Making a 12-28 cassette

markhewitt1978

I have an Ultegra 6700 11-28 cassette on my bike, however I'd much rather it was a 12-28 cassette.

It has the following:
11-28 11,12,13,14,15,17,19,21,24,28

If I was to get a 12-25 which has this:
12-25 12,13,14,15,16,17,19,21,23,25

Is it just as simple as taking off the 21,23,25 cog cluster from the 25er, replacing it with the 21,24,28 from the 28er and jobs a goodun? Just wanted to check it really is that simple before I buy anything.

The reason I want to change is that while the gears are fine at the bottom end I don't think I've even once used the 11T gear, so I'd rather have another cog somewhere else that I can actually use.

rolf_f

It may be worth being a little more scientific about it. In the case of Campag there are sheets that list the different sprockets - a 13 tooth in a 12-25 might be a different part than the 13 tooth in a 12-27; it depends on the ramping sequences. So, in theory you might find that using one cassette to make the Frankencassette works better than another.

But that said, I made an 11-29 for the Alps using a 13-29 and a 12-25 and just joined them somewhere in the middle without a second thought and it was absolutely fine - but that was the sort of cassette and riding conditions where I was either climbing on the bigger sprockets or descending on the smaller ones. There were few opportunities to get irritated by minor shift imperfections across the middle. In your case the point is to remove an awkward jump so I'd be more careful about it.

markhewitt1978

Thanks, it's possibly relevant that the at the point of the change between the two cassettes they are both going 19 -> 21, it's only the final two cogs which are of a different size.

rolf_f

markhewitt1978 wrote:

Thanks, it's possibly relevant that the at the point of the change between the two cassettes they are both going 19 -> 21, it's only the final two cogs which are of a different size.

Possibly - or possibly not!

Imagine, using hypothetical gears, that you have a

2 - 3 - 4 - 6 - 7 - 8

Each of these will be ramped in sequence with a gap where 5 was. Now, if you had a

3 - 4 - 5 - 6 - 7 - 8

You can see that either the 3 and 4 will match the first or the 6,7 and 8 will. But not all of them because of the ramping. That's clear enough.

Now if you have a

1 - 2 - 3 - 5 - 7 - 8

it is less clear. The 2 and 3 might be the same as on the first cassette but, on the other hand, it might be the 7 and 8. I'd imagine that there is a computer programme somewhere that determines for a given range of cassettes how to minimise the number of different sprockets that need to be made!

Of course, none of this matters for single shifts - it's only multiple shifts that won't work so well if they aren't perfectly matched.

styxd

markhewitt1978 wrote:

I have an Ultegra 6700 11-28 cassette on my bike, however I'd much rather it was a 12-28 cassette.

Is it just as simple as taking off the 21,23,25 cog cluster from the 25er, replacing it with the 21,24,28 from the 28er and jobs a goodun? Just wanted to check it really is that simple before I buy anything.

Yes,

Although I'd just buy a 12-27 105 cassette and sell your 11-28

markhewitt1978

I'd looked at that but I'm only just getting used to the 28T rear (from 30T) so don't want to go 27T just yet, even though the difference is small.

keef66

You could try a SRAM 12-28 cassette? Or there's a Tiagra 12-28...

Bobbinogs

markhewitt1978 wrote:

I'd looked at that but I'm only just getting used to the 28T rear (from 30T) so don't want to go 27T just yet, even though the difference is small.

I don't think many could tell the difference between a 27 and a 28. A 34x27 combo is 33 and a 34x28 combo is 32 inches.

rolf_f

Bobbinogs wrote:

markhewitt1978 wrote:

I'd looked at that but I'm only just getting used to the 28T rear (from 30T) so don't want to go 27T just yet, even though the difference is small.

I don't think many could tell the difference between a 27 and a 28. A 34x27 combo is 33 and a 34x28 combo is 32 inches.

You certainly notice it when you get to 27 and still have another click or two to go!