Wednesday, April 28, 2010

Choosing Cranks,
Figuring Out Single Speed Gearing,
and Riding Willowdale

I have a problem that a lot of people would kill to have. I am at risk of falling behind on ride reports, and there are even more potentially killer rides on the near horizon, so I guess I better get crackhead! (That's the expression isn't it?) But first I am going to answer a couple "reader questions" relating to those things I used to ride back in the day called the "Single-Speeds." Because I know you guys only come down here for my technological spouting (and, of course, my knowledge of James Bond films).

This from a Big Bikes reader who might be French and who might have a girlfriend nicknamed after a Martin Scorsese movie about the Dalai Lama:

Hey Dood,

Please help me with SS road gearing. I need to buy a SRAM crank. My project bike centers on a Madone frame and I have SRAM BB90 bearings.

Rival 39x53
Rival 34x50
S300 38x46
S300 48 - single ring

Which crank choice gives me the best ring to work with. I won't be hammering on the road but mostly riding with Kundun who will be on [her] Trek hybrid.

I just need a good place to start. Any help would be appreciated.


Blogger Big Bikes said...
Bonjour Jacques!

While any of those cranks will work just fine, I would lean toward the Rival crank with the standard road 130 mm BCD. The bigger the better, that's what I always say...when it comes to chainrings, and the 130 BCD will allow you to run as big a chainring as you like. Big chainrings mean slower wear as the load is distributed between more teeth and they just feel better when you turn them over — so smooth. That, and your drivetrain will look boss! Stupid people will think you are running a HUGE gear when they see that big frickin' ring and that enormous rear cog.

For casual cruising with your sweetie-pie Kundun, you probably want stay under 65 gear inches, for example: a 53 x 22 = (roughly) 65 in. But I would maybe go even lower, like a 50 x 21. To figure out gear inches you can either do the easy thing and google "gear calculator," or simply divide the number of teeth on your chainring by the number of teeth on your cog and multiply by your wheel size, which is roughly 27". Make sense?

Those cranks also let you run a ring on either the inside or the outside of the spider, giving you more options for chainline adjustment. (Which reminds me...I've been meaning to do a bit on chainline measurement, but it involves taking photos and thinking about how to explain semi-mathematical things which is daunting for me. We'll see if that ever happens.)

130 BCD chainrings are also the most common, so when you waffle one while trying to impress Kundun by bunny hopping your Madone single-speed onto a concrete planter after too many Dog Fish Head 90 Minute IPAs, you can lurch into your nearest LBS and buy a new one right off the shelf.


Although they are going the same speed on their singe speeds,
one of these guys is CRUSHING a 36 x 16 while the other is whirring a 34 x 18.

And this letter from a guy who actually has a birth certificate with the name "Skippolini" on it:

Hey Thom,

How's it goin? I would like to consult your ss expertise. I've been riding a 32x17 (26" wheels) for a couple of years now and wonder if that is correct for me. I typically ride Willowdale/Bradley Palmer near my house and do very well on the double track and fast single track. Howevahhhh, I generally get dropped on the single track. Obviously, part of this is do to my dorkiness and general lack of being fast on single track. But some of my friends think I would be faster if I went to a 19 or 20. Some think I should give up and start playing golf. I think my cadence definitely could be faster on the single track with a smaller gear and I certainly struggle on some of the climbs.

Anyway , I very much respect your expertise and as I was struggling to keep up with Raj today, it occurred to me to consult you. I would also love to have you come over for a ride in those woods. There are even more new single track trails that I think you would love.

What think you?

- Skippolini Delete

Blogger Big Bikes said...
I really did take Skip up on his offer to ride up in Willowdale and it was so worth it. That place is a twisty, smooth, flowy, speed-fest. "Ridiculously fun" as Skip says. It is also the location of the EFTA Weeping Willow race on May 23rd. I will be there.

Butanyway, the ride was also a consultation of sorts and it went well. On paper I thought that Skip was suffering from being over-geared and possibly bogged down in the singletrack, based on the fact that he was holding his own on the doubeltrack and fast stuff and getting dropped in the singletrack.

BUT when I got up there and started riding with him, he seemed to have no problem spinning through the singletrack, only getting bogged down on the steepest of climbs. Sometimes I think it helps to run a slightly larger gear in the singletrack, because it's like driving a car on twisty roads, wicked fast, in a low gear. You just have more control...but this only works out for you if you can really get on top of the gear coming out of the corners and eat up any rolling hills or technical sections without trouble.

By the end of the ride I realized that I was having a harder time holding Skip's pace on the fire roads than in the singletrack, and I was geared! What the crap? His leg speed was so high and so consistent that he just floated through the open sections. This lead me back to my initial, on paper conclusion, that he was over-geared and would benefit from going to a lower, that is LARGER cog in the rear, like a 32 X 18.

OK, I'll shut up now, see youz tomorrow...I hope.



CB2 said...

I think you're on to something here:
A weekly "Ask Thom" column.
Should I have soup or pizza for lunch?

Big Bikes said...

no pizza.
No...god this is hard.
How about Pizza-Soup?

Hey, you should come up and ride The Fells with Gary Fisher Saturday! Look for an official announcement with details tomorrow.


zencycle said...

Skipollini wrote:
"Some think I should give up and start playing golf."

I think we should all take up bowling

Anonymous said...

Dear Thom,

You recently started riding a geared bicycle. Are you selling out?

But seriously, I don't understand the whole single speed mtb thing. Is it similar to the urban messengers and now suburban youth who ride fixed gears instead bikes that would be better suited to their chosen activities, such BMX bikes, hybrids or geared road bikes? Or is there something that I am missing. While I was young enough to get swept up by the first fixed gear revolution in the late 90's I am now terribly old and unhip; my old and mature analytical mind tells me that the lack alternative gearing makes one slower.

Please Thom, help me understand. I just want to "get it."

Also will I gain some street cred if I convert to single speed. On the flipside, have you lost any friends or the respect of your family when you put the gears on your bike?


Hopelessly Old and Whooped in Cambridge

Big Bikes said...

Anonymous -

I just saw this comment, for some reason blogger isn't tellng me when I have new comments at the moment.

Oh, that's a Pandora's box of worms, it's gonna take at least a full post to answer that one.

I'll try to get to it next week.