Self steering and top speed

Talking to a frend yesterday who watched the MotoGP last weekend. He mentioned that they showed the inside of the Ducati cara van, and apparently there were three sets of fork yokes there. My seeley is the Mk3 1966 frame, and when I started racing it, I lent it to the same friend to ride because he still had a licence. He came back from riding it and said 'next year when you ride it, watch out. Under brakes, it stood up and turned left and nearly crashed me. I thought it was bull because another two friends ha ridden it with Laverda motor in it and never mentione a difficulty. The Next year I rode it at the same meeting, and went around the sweeper on Winton, as I would have ridden my old Triumph - with my backside hanging out. As I backed off and went to turn a bit right, it stood up and turned to the right. I was convinced I had lost it, so I decided to crash on the grass on the left hand side. I turned it on again and steered that way. The bike lay down again, and I survived with a slight increae in heart rate. From then under brakes I became aware of its negative steering. I looked for a different set of fork yokes, and was quoted $400, but I still did not really know what I wanted. I spoke to Rod Tingate who used to work for Colin Seeley. He told me that all the Seeley frames have 27 degree head angles. Photos of the old Metal Profiles forks on Seeleys showed very small offset. I started to think about it, and remembered that most 70s Yamaha two strokes have 18 inch wheels, and 26 degree head angle, and I just happened to have a set of yokes on a frame in the back yard. So I had the hole in the bottom yoke machined, and fitted them to the Seeley. The handling was transformed, now when you are halfway around a corner you gas it really hard, and it will self steer in the direction that you have it laid over as the weight comes off the front. It feels really strange when you do it, but you are on the gas so much earlier than most others, so your top speed is higher at the end of the straights.
I was recently reading an interview by Sir Alan Cathcart of Ago. Ago mentioned that the 500cc MV3 was slower that the equivalent Honda four, but was a better package. He used to drive it into the corners.
A lot of us use converted road bikes, and never change fork yokes, so we don't discover the effect. Road bikes are a compromise anyway. The effect of reducing the offset on my Seeley from the Ducati yokes to TZ yokes was dramatic and dangerous. I don't believe there is any formula which relates steering effect to rake and trail. - ANY CLUES ?

NOte: If you are going to play with this, be careful ! It can grab you by the throat.

Well as far as I can tell, putting on yokes with less offset increases the trail. increasing stability but reducing the quick turning ability. It would also , I think put more weight on the front wheel.

http://img.auctiva.com/imgdata/0/0/9/0/ ... 7887_o.jpg

The oriental contraptions characteristics were described as ' The honda Handleing horrors '.
http://www.vf750fd.com/Joep_Kortekaas/riders.html
Something their road bikes mimicked for some years , when pushed , or were inexpertly riden at speed .

Heres a third / replacement , something still common in the mid 70's ( British frames on Jap race bikes . )







Apparently the big soggey slicks of the current race bikes need the olde 4 in. trail , which the trigonic Dunlops required .

Heres ' our Boy , Pete '.



http://www.sintich.com/quattrovalvole.htm



The Olde ' Rake & Trail ' relate to use , and tyre . The Olde ( 50s ) Dominator yokes gave a forward sweep to the legs from stem .
rakeing the head out , or setting it out , to give 4 in. trail worked o.k.

Bike driftable and leanable, very. so picking it up a bit if youd overcooked it picked up traction . Steered with trottle and mass ( body language )
to ' trim ' the pointing .

Too many unknown variables for a fork formula so far, only trial and error rule of thumbs. You still got a wheel size experiment to do with the forks installed to learn what's helping or hurting the most on your Seeley.. Ken Canaga holds some guilt yet of sending a rider out on experimental lesser fork rake and it tossed rider off like you described for some permanent ill effects.

THE Gravel taught me best shortest safe effective braking is done pure upright inline or risk slowing up less quick while loosing it. It also taught me when much difference in traction between front and rear expect control reversals if staying on it. Hooking up enough power while leaned can lift front forks out of much traction then rear can over power its outward direction and force front to road follow into straight steering for a tank slap effect. Them right now surprise upsets is why I say other modern or vintage bikes are dangerous corner cripples, compared to one that ain't.

The handling was transformed, now when you are halfway around a corner you gas it really hard, and it will self steer in the direction that you have it laid over as the weight comes off the front. It feels really strange when you do it, but you are on the gas so much earlier than most others, so your top speed is higher at the end of the straights.

