Possessed bike!?!

Alright, I've been ignoring this for a while since I dont really use this bike, but I have a hardtail mountain bike, pretty old frame, but good components. I keep it tuned up myself, which is not saying much, but I try. It's my father's bike.

Anyway, to get to the point, it's possessed! When riding it above a simple 20 km/h it feels as though it's pulling from side to side, like it just wants to steer left, then when you adjust, it goes right, over and over again.

I know that the hub doesn't have very much play at all, and the headset is as tight as I can get it without it seizing... Also the wheel is pretty true.

I did tighten up the headset a few days ago, he said it helped, but still not 100% Does anyone have any idea what's up? thanks in advance

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The power bars and energy drinks... that's the only reason we all ride.

Did you check the spoke tension on the front (and, rear) wheel(s)?

No, I haven't... And I don't really know how, or I should say I don't have the tension meter. My good friend-mechanic usually does all the truing, spoke adjustments... as he has he truing stand and the spoke wrenches.

So you think that might be the issue? I actually didn't know that you could have all your spokes too loose or tight, I guess it makes sense, just didn't think of it before. So it's in true, just all around too loose? Thanks again.

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The power bars and energy drinks... that's the only reason we all ride.

Check the frame isn't bent. A long piece of string and a tape measure works wonders. Run the string from the headtube to the dropout for the back wheel and measure the gap at the seat tube - repeat for the other side. Do the same from the dropout on the front fork to the rear dropout measuring again at the seattube. All measurements should be pretty much equal. Check also that the forks aren't bent backwards slightly.

With the back wheel in the frame - do a quick 'eyeball' check to make sure that the rim is centered within the chainstays. Do the same with the front wheel in the forks.

... and make sure your tires are pumped up.

What adjustment are you making that causes the bike to change from steering left to steering right?

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One life, one chance. Don't waste it!

Before I try to answer, I have two questions. First, exactly what is the make and model of this bike? Second, is the fork original or is it something you or a previous owner installed?

I just meant you pull to the other side to try and stay straight.

bobcat... the bike is a shop bike, no make or model, pretty old. And as for the fork, it's not original, it was installed years ago, not by me, by a freind, but the bike was still mine at the time.

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The power bars and energy drinks... that's the only reason we all ride.

A friend of mine once built a frame that rode like this. Here's the deal. Your frame was originally made for a non-shock fork. When the shock fork was installed, the longer stantions (to allow for movement) raised the front end of the bike, effectively reducing the angle of the head tube and extending the trail of the steering geometry. For concise explanation of trail, see this page, Bicycle Steering Geometry.

The operative point in Phred's explanation is "The greater the distance between the steering axis intercept and the contact patch, the stronger the centering force becomes." When this distance is too great, the centering force is so strong that the rider's corrections shoot right past center. Attempts to maintain a straight line or a smooth curve result in a series of sloppy over-corrections.

The solution would be to find a shorter fork, most likely one without shocks.

That makes sense like putting an extension on a motorcycle. It might also raise the center of gravity causing any changes in side to side motion to be more exagerated.

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Dope,when training and talent just aren't enough.

So what would you suggest I have, aprox. for my trail? I drew the geometry over a picture of the bike, and it looks just about normal, the trail lands just a few cm's in front of where the wheel leaves the ground, so not very far in front. I couldn't measure the exact distance just because it was a picture, but it looks to be about the same as the geometry on that site you gave me. Color me confused...

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The power bars and energy drinks... that's the only reason we all ride.

Have you ridden the "possessed bike" subsequent to tightening the bolts on the fork's connnecting yoke?

I would have thought that the loose yoke was THE cause of the steering problem, particularly if the sliders are not equally lubed (i.e., if there is some MORE 'stiction' on one slider than the other).

Regardless, if you are only riding the bike on the road, the you should probably consider replacing the suspension fork with a solid fork ...

Okay, I'm an inquiring mind ...

Did your friend weld up the frame, himself, or are you saying that he added components to an off-the-peg frame?

What was the head tube's theoretical angle with the various (?) fork combinations that he tried?

That is, if he fabricated the frame, did the frame start with a 71º head tube angle when the frame had a solid fork OR was the head tube angle closer to 73º when a solid fork was installed in the frame?

