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Equal or different Wishbones?
TallGuySmallBike - 9/2/14 at 12:29 AM

I'm doing a Reverse Trike build, Front Engined FWD.

what wishbone setup would be best for this type of build? I would like to keep as much rubber on the deck at all times

Thanks All.

jossey - 9/2/14 at 09:08 AM

What has the wishbone geometry calculator suggested....

minitici - 9/2/14 at 09:30 AM

How long is a piece of string?

Many variables to take into consideration.

Sam_68 - 9/2/14 at 09:41 AM

quote:
Originally posted by TallGuySmallBike
I would like to keep as much rubber on the deck at all times


If that's your only criteria, then you'll be wanting properly designed unequal, non-parallel wishbones.

I say 'properly designed', because there's no inherent magic about them being unequal and non-parallel - the geometry can be worse than equal length, parallel wishbones if you get it wrong.

And...

If you really don't know what you're doing, equal length and parallel can be safer in many respects: it gives you a fixed roll centre at ground level and no camber change at all in bump. The downside is that it gives you no camber recovery at all in roll (so your camber in roll will equal the angle that the chassis is rolling at).

By contrast, the advantages of an unequal, non-parallel set-up are that it allows you to pick your own compromise between camber change in bump and camber recovery in roll, and you get to pick your own roll centre height... but you've got to understand what you want from that compromise, and why, before it becomes an advantage.

It's also worth pointing out that with a trike, the angle of your rear wheel will always equal the roll angle, anyway, so there's an argument to suggest that you don't want front geometry that gets progressively better than the rear, the more the cornering force builds up, otherwise sooner or later the rear might break loose and overtake the front... and in any case you'll want to restrict roll angles as much as possible to give the rear tyre the best chance of hanging on (and if you don't have much roll, there's no big disadvantage to using equal length and parallel wishbones).


Suspension design is complicated. There are seldom any straight answers.


quote:
Originally posted by jossey
What has the wishbone geometry calculator suggested....


I can tell you that without looking: it will have suggested that equal length, parallel wishbones are just fine in bump, but terrible in roll, and that unequal, non-parallel wishbones can give you whatever compromise you want between bump and roll performance, but that you've got to know what you want that compromise to be.

Wishbone geometry calculators are a tool, not an oracle.

[Edited on 9/2/14 by Sam_68]

britishtrident - 9/2/14 at 10:05 AM

With a trike car type suspension theory goes out the window.

Amount of lateral grip at the front has no real significance as the rear will always have greater slip angle.

Sam_68 - 9/2/14 at 10:10 AM

quote:
Originally posted by britishtrident
With a trike car type suspension theory goes out the window.

Amount of lateral grip at the front has no real significance as the rear will always have greater slip angle.


Not necessarily: if that were true, then all trikes would oversteer, all the time, which is certainly not the case.

The theory has some significant differences to 4 wheels, but the laws of physics still apply.

Talon Motorsport - 9/2/14 at 10:34 AM

I have always wondered do FWD trikes get lift off over steer the same as SWB hatchbacks if you go in too hot?

Sam_68 - 9/2/14 at 10:47 AM

quote:
Originally posted by Talon Motorsport
I have always wondered do FWD trikes get lift off over steer the same as SWB hatchbacks if you go in too hot?


They can, yes: the same physics apply. By lifting off, you're suddenly taking away a big component of the slip angle at the front, causing the slip angle at the rear to 'kick in' abruptly.

More unusual is the tendency for FWD trikes to lift a front wheel (with FWD cars you normally arrange the roll axis and relative roll stiffnesses so that it cocks its leg at the back), which with an open diff means that it acts like a safety valve: if you overcook it to the extent that the wheel lifts, the open diff spins off the power and the trike slows down and drops back onto the tarmac before it turns over.

...Hopefully.

But of course the diff is then effectively 'lifting off' for you, so things can sometimes get untidy.

TallGuySmallBike - 9/2/14 at 01:28 PM

Is this the calc you talk of? http://www.racingaspirations.com/apps/suspension-geometry-calculator

I'm a TOTAL novice at this!

Volvorsport - 9/2/14 at 01:38 PM

What running gear are you using?

Sam_68 - 9/2/14 at 01:45 PM

quote:
Originally posted by TallGuySmallBike
Is this the calc you talk of? http://www.racingaspirations.com/apps/suspension-geometry-calculator

I'm a TOTAL novice at this!


That's the sort of thing, yes, though on that one you seem to have to register and log in before it will calculate the roll centre for you.