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I am very happy for your better handling but a real transformation [opposed to a good incremental improvement] allows WOT attacks even before the lean begins w/o waiting for the early apex blast out. This of course can create great differences in front/rear traction, just like on THE Gravel, so when really getting on it bike will automatically fall over into straight steer, which is beyond strange but a real leap of faith because its like driving your self into that scary low side crash on purpose, but it hi sides back up just right - in time. This is also what I think knocks down the solid mounted chassis, twists frame up w/o compliance between tire conflict then suddenly snaps back or vibes, so fast can't tell what happened prior the crashing.
Fully Transformed handling allows tire squeal power where everyone else and their sister is hard on brakes slowing to turn in.
Fully Transformed handling allows this with no run off area on 9 ft wide lane. Just imagine how fun that feels. But ya got to work with what ya got so safe racing knowing what's lurking if you press further on the new found corner hook up.

I don't think I'd have a problem with the rear tyre breaking away, them grabbing and hi-siding me, unless I found another ten horsepower. The bike is extremely nimble and safe. My old Triumph had a featherbed frame and standard manx fork yokes. Years ago we all used to change fr om 19 inch wheels to 18 inch to get decent tyres. Doing that completely stuffed the handling. I was always dragging the bike away from the outside edge of the bitumen. With my Seeley, when you gas it hard is long before you can see into the next straight, and you do it with blind confidence that y ou will not end up taking the outside fence coming out of the corner. It always ends up in the centre of the bitumen, blasting away. It feels really weird doingb it, but it is really great. My initial comment was really about the top speed of commandos. If your bike handles a s mine does, on a big fast circuit it is usually really gassed up and strongly on power earlier than most other bikes, so even though the motor is tuned for torque rather tha n top end, it can actually end up with a higher top speed. Riding on gravel is a completely different matter. If I ever spear off into the loose stuff, I keep the bike carefully upright , and never put pressure on the tyres, It is not designed to handle that for you. When I first started racing, one of the then old riders said 'you need to get racing miles under your belt, and the bike has t o do something for you', but another old A grade rider friend of mine also said he likes to do his own steering. As I said, if you are going to play with this - watch it !

Oh ok you have done wheel size experiments on BI I haven't. Your sense of wild flung faith ain't lost on me so leaves me a bit adrenalized just reading your description. Necx to teaching folks how to re-grow their neck so everything else re-grows too, conquering stunt and handling skills is what motivated me to keep at Peel's slow going project. I don't have life long mc experience, just a few years in early '70's on P!! dragster that couldn't lean to steer, then found a Combat on '99 move to Ozarks. I thought I knew how to basically ride till THE Gravel hit me so often, and then first time the Cdo Hinge Hit me, should of died that day on elevated decreasing sweeper with 15 ft drop offs. Turning power handling is the killer buggaboo to conquer via bike set up and pilot sense to use it to max.

Please expand on these comments...

I think all the current fastest BI racers use 18" at both ends, so this confuses me.

18 inch to get decent tyres. Doing that completely stuffed the handling. I was always dragging the bike away from the outside edge of the bitumen.

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Fascinating description below want to understand better. I don't get much chance to compare notes with risk takers like you acelo-lot. I don't measure my turns by speed as much as the acceleration G's through them, so the extra speed is just a nice side effect. I like-try to turn in sharper than needed to get more acceleration sense than speed sense. I don't get no satisfaction except on compliant Peel as the others flop chassis or 'twitter' forks or suddenly let front or rear skip out > unintended. What-why does your Seeley feel so strange yet wonderful to you?

my Seeley, when you gas it hard is long before you can see into the next straight, and you do it with blind confidence that you will not end up taking the outside fence coming out of the corner. It always ends up in the centre of the bitumen, blasting away. It feels really weird doing it, but it is really great.

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My initial comment was really about the top speed of commandos. If your bike handles a s mine does, on a big fast circuit it is usually really gassed up and strongly on power earlier than most other bikes, so even though the motor is tuned for torque rather than top end, it can actually end up with a higher top speed.

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This is what most surprised me and sport riders, after Peel got all linked up to take the torque all the way around turns. Peel had a good power combo, significant better than her prior good Combat power or my current Trixie, which i just can't control flops in turns, nor on other hi power balloon tire cycles as you have noticed too. No one believes me but the hot shots that couldn't catch her even in long straights till I chickened out for blind crests I'd had close calls with farm machinery or school buses or cattle etc, to risk on a mere joy ride. No matter because they'd have to slow up again for the turn at ends but Peel didn't. Peel speedo would show 135 about anywhere I cared too as didn't take long to get there to top out. Was that real speed? Moderns said theirs was reading 130's too.

