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

acadian said:

Good explanation here:

What do Rake and Trail mean on a Motorcycle?

BeMoto Motorcycle Insurance asks: What on earth is motorcycle rake and trail - What does boring high-school Geometry have to do with cool motorbikes?

www.bemoto.uk

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Here is a blatant example of how citing a bad source can lead to false conclusions. For instance, the author claims:

"Finally, Fork Offset is the distance between the centre line of the steering head/stem and the centreline of the fork legs, with the steering pointed straight ahead. This is determined by the yokes, and the offset plays a big part in determining the trail – more offset will mean more trail, less offset reduces trail."

That statementy is obviously wrong. When you increase the offset (making it larger), the trail becomes smaller. This means the front wheel is closer to the steering axis. Smaller trail can make the bike feel more responsive and agile, but it may sacrifice stability.

I suggest you replace the link by a thrustworthy source!

- Knut

mdt-son said:

Here is a blatant example of how citing a bad source can lead to false conclusions. For instance, the author claims:

"Finally, Fork Offset is the distance between the centre line of the steering head/stem and the centreline of the fork legs, with the steering pointed straight ahead. This is determined by the yokes, and the offset plays a big part in determining the trail – more offset will mean more trail, less offset reduces trail."

That statementy is obviously wrong. When you increase the offset (making it larger), the trail becomes smaller. This means the front wheel is closer to the steering axis. Smaller trail can make the bike feel more responsive and agile, but it may sacrifice stability.

I suggest you replace the link by a thrustworthy source!

- Knut

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Yep that is 100% wrong

lcrken said:

Give it up, my friend. I've had the same back and forth with Alan a few years back, and he just doesn't understand the relationship between trail and handling. He means well, he's just wrong.

Ken

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He's the same guy that claims there is no relationship between compression ratio and power output.

Beware those evil 2-strokes....

Dan1950 said:

He's the same guy that claims there is no relationship between compression ratio and power output.

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By increasing compresssion ratio when your carburation is too rich, you are simply correcting an error. Mixture, ignition advance and compression ratio form a balance for maximum power. If you get your fuel/air ratio and ignition advance correct forthe compression ratio you use, you have almost as much power as you are going to get.

When you reduce the yoke offset, increase the wheel size or increase the rake - you get more trail. Featherbed 1950s Manx Nortons do not use the same fork yokes as swing-arm 500cc Dominators. Dominator yokes have miles too much offset.
In about 1958, I was 18. There were two brothers, their name was Bray - they used to race a Manx which had a pushrod Matchless motor. It was competitive against the best Manx Nortons. They made it PULL and used better gearing.
With a Commando motor, you are never going to win a power game. So play to your strengths. What I have been telling you about handling is NOT bullshit. When you can blast full throttle past the three leaders in a corner when they are at full lean on 1100cc superbikes, that is a convincing argument.
I know what I did and it worries me. If the last guy I passed had lost it, I would have been in big trouble - sometimes as they get going they swerve.
When you race, there is a transition point in corners where you stop braking and start accelerating while you are at full lean. Reducing yoke offset can move that point to occur earlier, it also reduces lean angle, so you can use more power.

These days,if I race it is in historic races. When I raced years ago,it was in Allpowers C Grade. These days none of the guys ride 750cc widowmaker Kawasakis, Where I passed those three guys, one of my mates threw himself and his bike up the road in a really big crash, as they got on the gas, coming out of the corner. Since then, I have not raced. Before I did that stupidity, I knew what was about to happen and I felt uneasy, and I still have that feeling. The speed differential is too high.

mdt-son said:

Here is a blatant example of how citing a bad source can lead to false conclusions. For instance, the author claims:

"Finally, Fork Offset is the distance between the centre line of the steering head/stem and the centreline of the fork legs, with the steering pointed straight ahead. This is determined by the yokes, and the offset plays a big part in determining the trail – more offset will mean more trail, less offset reduces trail."

That statementy is obviously wrong. When you increase the offset (making it larger), the trail becomes smaller. This means the front wheel is closer to the steering axis. Smaller trail can make the bike feel more responsive and agile, but it may sacrifice stability.

