Originally Posted by
cyccommute
Let's look at this from the stand point of speed at 90 rpm and go back to my example. With a 3x7 system in the 46/24 gear at 90rpm, you'll be traveling at 14 mph. When you shift from the outer ring to the middle ring, say in preparation for a hill, if you maintain 90rpm the 36/24 combination give you a speed of 11 mph. You could maintain the same speed by increasing your rpm to 120 if you wanted to or had to. But the speed differential is small enough to that you'll slow down quickly enough and can maintain a comfortable 90 rpm.
With the double and a 10 speed cassette, in the same 24 tooth cassette cog, you'll be doing 13 mph. Changing to the 24 tooth inner drops the speed roughly in half at 90 rpm to 7mph. If you increase your rpm to 120, you'll be able to develop 10 mph and you'd have to pedal somewhere around 140 rpm to get to 12 mph. I can do 120 for a little while but 140 is just way too fast and too uncomfortable for even short times. About your only option is to let the bike slow down to around the 90 rpm range and just eat the loss of momentum.
If you go the other way...an upshift...let's say that you are tootling along at 12 mph at 90 rpm in the small ring for whatever reason (this will work with any speed in any gear combination but let's just pick one). That's going to be a 24/14. You upshift to the outer ring. If you could maintain the 90 rpm...you won't be able to...your speed would jump to 21 mph. In reality, you rpm would drop to somewhere around 50 rpm. That's mashing range. To get your rpm back up you'll have to either drop back down to the inner ring or make 4 downshifts on the cassette.
With the 3x7 system, you could be rolling along at 11 mph at 90 rpm in the 36/24 gear, upshift on the front to the 46 and you'd be at 14 mph while still maintaining an rpm of 90. In my opinion, I'd prefer a single upshift on the front chainring to an upshift on the front chainring and 4 downshifts in the back.
While the 10 speed system might be marginally better than an antiquated 7 speed system, when it is compared to a modern system or even to a triple crank and a 10 speed cassette, it falls far short. A 42/32/24 (or 22) 10 speed system would be almost ideal. It splits that 60% difference between the compact nicely in half.
I too go by pedal feel but I don't know of anyone who downshifts until they can't downshift anymore. Most people will learn that downshifting until you hit the largest cog on the cassette leaves them in a bad gear combination where further downshifting only leads to having to do high rpm to maintain speed. A bike drivetrain isn't linear like a car's drivetrain is. It doesn't take too much time to learn the difference and how to make better use of the bike's gears. You don't have to ride like you are in the Tour de France or like the bike is a car to appreciate a good gear pattern. My objection to the compact double idea is that the gear pattern are like a linear gear pattern in a car...just really poor versions of it. If you look at the speeds, the gear inches, the gear ratios or whatever is you favorite flavor of gear calculation, the compact double system is like two entirely separate drivetrains. It's got a high range and a low range and nothing in between.
That's the point to any triple crank, isn't it. You, with a double system, can only shift one time to go from high range to granny. It's a big 'KACHUNK!' and it goes from fast to slow. A triple has steps so that the rider can choose gears in between high and granny to fit the terrain they are riding.
Yep. Tighter ratios than a 3x7. But not tighter gear ratios than a 3x9 or a 3x10. Just fewer choices.
I think we are not debating gears, because I feel you think my gears are too high still for touring. This is simply a fitness issue. Every rider has different fitness level going into touring and typically the bike shop who sells a touring bike and knows about gearing ratios will look at the current bike the OP is riding and determine where the wear level on the chain rings and cassette. If the big ring isn't even close to even being worn out and that the middle ring and small ring teeth are shaped close to a shark fin, what does this suggest? The rider is needing more higher gears?!? But if the reverse is true and the 46T or 53T chain ring are worn more as well as the 42T or 36T and the 30T granny or 26T are barely touched. What does this suggest?!? The rider needs more lower gears?!? In touring, you would need more lower gears but that depends on the terrain and rider fitness. Most smart shops will want to see your current ride and determine the appropriate gears. The OP went to the shop and the owners suggested a 2x10 system rather than a triple. You don't suggest this unless you're sure you can make your customer happy, because suggesting other than the norm triple and if the customer isn't happy with the advice, the owner can become liable. If and when the 2x10 isn't suitable for the customer, the owner may have to install a triple possibly on his own expense. Why would a store owner be so stupid?
It's obviously now getting to a point that we are discussing what gearing we like and is no longer related to the gear ranges a 2x10 system can offer rather than a triple. As I said before, a less fit or a super strong cyclist would benefit from a triple without loosing the high gears either for ego's sakes or wanting to bomb down a hill maybe once in a blue moon with a 110 or 122" gear, because a 32/24T 2x10 double would be too limiting. A 36/24, 38/24 and 42/24T provide a good compromise with ranges similar to a triple while loosing 1 or 2 higher gears.
Like someone who said it correctly here. It's an evolutionary process and nun had said it well -- eventually, you don't even care which gears you're in or you're using. All you care about is being able to get from point A to B and having loads of fun.
Cheers.