As too THE Gravel being different animal than tarmac, yes and no, yes as can't lean on it like tarmac but no as once going so harsh tarmac gets as loose as THE Gravel, then its all the same but way faster easier on hard smooth surface. After horrific Cdo hinge hit me once I gave up on them and got the SV650 then worked up tarmac just short of loosing traction, as feared it'd keep sliding like THE Gravel. So took corner school to find out tarmac stops slides as soon as the loads released. ie: forks or power or both let off. I can't even practice Peel's lines of corner attacks on race type cycles as they get too upset before reaching Peel's energy level of merely "phase 3" two tire traction, with 2 more faster phases of one tire traction on tap. For Peel to pull this off she must always have power band to spare or she reverts back to corner cripple states of flying hi sides. So yes understand the scared committed faith remark.

Interesting thread.
When I went to Kaw triples from sweet/intuitive/forgiving steering Brit-bikes, the need to apply headlock tactics came as a bit of a wake-up, but I`d heard that some riders simply understeered off the corner instead, so that was not a viable option.
If of interest, check out the steering specs of the H1s in this chart, every year they tried something different to provide feel/surety.
http://kawtriple.com/mraxl/modelspecs.html

Note also with the later H2s, Kawasaki tried increasing W/B & trail, but steepened the rake, hence the self - correcting [but disconcerting] hi-speed tank-slapper phenomena, [ in my instance, also perhaps exacerbated by fitting 13.5 in gas-Girling shocks,twin discs & reducing the underslung weight 30+lbs - by fitting Denco pipes].

This a picture of my folly. - might interest you. It is an Egli TZ750 frame copy from the mid 70s. RG250 wheels and forks. The motor is H1 Kawasaki fitted with RD350 barrels, cases ported t o suit, and the barrels shortened - gives TZ750 transfer timings, with less exhaust height, and 600cc capacity. THe crank has labyrinth seals fitted. Wheel size is 17 inch, so I've set the head a ngle at 25.5 deghress as per the RG250. There was a complicated juggling trick to ge t the chain line right , which involved lifting the motor - hence the plates under the motor.. I've lost enthusiasm for it at the present, but one day I will complete it:

Your H1 stuffed buzz bomb there is inviting to let it rip alrighty but brings up issue of power band delivery to me, beyond its power to weight sprinting ability. At least the way I want to hang turns. I see 2strokes take on bigger bikes and take corners like smaller ones, so a mystery if that genre of cycles has some advantage over Peel's deal. Pilot faith capacity effects ability to play near limits of course. Maybe acetrel can compare its pecking order with the Seeley Commando or other vintage-ish racers.

Been thinking on acetrels description of transformation, which I am impressed + pleased to read how big an "incremental" improvement it is, plus the two reports of bike "Standing Up" surprise on prior lower trail forks. acetrel is one of the few I've heard mention "self Steering". Self Steering has a few meanings or aspects to me but mainly it conveys sense of Center of Gravity for Neutral Handling, ie: just as easy to throw down as to pick up or little tendency to keep wanting to fall down or to fight to hold down and not fly up unexpected.

Peel had about prefect balance, pilot fork input only needed for an initial instant then she'd just stay at any angle w/o further effort and held it with or w/o throttle applied and through shifts in longer corners. [staying in phase 2 counter sterering 2 tires in traction] - If kept pressing at same lean and fork turn all's she'd do is start to slide wide on both tires but didn't want to trip out or snag a high side nor jerk forks out. I did not have to hold forks but for throttle until she'd began to slide then forks wanted to counter steer too much while crossing road texture at oblique scrub angles, so at that point I had to sort of hold forks to damper tank slap or counter steering more to transition into wider flat tracker style where rear is wanting slide more than front twisting bike aim that relieves the inward desired tuning forces. Also them flat trackers rarely trust their CoG lean stability so put a steel shoe down to become a tricycle instead of a bicycle. Supermotards too. When her two tire slide stopps she just picked up where she left off in turning radius. This is what I think acetrel is describing flying out of turns just on the edge of traction but w/o drifting too far before bike just self uprights from a mild hi side effect as tires line up again.

