Shimano Cassette top sprocket

[fausto99]

I know this is probably a silly question but I'm going to ask anyway. What is the reason for the top sprocket having its own spacer built in? Could one use a regular sprocket with a plastic spacer to get a 14, 15 or even 16 top sprocket? Would the lock ring not be able to hold this in place?

[Eyebrox]

The final spacer allows the threaded locknut to sit snug and flush at the end of the run.

[NATURAL ANKLING]

Hi,
By design The freehub is shorter than the cassette stack.
Therefore you need clearance for the Thread to tighten the Stack.
Because the top Sprocket teeth is on an adjacent plane to the lock ring, Clearance for tightening stack is Incorperated In the sprocket Depth.
Thus You have a little Room for cassette spline engagement, That is why it has an integral spacer which contains the spline for drive engagement.

(Typed by voice)

[Brucey]

shimano freehub bodies went through various flavours of UG, then HG/UG hybrid, then UG, then UG-C, in 7s, 8/9/10s, and finally 11s.

Obviously UG cassettes have the top sprocket threaded so have a built-in spacer of some kind (else not enough threads).

Original HG cassettes had a top sprocket with a built-in spacer (*). This overhangs the end of the freehub body slightly (and has to else the lockring wouldn't work).

UG-C allowed for an 11T top sprocket; to make room for this the splines no longer went full length on the freehub body and (IIRC) they may have increased the spacing on the 11T sprocket slightly. Obviously a different lockring is required with an 11T top sprocket. The sprocket overhangs the end of the freehub body; the overhanging part of the sprocket is probably required to make an 11T sprocket strong enough; the wall thickness of the integral spacer is not very large even though the splines on the freehub body are truncated. Occasionally 11T sprockets fail despite this. (They can also bottom out on the freehub body if the spacers are wrong, worn or just compressed.)

(*) [Original HG top sprockets look a lot like penultimate 12T, 13T (and some 14T) sprockets that sit next to 11T (and some 12T top position) ones in later cassettes; in fact these 'second smallest' sprockets usually have serrations so that they can still be used as top sprockets if you use them with the correct lockring...]

So the short answer to your question is (with a standard spaced cassette on any UG-C freehub body i.e. all shimano freehub bodies for the last 27 years or so) 'no'; the chainline onto the smallest sprocket is certainly off the end of the splined part of the freehub body and may in fact be off the end of the freehub body altogether. This means that top sprocket has to have an integral spacer. The splines on the integral spacer may engage with the freehub body by 1mm or less in some instances.

So your options for building a standard spaced cassette onto a standard freehub body are essentially restricted to;

a) using top or penultimate position sprockets from standard cassettes (with a suitable lockring) or
b) using a top sprocket/lockring from a 'junior' cassette or
c) using an aftermarket top sprocket.

If you stray to different spacings/numbers of sprockets there are options using flat sprocket in the final position, provided that the sprocket sits over the splined part of the freehub body (i.e. so the cluster is shorter -by virtue of spacing and/or number of sprockets- than the freehub body is designed for). It can only be secured if you use a spacer between the sprocket and the lockring, and since there are no serrations on the lockring, a little threadlock on the lockring is a good idea.

If you respace the hub so that the lockring is practically brushing the inside face of the RH dropout, you are only going to waste a little bit of the available space.

Another option is to shorten the freehub body, i.e. so that the unsplined part of it is removed. The danger with this route is that the lockring threads are barely long enough to start with; it is easy to end up with not enough lockring threads remaining.

cheers

[Brucey]

this picture shows the difference between some freehub bodies


uniglide, UG/HG, and HG-C freehub bodies

For completeness, the dura-ace UG freehub body has a smaller threaded top sprocket position (to allow a 12T top sprocket, vs 13T for standard UG) and note that UG bodies existed in several different widths, including 4s, 5s, 6s, 7s, (and even 8s I think). Again for completeness, shimano have made steel, aluminium and titanium freehub bodies in recent years. This introduces a whole new swathe of complications even in fitting standard cassettes to standard freehub bodies;


a freehub body made to the same dimensions as used on genuine shimano aluminium 10s freehub bodies. Note the splines are stepped, but have the same minor diameter as other shimano freehub bodies


note that only a subset of 10s cassettes (basically 105, ultegra and not much else) will even fit a genuine shimano 10s aluminium freehub body, because the major diameter of the spline is larger than normal on most of the sprockets; other makes of hub used the standard HG spline for the freehub body and these will accept a wider range of cassettes, albeit they will often 'notch' terribly in the process


HG-C and HG freehub bodies

you can see that the 'straight' HG freehub body won't accept an 11T top sprocket (unless it overhangs the freehub body further than normal). 'Straight' HG freehub bodies (i.e. not HG-C) were made for a few years in 7s width but only for a year or so (and only in a restricted range of models IIRC) in 8s format. If you can find one there is a fighting chance that a flat sprocket can be made to work in the top gear position, depending on the exact length of the cluster.

