Tuesday, November 15, 2011

Fork and headset options for old French frames.



I mangled the fork on my MB, as a result of an epic curb smash. Of course there was a vehicle involved. My helmet was crushed, my noggin was hardly scratched, and my was bent. I’m lucky it didn't fold the tiny split top tubes. Even the rim, technically worth more than the bike, survived. I guess the fork gave itself to save it’s comrades. The Panaracer T-serv 32c Messenger tire survived as well, it should be noted.

Changing the headset out on an old French bike isn’t much of a hassle. You may or may not have to ream. If you do, take a little at a time. You want a good, tight fit on the bearing races. It should take a moderate amount of force to seat the races.

I used a block of 2x4 construction wood the protect the race and distribute the impact evenly, and a firm rubber mallet to do the driving.  The materials are important. . . you can only put so much power through them. If it’s not enough, take a another tiny shave. Don’t beat it repeatedly. It’s not easy, but I’m sure you can destroy not only the replacement headset but the steer tube itself, if you really try NOT to use your brain. It would be hard to with the wood and rubber set up. I’m sure there’s a special tool, but I learned this from an old pro.

I managed to fit a threaded Shimano standard-thread headset with just the teeniest bit of reaming.  Which opened up my options tremendously to 2 decades of more standardized threaded forks, though closed the door to ever putting another original MB Mirage fork on. So that was a tough decision, forced by the fact that this bike is my car, and there was no suitable length fork to be found in any of the local good-old-bike graveyards.  

Most carbon fiber forks are thread-less. A fellow bike hacker has also installed a thread-less headset in a similar vintage Peugeot frame. The real limitation, as far as trying to use a modern carbon fiber fork, is the one inch diameter. Carbon forks came in just as steer tubes were making a transition to larger sizes. There are a few 1“ carbon forks available, but not exactly a selection.  Don’t just jump out and grab the first one you see. You’ll want to understand how to measure the fork rake, and how fork rake affects handling.

As a general rule, pushing the front tire further ahead of you will give you greater straight line stability, at the a cost to turn in speed. Pulling the axle in, closer to the crank and the front-rear center of mass, will give you sharper turn in, at the cost of straight line stability. Small changes of a millimeter or two can have surprisingly big changes. If it’s dialed in somewhere you’re comfortable, we call this stable or quick. All things considered, unless you know what you intend and have a decent sense of the results, I would recommend erring on the side of stable.  Especially before spending out on a carbon fork.  If you’ve got a proper hacker’s stash of old parts, you might try a few dustbin forks of various rakes, after getting the new (to you) races installed.  This is how I did it, with my own fork too mangled to get an accurate read on it. The first on installed was too quick, so I picked another one with more rake. On the third fork, she felt much like she had before, if perhaps a bit more stable or sluggish, depending on taste. She rides like a Mercedes now. Definitely get the desired rake desired in before ordering a fork.

In my opinion, though, a classic curved rake fork gives the right smooth ride for this type of touring frame, and I would feel that a carbon fork would both look odd and feel strangely light on the front of such a (comparatively) heavy frame. But you may have more exotic steel than I, and different aesthetic tastes. And while carbon is lighter than steel and more compliant than aluminum, I don’t think it would feel enough different to justify the expense. I tend to want to replace aluminum forks with carbon. But I tend to want to sell aluminum bikes and get something either more or less advanced, as it were. They were a great improvement, especially in cost vs. weight vs. stiffness. But a terrible time for elbow joints. Good thing I was pretty young during the reign of aluminum.

If you need more information on fork rake and understanding how it affects handling, you might read the wikipedia article on motorcycle and bicycle handling here, just as a primer.

Livestrong offers a decently simple method to measure the fork rake here. Yours to figure out how to translate ‘lower the kickstand’ into something meaningful, since this is an odd bit of advice for anyone who rides with any seriousness, on any serious hardware. A kickstand? Really? (I’d find a hard time measuring the rake accurately with the bike at a kickstand angle and the wheel consequently trying to flop to one side.) But if the fork’s already off, and you have some to pick through, you can hold them side by side and see if, with the steer tubes lined up, the ends of the fork are ahead or behind the original fork. Provided the original fork isn’t as mangled as mine was.

Monday, September 21, 2009

Hacking with Motobecane and other French frames

Motob├ęcane was one of the premium builders of French bicycles in the 1970s, and along with Peugeot they seem to have been well known for their mixte frames. They were known for using Vitus and Reynolds 531 for their mid to high end frames. Mine says 'built with 1020 tubes and stays' which I've always taken to mean it's made of a less expensive cro-moly. It's light but not super light, and certainly tubing and not pipe steel. I've never actually come across any conclusive information about 1020 tubing, so this is just assumptions based on the weight and quality of the frame, and the lack of any manufacturer branding of the tubing.

