Science Behind the Magic IMG_2161

Published on December 16th, 2014 | by Brett

Science Behind the Magic | Drivetrain Compatibility

Can I mix SRAM, Shimano and Campagnolo shifters, derailleurs and cassettes? This article will answer that question and more. I’ve commented previously on the lack of standards in the cycling industry. It can be, at times, rather frustrating. Some new part comes out that I really want, but lo and behold, my seat post is the wrong diameter, or this tapered fork is incompatible with my straight head tube. It is a constant battle to keep up with the ever-changing times.

While the industry has advanced in leaps and bounds in the past few years, certain things have stayed relatively the same over the decades. Di2 and EPS excluded, shifting is one thing that is basically the same. Yes we’ve advanced from 5 cogs to 11, and derailleurs now have changed to account for a varying number of forward gears, but we are still talking about yanking on a cable a certain amount to move a chain up and down a line of gears.

This article contains tables with data for cable pull, derailleur shift ratio and cog pitch of SRAM, Shimano and Campagnolo drivetrains. This data can be used to show areas of cross compatibility for mixing and matching groups. Also, I want to discuss the differences amongst drivetrain competitors and the reasoning behind some of their decisions. Before we get into it all, lets define a few terms so that we are all on the same page.

The shifter determines cable pull. Every time you click your shift lever, the shifter pulls in or releases a certain amount of cable. Different brands and different drivetrain speeds (e.g. 9, 10, 11spd) pull different amounts of cable. For the most part, all the cable pulls are uniform for every shift, with the exception of some of the Campagnolo shifters. For example, a Campagnolo 10-speed shifter pulls 2.5mm of cable five times, 3mm twice and 3.5mm twice.

Derailleur shift ratios, also referred to as actuation, are the amount of movement from side to side of the derailleur relative to the amount of cable pulled. Older Shimano derailleurs all have a shift ratio of 1.7. This means that for every millimeter of cable pulled by the shifter, the derailleur will move 1.7 millimeters.

Cog pitch is the distance from the center of one cog on the cassette to the center of the next. Cog pitch changes between major brands and as more gears are added, usually cog pitch shrinks to fit more gears into the same width freehub body.

These three numbers are related by the following equation:

Cable pull * Derailleur shift ratio = Cog pitch

Looking at this equation, you can imagine the thought process behind some of the designs. If an engineer a few years ago wanted to design 10-speed drivetrains, but they wanted them to fit on the current 9-speed bikes, then the 10 cogs must fit in the same amount of space on the freehub body as the 9 previous cogs. To do this the engineer will reduce the width of the spacers between each cog. So now all the cogs are closer together. To save time and money, lets leave the derailleur design virtually the same; we will just slap a nice shiny 10-speed graphic on it. But if the cogs are closer together, we need to change the shifter design so that it only pulls the cable just enough to get to the next cog. So the shifter is redesigned with an extra “click” and now each shift pulls 0.2mm less of cable than before. Obviously the design process is not this simple, but hopefully this over-simplified example helps to explain how things work.

Tables below contain measurements for cable pull, derailleur shift ratio and cog pitch for varying drivetrains. We want to keep this table updated as new information becomes available, so feel free to comment on the bottom of the post if there is information that you think we missed or should be added.

Shifter
Cable Pull (mm)
Shimano 10 Road 2.3
Shimano 9 2.5
Campagnolo 11 2.6
Shimano 11 Road 2.7
Campagnolo 10 2.8
Shimano 8 2.8
Shimano 7 2.9
Campagnolo new 9 3
SRAM (Exact Actuation) 10 Road/Mountain 3.1
SRAM (Exact Actuation) 11 Road 3.1
Campagnolo old 9 3.2
Shimano 6 3.2
Shimano 10 Mountain 3.4
SRAM (X-Actuation) 11 Mountain 3.48
Campagnolo 8 3.5
Shimano 11 Mountain 3.6
SRAM (1:1) 9 Mountain 4
SRAM (1:1) 8 Mountain 4.3
SRAM (1:1) 7 Mountain 4.5

