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Sierra trailing arms
Kieran - 2/9/05 at 04:40 PM

I know this has been touched on briefly before, but I cant see why the trailing arms from the sierra subframe can't be used? I know that some of the kits use a complete subframe (Robin Hood etc), but why not just make up mounts just for the trailing arms?? Pilgrim do in their sumo.

Kieran
Rescued attachment sumo13.jpg
Rescued attachment sumo13.jpg

chrisg - 2/9/05 at 04:45 PM

didn't we do this?

James - 2/9/05 at 04:46 PM

If it's been touched on before and people have advised against it maybe that's for a reason!

Like:
Big, heavy, ugly, will make the car handle like a piece of crap, heavy and oh, again: heavy.

Oh, and also, the mounting point will firmly intrude into the seating area.

But other than that feel free to go ahead.

HTH,
James

[Edited on 2/9/05 by James]

James - 2/9/05 at 04:50 PM

quote:
Originally posted by chrisg
didn't we do this?


I didn't realise it was Kieran asking in the last one!

Kieran,
Robin Hood use it... is that not reason enough to stay the f'ck away!

James

chrisg - 2/9/05 at 05:03 PM

Either that or make the whole car out of girders and go tractor pulling!

Cheers

Chris

James - 2/9/05 at 05:05 PM

quote:
Originally posted by chrisg
Either that or make the whole car out of girders and go tractor pulling!

Cheers

Chris


I thought that was a Robin Hood!



Sorry RH boys!

Cheers,
James

JoelP - 2/9/05 at 05:36 PM

see my post on the other thread.

Kieran - 2/9/05 at 06:01 PM

I restarted this thread to get a bit more of an intelligent response than

quote:
Erm... the ends of the trailing arms would be where your arse wants to be still I suppose you could pad them with some foam, you know, make a feature of them


Im not talking about the full subframe. Just the two trailing arms. Im sure that the two trailing arms and diff can't weigh more than a live axle??

The RH references are a bit tiresome..... Surely its all about building a car and getting it on the road, rather than "mines better than yours and yours is poo cos its a Robin Hood" ????

Kieran

JoelP - 2/9/05 at 06:07 PM

well specifically, if you use the trailing arms you would have to put some effort into triangulating your chassis to take the loads, obviously the bump and acceleration forces would act in different places.

You also have less control of wheel camber in roll, than you would with 'real' irs.

One halfway solution would be to remake the semi-trailing arms in a similar manner to how steve guserson has made them. This, in his case, has made mounting it to the chassis easier, but he also admits that it isnt ideal for a sports car (his is more tourer i believe).

A dedion system is very simple to make, and uses the 5 'book' mounting points, hence its a simple solution. IRS adds complication but is do-able.

chrisg - 2/9/05 at 07:44 PM

ooooooooo

where's my handbag?

You'll still be sitting on the trailing arms no matter how many people you insult.

The things are dynamically unsuitable, but if you want to use them it's your car. That's the point they're all different - If you don't like the message, don't shoot the messenger.

The Robin Hood references are based on experience, ironically mostly by people who've built Robin hoods. It's got nothing to do with which car is the best.

You ever heard of a book called" How to win friends and influence people"?

Cheers

Chris

Peteff - 2/9/05 at 07:59 PM

I think Mr Gustavson who used to post on here occasionally has used some home made radius type arms on his not quite a locost lookalike Morganesque car. Chris, which handbag have you lost? I think you left your pink one at the Twin Oaks motel the other month

chrisg - 2/9/05 at 08:07 PM

I'll pick that up at your next fetish do Pete

Cheers

Chris

MikeRJ - 2/9/05 at 11:42 PM

quote:
Originally posted by Kieran
I restarted this thread to get a bit more of an intelligent response than
quote:
Erm... the ends of the trailing arms would be where your arse wants to be still I suppose you could pad them with some foam, you know, make a feature of them


Im not talking about the full subframe. Just the two trailing arms. Im sure that the two trailing arms and diff can't weigh more than a live axle??

The RH references are a bit tiresome..... Surely its all about building a car and getting it on the road, rather than "mines better than yours and yours is poo cos its a Robin Hood" ????

Kieran


The point is that a semi trailing arm system, whilst simple, is a big compromise in terms of camber control. The whole philosphy behind the Seven is a lightweight, well handling car. The Cobra, (especialy the budget designs) have different priorities, i.e. mainly looking and sounding nice. You can get Cobras with decent handling, but they don't use the Sierras trailing arm suspension.

The point made abive about the location of the trailing arms mounts is perfectly valid, the arms are simply too long to easily fit into a book sized chassis. Of course, you can modify the chassis and make it longer, but it's a lot of effort for designing in an inferior suspension system.

In all honesty, you'd get better results sticking with a simple live axle system, which is a well proven design on the seven.

Just because the response is not what you want to hear, dosen't mean it wrong...

James - 3/9/05 at 12:53 AM

quote:
Originally posted by Kieran

The RH references are a bit tiresome.....

Kieran


Ah, I see... you mean a bit like people asking questions that have been asked (and answered) many times before that a search or two would have answered! I see your point!


At the end of the day, if you want to do it then just go ahead and do it- it's your car! I suspect though that 90% of people on here would say it's not the best way to go about it. And those that *have* done have definately said it's not a good idea!


