simon redshaw Posted January 2, 2008 Share Posted January 2, 2008 Can anyone explain the true meaning of: Understeer and Oversteer relating to a Caterham? many an experienced blatter talks freely about the terms under and oversteer. This is impressive but a few do not fully understand the phenomenon and suggest we are not truelly understanding how to improve the handling of our cars as effectively as others! Simon7R Link to comment Share on other sites More sharing options...
Gambo Posted January 2, 2008 Share Posted January 2, 2008 Understeer is a term for a car handling condition in which during cornering the circular path of the vehicle's motion is of a greater radius than the circle indicated by the direction its wheels are pointed. The effect is opposite to that of oversteer. In simpler words understeer is the condition in which the front tires don't follow the trajectory the driver is trying to impose while taking the corner, instead following a more straight line trajectory. Understeer covers several different phenomena, in particular, there is a big difference between linear range understeer, typically between 0 and 0.4g, and limit handling understeer, which is at higher lateral accelerations, and is what racing drivers are talking about. The latter is also often referred to as pushing, plowing, or refusing to turn in. The car is referred to as being 'tight' because it is stable and far from wanting to spin. As with oversteer, understeer has a variety of sources such as mechanical traction, aerodynamics and suspension. Classically, understeer happens when the front tires have a reduction in traction during a cornering situation, thus causing the front-end of the vehicle to have less mechanical grip and become unable to follow the trajectory in the corner. Oversteer is a phenomenon that can occur in an automobile which is attempting to turn. The car is said to oversteer when the rear wheels do not track behind the front wheels but instead slide out toward the outside of the turn. Oversteer can throw the car into a spin. The effect is opposite to that of understeer. RED 2.0 HPC 230BHP here Link to comment Share on other sites More sharing options...
simon redshaw Posted January 2, 2008 Author Share Posted January 2, 2008 Thanks Gambo, Is under and oversteer a phenomenon of just hard cornering or could be experienced while driving along fast country lanes? How can you improve the front end to make sure that it is well planted onto the road/track? I am also wondering that suspension set up is critical up front and i need to invest in wide track dampers. I have std dampers on wide track. On the track this seems OK, but on the road, the suspesion travel is too small and the lowest point of the sump is 5 mm from the road! bump steer may well be an issue also! I have a nice set up of springs from Freestyle (front and back), but i am certain that the front dampers are at fault here! Rgds 😬 Simon7R Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted January 2, 2008 Share Posted January 2, 2008 5mm clearance ?????? Are you sure ....... FIVE mm !!!!! Sump would be wiped out by dead ants or small twigs !! Too low by far. 50mm (or 5cm) also too low ! 7 related photos Link to comment Share on other sites More sharing options...
CharlesElliott Posted January 2, 2008 Share Posted January 2, 2008 Understeer and oversteer can happen anytime the grip available is exceeded by the grip required. Obviously the idea is that this limit is not reachable every day, but it certainly can be. It's an oversimplification, but generally reducing understeer (i.e. increasing the proportion of grip available to the front wheels) increases oversteer. I have narrow track but haven't ever seen standard dampers on widetrack - it does sound like it could be an issue. Charles --- My SuperGraduates 2006 diary My SuperGraduates 2005 diary, My Caterham Academy 2004 build and race diary Link to comment Share on other sites More sharing options...
simon redshaw Posted January 2, 2008 Author Share Posted January 2, 2008 Sorry, 5cm, not mm! Great aerodynamics but a wrecked undercarriage! Cheers Simon Simon7R Link to comment Share on other sites More sharing options...
Area Representative Richard Price Posted January 2, 2008 Area Representative Share Posted January 2, 2008 I have std dampers on wide track Simon, If you have standard track dampers fitted with wide track wishbones, then you, potentially have an issue with bump stop hights! You'll not start to compress the bump stops until the sump or bell housing has already hit the ground. The bump stops are an essential part of a good suspension set up, allowing you to run soft enough springs to give good grip and ride, but the bump stops effectively add a progressive rate spring at the extent of bump. Link to comment Share on other sites More sharing options...
