Author Topic: 11-32 vs 11-34  (Read 21934 times)

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Offline salabes

11-32 vs 11-34
« on: April 16, 2014, 11:38:44 pm »
11-32 vs. 11-34
I'm hoping that some of the frequent and knowledgeable contributors will weigh in on their opinion. I'm 69 years old. At 65 I rode self-contained from Chicago to Boulder (1,250 miles) without too much trouble. I have stamina but lack power. In May 2014 I plan to attempt the TransAm east to west self-contained. My bike is a Trek 520. The current configuration which has served me well is:
   Years ago I swapped out the crankset for a 22/32/44.
   The cassette is the original 11-32
   Tires are 700 x 32c
Do I have much to gain by replacing the 11-32 with an 11-34 or will the benefit of a slightly lower gear be negligible. I'm thinking that with the low 22 granny chainring the benefit will be slight. Shifting has been smooth and I've had no problems. What do you think? Do I have much, if anything, to gain by going to an 11-34?
Thanks in advance.
George

Offline staehpj1

Re: 11-32 vs 11-34
« Reply #1 on: April 17, 2014, 06:27:59 am »
It is a personal preference thing, but...  I wouldn't bother.  Your 22-32 is low enough and two teeth on the rear won't make all that much difference.  If it actually did make the difference between walking and not (unlikely), the steepest climbs on the TA are in the Appalachians and worst case they are short enough to walk in a reasonable amount of time.

Offline John Nelson

Re: 11-32 vs 11-34
« Reply #2 on: April 17, 2014, 08:04:43 am »
Ride your 11-32 until it wears out and then buy an 11-34 to replace it. The difference is small, but every little bit helps.

Offline Cyclesafe

Re: 11-32 vs 11-34
« Reply #3 on: April 17, 2014, 09:33:42 am »
What they said.

But you might want to try an 11-36 (after you wear out your 11-32) if your rear derailleur is a long cage model.  As a practical matter, however, the difference will still be small.....

With your tires, a 170mm crank arm, and a "spin" of 80 rev/min a 22/32 yields 4.4 mph, 22/34 yields 4.2 mph, and 22/36 yields 4.0 mph.  As important is your second to the lowest gear combination of 22/28 (5.0 mph), 22/30 (4.7 mph), and 22/32 (4.4 mph), respectively.

Offline Pat Lamb

Re: 11-32 vs 11-34
« Reply #4 on: April 17, 2014, 11:44:18 am »
As John said, it'll make a little difference.  As Pete said, it probably won't be enough.  Get some Shoe Goo and put it on your shoes in Charlottesville so you don't wear the soles out walking before you get to Missouri.

Offline dkoloko

Re: 11-32 vs 11-34
« Reply #5 on: April 17, 2014, 01:31:55 pm »
You don't say how many cogs your bike has, 8-9-10 or what; that may limit which cassettes are available. If change, I would change to 12-36, not 11-34 or 11-36. Personally, I would use existing cassette, and not change unless I had to; but, since you asked, maybe you'll be more comfortable changing before you begin trip.

Offline mbattisti

Re: 11-32 vs 11-34
« Reply #6 on: April 17, 2014, 07:27:31 pm »
I have stamina but lack power.
You're a spinner.  If you have a long-cage derailleur, give yourself peace of mind and put a 36 tooth on.  You may be able to proudly tell your grandkids you never had to walk a single hill in the steep Appalachians.  We did (walk) with our loaded tandem with our lowest being a 34 x 24 (700 wheels).

Offline zzzz

Re: 11-32 vs 11-34
« Reply #7 on: April 17, 2014, 10:45:16 pm »
Hi George:

You haven't mentioned how much weight you're carrying and that has a significant affect on how low a gear you need.

22 up front and a 32 in back is an 18" gear, that's a really low gear. It's 1/2 the gear (38.4") that led mbattisti to walk his tandem up those hills. Frankly, if I had a low gear of 34/24 I probably would have been walking up that hill from Vesuvius to the Blue Ridge Parkway myself.

69 no longer counts as young but you've ridden a 1200 mile trip in the last 4 years, thats relatively recently so you got a pretty good idea of your abilities. If you're carrying under 40 lbs (a good ides anyway) I would think you'll be fine. Those hills are tough... but they're not that tough.

Pete

Offline mbattisti

Re: 11-32 vs 11-34
« Reply #8 on: April 17, 2014, 11:14:47 pm »
It's 1/2 the gear (38.4") that led mbattisti to walk his tandem up those hills. Frankly, if I had a low gear of 34/24 I probably would have been walking up that hill from Vesuvius to the Blue Ridge Parkway myself.


Recalculate. That's a 34 driven by a 24 tooth ring gear (should have typed 24 x 34 I guess)

Offline Patco

Re: 11-32 vs 11-34
« Reply #9 on: April 18, 2014, 12:38:01 am »
My touring bike has the same setup that you are contemplating (except I ride on 700X28's). I have elected to have low end gears I may not use versus high end I use on the downhills only. I haven't experienced the need to walk on the steeper and longer climbs....but that doesn't mean I don't stop for a break.

Offline mathieu

Re: 11-32 vs 11-34
« Reply #10 on: April 18, 2014, 03:11:09 pm »
If you have to ask this question, the best advice is: take 11-34.
As others have said, the difference between 32 and 34 is about half a gear change or -6% in speed at the same cadence. This doesn't sound much, but feels big in the lowest gear.