I suggest you replace the link by a thrustworthy source!

- Knut

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The excerpt you've posted may be factually incorrect, but the the author's analysis of the relationship between trail and stability is not.

You've simply cherry picked an error to erroneously discredit the substance of the article, that's a bad faith critique

I will not replace the link

concours said:

Beware those evil 2-strokes....View attachment 115173View attachment 115174

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Wow, Green Meanie…haven’t seen one of those for ages

acotrel said:

These days,if I race it is in historic races. When I raced years ago,it was in Allpowers C Grade. These days none of the guys ride 750cc widowmaker Kawasakis, Where I passed those three guys, one of my mates threw himself and his bike up the road in a really big crash, as they got on the gas, coming out of the corner. Since then, I have not raced. Before I did that stupidity, I knew what was about to happen and I felt uneasy, and I still have that feeling. The speed differential is too high.

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So Al was it you that caused him to crash and put you off racing again as the way you put it, since then I have not raced, a bit of guilt in your own words maybe.
Maybe it was good that you never rode on the road after you turned 29 years old.
As you get older you leave yourself too more mistakes so maybe it was time you gave up racing, I see a lot of old bikers on them mobility scooters with front forks and high handle bars getting around on, old habits are hard to get rid of lol.
We all get old and comes a time when the day will come we get to know it's time to get off the bikes.

After 44+ years of my Commando/Featherbed set up I got it perfectly set up for my riding style, I am the rider with my hand controlling the throttle, the bike does the rest, it sort of blows me out sometimes as it feels so natural in the tight twisties and with the work done to my motor both motor and frame, works so well together and the Lansdown internals and Koni rear shocks it handle very nicely as well the Avon RR tyres grips the road pretty good, it's a fun bike to ride.

Ashley

Perhaps an illustration in the extreme at very low speeds will make the point:

In anticipation of a loaded-touring bicycle trip I had a bicycle built. The builder had built hundreds of light, sport cycles but they weren't all that experienced at touring bikes. After the fitting to my body I got the dimension sheet and made some modifications: Longer chain stays (equivalent to a swing arm) for a longer wheel base for more room for panniers; larger diameter tubing for less flex under loaded cornering; and most significant, I had them reduce the fork offset to increase the trail for high speed stability on twisty descents in the Italian hill country and mountain passes where I didn't want car drivers attempting to pass me in the tight corners, thinking "oh a slow bicycle, I'll go around him despite oncoming traffic" (it happens). It turned out to be a fast bicycle on the descents and as stable as my motorcycles at 50 mph.

Now for the downside: climbing up to the hill towns or Versitch Pass in the Alps, it was a solid hour and more in bottom granny gear at 3 to 3-1/2 mph. Versitch Pass in 14 kilometers of a 14% grade. With the extra trail it was a chore and more just keeping the bike upright much less on a straight line. I had previously toured on my sport bike (much less trail) and it was much easier to handle on the upgrades.

When I returned I fitted smaller tires which quickened up the handling significantly. Then I had the shop modify the front fork to increase the offset and quicken the steering with big touring tires. They did this by adding a nice arc into the fork tubes which had the added benefit of adding some spring to the fork for a softer ride. It's now a much easier climbing bike at slow speeds. The trail dimension is now what the original spec sheet listed. They may have actually known more than I from the get go.

Bigger wheels = more trail
Increased rake = more trail
Reduced Offset = more trail.
When you brake the rake reduces = less trail - stable under brakes
When you accelerate the rake increases = more trail - unstable going into corners.
So brake into corners then accelerate.
A neutral handling bike can need countersteering to tip into corners. A bike with a lot of trail can be flicked into corners

Al, I think you are using the word 'stable' differently to how many of us use and understand it. It seems to me, you are referring to the bike's reluctance to turn when you say less stable. I.e. it doesn't do what you're trying to get it to do. As I understand it, more trail, like on a chopper, = reluctance to turn. But that is because it is so 'stable', i.e. = more stable in a straight line, it wants to just keep sitting upright, ploughing on in a straight line.

