Dear friends, again I need help. I am filling the data of an WM20 for the Italian Federation, and I have not with me all the data of the bike. I kindly ask you data as Wheelbase - tot lenght - weight - wide - height - max speed - and total ratio engine-gearbox....can someone help me? Many thanks D

email (option): vadori@libero.it

Devis, I have used several sources for the following information and, even so, there are some estimated numbers.

Wheelbase 54 inches
Length 85 inches approximately
(BSA stated 85 inches for later bikes with hydraulic forks, and same wheelbase)
Weight (dry) 369 pounds
Width 28 inches
Height 38 inches approximately
(BSA stated 39.25 inches for later bikes with hydraulic forks)
Saddle height 29.5 inches approximately
(BSA stated 30.5 inches for later bikes with hydraulic forks)
Ground clearance 4.625 inches
Gearbox ratio 1st 2.985
2nd 2.059
3rd 1.318
4th 1.000
Transmission ratio 5.281
Top speed 58-62 mph officially.

Note: one writer quotes WM20 saddle height as 28.5 inches but that doesn’t agree well with other data and I think 29.5 inches is closer to the truth. I suppose it makes a difference which part of the saddle you measure to – I don’t think there was ever an ISO standard for saddle height measurement!

To convert inches to millimetres, multiply by 25.4
To convert pounds to kilograms, multiply by 0.454
To convert mph to kph multiply by 1.609
To convert guesses to facts, …….?

ChrisJ

chris i alway understood that the rake of the steering heads were different angles between the girder/hydrulic forks if so would'nt this make the the wheel base different between them i was told sometime ago you could'nt fit girder to a bike with hydrulic forks because of the different angles of the steering heads

Hi Roger, Steering head angles are the same to within a degree across all BSA frames of the period.
The reason you can't fit tele forks to a 'girder' frame is that with girders the wheel moves away from the frame when the suspension compresses, but with teles it move towards it..This will lead to a collision between the frame and the front muguard under full compression if teles are fitted to a 'girder' frame.
Later (tele) M Series frames had the front down tube shortened , pulled back at a steeper angle and connected to the top of the front engine plates to solve the problem...Ian

email (option): ian@wright52.plus.com

Roger, I understand where you’re coming from and I did think about it before I posted. But given that the 54” wheelbase was common to both girder forked and tele-forked frames, and they both used 19” wheels, I figure that the overall bike lengths must be very nearly the same.

ChrisJ