Bicycle Mechanics - please be kind

For a trained mechanic this is probably a no brainer, but here it is anyway. I adjusted my stem yesterday and reinstalled it by eye. I went for a ride and after 30 minutes it was evident that my 'bars were not lined up correctly. Is there a precise method for doing this?

Precise method? Probably not.

I find that when I turn the wheel to one side I am less distracted/confused by the overall bike and can focus more on the stem and fork relationship. Even so, I often have to tweak it a bit after riding it around the block.

jim

There's no super precise method because none is required, eyeball alignment is accurate enough. Years ago someone marketed a tool to help, but most mechanics found it not to be worth the effort.

Loosen the stem slightly so the bars can rotate, but keep it tight enough to stay in place. Eyeball the stem against the front tire looking from both sides and try for perfect symmetry. If you have a very short stem try this trick; put your front wheel squarely against a wall, and looking from the top align the bars to the joint betwen the wall and floor.

Years ago my Dad taught me this method - though I no longer use it.

Tie/tape a piece of string long enough to go from one end of the handlebars around the seat post to the other end of the handlebars - mark the center with a Sharpie/piece of ribbon. Now turn the handlebars until the mark/ribbon cannot be seen - should be centered within a couple millimeters this way.

ayceejay, Compare the handlebars to the front axle by looking down while straddling the bike. This is as close to a measuring tool that I can think of.

Brad

As mentioned before, turning the fork and wheel so it's at an angle to the frame can help you to see the alignment between only the stem and wheel. And then eyeball that sucker.

I straddle the front wheelm holding the wheel with my knees, line up the wheel with the frame, then eyeball the handlebars in line with the frame. As said before, i have the headset tight but still able to me twisted. Then I screw down the bolt so it doesn't move and finish the bolt off with a torque wrench.

Have my wife do it. I can never get the bars/saddles straight but she hits it perfect every time.

I place a metal yardstick edge on so it is centered on the stem bolt and over the handle bar clamp (these points are pretty easy to find accurately) and extends forward over the front tire. If the bars are centered, the straight edge will exactly bisect the tire.

You must be straddling the bike to make this or any other eyeball centering method work.

I've always used the stand over/trial and error method.. but thinking about the problem led me to:
What if you used a Plumb Line (String with weight attached) and held it from the center of the handlebars so it hangs above the front tire? Then it would dangle a line straight down that you could use to line up with the center of the wheel.
The only variable then would be making sure that the bike was standing straight up and down.. that could be accomplished with a level across the top of the handlebars. Maybe that would do the trick. Or did I just way "overgeek" this? :geek:

did I just way "overgeek" this? :geek:

Yes. Good plan for perfection but a simple trial and error would be quicker and work just fine.

When I do it for a customer I ask them to tell me when the bars are aligned so I can tighten it. That way I don't get any repeats.

When I do it by myself, I close 1 eye.

I've been riding/working on my own bikes for 30+ years and still no precise, engineered method.

I once tried to make an aligning gauge. Imagine a 36" long threaded rod that is secured to the front dropouts with wing nut and washers, then the rod is centered by measuring the distance from the fork dropouts to the end of the rod (this was by trial and error). Then I would make measurements from the ends of the rod to the center of the stem (like a bolt feature on the stem's faceplate). Theoretically, the bars are centered when the distance from the rod end to the common center point are equal (like an isosceles triangle). There was always uncertainty in the process (is the threaded rod exactly centered, am I measuring from the same points...) and took a lot of fiddling and adjusting Bottom line, the threaded rod went to serve another garage project and I went back to the above forementioned eyeball methods.

There's a method using two lasers and an alignment chart on a wall about 10m away.

I just standover the bike and eyeball it. But for the perfectionist, couldn't Park come out with a tool similar to their rear derailleur alignment tool that does this? Fasten it to the handlebar and have two rods with feelers to see if the distance between the forks are equidistant.

I just standover the bike and eyeball it. But for the perfectionist, couldn't Park come out with a tool similar to their rear derailleur alignment tool that does this? Fasten it to the handlebar and have two rods with feelers to see if the distance between the forks are equidistant.

My alignment gauge (see #13 above) tried to replicate said. As I found, there were too many variables using tape measures. I thought about measuring from the handlebar, but that assumes the handlebar is centered. I tried to reference a "fixed" spot, like the center of the stem's faceplate.

I always thought the fork manufacturer can put a scribed mark (or notch) on the steer tube that is points straight ahead. Then align a "straight ahead" feature on the stem to the one on the steer tube. It's easier to place these marks in a controlled, manufacturing environment. (For example, after the steer tube is pressed into the fork crown, the assembly is placed in a precision jig and marked. The stem and fork manufacturers would need to stanardize, and I wouldn't consider it "proprietary", so it should be relatively easy to implement. Of course, this only would work with threadless systems.

Thanks to everyone for their input, I thought it was just me! It seems that a jig of some sort would be the definitive answer but I don't intend doing this very often so I had my wife help me, at least if it is still wonky I know who to blame!

Yeah, eyeballing is good enough but I make adjustments after the first ride cos it irritates me knowing its not dead straight. The same problem applies to saddles too, but since I don't see it while riding it does not bother me.

I've had good luck with this method.

Stand in front of the bike, facing the handlebars. Lock the front wheel between your knees/legs. Line the stem up by eye with the center of the wheel and tighten.

That method has gotten me "close enough" that I haven't noticed it being off. YMMV

A lot of cheap bikes have mis-aligned forks that are visually way off centre. Assuming you have a proper bike and correctly aligned forks, you can centre the stem :
Loosen the stem binder bolt(s), depending on the headset style these are at the side or the top. You need some resistance to maintain the position.
Stradle the bike and hold the wheel in place with a foot.
Centre your head by aligning the tyre midway with respect to the hub.
Rotate the stem so the bar clamp part centres on the tyre.
Tighten stem.

Yeah, eyeballing is good enough but I make adjustments after the first ride cos it irritates me knowing its not dead straight. The same problem applies to saddles too, but since I don't see it while riding it does not bother me.

Even though you can't see the saddle skewed to one side while you are riding: http://www.bikeforums.net/showthread.php?693336-Excruciating-inner-thigh-pain-and-solution!

Don in Austin