Avoneer
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| posted on 1/9/07 at 09:20 PM |
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IRS / Live Axle Debate...
Sorry to open a can of worms, but would just like to share my limited experience.
After driving my Avon (IRS) around Elvington, which I though handled well at the time and driving the Bitsablade today (Lie Axle)...
I vote for Live Axle every time.
Handling was spot on and very smooth and a real pleasure to drive.
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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smart51
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| posted on 1/9/07 at 09:32 PM |
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Live axles do well on even ground, like at Elvington. On uneven ground they get unsettled more than IRS.
An IRS setup should give better ride, IF it is set up properly.
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craig1410
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| posted on 1/9/07 at 09:56 PM |
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quote:
Originally posted by Avoneer
Sorry to open a can of worms, but would just like to share my limited experience.
After driving my Avon (IRS) around Elvington, which I though handled well at the time and driving the Bitsablade today (Lie Axle)...
I vote for Live Axle every time.
Handling was spot on and very smooth and a real pleasure to drive.
Pat...
Hi Pat,
Very interesting and no doubt contentious statement.
I'm using de-dion on my car and hope to sample its driving characteristics very soon now! 
My feeling has always been that typical "Locost" builders (myself included) are unlikely to possess the suspension setup knowledge,
experience and equipment necessary to get IRS working properly. Therefore de-dion and live-axle are likely to give better results "out of the
box" so to speak. I would have used live axle if I'd been able to bet my hands on a suitably serviceable axle for a +4" chassis.
Cheers,
Craig.
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Avoneer
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| posted on 1/9/07 at 10:10 PM |
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Just to add, and I't not just me, it seems a hell of a lot smoother at the back than my Avon ever did on the road.
And this car has hard GRP seats, not comfy Richfields like the Avon.
Yep - I agree Smart 51, but like everyone says, IRS has to be set up properly and probably beyond most of us locosters.
My Avon was set up out of the box, as is my Bitsablade and I can only compare the two and I know what I'd have again!
Pat...
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However a large number of electrons were terribly inconvenienced.
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t.j.
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| posted on 2/9/07 at 06:06 AM |
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The avon didn't have a good setup.
As they give positive camber in drop. And you need negative.
I hope mine will drive nicely as i followed the pricipals as good as possible.
Grtz
Please feel free to correct my bad English, i'm still learning. Your Dutch is awfull! :-)
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Avoneer
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| posted on 2/9/07 at 07:06 AM |
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Didn't have a good setup - but it handled suprisingly well when pushed hard.
Pat...
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However a large number of electrons were terribly inconvenienced.
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scoop
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| posted on 2/9/07 at 08:21 AM |
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Its my understanding that the live axle is the lighter set up as well by some margin.
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Volvorsport
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| posted on 2/9/07 at 10:35 AM |
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well after blasting around RAF marham yesterday , the car oversteered like a mother f****r , wanting to spin everywhere , until we swapped the springs
front to rear after that it was very forgiving , giving power oversteer on demand .
Big bloody Volvo live axle gets my vote ,lol.
unfortunately the tit behind the wheel was the reason for the 100 mph spins searching for a box of neutrals .
the colway intermediates , were pretty good too .
before i sorted the spring problem , on the bumps it was pretty dangerous , now it does bottom out and i need more travel .
that said , i had no problems with the front inboard suspension , apart from not being able to find a significant amount of understeer .
www.dbsmotorsport.co.uk
getting dirty under a bus
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ChrisGamlin
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| posted on 2/9/07 at 11:02 AM |
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Ive driven a few well set up IRS Westfields on track as well as my own fairly book live axled Locost, and what Ive found is that although the Westies
seem to grip if anything a little more and the car feels very planted and will no doubt lap quickly, they don't tend to communicate on the limit
as well as a live axle (and De Dion I suspect), and feel a bit "dead" so you don't really know how close to the limit you are.
In contrast the live axle tends to move around more with the need for minor corrections throughout the corner, and if going from an IRS car to live I
suspect it could feel a little un-nerving, but once you realise that just because its moving around a bit more doesnt mean its about to swap ends, I
think its more fun to drive on the limit and probably as quick because you can feel and therefore push to the limit more often.
Chris
[Edited on 2/9/07 by ChrisGamlin]
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craig1410
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| posted on 2/9/07 at 11:13 AM |
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quote:
Originally posted by t.j.
The avon didn't have a good setup.
As they give positive camber in drop. And you need negative.
I hope mine will drive nicely as i followed the pricipals as good as possible.
Grtz
Not sure if I'm misunderstanding you here but I would want positive camber on drop myself.
