1971 Experimental F750 Racer

I think that Doug MacRae has said that with Herb Becker's mods his commando handles as good as a Seeley. I don't know if he has ridden both however he seems to compete well against Kenny Cummins, if that means anything. I think the main thing with any frame is that the total package must inspire confidence and the unmodified 1961 500cc Manx I rode certainly did that. I think the main thing about the commando's handling is that the isolastics must be adjusted correctly. On any bike, if you can feel flex it will put you off a bit, especially when you are cranked over on a big radius bumpy bend doing over 100 MPH.
There is a friend of mine who used to work for a dealer in the 70s doing pre-delivery on Commandos and Kawasaki triples, he has been involved in road racing for about 50 years and still rides his Suzuki Bandit far too fast on public roads. He has good words to say about the commandos, and I respect his opinion. The guys used to get the new bikes onto the Richmond Boulevard in Melbourne and really give them heaps. If the commandos were not up to it, he of all people would know.
I suggest that if you want to talk about handling, you need benchmarks and it is worth even paying to ride a genuine manx, a Ducati 900, and a TZ350 Yamaha - they are all good in their own way, for different reasons.

When one aims at some speed by COUNTER steering the fork is aiming tire to the OUTside of the turn while the rear is tipped over trying to thrust to INside of turn, this tire vector conflict puts a twist load on connecting frame work. Put enough conflicting tires loads on this way and frame can twist. In iso'd C'do the rubber cushions compress first so tips power unit-swing arm into rubber Lord's mount head steady helping to resist but when rubber compressed fully then the frame tubes begin to bow-twist-flex, which makes for a nice ride up to point rubber and tubes can spring back and re-verb into tires even more out of line and wiggling to upset handling and pilot. On rigid mounts the frame will resist tires changing vectors better so takes more loads before lenght/strength of frame gives some but even rigid can ring and spring back but at higher freg than sloppy ear C'do, but still not really able to compensation-give enough to allow tires to cooperate with each other rather than going separate ways.

Herbert Becker's > McRae's iso racer has 3 robust swash plates that essentially make a rigid frame to twists but still allows the jumping of front of engine up/dn to take away the severe engine orbital vibes. So yes Alan MacRae's real iso C'do is as good a handler as other rigid frames yet a bit better as smoothing to pilot. Police and racers in past would tighten up the iso gaps to point of bad buzz to feel but frame could still tolerate w/o fracture. That is ya had to order and pay police to ride em like that or have mental-emotional-fame competition reasons to endure for short race heats.

When hi turn loads put on iso C'dos the engine tip and down tubes bow/twist along their long axis to contact the tabs for a vibro engraver sensation. I have broken stout wood blocks to splinters and almost broke spreader bolts trying to get front tabs spread after deer mangled Trixie which sort of sprung cockeyed on dissembling yet I could not spread the tabs even .001" this way as just sprung back on release. The ONLY thing I could do was cause the down tubes tabs to twist apart which twisted a frame tube like a torsion bar, so tabs angled from vertical but sprung back exactly same as prior, measured to .001" accuracy. I put a screw driver in the tab hole and w/o bending the smallish dia. screw driver shaft was able to twist each tab enough to take up the std iso gap .010" by the skewed alignment. On trying to actually bend tabs the screw driver shaft would bend first and if let go it was like a steel cross bow release.
Oh yeah I gave up on frame/tabs as could not change one iotta and just machined off front mount to slide in between, mostly freely but still a bind requiring some pounding, but rides smooth and secure as any untamed C'do's tested on 1000 mile days back to back w/o wanting to get off my Cloud Nine at end of day.

I've quizzed Doug privately last year to get enough feedback to know Becker has equaled or to my mind and Doug's > surpassed the features of Seeley except maybe a few lbs of mounts extra that don't really matter more than taking a dump before riding or having a meal first. So what ya end up with is normal contests of power to weight performance and pilot wits and reactions like everyone else on similar power rigids.

None of above is good enough for a novice like me to want to test heated tires on anymore no thank you, thank you very much. Here' review to keep up with on cycle dynamics w/o as good a solution as I enjoy.
https://www.google.com/#q=GP+motorcycle ... +solutions

Freddie Spencer is my best model on how I like to do it and what it takes to learn it and what weaknesses cycles still trying to solve. I 'm still hunting his magazine remark that attempts to build in some frame compliance the parts either too weak to control loads or they just break. A non issue to me on Peel so maybe can talk him into a tamed Commando ride some day for the feedback.
http://www.cycleworld.com/2013/08/12/on ... e-of-five/

Rohan said:

wakeup said:

Do you KNOW that this is what they did, or are we just guessing here ??

