How do you figure this out, and compare different gears? well, first you should know about the term "gear inches." A gear inch is how far the bike moves for every rotation of the crank (in metric terms, it's called "development" and is measured in meters). So not only is it dependent on the gears themselves, but also the wheel and tire size. One turn of the cranks in the easiest gear on a mountain bike might only move you 18 inches, while a road bike in the tallest gear goes around 10 feet.
Here is a site that I like, bikecalc.com. It has a few options on the left where you can see how fast you will be going at a certain pedaling speed and give you a chart of gear inches for a bunch of different gear combinations. That is what I used the most until I just recently came across this place. That site lets you compare two actual drivetrains instead of giving you a chart with every tooth combination. Here is my old mountain bike drivetrain compared to the new one:
The top scale is gear inches, while the bottom is speed at a pedaling cadence of 90rpm. There are a few things to take from these charts. First, you see that yes, the range of gearing with the single front ring is narrower, but not by a whole lot. Secondly, there's a lot of overlap on the second chart. Even though a 2x10 gives you 20 speeds, you actually only get about 13 unique ratios. Now, going to 11 doesn't seem like that much of a change.
But still, an 11-42 cassette loses range over a mtb double or triple chainring so you have to give up something. My new setup is fairly well centered, and I don't mind running out on the top end but that slightly taller low gear is noticeable on long, steep climbs. Dropping a whole pound off the bike and having a simpler and more reliable drivetrain was worth it to me though. Now here's another link to that same website, but I put in a smaller chainring and sram's 10-42 cassette. That 10t cog was really one of the big keys to giving a 1x drivetrain an acceptable range for the majority of riders, along with a derailleur that would work on such a big cassette. However, you need a special freehub body to use them, and I couldn't get one for my wheels so I lose out a bit.
The takeaways are to run things through a gear calculator if you're changing your drivetrain, and if possible use a sram XD freehub. If you have a sram compatible hub, you don't even have to stop at 11 speed. Now there is a 12 speed drivetrain that uses a 10-50 cassette. The GX version isn't even much more expensive than an 11-speed system, and is probably the best option for a new mtb drivetrain.
Here are the same two charts for my cx bike
On this setup you can see I get an easier gear, which was really needed. 36x25 on a steep forest road or singletrack climb is not particularly enjoyable and I would actually like to take it a step farther and go with an 11-36 cassette (or maybe even wider), Here's the comparison of 40x11-36. That would be pretty nice on the trails and long climbs, but what I have now is pretty good for racing. Even the 2x setup was great on a race course as the gearing was so close. I'd frequently shift the front derailleur and find myself using all the cassette in both rings. I don't recall ever dropping the chain either and that has already happened once with the 1x despite the clutch and narrow-wide ring.
Well, there's a bunch of quasi-useful gearing information and some good resources for comparing things. Here are those links again:
http://www.bikecalc.com
http://ritzelrechner.de
No comments:
Post a Comment