Hangtownmatt

What causes this? Headset adjustment? Frame out of alignment? The frame has vertical dropouts so it wouldn't be rear wheel alignment.

Matt

HillRider

Could be a notchy headset or slight frame misalignment or slight dropout misalignment or....you aren't perfectly centered on the bike while riding.

dramiscram

Don't ride no-hand

Shimagnolo

The one time I saw that happen, the cause was a bent fork.
Both blades were bent to one side, so the dropout spacing was still correct.

FBinNY 

Here are two non-bike possibilities.

It could be that you don't sit centered neutrally so have to tilt the bike to get the line between the wheels under your center of gravity.

Or if you're riding the right side of typically crowned roads, you're riding across a tilted road surface, so it takes a bit of tilt to compensate for the bike's tendency to turn right and go downhill.

Or it could be the bike. Riding straight involves keeping your center of gravity above the wheel track, while compensating for any steering forces. Causes are numerous and complex working alone or in combinations. They include, bent fork, wrongly dished wheels, uneven tire wear, non-vertical wheels, offset rear triangle, and twisted head tube among others.

The one possibility I usually discount is a notched (brinelled or fretted) headset, since the notch is usually on the perfect straight position since that's where you do 99% of your riding.

The very first and simplest diagnostic is to reverse the front wheel, which will reverse the pull if it's the source of the problem. After that it gets more complicated, but I'd check rear wheel dish next, since that's easy enough. Then check for a bent axle by rotating the axle 180 degrees while in the frame with the QR open while watching for rim movement between the brakes.

If this is a new problem on a bike that never had it and wasn't crashed, I'd remove and remount both tires mounting them mirrored and on the other wheel. Tires are a rare cause, but easier to check than complex wheel alignment.

That wipes out the easy stuff, now it's a frame/fork issue, and while there are things you can do at home like using the string method to check frame alignment, the reality is too complex for a conclusive result.

fietsbob

Highway crown is higher in the center, for drainage of rainwater. ..
it's towards the left,
than to your right, and you overcompensate.. leaning , butt steering..

Myosmith

I had this happen once after swapping wheelsets on a bike and found that I had to have my rear wheel redished as it was a few mm off center. I didn't notice it riding straight so much as that the bike seemed to dive into left turns but took more effort to lean to the right.

crackerdog

The easiest test would be to have a few buddies try it without telling them which way it pulls. That should tell you if it is the bike or you.

otis66

Make sure your wheel is centered in the fork.

Chris Chicago

a couple years ago, i fixed up an old mtb and couldnt get the crown race to sit perfectly level. bike ended up difficult to keep straight with no hands. two years later it's much easier. I wonder if the crown race was the issue and eventually got worked into place through riding... or if I just got better at riding with no hands.

Hangtownmatt

Lots of good advice here. I appreciate the time everyone took to reply. I think in my case it is probably either me or the rear wheel dish. The suggestion to have others ride no hands and get their impression will resolve the issue of whether it's myself or not. But the rear wheel dish is a bit more challenging. How do I determine, down to the mm, the proper dish for a 700c wheel with 135mm spaced dropouts? Also, could it be the location of the hub on the axle?

Matt

FBinNY 

This is very simple to confirm one way or another. The rim is supposed to be centered between the faces of the hub's locknuts (the insides of the dropouts).

Since you have vertical dropouts, stand the bike up, open the QR and jiggle the wheel or frame so that gravity puts the axle against the top of the dropout. Note the position of the rim between the brake shoes or seatstays. (stays are more reliable since you might move the shoe by bumping it when mounting the wheel).

Now remount the wheel mirrored (cassette on left) using the same method to locate the axle in the same place in the dropouts. If the rim stays in the same place, the wheel is correctly dished, if it moves across then it isn't.

BTW- other variables like a bent axle, or not returning it to the identical place can throw this test off, so you should do it a few time and verify consistent results.

rekmeyata

The easiest thing to do is to reride the bike with the hands off except travel on the wrong side of the road to make sure it's not the crown on the road throwing you off. The second easiest thing to do is make sure your balanced properly...you probably properly balance since it sounds like you done that before on other bikes.

Actually this point, and the fact that a lot of people don't align the rear wheel properly either is the main reason for bikes to pull. Good news is, it's freaking easy to fix. Always do the easiest things first and recheck then work toward progressively more difficult and expensive fixes lastly while checking along the way.

All you need to do is to open the skewer on the front and make sure the wheel is firmly planted in the dropouts on both side then relock it.

For the rear check to make sure the rear wheel is centered in both the seat stays and chain stays, if not, simply loosen skewer just a bit, just enough to allow the wheel to move when done by your hand and not on it's own, center it then retighten skewer. Some frames are built so that the rear wheel will go all the way to back and against the dropout like the front did with the fork dropout, some are not designed that way, instead the hub is aligned with the seat stay going into the dropout which could leave a 1/8th of an inch or so space before contact with the back of the dropout. All my steel road bikes come with set screws in the dropouts that automatically set the hub correctly into the dropout. Occasionally you have to readjust the set screws, but I may only have to that once every 5 years or so. Not too many bikes come with those set screws anymore so you have to either eyeball it or put it all the way against the dropout.

otis66

Wow, after reading this thread I learned how to adjust/center my brakes. Now my bicycle is rolling smoother and brakes better. Has this ever happened to you guys. I will be getting a PARK Tool BT-2 cable stretcher first thing tomorrow.