1/8 mile drag Commando performance?

My friend Yves, the owner, calls is Norton 'The Big Spender'...he never stops improving it'and working on it.

Every year, Yves participates to a 1/8 mile drag race, bearing in mind that his is a road bike, he manages pretty good results. Here are his numbers for yesterday's race:

Reaction time: 0,368 sec
1/8 mile time: 8,825 sec
Terminal speed: 138,9km/h - 86,308mph

He would be pretty interested to compare those numbers with those from other Nortons. Does anyone on this forum have 1/8 drag race results that could be compared to Yves'?

Thank you in advance!

It is mentioned someplace that multiplying an 1/8th mile time by 1.56 gives an approx 1/4 mile time.
(Which are more more widely known and watched).

8,825 (where does that comma use come from, rather than point ? 8 thousand 8 hundred and 25 ?)

8.825 x 1.56 = ~13.8 secs for a 1/4 mile equiv.
Not bad for a streetbike/streetbike rider, 40 years old technology.

I see mention of a doorslammer class doing an 1/8th mile in 3.63 secs.
Now that is quick....


P.S.
For dances, before we say anything silly, yada yada yada etc, I have no idea where that 1.56 factor comes from...

Many years ago I attended a 1/4 mile drag meeting on an aircraft runway. the fastest time was just under 13 seconds and was set by a new Super Rocket BSA. I don't know how you would get a Commando to go fast in a 1/8 mile drag. I suppose if you wound the crank up enough and the gearbox didn't fail, you might be quick.

Rohan said:

8,825 (where does that comma use come from, rather than point ?

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Well, since you ask so kindly, you should know that in some parts of the world, some people speak other languages and/or use other punctation conventions. I am one of these people.

Once again, you are showing very limited elegance, please excuse my French.

The blurb on the factory hotrod 850 that Dave Rawlins ran some sub 12 sec 1/4 times mentioned that he leaned really forward on the bike and got the rear wheel spinning, so when it grabbed it really launched.
The leaning forward was also necessary to keep the front wheel from going skyward.

This took more than 2 secs off the time most mortals could achieve ?

Jagbruno said:

Well, since you ask so kindly, you should know that in some parts of the world, some people speak other languages and/or use other punctation conventions. I am one of these people.

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Humour us. Different folks, divided by a common language....

I'm sorry, but if I feed 8,825 into a calculator, it gives a rather different answer to 8.825 !!!!!
Also, how does that distinguish 8,825 from 8,825 (where one is 8 and a bit, and the other is 8000 and a lot of bits).

Rohan said:

8,825 (where does that comma use come from, rather than point ? 8 thousand 8 hundred and 25 ?)

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I'm in the US, but I believe it is a fairly common convention in Europe to apply a comma rather than a period to indicate a decimal point?

While I was drafting the above comments I see there was already a friendly conversation started on the topic

Regrettably I have no hard data to offer, but as noted above often a multiplier in the 1.5 to 1.56 is applied to the 1/8 mi time to estimate the ¼ mi time. There are quite a variety of calculators to do similar, e.g., where a single input is used to provide a wide range of outputs.
http://www.wallaceracing.com/etcalc.php

I have a book with all of the period Commando road tests including their quarter mile times, Cycle, Cycle World, Motorcyclist, etc

These were all supposedly stock machines showing from 600-1500 miles since newsupplied by the US importer presumably.

The 19 tooth Combat was of course the quickest with one magazine reporting a 12.6 quarter mile, one a 12.9 and the others around 13.3

Standard 750s and 850s (more torque but higher gearing) were all tested anywhere from 13.2 to 13.9, and the 75 Mark3 around 15 seconds.

WOF top speed tested, not estimated, were between 103-110 depending upon what tooth front sprocket was fitted stock

WZ507 said:

I'm in the US, but I believe it is a fairly common convention in Europe to apply a comma rather than a period to indicate a decimal point?

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There are some famous stories about space vehicles that have been lost from that exact cause ?
Very expensive comma. Very....

But we diverge..

