Norvin Weight

davidd

davidd

Well Known and Active Forum User
VOC Member
Someone brought a a 350 Velocette MAC to Miller for Dave Roper to ride and he came in a half lap in front of everyone else including ten time champ Norbert Nickel on his BMW. Of course, Miller is a two gear track. I can shift into third just after the finish line, but I then have to downshift twice, so it is usually easier to stay in second. That is with a 21T on the front and a 52T on the rear. That is 57 mph in first, 79 mph in second and 94 mph in third. I think a 54T is called for.

With the Twins, I think a big rear sprocket works well. I read in an old MPH recently that you need a 48T rear on a Rapide to hit the highest speed and it will be in third gear. I think it was Ted Davis. I do not know if that is true, but mostly I use the 52T. The trick is to go out in practice and gear for the fastest you can muster on the straight. Assuming the gearing works on the toughest corners it is a keeper. If it does not, with a single you are better off going to a bigger rear sprocket.jWith a single the more sparks per lap, the better. With a twin, you might have power to torque through the bad corners and use a slightly smaller sprocket.

But the rider is the key. The first year Dave Roper won on the MAC the owner/Builder had put regular street tires on the bike!

David
 
Bill Thomas

Bill Thomas

Well Known and Active Forum User
VOC Member
For a Slow rider like me, It is nice to see from Dave Roper's blog ? That he Falls off a few times, He looks a bit on the edge !! I used to use a 56 rear sprocket at most of the tracks, And on 1/4 ml sprints where at the end I did 110 and 111 mph on my Twin Road Special = 6,160 rev's. I whish I could have road like that when I was road racing, But it kept making for the Grass !! Cheers Bill.
 
B

Big Sid

Well Known and Active Forum User
Non-VOC Member
Certainly for fast street riding on a twin the 48 is superior in top speed , flexibility and acceleration . Far sweeter for town work too .
Top speed comes up quicker and is much higher . Simply put the twin is way overgeared , as is the Comet . Sid .


Sent from my iPad using Tapatalk
 
B

Big Sid

Well Known and Active Forum User
Non-VOC Member
Absolutely the best rear sprocket if you live in a hilly area or frequent such . We find a 48 often as the second sprocket on twins .
And it would be very useful to fit a 50 as a second choice on Comets . Note that adding a tooth MORE on the countershaft drive sprocket is like fitting a rear with four teeth LESS . A big difference . Only done on Lightnings for extremely high gearing , Bonneville speeds the aim . Sid .


Sent from my iPad using Tapatalk
 
Bill Thomas

Bill Thomas

Well Known and Active Forum User
VOC Member
Hello Sid, Thats messed me up, I thought it was 2 teeth, My road Special has the bigger gear box sprocket with a 48 rear, And I thought bought it back to standard gearing, Cheers Bill.
 
bmetcalf

bmetcalf

Well Known and Active Forum User
VOC Member
Starting from 21t/46t, going to a 22t sprocket, the decrease would be just 2 teeth for the same ratio.
 
Last edited:
B

Big Sid

Well Known and Active Forum User
Non-VOC Member
Std gearing on a new twin with a 46 / 21 is 3.5 of course , with a 22 front it is 3.34 to 1 with the same rear . The rear drum will take a 45 t , the smallest around it . Going smaller requires an adapter disc replacing the drum . This was found Black Lightnings . Sid


Sent from my iPad using Tapatalk
 
bmetcalf

bmetcalf

Well Known and Active Forum User
VOC Member
Sorry, when I divide 46 by 21, I get 2.1, not 3.5. Are you including the primary ratio?

Big Sid said:
Std gearing on a new twin with a 46 / 21 is 3.5 of course , with a 22 front it is 3.34 to 1 with the same rear . The rear drum will take a 45 t , the smallest around it . Going smaller requires an adapter disc replacing the drum . This was found Black Lightnings . Sid


Sent from my iPad using Tapatalk
Click to expand...
 
B

Big Sid

Well Known and Active Forum User
Non-VOC Member
On my recent top gear ratio figures . I lifted them right off the last page , 67 , in my tattered original 1951 Riders Handbook . My fading memories forced me to seek solid info , that dark blue source seemed good enough .
Noting also that a 45 t rear giving 3.27 on my ancient chart gives 6,075 rpm at 140 and at 150 it's turning 6,200 rpm . This for 3.25 and 3.50 by 19 inch racing tires . Used to figure these details and dream about them in the early 50s as I read of Rollie Frees exploits and many others thrusting Vincents into the Record Books around the world . I'm sure many of you did the same . Sid .


Sent from my iPad using Tapatalk
 
Top