Commando Top Speed? (2010)

Jeandr said:

daveh said:

Hobot — you can record your Commandos' top speeds with a Sat Nav or a bicycle computer. Failing those, rev counters are often more accurate than speedos and you can calibrate them from a borrowed electronic tacho (or maybe even from a dyno?). You can then calculate your speed from the workshop manual or (if non-standard) by using a formula, such as:

http://www.rbracing-rsr.com/gearspeed.html

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My formula is:

Mph = rpm x .00297 x tire diameter in inches / overall gear ratio

For example, a K81 4.25/85 H18 has a 25.5 inch diameter, a normal Commando has a 4.730769 overall gear ratio in top gear with a 19 tooth countershaft sprocket.

Mph = 7000 x .00297 x 25.5 / 4.730769 = 112 which is about what I saw indicated on the speedo, the real speed may have been a bit lower.

Now, to get a Norton to 130, 150 or 160, the engine must turn a whole lot faster or the gearing must be changed. What is the size of the countershat sprocket needed to get there assuming we keep the same 7000 rpm maximum engine speed?

for 130 the countershaft sprocket will need to be a 23 tooth, for 150, a 26 tooth and for 160, a giant 28. While a 23 tooth sprocket is available, it would limit acceleration in the lower gears to get the high speed as for the others, I don't think they are available and the accelaration would suffer even more if thew were. While it could be said the engine could be reved faster, I don't think it would survive very long at higher than 7000 rpm, especially while trying to produce a lot more horsepower to acheive those speeds.

Jean

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I have an excel spreadsheet that you can enter all this into and it spits out the speed.

Post your sprocket sizes and rpm and I'll tell you your speed.

As noted, I'm sure that a Commando can be modified to perform with current bikes, just as a 1932 ford can be modified to perform with a current Mustang (or whatever) but my personal interest in the Commando is to get the best performance out of it that I can with the bike in essentially oem condition. I don't want a bigger motor, a different or modified frame, a magneto, 12:1 (or whatever) pistons, etc, etc, etc. If I wanted that performance, I'd buy another Duck for a lot less money!

Hi John

7000 revs 5 gear quaife 38 front pulley 70 clutch drum 19 gearbox 45 rear wheel. Dunlop 124 tyre.
Thanks
Chris

grandpaul said:

Couldn't a different primary drive ratio give you higher speed without so many teeth on the mainshaft sprocket?

Couldn't a smaller rear drive sprocket also give you a higher ratio without such a big mainshaft sprocket?

Also, reasonable cam, crank, rod & piston swap would certainly yield higher safe operating RPM...

Re-calc!

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You have to go by what is available, if it has the stock triple row chain, then the primary ratio is 26 engine - 57 clutch = 2.19 for the ratio ( or 2.1923076 for Mr Spock)

Most belt drives would be around that same ratio because they build them to fit standard bikes.

The stock back sprockets have 42 teeth. As long as we are talking stock parts, the only possible change is the countershaft. I know Hobot has a custom back wheel from a Suzuki water buffalo (if my memory serves me right) and the back sprocket can be changed on that much easier to get at the claimed speeds. As mythbusters would say "plausible"

Now to spin the motor faster, sure cams, valves... can be changed to work higher than 7000 rm, but the stroke still is 89mm and the limiting factor is piston speed and unless longer rods are used, piston acceleration. Remember this is a motor designed in the late fourties as a 500, running it with longer strokes and bigger bores as an 828 from the factory or bigger by some builders is playing with very short fuse. Herb Becker made a 500 with a very short stroke, he could run it up to 10,000 rpm, worked until a valve went on strike (head broke from the stem) and destroyed it.

