850 yokes on 750 frame (yet again)

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84ok said:
i'm not clear on this late 750s part,
"FORK YOKES: 750 - Engine Nos. 221545-221644 and 230536-230685. All these had the revised steering geometry by new (850) frame 064140

Also new fork yokes 004078 (lower) 064080 (upper
with stem) the yokes must be used in pairs. Do not mix old and new ones."
Click to expand...

"004078" is a typo, it should be 064078


84ok said:
are these yokes angled like on the 850 ang type? must be a reason for
"must be used in pairs. Do not mix old and new ones".
Click to expand...

This is where confusion often arises as 064083 and 064084 are 'casting' or 'foundry' numbers. Various numbers on castings are often different to the final Norton part number so 064078 and 064080 are the actual 850 ANG yoke part numbers for 064083 and 064084.

Edit: The 750 lower yoke is one of the rare exceptions where casting number and part number are the same (061916).
 
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Well I guess I'm the lucky one, I'm still here. I had 850 ANG yokes on my '72 750 for about 25 years with no ill affects or scary handling in normal everyday riding. Right or wrong I was told way back then that this would "quicken the handling". I'm a flat lander, not much in the way of really interesting riding roads around here, so I don't push as hard as some here do. I only went back to 750, non-ANG yokes a couple years ago. At the same time I replaced the front wheel with a newly laced alloy and switched to new AM26 tires. I will say the bike is more stable now than before, can't say which of the mods made the biggest difference, but I'm leaning towards the tires.

B
 
kommando said:
The changed head angle provides the extra stability with an unchanged trail, you have to continue the headstock angle out along an imaginary line to see where it finishes.
Click to expand...

If Norton changed the rake of the headstock and then recorrected it with rake on the yokes to arrive at virtually the same trail they started with, then they didn't add any measurable stability.

The only way I could see this "double adjustment" modification to the rake angles creating 2 bikes with nearly the same trail numbers, but with one bike having better stability is if trail wasn't the single most important factor in stability.... and all my research shows that it is...

So how does it happen that 2 bikes which are 99% the same bike, with nearly the same resulting trail numbers, have one that is considered more stable???? What other thing made the bike more stable if the trail stayed the same??

I've done a lot of reading on this. It's hard to understand (as danno said) what the rakes and offset changes accomplish if the trail stays nearly the same.
 
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Interbak said:
Well I guess I'm the lucky one, I'm still here. I had 850 ANG yokes on my '72 750 for about 25 years with no ill affects or scary handling in normal everyday riding. Right or wrong I was told way back then that this would "quicken the handling". I'm a flat lander, not much in the way of really interesting riding roads around here, so I don't push as hard as some here do. I only went back to 750, non-ANG yokes a couple years ago. At the same time I replaced the front wheel with a newly laced alloy and switched to new AM26 tires. I will say the bike is more stable now than before, can't say which of the mods made the biggest difference, but I'm leaning towards the tires.

B
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That's just the info I was looking for I honestly couldn't see that it would be that different
But the fact is Norton thought it would and warned against it
After all it wasn't long after the widowmaker frame problem so I'm guessing they had to be careful
 
o0norton0o said:
If Norton changed the rake of the headstock and then recorrected it with rake on the yokes to arrive at virtually the same trail they started with, then they didn't add any measurable stability.

I've done a lot of reading on this. It's hard to understand (as danno said) what the rakes and offset changes accomplish if the trail stays nearly the same.
Click to expand...

But it isn't the same, according to ludwig;

https://www.accessnorton.com/NortonCommando/split-topic-triple-trees.5369/page-5#post-57699
some additional info :
trail with std 19" wheels :
750 with 3.50 front tire : 81 mm
750 with 4.10 tire : 82 mm
850 : 106 mm
Click to expand...
 
Has anybody ever measured the rake and trail of the different types of Commando ? When you talk about yoke offset and headstock rake, you are only talking about two determining factors. With a 27 degree rake, the TRAIL is extremely important. The wheel sizes and rear shock settings can change the trail.
What I am suggesting is that if you change your bike around, there must be an area of trail which is 'safe' with a 27 degree rake and 19 inch wheels. What I would do is make my changes, then measure the trail. With my own bike, I arrived at safe handling simply by chance - not good !
 
