just wondering...

The gas tank with fuel weighs about 25 pounds. It is a bad place to put that much weight but most motorcycles are gravity fed...at least the British ones. I'm sure some enterprising racer figured a way to move the fuel tank lower to about the level of the crankshaft which I think would make a good improvement in handling. It would need a fuel pump. I am not very familiar with Japanese bikes. I know the Goldwing had the fuel tank under the seat which would help. Any idea/pictures?

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

An area which was explored by British racing teams in the 50s at least. AJS I think ??? Their issue was getting enough fuel to go the distance and they used saddle tanks.

Fuel pumps activated by the swinging arm movement. Or was that someone else. Maybe even Norton.

Plenty of examples with modern bikes of course.

Everytime I pull off a full gas tank I wonder what it would be like to have all that weight down low. It seems like a good idea. An idea only for racing. I imagine it would require a special frame built around the gas tank. Of course it would need a dummy tank in the usual place. I'm sure someone, somewhere has built such a thing and tried it out. I would like to know his conclusion.

The thing about handling is where the bike's centre of gravity is, and a amount if trail there is on the steering. Bigger wheels and more rake and less yoke offset - give more trail. When you accelerate a motorcycle, the weight rotates fore and aft around the centre of gravity. And as the back goes down the rake increases at a rate which is controlled by the rear springs. If the front of the bike is light, the process will put you off and you will slow. That F Model MANX might not have enough weight on the front.

To a certain extent, the power delivery type determines the angle of lean which can be used, but a major factor is the trail. Manx Nortons had lots of trail, but did not lean much, and oversteered when gassed mid corner - made them feel great. Earlier two-strokes needed to be upright before being gassed, but had lots of lean in corners and were more tyre-dependent. They had less trail and were neutral handling. Lean is not affected much by lateral weight distribution - except that can steer the bike. With my bike, I do not consciously steer the bike. It steers when it is gassed and tips into corners very easily. It has lots of trail, and always stays very vertical.

johnm said:

An area which was explored by British racing teams in the 50s at least. AJS I think ??? Their issue was getting enough fuel to go the distance and they used saddle tanks.

Fuel pumps activated by the swinging arm movement. Or was that someone else. Maybe even Norton.

Plenty of examples with modern bikes of course.

Click to expand...

I'm trying to remember
But wasn't it a pannier tanked racing commando with a fish tank pump connected to the swinging arm ?
The rider was on the start grid jumping up and down to keep the fuel pumped up
He told the other riders he was warming his shocks up
And pretty soon the whole starting grid were jumping up and down on their bikes
Anyone know the proper story?

I was thinking that if the fuel weight was centered around the center of gravity the bike would roll side to side quite easily.

baz said:

I'm trying to remember
But wasn't it a pannier tanked racing commando with a fish tank pump connected to the swinging arm ?
The rider was on the start grid jumping up and down to keep the fuel pumped up
He told the other riders he was warming his shocks up
And pretty soon the whole starting grid were jumping up and down on their bikes
Anyone know the proper story?

Click to expand...

Some of this does ring a bell yes.

t ingermanson said:

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That looks like the ones I remember. Especially the Porcupine

baz said:

I'm trying to remember
But wasn't it a pannier tanked racing commando with a fish tank pump connected to the swinging arm ?
The rider was on the start grid jumping up and down to keep the fuel pumped up
He told the other riders he was warming his shocks up
And pretty soon the whole starting grid were jumping up and down on their bikes
Anyone know the proper story?

Click to expand...

monocoque Williams Norton used swing arm pump.

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.

Here is the AN video of Norman White running up his '72 style JPS at their open day.


You will see him bouncing on the seat, he does this to operate the swinging arm activated fuel pump! Same system used on later JPS bikes.

Imagine, it's a Commando forum and people go to Manx Nortons and Porcupines before the prime example!

Oh, and as a former Honda Pan European owner on which you sat over the fuel tank, low CofG is a wonderful thing, particularly if your bike weighs 600lbs plus!

SteveA said:

Someone from AN needs to post their video of Norman White running up his '72 style JPS at their open day.

You will see him bouncing on the seat, he does this to operate the swinging arm activated fuel pump! Same system used on later JPS bikes.

Imagine, it's a Commando forum and people go to Manx Nortons and Porcupines before the prime example!

Click to expand...

this one?



approx 2:35 in

t ingermanson said:

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Good post. I have never seen the picture of that prototype replica.
Mike

SteveA said:

Imagine, it's a Commando forum and people go to Manx Nortons and Porcupines before the prime example!

Click to expand...

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!

The only difference between a Commando and a Manx is the engine weight. Think about why the Manx handles better, and where the centre of gravity is in each bike, and the steering geometry involved. Back in the olden days, many of us made mistakes by trying to copy what was done with Japanese bikes. Fitting 18 inch rims to an old British bike to get better rubber was one of them. - The proof of the pudding is always in the eating.

Peter Williams was very involved in designing the Commando racers. Which would be the best way to go - faster down the straights or faster in the corners ? - He had ridden Tom Arter's 'Wagon Wheels', and the first Commandos had that steering geometry. At the time the Commando racers were being used - the fastest bike was the TZ750 Yamaha. Could a Commando beat one of those in a drag race ? - A good Commando based bike only needs to stay near the lead bunch in races. It's power delivery is more usable in corners. Those really high-powered bikes, usually need to be upright and pointed before you give them the berries. I do not believe I am a good rider, but I know how to stay alive. When I race, I like to be heavy handed. My Seeley 850 can be blasted at full power in any corner. It is not me- it is the bike. With most bikes you need to be very careful in corners. The difference is ridiculous.