1up3down said:

I have a book with all of the period Commando road tests including their quarter mile times, Cycle, Cycle World, Motorcyclist, etc

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The gold portfolio of Nortons.

Isn't there a story that Berliner flew out the factory test pilot to demonstrate to the US bigwigs how those sub 12 sec 1/4 miles were done.
There is a pic of them watching, so it may be more than a story...

Charts and equations could not possibly account for the virtually unlimited power characteristics available from the virtually unlimited gearing and tuning possibilities (forget about tower reaction time) that could produce sublime to extreme variations in speed and performance AFTER the 1/8 mile.

...unless you happen to be running an electric bike with extremely linear power delivery and no transmission...

Look at ANY power and torque graphs of combustion / motorcycle/ Norton / Commando engines and tell me how how a simple multiplier could be anywhere NEAR close to predicting the outcome of a 1/4 mile race from the 1/8 mile time.

Factory Interstate Combat no mufflers 7th day owning, 1st time on strip & burn out rear heat but not 1st time WOT clutch drops. Combat far lane vs 1200 Sportster camed for drag only with wheelie bar.

Good to see you back in action Steve.
My apologies if my bedside manner was not everyones cup of tea.
You have beaten me to it, better info too.

grandpaul said:

Look at ANY power and torque graphs of combustion / motorcycle/ Norton / Commando engines and tell me how how a simple multiplier could be anywhere NEAR close to predicting the outcome of a 1/4 mile race from the 1/8 mile time.

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Probably by recording LOTS of bikes and seeing what they do for the 1/8 mile
and then go on to do for the 1/4 mile. !!
At the same track and on the same run even (?).

But you are right, there should be lots of variation.
Especially where a tiddler say does a good 1/8 time, but doesn't have the mumbo to go on for a good 1/4 time.

BTW, this is real world measuring and numbers .
Charts and dyno numbers are optional (?)
Cheers.

grandpaul said:

Charts and equations could not possibly account for the virtually unlimited power characteristics available from the virtually unlimited gearing and tuning possibilities (forget about tower reaction time) that could produce sublime to extreme variations in speed and performance AFTER the 1/8 mile.

...unless you happen to be running an electric bike with extremely linear power delivery and no transmission...

Look at ANY power and torque graphs of combustion / motorcycle/ Norton / Commando engines and tell me how how a simple multiplier could be anywhere NEAR close to predicting the outcome of a 1/4 mile race from the 1/8 mile time.

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Sure they can. You make it sound like it's a total crap shoot to estimate from the 1/8 mi time what the ¼ mi result might be, when in fact this has been done for 10s of 1,000s of vehicles for decades and the resulting multipliers fall in a relatively narrow range of values. More specifically in this case the 1/8 mi times multiplied by 1.50 - 1.56 give results that are in good agreement to the literature values posted by "1up3down" who said "Standard 750s and 850s (more torque but higher gearing) were all tested anywhere from 13.2 to 13.9 [sec]".

In Yves case he's had 1/8 mi and 8.8 seconds worth of "ANY power and torque graphs of combustion / motorcycle/ Norton / Commando engines" delivered to the rear wheel so there is not much unknown about how the next 1/8 mi is going to go. For vehicles running a ¼ mi in the 13 second range, they have achieved ~ 80-90% of their maximum speed by 1/8 mi, so there is not really that much mystery surrounding what happens between the 1/8 mi and 1/4 mi mark. For a given vehicle, 1/4 mi top speed is very consistent run to run even though ET may vary run to run (primarily reaction time variability).

In a previous post "1up3down" provided more detailed information which is shown below.