This one is a bit better - it calculates the instantaneous centres (the pink dots) and roll centre (the green dot) straight away:

http://www.vsusp.com/

All the 'free' calculators available online only do the really basic stuff, but if you're a novice they're fine to play around with so you can see the effect of changes.

I use a 'semi-professional' program called SusProg, but only because I can't justify the cost of anything better - really decent software costs £thousands.

TallGuySmallBike - 9/2/14 at 02:00 PM

quote:
Originally posted by Volvorsport
What running gear are you using?


Front engined, FWD drive shafts from gearbox to hubs. Is that any help?


Also trying out the other calc now.

I used the one you had to reg for. there is no cost of it, some weight distribution calcs in there too

Sam_68 - 9/2/14 at 02:16 PM

quote:
Originally posted by TallGuySmallBike
Front engined, FWD drive shafts from gearbox to hubs. Is that any help?


The exact engine/gearbox configuration will make a difference, since it will dictate (in particular) how long you can make your wishbones before bits of engine start to get in the way.

At one extreme would be something like a V-twin Moto Guzzi or Harley engine mated to a longitudinal 2CV gearbox, which would be quite narrow and give you quite a bit of freedom over your wishbone lengths. At the other extreme (being silly) would be a transverse V12 out of a Lamborghini Miura, in which case I think I'd be looking at a sliding pillar arrangement if I were you!

In some cases (eg. the old Mini), you might find that it's convenient and sensible to retain the whole package of engine, gearbox and front suspension - complete with its subframe - rather than mess about designing and fabricating from scratch.

The problem with transverse front engined packages is that they tend to be tall and wide, so they both limit where you can place your suspension pickups and make it difficult to design sleek-looking bodywork.

Longitudinal front engine packages (like some Audis, old Saabs, etc.) tend to be too nose-heavy, 'cos they have big, heavy inline engines hung out in front of the axle line.

Which leaves oddities like the Citroen 2CV or the original Renault 5 (which had a longitudinal engine behind the axle line instead of hung out in front of it), or the option of mating a v-twin motorcycle engine to a light, longitudinal transaxle (like the 2CV or Hillman Imp gearbox).


[Edited on 9/2/14 by Sam_68]

TallGuySmallBike - 9/2/14 at 03:36 PM

Here is what i have to work with. Its a 1.9 DT from a 306

http://www.flickr.com/photos/116905236@N06/12397524854/




Overall Length 1500mm from Disk to Disk (Used disk for ref)
O/S Disk to gearbox 300mm - 250mm after frame.
N/S Disk to Pully on Engine 300mm - 250mm after frame
Overall width of engine+Gearbox - 900mm

If this helps at all?

[Edited on 9/2/14 by TallGuySmallBike]

Sam_68 - 9/2/14 at 06:17 PM

OK. I have to say that it wouldn't be my first choice of engines to use in a three wheeler (they make most sense to me, personally, if they're very lightweight, which you're never going to achieve with a diesel engine sitting in the nose), but each to their own:

For what it's worth the first things I'd do would be:

1) Google reckons that the track dimension for a Peugeot 306 is 1462mm, and runs a wheel offset of between 13-18mm. Your measurement of 1500mm. across hub faces would give an offset of 19ET on the wheels, which is near enough (you maybe haven't got quite the same plunge as Peugeot has designed for in the suspension's static ride position). Whether you decide to correct your figures to match Peugeot's is up to you.

2) Can you do technical drawing, basic geometry and (ideally) use CAD? If not go off and learn, and come back when you can.

Assuming the answer to (2) is 'yes':

3) Draw up the basic dimensions of the engine package on CAD, so you can work out where you can place upper and lower frame tubes around it, which will effectively dictate the 'zones' where you can place your chassis suspension pickups.

4) Decide whether you're going to try to retain the Pug's uprights (if you're a novice, I'd suggest you do, 'cos designing new uprights is not a job for the beginner), and if so how you're going to modify them from strut arrangement to double wishbones. Measure them up, with reference to the hub face very accurately, and create a drawing. This is a pain in the ass to do, but has to be done accurately if you want to be confident of your results, so take your time.

5) Your bottom ball joint position will be fixed by the upright design (remember to correct the position for caster when you're drawing the front view). You may have some scope to play around with the upper ball joint position, if you're designing a conical insert to convert the upright to double wishbone, but make sure it will clear the wheel rim. This will dictate either fixed positions (bottom ball joint) or a 'zone' (if you have some flexibility for adapting the upright) to place your upright pickups.

6) Decide how high you want your roll centre to be (I'd suggest 35-75mm as a starting point; 50-55mm if you want me to narrow it down even further).

