Steering geometry - confirmation bias

Just to make things more confusing, take a look at the variations in rake and trail in this table from Bradley's book



As you can see, trail on the street bikes and road racers varies from 76 mm to 108 mm, and bikes with both those values have been raced quite successfully. Best example I can think of is Aprilia RS250 with 102 mm trail vs. Rossi's Aprilia RSV250 with 76 mm trail. Both worked just fine. The takeaway from this is that good handling is a package deal, and the correct rake and trail depend on all sorts of other details, like wheel and tire sizes, center of balance, front/rear weight distribution, wheelbase, swinging arm pivot location, anti-dive and anti-squat devices, etc., etc., and last but certainly not least, rider style and preference.

Like Holmeslice, methinks we've had this particular discussion more than enough times for the basics to sink in, but I can't seem to resist preaching the faith to the heathens one more time.

Ken

Brooking 850 said:

Alan, sounds like you may need to put a really competent rider/racer on it to give you good feed back.
Other wise you may end up spinning your wheels but getting or going nowhere so to speak!
Regards Mike

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Good idea, but potentially quite embarrassing. After I quit racing, I started putting other riders on my bikes and wrenching for them, just to continue participating in a sport I loved. Unfortunately, some of them were very good, and the comparison of their lap times and trophy counts compared to mine was not pretty. I think I only ever had one first place in over 20 years of racing, but with someone else riding the same bikes, we collected lots of first place trophies, and several class championships. Very satisfying, but also kind of humbling. And I'm talking about bikes, including several Nortons, that I had absolutely no handling or performance complaints about. I just wasn't able to go as quickly as my friends were. Fortunately, I also occasionally loaned a race bike to a friend to race, who turned out to be slower than I was, so I didn't have to feel totally inadequate.

Ken

There was only one occasion when I intentionally geared my 500cc Triton too low, softened the suspension and dropped the tyre pressures. I led a race from the start for almost a full lap. The competition were on Z900 and H2 Kawasakis etc. I outrode them easily then got passed at the end of a straight because the bike ran out of steam. I had to pull the bike up to avoid hitting one of the guys who got past me and so I ran off. Then it was all too late. The question in my mind about those other guys who rode your bike is -was the setup identical with when you were riding them ? I have little trouble outriding the young guys these days, most of them are very tyre-dependent, especially in historic racing. If you put pressure on them, they often give up and if you pass them too quickly, they are likely to fall off. The only race I ever won back when I raced regularly, was on a friend's near-standard Suzuki Cobra. It had no brakes, so every corner was a big glide. I almost knocked another guy off his bike as I got under him - out of control.
The handling problem with my Seeley was not tyres - it was too much yoke offset. I don't know about that Minnovation Seeley - I don't think the owner would have changed it much after he bought it new. I think the fact is that anyone making bikes like that for customers, would make sure the handling was predictable and a bit slow.

A good bike makes a good rider. Riding a bad bike does not teach you much other than how to crash safely. I've ridden both 650cc and 500cc Tritons, a good 500cc Manx with thrash any Triton, simply because you can ride it faster and all race circuits have corners.

.......I think the fact is that anyone making bikes like that for customers, would make sure the handling was predictable and a bit slow......

You have said that before Alan, regarding Rickmans, but I think you totally miss the point that Colin Seeley and the Rickman Brothers built bikes to win races and the original versions were fielded with the best riders of the day on them, they didn't then 'soften the package' for Joe public they built what they knew worked....for winning races....

Makers of mass production road bikes on the other hand may well have wanted to make the whole package more 'user friendly' as evidenced by the standard Commando geometry.

acotrel said:

I don't know about that Minnovation Seeley

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I don’t think you have uttered a more concise and accurate statement.

Hopefully this thread has straightened you out (for the umpteenth time) about the relationship between trail, rake and off set. As mentioned earlier, read up on Tony Foale’s work for further enlightenment.

It seems like you have “an idea” of why your Seeley behaves the way it did and it does. Perhaps you need some more regular track time as I get the impression your track times are far and few between. Furthermore, based on reading about all your legendary get offs, perhaps your frame is now a little off and could use some straightening and realignment - just a thought.