How much travel did the suspension fork have which your friend tried on the bike he built?

It was a road bike so it didn't have any suspension travel. I ended up over here because the original poster cross-posted to the cycling equipment forum.

And he built it from a carton of Reynolds 531 Double Butted. I forgot the brand of the lugs. It was all beautifully brass brazed, with a Cinelli-style full sloping fork crown, stiffening tangs, and a fastback seat cluster. The fork blades were pre-bent, and they had the new (for Reynolds) fat, Columbus-style profile.

We designed the frame together based on the angles and rake of a British criterium bike I'd been riding, but a bit smaller. This bike had 73-degree parallel head and seat tubes with a 1-1/2" rake. In hindsight I recall that this was a pretty heavy-steering geometry--a patch of sand on a fast descent would cause conniptions--but this is what I was used to, so I accepted it as normal.

The angles of the finished bike came out on the shy side of 72 because the seat stays came up short, dropping the back end of the bike. The stay length was based on a profile drawing that failed to account for the angle of the 120mm spread at the dropouts to almost-zero spread at the fastback seat cluster.

The bike steered pretty badly--the front end constantly over-corrected, causing the back end to fishtail. It should have been a great bike, but that was 35 years ago and we didn't know anything.

Thanks for the info ... it sounds as though your friend brazed up a beautiful bike ...

BUT, how many frames had your friend fabricated prior to brazing your frame?

Based on what I discerned when I investigated building my own frames a long, long time ago, I figured I could buy a set of Cinelli long point lugs + a set of Columbus tubing for around $150-to-$200 ... but, back then, the conventional wisdom was that the first frame was basically a throw-away (unrideable) regardless of how skilled one was in crafting the frame, and it wouldn't be until at least the second or third frame before one might be successful in fabricating a frame that could be ridden ...

Because, no matter how beautiful a bike frame is, there are sometimes subtle alignment issues which the framebuilder must ensure don't detract from how the bike rides ...

Of course, there are ALSO not-so-subtle alignment issues during fabrication ... I saw a beautiful MASI which had ONE dropout at least a centimeter further from the BB than the other! WTF?!? How did that frame leave Italy? How did that frame even make it into the spray booth? The bike probably rode great, but it consequently looked terrible -- definitley a conversation piece.

My recollection is that at the time (c1980) you could buy an off-the-peg BOB JACKSON or COLNAGO for about $425+ ...

So, with a choice of spending $400 for tubesets & lugs + needing to make a fabricating a jig + the cost of several files + brazing materials & torch + the need for access to an alignment bed WITHOUT any assurance of a rideable bike OR just a little more money for a good-to-go frameset ... well, it seemed like a no brainer.

Oh, and, the fork is definitely an under appreciated part of most bikes ...

I had ONE fork which I didn't realize had been tweaked the wrong way until I changed the fork on the bike with another ... I sure couldn't see that the fork was out of alignment (I attribute the misalignment to a misjudged road hazard, but hadn't notice anything unusual immediately subsequent to the encounter) ...

THAT's a long way of saying that despite the 72º angles on your custom frame that if you still have the frame (and, presuming that the frame was aligned post-brazing) AND if you were to install a Reynolds or Alpha Q fork (to mention a couple of obvious choices) that your custom bike would probably handle much better BECAUSE I think it is harder to discern when a fork isn't properly aligned than when the frame isn't.

I think that one thing people which don't realize is how difficult it is to fabricate a good fork; and, it is one (but, not the only one) reason that I suspect so many framebuilders have embraced CF forks -- i.e., why spend/(waste?) the time fabricating a fork when it can be outsourced?

This was his second bike. He and his wife were silversmiths by trade, and his other hobby was hot-rodding Triumph Spitfires. I don't know if he ever made another bike.

His workmanship was beautiful and everything lined up with minimal cold forging.

Remember, this was 35 years ago and all we had for guidance was the Proteus book and the little book Joe Cossack had done for Bike World. There was no web where we could Google "bike geometry trail" and get instant answers.

Shortly afterward (summer of 1975) I had the opportunity to meet Ben Serrota and view some frames he had just built. There were some pretty wacky geometries there, too. Of course, he kept at it and his lugged steel frames of the '80s started a legend.