Me, I'm still wondering how testing sideways torsional stiffness like that actually relates to anything in the real world !
And why doesn't the Commando go around the IoM 3 times faster then ?

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That's broadly how it was described to me by the then Chief Draughtsman, who was involved in the tests. I didn't see the tests but I saw the place that they were done, and some of the other frame design exercises that led up to the Commando frame.

If the assumption is made that a frame needs to keep the wheels spindles more or less parallel, (a difficult thing to do with telescopic forks), or more precisely the steering head at 90 degrees to the swinging arm spindle, then measuring that stiffness in some way is required, rather than relying on the "she'll be right" approach. It is a requirement of good design that trials and tests are performed to check whether or not the design criteria have been met.

Why isn't the Commando 3 times quicker?? First off the featherbed frame is generally recognised as being pretty good, any improvement that could be made in the Commando era would be pretty small. What a threefold increase in torsional stiffness would contribute to something as subjective as a fast lap around the IoM is very debatable, because it depends on so many variables, weather, rider ability, incentive etc., and that's before we get to the motorcycle itself. However, if all the variables could be eliminated, which is next to impossible, a frame with greatly increased stiffness should be faster.
cheers
wakeup

@wakeup: Thanks for sharing that bit on the Commando versus Featherbed stiffness.

Your description of a way about determining torsional stiffness is pretty much how I would go about it - the KISS principle.

The question I have is what relationship, if any, is there between the subject Commando race frame (2" lower) and that of the frames being offered by Norvil (2" lower).

Dances with Shrapnel said:

The question I have is what relationship, if any, is there between the subject Commando race frame (2" lower) and that of the frames being offered by Norvil (2" lower).

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Have we actually seen a Norvil lower frame - is it only done with shorter shocks, etc ?

So there can't be any 'relationship' ?
Nothing much from a roadbike could possibly fit this race frame shown here ?
The scrunched up looking oiltank on the racebike brings this home - its a different shape and dimensions to a roadbike one,
and everything around the Z plate (or where it would normally be) likewise, so things are only going to get more difficult from there....

THE only reason for a smaller frame its smaller cross section to wind resistance. Period end of story and throw in the ole towel and search the world from GP to Salt Lake to see its not hobot opinion just reporting nothing but the face mam.

Why isn't the Commando 3 times quicker??

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My Ms Peel is 3x's faster in harshest most dangerous lumpy windy ice heaved and truck beaten tights in the world and I know why and keep telling ya there is incredible-flabbergasting fabulous magic lurking in the isolastic frame and all ya have to do is dampen the spring backs and enjoy the compliance that allowed our coconut palm trees to with stand hurricanes of 200 mph deflection that breaks the frames other trees or tears em over by the roots letting go. Motorcycle handling has been solved to take advantage of gravity and any front traction left to press the rear into more grip till front not needed no more and all mass on flattened out rear patch to freak leap though turns and hi angles this way and that faster than a brain can focus clear or muscle blood pressure to resist internal fluid slosh even the gas tank width is too dam far to wait on fuel to freaking catch up in time. I seek to put the Unapproachable term back in the Norton Commando Name. < Catch me if ya can > will be a motto under Peel thermal OIF color change paint. Ass Grass Gas another. Must have serous power/torque to weight also to surprise the current crop of bee line buggers I already know she can scalp when ever any leaning and conflicting hi G's on tire patches involved.

Let me put something to rest right here and eliminate some of these half-truths:

Doug and I switched bikes for a lap or two around Shannonville a couple of years ago. I have kept quiet about my opinions, while Doug voiced some of his here on this forum some time ago.

No, I didn't love the way Doug's bike felt on the track. Yes, it was smooth - really smooth - to the point of no feedback from the motor to the rider. He likes that. I don't. And Doug's bike is tall (as are most Commandos), and felt top-heavy to me. I never felt entirely confident in the front end, and to me that's the most important feeling I can get from a race bike. I will say, it had great power and torque, and I know it's a fast bike and rider combo. Perhaps with more seat-time for each of us we'd acclimate each others' bikes better. But with the short test, it was oranges and mangoes. (And as a small anecdote: shortly afterwards I realized my frame was cracked in half on the lateral cross-member behind the rear upper engine mount - damaged from the previous race's off, so there was a *slight* handicap in the taste test.)