Cassette
Sprocket Pitch (mm)
Campagnolo 8-speed 5
Shimano/SRAM 8-speed 4.8
Campagnolo 9-speed 4.55
Shimano/SRAM 9-speed 4.35
Campagnolo 10-speed 4.15
Shimano/SRAM 10-speed 3.95
SRAM 11-Speed Road 3.72
SRAM 11-Speed Mountain 3.9
Shimano 11-Speed Mountain 3.9
Campagnolo 11-speed 3.76
Shimano 11-speed Road 3.69

Derailleur
Shift Ratio
Shimano Standard 1.7
Shimano Standard w/ Hubbub 1.6
Campagnolo (new) 1.5
Campagnolo (old) 1.4
SRAM (Exact Actuation) 1.3
Shimano 10-speed Dyna-sys 1.2
SRAM (X-Actuation) 1.12
SRAM (1:1) 1.1

Update 2/13/15: Please note when using the equation relating cable pull, shift ratio, and cog pitch, the calculated values will vary slightly from the those listed above. The precision of measuring equipment leads to as much as a 3.24% difference in calculated and measured values. Below, the chart compares the measured values of cog pitch with those calculated by multiply shift ratio with cable pull. This percent error does not mean that the numbers are incorrect, it simply suggests that more precise measuring procedures would be required to eliminate the difference.

 

 
Cable Pull
Derailleur Ratio
Calculated Cog Pitch
Measured Cog Pitch
Percent Difference
Shimano 6 3.2 1.7 5.44 5.50 1.10
Shimano 7 2.9 1.7 4.93 5.00 1.41
Shimano 8 2.8 1.7 4.76 4.80 0.84
Shimano 9 2.5 1.7 4.25 4.35 2.33
Shimano 10 Road 2.3 1.7 3.91 3.95 1.02
Shimano 10 Mountain 3.4 1.2 4.08 3.95 3.24
Shimano 11 Road 2.7 1.4* 3.69
Shimano 11 Mountain 3.6 1.1* 3.90
Campagnolo 8 3.5 1.4 4.90 5.00 2.02
Campagnolo old 9 3.2 1.4 4.48 4.55 1.55
Campagnolo new 9 3.0 1.5 4.50 4.55 1.10
Campagnolo 10 2.8 1.5 4.20 4.15 1.20
Campagnolo 11 2.6 1.5 3.90 3.76 3.66
SRAM (1:1) 7 Mountain 4.5 1.1 4.95 5.00 1.01
SRAM (1:1) 8 Mountain 4.3 1.1 4.73 4.80 1.47
SRAM (1:1) 9 Mountain 4.0 1.1 4.40 4.35 1.14
SRAM (Exact Actuation) 10 Road/Mountain 3.1 1.3 4.03 3.95 2.01
SRAM (Exact Actuation) 11 Road 3.1 1.3 4.03 3.72 2.01
SRAM (X-Actuation) 11 Mountain 3.5 1.12 3.90 3.90 0.06

*Shimano 11-speed groups do not have any published data regarding derailleur ratio. The ratio listed was calculated by measuring cable pull and cog pitch and solving for the ratio.

If you find the tables a little hard to decipher and compare, then the next sections might make things a little easier. We will discuss popular combinations of components followed by three sections that each pertain to a specific manufacturer and discusses the history and revisions to the systems over the years.

While the market is large and there are many different varieties of derailleurs and drivetrains, I would guess that 90% of people reading this article are using Shimano, SRAM or Campagnolo 8/9/10 or 11-Speed systems so we will focus on those combinations.

Mixing and Matching

It is important to keep in mind that while you find a lot of information that claims compatibility between different brands and groups, experiences will always vary. Things might seem to work well for a while, but later on, chain’s stretch, teeth get worn down, and all of a sudden shifting becomes shady. Just keep in mind that Campy engineers didn’t design any of their components to work with Shimano or SRAM or any mix in between. Mixed component group compatibilities are more of a coincidence than anything. Yes, cyclocross racers, monster ‘crossers, steep road aficionados, I’m talking to you. These riders are most likely to play the component mix up game because they desire dropbar shifters with mountain cassette ranges that require mountain derailleurs with long cages for a larger maximum tooth capacity. Until SRAM CX-1, they had no choice but to play the mix and match game. Please watch this public service announcement to gain awareness about a real issue that faces all cyclocross racers in particular.

