my Dawes from the early nineties has a mountain bike groupset and gives a lovely wide range of gears, albeit with a triple chainset.
How to Convert your Derailleur.
So if Mullet drivetrains are so good, why do we not see Mullet drivetrains on stock bikes these days? Well in a nutshell it’s technically not possible. You see, since 10 speed drivetrains, the cable pull ratio has differed between road and mountain. Essentially the amount the derailleur moves for a single click of the gear lever, so Mountain bike derailleurs won't index properly with road shifters. SRAM achieves this differentiation by means of a plastic fin under the derailleur which the cable wraps around. The Mountain one is a different size and shape to the road one as can be seen below.
Now it turns out that on SRAM’s higher tier groupsets, this fin is actually removable by means of a circlip. So it is a simple matter of changing a mountain one for a road one and we now have a SRAM GX Eagle derailleur that will now function perfectly well with a road shifter. Something that SRAM fails to officially acknowledge is possible because they would rather you buy a wireless groupset if you want to create a mullet drivetrain.
There are other ways to create a mullet, with different jockey wheel cages, Jtek shiftmate etc, but with SRAM, changing the cable fin is by far and away the easiest and most reliable.
Upgrading to 12 Speed.
So now I have a mountain bike derailleur working with road shifters, I could leave it alone there and just fit a wider range 11 speed cassette. The problem with that though, is that I run the risk of increasing the gap between the ratios too much and I happen to actually like the 10 - 42 cassette I currently have. What if there was just a way of keeping the 10 - 42 cassette but adding a larger 12th cog for emergencies? I.E. use the 12 speed GX Eagle cassette I talked about earlier? Well it turns out there is. You see SRAM likes to keep it’s engineering quite simple and as a result it’s eminently possible to modify your shifters. There’s a company in the English Lakes called Ratio Technology who engineer and provide upgrade kits for SRAM shifters, amongst which is a 11 to 12 speed conversion kit. Here is the contents of their 12 speed upgrade kit for 11 speed SRAM Double Tap shifters. They also include a cable fin, but I could have just used the one from my old Rival Derailleur.
Modifying the shifter is a simple case of removing it from the bars, keeping the hydraulic hose attached and then remove the side cover. Using the supplied M2.5 bolt we can draw out the axle holding the shift components in and then we can remove it all. Here’s the original shifter stripped apart, with the old 11 speed ratchet and red cable spool in the middle and the new Ratio 12 speed ratchet below.
Swapping the ratchet and cable spool over is the work of moments and then we pop it all back together. The new cable spool isn’t a necessity for this conversion, but the original SRAM one is made from plastic and prone to failure and SRAM refuse to make it available as a spare part, thus writing off your shifters. The Ratio one is made from aluminium and much less prone to failure so now is a good time for an upgrade.
With the cassette I spent a good while with gear ratio calculators trying to work out the best combination and finally I settled on the 10 - 50 12 speed cassette, whilst this only gives me a 500% overall ratio, crucially if I keep my 34 tooth chainring the 10 - 42 range of the cassette stays the same as I currently like and the 50 tooth cog gives me a low gear of 19 inches. Also going with the smaller 50 tooth cog means that the jump up from 42 teeth is not as pronounced as with a 52 tooth large cog. Fitting the cassette is easy, the XD driver on my hub will take either 11 speed or 12 speed cassettes, so no fitment problems there.
So with everything bolted up, I followed the SRAM set up instructions to get the Hi/Low Screws set, then the chain sized followed by the B-Gap and then lastly the final fine tune. It now works lovely on the stand so I just need to get out there and get some kilometres on it. I’m really happy how it all went together and finally I have a decent wide range transmission that will hopefully fulfil my riding style and needs perfectly.
SRAM released their Rival 1, 11 speed groupset back in 2015, the first commercially available groupset aimed squarely at gravel bikes. Given the off road capability of these bikes, the groupset mirrored mountain bike groupsets with a single narrow/wide chainring and a clutched derailleur. Unfortunately though, they then chose to make the derailleur a medium cage with a maximum capacity of 42 teeth, giving an overall range of just 420% when used with a 10 - 42 cassette. With the standard 40 tooth chainset this gave a groupset that was far too highly geared and this is a trend that continues today on gravel groupsets, whether it's Shimano or SRAM.
So why is this a problem? Well for gravel racers or folk who ride compacted, almost smooth gravel roads, this is undoubtedly fine, but for those of us that like to seek more adventurous off road trails, or even go bikepacking, these gears are far too high for serious off-road use. So no doubt many are now laughing and thinking what on earth is wrong with a good old double chainset, well let's have a look at that.
