A guide to rear shifting
A guide to rear shifting
This page builds upon my article "Beat the System" published in Cycle magazine. It describes how to mix and match different types and makes of rear gear mechanism (mech), shift lever (shifter) and sprocket cassette or freewheel. According to the manufacturers catalogues you are not supposed to be able to do this. Except when a component is explicitly compatible with some other named system, they say it will not work. But they would say that, wouldn't they?
This is at a variance with anecdotal reports from many cyclists. According to them it would seem that almost anything will "index perfectly" with anything vaguely similar! But some people have rather a low definition of "perfect" and all indexed gear systems have an allowance for wear and tear that may allow disparate components to rub along okay, when they are new. Just don't expect them to keep it up very long.
The truth, as usual, is to be found somewhere between those extremes. There are indeed a few polyglot permutations of mech, shifter and sprockets that will index perfectly even though they were never intended to. Those are the only ones highlighted in the tables below. Unfortunately this page isn't wide enough for the one big table I had in the 2003 article, so I've split it according to the make of rear mech. If you want to skip all the introductory explanation and jump right into those tables, you can click one of the following links: first there's all the variations on a Shimano theme, then Campagnolo and Sram.
There are also some ways of altering a rear mech that increase your mix and match options. Some are rather technical, but the Hubbub modification is simple enough and provides some extremely useful Shimergo combinations. If that doesn't work for you there's Shift Mate: a ready-made cable pulley device that does all the common Campag/Shimano 9/10-speed conversions.
Freewheels & Cassettes
A freewheel is a bunch of sprockets with integral freewheeling mechanism and bearings. It screwsonto a simple threaded or screw-on rear hub and is the old-fashioned or nowadays the cheap way of doing things. (So you don't get freewheels with more than 7 sprockets.)
The modern arrangement makes your freewheel mechanism part of the hub. That kind of hub is called a freehub or a cassette hub: a cassette being the bunch of sprockets that slides onto the splined freewheel body of a freehub. Splines are lengthways ridges by which the sprockets drive the hub.
Whereas threaded hubs all have the same threads - so any freewheel will fit - each sort of freehub has differently shaped splines and/or a different length of body – so that you can only fit one sort of cassette or if you're lucky two sorts. But there are ways around that. Cassettes can be altered to reduce or increase the number of sprockets and the thickness of spacers (thick washers) between them, then fitted to the hub with a washer at the back if necessary to take up any leftover length.
A 9-speed cassette doesn't just have one more sprocket than 8-speed: it also crams those sprockets a bit closer together. And a Shimano 9-speed crams them even closer than a Campag 9-speed. The technical term for the distance from the middle of one sprocket to the middle of the next is sprocket pitch. The table below gives the sprocket pitches of all modern cassettes/freewheels and acts as a key to the main Mix'n Match tables.
|Cassette or Freewheel||Sprocket Pitch||Code|
|All modern 5 and 6-speed||5.50||S5/6|
|All standard 7-speed||5.00||S7|
In theory, we ought to be able to predict the overall width of a cassette from sprocket pitch × (n – 1) + the thickness of a sprocket. For some cassettes that works, but others are wider than we'd expect, with the top two or three sprockets spaced a bit further apart. That's not a problem because the first click of the shifter always pulls some extra cable so as to take up any slack, with indexing of the top sprocket provided instead by the mech's high-gear stop screw. The low-gear stop does a similar job at the other end of the cassette, so that only the intermediate sprockets are actually indexed by the shifter. This is part of the reason some "incompatible" combinations actually work okay – at least when new. With only seven out of nine sprockets dependent upon the subtle relationship between cable pull and shift ratio and with indexing set on the middle one, the maximum shifting error is only three times the error per click. If, for example, the mech shifts 4.55mm instead of 4.35mm, the most it'll be out is only 0.6mm, and only in next-to-top or next-to-bottom. The rest of the reason is that the guide pulley can float about half a mm side to side, allowing at least that much misalignment between mech and sprocket without any nasty noises. Add a bit of friction though, plus some wear and tear, so the mech position varies by a millimetre or two depending on whether you're downshifting or upshifting and that 0.6mm may be all the difference between shifting or just sitting there and rattling!