Willie. Posted January 2, 2008 Share Posted January 2, 2008 Simon, In the most basic/simple terms; Understeer is when you turn the wheel and the car goes straight...Oversteer is when you turn the wheel and the car goes sideways. Adjustable dampers are good for "tuning" the handling characteristics. Also, try adjusting the toe in/out. Willie Link to comment Share on other sites More sharing options...
ben7 Posted January 2, 2008 Share Posted January 2, 2008 No doubt people far more adept than I will explain it better or provide a more comprehensive response, but in simple terms either under or over steer occur when the tyres exceed their limit of adhesion. Putting the effects of weight transfer to one side for a moment, a standard tyre on a given road has a stickiness of say ‘x’. As soon as you ask the tyre to do more than ‘x’ it will spin/slide. For example, if you boot the throttle in 1st gear from a standing start, you’ll light up your rear tyres as you’re asking them to cope with more than they are able to – they exceed ‘x’. You also need to remember your basic physics and what velocity means. When you are cornering, your tyres are not only carrying your speed, they are also constantly accelerating around the corner. Simply put, you are asking them to do two things at the same time. As a result, you have to slow down to go around a corner to compensate. If you don’t, you’ll understeer off into the verge once you’ve exceeded ‘x’. As a driver you need to constantly assess where ‘x’ is. If it is wet for example, ‘x’ decreases, if you fit gripper tyres, ‘x’ increases. Your car’s set up e.g. camber, caster, toe, rake, tyre pressures etc all mechanically alter ‘x’. Things get decidedly more complicated when you take into account how the weight of your car alters as you drive it and the effect that this has on the way your car handles. You’ll notice that when you accelerate, the weight transfers to the rear and the nose of your car lifts and when you brake it moves to the front and your car dips. When you go around a corner the car will also lean. Oversteer is normally caused a combination of weight transfer and exceeding ‘x’. For example, if you approach a corner and brake heavily, the weight of the car will be at the front rather than the rear. If you then turn in to the corner whilst still breaking, the car will have less grip at the rear (‘x’ will be less as there is less weight on the rear wheels), and you’re likely to oversteer/spin. Similarly, if you are exiting a corner and still have a degree of turn on your steering wheel, then plant your foot on the accelerator, you’ll exceed ‘x’ because the car is trying to accelerate around the corner, accelerate out of the corner and has the outside rear tyre loaded up as the car will already be leaning on it. All of this means that you are likely to oversteer/spin. Lift off oversteer is basically when you’re going around a corner and lift off the accelerator, which results in less weight on the rear wheels, thus a reduction in ‘x’ and oversteer. The simple rule of thumb is to do a minimum number of things at the same time and as smoothly as possible. Get you’re braking and gear changing done before you enter a corner, ‘trail’ your throttle through a corner – i.e. use your throttle to maintain a constant speed through a corner to bed the car down, rather than driving around a corner with no throttle at all, and finally wind the steering off out of a corner as you smoothly apply the throttle. Once you’ve figured all of this out, you start worrying about all the other complicated techniques that Hugh and all of the racers on here talk about. Link to comment Share on other sites More sharing options...
SV Gary Posted January 2, 2008 Share Posted January 2, 2008 Can anyone recommend and good book on Driving Dynamics/Techniques? The lead dog always gets the best view. Link to comment Share on other sites More sharing options...
Casbar Posted January 2, 2008 Share Posted January 2, 2008 Car setup - Competion car suspension design, construction. tuning - Alan Staniforth - Haynes. Loads of setup info Race and Rally car source book - The guide to building or modifying a competition car - Allan Staniforth - Haynes. Not quite as good, but still ok Driving: The tecnique of Motor Racing - Piero Taruffi. -ISBN 0-8376-0228-9 Old book, but still relevant and loads of driving skills ie cornering, braking etc Edited by - Casbar on 2 Jan 2008 13:45:58 Link to comment Share on other sites More sharing options...
simon redshaw Posted January 2, 2008 Author Share Posted January 2, 2008 Brilliant help Thanks to all and will immediately change to longer dampers. Rgds Simon7R Link to comment Share on other sites More sharing options...
