Thursday, November 6, 2014

Poor Man's 1x Drivetrain And Other Mods

Recovering from my latest mountain bike injury left me with a weekend to kill and one good elbow, so I finally tackled a few projects that have been left decaying in a pile in the garage. The subject of this post will be changes made to the steed over whose bars I launched unceremoniously.

The 1x Drivetrain

One needn't read the MTB blogs much to see that the SRAM 1x11 drivetrain has gained considerable mindshare over the last couple years. The recent target of my fascination, the Kona Process 111 is a fine example:

There are several advantages to a single front chainring. A front-shift is far more violent and error-prone than a rear shift. I've broken a few chains by slamming the front and rear both into the granny, only to have the front ring get held up right as I'm approaching maximum torque. And no matter how well tuned your FD, you're sure to drop the chain on the inside once in a while. Other advantages include less gee-gaws on the bars, and significantly less weight. Indirectly related, a 1x setup is often accompanied by a clutched RD, which substantially decrease the risk of chain-slap and chain-wrap. Yee haw.

Of course the downside is also obvious: fewer gears. There are plenty of websites that cover the math, but with my Trek the stock gearing gives me a gain ratio of 42/11 (3.8) down to 24/36 (0.7). Replace the front triple with a single ring and, depending on the chosen chainring (I'm using a 30T) and that gain drops down to 2.7 to 0.8.

Now honestly I'm not doing a lot of longer trail rides on my Trek, so losing the high gears isn't a huge problem. But I am fat and slow, so I hate to lose the granny. So I'm also throwing on a 42T granny gear, which gives me back a 0.7 easy gear.

The Front Ring

I went 1x10 on a cross bike a couple years ago, but made the mistake of throwing a regular double chainring on. Imagine my surprise when, on the shakedown ride, the chain kept derailing. Turns out those are designed to derail.

SRAM's 1x rings are based on their X-Sync technology, which is designed not to derail. I bought a Chromag Sequence 30T ring.

Which will be replacing the old rings

The Rear Cog

I've been fascinated with apple "go-fast" green ever since I got my Volkl P40 F1s (with Energy Rail!). Just like the Volkl P9 single-handedly made chartreuse cool, the P40 has done the same with apple green.

So when I read this review (and this, and this) of the Oneup 42T cog, the fetching green was simply too much to bear. Not to mention going from a 36T granny cog to a 42T. So it ended up on my "to install" pile.

Adding a new granny means dropping the 17T cog. And since my bike came with a pie-plate, removing both meant the weight gain from the new ring was only 31 grams.

The Rear Derailleur

With the single chainring I may as well upgrade the rear derailleur. The newer generation of derailleurs have a clutch mechanism. This lets them swing backward easily, but not so easily forward. Thus nearly eliminating chain-slap. The price you pay is a tougher rear-shift, but this strikes me as a good bargain.

As usual Merlin comes through with a $60 clutched rear derailleur. With a single chainring, I went a little crazy, opting for the medium-cage.

XT Shadow M780 on the left, XT Shadow+ M786 on the right

Bash Guard

May as well add a bash guard, so I picked up a Hope 32-34T from Merlin.


Installing the bits went about as easy as such things always do. For some bizarre reason Trek opted to use Torx bolts instead of hex. WTF? Thankfully my recent torque wrench purchases included the necessary driver.
WTF Trek? Torx?
Dropping the three chainrings for one saves about 130 grams. Not that I'm counting.

I was able to install the new RD without using a new cable. Also salvaged the chain. Thank goodness. I left the front derailleur and shifter on for now, in case I decide to switch back to a double- or triple-chainring. After a few weeks, I'll take that off too.

Hope Bashguard and Chromag Sequence 30T. With a FD just cause.

42-teeth of apple green.

Shorter Bars

On one of the local trails I'm always threading through some narrow trees. So I decided to chop an inch off of each side of the bars. I used the Park steerer tube cutting guide and a hacksaw.

To be honest, with the benefit of hindsight, taking two inches off was too much. I should have started with maybe a half inch. Oh well. Go big or go home, right? Of course I was already home, so maybe I shouldn't have gone so big.

New Grips

When I bought my Trek it was already used, and the grips were pretty torn up. Oddly they haven't gotten any better over the last couple years.

So I bought a couple sets of ODI Rogue Lock-On grips, one for the Trek and one for the Lynskey. Only after the fact did I find that they're also available in green.

Oh well. Even in boring black they're still a big improvement over the old grips.
New Grips, Shorter Bars

The Verdict

Despite still nursing an elbow that won't quite straighten, I took my newly renovated bike out for a short ride yesterday evening.

The verdict? I'm very pleased with the shifting. I've got virtually the same granny that I had previously, and while I'm missing quite a few gears at the top end, the only reason I ever really needed the big ring previously was to combat chain slap. And the new rear derailleur takes care of that nicely.

The action is admittedly a bit stiffer when shifting up, due to the stiffer spring on the derailleur. Were I riding my mountain bike on a 300K brevet, I might choose to release the clutch. But for a typical 10-mile MTB ride, it really wasn't a big deal.

Dragging the chain onto the 42T rear cog was a delightful non-event. Now granted I've got the b-screw pretty much slammed, but that's what the b-screw is for after all. The shift across the missing 17T cog was slightly more eventful, with perhaps the occasional miss, but it was never a real problem.

And my goodness, the chain stuck on the front chainring like glue. SRAM really figured it out with their narrow-wide tech. This weekend I'll take off the now unnecessary front derailleur and shifter to finish the package. I see no reason to put the triple rings back on.

The new grips were fine. I really didn't even notice them, which I suppose is a good thing.

Now, the only real issue was my ill-advised decision to chop a couple inches off the bars. The bike was quite rideable, mind you, and I certainly never clipped the end on a tree. But I did miss the extra bit of leverage.


Max said...

You didn't tell us about the elbow on the phone last weekend! I think we are still at a 2 (you) to 1 (me) overall mileage ratio, though I'm working at closing that; on a miles per f**king oneself up, however, it is more like 1 (you) to 5 (me). Seriously. Ever consider bowling?

I love a blog post that includes a picture of Volkls. Not sure what else you were writing about; got hung up on reminiscences about the P9. That was a ski.

In the final analysis, all this apple-green stuff makes my overlarge collection of smooth-tire bikes look pretty trivial.

sam said...

The elbow was the inevitable result of a momentary lapse in judgement. Raining hard, but the dirt trails were still riding fine, so why not try a wooden feature? I deserve everything I got there.

How's this for a Volkl collection...

Unknown said...

Good stuff there on the 42t chain, er, cog ring. I would not have thought that possible with a standard derailleur unless I saw it. I see some new 1x11 cross bikes with a 44t up front and 11-28 in that's limiting even for a pro. Big honking range in back should take care of that.

How short are the handlebars? Pet peeve of mine; long handlebars; 635 max for me, we have trees in WI and, I watch some xc biking race videos; the "crouching spider" look is not good.

sam said...

Thanks for the comment Digger. Bars are now right about 630. They sure look stubby next to any other bike, but honestly I've gotten used to them already.

A few years back short bars were all the rage. Now it's long bars. Just like pedal styles (clip-in vs flat), everything old is new again.