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Checking Frame Alignment

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Checking Frame Alignment

Old 09-26-22, 07:22 PM
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Bad Lag
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Checking Frame Alignment

Which dimensions should I check?

How close is close enough?

Is it really viable to adjust a fork?

Last edited by Bad Lag; 09-26-22 at 08:00 PM.
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Old 09-26-22, 08:10 PM
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To start with https://www.parktool.com/en-us/blog/...pout-alignment Also there is a derailleur hanger tool https://www.amazon.com/Park-Tool-DAG...73816288&psc=1
Feel for that bump under the steering neck on the down tube .
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Old 09-26-22, 08:27 PM
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Bottom line, if the bike rides well, tracks well on corners in either direction, why bother?

And I have proper tools to check alignment...
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Old 09-26-22, 10:28 PM
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Of course look up Sheldon's section on frame alignment.

I have used the string method to check my rear triangle. I also ran string to check my front fork for simmitry. I have used large C Clamps to check my dropouts and derailleur hanger. And I have held a straight edge to the tubes to check for bending. I have also pinged a stripped down frame for changes in sound along the tubes and welds. Really these simple tests just give ya piece of mind.

Twice I have had to trash a frame. One had two tubes bent and the other pinged out soft rust spots on the inside of the the seat and top tube. But I knew these bike were shot before even checking them...
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Old 09-26-22, 10:56 PM
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Originally Posted by gugie View Post
Bottom line, if the bike rides well, tracks well on corners in either direction, why bother?

And I have proper tools to check alignment...
I love the way it handles corners, especially this one tight, high speed, down-hill, off-camber left handed turn I know of. It's almost a 180, but not quite. I think the sound the tires make is my favorite part, other than the lateral g-forces.

Still, I am bored, so I thought I'd check it out.

Last edited by Bad Lag; 09-26-22 at 11:09 PM.
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Old 09-26-22, 11:06 PM
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I think I will start with the string method for rear triangle alignment.

I'm tempted to buy the PARK Frame and Fork Dropout Alignment Gauge Set. That seems a worthy purchase for both front and rear but the tool would be used for all of five minutes. Too bad they don't lease them for use.
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Old 09-27-22, 02:48 AM
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Originally Posted by Bad Lag View Post
I think I will start with the string method for rear triangle alignment.

I'm tempted to buy the PARK Frame and Fork Dropout Alignment Gauge Set. That seems a worthy purchase for both front and rear but the tool would be used for all of five minutes. Too bad they don't lease them for use.
I think a used set of about any age is as useful as a new one.
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Old 09-27-22, 06:37 AM
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I used the string method to check a frame that I wanted to buy. It ain't the best way , but it worked. The bike rides like a champ. I sent my Colnago(different bike) to Franklin Frame for a paint job and asked Jack if the alignment should be checked , it is a 1975 , after all. He said just what Gugie stated. If you've been riding it for a year and you haven't noticed anything peculiar , it is most probably fine.
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Old 09-27-22, 07:27 AM
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Sigh, another alignment thread gives me another chance to complain about Sheldon's string alignment method. It can tell you something is off but not what. Park makes a tool that will do a better job (their Frame Alignment Gauge) but the front end needs to be checked first. The most important aspect of alignment is that the seat tube is exactly 90 to the BB threads. If it isn't, your pedals will not be perpendicular to the ground and that crookedness can introduce knee issues. This seat tube alignment accuracy is the foundation for framebuilders to make the rest of a frame.

To check if a seat tube is leaning, use some kind of straight edge (a 4' level works and isn't that expensive) placed against a bottom bracket cup with the axle removed. Use a small ruler to measure the distance from the level near the BB and again near the seat lug. They should agree of course. Next do the same thing along the down tube. If something is off, I recommend taking our frame to your local builder and let him fix it for you. The accepted industry standard is within 3mm. All of us good builders keep tolerances well within less than half a millimeter.

Now that you know the front end is checked and correct, you can see if the dropouts are equidistant from the centerline of the frame. The flaw in Sheldon's method is that he assumes the front triangle is correct. The Park tool works great for this but so does your recently bought 4' level. The straight edge is placed against the head and seat tube and the distance to the inside of a dropout is measured. Flip the tool to the other side and measure to the other dropout. You are good if they are the same distance.

Here is a picture of Dave checking the rear triangle alignment on the frames we made in Bucha Ukraine. This is where the Russians tried to stage their attack on Kyiv and did so much destruction. This picture was taken in 2009 when he was a seminary student. I wonder how his life has been after the Russian invasion. Eventually I took over a tool that works better than a level. Instead of using a ruler to measure, we taped M5 threads into the level and a bolt in the threads could be turned to check distance.


using a level to check rear triangle alignment

checking the drive side to see if the distance is the same as the non-drive side
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Old 09-27-22, 10:01 AM
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Very cool, guys, thanks. I have all sorts of straight edges, calipers and levels, dial micrometers and other gages.

If there's a shortcoming, it is I have only two hands.

Maybe tape and bailing wire can help hold things in place while I measure.
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Old 09-27-22, 03:00 PM
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@Doug Fattic The industry standard is within 3mm of alignment of the seat tube to the bottom bracket? Interesting.
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