With that disclaimer I will say that if the cable pull, ratios and cog spacing truly are matched, there won’t be an issue. The perfect example is cross compatibility between SRAM 10-speed mountain and road. These groups work together—period. Bicycle manufacturers, including Specialized, sell new bicycles with mixed groups like this. I fully encourage you to tinker and try different combinations with your new-found knowledge as you build your perfect steed.

Moving on from perfect matches, things get more complicated; we start mixing between brands. With varied success, there are a few different popular combinations today. Shimergo is the mix and match of “Shim”ano drivetrains with Campy “Ergo” shift levers. This is possible because the cable pull between the two is so similar. Routing of the cable a little differently through the derailleur effectively changes the ratio to make things line up. This is called the Hubbub routing method. But, as noted earlier, Campagnolo Ergo levers pull 2.5mm of cable five times, 3mm twice and 3.5mm twice and Shimano derailleurs are designed around consistent cable pull each time. There is a fudge factor of compatibility though and there are numerous reports of success online. The methods require a reduced speed; meaning 9-speed levers with an 8-speed cassette. If you are interested in setting up a Shimergo setup, there are plenty of articles and forum posts out there to help you with your setup.

With the Shimergo setup, it is also worth mentioning Jtek Engineering. Their most popular product, the Jtek ShiftMate, uses a pulley to change the ratio of the amount of cable pulled by the shifter. There are four different pulleys available to allow you to run numerous combinations of Shimano and Campagnolo 8 through 11-speed systems together. Here is an article that details one rider’s experience of moving from the Hubbub method to a Jtek ShiftMate.

Screen shot 2014-12-17 at 11.31.25 AM

JTek ShiftMates use a pulley to reduce or increase the ratio of cable pull to create compatibility between shifters, derailleurs and cassette spacing. Four different pulleys can be setup eight different ways to change the amount of cable pull in the system.

As mentioned earlier in this article, there are reports that XTR 11-speed cassettes use nominally the same spacing as SRAM 11-speed mountain systems. Some people are reporting success on forum posts.

And lastly, despite differences in cog pitch, it seems that there has been some success with mixing cassettes between 11-speed road systems as detailed in this VeloNews article by Lennard Zinn, the author of the popular Zinn Mountain and Road Maintenance books. Again, note that only the cassettes are being swapped, shifter and derailleur brands must still match in these instances due to significant differences in cable pull and derailleur ratio.

Shimano

Starting with Shimano, this could be the simplest section of them all if we could just talk about everything up to 9-speed. Basically everything Shimano did up until then was cross compatible. They used a derailleur shift ratio of 1.7 on everything. While the cable pull varies from 8-speeds to 9-speeds as they moved the sprocket pitch closer together, the derailleur remains the same. Shimano 10-speed road groups adhere to this design as well. It’s the 10-speed Dyna-Sys mountain systems that veered away from the norm—More on that in a second. So let’s say you have an older 8-speed Shimano drivetrain on your bicycle and your derailleur breaks. You hunt around and can’t find a replacement for your old derailleur anywhere… Fear not! Because a brand new Shimano Ultegra 6700 10-speed derailleur has the same shift ratio of 1.7, it is completely compatible. Your old 8-speed shifter will pull the same 2.8mm of cable as before, and the derailleur will move the same 4.8mm pitch required to push the chain to the next cog.

