tweeking the steering head

I had a quick look in the Commando service manual since I found it in the garage (pinion puller has been missing in there for months now) but couldn't see anything regarding rake or trail.

Edit.
rake-and-trail-specs-t12097.html

Surely somebody must have measured the rake and trail of both the 750 and 850 commandos ? Peter Williams ? Norman Hyde ? The commando production racer was intended for racing, there must be records somewhere of the design specification. I cannot believe that even as far back as the fifties the geometry of racing bikes was not well documented. How did people like Colin Seeley and Spondon know how to build frames that handled ? I suspect that the isolastics used on commandos were not stiff enough to transmit repeatable information to riders about the way the commandos were handling. It takes very little to make a bike tend to run wide in corners, and if it is doing that we tend to simply accommodate it by getting on the gas a bit later. I'm surprised that it was deemed necessary to make the 850 more stable than the 750. The torque difference wouldn't have been so great as to warrant that ? It sounds to me like the combat must have been a very feisty bike.

The rake is listed in the Norton Workshop Manual, on the frame checking data diagrams, for both the 750 and 850 frames.
A smart operator could figure the trail from there, if required.

Try looking up any of the steering data for racebikes back then, or back into the 1950s.
That stuff was treated like a closely guarded secret back then ?
It was rumoured that Jim Redman supplied a new Manx Norton to Honda in Japan, for them to copy the steering head treatment onto their race bikes.

acotrel said:

I suspect that the isolastics used on commandos were not stiff enough to transmit repeatable information to riders about the way the commandos were handling. .

Click to expand...

If you haven't actually ever ridden a Commando, you can post idle speculation here until the cows come home, but you will be none the wiser.
And we are getting sick of reading the same ill-informed rubbish, repeated ad nauseum... ?

Stock Commandos ride quite well, for road use. ?
Why would you want to mess with the trail, for something that was considered pretty good in its day. ?
I had both a CB450 and a BM 1000cc when I bought my first 850, and for common road use the Commando would eat those for breakfast, steering wise anyway.
Not that I tried any of them at 100%, or Monza, or against any MotoGP bikes.
Peter Williams et al piloted race Commandos in some good races, before the JPN race bikes diverged significantly from road bikes.

Trail is mentioned in the link up the page.

Here is another thread.
You put your mouse pointer on the link and left click. :wink: (for those still using steam powered PC's)
fork-yokes-triple-trees-t8769.html

Time Warp said:

Trail is mentioned in the link up the page.

Click to expand...

There are 2 or 3 different measurements quoted there ??

http://www.tonyfoale.com/software.htm

They are only numbers ?
A Commando would be regarded as a sport tourer in the day ?,the Moto Guzzi Eldorado (avatar pic) of the same time period is a long distance tourer for the most part.
Its specs are.
Rake 27°
Trail 81.94 mm
Triple offset 70 mm
18 " wheels.

The 700/750's have under 57 mm trail with the same rake and 90mm offset.

Less trail does not always mean less stability or quicker steering.

Wasn't the story that Nortons disk type fork yokes initially would have given about 5" trail.
But that was too much, it didn't want to go around corners, it was just too stubborn and slow in the steering dept.
So the fork tubes were slanted 'backwards' in the yokes slightly, to move the wheel slightly back.

Commandos are one of very few bikes that have resorted to this to get less trail in their steering ??
Wonder who's idea this was.... ?

Time Warp said:

Less trail does not always mean less stability or quicker steering.

Click to expand...

Bikes with zero degrees rake and zero trail - unicycles - have awfully direct steering !

Rohan said:

Commandos are one of very few bikes that have resorted to this to get less trail in their steering ??
Wonder who's idea this was.... ?

Click to expand...

5 inchs of trail would be getting into Ducati beveldrive territory. (29° + rake)
I seem to remember reading of at least one Bimota (SB1 perhaps) having the fork tubes rearward in the triple clamps like the 850 Commando (not that I knew that until reading here)
There must be some merit in it if Bimota did it also ?
Did they build the 850 as more of a 'tourer then find the steering to slow with a revised head angle so it was a band aid of sorts with the triple clamps ?
Perhaps it was cunning new technology.

Time Warp said:

There must be some merit in it if Bimota did it also ?

Click to expand...

Quite so - reducing the trail takes some of the stubborness out of the steering, for the Norton 850 at least.

You'd have to examine the Bimota on its merits, giving it some point-and-squirt capability could well be in there.
And adapting previous designs for something new isn't unknown in the motoring world either...

Time Warp said:

Did they build the 850 as more of a 'tourer then find the steering to slow with a revised head angle so it was a band aid of sorts with the triple clamps ?
Perhaps it was cunning new technology.

