Best Chain Ring?

[NEIL FROM BROOKLINE]

Hi everyone,
I have some questions on what size chain ring is most appropriate for me. I would appreciate the recommendations of the list. I have narrowed my choice to two options:*
•Truvativ Isoflow 22/32/42 (http://bikesmithdesign.com/Short_Cranks/IsoFlow.html)
•Truvativ Isoflow 28/38/48**
Whch of the above chain ring combinations would be best for me?

Here is some background:
•I plan to use the bike primarily for commuting & hauling heavy groceries & then next year for loaded touring.
•I am 5’11” & 170 pounds
•I am likely to purchase one of the following – Trek 520, Surley LHT, or Bianchi Volpe & mount the chain ring on one of these.
•I will use 700 wheels
•I prefer a triple chain ring
•I live in New England where long steep hills are abundant
•My knees are arthritic
•I will be riding the bike with short (145 mm) crank arms, which I will soon be purchasing from BikeSmith***

I have an additional question: how if at all does having short crank arms impact the choice of chain ring tooth combinations?

Thanks everyone!

Neil

* For the reader’s reference, I have settled on these two chain rings because they are the most affordable triples available from BikeSmith that will accommodate short crank arms
** Kindly note that I have the option to substitute a 26 tooth Shimano ring or a 24 tooth Sugino ring on the 28/38/48.
***Unfortunately, Mark at BikeSmith was unable to recommend a particular set of specifications for the chain rings.

[whittierider]

short crankarms, bad knees, steep hills, 700c, plus touring, shopping with big loads...I'd recommend the smaller crankset.

The short crankarms mean less torque on the crank but higher cadence, meaning your shift points move toward lower gears.  Contrary to urban legend, you do not lose power, only produce it differently.  Lab tests have proven the theory plenty of times.

[Tourista829]

For me, who use to live in West Newton, you can never go too low in gearing especially if you will be hauling groceries up long steep hills. 22-32-42 might be the way to go. I rarely have heard someone say, my gearing was too low, it is usually the opposite, not low enough.

[DaveB]

The most versatile gearing would be the 48/38/28 with the 24T granny substitution for the 28. 

What you haven't told us is what cassette gearing you are going to use as that has a major effect on overall gear range too.  An 11x34 or 12x23 are far different.

[NEIL FROM BROOKLINE]

The most versatile gearing would be the 48/38/28 with the 24T granny substitution for the 28. 

What you haven't told us is what cassette gearing you are going to use as that has a major effect on overall gear range too.  An 11x34 or 12x23 are far different.

Hi Dave,
Thanks for your reply. My thought had been (for no good reason other than cost savings) to use the cassette provided with the bike by the manufacturer. In the case of the Surly it has an 11X34, the Trek has 11x32, & the Bianchi has 11X32.  Will they match well with chainring combination that you propose?
Best,
Neil

[BrianW]

Did you peruse the FAQ on BikeSmith's site? They have some good comments, as follows:

What size chainrings should I get?

If you are getting spun out in high gear now, using the same gears with the shorter arms may fix this. For most riders, dropping 4 or 6 teeth on each ring seems to work well. If you currently use low gear far more often than high gear, you will want to use even smaller chainrings and/or a bigger cassette.

Most people with 26" drive wheels are going from 30-42-52 to 26-36-46 or 24-34-44. Faster riders are using 24-39-48. A few have gone to 22-34-42.

When I shorten Shimano 105s & Ultegras, about 1/3 of the owners have me install 24-39-48 FSA ramped and pinned rings to replace the stock 30-42-52 setup. Cost = $84

It's not unanimous, but a large majority of riders with 20" drive wheels and shorties do well with standard "Road Triple" gearing of 30-42-52.

http://bikesmithdesign.com/Short_Cranks/short_cranks_faqs.html

[paddleboy17]

The most versatile gearing would be the 48/38/28 with the 24T granny substitution for the 28. 

What you haven't told us is what cassette gearing you are going to use as that has a major effect on overall gear range too.  An 11x34 or 12x23 are far different.

I don't know why you think that a 48/38/38 is more versatile.  Yes, I disagree but I am curious about your reasons.

For a person with torque issues, you can never have too low of a gearing.

Support for big cassettes is really a function of the rear derailleur.  If you have a long cage derailleur that covers the range of the big cassettes, it does not matter what you have for a crank.  You do have to pick the right chain length, but that is what happens when you integrate a particular crank and cassette.

[NEIL FROM BROOKLINE]

Did you peruse the FAQ on BikeSmith's site? They have some good comments, as follows:

What size chainrings should I get?

If you are getting spun out in high gear now, using the same gears with the shorter arms may fix this. For most riders, dropping 4 or 6 teeth on each ring seems to work well. If you currently use low gear far more often than high gear, you will want to use even smaller chainrings and/or a bigger cassette.

Most people with 26" drive wheels are going from 30-42-52 to 26-36-46 or 24-34-44. Faster riders are using 24-39-48. A few have gone to 22-34-42.

When I shorten Shimano 105s & Ultegras, about 1/3 of the owners have me install 24-39-48 FSA ramped and pinned rings to replace the stock 30-42-52 setup. Cost = $84

It's not unanimous, but a large majority of riders with 20" drive wheels and shorties do well with standard "Road Triple" gearing of 30-42-52.

http://bikesmithdesign.com/Short_Cranks/short_cranks_faqs.html

Hi Briwasson,
I want to make sure I understand your terms:
1) by "high  gear", I assume that refers to the largest chainring?
2) what is meant by "spun out"?