7) Draw everything up onto one of the suspension calculator programs.

8) By playing around with those pickup positions where you've got some flexibility (ie.within the 'zones' mentioned above), use trial and error to come up with pickup positions that:
a) Keep your roll centre very well located relative to the chassis, no matter how you move the suspension around (ideally - it will take a lot of trial and error and you won't always manage it - you want to keep roll centre movement down to single figures in millimetres).
b) Give your desired combination of maximum camber in roll versus maximum camber in bump for your chosen range of suspension movement. This is a compromise, and there's no right or wrong answers. Personally, I'd be aiming for something between 25 and 50% camber recovery in roll and camber gain of between about 0.5 to 1.0 degrees per inch of suspension bump deflection (so between 0.02 and 0.04 degrees per millimetre in new money), Don't worry too much about what happens in droop, 'cos if the suspension's drooping, the loads on the tyres are small and they won't be contributing much grip anyway.
c) Keeps scrub to a reasonable level (I don't tend to fixate on scrub too much, but you probably need to start worrying if it's more than about 5mm).

Item 8 is where the 'semi -professional' software like SusProg comes into its own: you'll probably spend weeks, tearing your hair out, trying to achieve acceptable figures on one of the free online calculators like Vsusp. If you have SusProg, you can basically tell it the range of adjustment you have available in your pickup positions (ie, the dimensions of the 'zones' discussed above), the maximum camber gain you're willing to accept, the maximum roll centre movement you're willing to accept, press a button and the program spits out a list of coordinates for the pickups that meet your requirements.

This above is a very simplified overview - we haven't got into steering geometry, or correcting for static camber, or 3-dimensional geometry like anti-dive and caster (all of which the 'semi-pro' software like SusProg helps you out with), but it'll do to be getting along with.

TallGuySmallBike - 9/2/14 at 09:25 PM

@SAM_68

Sweet jesus, Thanks for that reply.

For the reasoning behind the engine, I'm looking to build something that will last me, but still be able to use on a daily basis. by using a VERY common Engine/Driveshaft/Hub set up, I'm hoping it will be a cheap/easy fix in the latter.

I was taught how to use Inventor by autodesk, I'm sure CAD ain't that far off, I've made 3D models of what i wish to build. but with no define measurements, it just looks right.. nothing more.

I Work on Manual Lathes/millers also Welders/Fabby type stuff All day. Making things is no problem at all.

Its just the actual size/Dimensions I need, The calculations in general that make my head spin.

As for the uprights i can knock some up. use the original hubs/Bearings so i can use the original


This is what i have so far, The upper wishbones look so wrong though?
http://www.racingaspirations.com/mods/mlsmnmgd - I Hope this link works.

Sam_68 - 9/2/14 at 10:08 PM

quote:
Originally posted by TallGuySmallBike
This is what i have so far, The upper wishbones look so wrong though?
http://www.racingaspirations.com/mods/mlsmnmgd - I Hope this link works.


I don't think that link is working correctly - it just seems to take me to the suspension geometry calculator with its 'generic' geometry.

Autodesk Inventor is a form of CAD (it's AutoCAD with bells and whistles added for mechanical design, basically), so if you can learn to use the full functionality of that package, you're fine.

Making your own uprights will give you better flexibility over positioning the pickups, but perhaps that just gives you even more confusing choices to make! You'll need to think about what caster, kingpin inclination and kingpin offset you want to use, as well.

I'd suggest maybe 6 degrees caster, 9 degrees KPI and 15-25mm kingpin offset as initial target, but I must admit that I'm not overly familiar with FWD design, so you'd be as well to do your own research... I don't know how far the upright geometry is influenced by the need to minimise torque steer effects.

What makes you choose a trike to go with that engine, if you don't mind me asking?

Have you seen this thread over in the engines section?:
http://www.locostbuilders.co.uk/viewthread.php?tid=188412&page=0&contribmessage=none

TallGuySmallBike - 9/2/14 at 10:41 PM

quote:
Originally posted by Sam_68
quote:
Originally posted by TallGuySmallBike
This is what i have so far, The upper wishbones look so wrong though?
http://www.racingaspirations.com/mods/mlsmnmgd - I Hope this link works.


I don't think that link is working correctly - it just seems to take me to the suspension geometry calculator with its 'generic' geometry.

Autodesk Inventor is a form of CAD (it's AutoCAD with bells and whistles added for mechanical design, basically), so if you can learn to use the full functionality of that package, you're fine.