My first hand experience is limited to the Seeley Mk2 and can say it’s an excellent platform for competition. The usual challenges include proper set up (ex. tires, air pressure, dampening, spring rate, weight distribution) which do not get sorted out with the snap of the fingers but usually take a few to several days at the track with very good note taking and a very knowledgeable and experienced person leading the effort (Kenny Cummings of NYCNorton)

Holmeslice said:

GOOD GOD, MAN!

I'm starting to think you are a troll.

As has been told to you before in so many different ways in so many different times on this forum, and at the risk of oversimplifying to make a point:

MORE YOKE OFFSET = LESS TRAIL = QUICKER STEERING!!!

I.E. more offset is NOT more stable!!!

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Dances - is this correct or is it wrong ? - And I have never crashed the Seeley, nor has anyone else ever crashed it. With the minimum yoke offset, it tightens it's line, - with the bigger yoke offset it become dangerous when braking. And I am not imagining it ! I cannot relate this difference in handling to the trail , because I did not measure it when I had the bigger offset yokes fitted.

Holmeslice said:

GOOD GOD, MAN!

I'm starting to think you are a troll.

As has been told to you before in so many different ways in so many different times on this forum, and at the risk of oversimplifying to make a point:

MORE YOKE OFFSET = LESS TRAIL = QUICKER STEERING!!!

I.E. more offset is NOT more stable!!!

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acotrel said:

Dances - is this correct or is it wrong ? - And I have never crashed the Seeley, nor has anyone else ever crashed it. With the minimum yoke offset, it tightens it's line, - with the bigger yoke offset it become dangerous when braking. And I am not imagining it ! I cannot relate this difference in handling to the trail , because I did not measure it when I had the bigger offset yokes fitted.

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"GOOD GOD, MAN!"


"I'm starting to think you are a troll."


"As has been told to you before in so many different ways in so many different times on this forum, and at the risk of oversimplifying to make a point:"


"MORE YOKE OFFSET = LESS TRAIL = QUICKER STEERING!!!"


"I.E. more offset is NOT more stable!!!"


Your experiences, in part, as stated above seems to support the facts stated by others so many times before though I don't fully understand what you mean by " with the bigger yoke offset it become dangerous when braking". When does this dangerous when braking occur: during straight line, during initiation and/or trail breaking a turn?

So your frame should not be twisted or distorted but have you checked wheel alignment, rake angle and other stuffto see if it is correctly fabricated?

As for your statement about "I cannot relate this difference in handling to the trail , because I did not measure it when I had the bigger offset yokes fitted"; now you have the information to relate the difference based on what everybody and their uncle has been telling you. See my note above about more track time and taking notes 0 very improtant.

You should be able to back calculate what the trail "was" if you know or recall the offset and hopefully you know what the trail "is" now. Please report back on this (what you find) as I for one am curious.

What you really need to do Alan is begin reading some texts on this subject; it is quite fundamental to motorcycle behavior. As stated before, Tony Foale has published some excellent work on the subject. Start with the fundamentals and work forward from there.

The severe mishandling happened when I used the 66mm offset fork yokes. My friend experienced it first and I encountered it a year later. It happened on one particular part of Winton circuit . I flew around the big left-hand sweeper with my arse hanging out, because I used to ride my Triton like that. After the sweeper it turns a bit to the right while you are braking fairly hard to the left. The bike suddenly stood up and turned right - the opposite way to what I expected. It threw me off-balance and I knew I was gone. So I looked for somewhere soft to crash, then got back on the gas to get there. The bike came back under control. I then recognised that the yoke offset was the problem because I knew of a few other instances where this sort of thing had happened. I found out that all Seeley frames have 27 degree rake and I had a set of TZ350 yokes which had the right centres and were intended for a frame of about the same length with 26 degree rake, also with 18 inch wheels. When I fitted the TZ350 yokes, the steering dramatically improved. Now under brakes, the bike doesn't even tend to rise. The steering is very quick with no need to counter-steer, and if you gas the bike hard halfway around a corner, it tightens it's line a lot - which is very good. However it leaves me with a problem. If I increase the pre-load on the rear shocks, I don't know how the bike will steer and I could still find myself in the situation where it mishandles. With steering geometry, it is obviously a matter of rake, trail, wheel size, length of bike, centre of gravity and suspension preload. I have all but the last factor already set. But if I need to raise or lower the yokes on the staunchions to get the handling right again after adjusting the preload on the rear shocks, I would not know which way to move them. Trial and error with this, is not good.