When cornering, the loaded side (outside) would compress and should gain a bit of dynamic negative camber to compensate for body roll while the
unloaded, inside wheel should gain dynamic positive camber. I don't know why you would want the unloaded (dropping) wheel to gain negative
camber as it would be tilting the wheel in ths same direction as the body roll and would result in just the inside shoulder of the tyre contacting the
ground.
Of course when I say positive camber I'm not sure that it would actually end up with net positive camber as you would start off with static
negative camber normally and the dynamic positive camber on drop might not be enough to counteract the static negative camber at ride height.
HTH,
Craig.
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TimC
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| posted on 2/9/07 at 11:18 AM |
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Matt @ Procomp must be having a day away from the PC! 
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ChrisGamlin
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| posted on 2/9/07 at 11:29 AM |
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Craig, I assume he probably means chassis "drop", not droop, ie in roll when the chassis gets lower to the ground.
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Avoneer
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| posted on 2/9/07 at 11:31 AM |
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quote:
Originally posted by TimC
Matt @ Procomp must be having a day away from the PC!
Nope - i've been keeping him busy on U2U about trailing arm bushes as I value his opinion and experience as a racer etc.
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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craig1410
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| posted on 2/9/07 at 11:38 AM |
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quote:
Originally posted by ChrisGamlin
Craig, I assume he probably means chassis "drop", not droop, ie in roll when the chassis gets lower to the ground.
Really? So the Avon gains positive camber on compression then? That's not brilliant is it... 
How on earth did Tiger manage that when designing the Avon? Is the upper wishbone longer than the bottom one or something?
Cheers,
Craig.
[Edited on 2/9/2007 by craig1410]
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ChrisGamlin
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| posted on 2/9/07 at 11:48 AM |
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Not sure if thats correct or not as I dont have any experience of the Tiger, just what I assumed from the comment made.
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procomp
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| posted on 2/9/07 at 12:10 PM |
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Hi ime not going to get drawn into individual chassis and geometry of irs.
But what Chrissgamlin says pretty much hitts the nail on the head.
When on the limits the irs setup still has a tendancy to be moving it geo around and in most of the kitcar world setups its moving in the wrong
direction for more grip.
This means that the liveaxle/dedion setup which has no/farless movement. When on the limit dose not let you down suddenly with grip it just stays
where it is and lets the tyres do what are doing. It dose not start moving the camber the wrong way or sudenly start changing the toe setup from in
to out.
It all meanns that on the limit it's more controlable as nothings moving where it shouldent. As to ride quality all you have to do is invest in
some decent dampers to suit the application. But they can be done for as little as £90 Ea to suit.
cheers matt
PS i am not saying that an irs cant be made to work . Its just that no one in the UK kit industry has done one as yet that is of any use Except the
first of the westfield irs setup done by Jenvy.
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TimC
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| posted on 2/9/07 at 06:35 PM |
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quote:
Originally posted by Avoneer
quote:
Originally posted by TimC
Matt @ Procomp must be having a day away from the PC!
Nope - i've been keeping him busy on U2U about trailing arm bushes as I value his opinion and experience as a racer etc.
Pat...
You and me both mate - can't speak highly enough about Procomp.
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t.j.
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| posted on 2/9/07 at 07:32 PM |
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quote:
Originally posted by craig1410
quote:
Originally posted by t.j.
The avon didn't have a good setup.
As they give positive camber in drop. And you need negative.
I hope mine will drive nicely as i followed the pricipals as good as possible.
Grtz
Not sure if I'm misunderstanding you here but I would want positive camber on drop myself.
When cornering, the loaded side (outside) would compress and should gain a bit of dynamic negative camber to compensate for body roll while the
unloaded, inside wheel should gain dynamic positive camber. I don't know why you would want the unloaded (dropping) wheel to gain negative
camber as it would be tilting the wheel in ths same direction as the body roll and would result in just the inside shoulder of the tyre contacting the
ground.
Of course when I say positive camber I'm not sure that it would actually end up with net positive camber as you would start off with static
negative camber normally and the dynamic positive camber on drop might not be enough to counteract the static negative camber at ride height.
HTH,
Craig.
Sorry, my fault.
As the inner top wishbone brackets are higher that the top off the rear-upright pick-up there is positive camber gain as that wheel will be loaded at
cornering. So your negative camber which is needed is not getting more at cornering but less due the positive camber-gain.
I replaced the top brackets lower and made a new upright, so that my roll-centre and camber-gain is following the book pricipals.
I ment with droop, dropping the car. Sorry
So droop is lifting the car and compression is pushing the car down?
BTW: Wheel alligment? it is one big compromise!