Now here’s where things get tricky, as more gears are added and everything gets closer together, tolerances get tighter. This means that with a little bit of dirt in the cable system, the derailleur doesn’t quite move as far as it should, and all of a sudden you’re in the wrong gear and your bike is ghost shifting like crazy. Enter Shimano Dyna-Sys. In the simplest terms, Dyna-Sys increased the amount of cable pulled and decreased the amount of derailleur movement per millimeter of cable pull. Because Shimano 10-speed road is the same 1.7 ratio as before, lets compare the 10-speed Shimano road to the 10-Speed Shimano Dyna-Sys mountain. The cassettes are the same width, with a cog pitch of 3.95mm. But the difference is that 10-speed road pulls 2.3mm of cable, compared to the 3.4mm of cable that Dyna-Sys pulls. So in order to end up in the same gear after a shift, the derailleur ratio is reduced from 1.7 to the new Dyna-Sys 1.2 ratio. The main reasoning behind this design change is that with more cable pull, a turn of the barrel adjuster gives much more incremental fine-tuning. Dyna-Sys allowed Shimano to squeeze 10-speeds into the same freehub body and still maintain quality shifting that stays in-tune. While I can’t speak for the engineers, I would say that Dyna-Sys was considered not necessary on road systems, because they weren’t being beaten around quite like a mountain system, until 11-speed road was introduced. Now the Shimano 11-speed road systems have a type of modified Dyna-sys that keeps them in-tune with tighter cog spacing but is completely incompatible with 10-speed road or mountain.

One of the most interesting things to happen to drivetrains lately is electronic shifting. The derailleur shift ratio is essentially programmed into the mechanism. Cable pull is completely eliminated. The shifters simply contain upshift and downshift buttons, with nothing internally that determines how many shifts you can perform beyond programming. In a perfect world you could plug your drivetrain into your computer and tell it how many gears your cassette has and the cog pitch. The derailleur and shifters could then reprogram themselves accordingly. Unfortunately we don’t live in a world like this yet. Perhaps someday someone will “Jailbreak” Shimano Di2 systems, allowing on-the-fly reprogramming of all components. Currently it is possible to swap a 10-speed derailleur for an 11-speed, resulting in your Di2 10-speed shifters reprogramming themselves with 11-speeds. This only works for specific models and firmware versions, so I encourage you to watch our video if you are interested in learning more.

SRAM

SRAM has basically approached the situation with the same method as Shimano with a few exceptions since they entered the arena a little later on. Early on, SRAM produced shifters that were cross compatible with the Shimano 1.7 ratio. This was called the SRAM (2:1) family of products. For the most part though, SRAM used their 1:1 actuation on 7/8/9-speed systems. Referencing the SRAM website, “Every unit of cable you pull moves the derailleur the same amount.” Comparable to the Dyna-Sys release, with 10-speed systems both road and mountain, SRAM introduced Exact Actuation. The nice thing about the SRAM system is that all mountain 10-speed and road 10-speed are compatible, all using Exact Actuation. So you can use road shifters, with mountain derailleurs and vice versa—though it will be necessary to throw an inline barrel adjuster in the mix when using road shifters with mountain derailleurs. I think the best easter egg of all of this is that Exact Actuation remained for SRAM 22 road groups. Meaning that if you wish to upgrade to SRAM 11-speed and you already have an 11-speed compatible freehub body, all you need is a new rear shifter, cassette, and chain. The cog pitch and derailleur ratio is the same on 10 and 11-speed road. So with a new shifter, your 10-speed derailleur turns into an 11-speed derailleur.

Unfortunately the same cannot be said for the SRAM 11-speed mountain systems. SRAM Mountain uses a new X-Actuation setup that once again changes ratios and increases the amount of cable pulled. So SRAM Mountain is only compatible with itself for the time being. Although interestingly enough, people on the forums are reporting that the new XTR 11-speed systems seem to run smoothly with a SRAM 11-speed cassette. Art’s examined an XTR M9000 cassette alongside a SRAM XX1 cassette and upon visual inspection and measuring as accurately as possible with our digital calipers, both cassettes seem to have a cog pitch of roughly 3.9. I say “roughly” because I am unsure of the accuracy of measurements and would like to use more precise tools to confirm. Unfortunately SRAM and Shimano both declined to provide hard numbers after I contacted them. Please note that shift pull and derailleur ratios are still different, so while you may be able to swap cassettes, you cannot use a SRAM shifter with an XTR derailleur or the other way around. Compatible cassettes do introduce some interesting combinations since XTR M9000 cassettes work with 9/10-speed freehub bodies while SRAM 11-Speed only works with the new XD driver bodies.

