thanks. I now have 2 dumb questions:

1. What's the circumference on a 700cc wheel? I want to do the math Plumb did above on the 650 to see if the 34-50 or maybe 36-50(?) would make sense for me. I went to a 12-27 on the back this year, and I liked it alot. It's hilly around here, and I would like to have something as easy (or easier) than the 39-27, but would also like no jumps in the gearing that gets me between 20 and 24 mph.

2. What the heck is a "fiple shift"?

mr mike. here is a gear inch calculator:

http://www.directleap.com/bicyclesource/bike/gear/gear-javascript.html

for speed multiply by.0003 and you will have the 100 rpm cadence. adjust as needed. i am not a mathemetician, but i belive this is close enuf for government work, as they say.

the "fiple" shift means that with no overlap available you must shift 4 cogs/teeth on the rear everytime you shift one ring on the front, if you want to access the nice line of ratios you have designed. see mike's chart. no skimping on this! you gotta hit it everytime or be spinning like mad, or blocked up in too big a gear at every transition from big/little ring. even more impoteantly from a nuisance standpoint - to aviod crossover you must do it right in the middle of the range, at the same speed everytime whether you want to or not.

I would have to agree with you in regards to a rolling course with lots of little hills where you spent all day between 16 and 23 mph. I am giving some serious thought to this gear ratio though. I usually ride in Florida. There I would probably never leave the 50 tooth chain ring in a race. When I head to Lake Placid every year, It seems like I spend over half the time in either my lowest gear or my highest gear going between 7 mph and 40 mph. I use a triple there now, because I am a certified nonclimber. I am thinking that a 50/34 might get me away from a triple. It would have a lot of potential in that case.

One comment that hasn't been made on this thread is that we are about to enter a 10 speed world. It seems like an 11-23 cassette would become more attractive with a 50/34. Effectively adding the 11 tooth cog to a 12-23 cassette would more than compensate for the 50 tooth ring, not give up anything in gear spacing, and provide a substantially lower climbing gear.

Maybe the real advantage of 10 speeds as opposed to nine is to make a 50/34 more attractive.

Does this make me a gear freak? Hope not.

Art,

I would be interested to know if you go with the FSA 50/34 set up. I am thinking of going this route my self. In your opinion how would this FSA 50/34 with say a 11/23 cassett work on a course like Kona. I am training for the Kona 1/2 Ironman in may.





Thanks...

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"You're guaranteed to miss 100% of the shots you never take" - Wayne Gretzky

I am certainly the wrong one to ask about Kona. The only way I get to Kona is if a rich uncle buys me a slot. I only have one uncle, and he isn't rich.

I am thinking seriously of giving it a shot, but don't hold your breath waiting for me. My triple works for me right now. I will likely sit back and wait for other's reactions.

My questions: How well will the front derailleur work? The new DA front derailleur is supposed to be stiffer, so maybe it will work well. Maybe not.

How good is the new DA 10 speed? Do you really get an extra gear, or just more crossover gears you can't use? Does picking up an extra gear and therefore an 11 tooth cog help? Don't know.

What kiind of course is it good for? The point above about requiring a lot of shifting in a course with small hills is a good one. Maybe on that kind of course you could be better served by swapping the 34 tooth chain ring for a 39 leaving you with a 50/39. I don't know if the FSA Compact comes with an available 39. I would imagine if it doesn't now, it would at some point be available from this manufacturer or others. When I have small rolling hills or wind issues now, i use a 53/42 which is essentially the same thing.

Specific to me is the question of whether a 34 chain ring is small enough without goiing to something like a 12-27. Probably not a problem with anyone else on this board, but I am old, fat and slow. I think if I can qualify for only two of those three adjectives the answer will be yes. I was hoping to no longer be old, but that isn't looking so likely, so I will to try to not be fat. Slow is a given.

Sorry, not a lot of wisdom here. Just a lot of questions.

OK, I think I have the math worked out, but would appreciate a once-over:

Speed in MPH=(Gear Ratio (Big/Little) x Cadence x 5,089.4)/63,360

This is for a 700cc wheel. Look about right?

Now, I need to determine gearing that gives me something at least as easy as the 39x27 that I now have as my easiest gear, and better fills in the gaps at 18-24 mph because the 12x27 gives me some big gaps there, which is my "sweet spot" (well, 24 ain't exactly sweet, but it's feasible for short stretches, sort of, hopefully, one day).

An incredibly good estimate if you are going at a cadence of 90 RPM is the speed is equal to the gear ratio (big/little) times 7 for 700c wheels and times 6.5 for 650c wheels.

I have ordered my set of cranks from Schwab in Colorado and should have them on the bike next week. I will be using either a new 105 deraileur and if that doesn't work will put on an Ultegra that I have. I actually have been thinking about buying a set since before the article, but the write up solidified the decision for me. I will let you know as soon as they are on and ridden. I was not so concerned with the deraileur issue as I was with the thought of having to pull a couple links out of my chain.

Brian

I figured out the formula a couple of years ago, and right now I am too tired to figure out exactly how I figured it out to explain it, but this is the formula I used:

((gear inches x 3.14 / 12) x cadence) x 0.0114



gear inches = front chain ring divided by rear cassette x wheel size

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Mike Plumb, TriPower MultiSports
Professional Running, Cycling and Multisport Coaching, F.I.S.T. Certified
http://www.tripower.org

  

This thread has interested me. I have a 12-25 and a triple chainring of 52/42/30. I calculated that I could replicate the 50/34 by putting a 36 as my small chainring. The only time I use the 30 is as a last shift when climbing a long tall hill. I’m usually all the way back on the rear 25 when I do this so I end up spinning up the hill (100+) and it seems hard to shift the rear derailleur back up a couple of notches because it interrupts my momentum. I rode last night and deliberately shifted to the 30 before reaching the rear 25 and I went uphill faster. So I ordered a 36 chainring and because I do like to ride the 42 but want a little more speed I also ordered a 44 for the center ring. This avoids the 16T jump by putting something in between. I will use the 52 just for the last 4 small gears for speed on flats and downhill. Yes, there is lots of overlap but do you really want to shift all the way back and forth on the back derailleur to use non-overlapped shifting.

By the way here is the full formula for speeds with gear combos:

Speed in KPH = (60 minute/hour* (Your tire computer setting) * cadence/minute (front derailleur teeth / rear derailleur teeth) ) / 1,000,000 mm/kilometer

Example: I ride 700X23 tires and my Cateye Astrale setting is 2097. This number is the manufacturers guess at what your actual tire riding circumference is, based on having your weight compress the tire against the road. Your weight creates a flat spot on the tire, which means it isn’t 700 mm in diameter (350 mm radius) anymore. So you can’t use 700 mm in your calculations. My cadence is usually 80 RPM. So here’s my numbers for a 52-12 combo:

(60 * 2097 * 80 * (52 / 12)) / 1000000 = 43.6176 KPH

To convert this to MPH multiply by .62137 or divide by 1.609344 the MPH formula is:

(60 * 2097 * 80 * (52/12)) / 1609344 = 27.1027 MPH

These formulas allow any tire size and cadence to be easily used. If you don’t know your computer setting it is easily found on Harris Cyclery (http://www.sheldonbrown.com/cyclecomp_f.html) . Also if you see a number for 700 and want to know what it would be for 650 just ratio 650/700 times that number for a quick answer.

JTee