Wheel alignment

[chrisx1]

My wheels are about 1/2" out of alignment. As far as I know the front wheel is correctly aligned in the forks and the rear chain runs straight as an arrow from sprocket to sprocket. Which leads me to the conclusion that my rear wheel needs to be rebuilt with the rim offset 1/2" to the right or away from the sprocket.
Would others agree?

[Allan G]

I remember mine is offset by a similar amount, If it put a stright edge down one side, both wheel touch the straight edge, if i put it down the other, you get an equal gap front and rear of the front tyre.

Bike handles fine and I never worried about it further, I never checked my A50 with the same frame type, but any unit twin with the later forks (69/70) and the pip on the front axels has a 1 degree defelction in the front axel which may cause an alignment issue.

[ferretjuggler]

I'm lucky (or unlucky) enough to be rebuilding a '69 Lightning basket case which came with no forks at all.
At present I've managed to source a set of Triumph forks which of course have the axle at 90°
They will do to build up the bike in the short term
I'm still trying to work out exactly what BSA were trying to do when they transplanted what was essentially a Triumph front end onto their unit twins.
I'm guessing that by mounting the front wheel 1° offset from the vertical, the idea was to move the contact patch of the tyre in line with the rear wheel.
Seems a very strange bit of engineering, but it must have worked as intended.
I'm still trying to get my head around it TBH.

[Allan G]

Don't forget BSA owned Triumph, yet Triumph was the more desirable marque of bike.

Using common parts was a cost saving exercise, the triumph forks were the better of the two available options. Even the bantam cub came about at this time and used a cub engine in a bantam frame.

The axel offset came about because the engine weight is biased in the frame to one side, not a problem on British roads but our stateside cousins complained of poor handling issues. The 1° offset was enough to correct this issue and was implemented across all unit twin models regardless of their destination.

[chrisx1]

Interesting information guys. Thanks for the replies.

[Bess]

Hi Chris,
             BSA engineer Ernie Webster designed the wheels 3/8" out of line. This was due to the large primary side the engine had to be pushed over in the frame. Then there were concerns, because when seated looking down the left footrest was already 1.5" further out than the right.

Unfortunately the bike in the US was then found to drift into oncoming traffic. So for the US market the front wheel had 1° angle from the horizontal added to counter the bias of the road camber.

In conclusion, 3/8" out of line and a front wheel vertical is fine, same in the US if you're happy with the steering issue.

Best wishes...

[Mike Farmer]

 

Ive had a variety of A50/A65s from about 1968 to date, and never noticed anything amiss with steering or wheel alignment etc. Sad really cos now iVe stopped riding I'll never have the thrill of riding an out of line bike.

Mike