It is possible to cram sprockets closer together only by slimming down the chain. This has been accomplished mainly by reducing the amount by which the rivet pins protrude from the link plates, thus 8-speed chain also works fine on 7-speed, 6-speed and 5-speed systems. With the development of 9 and now 10-speed cassettes it was necessary also to reduce tooth thickness, so 9 and 10-speed chains are incompatible with other systems. Exceptions to this rule are that Shimano 9-speed rear mechs will also accept 8-speed chain – so they can be used on any system with fewer rear sprockets – and that Campag "C9" chain will also run on Campag 8-speed sprockets, allowing a Campag 9-speed rear mech to be used.
The main job of a rear mech is to convert cable motion into sideways displacement. It is the middle piece in the indexed shifting jigsaw. The shifter pulls or releases a certain length of cable with each click and the mech converts that into a displacement that matches the sprocket pitch – or near enough. For example: a Shimano 8-speed shifter pulls some 2.8mm of cable with each click and the sprocket pitch of a Shimano 8-speed cassette is 4.8mm. That's 1.7 times as far, so we can say that the Shimano mech has a shift ratio of 1.7.
The clicks are in the shifter and that is the thing that determines the number of speeds, by pulling or releasing a certain amount of cable (and of course it has a corresponding number of clicks). The mech provides a conversion or shift ratio that is the same, road and mountain alike and regardless of how many speeds it says on the box. All that really indicates is how precisely the mech is constructed. More speeds means a closer pitch and that demands more precision to avoid the chain rattling against the next sprocket. So the difference is mostly just a matter of shifting accuracy and a 9-speed mech can be used in a 7-speed system.
Other manufacturers' mechs (or even other product types and old versus new systems from the same manufacturer) are designed with a different shift ratio. So shifters from other indexing systems give different cable pulls even when the sprocket pitch is the same.
The shift ratio of a mech is determined by the shape of the parallelogram and the how the cable is attached to it. You cannot change the parallelogram, but it is possible to alter the shift ratio by tinkering with the cable. One of the most useful and easiest alterations is described below as Hubbub Shimano. It is also possible to insert a device in the cable that alters the length pulled per click. The device is called Shift Mate and you can read about it below.
This portmanteau word combines a Shimano mech and cassette with Campagnolo Ergopower shifters. It keeps cropping up on this page because that's such a very useful thing to be able to do. The reason for that is Shimano gives more choice of rear mechs and cassettes, since their road and mountain bike systems all work the same with regard to rear indexing. (Or at least they used to before 10-speed MTB Dyna-Sys, which is completely incompatible – DOH!) And their cassettes are a bit narrower so there's less wheel dish, plus you can use a mountain-bike hub for even stronger wheels. Snag is, Shimano's front indexing is NOT the same for road and mountain, so if you want dropped bars and STI shifters you're stuck with big roadie chainwheels. Campagnolo however, do not index the front shift, just provide a kind of micro-ratchet – three or four clicks per chainring – so you can use whatever front mech and chainset you like with Ergopower controls.
Well, that used to be the case. In 2005 Campag quietly introduced front indexing. First it was just in the lowest groupsets, but by 2008 you had to pay Chorus prices to avoid this feature. Good news is that everything goes back to micro-ratchet in 2009. Except that Campag now call it Ultrashift, and have altered the cable pull a couple of times: but that's another story.
Another point in favour of Ergopower is that everything is neatly routed under the handlebar tape, whereas Shimano hang their gear cables out in front like washing lines (unless you trade up to 10-speed shifters, which won't play with their 10-speed MTB mechs).
So you can see why touring cyclists are especially keen on Shimergo: it lets them combine mountain-bike gearing and hubs with dropped handlebars and doesn't hang cables in the way of a handlebar bag!
Mix 'n Match Tables
It's not too surprising, when you consider all the possible permutations of cable pull, shift ratio and sprocket pitch, that we find a few happy coincidences of things that were never meant to work together but clearly do. And with a bit of rear mech shift ratio tinkering, we can make a whole lot more!
In the following tables combinations that are made for each other are coloured green, that also index perfectly in yellow and likewise in pink, except here the shifter doesn't have enough clicks to work the whole cassette. So those pink combos are not much use unless you don't plan to use all the sprockets – for example when you subtract one from a 9-speed cassette so it'll fit on a 7-speed freehub.
