Reducing Understeer

[Steve Causey]

My car is 2005 ex-Academy.  It's running with the red bushed (5/8") front antiroll bar, no rear antiroll bar, no LSD, on Yoko A539's and it was flat-floored a few years ago.  I sprint the car and struggle with understeer on tight corners.  A friend who has driven a number of Caterhams thinks that the undertseer is excessive and has suggested that a rear antiroll bar together with more negative camber would help.

So my questions are:

1.  Do the experts on BC agree with this recommendation?

2.  If 'yes' how easy it is to fit a rear ARB.

3. Can anyone explain the physics behind the rear ARB reducing understeer?

4. In terms of 'more' negative camber I have no idea how much more and don't have any equipment to measure it anyway, so can anyone suggest an expert/firm relatively close to me in Essex that could help with this?

5. Can anyone suggest a good book that will help me understand the basics of suspension and vehicle dynamics?

Thanks in advance.

Steve

[robmar]

Hi Steve - from my understanding this is a great book to start with

http://www.amazon.co.uk/Competition-Car-Suspension-Practical-Handbook/dp/1844253287

(updated link to be the more up to date version of the book)

Rob

 

[7 wonders of the world]

forget a RARB,

Fit the orange FARB thin one

Assume your springs / dampers are stock items and in good order?

Tyres are no so old they handle like wood?

Corner weights in the right ball park

Rake 15-20

check caster, camer, toe

ALL checks to be carried out with the car on level ground and ballasted to normal weight,

In general terms the sofest end will gain the most grip, so keep it simple first.

[paul richards]

To reduce understeer the basics are:-

Stiffen rear - i.e add anti roll bar or fit stronger springs

OR

Soften front i.e. fit softer anti roll bar or weaker springs.

[Shaun_E]

I've always been told to add grip where required rather than reduce grip from the other end! How true/practical this is I have no idea. I know suspension is hugely complex and sometimes counter intuitive but the real world experience with Caterhams suggests that to increase grip at the front one or more of the following are required:
More rake (which probably reduces rear grip)
More negative camber
Toe Out

My (admittedly somewhat lardy) Duratec car has about 2.75deg negative camber, a fair bit of toe out (1mm I think but not sure what that translates to in angle) and 20mm rake and it turns in brilliantly. It's not too oversteery so I think the balance is pretty good although it can be a handful in the wet.

Bear in mind I'm on list 1B tyres so your A539s might behave differently. I should also say that a lot of toe out makes the car a bit twitchy on the road and it follows cambers/bumps a bit too much but you do get used to it.

[Pendennis]

Yep forget rear ARB.

The red front ARB maybe too stiff for the A539s as well as the front springs. But initially I would apply more camber based upon tight hairpins being a problem, try circa 2.5 neg

[Mavic82]

Don't mix springs and ARB, the ARB should be used to control roll not general stiffness.

i would certainly look at camber but also consider softer front springs. 

[oldbutnotslow]

I  agree with 7 wonders (you dont say if it was flat floored for you or a previous owner--- If it was a previous owner and they are not the same weight as you then it needs to be done again.)

Orange ARB and at least 1.5 degrees negative camber moving to 2 after you have tried it.

Its very simple to fit a rear ARB but do the other things first

Lastly and I know that its very simple but try differant tyre pressures starting from 18psi and then doing back to back comparrisons  move them by 2 lbs up and down

Only do one thing at a time otherwise you wont know what is causing the effect.

[Richard Price]

Steve,

When I ran list1a tyres, I ran narrow track, red front arb, standard springs and dampers, no rear arb, Max caster (4 washers behind the wishbones). 2.5degrees negative and zero toe, and about 15mm of rake.

However,  it's also possible that you're trying to take too much speed through the corners? Slowing down more often aids a good exit (as datalogging and my son taught me.......)

 

 

[Simon.Rogers]

Richard.

Having seen Steve at our teaching day at Curbs and worked hard I have to go with your last comment - Sorry Steve. 

Too fast in = too slow out!

[2GBR]

Very interesting thread with an informative ending which i would certainly agree with the possability of what is actually happening data logging is so so valuable. Actual instance = In qualifying in our R400 race car son is 1.4 secs faster per lap around Brands Indy circuit than father who is 34 yrs older by the way. We run a V-Box data logger so we play the data and father and son are totally like for like all around the circuit other than paddock hill bend, Father is 11mph faster going in but 22 mph slower at same point towards bottom of the hill, Result = 1.4secs, Actual race = father improved to 0.8sec.

If anyone would like a v-box send me a pm

[Pendennis]

Hi Gerry, often wondered if a logger would help me, would you mind email me some info please.

Happy New Year

Ian

[2GBR]

Hi Ian, All the very best to you and your family also, The fun part is to translate the data from a logger into faster times or laps etc. A bit like going on a long journey and beating your sat navs ETA just by driving better with anticipation and not necessarily faster in mph terms.

