Gappy Cassette

cdaly_

I'm running a 9sp 11-28t cassette with a 52-42-30t triple. I've realised the 11t (and probably the 12t) sprockets are way higher than I'll manage to spin anytime soon and I'm also finding the cassette is too gappy for my liking. Now I'm very attached to the 30x28 bottom gear so I have a bit of a dilemma.

My normal cycling seems to be in the middle to low end of the cassette and on the middle ring.

I can get a 13-25t cassette which is much less gappy and will shift my normal range up the cassette into the closer ratios which is fine but I'll lose my 30-28t low gear.

Now I can get a 28t (74mm BCD) chainring from wiggle which would give me a similarly low bottom gear but I'm not sure:

1. Will this ring fit my Truvativ crank (Giant FCR 3)?
2. Will the 14t drop from the 42t middle be too much?
3. Am I mad? (and no, my knees will not HTFU even were I willing...)

There is also a 28t ATB ring from CRC but I don't know if that will fit.
I could go and fit a 39t middle ring but that puts my tail-wind assisted spinning home gear onto the big ring with a consequent extra shift to do...

blorg

I would get a 12-27 which is a pretty common cassette. SRAM also do a 12-26 which is another option. I doubt you would notice a major difference between 30-28 and 30-27, certainly not in this country. 12-27 is not too gappy compared to 11-28 (IMO.)

Ryaner

blorg wrote: »

I would get a 12-27 which is a pretty common cassette. SRAM also do a 12-26 which is another option. I doubt you would notice a major difference between 30-28 and 30-27, certainly not in this country. 12-27 is not too gappy compared to 11-28 (IMO.)

Not everyone is light or super fit. Some of the steep hills in Wicklow, or even the top of Howth make use of low gears. Weekend just gone I was in my 34x28 for a while, helps to be able spin at times

The 12-26 does sound like it would fit nicely too with that triple setup. 30x28 to 30x26 does have a 7.7% change but shouldn't be overly noticeable in Ireland.

rob1891

Campag do a 9 speed veloce cassette that is perfect for leisure cycling & triples. 13-28:

13,14,15,17,19,21,23,25,28

Ratios are kept close enough at the end. Compared to what I assume you are using now (a shimano):

11-12-13-14-16-18-21-24-28

The jumps from 18 onwards are very wide for someone who will rarely use the 11 or 12t ring. Might make sense on a Compact, but not on a triple with the 52t outer ring.

Now, offering a campag cassette to a shimano user isn't much use. If you want to get creative, you could buy 2 of the lower end sram/shimano casssettes, pull the bolts out of them (they are not essential) and make up the cassette any way you want it. If your current cassette is this way, you could merge it with a new one provided the old one has not seen too many 1000s of miles.

cdaly_

I did a detailed Lumenesque gear ratio analysis of various cassettes. I looked at the 12-27 as well as a 13-30.

The biggest issue for me is I tend to end up in the 14-16-18-21 set of sprockets in my current setup. I'm finding that even the 2-tooth jumps on a change leave me with too big a change of cadence. Since I'm on a 11-28t at the moment, I rarely get to use the closely spaced sprockets at the outside. If I move to a 13t smallest, I'll end up with more use of the closer-spaced outside sprockets.

Now I could change the middle ring from 42t to 39t and use the 12-27 and end up with something similar to the 13-25 at the high end but I'll still end up with only 3 sprockets with single tooth jumps while I would have 4 single-tooth jumps with the 13-25. (I'm avoiding using the smallest sprocket with the middle ring in these calculations).

rob1891 wrote:

If you want to get creative,

Now this sounds interesting. All three cassettes I've been looking at have 21t on sprocket 7. What I'd like is the 13-21 set from the 13-25 with my existing (and probably least worn) 24t and 28t from my current (4-month old, 2,000k) cassette. Any risk of freehub gouging if I go that road? Or was that just an issue with the 10-speed freehubs? There is a fat slot in the freehub so the sprockets line up correctly for shift ramps and such isn't there?

