Checking Frame Alignment...... ahem.
#1
Thread Starter
Banned
Joined: Nov 2009
Posts: 3
Likes: 0
Checking Frame Alignment...... ahem.
I was riding the bike I recently restored and on it's first long out of town trip, I noticed that the front wheel is twisted off to one side by about 1.2* and the rear wheel is dead straight in the frame.
The handle bars are dead square with the front wheel.
But the bike is pointing slightly sidewards - and the wheels are out of parallel.
The bike is running slightly sidewards.....
So I am thinking that the frame OR the forks, or the frame AND the forks are twisted - out of alignment.
Me thinks that someone has crashed the bike diagonally into a unforgiving object hard enough to twist the front end, or fallen on the frame when it was laying on the ground....
Two easy and basic ways to check it are by line of sight - with the front head stem tube and forks and front wheel (both separately and in combination) being in alignment with the seat post tube.
And or by measuring the diagonals between symetrical points with a big steel rule like to check the forks, one can measure from a centre point - like the brake mount hole at the top of the fork, to the top of the axle hole in each leg.
Etc.
Since the twist is fairly small, I figure that I can twist it back and or buy new forks....
The handle bars are dead square with the front wheel.
But the bike is pointing slightly sidewards - and the wheels are out of parallel.
The bike is running slightly sidewards.....
So I am thinking that the frame OR the forks, or the frame AND the forks are twisted - out of alignment.
Me thinks that someone has crashed the bike diagonally into a unforgiving object hard enough to twist the front end, or fallen on the frame when it was laying on the ground....
Two easy and basic ways to check it are by line of sight - with the front head stem tube and forks and front wheel (both separately and in combination) being in alignment with the seat post tube.
And or by measuring the diagonals between symetrical points with a big steel rule like to check the forks, one can measure from a centre point - like the brake mount hole at the top of the fork, to the top of the axle hole in each leg.
Etc.
Since the twist is fairly small, I figure that I can twist it back and or buy new forks....
#4
Chasing the horizon.
Joined: Feb 2009
Posts: 500
Likes: 1
From: Michigan
Bikes: 2016 Felt F75, 2008 Mercier Corvus Steel, 2006 Trek 4300, 1985 Trek 620 (modernized)
Dish wouldn't twist it off center though, dish would offset the wheel right or left in the fork. I think the OP's got it. Sounds like the fork is twisted, or one of the sides of the fork is bent. On old frames this is easy to fix but difficult to fix well. Sheldon Brown's site has a good walkthrough.
#5
Thread Starter
Banned
Joined: Nov 2009
Posts: 3
Likes: 0
To give you a visualisation
A B48 - B52 bombers, are sooooooo huge as in the "sail area" of the sides, under the effect of the cross winds when landing; that in essence the aircraft body is a flying beam; and the way to make an aircraft landing at 250kmh with a 50kmh cross wind is to blend the vectors by aiming the aircraft at about 7* off center to the runway - side slip.
The "magic trick" is to TURN the wheels to run straight down the runway by rotating them by 7*, so that the aircraft lands and is running in a straight line down the runway, but it's running slightly sidewards - as it runs down the runway. And they can do it up to 20* off center.
https://en.wikipedia.org/wiki/Crosswind_landing
Look at this picture and which way the plane AND the wheels are pointed.
https://ep.yimg.com/ca/I/mcmahanphoto_2090_89216671
In this picture - look at the wheels - and what their direction of travel is; and which way the plane is pointed.
https://en.wikipedia.org/wiki/File:XB...ab_landing.jpg
https://www.airliners.net/photo/USA--...ess/0642948/L/
This is what my bike is doing....
It's going in a straight line along the highway - but the frame / front end is running at a slight angle to the centre line of the highway.
Crabbing - I think is the name for it.
Me thinks - Best cure - dead accurate measurements with 1 meter ruler, 150mm ruler, string line, and by line of sight.
Determine exact problem. Apply exact solution.
The "magic trick" is to TURN the wheels to run straight down the runway by rotating them by 7*, so that the aircraft lands and is running in a straight line down the runway, but it's running slightly sidewards - as it runs down the runway. And they can do it up to 20* off center.
https://en.wikipedia.org/wiki/Crosswind_landing
Look at this picture and which way the plane AND the wheels are pointed.
https://ep.yimg.com/ca/I/mcmahanphoto_2090_89216671
In this picture - look at the wheels - and what their direction of travel is; and which way the plane is pointed.
https://en.wikipedia.org/wiki/File:XB...ab_landing.jpg
https://www.airliners.net/photo/USA--...ess/0642948/L/
This is what my bike is doing....
It's going in a straight line along the highway - but the frame / front end is running at a slight angle to the centre line of the highway.
Crabbing - I think is the name for it.
Me thinks - Best cure - dead accurate measurements with 1 meter ruler, 150mm ruler, string line, and by line of sight.
Determine exact problem. Apply exact solution.
Last edited by Coporate-Hoare; 02-15-10 at 08:27 AM.
#6
Senior Member
Joined: May 2005
Posts: 2,335
Likes: 133
From: SFBay
Bikes: n, I would like n+1
Not quite. even if there was nearly no sail area on the side of the plane you would still have that issue. The problem is that planes need to fly with air speed rather than ground speed. This leaves them turned. The fix to fly not quite in line with the wind is some rudder and elevator/aileron correction. At some point though, you can't correct enough to prevent the plane from having a roll offset. This is why passenger planes with the engines under the wings have flat spots on the bottom, better clearance for that roll offset. The turning wheels allow you to have more yaw error between the wind and runway vectors when landing.
#8
Old Fogy
Joined: Oct 2006
Posts: 1,225
Likes: 1
From: Murray, Utah
Front wheels don't have any dish. It shouldn't matter which way it is in. Tread may be directional is the only reason it has to be one way or the other.
#9
Senior Member
Joined: Jul 2009
Posts: 226
Likes: 0
From: Lincoln Ne
Bikes: RANS Stratus and a Mountain bike
One cheap easy way to check frame alignment is to take a string and tie one end to one of the rear drop outs -----run string forward and around head tube. Then back to the same place on the other drop out. Now measure distance from each string to the down tube. Make sure the string on the rear drop out is tied in the same location on both sides of the drop outs.
#10
Senior Member

Joined: Mar 2003
Posts: 8,521
Likes: 2
From: Beaufort, South Carolina, USA and surrounding islands.
Bikes: Cannondale R500, Motobecane Messenger
One cheap easy way to check frame alignment is to take a string and tie one end to one of the rear drop outs -----run string forward and around head tube. Then back to the same place on the other drop out. Now measure distance from each string to the down tube. Make sure the string on the rear drop out is tied in the same location on both sides of the drop outs.
Thread
Thread Starter
Forum
Replies
Last Post
hassouni
Bicycle Mechanics
12
06-07-14 03:00 PM





