Simon Crafer Gyroscopic Effect and Inertia

acotrel said:
As I understand it, Peter Williams was working for Norton when the first Commandos were produced and he specified the steering geometry. It was 'race' steering, probably similar to Tom Arter's 'Wagon Wheels', a Seeley 7R AJS, which he had raced. When the kids started riding the first Commandos. a few got chucked up the road, apparently usually after riding over the 'cat's eyes' reflectors. Commandos did not have steering dampers. The fork yokes were changed for the next model and probably has less trail. Peter Williams was embarrassed, about the bikes crashing. However I suggest he probably had the geometry correct. A steering damper on a Commando might have made the bike look as though it did not handle.
Peter Williams' story is on the web somewhere. READ IT !
Click to expand...

Why don't you do some reading about trail and correct your mistake

en.wikipedia.org

Bicycle and motorcycle geometry - Wikipedia

en.wikipedia.org en.wikipedia.org

Here's the quote directly from this page:

"Skilled and alert riders may have more path control if the mechanical trail is lower while a higher trail is known to make a bicycle easier to ride "no hands" and thus more subjectively stable."

So what part of the above statement says LESS trail makes the bike more stable? It seems like it's saying the exact opposite... Right?


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Ya know what Al.... I would bet that most of us would love to hear some of your racing stories from back in the day. I was part of a race car crew. I could tell stories all day long about crazy stuff that happened at our track. Why don't you tell some of your racing stories but leave out the part where you lecture about the science of how things work because you clearly don't have the basics right.... It's not a crime to be mistaken about some scientific principle that you've misunderstood for most of your life...... It's only really an issue if you refuse to check your own understanding in the face of a dozen people telling you that you have it backwards.

The Peter Williams story you tell over and over again doesn't seem to be true? Right??
 
o0norton0o said:
Why don't you do some reading about trail and correct your mistake

en.wikipedia.org

Bicycle and motorcycle geometry - Wikipedia

en.wikipedia.org en.wikipedia.org

Here's the quote directly from this page:

"Skilled and alert riders may have more path control if the mechanical trail is lower while a higher trail is known to make a bicycle easier to ride "no hands" and thus more subjectively stable."

So what part of the above statement says LESS trail makes the bike more stable? It seems like it's saying the exact opposite... Right?


***************************************************************************************************************************************************************************************

Ya know what Al.... I would bet that most of us would love to hear some of your racing stories from back in the day. I was part of a race car crew. I could tell stories all day long about crazy stuff that happened at our track. Why don't you tell some of your racing stories but leave out the part where you lecture about the science of how things work because you clearly don't have the basics right.... It's not a crime to be mistaken about some scientific principle that you've misunderstood for most of your life...... It's only really an issue if you refuse to check your own understanding in the face of a dozen people telling you that you have it backwards.

The Peter Williams story you tell over and over again doesn't seem to be true? Right??
Click to expand...
I'd also enjoy stories from back in the day
That'd be brilliant
 
For once and for all, I would like to make a clear statement on my position. To me, the word 'stable' means when you brake into a corner, you need to counter-steer to get the bike to tip in. Most road bikes are probably like that. If you read Tony Foale's book on handling, he says the extremes of trail are both self-steering. When I first got the Seeley, the fork yokes were off a Ducati 450 and had 65mm of offset. When I measured the trail, it was 94mm. After an incident, I fitted Yamaha TZ350 fork yokes had 53mm of offset and which gave 106 mm of trail. That incident I had was similar to the one my mate had when he rode the bike a year previously, and in exactly the same place. It is at the end of a long left-hand sweeping bend - track turns slightly right as it straightens. As I braked for the corner, the bike stood-up and turned right, throwing me off balance onto the left. I hanged on and gave the bike more throttle get it onto the grass on the left and crash it. It came out of it's stupidity. I rode it again but more carefully in the next race, and took note of what it did as I braked. On a right-hand lean, as I braked, it started to rise.
After I fitted the Yamaha yokes, the bike still felt the same, but it tipped into corners much more easily (less stable), and I found that when in a corner, it oversteered in the correct direction, when I gassed it when on a lean.
I suggest a similar but normal road bike might be good with 100mm of trail. The extremes seem to be 94mm and 106 mm. My bike has the motor as far forward as possible, it's wheelbase is 54 inches, and it has 18 inch wheels.
My front brake is extremely effective.
 
According to wiki, Peter Williams joined Norton in ‘69 so was obviously not involved in its development.

