just wondering...

Fast Eddie said:
UQAM. Really….?
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A Commando can be developed to be just as effective. In Australia in the early 1960s, the 650SS competed successfully in A grade races against Manx Nortons. The capacity difference is not a significant factor, under many circumstances. I do not believe my Seeley 850 would beat a 500cc Manx on the IOM.
 
hybridracer said:
One snag with lowering the C. of G. is that the the bike must be lent over more at the same cornering speed. The same applies when wider tyres are fitted.
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That seems counter intuitive to me. Can you explain why for both?
 
acotrel said:
A Commando can be developed to be just as effective. In Australia in the early 1960s, the 650SS competed successfully in A grade races against Manx Nortons. The capacity difference is not a significant factor, under many circumstances. I do not believe my Seeley 850 would beat a 500cc Manx on the IOM.
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When "Slipper Sam" broke the 100mph average at the IOM it was not due to power. The current 200 mph bikes at the IOM are only averaging about 135 mph (last I looked). To be fast there requires a large set between your legs, and handling.

Similarly, when the dual-carb Triumph 500s won Dayona a couple of years (so the model was name Daytona), they were very close to stock and produced minimal H.P. Those wins were due to expert riders with big balls and handling alone - they simply out handled all the competition and in fact they always could beat the Triumph 650s for the same reason - they handled better. I used to piss off fellow Triumph riders in back country street races - I was bigger than all of them and I had a Daytona and they had 650s but they could only hope to catch me on straight roads.

So, the question is, which Norton you mention can get around the in-town hairpin turns better, and which can fly better when turning.
 
marshg246 said:
When "Slipper Sam" broke the 100mph average at the IOM it was not due to power. The current 200 mph bikes at the IOM are only averaging about 135 mph (last I looked). To be fast there requires a large set between your legs, and handling.

Similarly, when the dual-carb Triumph 500s won Dayona a couple of years (so the model was name Daytona), they were very close to stock and produced minimal H.P. Those wins were due to expert riders with big balls and handling alone - they simply out handled all the competition and in fact they always could beat the Triumph 650s for the same reason - they handled better. I used to piss off fellow Triumph riders in back country street races - I was bigger than all of them and I had a Daytona and they had 650s but they could only hope to catch me on straight roads.

So, the question is, which Norton you mention can get around the in-town hairpin turns better, and which can fly better when turning.
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the monocoque had a lot of wind tunnel time with rider on bike to develop the fairing/screen, which was important for IOM particularly. Two wheel drifting on high speed corners was also possible, having read PW’s book. Slippery Sam had one wheel offset from the other by significant amount: not much of a problem apparently, and the engine was far from standard….
 
jan nelder said:
the monocoque had a lot of wind tunnel time with rider on bike to develop the fairing/screen, which was important for IOM particularly. Two wheel drifting on high speed corners was also possible, having read PW’s book. Slippery Sam had one wheel offset from the other by significant amount: not much of a problem apparently, and the engine was far from standard….
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The point was that everyone tried to go fast and modified their bikes but rider and handling won. Look at 1970 Production 750 Mountain Course. A 650 Triumph 1st, 750 Commando 2nd, Dunstall 750 Norton 3rd. Who here is going to say that a works Triumph T120 (650cc) has more power than a prepared 750 Commando and a Dunstall Norton?
 
hybridracer said:
One snag with lowering the C. of G. is that the the bike must be lent over more at the same cornering speed. The same applies when wider tyres are fitted.
Click to expand...
This is not so, at least in theory. And as long as their profile is circular, wider tires has absolutely no impact on the lean angle.

Lean angle is determined by 3 actions - centripetal, gravity, and transverse friction forces. Simple force equilibrium dictates the lean angle to be

angle = atan ( G / (m*v*v/R) = atan ( g * R / v^2 )

The variables are
g acceleration of gravity (approx. 10 m/s^2)
R radius of the curve
v bike's speed in the curve of the road

The ability to drive through a curve at a certain speed is determined by force equilibrium between centripetal and friction forces,

m*v^2 / R = CoF * m*g ==> v = sqrt ( CoF * g * R )

where
CoF Coefficient of transverse friction, which depends on the rubber and type of ground (sticky rubber and dry asphalt: 0.5 .... 0.8)

Thus, center of gravity has no impact on the lean angle. Height of CoG above ground (H) does affect the dynamic roll moment required to change the lean angle however.