Above is about the max out level for the rigid chassis I've tried and suspect applies to the Seeley frame and maybe MacRae's solid-ish non compliant linked iso Cdo. Its all I need to do in wider single turns on Peel too, [phase 2] though even there I feel Peel significantly more stable and hooking up better than anything else I've tried or contested with. But if path turns off sharply the other way after coming out a milder turn then things change a lot and so does Peel's style of handling them. Chicanes is where Peel's literal leaps of faith begin and phase 3 and 4 handling onsets. If I give more power than to just begin a drift, {Not Crossed Up] then Peel will fall over on her own so forks not needed to lean so they flip into road following straight steer, which stay that way by themselves as long as I match power to traction, but if i add more straight steer forks make Peel want to 'stand up' in a hi side which twists frame down hard on rear patch, so I can give a lot more power to rear suddenly, which wants to low side down, but Peels frame just twists up storing this tire conflict as long and hard as I care, to point the rear hooks so well it can lift the front up in a leaned over sideways wheelie,which sharpens up into a decreasing radius turn with the G's of a drag racer launch. hobot Roadholders really come into play here to lever down on rear with, but the touch down is soft easy on them. All the load is on rear thrust so thrilling way to end up faster leaving a turn.

So can ya slide a unicycle, Peel can...

Phase 3 can get Peel through first chicane turn but next opposite is on us so fast no way human can turn forks or toss bike the other way fast enough not to fly right off the far edge, so instead of just giving enough throttle to lift front while leaned in straight steer, if I give enough to spin tire out she trips down into full low side as she twists frame up to max then cut throttle so swung out rear grabs a hi side, she flys both tires off surface as frame unwinds w/o rebound to N, to add sling shot like thrust, bike twists in air on both its vertical and horizontal CoG, which I'm part of and occurs at about seat level and mid frame, to land on rear patch and severe fork side load, all lined up with new aim but patch smash so wide that instant I can nail power for a tire hook and rebound into fork floating launch out of there. In a series of these the rear sling out acts like brakes in one direction while thrusting ~90' into another direction. Phase 4 is a control crashed state Peel out races.

Then there's one more way around pretty dam sharp decreaser turns I can do on THE Gravel if brave enough to fly into narrow blinds 80-90 mph, drift car style or rolling burn out style, ie: mostly upright with tire spun into max traction of 10-ish percent slippage while straight steering so rear swings out till lined up with forks again then about wheelies out of there. This way has no hesitation in acceleration but if run out of power keep rear slightly loose, its all over in an instant. About anything is over powered on THE Gravel, so can't do this much till blower on line. Then may not if the reports of impeller gyroscope messes with the N balance and predicable chassis reactions and tires not really in what most call effective traction.
This is the most tire noise and heating state. Don't know how much narrow tires can take this before liquified. I want to see the grooves edges smeared out in flat sheets ~1/8" wide, not abraided nor melted away. I have done this to save my bacon on wet pavement a storm wind gust lifted out of normal lean.

Except for the wet wild surprise, all the other stuff does not wear me down as Peel don't take no athletics just throttle and bar and knee grip enough not to have bike fly out from under. Can take my breath and vision away so there's some breath forcing on phase 3 & 4.

Alan,

I recently had some frame repairs done. The guy who did the work has built a road bike around a Yamaha TDM 850 twin. He didn't know exactly how his chosen frame geometry would work with fork offset, and he wanted to experiment, so he made a set of yokes he could vary the offset on, using a set of spacers, the spacers looked about a 1/4" to me but they could be a little bigger.

He said he initially set it with one spacer, not too much offset, but he said the steering was slow and lazy. Now this is in line with Pommie Johns understanding/comment, he added a second spacer, and then a third. He says he had to re-learn to ride it because it turned so quick with very little steering input such that he kept running into curbs. This is a road bike not a race bike, but he is very happy with it, and like a lot of fabricators just has not got around to making a (prettier) fixed version of his yokes! Luckily they are hidden in this picture.....

I think you will see from the site he has a lot of background and knowledge of bikes frames.

http://www.mojomotorbikes.co.uk/contactus.html

I have a set of yokes made for my Seeley to about standard Seeley/Norton offset, but like you I had wondered if using smaller offset TZ yokes would be better, the message from this guy was no, don't go there, they work on TZs because of other differences in the geometry....but then again, I have ridden a Seeley MkIV and had none of the issues you mention that started your desire for changes and no one else has mentioned that chracteristic to me!

Steve

Steve, I haven't been riding the Seeley very often these days. When I do I usually ride about 4 laps of the 3Km circuit before I start pushing it. THen I carefully gas it hard when I am halfway around the tight corner leading into the back straight. It feels weird doing it because you are nowhere near coming out of the corner, and you a lways suspect it might run wide. Once I get used to the self-steering again, I use it on every corner a nd bend. It is quite pronounced if you are looking for it, and relax as you gas the bike out of the corners. The yokes I was using when it stood up and turned the wrong way under braking , were Arces - off a 450 Ducati, and they had a lot of offset. I'll put an old photo of the bike up, so you can see what I'm talking about. It was a very nasty experience, and both myself, and my friend had it. We've both raced many times over many years - it would have decked a beginner.

