Steering geometry - confirmation bias

In general terms, there is no such thing as a dual purpose motorcycle. What suits the bitumen usually does not suit the dirt. If I ever run out of road with the Seeley, I stand it up and try to turn it as gently as possible.

Ugh - In general on and off road require different types of cycles and pilot skills but in fact they are almost identical if tires are in nil traction states. At risk of alienating real racers more, Ms Peel so conquered pavement its mainly off road wildness crashing she's been set up for. Peel only ever had hard deep cleated tires fitted which gave limited tarmac traction yet d/t her dampened frame compliance was able to beat myself on SV650 and all others - some risking lives passing cars in blinds - so much so I'd wait a min behind slow cars for sane/safe pass to end up back on their tails in 30 sec or so in some the most dangerous Mt. roads long trucks excluded d/t sharpness. You know how much faster/harsher to over take a race leader with long lead on more powerful cycle - Peel could w/o a skilled pilot or decent street tires.

Your off tarmac saves shows ya know one can not lean much or at all if tires are in nil traction states and fork must be cautiously dampened, so most my reflexes acquired on THE Gravel, grass, ice/snow and ugh mud. A cycle can only go so fast/harsh turning before front looses effective traction and risks crash by more counter steer.

Peel plan$ are data logging angles of fork and leans, vibes, skews and leaps to show world what they are missing out on and make naysayers eat crow with objective data no other cycle can approach. Then might fit real road tires to break her own on road records.

acotrel said:

In general terms, there is no such thing as a dual purpose motorcycle.

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In specific terms, there is such a thing as a dual purpose motorcycle.

A flat track Harley ? Or a Paris-Dakar BMW ? Name one bike that handle on-road and off road equally as well as bikeswhich are specifically developed for either purpose. Generally speaking the steering geometry and power characteristics are very different after they have been optimised for either purpose. What is good on bitumen is usually hopeless on dirt and vice versa.

acotrel said:

A flat track Harley ? Or a Paris-Dakar BMW ? Name one bike that handle on-road and off road equally as well as bikeswhich are specifically developed for either purpose. Generally speaking the steering geometry and power characteristics are very different after they have been optimised for either purpose. What is good on bitumen is usually hopeless on dirt and vice versa.

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Whilst I would agree with you in principle I think you should ride a BMW GS1200 etc and report back,things have changed in recent years,of course they are not going to be as good as a specific bike in racing terms,but for the average rider these types of bikes are as good as it gets,on road or off

con·fir·ma·tion bi·as
noun
noun: confirmation bias

1. the tendency to interpret new evidence as confirmation of one's existing beliefs or theories.

I had no doubts that this "Question" that was asked originally was going to turn out to be a lecture by the person who asked the question in the first place... Right in line with the definition of confirmation bias ...

acotrel said:

A flat track Harley ? Or a Paris-Dakar BMW ? Name one bike that handle on-road and off road equally as well as bikeswhich are specifically developed for either purpose. Generally speaking the steering geometry and power characteristics are very different after they have been optimised for either purpose. What is good on bitumen is usually hopeless on dirt and vice versa.

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Equally well? No, that was not your silly assertion and apparently you took the bait!

Historically, early motorcycles were (by necessity) dual purpose as there were few asphalt roads. So were they all dirt bikes or all asphalt?

As baz alluded to, it might do you well Alan to get current on things. From my first hand experiences, the BMW GS1200 will make a Commando look silly on the road and is more sure fitted than many historical "off-road" only motorcycles.

In the real world, there is compromise, both in design and use.

The main difference of on or off road cycle is mainly the tires and taller stance to take bigger bumps and less hi centering snags. Generally off road bikes will have rather weaker smaller front brake because front traction so touchy *especially* if fork turned even slightly. Consider that supermotards are off road intended cycles fitted with street tires and visa versa the big BMWs are essentially big curiser fitting with dual propose tires. AGAIN one can not do much or any countersteering when tires are in low traction states. MAIN difference to keep going well on cycles on or off road has to do with pilot behavior in hi or low traction way more than cycle configuration.

