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Author Topic: New Record at Bonneville ACTUALLY 4 NEW RECORDS  (Read 1181 times)

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Offline jgger

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #50 on: September 02, 2018, 08:17:01 pm »
Tire size is also different by almost 3 inches. Plus on the dyno the tire circumference may be larger at speed due to "throw out" size of the tire (the faster it goes, the taller it gets).

Online kmb69

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Re: New Record at Bonneville
« Reply #51 on: September 02, 2018, 08:18:54 pm »
.....
"My dyno" is a Dynojet 200i. ;) My MPH was measured, not calculated.

What accounts for the lower than calculated mph? Tach error? Clutch or tire slippage?


Offline scottly

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Re: New Record at Bonneville
« Reply #52 on: September 02, 2018, 08:32:49 pm »
.....
"My dyno" is a Dynojet 200i. ;) My MPH was measured, not calculated.

What accounts for the lower than calculated mph? Tach error? Clutch or tire slippage?
I suspect Nick multiplied when he should have divided, or something along those lines. I've witnessed tire slippage of a much lesser degree that deposited a layer of rubber on the deck of the dyno behind the rear tire; this was not the case here. 
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Online kmb69

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Re: New Record at Bonneville
« Reply #53 on: September 02, 2018, 08:58:33 pm »
.....
"My dyno" is a Dynojet 200i. ;) My MPH was measured, not calculated.

What accounts for the lower than calculated mph? Tach error? Clutch or tire slippage?
I suspect Nick multiplied when he should have divided, or something along those lines. I've witnessed tire slippage of a much lesser degree that deposited a layer of rubber on the deck of the dyno behind the rear tire; this was not the case here.

Calculated 4th gear MPH with a 82.75" circumference tire:
8000 101.570
8500 107.918
9000 114.266


Offline scottly

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #54 on: September 02, 2018, 09:26:16 pm »
Your calculations are very close to my measured data. The discrepancies are most likely due to a small amount of tire slippage (about 1%) plus the rear tire circumference was measured unladen; the effective diameter is smaller with weight compressing the tire at the contact patch. 
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Offline 754

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #55 on: September 02, 2018, 10:09:54 pm »
 Slippage is likely a problem there.
 Many people at the175 to 200 Mark start adding weight to the rear.
IIRC Dennis did mention that on one run it had a period of noticeable slippage.
It's salt that you can sometimes scratch with your boot or fingernail.. nothing like pavement..
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Offline scottly

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #56 on: September 02, 2018, 10:24:30 pm »
IIRC, Dennis once guesstimated his slippage on the salt at 10%, but that was also without a reliable tach. 
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Offline RAF122S

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #57 on: September 02, 2018, 10:37:08 pm »
Still doesn't have a reliable tach ;)
Especially since it died, at least it gave up the ghost and did the honorable thing of dying rather than continuing to give false  readings...a falling on your sword gesture by the tach, eh?

Wow, you picked up a Dyno Scott?  Cool. Hope you are making a little money from it when the need arises for those you aren't assisting like Dennis.
David stuck in the curvy back roads of "Upper East" TN

Offline scottly

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #58 on: September 02, 2018, 10:53:42 pm »
David, I traded the Cobra "kit car from hell" for the dyno, five years ago or so. I need to mount it on a trailer and haul it up to B'ville so we can do testing on-the-spot for existing conditions. :)
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Offline NickO

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Re: New Record at Bonneville
« Reply #59 on: September 03, 2018, 03:29:04 am »
If somebody can give me the:

1. primary reduction ratio
2. 5th (top) gear ratio
3. Precise circumference of the back tyre

I can provide a gearing chart for you. This will show the top speed for a given RPM for various combinations of final drive reduction.

1. 1.708
2a. 4th gear 1.097
2b. 5th gear .939
3. plug in a circumference of 80" as a guesstimate, with 4th gear and a 17/48 final drive, and I'll see how it compares with my dyno readings.

8,000 RPM
4th 114.5
5th 133.8

8,500 RPM
4th 121.7
5th 142.2

9,000 RPM
4th 128.9
5th 150.5
My dyno said, with 4th gear and 17:48 sprockets:
8000 98.3
8500 105.2
9000 111.1
I also measured the rear tire by wrapping a string around the center of the tire tread and came up with 82 3/4".

I forgot to account for the secondary reduction factor of 1.167. This would change my original speeds to:

98.1 mph @ 8,000 rpm
104.3 mph @ 8,500 rpm
110.5 mph @ 9,000 rpm

It would also suggest that tour rear tyre has an effective circumference of approx 80.5"  when rotating at 111 mph (about 1,700 rpm)! :o
« Last Edit: September 03, 2018, 03:34:59 am by NickO »

Offline Old Scrambler

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #60 on: September 03, 2018, 06:35:21 am »
I like the calcs.............but the salt and elevation/wind are known as the 'Great White Dyno'..............with minimal wind, the 16x45 allowed the motor to get into its sweet spot..........I believe the 16x44 would have pulled about 5 mph in either open (naked) or PS.........but most of the good news is that the motor feels, sounds, and now looks like the rings have seated (no honing marks) providing a bit more compression........on more than one run I felt the rear wheel spin and attributed it to loose salt from other bikes....my crew said they could see a rooster-tail when in 2nd & 3rd gear........the bike stayed straight and always felt well planted.....Frank did take one trip with us to the starting line and said he felt more 'into' the experience........The '69 Triumph Trident was built by Tom Mellor and has a reported 85 RWHP...........Scottly, if you bring your dyno you will also need a good generator.
Dennis in Wisconsin
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CB750 Classic Bonneville Racer thread - http://forums.sohc4.net/index.php/topic,135473.0.html
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #61 on: September 07, 2018, 03:23:44 pm »
We debated saying something to these guys about tearing down their engine to save them the trouble. In the end we let them bask in their momentary glory  ;)

https://www.msn.com/en-us/autos/motorcycles/clear-for-takeoff-distillers-vodka-fueled-motorcycle-sets-land-speed-record/ar-BBN0vZU?li=BBnb4R5
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Old Scrambler

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #62 on: September 11, 2018, 09:06:43 pm »
Jerry Wins...............According to the BMST records listing, we DID SET 4 RECORDS this year. Somehow I was able to get a tenth of a MPH ahead of the 2017 M-CG record set by the Triumph Trident at 136.62-mph

http://www.dragbike.com/bonneville-motorcycle-speed-trial-2018/
Dennis in Wisconsin
'64 Triumph Cub & '74 Honda CB750 Bonneville Salt Flats AMA Record Holder (6)
CB750 Classic Bonneville Racer thread - http://forums.sohc4.net/index.php/topic,135473.0.html
'63 CL72 Project(s)
'66 CL77 Red
'67 Triumph T100C
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'77 750F2 Cafe Project
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Offline RAF122S

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Re: New Record at Bonneville ACTUALLY 4 NEW RECORDS
« Reply #63 on: September 11, 2018, 10:57:58 pm »
Congratulations!!!!
David stuck in the curvy back roads of "Upper East" TN

 

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