Steering geometry - confirmation bias

When my bike mishandled when I had too much yoke offset, it did not feel 'squirelly'. It simply stood up as I braked and turned the wrong way, throwing me completely off-balance. It came from nowhere. I knew immediately I was gone, so I tried to soft-crash it on the grass at the side of the track. When I turned it on again to get there, it came back under control. With the TZ350 yokes, I have none of that idiocy. In fact, it's self steering when gassed coming out of corners inspires a lot of confidence. I've never previously had a bike that I could ride so hard.
The simple fact that it DID mishandle once, makes me think It can happen again, even though I seem to have fixed the problem - especially if it self-steers too much.

You will notice that in almost everything Peter Williams ever says or writes about, he almost always mentions the way his bikes steered.

Dances with Shrapnel said:

We appear to be regaining traction on this thread. What's the old saying, 1,000 words are worth one picture. Thank you o0norton0o for the GIF.

In reference to some of Alan's earlier comments about bike behaviour coming out of the turns on the gas, how your rear suspension and drive components geometry are set up will have a direct bearing on motorcycle behavior. If your on-the-gas set up exhibits "squat" behavior, your rake and trail will increase whereas if your on-the-gas set up exhibits "anti-squat" behavior, your rake and trail decreases. If your on-the-gas set up exhibits neutral "or no squat nor anti-squat" behavior, your rake and trail remain constant.

Even front and rear spring rates have a bearing on effective rake while loading the suspension in a turn.

Something to think about.

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Perhaps if you are not sensitive to the way your bike steers, it probably does not matter - you simply rely on your tyres and adrenalin to get you around corners fast ?

Do note Williams only remarked about the frame construction/behavior in regards to its peak of secure steering - maintaining the reputation of prior proven Roadholder fork and geometry. Cycles are like old wooden piano frames, tune one octave of strings - distorts forces/tension on the other string octaves tone, so what worked pretty good prior now hurts to listen too. Takes pure faith/luck/foolish bravery to squeeze just a tiny bit of extra thrill out of various cycles so salute those surviving their kix.

Here clips missing pavement section edge, ok, then ~ bike length later strikes a tar seam ridge before tank slapper save pull off panty check.


Elites ain't got fork geometry fully solved. Stop frame forks tripping or saving insights hobot abhors about corner cripples.

acotrel said:

When I turned it on again to get there, it came back under control.

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Was this truly a result of getting on the throttle or getting off the brake? If getting off the brake, this typically increases rake angle and increases trail. If getting on the throttle, this suggests your squat configuration is impacting the overall geometry of the bike. A lot of things going on and glad you are past that.

Brooking 850 said:

Keyboard warriors it seems!!!!
Sometimes these guys seem to forget there are a huge amount of guys actively road riding and racing Nortons and riding and racing offroad bikes as well but dont blow smoke up their own arses of how good or bad at it they are.

Great GIF on steering geometry thank you
Regards Mike

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I did not post this topic to 'blow smoke up my own arse'. I put it here so other guys would know about what happens when you get your steering geometry right. The first Commandos had steering geometry which was prescribed by Peter Williams and a few inexperienced riders crashed them. I suggest that steering geometry was probably correct for road racing.
I am not a beginner. Back in the old days, I raced regularly for about 12 years - mainly on Winton Raceway. It is a 'rider's circuit' - it is 3 Km long, has twelve bends and one of them is a high speed sweeper. There are three hairpins and two fairly long straights and one short one. I know very well what it takes to win there when there are relatively modern bikes involved, my bike now has that potential. Unfortunately due to a family situation which involves three young kids and domestic violence and a custody dispute , I currently cannot afford even a track day. This won't always be the situation. Even at age 76, I will still race.
For years I have raced bikes and never even looked at the fork yokes. However the change I made to the Seeley has been of major benefit. I was lucky to have the TZ350 yokes at hand. If you pay to have fork yokes made in Australia, the cost is about $600. On Ebay, TZ350 yokes cost over $1000. If you were having yokes made to improve your bike, what offset would you specify ? - That is the dilemma I was faced with. You might assume that a Minnovation Seeley is as good as it ever gets, but you might be wrong.

acotrel said:

....... You might assume that a Minnovation Seeley is as good as it ever gets, but you might be wrong.

