I seem to remember some discussion a while ago on whether to go harder or softer on the roll bar setting to reduce understeer. Well I bumped into Alistar McQueen (who my car calls daddy) at Donnington and asked him. He says… softer. I guessed he’d know!
I didn’t get a chance to try it out. May be next trackday.
Ian
I await Lord Scuffham’s response to this one
Over to you Simon
Ah Ha !
This question could be interesting
Al the “books” say a softer front roll bar means less under steer.
The other thing is TOE - if you have toe IN it will tend to not so good to turn in - we need Toe out and maybe a little more than the “book” tells you - but then you run the risk of straight line instability a bit.
I think Simon will tell you that a stiffer anti roll bar works best on an Elise/Exige …
Best thing to do ? - Experiment
I have Nitrons 400 rear 325 front and found stiff setting works best so far ( on the track ) with relative standard geometry - but now I’m trying to work out if 12 clicks all round is a bit too harsh !
Not about to get into a [censored] fight on this one.
All I will say is from playing, the stiffer the ARB, the less understeer.
I know this flys in the face of all the books, but, that’s how it is.
If you get to the point where you have as stiff a ARB as you can get, then start raising the front spring/damper rates.
be awaire that too much damping will give less grip, don’t try and use the dampers to make up for lack of spring rate, it just does’nt work, you end up with a car that will turn-in, then spin out of big corners.
Why doesn’t the Exige have a rear ARB? - from ol’ F Ford days IIRC - rear ABS was used for the fine tuning, whilst front was used for major adjustments for O/S & U/S? - my M100 has F & R…
Simon,
there are a couple of people that run with rear ARB’s.
I have tried to get one to work, but it seemed to have some very undesirable effects, (to be fair, I probably should have spend more time working on it though).
Main thing to remeber though is that it’s the springs that hold the car up, not the ARB’s or dampers, they just fine-tune the transient charicteristics.
Is there more chance that a rear ARB will tend to lift a wheel and then you start to need an LSD etc etc ??
Whereas I get the best results (for a lap, not individual corners) with the standard ARB at full soft (but not disconnected).
Depends on spring rates and ride height, and your cornering technique.
Best way as always is to try different settings yourself…
Cheers
Is there more chance that a rear ARB will tend to lift a wheel and then you start to need an LSD etc etc ??
Yes, but an LSD woun’t do you much good when a wheel is in the air…
A locker would, but that will have some very undesirable side effects…
The problem I had with a rear ARB is that it worked fine right up to the point where the tyres start to drift, then it would snap rather that drift, normally provoked by the un-loaded wheel going over an undulation (like the inside kerb)
Resurrencting this thread I think I may have an explanation for why a stiffer anti roll bar may actually reduce understeer.
Not claiming the credit, but just read something in Allan Stanniforth’s excellent ‘competition Car Suspension’…
He says that modern tyres are so good that sometimes they are not used to their maximum efficiency, and sometimes adding weight transfer to the outside front wheel by use of a stiffer anti roll bar loads up the tyre causing it to run hotter and get a better contact patch shape, and hence better grip and LESS understeer.
Thats Scuffhams explanation too.
Thats Scuffhams explanation too.
Doesn’t make it correct though!
Don’t expect simple answers to complicated problems…
In steady state cornering, given a stable platform, the end of a car with the softest wheel frequencies will have the most grip. This means that the likelyhood is that steady state understeer can be alleviated by fitting a softer ARB.
It’s pretty rare that a car is in a steady state around a track or on the road though. This is where the problems start. Having overly high wheel frequencies is only one of many causes of understeer and to cure a handling problem first you have to work out why it’d happening.
Simon believes, and I’m sure he will be along to correct me I get this wrong, that the front wheels on the Elise fight each other to cause understeer. His way to solve this is to unload the inside tyre by fitting a big ARB so the outside tyre does the work. Having driven a car that he has set up I can definately say that his thinking works. It’s not the only way to cure the problem and may not be the best but it works.