The trailing arms are too long to fit the driveshafts where they are currently without bolting the trailing arms 'inside' the car as per Chris' comments. So just extend the whole axle 'arch' area backwards approx 6" or shorten you're Sierra trailing arms (which will then affect the bump) but it may not matter much. If you're keep them standard then the shock mounting will be different as the shock will have to be at an angle which will change the effective spring/damp rate of the shock. But you can of course calculate the change and buy appropriate shocks.
You'll also possibly need different wheel arches as the axle area will be wider- but I'm sure you can fabircate them!

At the end of the day you can physically do it but I think most people will suggest it's not such a good plan. If it was then I would think that atleast some of the more credible manufacturers would use it: MK, Luego, GTS, MNR etc.... and they don't!

ATB,
James

P.S. Doing your own IRS is a pain, in my opinion the best advice really is to buy a DeDion kit from GTS or MK and fit that- easy, cheap and light. A very good compromise which I'd have done if I'd known better at the time of doing my chassis!

[Edited on 3/9/05 by James]

britishtrident - 3/9/05 at 06:58 AM

Lets call a spade a spade the correct name for this type of suspension is diagonal swing axle --- but the marketing guys take fright at the words "swing axle".

Camber changes aside the real problem is toe variations on the rear --- on both bump and droop it moves in to toe-out lots of it.
This can be partially corrected by lots and lots of static toe-in and making the car very stiff in roll -- either by very hard springs/anti-roll bars or by using high roll centres but that introduces the second problem you can set up this type of suspension to work pretty well in dry conditions but the settings that give good dry handling will give very sudden snap oversteer in the wet. Every single car that I have owned or driven with this type of suspension was tricky in the wet -- everything from ultra light Davrians to massive nose heavy Austin 3 Litres. Even BMW never tamed this type of suspension they only finally sorted the wet weather handling when they switched to the much more expensive Z axle.. For many years Mercedes used semi trailing arms on saloon models but the sports models never used it -- perhaps hey know a bit more about suspension design than Robin Hood.


[Edited on 3/9/05 by britishtrident]

Peteff - 3/9/05 at 08:33 AM

It's your turn for the next one. Can I have the gimp mask we found in it?

NS Dev - 3/9/05 at 09:36 AM

I think the question has been intelligently answered now.

1) Camber control, look at a 90's sierra RS500 touring car.............they ran that ridiculously high ride height bacuse lowering the car buggered up the trailing arm angles and led to vast amounts of negative camber even at static ride height.

2) weight, the arms are hugely heavy. They were designed for the scorpio, all sierra testing in terms of rear suspension was conducted at scorpio weights so the same parts could be used. They are designed for a 1375kg car plus a trailer, roofrack and 5 large occupants....................not just too heavy for a locost, more like trying to put wheels on the Forth Road Bridge!

3) Toe change in roll, as Britishtrident mentioned, no need to elaborate any further!

4) no matter what you do to mount the arms, they still intrude into where you need to sit!!!! Look at a Tiger (don't know the models but the one that uses the complete rear arms) and you'll see the mounts inside the cockpit getting in the way!

5) it's much easier to use a de-dion setup, and in answer the the "no heavier than........" point, yes it is!! The lightest 7's are generally live axled ones, as long as you use a lightish live axle (marina or english axles, former being lighter) I won't go into unsprug weight!

[Edited on 3/9/05 by NS Dev]

Volvorsport - 3/9/05 at 11:17 AM

ill agree with everything said , apart from , -- daRrian cars use semi trailing , theyre a lot better than the daVrians , but still can be described as being on a blunt knife edge .

trouble is theyre mid engined and have no relation to a seven - all major manufacturers stick to tried and tested for the weight of the components , even i have done that

Avoneer - 3/9/05 at 11:31 AM

Text"""Im not talking about the full subframe. Just the two trailing arms. Im sure that the two trailing arms and diff can't weigh more than a live axle??"""


I'm sure that a Sierra diff and shafts on there own will not be far off the weight of my whole live axle with shafts and diff fitted.

Pat...

[Edited on 3/9/05 by Avoneer]

chrisg - 4/9/05 at 10:15 AM

quote:
Originally posted by Peteff
It's your turn for the next one. Can I have the gimp mask we found in it?


it's yours Pete, your need is greater than mine

Cheers

Chris

Kieran - 4/9/05 at 12:30 PM

Excellent, We finally got there in the end then.

Thanks for all the responces, I have reclaimed my teddy, and it is now residing next to me, back in my pram!

Kieran

p.s. What kind of weights do Locosts come in at??

JoelP - 4/9/05 at 01:50 PM

min 400kgs bike engined, upto 750 maybe for a heavy engined one full of fuel etc.

MikeRJ - 4/9/05 at 03:15 PM

quote:
Originally posted by JoelP
Ask a donkey if its an ass, it'll always say 'neigh'.


No it won't, horses go "neigh", donkeys go "eee-orr". I have a feeling I have the the point of this joke tbh

[Edited on 4/9/05 by MikeRJ]

Kieran - 5/9/05 at 08:45 AM

My friends Robin Hood 2B weighs in at 718kgs with him and a full tank of fuel. Not that heavy then huh??
Stainless panels, pinto, steel chassis etc.

Kieran