They are also noted for beautiful and high-quality paint, which my example certainly confirms. Over 30 years later, the paint is not so beautiful, but it is all still there, in itself a testament to quality.

These bikes make excellent fixed gear conversions, with a few caveats. The biggest complications to be faced in such a conversion relate to the weird threading of the headsets and bottom brackets, which were unique to the French bike industry.

With the headsets, other 1 inch headsets may fit, but to use the original fork with the frame, you'll need an original French headset. I got lucky; the headset on this bike took some rubbing out with steel wool and fresh bearings and grease, and was like new. A lot of these parts can be reconditioned and re-used with a little polishing of the bearing races. Look out for deep pits or scars that may interfere with the smooth rolling of the bearings.

The bottom brackets are likewise threaded unusually. They are not interchangeable with bikes from other countries, or most new bike parts, which use the now-standard English threadings. Because you will be limited to using 30 year old cups and crank axle, you'll be limited to the square tapered bottom bracket style of crank arm fitting. This was in common use on performance road bikes of the time, and single speed specific cranks are widely available in many grades.  I'm using an Origin8 crank from J&B, you can order it at your LBS. I got lucky in Lafayette, IN. The old road crank I'd been using collapsed on my first day in town, and it turned out I was right around the corner from Hodson's Bay, the best LBS if you're in that county.  They had the part I needed on the shelf.

When I orginally built this into a fixed, it took a bit of digging around in parts bins to find a crank axle that was right. It needed to be the correct width for a decent chain line; it also needed use the square taper fitting rather than the older, cheaper cottered design the bike originally featured. Again, some steel wool was used to rub out any corrosion in the cups and races. There is no hope of fitting a more modern sealed bearing design, if one was so inclined.  However, the old one's should be possible to keep in service indefinitely with a little preventative maintenance.

Of course, these are also frames for 27" wheels, not the more common 700c, so finding a brake to reach the front wheel correctly may take some experimenting. One will need a source with a bunch of old 70s era performance bike brakes to find one with the right reach.

Finding a modern seat post was fun too. This involved measuring to the nearest larger size and then reaming out the seat tube a bit on my bike.

If these problems don't scare you off, and even seem like part of the fun, then converting an old French bike to fixed can be a relatively inexpensive path to a unique bike with history and style all it's own. Otherwise it may be best to stick with modern parts or to start with a new factory built fixed gear. But where's the fun in that?

Sunday, September 20, 2009

Fording a stream


 This is certainly the wrong bike for the situtation at hand, but there we were, a rugged old steelie with messenger tires and a path of streams, gravel, mud, and grass.  The most fun were the combo stream filled with grass. She almost made it through this one.

She's a noble forder of streams, sometimes...I took off the toe clips so I can use boots on my fixte. Fancy attachment system, and unfancy ones as well, put too many constraint on footwear. Unfortunately, I can't always have the right bike for the right adventure, sometimes I just have to follow where the questions lead. That's what this bike is for. Too bad the camera died before she got really muddy.

I was digging around the edge of town when these pictures were taken, more on where the sidewalk ends here.

Some pictures of the beater motobecane.



Here's some pics of the 1976 Motobecane Mirage mixte, as it's evolved into my around town beater fixte.

First up is the steer tube badge, which was nicely enameled and has held up perfectly all these years. The bike has never been repainted, and the silver is quite mottled with rubbed off places and cracks in the yellowing clear coat.




This is the original bike registration sticker from the 70s.  The cops don't register bikes here anymore, so it's just vintage memorabilia.  That sticker and the badge have much to do with why I've never painted my frame.









The rear end running gear, with a spoke card representing the local bike community blog at bellovelo.com Ponyhorse complains that his blog didn't make the picture, but he didn't stick a spoke card in my bike wheels when it was parked down town.











I've picked up some nice vintage parts along the way to customize and improve performance, while maintaining that vintage esthetic and general ruggedness. Here's the triple T stem I picked off an old raliegh racing bike I found at Outdoor Omnibus in Huntsville, AL.








And a really stiff and solid universal branded shift lever, from the same bike. All the steer and bar gear is roughly period correct for the frame.















The whole bike in profile, to show off the unusual mixte lines.  Some heavy duty messenger tires and classically styled 32 spoke wheels have proved a versatile combination for all road and remains of roads I try to traverse.

Tuesday, October 28, 2008

Some thoughts on riding a fixed and using brakes, or not.

I have been riding fixie predominantly for a while now. Of course, there's an ongoing discussion about whether a fixie should or should not have a brake. I have run with and without a brake on the hack-together Motobecane. I can ride either way, with reasonable control without a brake.