Proof is in the pudding. I'm sticking to my Seeley for the track, and my Commando for the street.

The only comment I can recall posting is that the vibes would take some getting used to compared to the Commando, which they would. The Seeley does feel like a sharp implement though, it feels like it has more forward weight bias. It is apples and oranges to compare, you get used to the feel of your bike. It is a lot of work to get the Commando to handle even close to the Seeley though.

hobot said:

THE only reason for a smaller frame

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Steve a smaller bike will likely have a different centre of gravity, possibly a shorter wheelbase, different vibration characteristics and different relative stiffness of various components. And possibly an easier configuration to install various race components, like carbs, exhausts, fuel tanks, etc.
So all in all, a few changes can make it a quite different bike, which without the inside story we can only guess at.
Who knows, it may have been purely to get space for more downdraft carbs, and the rest was just incidental.

But lower frontal area in a race bike would definitely be up there as a primary reason for the change, like you say.

We'll let someone more familiar with the rest comment on the rest...

Dougie, don't try and talk sense around here.

Remember when you and I were racing at DaytonaSportBARBERSSPABrands and we actually caught massive air for about half a mile... our bikes actually flew!!!!

Flew right over the top of Jorge Lornzo and Valentino, and Spencer and Minter, and Foggy too.

When I first started racing my 500cc Triton, it felt vague in the front end and did not inspire confidence, however the motor was extremely top end so that stuffed any quick lap times as well. I made new engine plates and moved the motor forward until the mounts touched, then it felt OK. When I rode the 500cc manx, I found out how a good bike feels - it inspired a lot of confidence. The way my Seeley is set up at present with the TZ350 fork yokes, I have no apprehension or anxiety whatsoever, I know I can use it to the max- safely. I suggest that if a bike worries you there is always a reason however much you might adjust to it.
I loved my Triton, it was a thrill a minute, however you always had to be really switched on or you felt pain. I sold it after 12 years racing and I was not sad to see it go. I still sometimes have nightmares about when I was racing it. The most common one is flying down the front straight at Phillip Island and watching the revs drop on the tacho - it is downhill most of the way.

Kennie you just solved my last mystery in rigid vs the isolastics by the dependance on front tire traction to steer, Yippee Kaye ! exactly what I thought was going on with what I term corner cripples. Stick to what ya know and don't mind me as I am not following either of your paths thank you very much. Peel is extra tall in front so never a worry to peg pogo and also no excessive road room for a bent knee sticking out changing CoG reaction and wind drag, so no leverage anyway to push off of. Pure confident faith to tuck in tight as a land speeder all the way around. If ya live for adrenalin G thrills way ahead of others might double think why I'm such an internet annoyance. Let it sink in to your bones powering up fully on rear acceleration grip can and should lift the front out of traction and put all pilot bike mass on rear patch, so what ya think is faster less rear thrust to keep front in effect or blasting right pass it the sharper and faster reversing the better it gets... Only robocycles do turn like Peel, ie: with no change in body position possible or required. No Fear Robocycyles just don't feel the adrenalin highs though so don't have same harsh throttle desire, poor things don't know what they are missing out on. If ya don't understand above even better as vintage things are not Peels prey.

My first road race meeting was when I accompanied my uncle at age 14, and watched Geoff Duke on the Gilera do it to all our top guys at Fishermans' Bend. I remember I was disappointed that the bike had black exhaust pipes, however it was extremely impressive. When I was 18, I started to going to every road race meeting in Victoria. After 9 years, I started racing myself, - there was a guy called Jack Casey who was a very good rider (died 3 years ago). He said to me 'you need lots of racing miles' and 'the bike has to do something for you'. He was so right.

Steve a smaller bike will likely have a different centre of gravity, possibly a shorter wheelbase, different vibration characteristics and different relative stiffness of various components. And possibly an easier configuration to install various race components, like carbs, exhausts, fuel tanks, etc.
So all in all, a few changes can make it a quite different bike, which without the inside story we can only guess at.
Who knows, it may have been purely to get space for more downdraft carbs, and the rest was just incidental.

But lower frontal area in a race bike would definitely be up there as a primary reason for the change, like you say.

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Without ego I am surprised by your not digging a bit deeper in the references that describe how and why racers want tight compact frontal area, way more than any the mere slight side effects you list over pure aero dynmanics. Shit i'm just laying out what I've read or learned the hard way, so don't attack the messenger but do verify the vital message.