That would also save changing chainrings. BTW. Are 130mm and 74mm BCDs the normal one for road chainrings? Or does it depend on whether it's a double, compact or triple?

Lumen

11-28 has massive jumps where you really don't want them, i.e. at the "wall climbing" end of the cassette. The last two jumps are 12.5% and 14.3%.

With 30-28 your current lowest speed @ 60rpm is 8.1kph.

With standard cassette options it's not until you get to 12-25 that those gaps go away (to a much better 9.5% and 8.7%).

So if you really need the gearing I'd be inclined to change two of the chainrings (e.g. 52-39-28) and go with a 12-25. Your easiest gear will then be 25-28 which is 8.5kph @ 60rpm; if you're going any slower than that you may as well get off and walk.

Alternatively just stick a 12-25 on with your existing chainrings and live with having to push for the extra 1kph.

rob1891

The larger sized sprockets wear slower, and you probably haven't spent the majority of your time in them, so I would guess that they are perfect to combine with a brand new set if sprockets. It is a good idea to get a new cassette with the smallest sprocket that you intend to use as this is differently shaped to the rest. You could have trouble taking your current 13 from the middle of the cassette and trying to use it in the very smallest position as it would not reach the splines of the freehub.

You will get gouging when using the cheaper individual sprocket cassettes on aluminium freehubs. Even though they are usually bolted together, the bolts don't distribute the load across the spline of the freehub at all.

Here is a thread about preventing gouging, I'm trying the flattened staple trick at the moment, but I don't expect it to work! Nor do I care really, most gouging is cosmetic ...

http://weightweenies.starbike.com/forum/viewtopic.php?f=3&t=64623&start=0

Getting a second tiagra cassette is 18 euro, you probably won't get a single middle ring for that price. Granted, the 12-25+rings may have smaller jumps, but so would 11 speed!

Russman

So, on a 12-25 cassette with a 52-42-30, is there any real benefit in switching the middle ring from 42 to 39 ? Will it result in staying on the middle longer before having to drop to the small ring, or do 3 teeth on the front make a huge difference ?

I think I'm getting confused reading my own post, never mind the ones above !:D

Lumen

Doh, just re-read and see that you're using 9sp, I had assumed 10sp. That makes the gaps far worse - up to 16.7 %.

I'd probably spend the money on some used 10sp parts, or go the whole hog and splash out on a complete 11sp Athena groupset with a 12-27 cassette. :pac:

cdaly_

Russman wrote:

So, on a 12-25 cassette with a 52-42-30, is there any real benefit

Yep. Basically, 42 to 39 moves your gear ratio 1 sprocket to the right. If you're trying to avoid the bigger jumps between gears this is an improvement. OTOH, you need to consider where your usual cruising ratios are 'cos if you move them too far right you end up having to switch back and forth between middle and big rings.

Lumen wrote:

11-28 has massive jumps where you really don't want them, i.e. at the "wall climbing" end of the cassette. The last two jumps are 12.5% and 14.3%.

For me it's not having to get off and walk that matters more than how big the low end jumps are. Mind you, some day I'll have time to head out into Wicklow and I might learn to climb...

blorg

rob1891 wrote: »

You will get gouging when using the cheaper individual sprocket cassettes on aluminium freehubs.

Fixed that for you, unless you consider Ultegra to be "cheap" :pac:

cdaly_

Lumen wrote: »

Doh, just re-read and see that you're using 9sp, I had assumed 10sp. That makes the gaps far worse - up to 16.7 %.

I'm not sure where you're getting the 16.7%. My calculations (based on Sheldon Brown's Gain Ratios) give me a max of about 14.3% on the 30x24-28t jump.

I'd probably spend the money on some used 10sp parts, or go the whole hog and splash out on a complete 11sp Athena groupset with a 12-27 cassette. :pac:

Yes. You would wouldn't you...

Lumen

cdaly_ wrote: »

I'm not sure where you're getting the 16.7%. My calculations (based on Sheldon Brown's Gain Ratios) give me a max of about 14.3% on the 30x24-28t jump.

28/24 = 116%

cdaly_ wrote: »

Yes. You would wouldn't you...

