Monday, March 18, 2013

How far can 1x drivetrains go?

As I've noted before, I think front derailleurs are dead. There's still some controversy about this amongst mountain bikers but I think in a few more years it will be rare to see a front derailleur on a high end mountain bike. I could be wrong.

I was recently interviewed (though I don't think they used any of my gibberish) for BRAIN about whether or not I thought single chainrings would become popular for road/cross bikes as well, which honestly I hadn't thought much about. But when I did think about it, I'd be surprised if we didn't see some form of 1x road drivetrain soon, because it makes a ton of sense:

-Let's assume you want to get at least as much gear range as a typical compact double - for the sake of argument, that's a 34/50 chainring combo in the front (note that a non-compact crankset is inherently going to have a *smaller* range of gears) and an 11-28 (the widest ratio commonly used) in the back.  That's a (50/34)*(28/11) = 3.74:1 overdrive (meaning the highest gear is 3.74 times the ratio of the lowest).

-Now assume we don't want to lose any of the top end, so we need a top gear that's equivalent to 50x11 (or 4.55:1). If we're using something like the XX1 cassette (with a 10t as the highest gear on the cassette) then we'll need a 46t chainring (rounding up to be conservative).

-Let's also match the lowest gear - 34x28 (or 1.21:1). That will mean our easiest gear will be 46x38 - actually a considerably smaller cog than the existing 42t on the XX1 cassette. So the total range can easily be achieved.

-The downside, of course, is the gaps between gears. With an 11-28 Dura-Ace 11sp cassette, the gearing looks like this:

So our biggest gaps, percentage-wise, are the 15-17 and the 25-28 which are 13/12%.

Contrast that with an XT 10 speed cassette:

Now, we're going to add a 10t, and then jump up by 5 teeth after the 28th (so 10, 11,13,15,17,19,21,24,28,33,38) to minimize gaps and still get us the range we need, but we now have some big gaps: 11 to 13, 28 to 33 (18% each, roughly).

For folks who don't need as big of a range, you could go to a 10-34 or even 10-32/30 depending on your local terrain and needs, but there's no question that the gaps between gears are going to be bigger if you throw away the front derailleur.

-So the gaps between gears are about 50% bigger through a significant portion of the range of the cassette. For recreational riders or folks who aren't super cadence sensitive, this probably isn't a big deal and getting rid of the weight and hassle of the front derailleur is most likely worthwhile. For very serious racers or time trialists, or someone who wants both a big range and tight gears, the front derailleur will probably stay.


NickS said...

Totally disagree.

I know this will come to market for the weekend rider and will probably be adopted for cyclocross, but any cat 2 or higher road rider racing will tell you they want closer ratios not huge jumps between sprockets.

Most people buy their bikes and equipment because they see the pros riding it. That's why most people ride standard cranks and not compact, and why most won't ride a single ring up front and huge range out back. It doesn't work for the pros and most people want to be the same as the pros.

Walt said...

Yeah, that's why I said "not for very serious racers" in the last paragraph. :)

NickS said...

Yeh missed last para, the kids pulled me away and when I came back to it, I started commenting straight away without finishing reading.....


Meriwether said...

Cross has been 1x for years and it is way better IMO than 2x. Just makes a ton of sense for all conditions if you can keep the chain on with guides.

A 1x ring would be great for cross bikes, i bet you'll see such an "XX1" type 39t and 42t ring very soon for road cranks for cross use. (In fact, i just googled it and SRAM has a proto already.)

The bigger gap is no biggie in cross either, almost a good thing since you only shift when you really need to in my experience and a big jump can be a good thing.

I know nothing about road, except that it's in between the trails.

The guy doin' the thing said...

You can have my front derailleur when you pry it from my cold, dead hands!

The guy doin' the thing said...

you can have my front derailleur when you pry it from my cold, dead hands!

Feldy said...

I couldn't find it, but Shimano has a patent out there somewhere for a 16 speed cassette. Instead of having inner and outer links like a normal chain, the outer links are super narrow and the inner link is solid and curves around the outside of the teeth (it's U-shaped). So, that sort of system could potentially solve having no front derailluer and not having big steps at the same time.

Anonymous said...

sorta on topic but have you seen the pinion transmission 18 speed? it's all in the bb/crankset. it requires a special frame. it's a step in a different direction.

Walt said...

I think gears/cassette is probably not going to get replaced by any kind of alternative transmission system, because they all suck for efficiency no matter how you set them up. For the road, that's not going to be acceptable to anyone. For commuters, a hub gear or BB/crank gearing system is great.

NickS said...

I'm with "the guy doin' the thing"

On all bikes except cross, I'll run a front mech.

I prefer a MTB with a triple and 11/28 over a new 2x10 with 11/36

Chris said...

It's 14 sprockets, Feldy, not 16.

What I want is an electronically shifted, wide range (400%+), 8 speed, narrow Q version of the Pinion 18 speed gearbox.

Jase said...

Wow, I hadn't heard of the Shimano 14 speed before.

I'm hoping we see a resurgence of the Capreo style system. Mountain bikers are using this already in their 1x drivetrains, but if it's range you are looking for (tourers for instance), imagine a 9-42T cassette!