Click to expand...

Who knows - I haven't seen that story put down fully in writing yet, anywhere ?
Wonder who signed the drawings for the fork yokes ??
Getting it stable under the power of the new-fangled disk brake could well feature somewhere in there too... ?

The flavor I got form shops and more seasoned knowing cyclers of the era was the Honda and others so overwhelmed Norton by lasting performance Norton reverted to loafing quaint cruiser market. Oh my I know them 850 can hang turns very well for a Commando but does have a sluggish effort to do so compared to 750's that won the magazine world best 5 yr running. If ya try to really race that sluggish effort can build up to fight the tires or isolastic frame right out form under. Alan is on the money about seeking a self steering geometry that the harder ya press it the more it tends to go the way ya want w/o having to compensate just hang on in repeated faith. Experiment and let us know. Even with the 25' rake my SV650 on hard air tires feels pretty light at first then the sense of its sluggish big tires sinks in compared to the C'do and even just touring starts to be work compared to my 750's. Our Honda 250 scooter is a bit lighter steering than either, why is that?

hobot said:

Our Honda 250 scooter is a bit lighter steering than either, why is that?

Click to expand...

Because its seriously light ? And seriously narrow tires.
And not getting faintly near 100+ mph, the steering isn't going to be too critical.
And depending on the type, could be some of those leading link type steering setups,
with very limited travel can be quite stable.

And, we iz gittin seriously off topic here.

A few days ago I bought a secondhand book for $8 titled '60 years of MotoGp & the world motorcycle championship' by Michael Scott. I've just started reading it. The chapter 'Birth of the series' is interesting - says this:

'The improved handling of the featherbed was little short of revolutionary.The highly influential McCandless brothers added yet more value, though this was less obvious. Study of weight distribution had led them to conclude that handling difficulties of the time - particularly a tendency t o run wide in corners - could be addressed by putting more weight on the front wheel. The new Norton was shorter and taller - what they used to call 'cobby'; - compared with the long and loping Moto Guzzis and Gileras. It paid dividends in quick steering, stable handling and faithful responses to the rider. It might have been made for Geoff Duke.
Riding style is dictated by the technology of the time : most especially tyres and suspension. High-grip rubber was far in the future; treadless slick tyres almost 30 years away. Racers of the 50s used treaded tyres, ribbed up front. What they lacked in grip they made up in endurance, but the former characteristic meant that riders had to take wide sweeping lines through the corners: smoothness was paramount, as it remains today when racing on wet surfaces where the grip is low.'

In Australia we didn't get decent tyres until the mid 70s.

The book also mentions Les Graham's fatal crash on Bray Hill in 1953 while riding a Gilera fitted with Earles forks. The bike used to shake it's head at high speed.

Have fun, fellas !

You might remember that I asked the question on this forum about whether anyone has hi-sided a commando. My Seeley really tightens it's line in corners, and when I gas it really early, I usually think that I should not be doing that. Modern tyres are really great in the hands of old idiots like myself.

Ken Canaga mentioned trying a less raked fork on one of his isolatic racers to have pilot badly inured so reverted back. Un-tammed Cdo's get into cyclic wobble before they can flip off front in classic instant hi side unless on rough off road runs going in and out of counter and straight steer essentially straight ahead and not staying on scary acceleration enough. Norton were all famous for good easy handling geometry until the 850 curiser models, which still go around good but work pilot more and therefore likely load front to loose it in low side before can hi side off sudden extra front grip at wrong angle.

Mick Doohan realized that if the back end steps out, you are better to turn the bars in the wrong direction and slide the bike to the ground rather than turn them to catch the rear wheel and get the hi-side . With a commando this is usually only ever going to happen in the wet or on a loose surface, unless you are Steve Maney.

Yum, Alan you are one the few to have decent concept of this to even know its possible. Alan with isolastic tri-links with 2 that are compliant enough not to mimic the limits of over rigid frames that is exactly what I do on Peel in eager glee in most tightest dangerous plateau face wagon trails - Straight steering like an offroader but on pavement so rather safer easier to do, if your cycle can take the loads and not spring back like diving board. The faster you go the easier it is to do, but to do so mean leaving ordinary two tires in full control so bike is actaully low siding but is caught restisted by the flip into straight steering. Ya have to ride past what would ordinary be a crash state, and would be if not blasting in past any recovery reserves. What you describe on your Seeley is not as intense a way around as this, so you have run into you rigid limits w/o realizing there a couple more ways around even more fun. Also bike has to have enough clearance to get over far enough not to hi side work up to this level of super thrilling handling. No slide or drifts No Sir Ree Bob but d get some tire skip outs at either end but just re-aligns tires to take loads and better thrust aim but boy Howdy with the forks flip to opposite steering its like a sail boat tack that snaps the boom across the deck, you better not restrict in in any way or can blow boat right over. If you ran out of harsly increasing power band or rpm before getting past apex, bad ju ju, uless bike can take the instant let off and re-hit on defromed/spring back tire ya can just snick another shift mid apex and leave the follows a ful shift of speed behind. Neck and neck don't count to me as superior performance.