Stable on two patches with differing vectors/directions and loads of surface lumps encountered is good up to a point > but with more forgiving two part 'chassis' there's more fun to be had. THE Gravel turned me into a one patch at a time only man, can't accelerate faster than floating front so not so high ya have to back off and can't stop better than lifting rear a bit but not so much ya about to tip on nose so have to let off. If ya think turn losds are any different, ya don't know what ya missing out on with uncanny 'unstable' flexy UFO. RR cars are stable on rails but motocycles should be able to jump tracks.

To me its apples vs asteroids, where everyone else is having to grit teeth not to break free or slip down >on Peel I'm gritting teeth I can stand the entry speed-energy to be able to catch enough air sideways to line up for next snatch the other way even faster. If you are working to have fun or race then ya can't relate to mere wrist action power steering only on smoothie Peel. If you can only see me me me me, then sorry you will likely never know what ya missing out on. There is no other cycle constructed as loose as Peel w/o rebound so nothing to compare with to make pavement feel like perfect moist Gravel Travel. Think flat tracker and speed way and supermotard bikes do they need brakes? Turns are not really turns unless past 45' and Peel takes those WOT same the relaxing straights. Feddie Spencer said 30% pilot 70% cycle allows winners most fun.

I do recall Kenny that my bike actually flew slightly higher than yours, I believe it was due to my more aerodynamic footpeg design.

I love hearing the excrement of your trills on flying leaps but that what i got into on P!! in mid 70's on public road humps like some bridges and over passes but couldn't lean like yoose guys. Here's a search that covers main reason for low compactness of frontal area. I ain't in Ken or Doug league, just Peel is.
https://www.google.com/#q=importance+of ... ontal+area

Doug, were those the low cross sectional foot pegs; exactly 2" lower?

No where else to stick this but note the lean, note the black strip and note the straight steering > hook em up by Fast Freddie.

hobot said:

by your not digging a bit deeper in the references that describe how and why racers want tight compact frontal area, way more than any the mere slight side effects you list over pure aero dynmanics.
.

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Steve, aerodynamics is not so simple that you can just google for a result ?
Getting the mechanicals in place for a good racer could well be way more important that just 'low frontal area'.

And as more than a few folks have found, aero is not something you can just look at and arrive at the correct conclusions.
Heck, back in the 1920s it was realised that the shape at the REAR of the bike was more important for getting a good top speed - at the front, the pressure wave sets its own boundaries. Its how you recombine the airflow at the BACK to minimise drag that gives the big speeds.

2 examples.
Joe Petrali on a HD streamliner was somewhat disappointed with his speeds on an ultra low streamliner.
Especially when they noticed that something with a large barn-door windscreen was faster !
That really sent em back to the drawing board.

And VW were vastly amused to discover that a Porsche 924 would do a certain speed.
And the exact same engine, fitted in a VW Golf was faster !!
Don't know if you have those 2 over your way, but one is pointy, and the other like a barn door.
Airflow is weird stuff, and folks that truly understand it even weirder....

Yes Rohan I'm up on the exceptions of fuller fairing giving less drag than smaller one that didn't quite cover bars or feet. Dunstall reported this in his Tune up Book. Still I'm not misleading ya that the main reason stated by those who did lower and narrower frames and packaging was air drag, not lower CoG or stiffer structure that might also result.

Back on point I can't help looking at the Experimental and think how much stiffer if just 6" added to connect down tubes to rear runners. Its takes dam intense loads to twist frames by turning forces so likely only the seasoned racers experience it to matter. Its not academic to me though as I have come to depend on it but garantee scares me to pull off in public as only places are into deadly blinds and no braking possible as way too fast, like THE Gravel only effect is change of lean by jerk fast up or down to save a crash or cause one end or the other lock up to spin on the other patch pivot. God Forbid need to lock both up to slow by full side ways frame drag. The first time I felt the difference between bars and foot pegs change distinctly was shocking but soon turned to shear joy. Fork brace comes into its own about then too.

Btw the little cross brace ya see on some down tubes is not to keep them from bowing, but from each twisting like torsion bar springs, at least in the two part C'do frame tabs. Frame and compactness can't solve fuel slosh or ground effects of air ram/gusts at max leans. Peel took me into aero limits becoming the main handling influence. One reason to leave center open to view through on Peel. I hope i sound off my rocker here as that's what its like to snap up flashy bait fish. If ya did understand that would mean only neck and neck type differences among our cycles, pashaw.