Highest speeds on standard gearing under favourable conditions, (but not sustainable) | ||||
Engine Sprocket | Gearbox Sprocket | Model | Speed | Rear Tyre |
21 | 19 | Norton Atlas | 110 mph @ 6400 rpm (M) | 18 x 4.00 19 x 3.50 |
21 | 17 | N.15 C.S. and G.15 C.S. | 100 mph @ 6400 rpm (M) | 18 x 4.00 |
22 | 17 | G.15 Mk.ll | 104 mph @ 6400 rpm (M) | 18 x 4.00 |
22 | 19 | G.15 C.S.R. | 115 mph @ 6600 rpm (M) 116 mph @ 6400 rpm (M) | 18 x 3.50 19 x 3.50 |
22 | 19 | G.15 C.S.R. (U.S.A.) | 106 mph @ 6000 rpm (C) | 19 x 3.50 |
21 | 19 | P.11 | 105 mph @ 6200 rpm (C) | 18 x 4.00 |
M = magneto/Monoblocs C = coils/Concentrics |
ThanksThe above would suggest your engine sprocket is too small. I am running a 21/19 on my G15 and find it a decent compromise- the bike can run smoothly at road speeds of 60-75 and still have enough grunt for good acceleration. My rear wheel is the same as your Atlas so the overall should match- clutch and wheel sizes are 42 on all.
ThanksI went up one tooth on my engine sprocket from stock ..... IIRC, i am now 22 vs 21.All else stock Atlas.
The vibes are comfortable at 3500 rpm, but become uncomfortable over 4000 rpm.
According to calculations, with 21 tooth engine sprocket, I got 17.5 mph per 1000 rpm, with 22 tooth engine sprocket, I now get 18.33 mph per 1000 rpm.
This translates to the following road speeds at the critical rpm's:
Sprocket. RPM. Mph
21T. 3500. 61
21T. 4000 70
22T. 3500 64
22T. 4000 73
Loss of acceleration is insignificant...... cruise comfort over rules winning stop light drag races.