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Old 11-21-09, 12:31 PM   #1
daven1986
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Real world difference between 28/34t and 32/34t (and Rear derailleur & shifter Qs)

I am currently trying to find a cassette and chainset to suit my new build. My current bike uses an 11-28t cassette with a 34-50t compact chainset. I find that the lowest gear this provides isn't really low enough for some hills and I find myself having to mash a bit. How much difference would using an 11-32t cassette with a 34-50t compact chainset give? I know the numbers - using an online gear calculator and it says at 70rpm I would drop from 6.8mph to 6.0mph.

I want something that is easier than what I currently have but also that isn't too easy such that it would never get used.

Alternatively I can go for a triple chainset (30/39/50) and an 11-28t cassette - what kind of real world difference would the 28/30 combination provide?

Also if I get the 32t cassette then I would need to get a MTB cassette and probably a MTB derailleur. Would these work ok with a 9 speed road shifter (say 105 or ultegra)?

I know I am asking a lot with these questions as they are somewhat subjective!

Thanks

Daven
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Old 11-21-09, 12:41 PM   #2
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Since you've done the gear calculations and have that info, there's really no good answer except for you to try different gearing and see if it works for you. No matter how many people chime in and say "here's the right gearing for you," the reality is that they're not riding your hills on your bike with your body with your preferences.

As for the mechanical question, yes, the nine speed rear road shifter will work with the nine speed Shimano-compatible mtb cassette and Shimano mtb rear derailleur. You will probably need a longer chain, make sure you can safely shift to the big/big combo no matter what gearing you go with-
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Old 11-21-09, 12:56 PM   #3
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Your gearing needs really are up to you and where you ride. If you have been happy with the 50 - 34 compact crankset then perhaps you should stay with that. And I agree with "well biked" above.

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Old 11-21-09, 01:35 PM   #4
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I suspected that that would be the response! Thanks for the useful information though. I am not 100% happy with the compact as I find the 50 never gets used as the gearing is just too high for the roads I use and the stop/slow/go nature of city riding. I would be happy if I could find a decent double that was 34-45 or something then I could use the 11-32 cassette. I really wanted the triple only to get the "39" middle chainring so I have something a little higher geared that also isn't too high!

I think one thing I may try is to get a similar gear ratio out of my hybrid so I can feel what it is like.

Thanks

Daven
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Old 11-21-09, 01:43 PM   #5
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"In for a penny, in for a pound." (I love saying that to a Brit.)

A road road rear derailleur MIGHT be able to handle a 32t rear cog, but I wouldn't count on it. As long as you are switching to a mountain bike rear derailleur (which will work just fine with road bike shifters), why not go to a 34t rear cog?
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Old 11-21-09, 01:47 PM   #6
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You should be able to put a 45 on the compact and a 33 small ring if you can find it. A triple with a 24t small ring will give you any gears that you might need. It's nice to get an 18 to 20 inch gear when yuou need it.
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Old 11-21-09, 01:47 PM   #7
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As an engineer, I like to consider the percentage difference in the gear ratios. A typical 1-cog change is in the range of 8-11%. I've used a 53/39/28 triple with a 12-25 for the Colorado mountains, but I now use a 50/34 with an 11-25 (11 speed). Over several years of riding in the mountains, I've apparently gained some strength, plus I chose to pedal standing on some of the extreme sections if I found my lowest gear to produce an overly low cadence when seated. My lowest gear is about like my old 28/21, so I've lost my two lowest gears.

Personally, I would not like the big jumps with an 11-28 10 speed, let alone 9 speed. If you have a short cage RD now, then a longer cage RD would be needed, probably an MTB model. To figure the change in the gearing between the 28 and 32, all you have to do is divide 28 by 32 to get .875. That means the ratio is 12.5% lower, which is a little larger than the average shift, but not excessive at the low end, where larger jumps are the norm.

A typical triple would have 53/39/30 setup to begin with. If it was combined with a 12-27, the low gear ratio would be equivalent to a 34/31 or 8.5% lower than what you have now. To go even lower, you could change the little ring to a 28T.
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Old 11-21-09, 02:01 PM   #8
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Just to clarify this is for a new build - I am just using my current gears as an example - I would prefer to buy the chainset off the shelf (i.e. not have to mess around with adding and removing chainrings). I too do not like the big jumps with the 11-28 10 speed I have currently, I always find I want the missing gear!

I was thinking about 34t on the cassette - but I figured it would add larger jumps again.

Thanks for the information - it is something for me to mull over tonight. I suppose a compact would be fine to use if only I could find one off the shelf with a 45/46 largest chainring. Otherwise I suppose I could just put one on!