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There are some people I trust, this was writen by a young man I like and who impresses me, his brother is the fast racer in the family and his father has built some incredible bikes, including the fastest single cylinder 500 ever through the TT speed trap. 2017 was his first year racing on the IoM, he said this but a few days ago:


From my limited knowledge I would agree with Will that the customer support available via Martin at Minnovation is the best available for a privateer, so this is the route I would go as well.

From a chassis point of view the Seeley I rode this year was incredibly planted and did everything I asked of it with ease, whereas the Ducati was all over the place in comparison. I think you would go very well on a well set up Seeley

And no talk of TZ fork yokes on these bikes!

acotrel said:

.......

A while back I visited a website which gave the specs of Kenny Cummins' Seeley. I noticed that he uses small offset fork yokes.

http://nycnorton.com/nyc_products/alloy-fork-yokes/

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Alan, those yokes sold by NYC Norton are identical to those sold by Minnovation and used on their bikes. They are not small offset, NYC says for Commando, Featherbed and Seeley....more importantly Minnovation say this:

All yokes feature the standard Seeley/Norton offset of 2-1/4"

Kenny Cummins sells fork yokes. I have been trying to find his web page which told what offset he uses on his own Seeley. It seems to have disappeared and been replaced with an email address to direct any questions to Dan Rose. - A yoke offset of 2 - 1/4 inches is about 56mm. Mine are about 40mm.

I am surprised that NYC specify those yokes for a Featherbed. Usually on a Manx, it is impossible to reduce the yoke offset and the rake is much less anyway. In the old days some guys tried to use yokes off a garden gate Manx, on a featherbed - gives a pretty bad result - too much offset..

acotrel said:

Usually on a Manx, it is impossible to reduce the yoke offset and the rake is much less anyway.

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I thought we already sorted this out in previous posts. Rake on a Manx is not less than on other featherbeds. Stock rake on both production Manx racers and featherbeds for the street (wideline and slimline) was 26°, at least according to Ken Sprayson, who certainly should know. Might have been different for the factory team bikes, but I've never seen anyone claim that. For Commandos it was 27° for the 750s and 28° for the 850s. On my 1959 Manx it was 26°. If you have some evidence to document this not being correct, please post it. As far as I know, the only featherbed frames with less than 26° rake are reproductions or originals that have been crashed.

Ken

acotrel said:

Kenny Cummins sells fork yokes. I have been trying to find his web page which told what offset he uses on his own Seeley. It seems to have disappeared and been replaced with an email address to direct any questions to Dan Rose. - A yoke offset of 2 - 1/4 inches is about 56mm. Mine are about 40mm.

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What I am telling you is that as far as I know he uses what Minnovation use, he has had a relationship with those guys for several years.

Not only that, they are a pretty standard Norton dimension.

Standard rake on a Manx is 24.5 degrees with 19 inch wheels. Replica Manx frames often use 26 degrees and 18 inch wheels and handle like Suzukis. A Seeley frame is nothing like a Manx frame - the yoke offset is usually much greater on the Seeley because the rake is 27 degrees and the wheels are 18 inch. TZ350 Yamahas use 26 degree rake and 18 inch wheels and have neutral steering. The difference with my bike is that it has one degree more rake than a TZ350 Yamaha - the wheelbase is similar.
- You can argue all you like - IT WORKS and works well !

Original Seeleys used Metal Profiles forks. I've never heard of Norton forks being used on Seeleys. However it probably happened. The yokes would have to be different.

acotrel said:

Standard rake on a Manx is 24.5 degrees with 19 inch wheels. Replica Manx frames often use 26 degrees and 18 inch wheels and handle like Suzukis. A Seeley frame is nothing like a Manx frame - the yoke offset is usually much greater on the Seeley because the rake is 27 degrees and the wheels are 18 inch. TZ350 Yamahas use 26 degree rake and 18 inch wheels and have neutral steering. The difference with my bike is that it has one degree more rake than a TZ350 Yamaha - the wheelbase is similar.
- You can argue all you like - IT WORKS and works well !