Expect incoming mail from brad@defineperformance.com who is fully up to speed with the V-Box system and data interpretation

[DJ.]

I've been reluctant to make suggestions as I've never competed in a car.

My experience that might be relevent though is at a tight airfield trackday circuit.I was driving a Lotus Elan Sprint which I had always considered had superb handling. However, on that day I was really struggling with understeer. It didn't matter how slow I turned in, the front would wash out.

I have 20 minutes tuition, and was taught how to trail brake into the slow corners. The difference was incredible, suddenly I was turning into corners 10 mph faster with no understeer and no changes to the car even to tyre pressures. It was a real eye opener to me.

I hope this is of interest.

Duncan

[2GBR]

Duncan totally agree trail braking to the correct amount will help to set a car up into a corner nicely, Just like everyone and everything mentioned above if all is set up to the best balance for car and driver then as we all know it will be a fast lap / run without even looking or feeling fast it will just be fast

 

 

[Gregs79]

Some intersting thoughts. Book purchased. :-)

[Graham Howard]

Hi Steve

I think the thoughts at looking at driving style are right.  Several  years ago I had a session with Don Palmer. Whilst I have not always been able to put into practice what he taught, he does instill some thoughts which give an understanding of car behaviour in a corner. 

It is easy to forget that the tyre is flexible so when you turn the steering the first thing that happens is that the tyre deforms and will not grip until it has settled into its deformed shape. So if you turn into a corner very quickly you are bound to get initial understeer as the outer front tyre flexes. Being more gentle with the initial turn will help.

During my session with Don Palmer he got me to drive through a slalom marked out with cones and the car was under steering.  I was having to lift off to get through. He then drove my car, power sliding and playing with the brakes. His question was,  why does your car understeer and mine oversteer? Obviously it was just the driver!

Don has a book on all this, available from Amazon.  I am not sure if he still does tuition,  but you may find this is a better way to spend your money than on the car.

Graham

 

 

 

[Pendennis]

Very true, but the tyre shape is also influenced by geometry as well as force. So if the geometry is wrong the tyre would not fulfil its contact potential thus not provide optimum grip which would be available.

Steve could be entering corners too hot, but if the car is not set to obtain optimum grip levels from the tyres being used, your never know. The subject of car handling is vast, we all have opinions that are valid. Causes of poor handling could be due to many many reasons as well as driver error but if you were me I'd look at both.

[andrew mckay]

Data logging was mentioned. I know a few folk use cheaper alternatives such as a fast responding Bluetooth gps fastened to the car and freeware such as a Race Chrono running on a phone or tablet in the car. Perhaps there is a potential LowFlying article in there somewhere. 

The more expensive vbox with predictive lapping will let you experiment on the offending corner and see the results as a delta velocity or time as you come out of the bend in real time via the display. They're not cheap whereas the alternative option just means you check in the paddock as long as you remember what did and on what lap.

I hope to try the cheaper version this year. 

[Steve Causey]

Firstly, thanks to everyone for your contributions.

I've realised that I should have been more specific in the original post in that the issue is power-on understeer.  The car seems to turn in fairly well but if I go anywhere near the accelerator later in the corner the front starts to run wide.

The consensus seems to be to increase the negative camber so that's what I'll do.  I'll also take the opportunity to have the rake, corner weight, etc rechecked.  The previous flat floor was done for me but it was a while ago now.  Once that's done I'll experiment with the softer front ARB.

Oh and I've bought the book - thanks for the tip Rob.

Lastly, I have two responses to Mr Rogers comments re my driving skills.  Firstly, it's not often that I'm 'accused' of carrying too much speed, usually the reverse is true, so thanks for that!  Secondly, obviously my skills are superb so it follows that as I'm slower than the rest of the Class there must be something wrong with the car!  

Seriously though, the 'slow in fast out' comments are valid but I'm hoping increasing the negative camber etc. will help as well.

Thanks again to everyone.

Steve

 

 

 

[Simon.Rogers]

Steve - I feel like I have been  with you now 

Seriously now - not sure who is due to attend the various days of tuition/practice comming up at Curbs.  I know there are a few I would be happy to attend if enough people wanted me to with my scales and spanners.

I suggested to Curborough last year they could benefit from a "Flat Floor" car set up area which may well have been completed by now and Meteor will be the long term sponsor of.

It will be behind the sign on office and hope fully with aroof also 

It may be opportune to let someone else have a go in your car just to see if anything is very ammis 

[Pendennis]

Are you sure you don't have an LSD?

[Steve Causey]

Simon,  Thanks for the offer re Curborough but, unfortunately, I'm not booked on any of the practice days there, although I am doing teh day at Bluton organsied by Graham Howard.  I think Andy McKay has organsied one of the Curborough days so it might be worth contacting teh participamnts through him.

Pendennis, pretty sure I don't have an LSD.  I've had the car from new and thee original invoice states 'non LSD' for the axle.  Unless, of course, Caterham made a mistake and gave me an LSD....