These are STOCK bikes:

August 1968 Cycle World Norton Commando 750 13.47 seconds at 96.35 mph
September 1969 Cycle Norton Commando S 13.18 seconds at 101.69 top speed tested 110mph
December 1969 Motorcycle Mechanics Commando S 13.4 seconds at 102
March 1971 Cycle World Commando 750 Fastback 13.11 at 101.67 top speed 116mph at 7380rpm
March 1971 Cycle Commando 750 Roadster 13.01 at 102.16 top speed 110
September 1972 Cycle World Commando 850 Interstate 12.96 at 102.38 top speed 116
September 1972 Cycle Guide Commando 750 COMBAT Roadster 13.09 at 103.68 top speed tested 109.5
June 1973 Cycle Commando 850 Roadster 13.06 at 100.78 actual top speed not tested
June 1973 Motorcycle Mechanics Commando 850 Roadster 12.9 quarter mile, no top speed tested
November 1975 Motorcycling Monthly Commando 850 MARK 3 15.0 at 88mph

In summary I think it's quite clear from the 1/8 mi time that the performance of Yves bike is in the +13 second range. And regardless of how it runs on the drag strip, it is an absolutely spectacular bike.

Hello Hobot,

Thank you very much for chiming in.
If I read correctly, your second ticket shows a 1/8 mile time almost identical to Yves' bike, albeit only displaying 76.67 mph velocity at that point, to be compared to Yves' 86,39 mph. Your terminal time (1000ft - 304,8m) on the ticket 11,5 sec suggest that Yves' bike could be considerably quicker as it has a 5 speed TTI gearbox, PW3 cams, fullauto head an Jim's light pistons and distribution packaged on a much lighter frame than stock and as such be able to reach a higher terminal speed than a (very good) stock Combat!

Dou you have tickets from 1/4 mile drag races with the same bike, it could be interesting!!

Just one more thing, Yves' bike has a TTI close ratio gear box which has a 'tall' first gear which surely is a disadvantage for the first part of a 1/8 mile run and shows that charts CAN'T predict everything. As I wrote earlier, Hobot and Yves share a nearly identical time at 1/8 mile but Yves' bike is over 10mph faster and will surely continue to accelerate at a faster rate than a (very fast) stock Combat.

GrandPaul is right.

Jagbruno said:

Just one more thing, Yves' bike has a TTI close ratio gear box which has a 'tall' first gear which surely is a disadvantage for the first part of a 1/8 mile run and shows that charts CAN'T predict everything. As I wrote earlier, Hobot and Yves share a nearly identical time at 1/8 mile but Yves' bike is over 10mph faster and will surely continue to accelerate at a faster rate than a (very fast) stock Combat.

GrandPaul is right.

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YAHTZEE!

In the entire world, you're going to get such extreme variation between bikes, no chart can predict within the "clinical" range that magazines and factories typically go by.

hobot said:

[/img]

Factory Interstate Combat no mufflers 7th day owning, 1st time on strip & burn out rear heat but not 1st time WOT clutch drops. Combat far lane vs 1200 Sportster camed for drag only with wheelie bar.


]

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Re-testing the waters eh.

The 5 speed TTI box in Yve's bike might help a lot. When I changed the standard 4 speed box to a 4 speed close ratio box, the bike accelerated much quicker ONCE IT WAS ROLLING. A larger gap between gears seems to cause the revs to drop too much, so after a race-change the crank has further to spin up to get the motor on the boil again. One thing I have noticed - when I bought the 6 speed TTI box it had the Triumph direction gear change and I wasn't aware of it. I tried to ride the bike in what must have been 5th gear and I couldn't work out what was wrong with it. So while it was moving slowly, I slipped the clutch and gave it heaps. It took off in 5th and I nearly stuck it through a fence. I'm amazed what the commando engine will do once that heavy crank is wound up. I would not have thought any bike would accelerate like that when starting off in 5th gear.

grandpaul said:

In the entire world, you're going to get such extreme variation between bikes, no chart can predict within the "clinical" range that magazines and factories typically go by.

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You guys may be completely missing the point a little though. !!!

A good fast bike over the 1/8 will give RATHER A LARGE CLUE what the 1/4 performance is going to be.
They sort of go together... !!!
Once you are at the 1/8 th mile mark, you are ~ 2/3 of the way there, time wise.
(and as that simple formula seez)

Maybe someone should try to match the performance to the maths, BEFORE burning the witch. !
Seems to be a popular sport on this forum.....