What is the effect of LESS TRAIL (Racers encouraged to answer)

I am still fairly certain that what I have said is correct. My Seeley 850 has the same wheel base as a TZ350 Yamaha and the same fork yokes. The yoke offset is 53mm, rake 27 degrees and wheel size 18 inch. My motor is as far forward as possible. Use a steering damper, and I wish you well.
I found this video which is relevant , he mentions the trail but does not tell the effect of changing it:

Carl H said:

This is what I'm talking about The 1968 Commandos ridden by George Kerker and Art Ninci. Just leaving the 1 foot square license plate air dam was worth negative 5 MPH down the straights. The tires were scary and the riders were brave. If the Nortons could win like they did in stock trim, there was a heck of a lot more you could get from one, just with simple mods.

Back when I rode in the late 1980s, the grids were filled with big bikes and pro level riders in the field with some well developed "factory like" equipment. I did OK winning #1 plates several times in a row. Then when I finally got real racers needing rides, the fun really began, and they made CHR Commandos a frequent visitor to Victory Circle. Our club USCRA was like a wrecking crew when it came for AHRMA and Can Am races, lots of fast bikes from elsewhere went home with few points due to the USCRA's stranglehold. Commandos actually became respected again as the great bike they are. And old racers got to do what they do best, ride like the wind.

No matter who the racer is , he needs a decent bike to win and one that can finish.

Archives: The Pipe Man

George Kerker was an innovator and an unforgettable personality

www.cyclenews.com

Norton Commando | Cycle World | SEPTEMBER 1968

magazine.cycleworld.com

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I have read the article about Kerker. Ever the siren under the seat to warn other riders of what is happening, might not be enough. If you pass another rider too fast, they sometimes fall off their bike. And if they know you are coming and they have ego, they sometimes over react, and make mistakes. It makes me apprehensive. When a Commando-based bike can accelerate past in that way, it is very different from other bikes, and unexpected.

But one of the main points of the story is when they started racing the 1968 Commando it was the first time they raced and still mopped up the field and did it on a stock production bike VS. some highly developed "GP" type bikes with experienced riders. I Believe the 1968 Commando has the steepest folk angle especially with the low 3.25 Avon Speedmaster ribbed tire The thing about real racers is they don't complain, they adapt to all the ills of the machine they are on and push them to the limit. Art Ninci told me he didn't know about the weak frame breakages or any frame flex issues.

It's pretty simple actually. The longer the trail, the longer the lever length distance between the axis of the steering and point where the force is applied to the wheel. It's distance that dictates the amount of force, so more distance between steering axis and where the wheel touches the road, (trail) the more force is driving the wheel back to the point where the left side and right right side forces balance. (the shopping cart effect) That's why more trail equals more stability. The force driving the wheel to centralize is greater with the increase in distance.

Less trail equals less stability, (but also less effort to make the bike turn in) because the force needed to drive the wheel off it's balance point (centered) is less because there is less (lever length) distance between the steering axis and the point where the force is applied to the wheel. Simple...

o0norton0o said:

It's pretty simple actually. The longer the trail, the longer the lever length distance between the axis of the steering and point where the force is applied to the wheel. It's distance that dictates the amount of force, so more distance between steering axis and where the wheel touches the road, (trail) the more force is driving the wheel back to the point where the left side and right right side forces balance. (the shopping cart effect) That's why more trail equals more stability. The force driving the wheel to centralize is greater with the increase in distance.

Less trail equals less stability, (but also less effort to make the bike turn in) because the force needed to drive the wheel off it's balance point (centered) is less because there is less (lever length) distance between the steering axis and the point where the force is applied to the wheel. Simple...

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The resultant force in a system is found by addition of vectors. There are two main forces involved in steering a motorcycle - its mass and the gyroscopic effect of the front wheel. The resultant required to steer the bike is found by addition of vectors, and the biggest one acts through the front axle. If you ride you bike without a steering damper and get into a lock-to-lock tank slapper let go of the handle-bars and grab the tank and wait. Do not grab the handle bars again, place your open hands on them to slow them. If you grab the bars, the force which launches you is immense.
The theory behind what happens is beyond most physics experts. I have studied third year uni physics. I know what works with my Seeley 850. My previous race bikes were different. The problem is, the rider adjusts to the bike - who is in control ? A road bike is not a race bike. Most road bikes can be ridden fast safely. But a really good race bike is something else. It is a common mistake beginners make, they believe other riders are better, however I suggest the main reason other guys are faster is usually the way their bikes handle - not horsepower. Mike Hailwood began his racing career on the Mondial 250 world championship winning bike. The bike trains you. Learning on the Mondial would teach the rider right from wrong - other guys have already done the crashing.

Some people have some strange problems :

Getting better ?

What is the best fork yoke offset for a road racing Commando which has 19 inch wheels ?

In watching the last video - he is still getting on the gas too late. It is very deceptive, unless you usually race continually trying to move the transition point earlier in corners. 'Feel' is about confidence. If he just knocks-off speed until he enters the corner, he might be able to start accelerating immediately. It is not something we would normally do.

Simon Crafar gives a better explanation of this stuff than I can, however he does not explain the effects very well. As he says, thinking about this can 'fry your brain'. When you are doing this stuff, the observations are both objective and subjective - you assess feedback from the motorcycle and adapt to it. - The video is Simon Crafar MotoGP setup.

Happened to meet an old friend today. Supposedly knows a lot about steering geometry. MotoGP teams thinks so as they follows his advice. Trail being adjusted to suit track and rider during practice.
He laughed about the idea that less trail makes a bike more stable.

From 1:20 stated, "decrease the trail make the motorcycle steering quicker. It will also make the motorcycle less stable....."

o0norton0o said:

From 1:20 stated, "decrease the trail make the motorcycle steering quicker. It will also make the motorcycle less stable....."

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Might be in the way 'stable' is defined. More trail makes it easier to tip into corners and tighten the line as we accelerate out. Less trail creates the need to counter-steer to tip into corners as we brake, and a tendency to run wide as we accelerate out. The first condition is oversteer (desirable), the second condition is understeer - safer for beginners. If you ride a genuine Manx Norton and gas it at the transition point, when it squats slightly it will oversteer and feel great. It is almost impossible to get a Manx to lean much. To me both oversteer and understeer conditions feel equally stable. The problem is that when you have really good handling, you need to use it to recognise it - that involves sticking your neck out.
When I found this happened, it was only because I always try to accelerate earlier when coming out of corners.
I noticed I could accelerate much earlier after I reduced the yoke offset by 12mm.

acotrel said:

Might be in the way 'stable' is defined. More trail makes it easier to tip into corners and tighten the line as we accelerate out. Less trail creates the need to counter-steer to tip into corners as we brake, and a tendency to run wide as we accelerate out. The first condition is oversteer (desirable), the second condition is understeer - safer for beginners. If you ride a genuine Manx Norton and gas it at the transition point, when it squats slightly it will oversteer and feel great. It is almost impossible to get a Manx to lean much. To me both oversteer and understeer conditions feel equally stable. The problem is that when you have really good handling, you need to use it to recognise it - that involves sticking your neck out.
When I found this happened, it was only because I always try to accelerate earlier when coming out of corners.
I noticed I could accelerate much earlier after I reduced the yoke offset by 12mm.

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If I were you, I'd quit the replies while I'm ahead only significantly behind.