Originally Posted by
pacificcyclist
I personally think that this discussion is turning into my triple is better than your double and double is terrible. Whereas the double camp says otherwise.
No this discussion is turning into a "I'm more manly than you because I ride a double" discussion as most gearing discussions do. More on that a little further down.
Originally Posted by
pacificcyclist
First of all, I have toured with a triple. It's funny that nobody recognized the Sugino Super Maxy triple crankset. It's an OLD SCHOOL triple crank known for its good quality in the 80s so you know how long I've been touring. It's 110/74BCD which means, it is a triple not a double. Not sure what so many people here think that with a 110/74BCD, you can not choose a lower gear. Mounting a 24T on the 74BCD is as low as you can get it on. Anything lower than a 24T needs a mountain triple crank!
Yes a Sugino Super Maxy is very old school. Like 1982 old school. We've moved on. A 110/74mm BCD is okay but they were mostly obsolete by 1995. A better choice from 1995 is a 94/58mm BCD which allows for a extremely tiny 18 tooth inner ring.
And what's the problem with going to a mountain triple? I have several. They work very well. Mountain bike cranks came out of touring cranks in the mid-80s. The Avocet Touring Triple was the first affordable crankset to offer a 24 tooth inner ring. They were quickly followed by the Sugino AT (better than the Super Maxy) and others. Both were available before mountain bikes. Then the mountain bike arrived on the scene and started using the touring cranks and then started refining them for lower and lower gears to meet the needs of mountain bike hill climbing. Touring bikes have benefited from the cross pollination.
Originally Posted by
pacificcyclist
There seemed to be a confusion that all double cranks are all a like. This is completely false. A road double crank is a 130BCD and the smallest ring is only a 39 or 38T. A compact crank is a 110BCD and the smallest ring you can fit on is a 34 o 33T. A mountain double crankset that can be adapted to road touring comes either a 45T/28T or 40T/28T.
Nope. No confusion that I've seen. A "compact" double is short hand for a 110mm BCD double crankset. A "road" double is short hand for a 130mm BCD double. Most everyone I've seen so far has been consistent. Mountain doubles are relatively new and just started to filter below the XT/XTR range. Most people that I've seen aren't usually running that level of components on their touring bikes.
Originally Posted by
pacificcyclist
The double crank we are taking about in the double camp is NOT a standard crankset unless you buy a Rene Herse double crank from Compass cycles (Jan Heine's company) or you make your own with a 110/74BCD triple crankset turned double. We call this a touring double or mountain double but this confuses with the SRAM double that comes standard on the Salsa Fargo.
With a touring double, 42T/24T or 40T/24T is possible. Compared this to a stock 46T/36T/24T or 26T Sugino triple crankset (XD-600 or 500 or equivalent) and the 42T/24T, you have exactly the same low gears as a triple, because the triple has the same chain ring in 74BCD as the touring double. I don't understand why there are so many people here still think a touring double with a 24T chain ring can not give the same ratios as a triple with the same 24T as its smallest chain ring. Math I suppose must not be their most strongest subject in high school. There is no difference in low gearing performance between a triple and a touring double.
You are missing the point. I know that a 24 tooth chainwheel will give the same ratios no matter how many other chainwheels are on the crank. To imply that we don't understand the math is, frankly, insulting. My objection to doubles is the
other gears that are missing. The doubles have a similar range...the ones you referenced above have a 28 inner not 24...but they don't have the same spread. A touring bike with a compact double or even a mountain triple has huge gaps between the upper and lower range. Mountain bikes tend to be ridden as if they have 3 separate drivetrains but the rigors of off-road riding dictate that kind of usage. A touring bicyclist uses the drivetrain more like bud and I have detailed. More a double with a bail out low gear.
Originally Posted by
pacificcyclist
There is absolutely NO problems climbing a 18-22% grades with a 19" gear unless you need a 16". But then, you will need a 20T small ring but that's available on a mountain triple crankset as the 74BCD can not take anything smaller than 24T.
A touring double is not recommended if
1, You need a 48T to 53T chain ring (apparently some people think they need and can go fast with a 48T or 53T or 120" + with 4 panniers)
2, You need a 16" gear or lower where a mountain triple crankset can accommodate
But these are the 2 extreme cases. It's like telling someone you need 4 spare tires on a car because it's likely all 4 tires can go flat. That's true, but how often that's going to happen?
And now to "I'm more manly" part and my largest objection in any gearing discussion. Neither you...nor I, for that matter...get to decide whether there are "NO" problems with climbing
any grade in
any gear other then how it applies to us individually. I have no opinion if you have no problem climbing an 18-22% grade in a 19" gear. But, by the same token, you
can't have any opinion if I climb the same grade in a 16" gear. It's not your place to judge. Nor is it your place to judge if I need, or can, go fast on a downhill on a loaded bike. Just as it is not my place to judge your downhill speed. Personally, I don't consider having a range from 113 to 16 gear inches to be that extreme. I can go stupidly fast on downhill and climb to the top of the same hills without wrecking my knees.
Originally Posted by
pacificcyclist
We can speculate on extreme cases, but I think the majority of cases people are just going to use what ratios they want. Triple is a no brainer because it got all the ratios, but a double is sometimes a necessity for people like myself who has a double shifter and is a huge expense going to a triple because I have to change shifter, front DR when I can just change to a triple crankset 110/74BCD which in my shop happens to be bountiful (people upgrading to fancier inboard cranksets) so it lowers the cost. With people doing this and seeing them last year on tours goes to show that a touring double is feasible. But sometimes, it's just not everyone's cup of tea.
Let's get back to jisho's original question
Originally Posted by
jisho
I'm currently in the preliminary stages of building a touring bike. My thoughts for the drive train include a Shimano XT 10 speed setup. The LBS guy advised that I should go with a double as with this setup the ratios are the same as a triple if one gets the rear cogs right. I haven't done the math and wonder if this is true? Any advice would be helpful.
Can he get the same ratios with a double as with a triple? My answer would be no. He can get the same range. But he's going to be missing ratios in the middle of that range that make the transitions from high range to low range smoother. No choice of cogs or chainwheels is going to change that.