Shimano’s GRX groupset is aimed squarely at gravel bikes as well and as we can see below, it has a whopping 502% range, so already much better. Look closer though at the ratios and we can see again, it’s heavily leaning towards the top end, with the lowest gear being only 23 inches, far too high again and this isn’t just Shimano, but an industry wide trend.
Introducing the Mullet.
So what’s the solution? Looking across at mountain bikes and specifically SRAM GX Eagle 10 - 52, we can see it has 520% of range and more importantly a lovely low 18 inch gear when paired to a 34 tooth chainring, perfect for steep ascents loaded up. Yes we are losing some of the top end, but really if you're not racing this isn’t a problem.
This notion of sticking mountain bike gears on a drop bar bike is known as the Mullet drivetrain and it’s not a new concept, my Dawes from the early nineties has a mountain bike groupset and gives a lovely wide range of gears, albeit with a triple chainset.
How to Convert your Derailleur.
So if Mullet drivetrains are so good, why do we not see Mullet drivetrains on stock bikes these days? Well in a nutshell it’s technically not possible. You see, since 10 speed drivetrains, the cable pull ratio has differed between road and mountain. Essentially the amount the derailleur moves for a single click of the gear lever, so Mountain bike derailleurs won't index properly with road shifters. SRAM achieves this differentiation by means of a plastic fin under the derailleur which the cable wraps around. The Mountain one is a different size and shape to the road one as can be seen below.
Now it turns out that on SRAM’s higher tier groupsets, this fin is actually removable by means of a circlip. So it is a simple matter of changing a mountain one for a road one and we now have a SRAM GX Eagle derailleur that will now function perfectly well with a road shifter. Something that SRAM fails to officially acknowledge is possible because they would rather you buy a wireless groupset if you want to create a mullet drivetrain.
There are other ways to create a mullet, with different jockey wheel cages, Jtek shiftmate etc, but with SRAM, changing the cable fin is by far and away the easiest and most reliable.
Upgrading to 12 Speed.
So now I have a mountain bike derailleur working with road shifters, I could leave it alone there and just fit a wider range 11 speed cassette. The problem with that though, is that I run the risk of increasing the gap between the ratios too much and I happen to actually like the 10 - 42 cassette I currently have. What if there was just a way of keeping the 10 - 42 cassette but adding a larger 12th cog for emergencies? I.E. use the 12 speed GX Eagle cassette I talked about earlier? Well it turns out there is. You see SRAM likes to keep it’s engineering quite simple and as a result it’s eminently possible to modify your shifters. There’s a company in the English Lakes called Ratio Technology who engineer and provide upgrade kits for SRAM shifters, amongst which is a 11 to 12 speed conversion kit. Here is the contents of their 12 speed upgrade kit for 11 speed SRAM Double Tap shifters. They also include a cable fin, but I could have just used the one from my old Rival Derailleur.
Modifying the shifter is a simple case of removing it from the bars, keeping the hydraulic hose attached and then remove the side cover. Using the supplied M2.5 bolt we can draw out the axle holding the shift components in and then we can remove it all. Here’s the original shifter stripped apart, with the old 11 speed ratchet and red cable spool in the middle and the new Ratio 12 speed ratchet below.
Swapping the ratchet and cable spool over is the work of moments and then we pop it all back together. The new cable spool isn’t a necessity for this conversion, but the original SRAM one is made from plastic and prone to failure and SRAM refuse to make it available as a spare part, thus writing off your shifters. The Ratio one is made from aluminium and much less prone to failure so now is a good time for an upgrade.
With the cassette I spent a good while with gear ratio calculators trying to work out the best combination and finally I settled on the 10 - 50 12 speed cassette, whilst this only gives me a 500% overall ratio, crucially if I keep my 34 tooth chainring the 10 - 42 range of the cassette stays the same as I currently like and the 50 tooth cog gives me a low gear of 19 inches. Also going with the smaller 50 tooth cog means that the jump up from 42 teeth is not as pronounced as with a 52 tooth large cog. Fitting the cassette is easy, the XD driver on my hub will take either 11 speed or 12 speed cassettes, so no fitment problems there.
So with everything bolted up, I followed the SRAM set up instructions to get the Hi/Low Screws set, then the chain sized followed by the B-Gap and then lastly the final fine tune. It now works lovely on the stand so I just need to get out there and get some kilometres on it. I’m really happy how it all went together and finally I have a decent wide range transmission that will hopefully fulfil my riding style and needs perfectly.
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nice work dude.
