306 replies to this topic

[Exmantaa]

(Now where's my popcorn emoticon..? )

 

Interestingly, the Exige V6 has a rear ARB... Still rear wheel drive and basically the same chassis set-up...

But I read an interesting article about what was changed for the V6 and the interesting part was said about the V6 rear subframe being loads stiffer so the car now properly rolled along the centre axis. Now they did not need to go that stiff in springs and could add a rear ARB to control roll...

(something about the line-4 subframe flexing and the Elise/Exige rolling diagonally, therefore the need for stiff springs and dampers to control that. Will look for a link.)

 

The VX subframe seems loads weaker than the S2-Toyota frame (no cross beam) and not sure how the S1 subframe compares? Only know the V6 frame is loads heavier (45kg or so?) than ours (~24kg) and heavily braced and reinforced...

Edited by Exmantaa, 12 October 2015 - 09:10 PM.

[The Batman]

I was looking at a v6 subframe a couple of weeks ago. It's completely different and looks ALOT stronger

[Scuffers]

The v6 exige is another 400+kg heavier, making any comparison meaningless.

[Exmantaa]

So if my car has a heavy rear end, a rear ARB can be OK then? 

 

(some constructive talk what and why would REALLY help here...  )

[alexb]

***Theory warning on***

 

Assuming you have made your choice of springs, whatever that's based on. Without ARB, back or front, there will be a certain roll at the back and at the front. Just determined by the rates of the springs. Roll gradient, the amount of roll in degrees per g, will be different at the back and at the front, determined by weight distribution, spring rate, track etc. Adding an ARB does two things, it decreases the roll gradient and it gives you the opportunity to balance the roll back to front. 

 

As an example, if you have 400 lbs/inch front and 550 at the back, the roll rate distribution is about 65% at the back, 35% front. Guideline is that the front should be about 5% more than the static weight distribution. For my car that's about 60% back, 40% front. So in this case I should add a front ARB and get the 35% to about 45%. That's a 1" ARB on setting 1 or 2 (with 1 the weakest setting). With that set up the total roll gradient of the car is still over 2 degrees/g. If I want to decrease that any further, I have to go to higher rate springs, or add an ARB at the back and balance that with the front.

 

***theory warning off***

[Scuffers]

in theory, that's all good stuff, the hard bit is actually relating it to sprint and ARB rates on the VX.

 

to put this into context, the EP1" ARB at it's stiffest is still only some ~230lb, and then remember that it;s connected to the wishbone on ~1.5 ratio to the wheel (different from the Spring&damper).

 

This is one of the reasons people reading books that say too stiff an ARB make a car understeer, and then try and relate this to the Elise/VX, well, yes the book is not wrong per say, but too stiff in the context of the VX would need a 2"+ think ARB at least, and even if you made one, the chassis mounts would flex rather than the ARB!

 

At the end of the day, you need to add as much anti-roll to the front undriven wheels before trying to transfer any load across the rear, as the last thing you want to do is reduce the weight on the unloaded rear, once the front unloaded is off the ground, then by all means using some kind of rear ARB may help, BUT then you have to account for this in the dynamics of how it's going to unload when presented with a less than perfect road surface, as any bump on the unloaded side is now going to get transferred to the loaded wheel, which if on the limits of grip will likely be enough to make it let go.

 

this is why whenever people have put rear ARB's on the Elise, they end up either running it at extremely low rates or disconnecting it. (and yes, been there, tried that!)

[CHILL Gone DUTCH]

Love a bit of front wheel in the air

[ArticMonkey]

Scuffers is the front wheel off the ground (of my car) any sign of suspension tweaks needed? Or is this totally fine and an inherent action from running a 1" roll bar?

[smiley]

Isn't wheel off the ground also poor droop?

 

[Captain Vimes]

It looks like the surface dips there so maybe not a suspension issue and more a feature of the track/airfield?

 

I'd be surprised if you got that kind of undulation on a 'normal' circuit.

