Road bike cassette choice

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Duck!
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Re: Road bike cassette choice

Postby Duck! » Mon Jan 29, 2018 11:02 pm

RobertL wrote:From the information that Duck has provided in the past I believe that there is never a problem with the upper jockey wheel clearing the 30t cassette, because the upper body part of the short cage and medium cage RDs are the same. You just need to adjust the B screw to suit.
True, to a point. The critical point is within a compatible model series. No Shimano road derailleur prior to 2012 model year (mid-2011 release) is compatible with larger than 28T. Longer cages were always available, but they were for use with triple-ring cranks. 4600 Tiagra, released in '11 for '12 model year was the first model to be available from launch with 32T compatibility. 5700-A/5701, a second-year update to that 105 series, followed soon after, and 3500 Sora & 6700-A/6701 Ultegra update the following year, and 2400 Claris the year after that. Dura-Ace finally got 30T compatibility with the current R9100 series, released around 18 months ago.

The problem is whether the short cage RD can carry enough chain in total to allow you to access the big-big combination. That is down to the specifics of the bike (chainstay length) and the length of the RD hanger.

Even if it doesn't quite work, the worst outcome is not being able to crosschain to the big-big combination. Everything else will be fine.

Hanger length doesn't really have a lot to do with it, beyond possibly extending the tolerance for a model that may not officially be compatible with a particular sprocket size. When the B-screw is properly adjusted the clearance between cassette & derailleur should be about the same regardless of hanger length. What does matter, and which by extension is where the chainstay length comes into play, is the difference between the front rings. Compact & mid-compact, which have a 16T difference, need the derailleur to hold more chain than a tighter ring pairing, such as a traditional 53/39 (14T difference) or CX-type 36-46, with a mere 10T difference. The actual chainring size isn't relevant at all, because you just cut the chain to suit.

Chainstay length dictates how much tension (using the small ring/small sprocket method of chain measurement) you need to pull on the derailleur from its fully contracted state to reach an appropriate join without any chain slack. Short stays are not necessarily better.

And yes, if it does all go wrong, the only gear you'll lose is big ring/big sprocket, but you should always aim to avoid that combination anyway, regardless of what gear combination you have, because that's the most damaging to your drivetrain.
I had a thought, but it got run over as it crossed my mind.

ScottD439
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Re: Road bike cassette choice

Postby ScottD439 » Mon Jan 29, 2018 11:12 pm

So been advised that the only way my setup can achieve 11-32t here is the suggestion
Because you have 10 speed components we only have one option for a rear derailleur that will allow you to use a 32t cassette.
You will need a longer chain because of the larger cogs and most likely a new inner cable.

Shimano 5701 medium cage $99.95
Shimano H5500 11-32 cassette $59.95
Shimano 105 10 speed chain $49.95
Shimano Inner cable $5.00

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Duck!
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Re: Road bike cassette choice

Postby Duck! » Mon Jan 29, 2018 11:26 pm

As noted - several times now - above, if you have, as appears, a 2014 5700(/-A/01) derailleur, you do NOT need to change it; it is compatible with 32T, and any available double-ring crankset (but as noted, some care does need to be exercised around big ring/big sprocket). HG500 is the only "road" model 10-sp. cassette series with that combination, but the "MTB" HG81 SLX (roughly 105-equivalent) and M771 XT (Ultegra equivalent) also have the 11-32 option, and are totally compatible. Similarly there are also 4600/HG500 Tiagra-level, and 6701 Ultegra chains to pick from as well. Link shaping for all three is the same, so there is no difference in shift performance, but each level has different surface treatments, which improve corrosion and wear resistance.

You do not need to change the cable because of gear combination, but it's worth doing periodically as a matter of routine. Gear cables will fray and break inside the shifter mechanism, and although newer models are much easier to get broken-off cable heads out of, it's still easier to change them before they get to that point.
I had a thought, but it got run over as it crossed my mind.

ScottD439
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Re: Road bike cassette choice

Postby ScottD439 » Wed Jan 31, 2018 10:04 pm

Thanks to all that help me with the provided information it took me a while to work through the what I needed but with all your help made it easier. So thanks again I'll be purchasing the parts required and will give updates when completed.

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Mububban
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Re: Road bike cassette choice

Postby Mububban » Tue Feb 06, 2018 6:49 pm

ScottD439 wrote:Thanks to all that help me with the provided information it took me a while to work through the what I needed but with all your help made it easier. So thanks again I'll be purchasing the parts required and will give updates when completed.


I'm about as skinny and weak as you'll meet on a road bike, I have a 50-34 and 11-32 and I can get up anything that I personally would realistically attempt with that combo. Even on climbs that make me suffer, I'm not often in the 32 but it's great to have for when I'm really knackered. So chances are, you'll be fine. Let us know how you get on!
When you are driving your car, you are not stuck IN traffic - you ARE the traffic!!!

ScottD439
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Re: Road bike cassette choice

Postby ScottD439 » Tue Feb 06, 2018 10:12 pm

I have decided to go
12/30 Ultegra 10 Speed
CS-6700 Ultrgra chain
Shimonoseki 105 rear derailleur 10 speed double

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