Do the Ton.

[Triton Thrasher]

Excepting the arguments about rider weight  , this recent  magazine article covers it nicely

It's three years old and it will just about do 100 mph, they claim.

[Rocket Racer]

cowhorn bars and a belstaff are hardly aerodynamic. I'd expect to have the rider on the tank for ton plus on a 40 horse motorcycle.
They said 102 comfortably, but was that just the speedo reading 
I'd certainly expect a reasonably geared A10 (without a sidecar  ) to reach the ton if in reasonable tune.
But agree, with a box that won't hold 3rd, and revs unknown, top speed is fairly redundant
My sidecars actually quite mildly tuned and happily pulls to its geared ceiling of 90 with two lardy blokes on it and no streamlining.

[Rocket Racer]

Coming back to gearing; if you take your sprockets (in Muskies case 23/43 and 19/40), multiply that by your revs (say 6500) you get rear wheel revs per minute, so multiply by 60 to get wheel revolutions per hour and multiply by your rear wheel circumference (say 2.04 metres - tyres can differ quite a lot)and divided by 1000 to give us kilometres not metres; then we come up with 6500rpm equates to 202 kph or 126mph. Fairly tall gearing...
If we do the maths backwards from 160kph (approx the ton), with that wheel circumference and sprockets  we're only pulling 5145rpm which I suspect will need a light prone rider, a decent fairing or a tailwind to get to the ton but will do 90 all day

I recently read a period article on the A75 outlining that while the bikes could genuinely pull 130mph our American cousins preferred to gear them for redline at the ton as the mid range acceleration was spectacular. In most cases for road bikes gearing is set for comfort at best touring speeds rather than being able to hit 105 with the engine hard on the redline.

[RichardL]

Four reasons I won't be attempting the ton any time soon:

1. I built it.
2. I would be the one repairing it.
3. I would be the one paying.
4.  250 lb. Payload.

By the way, should it even be called "The Ton" if it's not in MPH? For some things you just have to forget metric elitism.

Richard L.

[Rocket Racer]

In pre motorway UK or for that matter here, on rubbish roads and with limited suspension, the ton was a bit of a holy grail for bragging if you lived... but these days with modern cycles, even (200kph) 120mph is pretty ho hum. Modern bikes on the IOM doing over 300kph. You dont ride a fifties or sixties pommie bike for its performance.

Over here the police love it if they can have some customer interaction with any motorists travelling more than 110kph , so practically on the road here all I want is to sit on 70 mph.
For a track day though... I'd be lowering my gearing for the red line and some red mist...

Nothing wrong with pedaling an old un out to the red line and waking a few car alarms though...

[bsa-bill]

By the way, should it even be called "The Ton" if it's not in MPH?

Ah but it is Richard the ton = 100 mph  in metric 100 kph I think is around 60 mph hardly much to boast about

[RichardL]

Right. I was bemoaning the temptation to convert the fabled "Ton" (100 MPH) to metric (approx. 160 kph) where it loses its aura.

[worntorn]

I have a 1958 A10SR with a RGS tunede engine, But I find it hard to "do the ton"
Hard to reach the Ton..

Engine rebuild in 1996. All re-done. SRM every thing. Incl. re boring of the to engine half.
Crank dyn. ball.

Engine tuned with: 1 3/16 monoblock ,
Cylinder head complet re-done by the cylinderhead shop with modern race valves.
Cylinder head: late type Big valve type.
Cam: spitfire scr. 357
Pistols, high comp.
New SRM cam followers
New rocker box parts....
Engine running a tad bit rich ( do not dare running to lean )
23T engine sprocket.
Std. Solo gearbox sprocket.
Running with octan 95...
Automatic advance unit
Magneto ignition
SAE 40 oil
19" wheel, with 3.25 front, 3.50 rear. Mitas tyres.
Silencers: SR twin.

Engine run like a "bat out of hell"
Power full and strong

But reaching the Ton, is a hard struggle.

What does it need to reach the Ton with ease ?