Let's say I beleive 130 is possible, I may even beleive 135 on a good day, but 150 or 160 no way, I even have a hard time beleiving anyone who says ALL Hayabusa riders took their bike up to those speeds, I would be surprised if more than 50% have ridden their crotch rockets faster than 150 mph let alone taking them to the red line in top gear :!:

Top speed stories and fishermen tales both seem to have something in common, I just can put my finger on it :roll:

Jean

Chris said:

Hi John

7000 revs 5 gear quaife 38 front pulley 70 clutch drum 19 gearbox 45 rear wheel. Dunlop 124 tyre.
Thanks
Chris

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Ok, I haven't got the circumference for a Dunlop KR 124 I'll assume 80" which won't be far off.

Top gear in a Quaife is 1:1 isn't it?

My calculator gives me 121 mph

If you let me know you email address via PM I can send you the spreadsheet.

john

Jeandr said:

You have to go by what is available, if it has the stock triple row chain, then the primary ratio is 26 engine - 57 clutch = 2.19 for the ratio ( or 2.1923076 for Mr Spock)

Most belt drives would be around that same ratio because they build them to fit standard bikes.
Jean

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Actually, a lot of the belt drives, particularly the ones used by vintage racers are much taller than the stock 2.19. The Bob Newby kit that I use is 1.75, and the two Norman White drives I've used are 1.78 and 1.82. All of them allow a much higher top speed with the available Commando sprocket combinations. The trick is building a bike that will actually pull that sort of gearing at redline.

Ken

The belt drive I just got is 36 tooth front and 72 back. 2:1. Most belt drive setups have options for both sprockets.

One of the problems with running a taller ratio belt drive primary is the limitation of front pulley size if you want to run the stock alternator. Not usually a problem on a race bike. The BNR drive I use has a 40T front and 70T rear pulley. No way it would fit with stock alternator studs. One of the pluses of the Norman White drive was that it could be used with the stock alternator, and still provide the taller ratio, good for gearbox life and convenient for taller overall gearing. Norman used the bronze plates from an AJS clutch, which are smaller in diameter than the Commando plates. That let him use a smaller diameter clutch pulley. The two drives I used from him had 33/60 and 36/64 pulley combinations.

Ken

36 crank/72 clutch 2:1, 1:1 4th, 21T-42 rear 2:1, 120x80 tyre circumf. 82"= 6'10"
@ 6100? I swear I felt tire expand right before top out, few more mph needled but not rpm? Must try foam against tire to see if or how much it does for sure.

Peel's new variable gear rear, plenty potential to reduce teeth # upping tire rpm.

hobot said:

36 crank/72 clutch 2:1, 1:1 4th, 21T-42 rear 2:1, 120x80 tyre circumf. 82"= 6'10"
@ 6100? I swear I felt tire expand right before top out, few more mph needled but not rpm? Must try foam against tire to see if or how much it does for sure.

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My gear calculator says that's 118 mph.

Is your rear rim 18 or 19"?

18" Wm3 rim.
Boy if only 118 mph them moderns were sure scared to hit even 120. If ya think they weren't trying - oh well - I'm still so chuffed by it I can take the doubts here.

Peel whomped my SV650 after 60, which could barely hit 120 indicated = 117 if I found opens enough to wait on it after 110 or so. I also had to be careful to hold on tight before much throttle in lower 2 gears. But its Peels turning capacity I'm so flabbergasted about. Her old power plant and speed is a dead horse to whip. But it was so good I'd like to reproduce it in factory Trixie Combat - if it works again, then the set up would increase in value to sell off, as not up to what new Peel needs and it'd would too much power for temptation on un-tamed isolastics in my twisted area - even ordinary Combat power scared me terrible in pre-Peel. I only rode Trixie into-out of hinged horrors a few times just to know its innate to avoid going around that harsh or accelerating through longish sweepers. I did not like Peel's tallest ratio in 1st d/t committed launch speed on clutch release to 'ease' into pasture or onto THE Gravel.

Imaging if next Peel had power to pull 160 what tranny and rear sprocket T-count would give that at 'safe' 7000 - given the 2:1 primary belt ratio and same size tire circumference - 82". Ken Canaga has chart of what's been run at various tracks and various Nortons but I loss 3 yr of files d/t 'puter crash.
Some of his show gearing to 160+. Peel may even pull a good load up to 8000.

