I came up with this cool idea for a new bicycle lock. I call it a drivetrain lock (or drive lock for short).

Basically you take a very small padlock and attach it to your bike's chain. This prevents the crankset from fully rotating, which means the bike can't be ridden away. This pretty much eliminates the use of the bike as a getaway vehicle.

Lots of useful situations:
1. It works great for messenger use or errands. For all those times when you have to leave your bike within site but unlocked.
2. It's also really useful if you put your bike on the front rack of a city bus. Use a drive lock first, and it will stop the "grab and ride" thefts of opportunity.
3. It also makes a pretty good supplementary deterrent for short-term use. Like if you only have a cable lock and need to stop in a store for a few minutes.
4. Or for locking up while you are at work or school. In downtown or high-crime areas, a drive lock provides one more barrier of resistance (in addition to a U-lock and cables).

The lock I use is made by Masterlock (model 121T). Most chain drugstores like Walgreen's sell them for $6. You can keep it on your keychain since it attaches as one piece.

Hope everyone likes the idea. I always get a lot of interesting comments from people when I use it. Most have never seen anything like it before.

A few notes I wanted to mention:

On Single-Speeds and Fixed Gears:
On a single-speed bike, it will flip the chain off the bike. On a fixed gear bike, it will not even allow the bike to be walked.

Placement of the lock:
You can place it anywhere on the chain, but it seems to work best if it is at the bottom. When the pedals turn, it locks up at the rear derailleur. If you place it on top, it could go into and damage the front derailleur.

Keeping Your Chain Clean:
Drive locks work best when keep your chain clean. Otherwise your hands and lock will get dirty. The best lube I've found for this purpose is T9 by Boeshield. It doesn't pick up dirt from the street, so your chain stays very clean.

Places to buy:
Most chain drugstores like Walgreen's sell the type by Masterlock (model 121T). Other places to look are hardware stores like Home Depot, travel stores (as luggage locks), and student bookstores (as backpack locks). It would be cool if some of the big companies like Kryptonite would make a bike-specific drive lock.

Um.

Looks like a huge opportunity to break something in your drivetrain. And I can't see it being all that much quicker than a ulock. And on my bike it would be WAY the heck dirtier (my drivetrain is NOT clean).

Also I'm a bit skeptical of your claim that it won't let a fixed gear be walked. I suspect it would just go around the chainring while doing damage to the lock or the chain or both.

I wouldn't bother with it if your bike is left outside all day. Whatever tool a thief uses to cut your other locks will make short work of that little one. Great idea for bus racks, though!

I think that's innovative for a low-tech, low-cost deterrent. I would, however, be inclined to paint mine some eye catching, brightly fluorescent color so it is immediately obvious to would be thieves that there's something there.

Sorry, dumb idea.

Beyond the possibility it could damage expensive bits, one could still walk it away quite easily. And it does nothing to prevent a lift-and-carry theft.

Besides, give me a minute and a chain tool and I'll ride your nice Bianchi away leaving your silly little "Dear Diary" lock behind.

Edit: Oh, wait a minute. SRAM rear dérailleur on your Bianchi. Betcha it even has a PowerLink on that chain. No tools required to defeat your lock.

I think you're being a little harsh, the OP was suggesting it as a "slow down the thief because I'm standing somewhere nearby" not "going into the office for 8 hours" lock.

However I am 100% certain that if I used that method I would one day forget it was there, hop on, and inflict some expensive drivetrain damage on my own bike .

Interesting, but wouldn't work for me. I use Phil Wood's Tenacious Oil on my chains. Only time I want to be touching my drivetrain is when I'm cleaning it and have gloves on. Also, I use power links on all my chains.

I like the innovative thinking, BUT....

I don't even lean my bike on its right side. There's no way I would ever, ever, ever put something on my chain that's intended to jam itself into the rear derailleur.

Yeah, I'll be the first to admit that this type of lock has some obvious disadvantages. However if you commute every day, there are lots of situations where you have to leave your bike unattended for "just a few seconds" while running errands. The cost of losing my bike for me is bigger than any of the potential problems with the lock.

The most obvious flaw is that is has the potential to damage your components. This really can only happen if someone gets on your bike and tries to ride away with it. It's kind of like choosing between having no bike and a bike with damaged parts. (If you place the lock at the bottom of the chain, you only get a half turn of the cranks which is not that much leverage. Realistically it's not going to do much damage.)

Another flaw is that a theif can just cut the lock with bolt cutters. This requires them to turn the bike upside down- anything that risks attention they might choose to avoid.

Another flaw is that someone can still walk off with the bike. A drive lock at least eliminates the quick getaway- one of the main reasons it's so easy to steal bikes.

And finally if your chain has a MasterLink, they can just disconnect that. This is true, but without a functional chain they still can't ride the bike.

I think it's a good concept- a lock that prevents a bike from being ridden. In Japan, they use the O-lock (which bolts the rear wheel to the seat stays). They do this because there are more bikes than bike parking spaces. Ideally Kryptonite or some other company would make a rectangular shaped drive lock that attaches flush with your chainlinks. No boltcutters could defeat that.