Remarkably one the best off road cycles I've experienced was a 1940's Indian Chief - full bagger, Long horn wide bar, car size tires on leaf spring front with huge tractor like seat. Uncannty smoothness across rocks, ruts roots, could dougnut on grass and sand pretty easy but my favorite fun was arriving home, would skip the steep paved driveway to aim straight into few feet deep drainage ditch at 30's mph on power to zoom up the far bank 10ft hi about 40'mph to catch air cresting 4ish ft off ground to land on both tires for a soft bottoming and bounce up a few inches off surface in empty grass lot to ease on brakes till slow enough to spin rear around and idle onto steep driveway across its crub from the side. The main memory that still lingers was feeling like a blimp with sluggish suspension oscillating below while air borne many bike lengths. Watch 1940's military and police tests of Hogs having a blast in rough off road testing delights.

Also off roaders tend to mainly steer with rear power, ALWAYs scared to depend much on front traction - but not to point of slides like flat tracker, which is not off road but on nice smoothed hi traction stuff so ordinary vintage and sports bikes successful w/o modify fork geometry or anything but power, tires and maybe spring/shocks rate.

Would you say that a dual purpose KTM or GS 1200 BMW is as good on the dirt as a specialised motocross race bike, and as good on the bitumen as a specialised road race bike ?

Incidentally, to claim that early motorcycles were dual purpose, ignores the number of really bad crashes their riders had because of ignorance. Some of those old vintage bikes are inherently dangerous. Even as late as 1948, garden gate Manxes used to stand up in corners. What really amazes me is that the McCandless brothers got it so right with the featherbed Manx. I have often wondered where their knowledge came from. Same with Colin Seeley, who was primarily a sidecar racer.

o0norton0o said:

con·fir·ma·tion bi·as
noun
noun: confirmation bias

1. the tendency to interpret new evidence as confirmation of one's existing beliefs or theories.

I had no doubts that this "Question" that was asked originally was going to turn out to be a lecture by the person who asked the question in the first place... Right in line with the definition of confirmation bias ...

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At least now, I have got my head straight about what caused my Seeley to mishandle so badly. I've been reading about the 1992/1993 Muzzi ZXR750 Kawasakis of Rob Phillis and Scott Russell - how they handled. It confirms what you guys have said - that reducing the yoke offset quickens the steering. However is 'quick steering' the same as 'self-steering' when the bike is gassed hard when cranked over coming out of corners and the bike tightens it's line ? In 1993, Suzuki won the 500cc MotoGP championship with a bike that did that but was underpowered.

acotrel said:

Would you say that a dual purpose KTM or GS 1200 BMW is as good on the dirt as a specialised motocross race bike, and as good on the bitumen as a specialised road race bike ?

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No, and this has nothing to do with your original silly assertion of no such thing as a dual purpose. Remember, there is compromise; even within a finely tuned MotoGP bike there is compromise.

acotrel said:

Incidentally, to claim that early motorcycles were dual purpose, ignores the number of really bad crashes their riders had because of ignorance. Some of those old vintage bikes are inherently dangerous. Even as late as 1948, garden gate Manxes used to stand up in corners. What really amazes me is that the McCandless brothers got it so right with the featherbed Manx. I have often wondered where their knowledge came from. Same with Colin Seeley, who was primarily a sidecar racer.

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Earlier motorcycles were built to the prevailing conditions to the best of their ability. Ignorance is ignorance; don't confuse it with inadequate or inappropriate equipment. Ignorance does not seem to be time dependent. Have you watched videos recently of young road squids in flip flops, shorts, tank top shirts and w/o helmet and gloves doing wheelies and stoppies and all sorts of acrobatics on crowded highways at speed - on the most modern and advanced equipment of the day?

Yoose road and track guys should get out in the woods 'more' to hone skills discovering how fun hot sport - race cycle is in rough low traction paths where direct steering onsets naturally or ends on ground like these 2 do on purpose for kix.

acotrel said:

It confirms what you guys have said - that reducing the yoke offset quickens the steering.

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I don't think your head is straight on this one; you've got it bass ackwards. What guys said this?

Revisit Kenny Cummings post way early on in this topic to get it straight.

Peel advantage with newly installed 3rd, front breast support was discovered/proven 1st in more severe serious dangerous frightful conditions the shop owner essentially begged me not to attempt on heavy wt twin offering MX and AVT to follow them around. Most scary were the 30 ft raven drop offs Peel hung up hi centered unless I sucked nuts up to ovary level to blast thru lip to stay on accelleration to keep some steering effect dodging the bigger lumps stumps gritting teeth not to back off any of would not have enough momentum to power up the steeper 50 ft far side. The slighter milder ravine shoot were not straight shots but almost as twisted as wooded trails. They/me were delightfully amazed hear big twin amount chainsaw sounding Trials and MX cycle even more so after I got hang of it to out race em so easy I left the beaten paths over roots rocks brush and sometimes a stump hi centered on frame rail to pitch onto side. They did not have the power and mass to break through what a Commando can and also discovered I could do it mostly staying seating where they'd be standing on pegs to take the impacts and toss abouts.
ONLY thing Peel could not do was leap up on tractor tires or chest hi log piles d/t hi centering. Hopeful solved by lifting front/rear 2". This of course sucks on smoother pavement so air devices needed to suck back down stiffening suspension for embrassing modern hot shots.