Pezky Posted January 2, 2008 Share Posted January 2, 2008 Understeer you see what you are going to hit, with oversteer you don't! Link to comment Share on other sites More sharing options...
Setok Posted January 2, 2008 Share Posted January 2, 2008 What would be the standard way to deal with normal understeer? I cannot adjust the height of the suspension, but I can adjust how hard it is. On a related issue if I have a fair bit of load in the car and I hit a harder bump on the road, the suspension can sometime hit its limits, which sounds a bit nasty. Would adjusting it to be harder be the right solution when carrying luggage? --- Kristoffer Lawson Link to comment Share on other sites More sharing options...
Paul McKenzie Posted January 2, 2008 Share Posted January 2, 2008 Simon, Have your Billies got extra circlip grooves cut in them?....if so you can move the lower platform to bring you into the correct ride height zones, you don't need new dampers, just give me a call if you want to talk, you've got my number Paul Link to comment Share on other sites More sharing options...
ben7 Posted January 3, 2008 Share Posted January 3, 2008 Simon, If you are currently experiencing understeer (once you've sorted the dampers), this is likely to be the size of the front arb you are using. The Freestyle set up runs much harder springs, making the front end less reliant on the arb than on a std set up. If you are still using the original (std thickish) arb, then this could well be the cause. I experienced similar problems myself. The solution (on advice from Freestyle) was to completely remove the front arb, which resolved the issue. If this is a tad extreme for you, it could well be worth moving to the skinniest arb you can get hold of. After that, follow Oppositelock's advice and toe out your wheels a little. Link to comment Share on other sites More sharing options...
neilg Posted January 3, 2008 Share Posted January 3, 2008 Understeer is when you you go into the gravel trap ( or hedge) nose cone first. Oversteer is when you go into it backwards , probably after spinning. 😬 😬 Oversteer is for men.....understeer is for complete girls!.....or so they say. Link to comment Share on other sites More sharing options...
simon redshaw Posted January 5, 2008 Author Share Posted January 5, 2008 Hi Paul, Good to hea from you. Actually i have Avo dampers from Freestyle, so i am wishing to discuss the matter in detail with them first. As the rear is also avo i do not wish to have to change all to Billstien, so will opt to get longer Avo's intead after advise from Fstyle. Cheers Simon Simon7R Link to comment Share on other sites More sharing options...
db Posted January 6, 2008 Share Posted January 6, 2008 Important to distinguish between under/oversteer and terminal under/oversteer. The terminal cases are the classic tail-out spin (into the hedge backwards) and won't turn (into the hedge forwards). Dynamically, they aren't that interesting - you have used up all the grip at one end of the car and the other end takes over. Front tyres winning (ie loss of traction at back) make you terminally oversteer and rear tyres winning for terminal understeer. All sorts of causes for terminal understeer, but most common are jerky and/or excessive steering inputs and excessive braking, as well as sudden or excessive power. Terminal oversteer similarly jerky steering inputs, excess or jerky application of power etc. Dynamic understeer and oversteer is a little more interesting (ie complicated) and defines the vehicle response to steering inputs during the normal grip phase of the tyres (ie nothing is squealing and noone is going into any hedge). It is primarily characterised by the weight distribution of the car and the suspension rates. As described earlier - it is about whether the car describes a tighter arc or wider arc than the ackermann steering angle would suggest -- ie l/r where l is the wheelbase and r is the radius of the turn. Most production cars understeer in the normal run of things. This is simply because it's safer to design cars that way for two good reasons:- i) oversteer cars have a critical speed above which you cannot steer them. ii) understeer works well in the vehicle/driver feedback loop as a damping mechanism HTH. My ... Preciousss! Link to comment Share on other sites More sharing options...
db Posted January 6, 2008 Share Posted January 6, 2008 What would be the standard way to deal with normal understeer? I cannot adjust the height of the suspension, but I can adjust how hard it is. Just think you want to be careful engineering out the understeer - neutral steer vehicles (at least the one that I know of) have reputations for being - shall we say - an acquired taste to handle. My ... Preciousss! Link to comment Share on other sites More sharing options...
