still confused about a arms..

[danilo]

Been reading my new Haynes book :-)
Been perusing the A Arm designs and have noticed, beyond the 'strange' offset of the lower shock mount (although explained somewhat by Talon.. thank you :-)
Or that the upper A Arm is suggested to have an 8 degree angle on the track rod tube.. erm Why? the angle would then be even less than optimum at actual use settings... besides it's a Ball joint :-)
I was marveling at the lay down angle of the shock /spring unit.. All literature claiming that such extreme angles deteriorate effectiveness.
Notably the lower arm is 17"~ !! ? long.
A Caterham SV (the large one :-) is 12"~ centre to centre. That particular 7 handles pretty well by most yardsticks.
My guess is that this 'extra' width was generated in attempt to accommodate the Sierra track dimension?
Silly observation: but it seems to my dim mind that widening the front chassis rather than the A Arms may have been the superior suspension design route? Certainly would have resulted in a more favourable angle for the coil units. Likely negated the need to hacksaw up the steering rack as well.
Yess the result would have been a wider nose section. Dunno if that's better or worse visually though.

[baz-r]

top arm angles to the draglink/balljoint as it stops it straining at its limit if the arm was stright it would break the joint

[twinturbo]

My guess is that this 'extra' width was generated in attempt to accommodate the Sierra track dimension?


Not sure how close it is to the sierra track at the front given it uses escort rack and extensions.


Likely negated the need to hacksaw up the steering rack as well.


No need to hack a rack, the escort one is used.



Sounds like you should set up and build a revised design ;)

TT

[danilo]

The A Arms in Caterhams and even Locusts don't feature an angled upper balljoint fittment .

Without doubt a different chassis design is suggested :-)
I ...have... drawn an SV clone chassis as a .dwg, down to the last detail.
And the geometry works fine :-) ALL of it.
Using Caterham SV overall dims. And Cat A arms.. why not? they are of good proven quality/design, as well as easily available for similar to clone pricings.
No inordinately long A Arms, No lay down coil overs. No boiler plate shock mounts.. in the wrong place :-) No hacksawing a steering rack :-)
I've solved the design for my chassis build to my complete satisfaction :-) Anyone else can do it too, it's no longer rocket science, with the plethora of excellent programs available these days.

Was only wondering aloud about the design, being so out of step with proven practice, is all and why seeming adults presumably with a fair amount of life experiences, are so complacent/ accepting of it.
Is it just because it's printed on a piece of paper ?

[danilo]

The A Arms in Caterhams and even Locusts don't feature an angled upper balljoint fittment .

Without doubt a different chassis design is needed.:-)
I ...have... drawn an SV clone chassis as a .dwg, down to the last detail.
And the geometry works fine :-) ALL of it.
Using Caterham SV overall dims. AND Cat A arms.. why not? they are of good proven quality/design, as well as easily available for similar to clone pricings.
No inordinately long A Arms, No lay down coil overs. No hacksawing a steering rack :-)
I've solved the design for my chassis build to my complete satisfaction :-) Anyone else can do it too, it's no longer rocket science, with the plethora of excellent programs available these days.

Was only wondering aloud about the design, being so out of step with proven practice, is all and why seeming adults presumably with a fair amount of life experiences, are so complacent/ accepting of it.
Is it just because it's printed on a piece of paper ?

[minicountryman1961]

Was only wondering aloud about the design, being so out of step with proven practice, is all and why seeming adults presumably with a fair amount of life experiences, are so complacent/ accepting of it.
Is it just because it's printed on a piece of paper ?

It is printed on paper, it is also true that many have been built and their owners are quite happy with them.. If you fancy yourself a chassis designer, build what you want. The thing is, building a proven moderately standardized design means we can buy parts from suppliers with a reasonable expectation that they will fit and work properly. It also means we can get good advice from others who have gone before us on this path. If you chose to go with your own design, you will make mistakes and it will be up to you to diagnose and solve them.

[spud69]

Chassis and mainly suspension design is a bit a black art and always a compromise between certain handling traits, it's a shame that Chris Gibbs is not available online to explain why certain decisions where made regarding the suspension design and setup. The main thing being that Martin Keenan formerly of MK Engineering had a large part to play in the design of the car and suspension, Martin has built a reputation in the Kit Car community for his design and car building skills - he is well respected in this area.

Certainly from my experience and other builders i have been involved with the handling of the roadster is not compromised in any way and handles, on road and track, in a balanced and very predictable way and definitely on a par with other brands of a similar nature.

The main thing is that the guide is intended exactly as that and if a builder is not comfortable with certain aspects then they can be changed to suit the builders preference, the philosophy of the self build concept which is why most of us are building to the guide so that we can have the satisfaction of a self built roadster at the end of the day not just a bolt together kit. I have seen most builders customise certain parts of their build for personal preference some more than others.

The above is not intended to defend the Haynes Roadster for the sake of Saturn but is plainly a personal opinion as to why the guide and roadster has been quite successful and we all love the self build approach to the car. A main reason why i put a lot of work into producing a guide to supplement the book for a change of donor car to the Mx-5, some people have amended this also to suit their own preferences, it certainly hasn't been done to generate lots of orders but to keep the self build culture alive.