After I left the woods all warmed up reflex conditioned hit Ozark Mt wagon trail hwy hugging Plateau face. 15/10 mph warning signs with frost heaved broken lips - to see if could make the pavement as loose as THE Gravel or leaf clutter on top loose rocky soil to perfect Phase Three and Phase Four handling none of yoose seasoned races have a clue about expect worry to avoid it or bad juju.

You can not go by just equations and logic to set up fork factors as too many unknowns influencing fork reactions so only one way find out for sure, if ya dare.

Discussing this with yoose guys is like the joke of asking what someone is looking for under the street light to start to help til asking where did ya last have them, to be told the back yard but there's not enough light to see. No good answer possible if wrong questions/assumptions at base. Actually I'm well aware I'm only one disscussing this level so carry on as ya were.

I want to create Richochet Rabbit Riding Range and Rifle Ranch RRRR with graduation certificates giving if can climb to top of Gravel cone by starting out at bottom 90'-sideways to peak above. Alas someone beat me too it by teaching road racing pilots off road. Bet they don't have targets to shoot like horse back Indians did to buffalo. Rolled, pulled moving targets and maybe air drones too, on rough ground.
http://www.cornerspin.com/overview.html

Dances with Shrapnel said:

I don't think your head is straight on this one; you've got it bass ackwards. What guys said this?

Revisit Kenny Cummings post way early on in this topic to get it straight.

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On re-reading the Muzzi stuff, they increased the yoke offset to reduce the trail to get the bike to steer quicker. I did the reverse - I decreased the yoke offset which increased the trail, so the bike steered slower. - So you are right and I still had it wrong. My mishandling experience was probably due to not enough trail ? It happened as I braked when cranked over approaching a corner.
What confuses me is that when measuring the trail, the line through the steering head to the ground usually crosses over the vertical through the axle to the ground.
What does pushing the yokes further down the stanchions do ? Does decreasing the rake decrease the trail ? The Muzzi ZXR750 used the 24.5 degree rake, where we use 27 degrees.

I don't believe this is as simple as - 'increasing the yoke offset, reduces the trail and makes the bike steer quicker, so it tightens it's line as you accelerate out of corners'.
The criticality of the yoke offset is probably different with different rakes.

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/

I'm not sure why you are reversing the offset and trail relationship when you write your posts here. Maybe it's just because their values are reversed. As you increase one, the other one decreases and visa versa.

Here's a cool GIF of yoke offset changing and the trail effect it creates. The GIF makes it easy to remember and also visualize other ways to change the trail.




check out how decreasing the offset, increases the trail.... and visa versa

Regarding what you said about braking hard and the bike feeling squirrelly... If your front end compresses, your rake steepens slightly which also momentarily reduces your trail, so if your bike is set up with minimal trail to begin with to have quicker steering then possibly you get some instability from that momentary reduction in trail under braking.

The solution could be any mathematical change that gives you a little more trail. You could shorten your rear suspension slightly to increase the rake angle for a bit more trail or you could reduce the offset with new yokes for more trail... I would bet a frame shop could change your actual rake angle too, but I bet people don't do that when a new set of yokes or shorter shocks can make the same adjustment to the trail number.


I'm not nearly an expert on this sort of thing. I'm just very good at geometry and math... but here's how I see it... There's a range of motorcycle geometry where you have so much trail that your bike is only for riding straight down the hiway looking cool. There's also a geometry where you have very little trail so your bike handles very quickly, but gives up stability to have that quickness. IF you feel you've give up too much stability for quick handling, then you need to increase the trail a bit until you are comfortable again.

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

o0norton0o said:

Regarding what you said about braking hard and the bike feeling squirrelly... If your front end compresses, your rake steepens slightly which also momentarily reduces your trail, so if your bike is set up with minimal trail to begin with to have quicker steering then possibly you get some instability from that momentary reduction in trail under braking.

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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.