Monday, March 23, 2009

How will you stand it?

Ham, in the UK writes:

I have a question for you - I am about to join the ranks of the carbon fibre road bike brigade, courtesy of the UK government bike scheme and Greg LeMond's fight with Trek. (I'm getting the equivalent of 2,000GBP of Trek Madone for 600GBP). Thinking about this, I need to get hold of a bike carrier for the car, and a workstand. Do you have any thoughts of the suitability for carbon fibre, please? I'm thinking of a fork-holding roof carrier for the car, but I can't choose between the BB holding sort, or the seatpost clamping sort (recognising that I need a steel seatpost in there) for the workstand.

All thoughts appreciated

Welcome to the ranks of the test pilots! You'll learn to ignore those snapping and cracking noises.

I jest. Right? Heh heh heh.

Regarding work stands, I never met a BB mount work stand I liked. The bike never seems stable. The parts intended to stabilize it always seem to interfere with some aspect of the work. Seatpost clamping racks hang the bike with all the operating systems unimpeded.

For clamping in a seatpost type stand a steel post is overkill. An alloy one will do. Or you could invest in the Park ISC-4 internal seat tube clamp. That is designed to provide a secure clamping area on fragile frames. A bit pricey, but solidly built.

A torque wrench will become like a crucifix to you. It will be a sacred object never far from your hand. Carbon riders live and die by the small windows of correct torque, aiming to ride that straight, narrow path between a component that slips and the one-way trip to the junkyard that follows the ominous crack of over-tightening. This applies to the seat post you clamp in the frame for repair operations as well as the parts with which the bike is built.

Speaking of torque, beware of twisting too vigourously on the bike in the work stand. No matter how the bike is supported, you can load it in directions for which it was not designed. Have my brother tell you about the jolly night we wrenched the seat tube right out of his favorite touring bike, trying to get a frozen seat post loose. That was a steel frame, so the shop's frame guru just torched out the remains and put in a new seat tube. Then I painted his frame a rather experimental color. He rode it for a few more years before it vanished in the mists of the larcenous underworld.

In the case of carbon fiber, consider all mistakes terminal. It isn't strictly true, but no manufacturer will risk telling you how much of a ding they think a carbon frame or part will withstand and still be ridable. Officially, anything that goes through the gel coat is a death sentence.

Back in 1982 or so, a shop owner in Maryland took a big honkin' crescent wrench to the top tube of his Graftek to prove its durability. But the Graftek was not a true, pure carbon fiber bike. It held up well to the wrench, though. Not like these modern egg shells. Can't so much as brush them lightly with a ball peen hammer...

1 comment:

Ham said...

Thanks for that - much appreciated. I was leaning that way because of the way that most seem to be seatpost clamps. I was only going steel because I have an old one lying around. The torsional stresses were what was worrying me - a little counter intuitive, but sounds the best option.

"A torque wrench will become like a crucifix to you" You mean, a symbol of torture ignored most of the time, but very useful for wrapping around people's heads? Sure.

My two torque wrenches are from my old car toolset, and may need augmenting if 1/2" square drive proves to be a little on the large side. Still, you never know when you might need to use 180 ft lbs on a bike.