With the Ducati yokes :


With the TZ350 yokes :


I don't know whether you can see it but the front wheel in the second picture is a bout one inch futher back

J.A.W. said:

Note also with the later H2s, Kawasaki tried increasing W/B & trail, but steepened the rake, hence the self - correcting [but disconcerting] hi-speed tank-slapper phenomena, [ in my instance, also perhaps exacerbated by fitting 13.5 in gas-Girling shocks,twin discs & reducing the underslung weight 30+lbs - by fitting Denco pipes].

Click to expand...

Probably just its a indifferant copy of a Rickman frame with tube of half the crossectional area , Braketry meeting no
estabished engineering norms , and then theres the swinging arm . Note; fish oil shocks replaced .

Acotrel, thats a cool triple you have there, dont be amazed to get an offer for it ....from Worntorn.
Seriously though, have you seen Warren Willing`s `70s version? http://www.deejay51.com/coca_cola_800_gallery.htm
Scroll down & check out all kinds of wild & woolly downunder race bikes of the era.
I stuck an H2 mill in an RD LC chassis with good results, I have another to put in a G.P. 250 chassis, would like to put an iso/Commando mill in one too..

http://www.amazon.com/Motorcycle-Dynamics-Edition-Vittore-Cossalter/dp/1430308613#_

This looks like a pretty dense read, but might provide some insight.

Jim H.

Here's something exotic to read while awaiting book delivery. Snagged off mc-engine list today.

I came across this very intelligent blog referenced in a recent crash.net 'Comments' section. If you grind it out through Google Translate (from the Italian) it will be pretty easy to follow:

http://gpone.com/albertocani/2012/07/18 ... rta-corta/

I found this paper interesting. I'm surprised that anyone ever used Isolastics on a Seeley with that silly balance factor :
http://guskuhn.net/GKMLtd/Racing/1996TrackTest.htm

Thanks for the reference to the book on motorcycle dynamics , I've just now ordered a copy after reading the index.

acotrel said:

I found this paper interesting. I'm surprised that anyone ever used Isolastics on a Seeley with that silly balance factor :
http://guskuhn.net/GKMLtd/Racing/1996TrackTest.htm

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By silly balance factor, are you referring to the 53% dry BF for the isolastic Norton twins? I seem to recall this remark elsewhere on this list; maybe from you.

Care to expound on this - just trying to understand exactly what you are referring to and why.

All fast Triumph twins have for years used balance factors up around 80%. If you tr y t o rev a motor with the crank balanced at 58% the crank and bearing loads at high revs must be horrendous. I've already got one set of cases which have been split by a young guy who used to ride his commando on our Great Ocean Road with his mates, really fanging the poor old Norton. You have to look at the intention of the designers w hen they built the Commando. It appears to have been designed to both cope with low speed traffic conditions, and higher speed riding - I believe that is impossible with these big longstroke motors. You have a choice - either you mount the motor rigidly and tolerate the low speed shake using a high balance factor, which dramatically smooths out at high revs, or you stay with the isolastics and 58% balance factor, try to make your motor develop more torque, up the gearing and don't rev it hard. If you are going to race the bike, I suggest that making the motor develop top end and destroying the power at low revs might be the wrong way to go. I believe the 750cc production racer was a fail because it was trying to be a Triumph - the stroke was very close to being the same, and the advantage of being able to independently change the inlet and exhaust cam timing easily, was not there. The ultimate development of the Triumph engine is the Nourish-Weslake, Rickman head engine. If you want a really fast Norton , save your money and start with one of those.
81mm stroke 650/750 Triumph engines have always been able to cop 8,000 revs, but one which develops a lot of torque is ultimately faster and doesn't blow up so easily, especially if you use a five or six speed box which gives it an easier time. My preference for a 750 would be a Nourish engine with a 75mm stroke billet crank, and the same sort of bore size as their 900cc engine. You'd be able to rev the tits off it, and get full advantage of the four valve heads, especially if you used titanium valves. I'd also be using the superblend bearings - not usually used in Triumph engines.
It would be easy to find a five speed unit triumph bottom end, make your own crank and buy the head and barrels from the grass track sidecar guys in the UK. It should be able to cop 10,000 revs easily with light modern teflon coated pistons from a japanese motor.