You mentioned in another thread that this bike has a 21 tooth gearbox sprocket in place. If this is so it is severely overgeared as standard for the SR is 19 tooth on gearbox and 21 on the engine. If both your gearbox and engine sprockets are 2 teeth more than standard gearing, then it likely would be too much for the bike to pull. Whether the bike has some hotrod parts on it or not won't make much difference, it is only 650 CC s of old design pushrod engine.
When I changed the engine sprocket on my SR to 23 teeth ( but gearbox still at 19) the top speed dropped a few MPH, but the relaxed relatively smooth running at highway speeds is nice. The reduced amount of acceleration isn't.
I'm thinking of changing it back to standard gearing.
Also, relative bike to bike top speed numbers with the Smiths speedometers don't mean much. The speedometers as fitted on old British bikes tend to read optimistically high , some more than others.
Trevor made me aware that the cable ratio on my speedo was wrong. It is a 1650 whereas a 1450 or thereabouts is correct. It turns out that a 1450 reads  high by about the same amount as a 1650 reads low. I mounted a 1550 ratio speed on there and it is bang on with the GPS.
I'm sure BSA deliberately fitted speedos which gave a nice high number as did the other manufacturers. Most magazine articles of the day used these optimistic speedo numbers in their reviews. We read them and dreamt of owning a bike that could so easily top the ton. Now we are old and maybe not so skinny but finally have the money for the bike, but it's not quite as fast as the magazine article said, especially if you fit a GPS!


Glen

[edboy]

how is the scratching going viking?
maximum revs for high speed running is 7,000 - 7,250 rpm and an alloy head model should reach 100mph with tall gearing eventually. originally there was no traffic lights after london until  brighton and the problem now is stop start and a more revvy enging is preferable. i ve found on my triumph that the main jet if spot on makes a great difference.your engine will run hot but main jet factory settings i have found are spot on and would be my first hurdle.

[paulmbsa]

you wouldnt ask your gran to do a cartwheel so why ask your bike

[Viking]

The bike is in fine mechanical shape... Few bikers I know, has spent the same amount, and att. to details, as I have.

Yes 3.gear jumping is an issue now, it will be addressed this Winther. I will enjoy good days in October to end an active 2015 BSA SR season. 

Is the Ton so important ? No...

A UK Ton up bike can't hold this speed for hours anyway...

For us on main land EU , km/h is more important , especially 200 km/h , was is the Magic limit in the 70ties

But the SR was "Born" for UK use and was on "the Island" until year 2000, when I moved from the UK to Denmark.
So the odometer is still in MPH and the Ton is the Magic number.

It is running non stressed 80-90 MPH , from there is takes time.....
 
The weight is an issue: helmet, safety gear etc., and belly after bacon and beans in the UK all has an effect :-)

[RichardL]

You have to give up on metric. Metric is dead. It was given a fair chance but has clearly lost out to the inch, foot, yard, furlong, mile and league (oh, and let's not leave out the cubit)

Richard L.

[Rocket Racer]

You have to give up on metric. Metric is dead. It was given a fair chance but has clearly lost out to the inch, foot, yard, furlong, mile and league (oh, and let's not leave out the cubit)

Richard L.

Earlier this year my daughter sat her driving test in her 1964 Mk1 mini with the big speedo in the middle; the instructor had to ask her several times what speeds her MPH speedo equated to as all our speed limits are in KPH and she was passing through various speed limits during her test... He had no clue 

[groily]

Nice one Richard!
But you can eat up the 'miles' satisfyingly fast when the road signs give distances in kilometres  . . .
I've come to like metric over the years - it has the merit of simplicity for those of us born with ten digits at both ends.

[Butch (cb)]

I think that was a significant balls up in a recent (ish) adjustment to one of the motorcycle license tests in the UK. Rules were adopted from Europe and we ended up with a requirement to emergency stop from 50 kph rather than 30 mph. That 50 being higher that our suburban permitted 30 mph (it's just over 31 I think) meant that it all had to be done off road at specialised test centres ... which still had to be built and were always going to be few and far between.