Mr = m*v^2 * H / R

The main objective for lowering the CoG is to reduce the aerodynamic frontal area Cd*A in order to gain a higher top speed. Fitting a pannier tank means the driver can tuck in behind the wind screen or fairing.
A pannier tank may act as a fairing for a small rider, as shown above.

- Knut
 
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  • Wow
Reactions: TBW
marshg246 said:
That seems counter intuitive to me. Can you explain why for both?
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What happens when you run wide tyres? For a start they don't turn as fast, so you have to lean further! There is a limit to that! You end up on your ear. Read Knut's maths.

Really you need to lean a lot, that knee slider will touch down in a few more feet, but since there are limits you have to hang off the bike like this to place your weight in the right place to compensate for not leaning the bike as far as you would on narrower tyres!! What have I achieved by sliding off the seat? I have lowered the CofG and messed with the values in Knut's equations. And in this case I have done nothing positive for aerodynamic drag, so I need to get back on the seat and tucked in for the straight bits.

Yes, I can see that might seem counter intuitive. Of course there are 'heroes' who hang off and get their knees down with skinny tyres, I am not one.

This is a 190/50 x17, the standard road tyre size for the bike, the preferred track tyre size for this bike is a 180/55 x 17 because people say they turn faster. My Rickman runs a 130/70 x 18, and others prefer to use a 110/80 x 18 for faster turning.

Older guys like to criticise as 'fashion' the techniques that are demanded to go quickly on these bikes. Demanded in particular by the tyres. You just ride them differently, because, they are different.



1705241827682.jpeg
 
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t ingermanson said:
Pearls clutched!
🤣
🤣


Perhaps showing two examples of a failed idea that preceded the (prime?) third failed attempt by 20 years, exemplifies perfectly the reason why Norton found itself in the position it was in: holding tightly to old ideas despite all signs. And by "failed attempt", I mean the feature did not last, and it got the organization no further toward a goal of sustaining itself. If the goal was to watch the entire starting grid hop up and down, I guess Norton was a rip roaring success. Tally Ho!
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They weren't failed ideas. They were perhaps poorly timed ideas!

The Porcupine was intended to be a supercharged engine, and they banned superchargers.

The Manx was a very successful single cylinder racer, and the multi's arrived.

The JPS was a fast F750 machine that relied on chassis technology for speed rather than engine technology, and Yamaha and their 2 strokes arrived with a different interpretation of the F750 production based rules.

Using 2 cylinders from a Cosworth F1 engine?, now that was a failed idea, because the people who commissioned Cosworth chose people with the wrong experience and wrote a brief that could not be met by one power plant.
 
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mdt-son said:
This is not so, at least in theory. And as long as their profile is circular, wider tires has absolutely no impact on the lean angle.

Lean angle is determined by 3 actions - centripetal, gravity, and transverse friction forces. Simple force equilibrium dictates the lean angle to be

angle = atan ( G / (m*v*v/R) = atan ( g * R / v^2 )

The variables are
g acceleration of gravity (approx. 10 m/s^2)
R radius of the curve
v bike's speed in the curve of the road

The ability to drive through a curve at a certain speed is determined by force equilibrium between centripetal and friction forces,

m*v^2 / R = CoF * m*g ==> v = sqrt ( CoF * g * R )

where
CoF Coefficient of transverse friction, which depends on the rubber and type of ground (sticky rubber and dry asphalt: 0.5 .... 0.8)

Thus, center of gravity has no impact on the lean angle. Height of CoG above ground (H) does affect the dynamic roll moment required to change the lean angle however.