Phil Irwing once said that tank slappers on Vincents with Giradraulic forks can be cancelled by simply get your hands off the handlebars. A very brave rider tried and said it worked.
The Giradraulics have anti-dive properties.
Steve McQueen had a Vincent a short time. Complained of poor handling. Bikes next owner turned the fork eccentrics from sidecar to solo position. Increasing trail.
Norton made sidecar yokes for featherbeds with less trail.
A bit off topic. Race department did s lot of experiments on moving engine forward/backwards to find best weight distribution for the Manx.
Long time ago tried the first road legal Sportster chopper in Sweden. Much trail made it hard to turn in and out of bends.
When braking hard, compressing front fork, increasing rake and shortening trail the bike turns in quicker. Less stable.
Modern sports bikes need hydraulic steering dampers. Guess it's because of slightly shorter trail.

We're getting a bit off topic with the chopper reference because it depends if we are talking teles /girders or springers
If springers the trail can be corrected with extended bottom rockers
With teles you can use raked yokes to correct it
I'm not sure with girders

nobody has mentioned wheel diameter as a determinant of trail, important consideration for me at the moment as I ponder whether or not to go with 18" wheels on my race bike

acadian said:

nobody has mentioned wheel diameter as a determinant of trail, important consideration for me at the moment as I ponder whether or not to go with 18" wheels on my race bike

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As it is the radius that affects trail, the 1/2" difference between 18" and 19" don't mean much. For me it's more a question of race tyres available.
Had to change wheels on a Suzuki which had 16 and 18 to TZ 17" wheels because slicks only made in 17".

All of my Nortons, wideline racer, slimline model 50 and ‘68 commando, were very stable at any speed and I never gave any thought to what the rake and trail were. One characteristic they shared was that whatever course they were on, they wanted to stay on it. Rider actions such as shifting body weight and putting weight on one footrest they just laughed at - at any speed. A friend tried my combat engined wideline racer in the paddock at Brands Hatch, got to the end, tried to turn as if he were on his gs750 Suzuki and the bike carried straight on up the bank! He didn’t mention that on his return but did say that the Norton had more power than his Suzuki.
Using counter steering to force a change in direction does not indicate understeer. Most owners of Commandos and featherbed Nortons probably use counter steering without realising it as it is such a natural thing to do.
I don’t think that anyone riding a standard road bike needs to worry about rake or trail. Leave it as it is and buy the best tyres you can afford.

Mart UK said:

Al, I think you are using the word 'stable' differently to how many of us use and understand it. It seems to me, you are referring to the bike's reluctance to turn when you say less stable. I.e. it doesn't do what you're trying to get it to do. As I understand it, more trail, like on a chopper, = reluctance to turn. But that is because it is so 'stable', i.e. = more stable in a straight line, it wants to just keep sitting upright, ploughing on in a straight line.

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You are correct. More stable means reluctance to turn - understeer. With more trail, the bike is easier to flick into corners, and it has less lean, so you can accelerate harder and earlier. When you brake on a road bike, the handling is usually on the stable sideof neutral,and it will usuallyundersteer in corners and tend to run wide, until you gas it. With more trail the spectrum shifts and the bike witll usually turn tighter.
I never intentionally try to lean a bike, unless I go into a corner miles too hot and start to run wide - then I keep the bike as vertical as possible. It is a normal occurrence. In this video, the commentator never mentions trail. When you race, it sometimes helps to notice what the other guy is riding. I usuallyknow what they can and cannot do. Your bike only has to be fast enough to be near them.

This thread started with a poll. Watching present result one person has different opinion than the rest. Guess who.

Mike40M said:

This thread started with a poll. Watching present result one person has different opinion than the rest. Guess who.

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This person was a scientist in his working life, not all scientist gets it right, facts and figures don't seem to match the real world facts, his facts seem to be never wrong no matter if he has been proven wrong in a lot of things, maybe he watches too much YouTube as everything on You Tube is right.
All I know my own bike handles pretty good whether it's leaned way over or upright, more tail, less tail it's just right for my riding style, as long as my tyres don't let go when its cranked right over as that be the only thing to make me come unstuck.
But then I am just a dumb old biker who enjoys his time in the saddle more than anything else, facts and figures, who needs them.