Take care guys.

I could see a theif not noticing the tiny lock,jumping on your bike,and then riding away only to tear up your drive train. Better to add a streamer or maybe a thin cable run around the seatstay.

Actually,you're really better off doing a proper lock-up. It drives me nuts when I see people freelock their bikes. Reminds me of the people who have to have the parking spot by the mall entrance because they don't want to walk a few yards. Take the time to lock it proper and it will be there when you get back.

I don't see this being a great idea for us urban commuters although I understand Halo's scenarios for its use. I would hesitate to rely on a padlock that was thin enough to fit through the chain since it is so easy to cut with a large pliers or very small bolt cutter. Even as an extra deterrent in the commuting scenario it wouldn't be that great.

I looked at it and thought it might be a good idea for bike tourists who don't want to carry full U-locks. If I were to use it while touring I would use a little larger padlock that I could run through the bottom of 1 or 2 chainrings and hence around the chain. That would certainly stop a ride off, but it would not stop someone walking off with the bike or tossing it in the back of a truck. Again I would not use it in an urban center but if I wanted to stop for a short bit, it might be a decent idea in conjunction with a light cable lock.

You want harsh? Step out of Starbucks or wherever and find your bike gone. That's harsh.

The OP demonstrates his lack of knowledge about something as simple and low-tech as chains with his statement:

Um, if it is a master link, wouldn't I just reconnect it and ride off? And if I have to use a chain tool, I carry spare PowerLinks with me at all times. I wouldn't even have to mess around with replacement pins. Under a minute and I own your bike, leaving your cute little lock behind.

Sorry if anyone thinks that's harsh. Sometimes life outside Podunk or Lake Woebegone is harsh. Me, I'd rather lock properly and ride my own bike, rather than supply my bike to someone else.

What? Why would he have to turn it upside down to cut that little lock?

I don't see how this would be quicker/easier than using a u-lock and freelocking through the frame/wheel. Just using a cable lock to attach it to something immovable is better than this. (well, that's all I do, but that is based on this town, and my POS bike)

edit: Maybe something that locked the crank to the frame - but then you still have the possibility of the wheels being swiped.

Would be better off just putting the lock through the sprocket/chainwheel/chainring and around the chain at the bottom inline with the crank arm to prevent thieves from riding off or getting a bolt cutter in there easily. Won't stop the lift and carry thief or the people that just want your rims/wheels or other easily removable parts.

Let's face it...if your bike is targeted, thieves will find a way to steal it or the parts quickly and many either carry the tools they need or find the tools right on the bike. Plus it really doesn't matter if your bike is a low end or ultra high end bike or a rusted hulk...it's all fair game and a sad reality in today's society.

I don't think it's visible enough to be a theft deterrent. It's so small, you might even forget it's on there. Then all of a sudden -- CRUNCH, you mess up your crankshaft or chain.

Plus, most people's chain's are dirty. Hence the lock and your fingers will be really dirty.

Don't bother patenting it. I did that as a kid back in the early 1970s.

Outside of the US they have locks that ace circular and attach to the seatstays. they clamp aroung the rear wheel preventing it from turning. The do work to prevent rideoffs but do nothing to prevent someone from picking the bike up and walking oss with it; to remove the lock later and at thier convience.

Look at the seat stay and you will see one.

A better idea would be to get a U-lock just long enough to route around the crank arm, both chainstays, and the spokes of the rear wheel. If it was just that long, and no longer, you'd lock the drivetrain and the rear wheel.

I would love to see this become popular, it would mean that my properly locked up bike would be that much less attractive to a thief when its surrounded by bikes 'locked' like this.

I have one of those on my Breezer and I use it along with a good U-lock and a cable for the front wheel.

I have recently been using a small cable type gun-lock through my rear wheel and around the chain stays to achieve the same type of low-security lock when I am near my bike. Perfect example is at the barbershop. The bike is parked on the sidewalk about 10 feet from me, but if not locked in someway the theif might be able to get away before I could get out the door. The locks are typically given away free at police departments (I bought mine!) and look like this:

Interesting idea, but it really only seems slightly better than not locking it at all. Carrying a lock when I need to use it is a very minor inconvenience to me, especially when compared to worrying about it even for a few minutes.

At my college there are a few other bikes I see in the rack fairly regularly, one or two just lock the front wheel, the other one or two sometimes lock the front wheel and through the main part of the frame. All of these bike have quick release wheels/seats etc. Often helmets, tools and lights are left on them as well. Bike theft isn't all that big around our city, at least it doesn't seem to be. I'd feel bad if something happened to one of their bikes, but they make mine look like an armored tank, hopefully also making mine less of a target. I don't leave anything on it, and it's U-locked with a thick cable catching more of the bike rack and the front wheel and running back to the U-lock.

OK, we need some stats.

What percentage of bike thefts are ride offs, vs. someone carry's the bike away or puts it in a vehicle.

Does anyone have those numbers?

I'll bet you've got a low rate of bike theft in your small town, don't you? <sigh>