Daven
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Old 11-21-09, 05:31 PM   #9
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Originally Posted by daven1986 View Post
Just to clarify this is for a new build - I am just using my current gears as an example - I would prefer to buy the chainset off the shelf (i.e. not have to mess around with adding and removing chainrings). I too do not like the big jumps with the 11-28 10 speed I have currently, I always find I want the missing gear!

I was thinking about 34t on the cassette - but I figured it would add larger jumps again.

Thanks for the information - it is something for me to mull over tonight. I suppose a compact would be fine to use if only I could find one off the shelf with a 45/46 largest chainring. Otherwise I suppose I could just put one on!

Daven
I faced a similar situation. Not needing any gears over 100 inches, yet wanting low gears to climb the steep hills where I live, and finding large heavy rear casssettes with big gaps in the gearing to be unacceptable.

The solution for me was a 21/30/44 mountainbike triple...

...with a small lightweight ultra close ratio 12-13-14-15-16-17-19-21 rear cassette. This combination yields seamless gearing witn no crosschaining from a 27 inch 21-21 low... to a 99 inch 44-12 high.

34-28 is 32.8 inches.
34-32 is 28.7 inches.

4 inches is roughly one gear shift... so if you can feel the difference between your first and second gear... that would roughly be same the difference between your present first gear and the new lower first gear. Personally, I wouldn't be able to stand having such a large heavy widely spaced cassette on my bike.

Last edited by oldpedalpusher; 11-21-09 at 06:30 PM.
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Old 11-22-09, 05:39 AM   #10
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Oh DING! That sounds perfect. Now my next question on which this whole endeavour hinges.

Can a MTB chainset be used with a triple road shifter and road derailleur?

Also does it matter if the chainset says "for 9 speed", surely it shouldn't make a difference if it is used on a 10 speed cassette?

Thanks


Edit: I made a little excel spreadsheet which works out the gear Gain Ratios (from Sheldon Brown) and using a 22/32/44 chainset with an 11-21 cassette I get 2 gears lower than I currently have (5% and 16%) and 4 gears higher than I get on my current small ring (1.5%, 8%, 15%, and 22%) which should suit me quite well Also if I stick with the middle ring then I get most of the range I was getting before and I can jump to the small ring / big ring when necessary.

Thanks for all the help - hopefully someone can answer the above compatibility questions too!

Last edited by daven1986; 11-22-09 at 10:27 AM.
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Old 11-23-09, 01:33 AM   #11
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Certainly get a triple crankset. You can switch out the standard inner 30 tooth ring for anything down to 24 teeth (except for the new 6703 Ultegra, which is limited to the stock 30 tooth ring). I use one of these with only two rings mounted on all of my bikes (one in the inner position and one in the middle position). The fast road bike gets 28 and 46 tooth chainrings, with an 11-26 cassette (10-speed).The touring and cyclocross bikes get 26 and 42 tooth chainrings with 11-28 or 12-28 cassettes (all 10-speed). Shifting can be done with standard road derailleurs, but you could use a MTB front derailleur if you're able to use a MTB shifter, or a barend / downtube shifter for the front derailleur (but not an indexed road shifter).

There's some info on cranksets like this in the Long Distance Cycling forum, just do a search for "Super compact."

Last edited by Chris_W; 11-30-09 at 08:42 AM.
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Old 11-23-09, 09:33 AM   #12
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Originally Posted by daven1986 View Post
Can a MTB chainset be used with a triple road shifter and road derailleur?

Also does it matter if the chainset says "for 9 speed", surely it shouldn't make a difference if it is used on a 10 speed cassette?
Generally, the answer is yes to both questions.

An MTB crank can be used with a road front derailleur even though the curvature of the cage isn't ideal. Shifting may be a bit less than wonderful but should be adequate. You will have to retain the road fd if you want to keep using road brifters. As an example, Trek factory installed an RX-100 (road fd for a 52T big ring) on bikes with RSX triple cranks that came with a 46T big ring and they shifted quite well.

"9-speed" and "10-speed" cranks differ so little that they can be used pretty much interchangably.
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Old 11-23-09, 10:07 AM   #13
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Thanks, after reading a bit of sheldon brown he says that rear derailleurs don't care how many speeds you have - which makes my life a bit easier at the back! I worry slightly about using a 44t chainring with a derailleur that says 50t, so perhaps I will get a slightly bigger rear cassette and use a standard road triple.

Thanks for all the advice. Now I have to go and ponder whether I should go completely custom or just buy off the shelf and customise it a bit! It all gets a bit complicated tbh!
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