Fork doesn't track straigh
 

I have reason to believe that my carbon fork blades are asymmetric. At low speeds, I cannot let go of the handlebars for one bit without my bike veering off the road almost immediately. The bike is controllable; I just have to keep my hands on the bars at all times.

How can I definitively conclude that the fork is at fault? My front wheel is literally fresh out the shop after a truing ... and it's very, very true. It also looks dished correctly. Headset adjustment is fine. Any other possible culprits? I know that if I send the fork to Calfree they can put it in a jig and test it but I'd rather not shell out the cost of shipping both ways ... if my fork is defective I'd put that toward a new fork. Or maybe I'll just live with my asymmetric fork - it seems like the condition can be dealt with by keeping my hands on the bars! However, I read that at high speeds (30+ mph) asymmetric forks can result in severe wobbling ... is this true? Any experiences? Not that I expect to go 30+ mph around here ... it's completely flat here.

Too much cable housing on one side maybe? If you pick up your bike does the fork move toward the side you veer to?

OK, here' a definitive at home test to confirm whether a fork is straight or bent to one side. You'll need a table, a tri-square or ruler, some books, and a friend or two.

Start by removing the bars and/or the stem, then add spacers so the headset can be adjusted. Stack up books or something similar on the table to about 3 inches or so. Make a few stacks to support the top and down tube with the cranks clear, (or remove a pedal) or support the top and down tube and rear triangle. In short you're trying to float the frame over the table roughly parallel however you can. Have your friend(s) press the frame down and hold it firmly in place.

Using the square, rotate the fork so both tips touch, and note the height of the lower one. Rotate the fork 180° and repeat the measurement, and compare. It's important that the frame is held steady through this operation, so you might want to repeat a few times. If the measurements aren't equal or within 1-2mms the fork is off. Otherwise look elsewhere for your handling problem.

BTW- even a bike with a pretty bent fork can be ridden no hands, it simply calls for tilting the frame to compensate.

How old is the headset? A "brinelled" headset with little dents for the balls will be very difficult to ride no hands. Try turning the fork with your hand close to the crown and see if you can feel fork indexing as the balls fall into then are forced out of the dent's. (I say "brinelled" in quotation marks because what happens to headset crowns is simply wear and not caused by actual denting, but those dents have been called brinelled for decades.)

Ben

Larger bikes are completely unstable. There is a reason that Zinn builds his custom "project BIG" bikes with headtube extensions, but tries not to let the seat tube get above 58cm, even for a bike that is for someone 6'9" and will be an effective 69cm/70cm bike. They show a lot of seat post, and the head tube extension allows the handlebars to be in a relatively neutral position to the saddle.

If you have a big frame, you can't ride hands free on most of them without veering immediately or death wobble just instantly crashing you. Even on a XXL compact geometry Giant OCR1 I've had shimmying and death wobble so bad on a descent (even with my hands FIRMLY in the drops) that I was terrified I was going to crash. I was really moving, but big bikes are inherently unstable.

Get a bit of string. Loop it around the front and rear wheels as far up as you can without it touching the spokes. With the front wheel straight ahead the string should be just touching the rims on the back of the front wheel and the front of the back wheel. If it isn't, ie there is a gap on one side of the rear wheel, then either the front forks are out, the rear triangle is out of alignment or the dish is wrong on one of the wheels (most likely the back). The dish being out on the rear wheel is the most likely culprit.

I wonder if having your hands FIRMLY in the drops didn't contribute to the wobble problem. Keeping your arms and elbows rigid and stiff can exacerbate the wobble. I've notice on a local 40+ mph downhill on all of my bikes (56 and 57 cm frames) that I can generate a bit of instability by locking my arms and it goes away completely when I relax a bit.

Yes, large frames are not as shimmy-free as small ones but the current use of oversize tubes and very stiff frame designs has greatly reduced the tendency.

What do you consider "low speed"? Most bikes will not be stable with no hands at low speeds. Depending on the amount of trail, wheel flop can be pretty significant at low speed. Crowned roads will also cause your bike to veer toward the shoulder of the road unless you lean toward the center of the road to correct it. You don't say what kind of bike this is, but I'm assuming its a road bike because of the carbon fork. I doubt that any decent carbon fork made it past QC with a significant misalignment. I suspect that, if there is a problem, it is one of the suggestions above.(cable causing the wheel to turn to one side or headset problem)

OMG. Let's just acknowledge that you have no frame of reference to actually have any sense/clue to how different tubing materials or tubing diameters handle for a bike on say a 45cm frame or a 68cm frame, and realize I make that point because both those sizes are the +/- cm difference between what I ride and what you're trying to offer advice and seemingly expertise about.

