tweeking the steering head

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I got the impression from some of the posts on this topic that some might think there is a lot of tolerance on frame straightness. I'd point out a couple of things. - If you are riding behind a motorcycle and can see the twist, i.e. the rear wheel is not in line with t he front in the vertical direction, the wheels are not tracking the same. It can make the bike feel difficult to lean. The other thing is that very small difference in the steering head angle in the fore and aft direction can have a major effect. If it causes the bike to be come more stable by increasing the trail, the bike can either stand up under brakes and turn the wrong way for a corner, or it might reduce the trail and become more unstable and twitchy and possibly crash you. I haven't ridden a standard commando, however I think a lot of guys simply adjust t o the bike when they have got subtle handling problems, and simply ride around their difficulties. It is obvious that the isolastics must be alright or guys would be regularly crashing commandos because of them. However it could be the situation where people simply adjust to the flexibility and if the frame is twisted, it could put the geometry outside the safe limits. When steering geometry is wrong, the mishandling can arrive without warning, and it can be devastating.
 
acotrel said:
... If it causes the bike to be come more stable by increasing the trail, the bike can either stand up under brakes and turn the wrong way for a corner...
Click to expand...

Braking whilst banked over....eek ! Back when the Commando was built, road riders just didn't expect to be able to do this on road bikes with road tyres. It usually meant a trip down the road on one's arse. It's still not something that I would ever do by choice. Perhaps some people have become spoiled by riding modern machinery (which is something that I've never done).
 
acotrel said:
I haven't ridden a standard commando, however I think a lot of guys simply adjust t o the bike when they have got subtle handling problems, and simply ride around their difficulties. .
Click to expand...

Oddly enough, riding within a bikes limits is something that EVERY motorcycle rider does, all the time ?
Even an 1199 SP Duc wil not always go around a 60 km/hr corner at 200 mph, so the rider 'allows' for this.

Kind of like stating the bleedin obvious ??
But then, you haven't ridden a bike on the road, for how many decades now...
 
olChris, years ago I built my own Commando frame straightening jig same set up as yours 16mm plate anchored to the floor, my base plate was 3ft x 2ft, on this was welded very strong supports which accepted bolts which would pass thru the front and rear frame mounting points, the frame was only bolted to these points (front and rear) not to the main base plate, I originally used a straight frame bolted to the jig to determine my datum points. I straightened quite a few frames with this setup.
 
The quickest was around a corner is to brake right down into it while cranked over, and get back on the gas while still cranked over, minimizing the rolling distance around the apex.
https://www.youtube.com/watch?v=V3BHLRQTBts
If your bike is under powered, it helps if it is set up to tighten its line (oversteers) so that it doesn't run wide, then you can get back on the gas much earlier in the corner. If the other guy has more power he usually cannot afford have his bike set up to tighten it's line without the greater risk of hi-siding it. You then usually see him do 'point and squirt'. What I've found is that I sometimes have the run on other guys who have more powerful bikes coming out of corners. It is rare to hi-side an old British bike especially with the modern tyres. What can happen is it can slide out if you are not smooth enough through the apex of the corner (or you hit an oil patch). There is an interesting video by Alan Cathcart about the 1993 Suzuki 500cc MotoGP bike which explains why it was competitive against the more powerful Hondas in that year. There is also several videos titled MotoGP Workshop on Youtube which mention the effect of bikes running wide in corners - they don't mention the fact that those bikes often steer strongly on the throttle. Have a look at the one on suspension:

https://www.youtube.com/watch?v=aOlDGxTN9vI

https://www.youtube.com/watch?v=J73XRDGPcpE

https://www.youtube.com/watch?v=f1QJg8qJOzg
 
If youve a smooth floor . and a 6H pencil , which will draw a 1/10 mm line :) sharpened - clamping the seat cross member to say a angle iron for a horizontal lateral datum , and shimming there
so the basic triangulated rear braceing is square :shock: IF it is :? , will get you underway .
String lines from upholsterers thread , which is heavy duty cotton , or suchlike - combined with a large builders square & level is usefull .

I think knocking the steering head bearings out & checking you havnt didtorted there would be essential . If the races make irregular contact - its liable to be awkward - behaviorally .

A couple of round packers for the lever bar , so as to take up play - is a safer benderiser there .
 
I am sorry that I cannot link to the Alan Cathcart 1993 Suzuki video. I captured it off our local TV, however when I uploaded it, Duke Video claimed ownership, so it was removed from Youtube. If you can find it, it is worth watching - it gives a few good clues, and you can actually see the way the bike handled. It was simply a better package than the more powerful Honda, and it was done mainly on steering geometry. It was the bike that Kenny Robert's son rode.
Rohan, get your arse and your commando over here - let's have a look at you under duress.
 
So we should tweak a Commando steering head to an old Suzuki's dimensions ??
We dont think so....