Mr = m*v^2 * H / R

The main objective for lowering the CoG is to reduce the aerodynamic frontal area Cd*A in order to gain a higher top speed. Fitting a pannier tank means the driver can tuck in behind the wind screen or fairing.
A pannier tank may act as a fairing for a small rider, as shown above.

- Knut
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marshg246 said:
That seems counter intuitive to me. Can you explain why for both?
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Knut,

You have overlooked one vital point in your analysis. As the bike leans over the contact point with the road moves from the tread centre towards the edge of the tyre. The resultant force vector to use in equilibrium calculations is between the C. of G. and that contact point, not the middle of the tyre.

If you sketch a force diagram using this actual contact point, it should become clear that as the tyre is widened, or the C. of G. is lowered, the resultant force vector becomes more upright for the same bike angle of lean. If it is not obvious to you that this must result in a slower speed, you can calculate the cornering speed at an arbitrary lean angle using your method, in which the contact point remains at the tread centre, then recalculate the speed with the resultant force vector from the actual contact point.

I hope this makes sense without including diagrams.
 
marshg246 said:
The point was that everyone tried to go fast and modified their bikes but rider and handling won. Look at 1970 Production 750 Mountain Course. A 650 Triumph 1st, 750 Commando 2nd, Dunstall 750 Norton 3rd. Who here is going to say that a works Triumph T120 (650cc) has more power than a prepared 750 Commando and a Dunstall Norton?
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Malcolm Uphill! A much underrated but brilliant rider. However:

The first race I ever rode in at Cadwell Park in 1975 on my standard Commando Fastback was won by a decent margin by a chap riding what was referred to as an 'ex-Malcolm Uphill Thruxton Bonneville'. (use reference with caution because if all the bikes described as 'ex-Malcolm Uphill Thruxton Bonneville' entered one race, there would be a grid of 30 or more 'ex-Malcolm Uphill Thruxton Bonnevilles' and a few reserves and nothing else in sight).

Talking to the thoroughly nice chap who rode it, who happened to work at BRM in Bourne, he told me it was his first race too, pointing to his orange novice jacket (a statement which I later found rather ignored his successful earlier motocross career). Why so fast then? I asked, 'Oh it's just so easy to ride' 'just open it up in 2nd and 3rd and ride round'.

Ease of use for a race bike is a much bigger thing than most people credit. The Daytona 500 Triumphs had it too.
 
hybridracer said:
Knut,

You have overlooked one vital point in your analysis. As the bike leans over the contact point with the road moves from the tread centre towards the edge of the tyre. The resultant force vector to use in equilibrium calculations is between the C. of G. and that contact point, not the middle of the tyre.

If you sketch a force diagram using this actual contact point, it should become clear that as the tyre is widened, or the C. of G. is lowered, the resultant force vector becomes more upright for the same bike angle of lean. If it is not obvious to you that this must result in a slower speed, you can calculate the cornering speed at an arbitrary lean angle using your method, in which the contact point remains at the tread centre, then recalculate the speed with the resultant force vector from the actual contact point.

I hope this makes sense without including diagrams.
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An effect that can be seen on the tacho, if you have time to watch the tacho! rpm increases as you lean over! And it's not that you are slowing down significantly at this point unless you are a real hero and still braking hard. Because indeed the edge diameter is also reduced compared to the centre diameter.
 
ashman said:
I think you might be over thinking things, our old British MC are a lot lighter than any Japanese MCs of the day and most British MC do have the weight down low even the new modern Triumphs also have the weight down low, my 2016 Thruxton is a heavy weight bike but it feels very light when riding it as well pushing it around the workshop, its the same weight as my old 2013 Thruxton but feels so much lighter, the 2013 900 Thruxton felt top heavy compared to the 1200 Thruxton.
But all the modern bikes that had fuel pumps and injection they could put the fuel tank down low but they also had a fake fuel tank on them where the normal tank sat as really a bike will look stupid without a normal tank on it.
My 850 Commando/Featherbed is a very light weight bike having the fuel tank on the top rails just help the bike grip the road a bit better even when I have everything down low and the tank just looks right where it is, a Commando wouldn't look right as well if the tank was somewhere else.
Does the bike feel any different when the fuel tank is low compared to being full, after 50 years of riding I have never really taken any notice and your tank never stays full anyway.
You could run with a small fuel tank, but I am sure you get sick of stopping all the time for fill ups.

