Trike fork geometry

[ratwing]

After talking about it for ages I've at last got around to building a trike and happily there's an ongoing 'here's how I did it' in the mag. which is really useful - well done that man. However in episode 3 its saying that around 4" of trail is a good amount to aim for and whilst I'm not doubting it, it sounds like quite a lot. More than my solo bikes in fact. Is this because of the width of the front tyre, could I get away with less (ie lighter steering) because I'm using a narrower one?

[Creature]

ahhhhhhh the art of trail :) :)

the idea is to get a good compromise (dont ask me i always do it by guess and god). my last chop had 6" and was very stable and resoably light at low speeds

but grab yaself a beer n some snacks n have a read :) :)

http://www.american-suspension.com/html/instructions_0.html

[trikerdrew]

Shows leading link front end-YIPEE!

Also talks about angle of dangle! :D

[Blackjack]

There's a different trail calculator at....

http://www.choppers101.com/

This one has the advantage that it works for springers, girders and leading links, as well as teles. It also need a lot less info, so it ought to be more accurate...............

It uses the same principle that most British race frame builders use to work out or measure trail.

:D

[ratwing]

I can work out trail & rake no problem, its just the amount to build in and the difference - or not - that tyre width makes I'm wondering about. I can make up an adjustable swinging arm to find the optimum figure and then make one the right size I suppose but its more work :(

[guydewdney]

It constantly amazes me that with al the incredible expertise and knowledge about in the custom bike / trike world - that nooner has ever made a program or somthing of trike suspension setup systems

such as -

length:-
rear width:-
tyre sizes:-
springers / girders etc:-
quick / med / slow handling wanted?
etc etc

this then spits out a rough guide...

I have a long-way-off project of a 4.5 litre mercedes V8 auto - but i want easy riding, slow steering etc etc -


just seems that someone clever(er) than me could do this so easily........

[Alik Windrush]

Y'know what I really like about trikes is that however much research, testing or experience is applied then people will queue up to prove that I'm wrong.
Well the fact is that of course I'm wrong. I mean I've only spent the last 12 years trying this stuff out, so how could I possibly know what I'm talking about.
And all that stuff I've written in the mag for the last five years.... I make it all up. I wouldn't know one end of a metric chronometre from the other.
It really makes all the effort worth while. Thank you everyone; my aim was to make you believe that you knew more than me and it worked...!
I'd call that 1000% successful....

[Blackjack]

It constantly amazes me that with al the incredible expertise and knowledge about in the custom bike / trike world - that nooner has ever made a program or somthing of trike suspension setup systems

such as -

length:-
rear width:-
tyre sizes:-
springers / girders etc:-
quick / med / slow handling wanted?
etc etc

this then spits out a rough guide...

I have a long-way-off project of a 4.5 litre mercedes V8 auto - but i want easy riding, slow steering etc etc -


just seems that someone clever(er) than me could do this so easily........

Consider this....

Cars. There a few thousand people on the planet that know what makes car suspension tick and can design a set up from scratch.

Bikes. There are a few hundred people who really understand what makes bike suspension tick and can reliably build good handling bikes from scatch.

Sidecars. Now we're talking about a few tens of people who really know what the hell is going on with them

Trikes. Ain't nobody using a scientific approach.

You have to bear in mind that the car guys who are getting results are all using different design models, fall into several camps as to what is and isn't important, and can achieve pretty much the same effect several different ways.

I happen to know a bit about designing suspension set ups and here are some random suppositions for you that may or not be correct.

1/. Trikes are inherently more stable than bikes so the "trail" should be relatively small. Half an inch of trail is not uncommon on three wheeled vehicles.

2/. Longer wheelbases seem to translate into a lower "trail" requirement in almost all vehicles.

3/. Since IRS suspended trikes tend to exhibit roll in cornering and rigid trkes don't, it seems there would be a different requirement for the trail between two otherwise identical trikes.

4/. Front wheel size is going to make a difference, both because of the shape of the tyre contact patch (so tyre type is going to have an effect too) and because of the gyroscopic thingy (moment?).

That's just off the top of my head and is all stuff that would need to be researched before you could begin on making a start.

BUT....just exactly what are we trying to do?

You want a trike that will out corner a GTi? Bill Chaplin (Chapman?) builds 'em, though in essence it appears to owe a lot to GP sidecars.

Or do you just want a narrow trike with HUGE rear tyres and about 50 degrees rake and a 90/90 21 up front? Well that isn't going to outright handle, but perhaps we can make it handle acceptably?

Are we talking Gold Wing or Gixxer here?

"Handling" is actually one area of suspension design. You've got, handling which is essentially the way the thing changes direction when you want it to, and doesn't when you don't want it to. Then there's road holding which can more or less be described as the Gee force it can develop in a corner. And finally ride quality.

Rolls Royce are big on ride quality at the expense of the rest of it. Ferrari are big on everything BUT ride quality, though they do tend to wander about a bit.....

Which actually has just led me to another supposition, the required suspension geometry of a trike will depend on its polar moment of inertia rather more that it will in a four wheel vehicle.

Forget what a polar moment of inertia is for a moment, think about the word "required". Not "ideal" or "correct" but required, as in required to make it meet the purpose for which it was intended. Gold Wing or Gixxer.

And that, more or less, is why you can't just punch some numbers into a formula and get the answers you want.

[dracken1]

alik am i detecting a touch of irony in your post :)
alik if you were a grandmaster and had been from for the last 2 millenium. people would still try to prove you wrong. human nature

and like blackjack has posted there are so many variables.
2 trikes with the same geometry can be totally different to steer and maybe just because one has 27" wide bars and the other 34" wide affairs. the wider bars will give greater leverage meaning less physical effort to turn. 8" of trail and clipon bars may look the business but will cost you a small fortune in steroids :D

[Blackjack]

........ 8" of trail and clipon bars may look the business but will cost you a small fortune in steroids :D


That's the point though....

If you had a REALLY short wheelbase and the engine hanging out the back then 8" of trail MIGHT work OK....

[dracken1]

really short?
you mean like the headstock bolted to the water pump of the rear mounted hemi :)

if i have time when i going to pick up yoda's trike i'll pop in an see you tim, i'll phone first, to suss out your mood on the day :)

oh and everyone on the asme9 course sends thier regards, they have a pin up of you :D :D

[Alik Windrush]

Fortunately I have never been held back through knowing too much. My theory remains that the more you know then the more reasons you have; not to make an attempt

[ratwing]

Alik, I wasn't trying to say you don't know what you're on about - you've built loads of trikes, my first one is still in the 'piles of bits in the garden & garage' stage and its your articles that have inspired me to get off my arse and do something about it (hope this doesn't sound too sycophantic!). Bikes have different rake/trail/tyre sizes so I was wondering if it would be worth asking about different size tyres etc on trikes :confused:

[Blackjack]

Think about it for a minute.

Moto GP bikes, they're set up differently for different courses and different riders have different settings for THE SAME race track on otherwise identical (ish) bikes.

Conclusion?

There is no RIGHT answer.

Imagine a typical statistical bellcurve graph type thing. Put very crudely, any answer under the line will work, any answer over the line won't. This is true whether its a trike, car, or articulated lorry you're dealing with.

Only in reality its not a two dimensional graph, but a six or seven dimensional graph you're dealing with.

And THEN you have rider preference to take into consideration!!!!!!