How to build a custom 8-speed cassette ?

jejv

Hello.


The Problem:

We have some hybrid bikes which we use on and (mildly) off road.
We are neither super fit nor entirely unfit.

The gearing for these bikes isn't really suited to our needs -
the small cogs at the back are too small, and a mountain-climbing
34T gear would be good.
Also I find myself hunting up and down the gears.

All the bikes are 48/38/28 at the front, with 17cm cranks,
and we have 40-622 or 44-622 rear tyres.

The bikes we have now have one of these sets:
(1) 11-13-15-18-21-24-28-32
(2) 11-12-14-16-18-21-26-32
(3) 11-12-14-16-18-21-24-28


At least on the large chainwheel, I don't think we use 11, 12, or even 13
teeth much.

I think we might be better off with something like:
(A) 14-15-17-19-21-23-26-34
Or:
(B) 14-15-17-19-21-24-29-34
Or:
(C): 14-16-18-20-22-24-28-34
Or:
(D) 13-15-17-19-21-23-26-34


But none of these appear to be much like standard 8-speed cassettes.

I think we want to stick to 8-speed - If we went to 9-speed we'd be looking at:
(E) 14-15-17-19-21-24-27-30-34

Which is also pretty non-standard.


I'd be trying to maintain "hyperglide" transitions between cogs.


Solutions:

1) (D), which is non-ideal, because of the 13-tooth top cog, and (E), which
is good, but requires new controls and chains,are available from a US vendor well-known
for his cycling website.


2) Build custom cassettes, by dismantling off-the shelf cassettes, and re-assembling them.

This is where I think I need advice. I've never tried this - or any other fiddling with cassettes - before.


It sortof looks as if from these sets:

Shimano set "V" 13-14-15-17-19-21-23-26
Shimano MegaRange 11-13-15-17-20-23-26-34

that after removing the allen keys/rivets,
we could make (A): 14-15-17-19-21-23-26-34

since, as far as I know - there is only one 7/8 speed shimano 26-tooth cog pattern.

Both of these cassettes seem to be fairly readily available, and not too expensive.

I get the idea that the "HG50" branded parts use 2mm allen bolts, which are easier
to remove than rivets.

Hopefully, I can bolt together (though I understand that this is not strictly necessary)
a 17-19-21-23-26-34 group,
with something like a spacer, a 15T cog, and a ?self-spaced? 14T cog left over.

The problem I have then Is how to clamp the 14T gear onto the freewheel, since
the 14T gear is not a "Top Cog", with a bevelled recess for a clamping nut.

Is there a way round this ?



(B) 14-15-17-19-21-24-29-34 and (C) 14-16-18-20-22-24-28-34 come from looking at
other cassettes which may or may not be readily available, and the available
HG transition combinations:
Shimano 7-speed 14-16-18-20-22-24-28
Shimano 7-speed "K" 13-15-17-20-24-29-34

OK, I'm not sure about (C).


Any thoughts ?

John.

nicklouse

yes it is possible to build your own "block" and yes you may find a 13 or 14T top cog of a junior road block. time to play at the LBS. and see what they have, Or you could look at a smaller set of rings at the front.

jejv

nicklouse wrote:

yes it is possible to build your own "block" and yes you may find a 13 or 14T top cog of a junior road block. time to play at the LBS. and see what they have,

Hmm. I might get lucky. I'll take my vernier calipers.
But ideally, I guess I'd want a 14T that expected a 15 after it. Dunno how much it really matters.

So there isn't any kind of unusual lock-nut I could use to clamp a non-Top cog ?

Perhaps I could try machining out a bevelled recess in a standard 14T cog.

nicklouse wrote:

Or you could look at a smaller set of rings at the front.

Ho Hum.

John.

nicklouse

jejv wrote:

So there isn't any kind of unusual lock-nut I could use to clamp a non-Top cog ?

nope. or lets say i have not found one yet.

supersonic

I'd agree that the large chanrings are the problem, not the cassette!

jejv

OK. Right. Thankyou both.

I guess I was stuck looking at the problem in a particular way.