There are power to speed calculators but what the heck to plug in for motorcycle drag?

My calculator says that to get around 160mph you'd need 23/42 primary and 23/42 final drive ratio and 7000rpm

There is no doubt whatsoever that the Commando in common with any 1960s Brit machine can be improved enormously, through relatively simple modifications such as modern carburetion and ignition, and close attention to the suspension. In a nutshell with a few modern parts fitted the old bikes are more reliable, perform a little better, and are much nicer to ride.

However making ridiculous (and wholly unsupported) claims about 1960s bikes being able to outperform modern machines, with twice the horse power, as well as far better handling and brakes, is something that defies the laws of physics, and seems to suggest that anyone making such claims has little or no understanding of the subject matter being discussed.

The very act of posting this type of nonsense on the web seems to afford it a curious form of credibility, and serves only to create confusion, and might even result in those that know no better actually believing that a old 1960s bike with around 50bhp at the rear wheel is able to do 160mph, and outperform current sports bikes in pretty much every department.

The internet does not operate using the same physical laws that govern things in the known universe. Therefore, virtual Norton Commandos are quite capable of out-performing motorcycles that, in the real world, have more power, better brakes, better tires, better suspensions, etc. But since real world specifications/capability does not apply within the internet, anything can be claimed to occur.

Commandos are old school, but that long stroke and torque has to be the key that enables them to keep up with the modern stuff in traffic and twisties. This is a shot of us taking a short break on our run to Assen.The old girl held her own two up and fully loaded. Generally we ran at 80 to 90mph and strangely the Commando returned better MPG than the others. However, on the way home when we got to the Dam wall did those plastic rockets light up. I tucked in the slipstream of my younger brother and his wife on their new VFR and ran over the ton when my wife gave me a good dig in the ribs. Otherwise .... well I can only dream. Though I can believe a Factory Race Commado got close to 160mph and the 850 HP Commando did stomp a Kawasaki Z1 and achieved over 132mph to do it. And for an unblown long stroke pushrod twin that's bloody fast in my book.

Cash.



ps If you can zoom in you won't find an oil leak either. 8)

mike996 said:

The internet does not operate using the same physical laws that govern things in the known universe. Therefore, virtual Norton Commandos are quite capable of out-performing motorcycles that, in the real world, have more power, better brakes, better tires, better suspensions, etc. But since real world specifications/capability does not apply within the internet, anything can be claimed to occur.

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Thats pretty much spot on Mike...............lol

Carbonfibre said:

...an old 1960s bike with around 50bhp at the rear wheel is able to do 160mph..

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Your criticism fails in that you state "60's", when it should be "70's", and "50bhp at the rear wheel" when it should be "70bhp" (and leave out the part about the rear wheel if using bhp).

Other than that, I don't read a "slam" in your criticism, just a healthy level of skepticism and a bit of overexuberance in the interest of safety regarding newbies causing harm to themselves by reading hobots posts.

If you've ridden a Norton you probably know how fast they go. My experience has been that a 50-60 something year old person that sees my Norton will approach me and tell me about the Norton he once had, or a Norton someone he knew had, that went 140-150 mph. I recall the rumors of my youth were that a Vincent Black Shadow would do nearly 150 mph.

There are a few "legendary" classic bikes that frequently have excessive claims laid on them:

Norton Commandos
Triumph Bonnies & Tridents
BSA Rocket 3s
Kawasaki Z1s, KZs & triples
Honda 750 fours
Yamaha RD400s
HD Sportsters

Among these, some claims are more believable than others; most are excessive, a few are nearly achievable if you figure in speedo error on the high side.

...and thus shall it ever be...

Edit: included Sprtsters, how could I have forgoten the legend of legends?

Early Sportsters would pull fourth gear wheelies, too. I know. For I knew someone, who knew someone that had witnessed it.

One thing I can say for sure, there are reports on this site that indicate there are Nortons that go a hell'va lot faster than mine and get a hell'va lot better gas mileage than mine, too.