LOL. I just meant that I'm not sure it makes a lot of sense to spend loads on money on a 9sp setup.

blorg

cdaly_ wrote: »

The biggest issue for me is I tend to end up in the 14-16-18-21 set of sprockets in my current setup. I'm finding that even the 2-tooth jumps on a change leave me with too big a change of cadence.

Bear in mind that 2T on the big end is a lot less than 2T at the small end, in percentage terms. It is the percentage that really matters.

Have you considered getting a fixed gear? That takes all the thinking out of gear shifting and there is no gappiness whatsoever. On a slightly more serious note it will certainly help you develop your cadence range (or destroy your knees.) I have an effective range of around 60-120RPM now and indeed can go lower when necessary; I did not have this range before I got a fixed gear bike.

I generally shift two or three rear sprockets at a time so have a limited empathy with this problem although I know it is real for some people.

I am somewhat surprised that no-one has yet told you to HTFU and live with 30-25/26/27 (!?) :pac: for the rigours of Dublin urban cycling.

To be perfectly serious though getting a 12-27, 12-26 or 12-25 cassette and seeing how you get on with it is the obvious low-investment choice here.

Russman

cdaly_ wrote: »

OTOH, you need to consider where your usual cruising ratios are 'cos if you move them too far right you end up having to switch back and forth between middle and big rings.

Ah yes, penny dropped, I think I get it now ! Gaps are smaller coz you're working off a slightly smaller "base" but, could end up going from, say, "39/12" to "52/whatever" too frequently for comfort, thanks !

cdaly_

Lumen wrote:

28/24 = 116%

Ah ok. I was using (28-24) / 28 = 14.29%. Looking at the same thing but from different directions...

blorg wrote: »

Have you considered getting a fixed gear? That takes all the thinking out of gear shifting and there is no gappiness whatsoever. On a slightly more serious note it will certainly help you develop your cadence range (or destroy your knees.) I have an effective range of around 60-120RPM now and indeed can go lower when necessary; I did not have this range before I got a fixed gear bike.

Fixed? Holy crap no. I like my knees too much.

After following the cadence advice I got from you lot on t'internet, my normal cadence range is 80-100 with my comfort zone being about 90-95 and I can sprint out to about 115 max. It's all about staying in my comfort zone while cruising really...

I am somewhat surprised that no-one has yet told you to HTFU and live with 30-25/26/27 (!?) :pac: for the rigours of Dublin urban cycling.

Oh yes, I've tried that. Only trouble is I wouldn't be able to manage a clockwise circuit of Howth.

I've now ordered a 9sp 13-25 tiagra cassette for €18 from CRC and I plan to try out rob1891's custom cassette hacking proposal...

cdaly_

Yay! New cassette arrived.

In the meantime, on a circuit of Howth this morning, I stayed off the 11t and 12t and spun out 52x13 at 110rpm and 56kph. I reckon there won't be many occasions when I'll miss the 12 or 11t.

OTOH, climbing from Howth village, I totally needed the 30x28 bottom gear. There'll be a bit of hardware hacking going on tonight...

cdaly_

Took the two cassettes apart today. They're held together by pins rather than bolts (or at least there wasn't any screwdriver slots in the heads that I could see). Knocked out the pins, washed the 11-28 sprockets and reassembled a pair of cassettes. I now have a 13-28 (13 14 15 16 17 19 21 24 28) on the bike and a 11-25 (11 12 13 14 16 18 21 23 25) spare for whenever I end up racing...

I was considering re-fitting the pins but if they were to work their way out again, first I would know of it would be when they would foul the spokes and the bike would turn into a 9sp fixie...

rob1891

I guess they were pins on the cassettes I've had, though I remember small bolt heads on one. In any case, with them removed you can swap cogs in and out as you please, don't bother trying to refit them. They are only a convenience to allow you to remove the block as one.

Hope the new range satisfies you, it looks a lot more sensible than 11-28. If there's a gear that feels missing, you seem to have a pretty complete set of cogs now, so you can swap them in and out and turn your nose up at Freds riding simple stock equipment ;-)