The Norton yokes are interesting though as on the later bikes they altered the rake but then offset the yokes at the same time. Not too many bikes have offset yokes and even fewer then I guess.

I’ve not heard /read a good explanation of exactly why Norton did what they did with the rakes/ offset yoke combo. But even if I did, it’d probably be over my head !
 
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Reactions: TBW
Fast Eddie said:
According to wiki, Peter Williams joined Norton in ‘69 so was obviously not involved in its development.

The Norton yokes are interesting though as on the later bikes they altered the rake but then offset the yokes at the same time. Not too many bikes have offset yokes and even fewer then I guess.

I’ve not heard /read a good explanation of exactly why Norton did what they did with the rakes/ offset yoke combo. But even if I did, it’d probably be over my head !
Click to expand...
I believe they altered the offset first when they went to disc forks
Then later increased the frame rake 1° and de raked the yokes by 1° as I understand it
 
baz said:
I had thought the drum brake yokes were a different offset and width to the disc yokes?
Click to expand...

The yokes changed at 141783 (Jan. 1971), the disc brake appeared on the Combat at 200976, also the drum brake continued to be fitted into 1973 and there aren't two sets of yokes listed.
 
L.A.B. said:
The yokes changed at 141783 (Jan. 1971), the disc brake appeared on the Combat at 200976, also the drum brake continued to be fitted into 1973 and there aren't two sets of yokes listed.
Click to expand...
I had always thought the first commandos basically had a Norton atlas front end?
And only changed when they went to disc
 
L.A.B. said:
No, the yokes changed in January 1971 (to parts 061915 and 061916) which the 750 models had until 1973.
Click to expand...
Ok I think I understand
So from 67 to 71 they used one type of yoke
Then changed from 71 to 73 still using the drum brake or disc
Then went to the 1° de raked yokes when the frame changed to 28° ?
 
baz said:
It's the earliest yokes I wanted to find out about
Click to expand...

dynodave

Post in thread 'Fork yokes - simple question'

o0norton0o said:
Here we go again.... The yoke offset was changed (made about 1/2" greater) AND the yoke angle was increased from 27 degrees to 28 degrees. The result was a minor increase in trail of the later model so it added a little bit of stability to the later model and made it a tiny bit heavier steering with a slightly slower response....
Click to expand...

OP:
What were the yoke offsets for the first and second models of Commandos ?

These are the 3 configurations
1. series 1 commando rolling chassis (68-69-70) used 27 deg (as I said in post #3) 2-1/4" offsert same as featherbed/all late slimline but...
2. series 2A commando/ 71,72,73 750 rolling chassis still 27 degree but increased new fork offset and style top2.777" bottom 2.783"

3. series 2B commando / 850 rolling chassis NOW 28 degree and 850/ANG top 2.851" bottom 2.689"
 
Last edited:
L.A.B. said:
dynodave

Post in thread 'Fork yokes - simple question'

o0norton0o said:
Here we go again.... The yoke offset was changed (made about 1/2" greater) AND the yoke angle was increased from 27 degrees to 28 degrees. The result was a minor increase in trail of the later model so it added a little bit of stability to the later model and made it a tiny bit heavier steering with a slightly slower response....
Click to expand...

OP:
What were the yoke offsets for the first and second models of Commandos ?

These are the 3 configurations
1. series 1 commando rolling chassis (68-69-70) used 27 deg (as I said in post #3) 2-1/4" offsert same as featherbed/all late slimline but...
2. series 2A commando/ 71,72,73 750 rolling chassis still 27 degree but increased new fork offset and style top2.777" bottom 2.783"

3. series 2B commando / 850 rolling chassis NOW 28 degree and 850/ANG top 2.851" bottom 2.689"
Click to expand...
I must be really thick
Isn't this what I said?
Drum brake yokes
Disc yokes
Disc de raked yokes
IE 3 types of yoke?
Just trying to understand here
 
baz said:
I must be really thick
Isn't this what I said?
Drum brake yokes
Disc yokes
Click to expand...

No, as the later 750 yokes were introduced at 141783 in Jan. 71, the disc wasn't introduced until the Combat at 200976 so they can't be 'disc' yokes. Plus the drum brake was still fitted into 1973 but there's only one set of yokes.
 
Last edited:
L.A.B. said:
No, as the later 750 yokes were introduced at 141783 in Jan. 71, the disc wasn't introduced until the Combat at 200976 so they can't be 'disc' yokes.
Click to expand...
That's the bit I'm missing then
What's the difference between the early commando yokes and the 1971 yokes?
 
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