Also, I do not understand the recommendations that the Bikesmith website makes above for gearing. Can you please clarify for a non-expert (please note that I am seeking 700 wheels)? For example, the webpage indicates that purchasers who buy smaller crank arms often seem to buy smaller chain ring combinations?
Thanks,
Neil

[whittierider]

2) what is meant by "spun out"?

It is a condition where you are going so fast that even in your highest gear (ie, biggest ring and smallest cog), you are unable to pedal fast enough to put any power into it.  There is a wide range of what people consider to be the threshold of being "spun out," from maybe 110 to over 160rpm.  (For those who don't think it's possible, see this video.  The frame rate isn't fast enough to measure the cadence, but I've heard of over 300, and done over 200 myself although it would be too unstable at 70mph.)  In touring, spinning out is not really a concern.  If wind and hill enable you to go that fast (30-70mph), you can just coast and you will still get there, and you won't even lose much time.

the webpage indicates that purchasers who buy smaller crank arms often seem to buy smaller chain ring combinations?

That makes sense.  Your foot speed in meters per second tends to remain the same as you change crankarm sizes (lab tests prove this); so a shorter crankarm, although it translates to less torque on the crank, also results in higher cadence.  Power output is torque times cadence; but the lower ratio of torque to cadence that you get with shorter crankarms means it will be natural to use lower gears.

[BrianW]

Generally speaking, there is an inverse relationship between wheel size and gearing size. So, a 26" wheeled bike will need a larger chainring than a 700c wheeled bike would to maintain the same speed, all other things being equal (rear cassette, etc.).

[DaveB]

I don't know why you think that a 48/38/38 is more versatile.  Yes, I disagree but I am curious about your reasons.

You didn't pay attention to the rest of the sentence which said: with the 24T granny substitution for the 28.

The 48 to 24 range is the widest the OP could have and provides the potential for a suitably low low gear with a suitably high high gear. 

When I posted my comment, I didn't know he has a 11T small  cog which will probably give an unnecessarily high top gear (118 gear-inches) with the 48T big ring.

[paddleboy17]

I don't know why you think that a 48/38/38 is more versatile.  Yes, I disagree but I am curious about your reasons.

You didn't pay attention to the rest of the sentence which said: with the 24T granny substitution for the 28.

The 48 to 24 range is the widest the OP could have and provides the potential for a suitably low low gear with a suitably high high gear. 

When I posted my comment, I didn't know he has a 11T small  cog which will probably give an unnecessarily high top gear (118 gear-inches) with the 48T big ring.

I did pay attention to the rest of sentence, you just failed to justify your statement.  Now you have. 

I still might not completely agree with you.  It has been my experience that riders that are torque limited, and by torque limited I mean that there is a limit to how much torque they can deliver because of their knees, cannot usually take advantage of the high end that a 48 big chain ring provides.    I would still steer them to a compact mountain crank, a 22/32/42.  My reason is that when you swap out the small cog, like you suggested, that the shifting can be a little rough. I also think that the torque limited rider might pefer to have a 22 instead of a 24.

I guess it comes down to how much of a low end the rider really needs, and how much of the high end they are will ing to give up to get that low end.

[whittierider]

When I posted my comment, I didn't know he has a 11T small  cog which will probably give an unnecessarily high top gear (118 gear-inches) with the 48T big ring.

Ah yes, 118" is much higher than you would need in touring.  When I set up my touring bike years ago, I put a 91" top gear on it (45/13).  As a real spinner, I seldom used that gear.  But I did spin it up to 45mph once drafting a truck.  118" is a gear I never use below 37mph.  It's just not needed for touring.  You might as well trade the smallest couple of cogs for ones that fill in the cruising range better to get smaller jumps between gears.

[DaveB]

  I would still steer them to a compact mountain crank, a 22/32/42.  My reason is that when you swap out the small cog, like you suggested, that the shifting can be a little rough.

I've substituted 26T granny rings for the OEM 30T ring on numerous road cranks over the years.  The shift from the 42 to the granny is still good.  The only sluggish shift has been from the granny back to the 42 and I'm never really in a rush for that one.  A 48/38/24 crank should shift at least as well as my 52 or 53/42/26 cranks.

The OP's use of an 11T small cog does give him a 103" high gear with a 42T "big" chainring so that is a useful combination as you noted.   My only objection to a cassette with that wide a range (11x32 or 11x34) is that it leaves huge gearing gaps between the middle cogs where you spend most of your time.

[paddleboy17]

The OP's use of an 11T small cog does give him a 103" high gear with a 42T "big" chainring so that is a useful combination as you noted.   My only objection to a cassette with that wide a range (11x32 or 11x34) is that it leaves huge gearing gaps between the middle cogs where you spend most of your time.

You do raise an interesting point.  Unfortunately, most clusters have gears rivetted to a metal spider and you can not change the gear combos.  This could be an argument for 10 speed gearing. 

Does anyone know if 10 speed gearing has found its way onto touring bikes yet? 
Are 10 speed chains tough enough for touring?