Sheds Moderator Posted January 6, 2008 Share Posted January 6, 2008 OK, having got the terminology sorted, I'll add my 2p worth. Most non expert drivers, and I consider myself one, prefer for road use a car that understeers as it begins to approach the limit of adhesion. As stated elsewhere this gives you some warning that things are going to start getting a bit more challenging. If the back now steps out, you have had some prior information. I think part of the problem is that we are talking about steady state conditions, which seldom exist in a car. An expert driver who detects a bit of understeer may be skilled enough to say "tut" and either dial in a bit more lock or back off the power to even things up. He doesn't unsettle the car, so it retains a steady state. The rest of us, however, especially in a car as fast as a 7, may well say "ooer" and lift the accelerator. At this point you transfer weight to the front, which makes it stick and kills the understeer, but if you overdo it you can unstick the back end, causing it to come round rather quickly and spin the car if you are unlucky. This is lift off oversteer and a racer may set a car up to do this, but he's on a track. For this reason most road cars are set up so that you get a *bit* of understeer but lifting the accelerator mid-corner will kill it without bringing the tail round. Compare this with a 911 or a 1980s Skoda Estelle where there is no understeer, you push and push till the thing starts to slide, at this point if you panic and take your foot off mid-bend, you are going to spin, no question. Are you brave and skilful enough to be able to stay on the gas in all foreseeable road conditions? If not then you don't want a car with no understeer. Edited by - batteredoldsupersport on 6 Jan 2008 15:31:40 Link to comment Share on other sites More sharing options...
Setok Posted January 6, 2008 Share Posted January 6, 2008 I guess in my case I'm wondering if I have just a bit too much as I ran into it several times (not now in winter conditions as I'm taking it calmer). F.ex. the hairpin on the Hethel track after the longish straight and chicane. I was understeering every time. I've also experiences it in tight bends on normal roads when going at a fair pace. I'm sure an experienced driver could compensate, but for me it was just lifting the throttle to fairly mundane levels. I don't want anything dangerously unforgiving like the 911, but I'm also wondering what it would be like if it was just slightly tighter, and if tightening the suspension would do that. --- Kristoffer Lawson Link to comment Share on other sites More sharing options...
Graham Sewell Posted January 10, 2008 Share Posted January 10, 2008 One source of information is Don Palmers Createive Car Control Handbook. If you have the time/money, you can even get Don to show you on one of his training days. Expensive, but worth every penny. Cheers, Graham --- Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
MartinWoodham Posted January 11, 2008 Share Posted January 11, 2008 *arrowup*Don would point out the error in this: An expert driver who detects a bit of understeer may be skilled enough to say "tut" and either dial in a bit more lock... In many cases, dialling in more lock is the worst thing to do, you'll just understeer more. The reason for this is that tyre lateral grip has a peak at slip angles in the range 5-15%-ish. This means that understeer is usually caused when this peak slip angle has been exceeded, meaning that increasing the steering angle will worsen front end grip, whilst unwinding lock will bring the slip angle back to the peak grip point, increasing grip. This is highly counter-intuitive ie all instincts are to steer more in the face of dramatic understeer, but try it somewhere safe and I'll guarantee you'll have a 'eureka' moment. Do try to keep your clothes on! have a look at the 'understanding slip angles' section, especially the grip vs slip angle graph here for a more expert explanation, with pictures (which are really needed here!) And I'd highly recommend Don Palmer's course. I've muttered 'thanks Don' on many many occasions over the last few years, by no means all of them on the race track.... Martin supersported ex-Roadsports B Edited by - mwoodham on 11 Jan 2008 11:06:18 Link to comment Share on other sites More sharing options...
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