Its the whole package that all adds up.
Modern is better, more modern is more better.
Have a look at how a KTM or Duc or Suzook or Buell steers these days.
40+ years of development are 40+ years better...
Seeing those KTM v-twin 990s doing 200 km/hr in the Paris Dakar, in the DESERT, was just magic...

I don't expect MotoGP performance out of a Commando - nor expect to ride it like that.
Half your comments are just twaddle, in that respect....
 
Rohan said:
Time Warp said:
http://youtu.be/Q3lmj7LG6Jc
Click to expand...

I wouldn't mind a test fly of one of those myself. !
I've had the promo poster on the wall, for a while now...
Click to expand...

They are great bike,1078cc FI and maybe 90 rwhp stock,50 mm forks,Ohlins shock,Brembo radial mono blocks etc etc.
I put a couple more teeth on the rear (quick release carrier) sprocket.
The 12.5 litre fuel tank is a bit of a joke (110 kms to reserve some times)
You would have to be in a coma to not enjoy riding one,old school air cooled before they ruined them.

Since this is a steering head thread here is a Ducati I did long ago,new steering head,T.I.G root with a wire feed cap to duplicate what was there from the factory.
Around 6 degree reduction.
Given the other thread,it seems tube fit up on Norton frames may have been somewhat sloppy given the shrinkage in some cases.
I elected to not post in that thread but a measurement of 85.75 mm was quoted (from a unreliable source) checking my 750 frame returned under 81mm for the same location.

This style of tube layout goes back to 1971 Ducati wise.
tweeking the steering head
tweeking the steering head


Probably boring to most folk but I have always had an interest in the evolution (and de evolution) of motorcycle frames especially when frames from the same time periods are compared between manufacturers.
I seem to remember the Beveldrive Ducati frames (as above) had Colin Seeley influence.
 
It is obvious that the geometry of a 1993 Suzuki MotoGP bike won't work on a 1972 model commando. The tyres and wheel sizes and wheel base are different.What I was referring to was the resultant effect - i.e. whether the bike tends to run wide, or alternatively tighten it's line. If the bike is a bit under powered it is safer to have it's racing line tighten in corners than with a savage top end motor, where it is easier to get the hi-side. With that sort of motor 'point and squirt' is safer. I would think a commando with a 27 degree rake and 30mm yoke offset would self steer under power when cranked over, and it would tighten it's line in corners . My Seeley has 40mm shorter wheel base and 18 inch wheels, and that combination gives a strong effect. Then you would have to learn to use it without crashing , and you have the isolastics to contend with. The changes are subtle, however the result is interesting.
 
I was talking to a friend yesterday about his 650cc manx framed Triton on this subject. I rode it years ago when I was still racing my short stroke 500cc Triton, and at about that time I also rode another friends 1961 500cc Manx. I believe each of those bikes would have had 24.5 degree head angles and the same fork yokes. My 500cc triton was the worst of the three, it had 18 inch wheels, always tended to run wide and was exhausting to ride. My bike was also slightly longer. My friend's Triton 650 was extremely fast for it's time, neutral steering and not bad to ride fast - had 19 inch wheels. The manx was beautiful to ride, also had neutral steering and it inspired a lot more confidence - if you got offline with it, you simply gave it more stick. That manx was about 5 mph slower than my 500cc Triton down the straights , however my lap times on it were faster.
 
Alan, you can count the riders who make their 27' rake isolastic Commandos go around harsh enough to enjoy the self steer tighter under power on one or two fingers, and less than that w/o 3-locations of isolastic cradle/frame stabilizers, so don't expect much insightful feedback. 750's have a good light effort steering geometry to me but un-tammed they can't take turning loads it like yours and others Seeleys - so quite rubbing it in. No way can I get my un-tammed Combat near your level of handling before all hell breaks loose and for a time after seems like everything is mis-aligned and angled wrong and not well attached either. 850's with 28' [more or less] I've tried felt more sluggish to steer so made me not want to hot dog off road or fling for much thrill on hwys, just behave well below upsetting states and not get worn down working.
 
This thread has gone weird - if you take out all the BS, there is not much left. ??
And pray tell, how are folks altering their steering angles

And when one of the chief posters here says something like
modern tyres are so much more forgiving
Click to expand...
And someone then has to correct this with - "modern tyres feed so much MORE stresses into the chassis",
then we just KNOW that someone doesn't have a good grip on reality ere....

Commandos are primarily a road bike, why try to compare them with MotoGP bikes ?????
 
olChris said:
Well at least its still going
Click to expand...

Not too many threads here crash and burn in the ditch.... !?

Another thread on front forks here at least had folks reporting on what other front forks they had fitted, and the results.
40 years of fork developments in the motorcycle world have produced some seriously better forks.
Although going all out on the ole Commando is not the most logical of developments...
Jim Comstock (comnoz) had gone for possibly one of the best upgrades, without going overboard.
Anyone know the link to that thread ?
 
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