A good comparison between SRAM 11-speed mountain and road systems lies in the Force CX-1 Drivetrain. It is the result of a drunken hookup between a SRAM Force 22 road group and a SRAM mountain group. The result is a cassette with cog pitch, cable pull and derailleur ratio (Exact Actuation) from the road group. But with technologies like X-Horizon and a Roller Bearing Clutch made popular by the mountain group. Because the CX-1 derailleur is basically an X1 derailleur with some modification, it is easy to show the most substantial differences by putting them side-by-side.

IMG_1740

Force CX-1 and X1 Mountain derailleurs side by side. Main differences viewed here lie in the design of the cage. The mountain derailleur on the right is designed for larger maximum tooth cogs (42T) and take up the extra chain slack required in the mountain system. This picture shows the two derailleurs without cable routing devices installed—seen in the next picture.

IMG_1749

These two cable routers (Left: Force CX-1, Right: X1 Mountain) are designed differently to change the angle of entry of the cable into the derailleur body. They are interchangeable between the two derailleurs, but it wouldn’t do you much good as it will change the way the derailleur works. The CX-1 version has a built-in barrel adjuster since the shift lever doesn’t have one like its X1 counterpart.

IMG_1736

After running through the cable routers pictured previously, the cable runs around a lever arm guide before being clamped in the cable bolt. Comparing the two lever arms in the above picture, we can see how the length of the arm has changed to change the derailleur shift ratio so Force CX-1 will be compatible with 11-speed road instead of 11-speed mountain with a different cog pitch.

Campagolo

And finally we discuss Campy. This section is infinitely less complicated. There are no mountain components to contend with, just road groups. Lets discuss 8 through 11-speed groups. Instead of Dyna-Sys, Dyna-Sys11, 1:1, Exact Actuation, X-Acuation or any other fancy marketing terms you could possibly come up with, we will refer to the systems as Campy “old” and Campy “new”. Campagnolo changed the shift ratio and cable pull between the two systems. 8-Speed systems are Campy “old.” 9-speed systems come in both varieties. The “new” 9-speed systems were produced after 2001. Most likely you have a newer group, but if you are unsure, old-style controls are absent of graphics or have the groupset name on them and new-style will be printed with “9-speed.” Newer 9-speed derailleurs moved the “B” adjuster screw down by the cage, as opposed to the old-style that places it where Shimano derailleurs typically have it by the frame and mount point. After that its easy, 9/10/11-speed systems are all the same. Just match the number of gears on the cassette with the number of clicks in the lever (minus 1, because 10-speed shifters make only 9 clicks) and you are good to go. The derailleur ratio remains the same across the range.

This is a lot to absorb after one reading so I encourage you to reread the specific sections that pertain to you. I hope this sheds a significant amount of light onto the industry and compatibility amongst components. I think that one thing I took away from the process of researching for this article is that most of the decisions made around these differing designs were made to try and make upgrades easier. So while we might complain that 11-speed is expensive and you have to replace everything, just remember that without Dyna-Sys11 or X-Actuation shifting, the cassette would probably get wider, and then we would need wider wheels and wider frames and it would snowball from there. The tables earlier in the article show collected data for cable pull, derailleur ratio, and cog pitch for most component groups. I hope to keep this table up-to-date with new drivetrains and information, so feel free to comment below with any information you believe should be added as we try and make this a resource for everyone.

Science Behind the Magic delves into the inner workings of your two-wheeled steed. Web Content Editor, Brett Murphy, uses his mechanical engineering background to explain the latest industry advances and breakdown component design.

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About the Author

Brett

Murphy grew up in Idaho where he discovered the addictive nature of riding mountain bikes, only to travel out to California to study mechanical engineering and find out that riding skinny tires was just as habit-forming. Now he splits the time between the two with an equal-opportunity mileage policy.



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