The P11 thread

[Rohan]

What is the sprocket set on a P11?
5000rpm equals 87mph? mistake?
My P11 registers 70mph at 5000. bad speedo?

It makes it a bit tricky when you have spread this discussion across 2 threads,
but since, like Commandos, gearbox sprocket sizes are optional, and unlike Commandos so is the engine sprocket.
I'd suggest that 87 mph at 5000 rpm is going to need more than a 19t gearbox sprocket.
In a Commando, that would require at least a 21t gearbox sprocket, and probably likewise in the P11.

You definitely have to watch the data supplied in roadtests, they often seem to quote what figures were supplied to them,
without them verifying that it applied to THE bike they were testing.

 

[p400]

My crank LOOKS stock, I don't give a hoot what weight it actually measures at.

Yes, it must not be important data. On to more important details.

 

[Rohan]

If you do too much navel gazing, you too could become like hobot ??

 

[Rohan]

Having said that, even as a teenager I made up a chart for what mph my old dommie was doing in each gear at each 1000 rpm.
Involves noting the sprocket sizes, gear ratios, back wheel diam and anything else you think is relevant - like crank weight. (?)
Took all of a few minutes, and the measuring and tooth counting.

Given that early dommies don't have a tacho, it was book data only...

And I have not seen it published or quoted anywhere.
Nor the dommie crank, piston weights etc.
I have several to compare, so its easy to establish if they are stock or in the ballpark, or not.

Different tires make a (slight) difference to published speeds too.
Taller or skinnier tires can easily add or subtract a few mph, everything else being equal.

 

[p400]

just doing the math-
4.00x18 tire => 6.80 ft/rear tire rev
42 teeth/19 teeth = 2.210 and 42/21 =2>> leads to 2.21x2=4.42 rev of rear tire to rev engine.
5000/4.42=1131.22 rear tire rpm at 5000 engine rpm in top gear.
6.8ft/revx1131.22=7699 ft/min at 5000rpm
7699ft/min = 87.5mph
maybe both the tach and speedo are way off, maybe my math is off.

 

[texasSlick]

just doing the math-
4.00x18 tire => 6.80 ft/rear tire rev
42 teeth/19 teeth = 2.210 and 42/21 =2>> leads to 2.21x2=4.42 rev of rear tire to rev engine.
5000/4.42=1131.22 rear tire rpm at 5000 engine rpm in top gear.
6.8ft/revx1131.22=7699 ft/min at 5000rpm
7699ft/min = 87.5mph
maybe both the tach and speedo are way off, maybe my math is off.

Your math is basically correct. Line 2 should read 4.42 rev of engine to rear tire rev.

The proper tire diameter must account for the LOADED radius of the tire. Assuming the tire squats 1/2 inch with the bike and rider weight, this makes the effective tire diameter 1 inch less.

then the tire circumference is 3.1416 x 25 inch/12 in/ft = 6.544 ft.

6.544 x 1131.22 = 7402.7 ft/min = 1.402 mile/min = 84.12 mph

We see that the actual distance traveled will vary slightly with the loaded tire diameter...your value of 87.5 mph is the theoretical max if the bike and rider are weightless. if the tire squats less than 1/2 inch, the actual road speed will be somewhere between the limits thus calculated.

You can check your speedo against the mile markers on the interstate. Then use the gearing math to check tach.

Slick

 

[CanukNortonNut]

You could try using a GPS
The faster you go the more accurate this system becomes. I traveled with my 850 and compared the gps to smith gearbox speedo and found these two gave very accurate results. I’m running 19" front and back but it should be similar with your set up.
Regards,
Thomas
CNN

 

[p400]

I am trying document what an original P11 balance factor appears to be. And this must be the same for pre Commando 750. and maybe same for early 68-70 Commandos.

So I modified a wheel truing stand to accept a P11 crank resting on ball bearings.

I went back and found the "stiction" of the rods to be too high to give an accurate "Bob" weight.
Hanging all weight from thin wire around rod journals, I have a new Bob weight of 1460 g total.
This is a little higher balance factor, maybe 94%.
I am not looking for a regurgitation of how sloppy Norton was ....what is needed is more actual data.
My weights may be all off, my math not correct

Last time you had a motorcycle crank assembly balanced, in addition to discussing the balance factor, what actual data did you capture relating to the crank?

 

[p400]

I have seen a very nice P11 Norton with panniers and a tank bag on some website, I think traveling Europe.
Anyone supply a link to these photos please? I cant find again

 

[Rohan]

Thats Ludwigs bike, on this very forum.
Mit Commando disk up front.
Search button up top RHS.

On your speedo/tacho accuracy

You could try using a GPS

Excellent suggestion, takes all the guesswork out of it.

 

[BillT]

Thats Ludwigs bike, on this very forum.
Mit Commando disk up front.
Search button up top RHS.

Ludwig has an N15CS, hence the easy disc conversion.

I think the bike you're talking about is a Ranger in Finland. Check on the Yahoo! groups site.

There are also some nice pics of a Matchless P11A from a guy in Sweden

 

[p400]

I am not finding anything Ludwig n15cs p11 ranger finland. It was website with the bike pictured with panniers and tank bag, seems it was a p11 model,
any other leads ?
wait I found it , thanks Bill
appears true P11, wheels, oil tank

 

[Rohan]

Ludwig has an N15CS, hence the easy disc conversion.

It has an entire Commando disc front end grafted on ?,
why would that be any easier.
(His pics of it, the last hybrid produced, have gone off photobucket ?)

Very pretty touring P11 shot.
Panniers are (necessarily) somewhat limited in size.
Those brakes don't look very substantial in modern traffic,
are they better than they look ?

 

[Jerry Doe]

Please use the new P11 forum for further P11 topics.

http://www.accessnorton.com/norton-p11-f26.html

Cheers, Jerry