Grtz
[Edited on 2/9/07 by t.j.]
Please feel free to correct my bad English, i'm still learning. Your Dutch is awfull! :-)
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ChrisGamlin
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| posted on 2/9/07 at 08:06 PM |
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quote:
Originally posted by t.j.
So droop is lifting the car and compression is pushing the car down?
When talking about droop and compression, what's being referred to is the wheel / damper, not the chassis hence droop = raising of the chassis
and compression is lowering the chassis towards the ground.
The easiest way to think about it is if you jumped off a hump back bridge, the wheel / suspension goes to maximum droop when you take off whilst in
mid-air, and goes into compression when you land.
[Edited on 2/9/07 by ChrisGamlin]
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Bob C
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| posted on 2/9/07 at 09:47 PM |
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Some one had better make the case for IRS.... OK I had to do a bit of homework when I designed mine, but fabrication and setup is really no big deal,
no big deal at all.
You don't get the benefit of IRS in lap times because tracks are smooth and the setup is heavier than live axle. Where you win is out on real
roads with potholes & knackered tarmac. Here, a correctly setup live axle will spend a lot of time with the wheels in the air and you'll
soon suffer from compressed vertebrae!
The only part of my build I sort of tried hard with was to get unsprung weight down. I measured it using bathroom scales with the spring out -
it's 31kg on every corner, front and back. The up side of this is that I am able to run with 125lb/in springs at the rear.
I make no claims for the out & out performance of the thing - I do know it's nice & comfy!! I expect it would corner better than a live
axle setup on a poor surface but have no proof.
Bob
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craig1410
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| posted on 2/9/07 at 11:00 PM |
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quote:
Originally posted by t.j.
Sorry, my fault.
As the inner top wishbone brackets are higher that the top off the rear-upright pick-up there is positive camber gain as that wheel will be loaded at
cornering. So your negative camber which is needed is not getting more at cornering but less due the positive camber-gain.
I replaced the top brackets lower and made a new upright, so that my roll-centre and camber-gain is following the book pricipals.
I ment with droop, dropping the car. Sorry
So droop is lifting the car and compression is pushing the car down?
BTW: Wheel alligment? it is one big compromise!
Grtz
[Edited on 2/9/07 by t.j.]
Fair enough, when you said drop I assumed you mean't droop. Either way the Avon suspension design seems pretty sus' to me! I'm sure
this has been discussed before but I didn't realise it was so bad until now. I'm fully aware that the "ideal" unequal length
wishbone design is with the lower wishbone level at ride height and the upper one running down ffrom upright to chassis pickup.
For my de-dion I have designed in a little bit of static negative camber and a little bit of static toe-in. Hopefully these will give me good traction
and stability without excessive tyre wear. I should find out shortly...
Cheers,
Craig.
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Avoneer
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| posted on 2/9/07 at 11:34 PM |
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That's the thing though - I find my live axel and hard GRP seats much smoother and comfier than the IRS on the Avon which had comfy Richfield
seats.
Might be my age???
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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craig1410
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| posted on 2/9/07 at 11:44 PM |
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I'm not sure that it is as simple as, "IRS is comfy" and "live axle is hard". I think it all depends on spring and
damper settings. I've done the calculations in the Allan Staniforth book on race car suspension design and my GTS Tuning spring/damper sets with
275lb front and 175lb rear springs are very much toward the firmly sprung end of the scale. I'm also using rod-ends at the rear and nylon bushes
at the front so I fully expect to lose my fillings every trip! Seriously though, I didn't build this car to cruise through the Alps, I built it
to blast through the Scottish country roads with my teeth gritted. Who cares if it's harsh over the bumps!!
Craig.
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Avoneer
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| posted on 3/9/07 at 06:34 AM |
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They were both set up lcost style though without any engineering type help and on that gorunds, that's all I have to base the differences on.
Pat...
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However a large number of electrons were terribly inconvenienced.
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procomp
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| posted on 3/9/07 at 07:14 AM |
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Hi a well setup live axle will run with 120lb - 140lb springs.
And with the correct dampers for this setup ( wich no damper manufacturer offers off the shelf) you will be able to obtain virtually as good a ride on
the roads as you will with the irs.
Given that 50% of kitcars are driving around with dampers that are just not valved correctly for them in the first place kinda puts thing into
perspective. Unlike in the USA where they take thier dampers verry seriously. Verry few down at kitcar level in the UK even give them a second
thought they just order them and fit them. No balancing or checking or even finding if they are even remotley valved correctly. Its complete madness
considering we are running light weight cars where the damper plays such an important part of the package.
cheers matt
Ps sorry that turned into a rant again
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