Making your own uprights will give you better flexibility over positioning the pickups, but perhaps that just gives you even more confusing choices to make! You'll need to think about what caster, kingpin inclination and kingpin offset you want to use, as well.

I'd suggest maybe 6 degrees caster, 9 degrees KPI and 15-25mm kingpin offset as initial target, but I must admit that I'm not overly familiar with FWD design, so you'd be as well to do your own research... I don't know how far the upright geometry is influenced by the need to minimise torque steer effects.

What makes you choose a trike to go with that engine, if you don't mind me asking?

Have you seen this thread over in the engines section?:
http://www.locostbuilders.co.uk/viewthread.php?tid=188412&page=0&contribmessage=none



I've worked with mostly motorbikes, I Dont have a car licence.. Nor do i want one. Badass..

Trike is a viable option.. so why not Diesel!. The XUD engine I've picked has the same points for install as a GTI-6 Petrol version of the same 306 (Ish).. So petrol can be an option at a later date.

Back to the dieselness.. Its Capable to give 200bhp+ easy. with cheap(Ish) mods, And its an easy diesel to work/Learn on

Found this too http://forums.tdiclub.com/showthread.php?t=247471

Sam_68 - 9/2/14 at 11:45 PM

quote:
Originally posted by TallGuySmallBike
Trike is a viable option.. so why not Diesel!.


Mainly because of the weight, to be honest.

The design will end up being very nose-heavy, which will impact badly on both handling and stability. If I had to use a transverse car drivetrain package for a FWD reverse trike, I'd be looking for the lightest and most compact I could find - maybe something like the alloy 1-litre petrol triple from the Aygo/C1/Pug 107 (though even that remains quite a tall engine and dictates a high scuttle). Small, FWD diesels tend to be quite nose-heavy enough, without taking away one of the rear wheels and all the suspension and bodyshell that goes with it.

Also, aesthetics are quite difficult: I've yet to come across any trike powered by a transverse FWD engine that didn't look pug-ugly, simply because of the width and height of the engine. They dictate a high scuttle, which places all of the visual mass at the front and leaves everything behind the front axle line looking like a bit if an afterthought. To me, trikes with modern styling look better if they're mid-engined, so that you can have a low nose.

But I digress... let's stick to the handling issues, shall we?

TallGuySmallBike - 10/2/14 at 06:27 PM

quote:
Originally posted by Sam_68
quote:
Originally posted by TallGuySmallBike
Trike is a viable option.. so why not Diesel!.


Mainly because of the weight, to be honest.

The design will end up being very nose-heavy, which will impact badly on both handling and stability. If I had to use a transverse car drivetrain package for a FWD reverse trike, I'd be looking for the lightest and most compact I could find - maybe something like the alloy 1-litre petrol triple from the Aygo/C1/Pug 107 (though even that remains quite a tall engine and dictates a high scuttle). Small, FWD diesels tend to be quite nose-heavy enough, without taking away one of the rear wheels and all the suspension and bodyshell that goes with it.

Also, aesthetics are quite difficult: I've yet to come across any trike powered by a transverse FWD engine that didn't look pug-ugly, simply because of the width and height of the engine. They dictate a high scuttle, which places all of the visual mass at the front and leaves everything behind the front axle line looking like a bit if an afterthought. To me, trikes with modern styling look better if they're mid-engined, so that you can have a low nose.

But I digress... let's stick to the handling issues, shall we?


Ahh see. I forgot to mention this will the a 2 birth trike, Front and back end will be bulky. so its fine .

I'm not going for the lightest, best looking thing.. for other people

I my self am a 17stone 6ft8" beast.. so its going to be long ish (About 2.3m axel to axel) take a look here http://www.flickr.com/photos/116905236@N06/ Disregard the epic MS paint skills.. and the rear motorbike wheel was just there for a refrence, its not staying.

But yes back to handling!

Looking back at the uprights (if i dont make new ones) the bore for the spring to sit in, seems offset by 1/2 inch
I could make an insert making it inline with the fixture for the bottom ball joint making it about 190-210mm spacing depending on now i do it. Does this seem right? Or i can put an incert in to the bore to make it taller (see pic below)

Do the wish bones Need sit inline on the frame? Like the pic below.




Thanks. Sorry for being annoying by using a diesel

[Edited on 10/2/14 by TallGuySmallBike]

Benzine - 10/2/14 at 06:45 PM

quote:
Originally posted by TallGuySmallBike
Sorry for being annoying by using a diesel


XUD is king

TallGuySmallBike - 10/2/14 at 06:52 PM

quote:
Originally posted by Benzine
quote:
Originally posted by TallGuySmallBike
Sorry for being annoying by using a diesel


XUD is king


Indeed, There a guy on the 306oc forum. Tuned 4 XUD's To max, But headgasket/Too much heat was major problem / Also conrods and other parts.