I wouldn’t suggest a Scuffham set up for everyone though as he likes his cars to be very good turn in at the expence of stability.
Personally, I’m going for a soft ARB to start with and will go stiffer if I need to. I want a more stable car than Simon would like because I think it will alow me to spend more time with my right foot on the floor and this nearly always translates to good lap times. A bit of mid corner understeer is a good thing because it means the rear tyres have some grip left in them for acceleration.
His way to solve this is to unload the inside tyre by fitting a big ARB so the outside tyre does the work.
Hang on a sec…
Doens’t a stiffer ARB mean there’s less roll therefore the inside tyre is doing more work than if the car had no ARB at all surely?
The ARB is pushed down but the car, then then levers the otherside down meaning the inside tyres are stuck on the gound more…
Or have I got pished thinking again???
When you stiffen the anti roll bar it transfers more weight from the inside front to the outside front AND it transfers more weight from the rear to the front outside…
Hard to understand but here’s an analogy…
Imagine four blokes are carrying a coffin, and one softens his lifting a bit - you can imagine that weight transfers onto the other guys who are still ‘hard’ !!! It’s a bit like that…
Mark - when the outside wheel is in bump the ARB is trying to lift up the inside wheel as the ARB is in torsion. Roll is reduced but the load on the inside wheel is reduced also.
Ah I see! Thanks guys
Always learning more!
I’ll add to my original comment now I’ve more time.
The problem with a number of set ups it the reliance on a ARB to work as a spring during cornering. By limiting the roll angles by springs means that you will reduce the requirement to run very stiff ARB’s, also by running a higher wheel rate you have to run a stiffer ARB otherwise the ARB rate will be a small factor and have almost no effect. Therefore the decision to run a 2x or 3x stiffer bar is affected by the springs to decide to run.
There are a number of additional factors which need to be taken into account, primarily the actual driving to be carried out. On a road car a very stiff ARB can be uncomfortable as it will induce something known as Roll-Rock which is the sideways movement of the head, which helps make people sick!
But on our cars where handling is more important we need to understand the driving style as well as where. By going stiff at the front then you will improve the turn in with static toe out as it loads up the outer wheel less than a softer set-up getting more turn-in response, however this can be to the detrement of rear grip. If there are lots of high speed bends, then you are into steady state to a certain extent and this set-up can induce high speed understeer, this is a problem if you have a lot less roll stiffness at the rear. You may end up with more initial bite, but this will soon disappear.
I’ve countered this by running stiffer springs (again it is possible to go too stiff) and std LSS ARB at it’s stiffest position, but if I was running softer springs (like I was originally on the LSS) then I wouldn’t use the stiffest setting as when I tried this I ended up with loads of understeer. By running a slightly softer set up then the very initial turn in is slightly reduced due to roll and weight transfer, by removing some (or all) of the toe out it is possible to counter this. (I run parallel at the front). This is because as you turn into a bend the outer wheel which will suddenly load up is probably only just getting beyond the straight ahead position and therefore wants to push forward instead of following the direction the steering wheel (or driver) is expecting, remember the front bumpsteer goes towards toe out as well, so that outer wheel wants to turn the wrong way the further into bump it goes.
There is too much reliance on a single factor, like springs or ARB (althouigh in effect the ARB is just a spring), or geo settings, it’s not very common for people to take all factors into account. I see too many people fitting a stiffer bar because someone says so, then someone elses Geo setting as they like it, the spring and dampers because someone else says they are great, and bumpsteer, roll steer, roll camber, etc are quietly forgotten about.
If I remember I’ll dig out some graphs of the Elise suspension as measured on the K&C rig at MIRA and post them up.
There you go, a logical explanation.
I love it when people talk with their brains!
Resurrencting this thread…
Blime mike, that dig up was a bit of history!
Clearly too much time on your hands at the moment!
Ian