Seems like 42/32/24 would be about right.

Might still fiddle with the cassettes a bit though.

Regards,

John.

TommyK

Before you butcher loads of cassettes and spend money, think of the shifting ramps and teeth on a cassette. I have tried putting an 11t top sprocket on a 27-12t road cassette which caused it to ghost shift and generally be a pain as the shifting ramps (cutaways in the sprocket to aid chain pick up) didn't align. I think I undid years of Shimano's R&D in 5 minutes! If you can't replace your chainrings and you do give it a go don't mix 8&9 speed sprockets with 7 speed stuff as the super narrow chains won't shift well on thicker sprockets....happy tinkering

nicklouse

jejv wrote:

OK. Right. Thankyou both.

I guess I was stuck looking at the problem in a particular way.

Seems like 42/32/24 would be about right.

Might still fiddle with the cassettes a bit though.

Regards,

John.

just by coming down in size like you suggest will make the cassette gear ratios feel closer. as above happy tinkering. also have a good look at sheldons webby (linky below) as there is a whole pile of infos on building your own....

jejv

> just by coming down in size like you suggest will make the cassette gear ratios feel closer.

Yes, I appreciate that. wide-range cassettes tend to have closer ratios about 1/3 of the way up.

I have looked at sheldon's site quite a bit. A couple of the odd cassettes I mentioned are Harris Cyclery specials.

I suspect that even with the lower gearing, the 11T top cog still doesn't make much sense for us.

But I'm waiting for a couple of chainsets to turn up. When we see how they behave, we might think again about cassettes.

I'll let you know.

John.

> and (mildly) off road
Well, if the kids plan the route, that can turn into a kind of cyclocross-with-panniers...

jejv

[This was in MTB, because the transmission bits of our "hybrid" bikes are MTB bits]

Yes, changing the chainsets did the job. But I did mash up cassettes.

Went for Alivio 42/32/22 & M442 44/32/22: 22T was the smallest granny without throwing loads of money at the problem.

These gave us the lower gears for proper hills. Mashing up cassettes gave us slightly closer gears too,
without the jump MTB cassettes have in the middle of the "normal" gears.

My bike got 42/32/22 first. Tried that with 12-21 - enough range for Cambridge, but found gears were too close (!) for stop-start traffic. 12-25 (all 8-speed) was much better, and fine on the chalk hills south of Cambridge.

Adding an inch or two of chain seemed to make the road cassettes shift better with an LX SGS mech. Jockey wheel closer?

8YO (tall, spins) got 42/32/22 x 13-15-17-19-21-24-28-32.
Got Highpath to cut down Alivio cranks from 175 to 155mm. Seemed cheapest way to get a short crank with 22T granny.
He still wouldn't be allowed to race on 42x13.

Me and 12YO (V tall, masher-ish) got 42-32-22 x 12-13-15-17-19-21-24-28
OH got 44-32-22 x 13-15-17-19-21-24-28-32 on town bike, later 44-32-22 x 13-15-17-19-21-23-26-30 on Hybrid.

She had had 48-38-28 x 11-32, but didn't use the 48.

All with 40/44-622 tyres.


12-28 fine. Wth 13T top cog 13-15-17-whatever shifted OK, but just a tad slow arround the 15, regardless of tweaking.
No noticeable glitches shifting across "road" cogs and MTB cogs (19-21-24, 21-23-26).

Later realised that this could be because 8-speed shimano cassettes do NOT have even 4.80mm spacing.
The self-spacered top two cogs are wider than nominal 4.8mm - roughly 5.1-5.2mm.
So they have spacing more like: 5.0/5.1/4.8/4.8/4.8/4.8/4.8mm, by my measurements.
Sheldon Brown should have used his vernier calipers more.

Adding a 0.016" (0.41mm) shim next to the spacer behind the 15T cog got rid of the glitch on 13-15-17.
Would have gone for 0.33mm ish, but 0.41mm was what I had.

Hexhamshire common:

Is this an MTB ? And what's my FCN ? (passenger & family behind camera)