Refer to the Sprocket Pitch Table above to check what kind of cassette or freewheel (indicated in the Cass. columns below) each successful pairing of mech and shifter matches up with.
As already noted above, all current Shimano mechs have the same shift ratio, so you're free to operate mountain-bike mechs with road shifters, use an ostensibly 9-speed mech in a 7-speed system or whatever. And because Shimano 9-speed mountain-bike mechs can cope with sprockets from 11 to 34 teeth, they're something one most often wishes to combine with something else. Also note that Shimano 9-speed mechs will accept 8-speed chain, that 8-speed chain is the same thing as 7-speed chain and that it also runs fine on 5 and 6-speed sprockets.
The first Shimano groupset to go indexed was Dura-Ace. It was launched in 1985 with a slightly bigger shift ratio (hence shorter cable pull to get the same shift) from what soon became the Shimano standard, and remained like that until 1997. Currrent Dura-Ace mechs are nevertheless designed with an alternative cable route that gives the old shift ratio, so they can also work with old Dura-Ace shifters.
The Hubbub modification was originated by Brian Jenks, proprietor of Hubbub Cycles. It's just a different way of clamping the cable on a standard Shimano rear mech.
The clamp plate is simply rotated 90° and the cable passed around the bent-over tab as illustrated opposite (the normal clamping arrangement is inset, top right). This re-alignment of the cable gives the mech a slightly smaller shift ratio, opening up a lot of really useful Shimergo combinations – as you can see in the table above. At the time of writing (2003) all mid to high-quality Shimano mechs used to have a cable clamp plate of this design, that can be rotated and the cable re-routed in this way.
Newer designs have a plate with two ears, that can be rotated just the same once one has been cut off. Remember that it is always possible for Shimano to re-design things in future; so if you're relying upon this trick, keep an eye on the market and buy a spare mech before that option is foreclosed.
By this we mean pre 2001 Campagnolo indexing equipment, but not their even older Victory and Triumph indexed gears – for which I have no data and which didn't index very well anyway. Prior to the turn of the century, Campag rear mechs had a low shift ratio of 1.4 and their shifters pulled a lot more cable than Shimano's. These mechs had their angle adjustment screw in the usual place, up where they fix to the frame and the shifters did not say how many speeds they were for.
Then, in year 2000, Campag introduced 10-speed and new design of mech with a slightly bigger shift ratio – but still less than Shimano – and the angle adjuster down by the pulley cage. The next year (2001) they changed all their mechs to be like this and made new 9-speed Ergopower controls that pulled a bit less cable per click. Eight-speed had already been discontinued, so that's always old-style and 10-speed is always new-style, so 9-speed is the only area of confusion. Whereas old-style controls are blank or have the groupset printed on the front, new-style say "9-speed".
The good news is you can change the indexing ratchet inside the new-style controls and, for example, convert a new 10-speed shifter into old-style 9-speed.
Unlike Shimano, Campag's 9-speed mechs do not happily accept 8-speed chain, however their 9-speed chain runs okay on 8-speed sprockets, so best use that if you have to fit a new mech. And although in theory, this mech will overshift by 0.22mm per click in an old 8-speed system, Campag's website implies that it's near enough okay.
In 2009 a couple of top end Campag groups get an extra sprocket and initial measurements indicate that the 11-speed shifters ought to pull near enough the right amount of cable for 9-speed Shimergo. Beware that our information is provisional and these mix and match suggestions are as yet unconfirmed.
There is also the Sram 1.0 system, but that's so different (the cable moves a whole lot further) that nothing very useful results from combining it with other systems. But note that Sram also make Shimano-compatible shifters, which do all the same things as Shimano's own.
Shift Mate by Jtek Engineering is a gear cable pull converter that works exactly like one of those Travel-Agent devices for helping a regular brake lever to operate a V-brake.
The gear cable wraps around a duplex pulley in such a way that as you pull it off the smaller diameter side, proportionally more is drawn onto the larger side. The device sits on the back of the rear mech and also turns the cable through 90°. Several different pulleys are available to compensate for the differences between all the most common combinations of shifter, mech and cassette.
It's rather neat how you can reverse the pulley so as to convert from Shimano to Campag and vice-versa. A list of permutations facilitated by Shift Mate are on the Jtek website.