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Oh, I'm perfectly happy to believe that your bike setup works well. I've never said anything to the contrary. I just don't believe the standard Manx rake is anything but 26°.

Ken

My friend has a Triton which has a genuine Manx frame. The rake angle is 24.5 degrees. It is quite common to a lot of bikes. Even the Muzzi Kawasakis of 1993 used it. 26 and 27 degrees are also common. But the 26 degree rake is often used on replica Manx frames which are used with 18 inch wheels. All Seeleys were 27 degree rake and I believe Commandos are also that even with 19 inch wheels. RG250 Suzukis had 26 degree rake and 18 inch wheels, as did TZ Yamahas. When RG 250 Suzukis changed to the 17 inch front wheel the rake became 25.5 degrees.

I found this interesting. I never use point and shoot riding style. But with the smaller offset fork yokes, the steering is much more direct and the self-steering aspect requires anticipation.

personally I don't find it too helpful to equate riding style on a 'modern' machine to anything that is 'comfortable' on a 'classic', even when you have revised the rake/trail withh longer shocks and fitted (slightly) larger tyres. (yes I know many good classic racers do a lot of knee dragging, but, not every winning rider does, and I have yet to see one elbow drag! 70 degrees of lean on a classic usually means you are on your ear!)

Simply put, for me I found it fairly easy to drag my knee on a short wheelbase GSXR750SRAD with a 120 front and 180 or 190 rear, but on a Rickman or Seeley fitted with 90 or 110 front and 110 or 130 rear, I find I am grinding hard parts on the bike and boot toes, and my knee is nowhere near dragging, nor do I think increading lean is really agood idea since tyre wear indicates I am using most of what is available. I do shift bodyweigh for a high proportion of corners, but remember that physically you still won't achieve the same result because most classic seating positions are longer from seat to handlebar than most modern (sportsbikes), meaning that the longer tank will normally limit your sideways movement.

In terms of achieved lap times, generally just a little slower, but considering that the GSXR had a dyno sheet showing 120rwhp and that accelleration generally made my eyes rattle in their sockets, the fact that I am lapping at similar times indicates my corner speed however, is faster on the classic skinnier tyres!

I also recall that 40 years ago, racing the frame I know use again, in those days it had 19" rims, and that made a difference. For example, on several occasions when it felt like to only way to get around a particular corner at the entry speed, I leant my body outwards like those earlier riders! In effect pushing the bike into more lean angle to make the turn. Since at the time I also conciously used countersteering that should have been an option in these corners, but in places the opposite body lean seemed most effective. Now on 18" rims and slightly wider tyres and longer shocks, I have never felt the need to do that.

I've mastered all these styles on many types of surfaces and speeds/sharpeness. Main thing about knee out is sudden air drag on inside helps cycle start and stay turned and to feel how far away the road surface is. I am expert at Tazio and Freddie style which is mainly tipping cycle under you while maintaining mostly centered upper body. Good for lower speeds and poor traction. If ya look close will see them direct steering at speed. Danger of hanging very far off is raising CoG so much the cycle can suddenly pivot on CoG lifting tires as lower head till flying off at the tangent often taking out others. To take advantage of Peel prowless against any cycle leaned past 46' I lock down centered no body english at all, sometime with inside leg straight out behind as no room between tank and road for knee. Peel could lean nearly 70's at speed on skinny tires, so I'm not at all mystified nor impressed by ape like behavior.
Valintino won a lot of his races cutting others off to upset them more than out ridding them. Over rigid cycles take a lot of work to hold stable so moving body mass outward gives more leverage to fight back with them. Point being all other cycles require more and more pilot strength and skill to go faster while Peel became more and more easier/lighter/low skill. Peel has solved all handling issues and so far beyond anything yoose guys can even discuss I don't care what ya think of my rants - till life allows proving it in spades.