If you ride at 20 mph, the kinetic energy of your bike and body is about a factor of 20 higher than the energy input from one pedal rotation. If you stop pedalling for a moment the kinetic energy keeps you moving, speed drops slowly and as air resistance drops with the third power of speed, the speed drop is much less than linear with time.
But if you ride uphill with 3 mph, kinetic energy is only about half the energy input from each stroke and gravity weighs linear with speed (at constant gradient). Each pedal stroke has a sense of urgency and speed gets a sawtooth profile because the energy input is only substantial when the crank arms are near horizontal. This 'do-or-die' pounding of the pedals doesn't feel comfortable and doesn't look great.  The more rotations per minute, the smoother and more efficient the pedalling and the less the strain on body (knees) and mind. 

So why doesn't everybody opt for 34t? Well, there is a small weight penalty and the greater efficiency with faster pedalling stops at about 80 rpm. With a 22/32 combination and a 700-32c tires, at 80 rpm you advance about 2.0 m/sec (4.5 mph). At a gradient of 8 degrees, the altitude gain is 0.28 m/sec, which for a weight of 80 kg for rider+bike takes 220W (proportionally more if you are heavier or carrying an additional load). There are not many recreational cyclists around who can produce 220W power in steady-state, say over 20 minutes. Many will reach their limit at 175W steady power output. But those who can produce more power, are lighter or cycle lesser gradients, don't need 34t.

Slopes of  8 degrees is about the maximum you will see on the TransAm. Not in the Appalachians, but in the Ozarks. The Rockies and the Cascades are also less steep.
« Last Edit: April 18, 2014, 04:26:27 pm by mathieu »

Offline John Nelson

Re: 11-32 vs 11-34
« Reply #11 on: April 18, 2014, 04:26:35 pm »
Slopes of  8 degrees is about the maximum you will see on the TransAm.
I think you'll find a lot of people who would dispute that.

Offline mathieu

Re: 11-32 vs 11-34
« Reply #12 on: April 21, 2014, 08:54:36 am »
Slopes of  8 degrees is about the maximum you will see on the TransAm.
I think you'll find a lot of people who would dispute that.

John, there are probably few people who are more knowledgeable about the TransAm route than you, so I reverently give way. Still I tried to remember where those wickedly steep slopes occurred. Maybe in Kentucky, where the adrenalin from the many dogs in ambush drove me over the hills?

Did your remark take into account that I mentioned a slope of 8 degrees? More often slopes are expressed as the ratio of rise over run, which for an angle of 8 degrees amounts to a grade of 14%?

Offline staehpj1

Re: 11-32 vs 11-34
« Reply #13 on: April 21, 2014, 09:14:56 am »
Slopes of  8 degrees is about the maximum you will see on the TransAm.
I think you'll find a lot of people who would dispute that.

Did your remark take into account that I mentioned a slope of 8 degrees? More often slopes are expressed as the ratio of rise over run, which for an angle of 8 degrees amounts to a grade of 14%?
I don't know abut John, but I missed the "degrees" and thought "%" automatically.  Degrees seems like an odd way to express the steepness only because "%" is pretty much universally used.

Oh and based only on my impression of them...  The hills in Missouri climbing up out of the river valleys were pretty tough, but a few in the Appalachians definitely were harder for me so I'd assume they were steeper than the ones in Missouri.  Two that I remember were at Vesuvius and another that I think it was at Big A mountain.  Those were climbs for eastbound riders.  There were a least a couple others that seemed steeper to me than the ones in Missouri.

That said I don't have accurate numbers for any of them.  Furthermore I have decided that we seldom know the actual grades because the signs posted are often way off and even the maps can be pretty misleading.  Also the grades on smaller roads are generally extremely variable along their length.  So do you call the grade by a 100' section that is steepest, by the average from bottom to top, or something else?  In any case the numbers can be misleading wrt to the difficulty in riding them.

Offline John Nelson

Re: 11-32 vs 11-34
« Reply #14 on: April 21, 2014, 10:32:10 am »
I don't know abut John, but I missed the "degrees" and thought "%" automatically.  Degrees seems like an odd way to express the steepness only because "%" is pretty much universally used.
When I see someone give a road pitch in "degrees," I always assume they misspoke and mean "percent." Nobody, nobody, cites road pitch in degrees. So yes, I responded as if it said 8%.

With the exception of Kansas and eastern Colorado, the entire TransAm is hilly. There is no escape. Some of the hills in eastern Kentucky seemed insanely steep, perhaps only for 50 to 100 yards, but definitely made your legs work to maximum effort.

I don't place much stock in numbers to describe hills. On many 8% hills, there is at least one five-foot section that is 25%. Some people like to call that a 25% hill. The difficultly of a hill cannot be expressed by one number. In Colorado, you might climb at 6% for 30 straight miles. That's one kind of difficult. In eastern Kentucky, you might climb much, much steeper hills, each of which is fairly short, but there might be a hundred of them in a row. That kind of wears on you. That's another kind of difficult.

Clinch Mountain, near Hayters Gap Virginia, is regarded by many as the hardest west-bound climb of the TransAm. It's not that it's all that steep, but it the combination of steepness and length. Since I went east-to-west, I got to descend to Vesuvius, the hill where most west-bounders complain of having to stop frequently and let their brakes cool down. The psychological problem with both these hills is that they are very twisty and hemmed in with heavy trees, making it impossible to guess how far away the top is.

And yes, I remember well those Missouri river valleys, especially the valley formed by the Current River between Ellington and Houston. The Ellington park manager told me, "You got some hellacious mountains ahead of you!" Well, being from Colorado, I don't call them "mountains" but they were certainly difficult.