On this note Freddy Spencer and a few others have stated the cycle is worth 70% of wining with pilot only 30%. So on Peel I don't have to be very good just sure enough of the bike to let it do its thing. Look very close at ice spiked speed way racers and imagine the loads to hook up on pavement that I can only enjoy on one in a row cycle. No need for fancy race track with run out room galore and no oncomming traffic thrills. No way do I nor can I do this on regular C'do or sports bikes on best tires and great suspension. Oh have I tired and tried over the years and only lucky to recover the upsets in time to learn not to any more. With such secure amazing handling of Ms Peel watching race video is not instructive but to see where their weakness are to take more advantage over them. It ain't me its the innate wonder of isolastics once tammed but not fully restricted. 27' rake works an effortless treat to me.

An ice spiked speedway bike is similar in ways to a road racer before it reaches the MotoGP level. On older bikes, once you start sliding on the bitumen, you have a choice - you can ride it dirt speedway style or you can lay the bike down. If you choose the former with a Norton, you are a better man than I am. You don't have 200 BHP to play with, so if you run out of power you immediately get grip, and the hi-side. It all happens too quickly.
I suggest that once you have slide you need the power and the tyres to maintain it if you choose to keep fighting. What I tend to do is ease on a bit more power and steer gently in the direction the bike is going and feel the movement and try to recover as smoothly as possible. In road racing it usually only happens in the wet so a crash is very safe, and under those conditions I never do anything suddenly anyway. 'If it is bad for you, it is bad for everyone else.'

Alan Ms Peel has totally solved every issue you mention and then some with about 70+ hp [which I get flake on lists from but don't care as me and the ones I contested with sure believed it] I've a 70hp/365lb 6 spd modern twin that did not have enough power to keep up to play games with the inline 600's yet Peel out powered them till over 130 and usually had such a lead into the opens they'd only catch up by passing me over blind crests I'd slowed back to 90 for d/t having tractors to school buses waiting just over the crest. Only time Peel ever got out hp'd was on first take offs in straights to start a heat they could get by after 90 mph when I had to snick 3rd. Three times in about a year by 990 Monster, GSXR1000 and RS 1200 BMW. which was the fastest of them. But handling is no longer a mystery nor limiter at all on Peel > only tank fuel slosh if about 4 gallons left and air compression lift eddies on far over leans and of course much more power for more fun than GP bikers when any leaning at all involved. You bet it blew my mind and took my breath away literally on concepts of motorcycle behavior so don't expect anyone to believe me but its so so good I decided I had a chance to make a lasting impression on world so decided to go for broke on her and see if I can get record track times then throw down gaunlet to some major magazine shoot out with objective measures data logging. Peel could do those laid down supermotard tricks but way faster and in dangerous public places she was so secure predicable it left me refreshed not freaked out worn out. Flabbergstingly Fabluous is terms that pop to my mind. On Peel it was the power cuts that brought on the most severe G spikes not the power hits if that is any clue on how good it can get. I did have to set her for a controlled crash though as just cutting power on lean or over powering for a slide did nothing to upset her, just slid at same angle w/o pilot effort, so could shift any where any time in any turn, and did so now & then to make her slide at times for a relaxing way to widen arch to line up better for power on exit. When ya get to GP bike performance one or both tires will leave the surface so that was routine on Peel in her prime. I see flat trackers as lazy way around wasting tire time traction waiting and waiting to get hooked up for better acceleration. To me the basic 750 Commando is perfect but needs taming and more power and a lot lighter is all.

acotrel said:

The book also mentions Les Graham's fatal crash on Bray Hill in 1953 while riding a Gilera fitted with Earles forks. The bike used to shake it's head at high speed.

Click to expand...

Obviously they didn't have it set up right - should have asked BMW for advice.
Or just copied their design, ala normal motorcycle practice.

It can't have been too obvious, or Les would not have ridden it ?
All bikes used to have girder fork front ends once-upon-a-time, before telescopics were invented,
so there was plenty of experience with them, they reigned for 40 years....

But we diverge, as usual.