I do, however, refute the argument that one can stop faster by skidding the back tire. This is patently false. Stopping with traction is considerably faster and more controllable than losing all traction. Anyone who has ever raced an automobile can affirm that locking up the tires isn't much of a way to control the car, and the same is true for a bicycle. In short, it's possible to ride the city streets without a brake, but it is not the safest way to go. A decently set up front brake will stop the bike way faster, and in a more controlled matter.

For the most part, I have considered that choice a matter of personal safety. Riding without a brake has always required more attentiveness, and more grace, than with, and that in and of itself might have made me safer.

A recent experience forced me to reconsider. I was shooting down a long hill of medium grade, part of my daily commute. For the most part, I muscle up to the top, then shoot down the other side at a rapid cadence, easily breaking 20 miles an hour. If the light was working out right at the bottom, I'd shoot through the intersection and ride this all the way into downtown.

Then, one day, a little girl ran out into the street. She might have known to look for cars, but maybe not for bikes. I shouted, and she stopped within inches of being hit in the head by my bars. At the speed I was going, she would have been seriously injured, or possibly even killed. Nothing I was able to do would have prevented this. I passed her within inches, still moving at something between 20-25 miles per hour.

Thinking about it, If I had had a brake, I still might have hit her, if she hadn't stopped in time, but at considerably slower speed, and maybe she would have gotten a broken arm, something that would have healed soon and left nothing more permanent than a lesson. At the uncontrolled pace I was moving, she could have been in a wheelchair for the rest of her life...a high cost for her mistake.

I will not ride the city streets without a brake any further, because that incident taught me that it was not just my neck being risked against SUVs, but the safety of innocent pedestrians. If I want respect from the cars, I also need to show respect for the pedestrians, and riding without a brake presents an unacceptable risk to others.

Friday, October 24, 2008

About the commuter bike.

My hacker commuter bike started her life as a 10 speed French Mixte, about 30 lbs with steel wheels, 27 inch tires, and steel accessories all around. She's a 1976ish Motobecane Mirage, originally sold in the Peddler bike shop in downtown Huntsville, Alabama, which was then in the location of the Kaffeeklatsch bar. A friend found her in a thrift store for $20, rode the crap out of her, bent the wheels, and eventually gave her to me.

Now she's a much lighter, faster fixed gear. It's been an evolutionary process, scouring and picking up parts as I could find and afford them. The only new parts on the bike are the wheels and the seat post, everything else has been scavenged, mostly from a shop called Outdoor Omnibus in Huntsville.

I dug around in the parts bins to put together a functional french thread bottom bracket, finally scavenging an old Nervar crank axle, which is presently attached to a very light 170mm Nervar crank set, with the original 52 tooth chainring attached by shorter bolts. The wheels are Mavic Open Sports, laced to Formula hubs, with classic looking gumwall 23c tires. I found an old Sekai stem and handlebar, and that's bolted on, with some cushy black cork tape and a pre-aero Shimano 600 brake lever that runs to an antique sidepull brake, maker unknown but it had just the right reach to work with the 700c rim on a 27 inch frame. I replaced the old fashioned seatpost with a Kalin, since they are cheap and available in many sizes. I got the closest one, but still had to ream the seat tube a bit. It works great now, attached to a nice Sella Italia saddle with prostate relief and titanium rails.

On the back is a Delta rack, which I use to strap down extra layers of clothing, and to carry some cheap but functional Sunlight panniers, though I usually use one of my Timbuk2 bags, a medium for most day, and an XL for grocery shopping.

There's an SKS raceblade rear fender on the front, which I'm about to extend with mudflaps. I may end up getting some Planet Bike fenders, but I'd rather just keep it to this one little fender. On the front is a vintage headlight from a generator setup that I'm converting to a slf contained battery powered LED light.

I'll post some pics soon.

Upcoming Hacks

Here are some hacks I'm working on for the commuter fixie, documented here to keep me motivated to work on them.

I have an old chrome cased generator light, for the front of the bike. It looks really beautiful mounted above the font brake, and matches the overall vintage style of the bike. I don't have any desire to actually run a generator, though. I am much happier with modern battery powered LED lights. They have no drag, weigh very little, and can be seen from along way off.

The plan is to fit the circuit board from a 2-mode blinky into the casing, along with a tray for AAA batteries, and build up an LED light bulb that will fit naturally into the housing. In this way, I can keep the vintage theme of the bike and still enjoy the benefits of modern lights.

The other hack is to make a mudflap for the front fender, preferably out of old tubes, because I have a ton of that material laying around. This one is very much on my mind after this mornings very wet ride, with soaking feet.