Cassette and RD upgrade for easier climbs
 

Hi,
I currently have a Ultegra 6700 SS, 11-28 cassette and 34/50 chain rings. I would like to change the cassette to give me easier climbing gears. Could anyone give me some guidance on what I can do. I have been told I may have to change the RD to a long cage, which I'm OK with cost wise. Many Thanks:)

Long cage derailleur
The longer arm allows more chain wrap. This is needed for triple chainring bikes, for instance, since the small chainring - small cog needs way less chain than it's big - big combination.

A shorter cage arm doesn't have enough "chain wrap", so the bottom return chain could go slack, and will rub against the wrapped chain at the top pulley, since the cage is rotated all the way up.

Chain sizing
Normally, chains are sized by the "big-big +1 inch" method -- see this Park Tool guide. This is the minimal chain length that will work correctly when doing a big-big cross chain shift.

Derailleur pulley clearance
The upper derailleur pulley needs to be positioned far enough away from the biggest cog so the chain can shift to that cog. This is a derailleur design and/or derailleur hanger length problem, not affected by the cage length.

From a table of cog radius, measured to the center of the chain pin:
28 tooth cog is 56.7 mm
32 tooth cog is 64.8 mm
That's 8 mm larger diameter.

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I have Ultegra 6800 11-speed, and the bike came with 34/50 front, 11-28 rear.

I installed a 11-32 cassette, and the derailleur arm length was fine. It measures 58mm between pulley centers -- this is longer than a lot of older short cage derailleurs, which likely were designed for smaller cog sizes.

There's still a gap between the bottom return chain and the upper pulley's chain when shifted to the low-low 34-32. (Even if the chain wrap wasn't quite good enough, there would be some noise from the chain rubbing against itself in the small-small combination, but that's rarely used.)

My chain that was used on the 11-28 was still long enough for the 11-32 cassette. But carefully, by hand cranking, check the big-big combination -- the derailleur cage should still have some bend to it, or you could jam the chain. To check: hold the bike upright with the rear wheel off the ground and shift in and out of the big cog and big chainring.

11-32 worked for me, but it's a tight fit.
But the gap between the upper pulley and the 32 cog is very small. I adjusted the "B" screw to rotate the derailleur a little more, which helped. I think this 11-32 is bigger than the recommended cassette sizes, but I've had no problems shifting in or out of the 32 cog, either on the 34 chainring or cross chained on the 50 chainring.

This probably depends on the exact dimensions of the derailleur hanger. It might not work on every bike.

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Bigger than 11-32 cassette?
Want even more range? I think you need a mountain bike rear derailleur. I haven't looked into it.

I do like my 34-32 low gear on steep hills. I can stay seated on 10% grades, and I've even used it to spin up a 5-6% grade with a cadence above 90 rpm. But the tradeoff is bigger gaps between shifts in the middle of the range. That makes it harder to get the "just right" cadence on flatter roads.


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11-32 gaps (50 chainring in black, 34 chainring in red, at typical spinning cadences) :
The 18-16-14 cogs with the 50 chainring makes big jumps at 20-25 mph, right where I'm working hard to keep the speed and want the best cadence. On the other hand, the big ring can easily go down to around 12 mph, and the small ring is good all the way to 20 mph, so the front derailleur doesn't need to be shifted very often.

thread moved from User Assistance to Bicycle Mechanics.

I don't have direct experience with the Shimano 6700 level components. However, a little research shows that your current RD-6700SS (short cage) is limited to 28T max large cog and 33 tooth capacity. The RD-6700GS (medium cage) is still limited to 28T max large cog, but has 39 tooth capacity. Doesn't help as you want a lower gear (larger cog). There is a 12 - 32 10 speed Ultegra cassette, which would give you marginally lower gear, but is intended to be paired with the Ultegra RD-6700A RD, which has a 30T maximum cog size.

What you probably want to do is go with a 32T maximum cog to get a "significantly" lower gear to make this worth doing, which means you would need a MTB cassette. Shimano 10 speed MTB cassettes (11-32, 11-34, or bigger) have the same spacing as the road 10 speed cassettes, so no problem there. Its doubtful you could get your current RD to work with a 32T cassette let alaon 34T. You might be able to get the RD-6700A to work for a 32T cassette (depends on you rear derailleur hanger and whether you could adjust the B screw enough that the pulley would clear the largest cog). You can always go to a Shimano MTB RD, but have to get a 9 speed model, which usesthe same cable pull as Shimano road shifters (10 speed MTB derailleurs are not compatible with 10 speed road). Fortunately they still make 9 speed RD in several upper level groups (Deore M591 or XT M771 or M772).

Good luck.

I have a Shimano RD-5701GS and the instructions say 30T maximum cog with a triple crank and 32T max with a double. I assume the difference is due to chain wrap limitations as the rear derailleur's cog clearance shouldn't care what's up front. So a 32T should work fine as long as you don't use small-small with a triple.

The RD-5701SS listing also says 30T max but it's chain wrap is even less, so while a 32T probably also works with it you will be even more limited in small-small choice.

Dude has a 6700 setup.

None of those derailleurs were ever rated for more than a 28.

Having said that, doesn't mean you can't put on a 30 or a 32, you just don't know if the b-screw will allow enough adjustment on his *specific bike* to clear that biggest cog, in the small ring.

Good news is that you can put on a 9s mountain derailleur, with the correct spec for whatever, 30/32 you want to run and do it that way. Capacity will be in spec, max biggest cog will be in spec.

You basically said a whole lot of nothing.

He has a 6700 setup, not a 6800. Those groups and specs are completely different. The 6800 in particular has the option of putting on stupidly low gearing for weak ass mother ****ers.

The 6700-GS will easily run a cassette with a 32T big cog. Absolutely no issues with that whatsoever.

Source: almost 20,000 miles with a 6700-GS paired with a succession of XT M771 11-32 cassettes-- on 3 different rear wheels, no less.

If it were me, I'd go with an XT (771 or 772) RD and an XT 11-34 cassette. A 12-34 would be better, but I don't think anyone makes one light enough.

Nothing wrong with running lower gearing. I've gone to a triple with a 32t and may go with a 34t one day. Truth is, if you can't push a 34-28 up hills, you probably won't be pushing a 50-11 very often.

John

First, I haven't seen you here is quite a while so welcome back. Second, it seems nothing in your postings has changed. :)

I'm running an IRD 12-32 cassette with a 6700GS RD and 6750 crankset on my current road bike, it shifts fine.