I have read Tony Foale's book. There are too many variables and too few generalisations. I have also read a paper on bike handling from the Society of Automotive Engineers which effectively said 'we don't know what we are talking about'. The simple fact is that the guys who race modern bikes know what happens when you raise or lower the fork yokes on the staunchions. And I do not.
In historic racing, most of the guys ride modified street bikes and are probably blissfully unaware of how their bike handles. They simply ride around their difficulties and go a bit slower.

I would go with the Tony Foale guidance. Your original question on steering geometry is fundamental and I disagree and say there are not that many variables that one should easily be a grasp of what is happening and why. Not sure what SAE paper you are reading or from what epoch but I would be highly skeptical of it based on what you just told us. There is plenty of other current and concise literature on motorcycle geometry and handling that you really should not be wondering in the bushes with a SAE paper on the topic. Would you consult with the Journal of Proctology if you were interested in resolving a matter pertaining to the Cranial Cavity?

You describe what is happening but seem uncertain as to why. I suggest being more methodical and calculate your previous trail and compare that to what you have now and report back to us on what you find.

I am not the only person who has this sort of problem. In a Motorcycle Classics magazine, there was an article about a guy who races a bevel Ducati. He changed the rake to get it to steer quicker, but moved the steering head in the wrong direction and made the handling worse. The worry is that mishandling from this source can come from nowhere without warning. After the Seeley stood up and turned the wrong way, I rode it in another race. I could feel it start to stand up when braking into both right and left hand bends. Perhaps the need to counter-steer when approaching corners is an indication ?

acotrel said:

........ I could feel it start to stand up when braking into both right and left hand bends. Perhaps the need to counter-steer when approaching corners is an indication ?

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I really feel lost with this comment Al.....

If you brake when cranked over, any bike will tend to stand up...most of us initiate braking in a straight line, some stop braking before turning, others turn in whilst still braking, which takes more force.....yes counter steering force.....since there is actually no other way to turn a bike!

This has me right back at learning how to ride a motorcycle! Something you indicate you have been doing for some years!

Hi Alan, I am not offering to pay your way to get results with your bike, and yes I have raced against some of the Aussie races with similar bikes here in NZ. Check the likes of Barry Sheene Oceanic and Mike Pero Trans Tasman and Shorai Trans Tasman Challenges.
We get a very good turn out of Aus racers and early in those same years are the reciprocal events in Aus.
Your rules are different regarding carburation and ignition types, ours being more traditional, but my bike holds its own against them. Mine is a very standard Commando set up as far as forks, frame, wheels , clutch ,carbs and manifolds,cradle and engine profile.
Gearbox is after market as are the engine internals.
I let a very young guy ride my bike in a track parade last year and he is a regular on a Commando framed bike same as mine, he was 5 secs a lap quicker, and that wasnt even a race. he mentioned that it was more powerful than his regular ride, he is 19 and has won 125GP champs in NZ and races moderns as well.Wins alot on all his rides.
I did it to get his honest view on my set up. He said the only thing he would change was more front brake, as mine at the time was running a kitted MC and standard caliper. I have since upgraded the MC and still running the same caliper.
The idea from me to you was to enter it with another rider to get the best feedback from someone who races regulary so that you had an unbiased idea of how good (or not ) your bike is.
I still race mine often, the last round in early Dec just gone I had my first off in 4 1/2 years racing this bike.
There was no mention of a 120 on the front in what I have read on a Commando frame, perhaps on a Seely but I have no experience with that width of tyre on the front.
Regards Mike

Alan, Brooking 850 is giving you some solid and reasonable advice here.