NB all modern shimano freehub bodies are strictly speaking a form of HG-C, but are often (arguably incorrectly) referred to as just 'HG'.

cheers

[satanas]

^ There was definitely a Dura-Ace 740x 8 speed UG body; I have one. Shimano only made them for a year or do, then STI and HG came along. However, this body used the smaller diameter end section as per Dura-Ace 5/6/7 speed hubs, so only a Dura-Ace first position threaded cog will fit. On the positive side, Dura-Ace EX 11T cogs will fit, which they won't on the 740x HG bodies.

[fausto99]

Many thanks for all the info. It'll need a lot more reading and re-reading before I take it all in. My brain works best with pictures. Words are much harder work for me.

Meanwhile, as some may have guessed, I'm looking for low gears on my winter bike and I'm not going to be messing with the freehub part of my newish SA X-RDC any time soon. However, I have found some Tiagra HG50 14-25T, 9 Speed cassettes, much reduced in price on eBay, and that gives me a 14 top sprocket. I also got some very low cost 8 speed 11-32 cassettes, from Halfords, a while back. So, I'll be mixing and matching to make up my own 14-32, 8 speed cassettes in the next few weeks.

[fausto99]

this picture shows the difference between some freehub bodies

Image not working here.

[Brucey]

image is working fine on my computer....

cheers

[RickH]

image is working fine on my computer....

cheers

It's not an image file that's on your computer rather than somewhere on the Internet is it? (I can't see it either)

[Brucey]

no it is

https://bike.bikegremlin.com/wp-content/uploads/2015/07/uniglide-vs-hyperglide.jpg

which is the same as

https://sheldonbrown.com/images/k7hub-3-stylessm.jpg


cheers

[fausto99]

Mystery solved. I get

"Error 1011 Ray ID: 47ef222e89dfa69b • 2018-11-24 21:57:50 UTC
Access denied
What happened?
The owner of this website (bike.bikegremlin.com) does not allow hotlinking to that resource (/wp-content/uploads/2015/07/uniglide-vs-hyperglide.jpg)."

when I click on your link Brucey. You must have access rights to bikegremlin.com I guess. The Sheldon Brown link works OK

[NATURAL ANKLING]

Hi,
I get this also on link, also images some times do not show in posts but the image above does.
Might be outdated OS, I use 7 & 8.1

I am thinking for links that security setting for the posted pic site are (in your browser) set too high.

[fausto99]

Hi,
I get this also on link, also images some times do not show in posts but the image above does.
Might be outdated OS, I use 7 & 8.1

I am thinking for links that security setting for the posted pic site are (in your browser) set too high.

I'm using Google Chrome on a Windows 10 PC.

[Brucey]

Many thanks for all the info. It'll need a lot more reading and re-reading before I take it all in. My brain works best with pictures. Words are much harder work for me.

Meanwhile, as some may have guessed, I'm looking for low gears on my winter bike and I'm not going to be messing with the freehub part of my newish SA X-RDC any time soon. However, I have found some Tiagra HG50 14-25T, 9 Speed cassettes, much reduced in price on eBay, and that gives me a 14 top sprocket. I also got some very low cost 8 speed 11-32 cassettes, from Halfords, a while back. So, I'll be mixing and matching to make up my own 14-32, 8 speed cassettes in the next few weeks.

Sounds like a good plan to me. Note that where the 'join' is between the different cassettes, the ramps won't usually line up properly. This can make the shift at that point in the cassette a little bit baulky (*). However if you modify the cassette splines so that the wide spline is reduced in width, the sprockets can fit any one of nine ways onto the freehub body (as per UG sprockets in fact). This can be used to improve the 'timing' of sprockets that would otherwise be badly positioned.

(*) In most cases there is a 'bad' transition anyway; e.g. in shimano cassettes the sprockets transition from having two ramps per sprocket to having three as they get larger. Where this transition occurs only one ramp lines up between sprockets, so there is one shift that is always going to be less good than the others. This is often accommodated by making the cable pull on that shift fractionally longer than in the neighbouring shifts. I don't know what the story is with 8s but in shimano 9s, this transition occurs in a different place depending on whether it is an MTB or a 'road' cassette, hence road and MTB shifters are actually very slightly different too. In practice folk either don't notice the difference in shifts or learn to shift differently so that this shift goes OK anyway.

You are meant to assemble cassettes using sprockets from the same (or a compatible) 'group'. You can read the group on the sprockets themselves (often more than one group is marked on each sprocket because smaller sprockets are 'shared' between groups) and in addition the group is usually marked on the EV techdoc for the cassette.

cheers