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If you read some of Tony Foale's stuff, he seems to be saying that there are two extremes which can be reached by changing the trail - stability and self-steering. I tend to think of it slightly differently - oversteer and understeer. More trail causes oversteer (line tightening in corners), less trail causes understeer ( tendency to run wide ).
 
acotrel said:
I tend to think of it slightly differently - oversteer and understeer. More trail causes oversteer (line tightening in corners), less trail causes understeer ( tendency to run wide ).
Click to expand...

Well,... I think you have that backwards... MORE trail makes a bike want to run wide. Think of how some of those choppers with a lot of rake and trail handle. They want to go straight, and want to run wide on the turns...


I'm lucky I have the early yokes on an early 750 with less offset so my trail number is somewhere between the later 750 yokes and the 850 yokes. I'm not worried about handling or stability...
 
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We recently had a bog discussion on this form about rake and trail and the effect of changing the yoke offset. It probably did not help me much, but the conclusion was that more offset causes less trail. I have never known what the trail figure should be for a 27 degree rake. There is obviously a range within which it is safe. Those choppers you mentioned were unsafe. A friend of mine watched a guy carried out of a stand of trees by police and ambulance men, after a chopper had taken him off the road due to that absurd steering setup. With ,my own bike, I reduced the offset, which apparently increased the trail - it then started oversteering - tightening it's line in corners when gassed. I think there are three variants of Commando steering. The first 750 had the race steering specified by Peter Williams which crashed a few inexperienced guys. The other two variants are the next 750 and then the 850. You don't need the trail wrong by much to get serious mishandling.

I would help if we knew what the limits of trail for the 27 degree rake with 19 inch wheels should be. It is not easy to measure, but if you have it seriously wrong, you find out when you crash. Sometimes a steering problem does not appear until the bike is under duress - something unusual occurs - like running over a cat's-eye in the wet.
 
So from the lack of comment, I take it that nobody on this forum has ever measured the TRAIL which their Commando's steering geometry creates ? - The number for a near-standard Commando is something which I would dearly like to know. From memory, on my bike with 18 inch wheels, it is about 92mm - very roughly measured. If I can get some comparison figures, I will measure it accurately. It would be good if somebody could ask Peter Williams about this - he would certainly know what it should be.
 
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I like this diagram to help learn the frame measurement terms.

850 yokes on 750 frame (yet again)
 
Has Ludwig actually measured the trail on commandos, or is he only quoting the makers' nominal specs as supplied ?
 
acotrel said:
Thanks for that, I had not noticed the fine print.

(some additional info :
trail with std 19" wheels :
750 with 3.50 front tire : 81 mm
750 with 4.10 tire : 82 mm
850 : 106 mm)

106mm is a big difference from 82mm , I would have only expected differences of about 5 or 6 mm.
Click to expand...

Looking at the drawing, one can see that raking the frame an extra 1 degree and de-raking the yokes by the same amount increases trail at both ends.

The SS clone, with 750 frame and Mk III yokes should make for some pretty quick steering. It seemed especially quick with the 90/90 front tire.
 
While the following offers no hard data it does illustrate the difference.

When I was a kid I had a Schwinn ten speed bike. I could ride it for hours without using my hands. I later came into a Motobecane racing bike. Great bike, but you couldn't take your hands off the handle bars without having it throw you to the pavement. It was all about trail but I didn't know that then. The Motobecane was designed for quick lane changes and fast acceleration. Not so with the Schwinn.

At high speed the Motobecane felt fine, but you had to keep both hands on the handlebars. No it did not come with warnings. It was difficult to keep it pointed in the intended direction if you so much as scratched your nose. Which is a hard thing to do over an extended period.

It obviously has its place.
 
The problem with this steering geometry thing is that the bike can feel OK most of the time, but under certain circumstances mishandling can come from nowhere and crash you. With a push bike, the steering is usually much quicker than with a motorcycle, so the problems appear quicker and at lower speeds. If your steering is neutral, that is usually safe. If it tends to oversteer or under steer, you adjust to it, but some types of steering can bite you more easily. Most guys who ride road bikes are not philosophical about crashing because they don't usually have that sort of experience. With a road race motorcycle, over steering inspires confidence but is probably dangerous.
 
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