Customising cassettes / Building a custom cassette

A friend and I got talking gearing, and I said that I was thinking of switching to an 11-28T soon (I currently have a 10spd Shimano 12-27T).
He said, "I've a part-worn 105 one you're welcome to. Give it a go, it's not damaged and probably has about 1500 miles on it."

So I gave it a go with my current chain (also wearing similar mileage), and there was something about this 11-28T that just didn't feel right.
I spend a lot of time on the big ring and in the middle of the cassette, and I just couldn't get comfy with this one.
It wasn't until I checked the specs that I realised the Shimano 11-28T is missing one of my most-used cogs - 16T. The 15-17T jump in the middle of the standard 11-28T felt 'orrible.

So I did a bit of searching and decided to create a custom cassette using what I had:

Standard 11-28T Cassette: 11-12-13-14-15-17-19-21-24-28
Standard 12-27T Cassette: 12-13-14-15-16-17-19-21-24-27
Custom 11-28T Cassette: 11-12-13-15-16-17-19-21-24-28

Just back from a test ride and it feels way better. The grouping seems more natural, the centre portion of the cassette is back to how I like it, and the 'gun it' gears (starting with 13T) kick in one click sooner.
Of course, the old 12-27T is now useless as it contains two 14T cogs, but tbh that's likely going to sit in a ziploc bag until I either need or bin it.

Thought I'd share. I'm likely not the first person to do this.

just out of curiosity, what cadence are you aiming for when sprinting? if you are customising cassettes, why not have your top "gun it" gear 12t, or even 13t. the gear rations for 11t are just stupid, and nobody can spin them up.

typical track gear inches for sprint events are 92-94 GI and they sprint at 70km/h+

if you are a standard chainset 53t/11t is an enormous 126 inches. at 70km/h your cadence would only be 122, not exactly high when sprinting.

If you went to a low of 12 or 13t, your jumps would also be much smaller, thus easing your transitions.

And 11t sprockets wear quickly and are inefficient .

I like the 11T on the TT bike to keep cadence down on faster descents. I don't really customise cassettes, I just have a variety and choose the appropriate one for the race.

I don't measure my cadence. Running a 50/34T.
Tbh I wanted an 11T not for sprinting, but to keep up with the group on long descents.
If it proves useless, or wears out, I can always reinstate the last 3 cogs of my old cassette and have it as a 12-28T.

Ultegra 6800 (11-speed) cassette question:

I want a 12-28 but bike came with 11-28. Any reason I can't combine bottom five cogs of 12-25 with top 6 cogs of 11-28 and vice-versa, keep resulting 12-28 and sell 11-25, and thus avoid having to spend silly money on Dura-Ace.

I've had a bit of a Google fail here and couldn't can't find these details on the official Shimano website, so cogs are unconfirmed but listed as here.

Plan is:

11-28 original:
11-12-13-14-15-17-19-21-23-25-28
12-25 original:
12-13-14-15-16-17-18-19-21-23-25
11-25 new:
11-12-13-14-15-17-18-19-21-23-25
12-28 new:
12-13-14-15-16-17-19-21-23-25-28

If, as on previous generations Shimano stuff, the biggest 3 are a block and the rest are individual with spacers, then this seems feasible to me, but can anyone here confirm/deny?

Even if I couldn't shift a 11-25 without the magical 16T cog, buying 2 new Ultegra cassettes would still work out a lot cheaper than buying a DA one.

TLDR: Wish Shimano made an 11-speed 12-28 that cost < £100

Will the ramps and pins still be in sequence?

Hippy has been butchering 11 speed cassettes, so he could probably tell you of any pitfalls.

So curiosity got the better of me and I bought two 105 cassettes from Merlin for just over £40.

I can confirm that it is definitely possible to assemble a semi-custom 12-28 in the manner that I suggested.

However, the cogs used in the 12-25 and the 11-28 are not identical. They carry an alphanumeric designation relative to the number of teeth and the exact design.

So on the 12-25 the 17T cog is called "17A", and on the 11-28, it's a "17B" or something like that. The difference appears to be the positioning of the teeth relative to the splines.

Anyway I assembled a 12-28 with the 17T cog from the 11-28 as this just looked better (unscientific), and gave it a go with the bike in a stand. It worked and shifts across the cassette in both directions with no discernible difficulties.

This cassette is probably sub-optimal since the positioning of the teeth is not the same as on an "out-of-the-box" one, but given that it seems to work, it is almost certainly better for me than one which gives me a top gear of 52x11 which I will hardly ever use.

If my cassette/chain/hub/wheel/bike/face explodes from the use of this deviant equipment, I will be sure to post an update.

TLDR - cheap Shimano 12-28 11-speed. Works.

I've been running a hybrid 10 speed 13-28 for years on my race bike, made from a 11-28 DA 7900 cassette, and a 13-25 ultegra junior cassette. That way it's straight through to the 19t. Shifting is as good as either original combination.