Please don't take this the wrong way Dan, it's just my opinion that's all whether it be right or wrong.

Regards....AndyH

[MarkB]

The Sierra based Roadster handles like a shopping trolley and understeers for a past time but that is my opinion and no doubt will be frowned upon.....:D

[spud69]

The Sierra based Roadster handles like a shopping trolley and understeers for a past time but that is my opinion and no doubt will be frowned upon.....:D

I must be doing something wrong then cos mine and the ones i've put on the road dont and i'm sure the people i've taken out would agree......:D

[mark]

The Sierra based Roadster handles like a shopping trolley and understeers for a past time but that is my opinion and no doubt will be frowned upon.....:D

If only someone could design a fabricated upright and revised wishbones so my roadster could go around corners, ive been trying to get out of my street for the last 18months but this damn understeer wont let me!

[Bonzo]

[QUOTE=MarkB;68379]The Sierra based Roadster handles like a shopping trolley and understeers for a past time but that is my opinion and no doubt will be frowned upon[/QUOTE

That is only my personal opinion of that post :p :D

What a pity that you never took the time to build one & by your own admission, wouldn't even drive a 7 type car ;)

Hey ho, you have to get your kicks somewhere & I guess this forum is as good a place as anywhere :D

[spud69]

If only someone could design a fabricated upright and revised wishbones so my roadster could go around corners, ive been trying to get out of my street for the last 18months but this damn understeer wont let me!

Is that why you only ever go straight on at roundabouts Mark....Wondered why that was....;)

Seems okay on front end grip here mind:

http://www.youtube.com/watch?v=4NdClc5ZaCU&feature=feedu

:p

[ayjay]

Danilo I dont normally get involved in these technical conversations because I dont know enough about it so its best to keep quiet-Better to keep your mouth shut and appear a fool than to open it and remove all doubt!
What I do know however is that your posts re roadster design come across as self indulgent to the point of arrogance. --Why doesn't everyone out there know as much as I do? ---These things should have been blindingly obvious to the roadster designer if only he had known as much as me!---
You may be pretty good on the cad thing but have a lot to learn otherwise.
Its always best not to damn someone else--certainly not in public if you dont know the reasons for the decisions they made and certainly if they are not in a position to respond. Most of us know that design is always a balance between form and function and perfection is impossible because we all see things from differing points of view.

[shh120m]

il stay out of this one BUT,

is the point of building to get it finished and drive it to have FUN,

yes there may be compromises here and there for some reasons or another, i dont recall ever driving the "perfect" car, and iv had a few quick motors.

Once youre on the road in a haynes all this crap about handling is soon forgotten and replaced by a big grin (unless marks driving ofcourse then its sheer fear:D )

[Bonzo]

Once youre on the road in a haynes all this crap about handling is soon forgotten and replaced by a big grin (unless marks driving ofcourse then its sheer fear:D )



Wait till you have a ride out with AshG :eek:

I done a very childish thing in Ash's car .... Found out that adrenalin was Brown :D :o

[davidimurray]

I think you need to consider the context in which the Haynes Roadster is designed - i.e. it is a 'sporty' road car, for occasional track use, based around a single donor.

As such you begin with a number of design constraints, in terms of suspension you have the uprights and brakes to contend with as a starter. In an ideal world you start at the tyre and design backwards, through the upright design , wishbone and then finally the chassis, which at the end of the day is only there to connect everything together. Of course to do all this you need a set of target design parameters to aim for - to do this you have to make a number of assumptions, such as the CoG. There will be a number of driving conditions to then consider - e.g. high speed cornering, low speed cornering, braking, acceleration and all the combined load. A car setup for low-speed autocrossing would be totally different to a high speed circuit racer.

Unfortunately for us we want the roadster to be all things to all men using a number of predefined parts - so the poor car is up against it to start with.

There are plenty of possible improvements you could make - e.g.
Re-designed wishbones with rod ends - although you would need to redesign to prevent rod ends in bending. Also for correct adjustment rather than having adjustable rod ends, staked in bearings would be better along with packers on brackets at the upright - so now you need new uprights.
Then of course there is the round tube chassis - but why even use tube when you could build a excelite monocoque. You can go on and on for ever!

Having been lucky enough to be involved in project managing the build of a simple single seater, while not a designer myself, I've been invovled in quite a few discussions and basically every decision is a compromise of time, money and engineering.

So having been involved in building such a car - why build a roadster?? Because I want a good fun road car that I can have some fun on track in and more importantly build it all myself.

Ramble over :p

[monsterob]

Ive messed around with all the critical bits on mine ! Rear hubs front hubs wishbones are longer blahh blahh havent a clue how its all going to work or even if it will atall, i know bugger all about suspension hence using four bike shocks instead of the coilovers .

Its a hobby if it doesnt drive ill sell it on ebay to some unsuspecting mug as an unfinished project :D

Or just weigh it all back in as its all scrap anyways !!!