I would see to it that you get your geometry as close to as what Minnovation recommends for their bikes. My Seeleys do not stand up nor go wide and I occasionally brake extremely hard and trail break. My bike goes where I want it to go.

At this point I don't know if you are lamenting on how foul a set up you once had or if you are having difficulties now. As I said, figure your rake and trail now and attempt to back calculate the trail you had with the previous yokes. There's a story in there somewhere.

acotrel is not a troll. Last year we had lots of private contact to teased out all the details and combinations of acotrel sincere claims to align or not with my own. The kind of turn loads he enjoyed occured by a sort of power steering hook up assistance against competition. This aligned with linked-flexy Ms Peel behavior, so asked if he'd done anything to reduce rigidity, to be told yes a lighter tube or brace replacement in forward area of frame. I suspect frame distortion luck out to compensate for yoke and trail affects. Who knows maybe acotrel is on to something and never weavers in his reports despite the whippings here. His words convey more wanting similar benefit for others than his own praise. Shit he did almost as many limit experiments crashing as Burt Munro so some gotta hurt forever.

Alan, Are you running a Seeley Mk3 or Mk2 frame?

Dances with Shrapnel said:

Alan, Brooking 850 is giving you some solid and reasonable advice here.

I would see to it that you get your geometry as close to as what Minnovation recommends for their bikes. My Seeleys do not stand up nor go wide and I occasionally brake extremely hard and trail break. My bike goes where I want it to go.

At this point I don't know if you are lamenting on how foul a set up you once had or if you are having difficulties now. As I said, figure your rake and trail now and attempt to back calculate the trail you had with the previous yokes. There's a story in there somewhere.

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You are correct that most bikes will tend to rise under braking conditions and tend to run wide in corners when it happens. But standing up and turning the wrong way, throwing you off-balance is something else. I've felt bikes go stiff when braking, but never definitely rise and turn, before this. I was riding slightly left as I braked hard, and the bike suddenly stood up and turned right. And I was not the only person who got caught with it's antics. My friend is an excellent rider and it still grabbed him. When he told me about it happening, I did not believe him, so it grabbed me too. It was definitely a yoke offset problem, because I have cured it and now the handling is excellent. The only problem I have is in deciding which way to adjust it when I have to put more preload on the rear shocks. What Minnovation do with their bikes is only relevant in that they provide a benchmark which is probably slightly too stable. The one I was talking about is not so fast around Winton. Mine is apparently much quicker steering. But with that quicker steering there comes a risk - it might tie itself up in knots. Everything happens extremely fast.
I think I'm going to have to go back to suck it and see. Try moving the yokes up and down the stanchions a bit and see if that restores the quickness after I have increased the preload on the rear shocks.

Usually when you are in the middle of a high speed bend and start to lose the plot - if you brake you run wide. So you try to turn away from the edge of the bitumen while carefully braking - makes the situation slightly worse until you stop. If the bike tightens it's line when you gas it if it is cranked over, you often come out of the corner much better, by accelerating instead of braking. I've never heard of a Commando hi-siding anyone except when a chain has broken.

Dances with Shrapnel said:

Alan, Brooking 850 is giving you some solid and reasonable advice here.

I would see to it that you get your geometry as close to as what Minnovation recommends for their bikes. My Seeleys do not stand up nor go wide and I occasionally brake extremely hard and trail break. My bike goes where I want it to go.

At this point I don't know if you are lamenting on how foul a set up you once had or if you are having difficulties now. As I said, figure your rake and trail now and attempt to back calculate the trail you had with the previous yokes. There's a story in there somewhere.

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To find out what trail I was using with the Ducati yokes, I would have to reassemble the old front end arrangement. I am beyond that. The Seeley is now extremely direct and quick steering and tightens it's line a lot when gassed if cranked over. It is really great to ride, but I always have to anticipate a lot about where the bike will end up as it comes out of corners. I'm putting more preload on the rear shocks and expect the steering will become slower with a bit more tendency to run wide in corners. I know the variable is the trail, but I don't know in which direction I should change it to restore the quickness. I don't want to do anything silly and get bitten.