If you have only ever worked on air cooled volkswagons my suggestion would be don't go to a Ferrari technical forum offering expert advice on sequence mistakes someone made trying to rebuild a vintage engine.

Quite honestly you don't have any frame of reference about BIG/TALL frames. You ride a small frame. There is a reason that Zinn, the tech guru for Velonews, who specializes in building custom frames for BIG/TALL riders has to use small triangles with tall head tube extensions.

Your point about oversize tubing and stiff frames being the solution locates that you completely just do NOT understand the issue. Cannondale frames of the era I ride were the stiffest frames ever tested on the Bicycling magazine 'tarantula' testing jig. I exclusively ride oversized tubing. I'm trying to say this politely, but you truly don't know what you are talking about, you couldn't possibly have any insight or understanding to the problem, and your attempt to communicate that the problem is that BIG/TALL people are just riding with their arms and elbows "stiff and rigid" is actually downright laughable.

Do me a favor. Send Leonard Zinn a note at his Velonews tech column and tell him that his design for all the custom BIG/TALL bikes he sells is all wrong. That he doesn't actually have to use top tubes that are absurdly low in proportion with goofy head tube extensions. Let him know that your insight has revealed that the problem is that we, including him (he's 6'5"), are all just riding with "keeping [our] elbow rigid and stiff [which] can exacerbate the wobble." He'll be glad to know you've got this figured out from riding 56/57cm frames. That those of us 6'5", 6'6", 6'7", 6'8", and 6'9" all just have bad bike handling. That your 56/57cm frames reveal how bikes handle when they are say 10-11 sizes smaller and larger.

I'm laughing reading your post. The internet is full of Expert Forums where people who have no frame of reference, knowledge, understanding or insight to someone's question/problem/issue post piping up to offer advice, that is then worth what people pay for it.

Zinn was a roadie, almost an Olympian on the Olympic developmental squad. He's still been a competitive cyclist on the road and in cyclocross since. He could probably teach you more about bike handling technique than any reasonable person's ego could bear. For those ignorant of this issue read some of Zinn's thoughts here and edumacate yourselves:

http://archive.constantcontact.com/f...577557261.html

The reality is that those of us on BIG/TALL frames do NOT have the same riding experience as those on small 57cm frames. Its like we're riding bikes with 24" wheels and everything is inherently unstable, especially at speed. Holding the handlebars FIRMLY is NOT the problem.

Which is why, for me, wanting to ask the OP what frame size he was riding made sense. If he's riding a 63cm the issues could be he's a large/tall cyclist trying to squeeze on a too small 63cm frame and there could be nothing wrong with the bike at all, just that a 63cm is more inherently unstable than something smaller, especially as the cyclist perched on top gets bigger/taller proportionate to the bike.

http://bikeforums.net/attachment.php...hmentid=473033mtnbke- Chill out a moment. Hillrider's comments reflect years of frame design thinking and results. I respectively ask what are your credentials in frame design and building? I don't take any issue with your depiction of Zinn's designs. I do take issue with your treatment of Hillrider's comments. I also am unsure about your statement of "Larger bikes are completely unstable." Certainly very large (as also with very small, my area of focus for years) frames present different challenges the commonly sized ones. Zinn's solutions are but one path.

I have only two data points, during my building, of extra large frames. One was a 72cm the other a 74cm. This was back in the mid 1985 and few were aware of OS tube use (Freddy Parr being one though) in steel bikes. We, Cyclery North, were commissioned to build two big bikes almost at the same time. We use typical racing steering geometry with traditional tube diameters. The walls were thickened and straight gage tubing was used in the TT and DT. The steerers were thick walled 4130 machined out for the stem and threads were chased. Both were built up with strong but common parts (36 spokes and good cotton sew ups). Both riders raved about their riding experiences and neither complained about any handling issues. One rider was a pretty aggressive guy, the other a skinny newbie.

The last addition t this discussion comes from my attending Albert Eisentraut's last east cost building class. the first few days we were lectured on building aspects including design and steering geometry. He said that larger riders with their greater mass were actually more stable. So to get a bike to handle nimbly under a large rider one had to "quicken up" the steering geometry. (By the same token a small rider would benefit from a slower steering geometry. This does jive with my many small frames I've built and used).

I do agree with the smaller triangle makes for a stiffer frame idea. The extra large frames we made at Cyclery North were both hellenics (triple triangles for the young here). here's a shot of the 72cm I made. Andy.