Ashley
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We weighed an 865 T100 here on the hanging scales. It was 509 lbs full of fuel. The Thruxton R was 477 lbs full of fuel. I would guess that the Thruxton 900 is similar in weight to the T100 as its essentially the same bike with a different seat and tank.
So I suspect that your 2016 Thruxton 1200 is substantially lighter than your Thruxton 900. The standard Thruxton 1200 listed as being 4 lbs heavier than the R. I'm not sure why that is, although it could be in the suspension or brakes. The newest Thruxton FE is listed at 434 lbs dry, 14 pounds less than my 2016.
It also has a few more bph.
Triumph seems to be going the right way, less weight more power. It is a lot more power and a lot less weight if you consider their early 790 vs the latest 1200 FE .
Too bad that model is discontinued.

Glen
 
marshg246 said:
When "Slipper Sam" broke the 100mph average at the IOM it was not due to power. The current 200 mph bikes at the IOM are only averaging about 135 mph (last I looked). To be fast there requires a large set between your legs, and handling.

Similarly, when the dual-carb Triumph 500s won Dayona a couple of years (so the model was name Daytona), they were very close to stock and produced minimal H.P. Those wins were due to expert riders with big balls and handling alone - they simply out handled all the competition and in fact they always could beat the Triumph 650s for the same reason - they handled better. I used to piss off fellow Triumph riders in back country street races - I was bigger than all of them and I had a Daytona and they had 650s but they could only hope to catch me on straight roads.

So, the question is, which Norton you mention can get around the in-town hairpin turns better, and which can fly better when turning.
Click to expand...
My short stroke 500cc Triton was built with 650 motor parts and a 63mm stroke crank. I have photos of myself racing it which embarrass me. I can see the anxiety on my face. My Seeley 850 is a world apart. I can ride it extremely fast with no anxiety whatsoever. The Manx I rode was similar. My mate's Triton is a 650, has 18 inch wheels and neutral handling. It is an easy ride but not quick enough in corners - really quick down straights. Nobody should have to be brave to road race a motorcycle - it needs to be done safely.
 
When I ride my Seeley 850 and I am approaching a corner, my mind needs to be where I am coming out of the corner. I just flick the bike into the corner and almost immediately gas it hard. As the back of the bike goes down, the bike will turn in the direction of lean and stay more vertical - so the motor stays on full blast. A Manx is saner than that. On the IOM, I would need a memory like an elephant.
 
I am not bragging when I talk about the handling of my Seeley. I did not realise how it could be used until the last time I raced it. It is ridiculous. It has got shit tyres and a slow motor and is still fast enough. In slow corners it loses traction at the rear wheel as I accelerate through, but it does not matter. The whole thing is relatively brainless, but I need to watch where the bike is taking me.
 
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It is a big difference in weight from the 900 Thruxton compared to the 1200 Thruxton but the 900 was a lot heavier up the top of the bike, on the 1200 the weight has been mover down lower as lifting both bikes up off the side stand the 1200 was so much easier, as for the weight of both bikes I was going by the sales broacher's of both bikes and the dry weigh was around the same, about 5lbs less on the 1200 about 485lbs give or take for both bikes, but what ever Triumph has done to the water cooled models the weight is more down lower in the frame, my Norton 850 Featherbed is built even lighter than when it was a full Commando it would be close to 300lbs and a light weight but when riding the 1200 Thruxton it feels as light as my light weight Norton.
Once the Thruxton fell off the side stand on its side and I can tell you it was a struggle to lift it back up on its wheels by myself, my Norton is very easy to pick up as I have been down on it a few time in the 47+ years of riding it, one day I will get the Norton weigh.

Ashley
 
The brochures seem to be hit and miss on weight numbers. That is true with all makes, according to publications such as Sport Rider.
 
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