He then took a HDI.. REMOVED all the electronics. ECU ect..ect..
Added on all the Xud parts... He now runs 1 Small Turbo - To power a TRUCK turbo. and a supercharger thrown in for good measure, Large Truck turbo spools at 1k revs or somthing stupid lol
I'll see if i can find it.

FOUND IT!
Here is a pic of the bay.


http://306oc.co.uk/forum/thread-69.html
Project page - Seems to have stalled a little

[Edited on 10/2/14 by TallGuySmallBike]

Benzine - 10/2/14 at 06:57 PM

Is that mr lobb? I'm xud missile on 306oc btw

TallGuySmallBike - 10/2/14 at 07:09 PM

quote:
Originally posted by Benzine
Is that mr lobb? I'm xud missile on 306oc btw


It is his yeah! Ha i was talking to you about the heater matrix reduction a while back .. YOU SENT ME HERE!!

[Edited on 10/2/14 by TallGuySmallBike]

Sam_68 - 10/2/14 at 07:56 PM

quote:
Originally posted by TallGuySmallBike

Looking back at the uprights (if i dont make new ones) the bore for the spring to sit in, seems offset by 1/2 inch
I could make an insert making it inline with the fixture for the bottom ball joint making it about 190-210mm spacing depending on now i do it. Does this seem right?


I'm not sure I understand you correctly. If you're suggesting making the top ball joint sit vertically inline with the bottom ball joint, then no, you definitely don't want to do that. Google the term 'king pin inclination' or 'steering axis inclination' (they mean the same thing). You need a KPI/SAI of about 9-11 degrees, and the top and bottom ball joint positions will need to be arranged to suit. You can use an insert to make it taller, though, yes, if it helps your geometry (but check the clearance of your wheel rims).

quote:
Originally posted by TallGuySmallBike
Do the wish bones Need sit inline on the frame? Like the pic...


Not necessarily directly in line, no, though you need to keep any offsets small (those brackets are far too long and place the pickups too far out from the chassis, for my liking). But now we're getting into spaceframe design, which is yet another, quite different, subject!

quote:
Originally posted by TallGuySmallBike
Sorry for being annoying by using a diesel


It's not the diesel that's the problem, it's the fact that you're hanging it out in front of a trike that worries me! Most diesel hatchbacks have four wheels, four seats, a longer wheelbase than yours (the Pug 306 is almost a foot longer, at 2580mm), and they're still seriously nose-heavy.

And 17 stone offset to one side, and the bike swing arm and rear wheel shown in your photos at the back? I'm beginning to sense a wind-up?

TallGuySmallBike - 10/2/14 at 08:42 PM

Damn it. i just found out what it was

You got me first.

Found this


[Edited on 10/2/14 by TallGuySmallBike]

Sam_68 - 10/2/14 at 08:56 PM

quote:
Originally posted by TallGuySmallBike
Also as for the king pin.. I was talking of this off set. Is this some kind of different angle needed?


Yes, you need caster as well... about 6 degrees worth of it, as a ballpark figure.

TallGuySmallBike - 10/2/14 at 09:02 PM

Right well, Going off this i can try and work somthing out. Back soon!

TallGuySmallBike - 10/2/14 at 11:27 PM

300 mm Lower wish bone.
240 - 250 mm Top Wishbone

300mm between the centres of pivots that attach the wishbones to the frame.

Thus giving a 9 degree King pin tilt thingymebob.

PhillipM - 12/2/14 at 02:03 AM

What's the roll centres/instant centres like with that setting? They seem pretty short wishbones is all....

You'll want to be careful with the plunge on the driveshafts too, shouldn't be quite as bad with a double wishbone generally but it's worth checking just in case.

P.S. XUD's suck balls - Ripp

[Edited on 12/2/14 by PhillipM]

TallGuySmallBike - 12/2/14 at 06:54 PM

quote:
Originally posted by PhillipM
What's the roll centres/instant centres like with that setting? They seem pretty short wishbones is all....

You'll want to be careful with the plunge on the driveshafts too, shouldn't be quite as bad with a double wishbone generally but it's worth checking just in case.

P.S. XUD's Are so amazing.. They are just the best - Ripp

[Edited on 12/2/14 by PhillipM]


This is a rough calculation.. Still finding my feet here.

https://www.flickr.com/photos/116905236@N06/12484459283/