[Captain Vimes]

...

 

This is one of the reasons people reading books that say too stiff an ARB make a car understeer, and then try and relate this to the Elise/VX, well, yes the book is not wrong per say, but too stiff in the context of the VX would need a 2"+ think ARB at least, and even if you made one, the chassis mounts would flex rather than the ARB!

 

...

 

My experience of adding a 1" ARB to my car is that it has increased understeer. Here's a lap comparison before and after adding the ARB. The extra steering lock needed is clearly visible:

 

 

On the plus side, tyre wear has improved greatly..

[smiley]

Interesting movie Vimes.

It cured my appetite for a shiny 1"

[ArticMonkey]

It looks like the surface dips there so maybe not a suspension issue and more a feature of the track/airfield?   I'd be surprised if you got that kind of undulation on a 'normal' circuit.

Yes the track dips quite a bit at that point. I still had the wheel 2" off the ground at Bedford on Saturday though.

[Rosssco]

 

...

 

This is one of the reasons people reading books that say too stiff an ARB make a car understeer, and then try and relate this to the Elise/VX, well, yes the book is not wrong per say, but too stiff in the context of the VX would need a 2"+ think ARB at least, and even if you made one, the chassis mounts would flex rather than the ARB!

 

...

 

My experience of adding a 1" ARB to my car is that it has increased understeer. Here's a lap comparison before and after adding the ARB. The extra steering lock needed is clearly visible:

 

On the plus side, tyre wear has improved greatly..

 

 

So if you are getting understeer through a bend, but less tyre wear, does that not indicate you need a geometry change to account for the added stiffness of the ARB?

[CHILL Gone DUTCH]

Captain How old were your RSRs in each video As once you lose the byte on RSRs you may as well chuck them in the bin

[Captain Vimes]

 

 

...

 

This is one of the reasons people reading books that say too stiff an ARB make a car understeer, and then try and relate this to the Elise/VX, well, yes the book is not wrong per say, but too stiff in the context of the VX would need a 2"+ think ARB at least, and even if you made one, the chassis mounts would flex rather than the ARB!

 

...

 

My experience of adding a 1" ARB to my car is that it has increased understeer. Here's a lap comparison before and after adding the ARB. The extra steering lock needed is clearly visible:

 

On the plus side, tyre wear has improved greatly..

 

 

So if you are getting understeer through a bend, but less tyre wear, does that not indicate you need a geometry change to account for the added stiffness of the ARB?

 

 

The tyre wear was caused by the car rolling too much in the corners or not running enough negative camber to account for the roll depending on how you look at it - the front camber was already pretty much maxed out though. The ARB has helped reduce roll and therefore tyre wear but has also moved the balance towards understeer. The way I see it, the ARB needs to be matched to the springs. At present it's too stiff for my springs, which isn't quite what scuffers said.

 

Captain How old were your RSRs in each video As once you lose the byte on RSRs you may as well chuck them in the bin

 

RSR's were more worn on the video pre ARB. The current set are still reasonably fresh. I have changed from the 205/50 to the 205/45 (and reset suspension height) but very little other differences apart from the ARB.

[Matthew Bentley Racing Ltd]

Don't be too worried about lifting a front wheel. As Simon as explained, you always want an un-driven wheel to lift first. So you also set the bump/droop levels so that the front will run out of droop first.

 

Edited by Matthew Bentley Racing Ltd, 14 October 2015 - 09:32 PM.

[CHILL Gone DUTCH]

I now want my unloaded front wheel to cock up

[Matthew Bentley Racing Ltd]

Easy:

 

http://www.metals4u...._wtVBoC_5Tw_wcB

[ArticMonkey]

So my droop is fine then Matt? I tend to get understeer but have learned to let off on the power for a split second to gain some better turn in grip. With the power my engine now runs I think I'd benefit from some stiffer springs on the rear at some point. I think I'm on 650lbs with helpers

Edited by ArticMonkey, 14 October 2015 - 09:39 PM.