[MarkB]

Oppsy I upset the spoons........:D

[minicountryman1961]

Oppsy I upset the spoons........:D
If you are having trouble getting your Roadster around corners, you should add rear-steer.

[robo]

If you are having trouble getting your Roadster around corners, you should add rear-steer.

Its all a load of crap, every car maker in the world builds in understeer in the car to stop people overcooking it in a bend and loosing the back end which in their opinion joe public could not control.Anyone can reverse this with set up and with a little friggin dial in a neutral or oversteering car.

Bob

[MarkB]

[QUOTE=MarkB;68379]The Sierra based Roadster handles like a shopping trolley and understeers for a past time but that is my opinion and no doubt will be frowned upon[/QUOTE

That is only my personal opinion of that post :p

What a pity that you never took the time to build one & by your own admission, wouldn't even drive a 7 type car ;)

Hey ho, you have to get your kicks somewhere & I guess this forum is as good a place as anywhere :D


There are plenty of 7's that handle, I have built a few but had no interest, time or space to build a Roadster. Sooner make something different....as for being a Troll well that made me laugh........:D

[MikeB]

can't wait to get mine built and on the track to have a look at this understeer problem.

From my understanding it will be the high g corners where theres a lot of body roll. Aparantly there isn't enough camber gain on the front suspension, i.e the camber angle can't keep up with the body roll angle. Thus causing the outside front wheel to camber out under heavy cornering. Thus causing a bit of understeer. The front shock angle is also quite low so effectively you loose stiffness the more wheel travel (or roll) angle you see.

Three things I'll be playing with to solve this (or minimise this)
1. Static camber angles, probably come up with a track and road setting.
2. Limit the body roll with some antiroll bars (or stiffer strings)
3. Weight distribution etc to give a more neutral oversteer charactersitic.

Other than Ash I'm not sure who else has actually experienced the understeer and this could just be down to the basic geo setup.

As said on the road it isn't going to be a big problem, on track you might feel like you not quite getting the most from the tyres. No biggy.

In my opinion a wider chassis would look naff

[flyerncle]

From experience of the Roadster I put together in conjunction with Saturn the total opposite is true and has a lot of oversteer when corner weighted and set up to suit the driver,it is wearing R1R Toyo,s at about 26 psi or there abouts and standard Protech,s and shorter springs.

[spud69]

From experience of the Roadster I put together in conjunction with Saturn the total opposite is true and has a lot of oversteer when corner weighted and set up to suit the driver,it is wearing R1R Toyo,s at about 26 psi or there abouts and standard Protech,s and shorter springs.

Yes you're right Paul, the roadster can be set up and corner weighted to suit the drivers preference. For the track my setup is the opposite with some understeer that i can balance out with my right foot and get some really nice 4 wheel drifts coming out of the corner, the front can really turn in while coming off the brakes into a corner. Really is good fun - wish it was spring / summer again.....:D

AndyH

[ozzy1]

wish it was spring / summer again.

It is :D :D just wish i had my car finished.:mad:

[davidimurray]

Yes you're right Paul, the roadster can be set up and corner weighted to suit the drivers preference. For the track my setup is the opposite with some understeer that i can balance out with my right foot and get some really nice 4 wheel drifts coming out of the corner, the front can really turn in while coming off the brakes into a corner. Really is good fun - wish it was spring / summer again.....:D

AndyH

Spud - any chance you would be kind enough to share your setup with us ????

[mark]

I personally find with my car it would be hard to quantify the setup as it currently is

I did use some inital numbers from locost builders but after driving it i altered things here and there to make it behave how i wanted

Spud has obviously played with these cars more than me so maybe he has some exact settings to start with, but with so many variables such as engine weight, power output, springs/dampers, wheel and tyre choices make everyones car different and behave differently

Im sure you will soon get it feeling "right" once you get it on the road and have a play

[spud69]

Spud - any chance you would be kind enough to share your setup with us ????

Mark is right there, a lot of it is just by feel and tweaking it to your own preference and will vary between cars. I've found that a good starting point is:

Front:

Toe in 2deg, camber 3deg (will vary on driving style), castor so that it just starts to self centre

Rear:

Toe in - none, camber 1/2 deg

Corner weighting the car is important with the driver in the car, adjust the springs to get the car even all round then you can balance the car between the front and rear. Adjust the ride height, 100mm front / 125mm rear, to as low as you dare for speed bumps and turn up the bump / rebound to as stiff as our crappy roads will allow. If you go on a track day you can drop the car right down and damper setting as stiff as they go and it will make quite a difference.

Hope that helps.....AndyH

[davidimurray]

Spud you are a star (and my wife says you're a darling :p ) !!!

Thanks for the setup info - duly recorded and noted!:D

[spud69]

Spud you are a star (and my wife says you're a darling :p ) !!!

Thanks for the setup info - duly recorded and noted!:D

Well David i dont know what to say, i'm redder than the post box red of the body we are gelling today.......;) Hope my misses doesn't log on today.

Have a good weekend......AndyH