Maximizing Speed in a Corner

maximising speed in a corner

Recently I had a superb day out at Silverstone in my Prosport 3000 Spyder. After some flaffing about I managed to download the data from the car onto my laptop and began to analyse what I had been up to. This has lead me to thinking about how I can see if I am maximising my coner speed.

The data recorded includes lateral and longitudinal G forces and from these numbers a combined G force is also displayable.

If I can corner on the limit at say 70 mph on a tight corner and pull 1.5G laterally (I am making these numbers up for now) but on a 130 mph corner the G reading is down to 1.3G, can I go faster in the 130 mph corner to take the G reading up to 1.5G without going over the limit, assuming the car can go faster in the corner?

I mentioned combined G as obviously you get some speed scrubbed off by cornering which decelerates you or you could actually be accelerating which will also help fling you off the track. Therefore instead of lateral G as the benchmark, I believe I should be using combined G readings to see if I am at my cornering limit.

If this theory is correct, then the target is to get as many corners as possible to the 1.5G limit to show that I have maximised my corner speed. If a reading is lower than 1.5G then I should be able to go faster in that corner without losing it.

Any comments?

Only two comments.

First, be careful out there!

Second, your ability to generate the same cornering force at 130 mph as you do at 70 mph would require that no aerodynamic lift be present. If you are actually making downforce at speed, then you should be able to generate more cornering force at higher speed.

I would be careful using combined G's...

That's the traction circle you are talking about - and ideally, a tire would provide a given amount of traction in any one direction. However, tires behave differently laterally then they do longitudinally (mostly because of sidewall and related asymmetry issues). All because you decrease longitudinal G's at a higher speed, I don't think you can gain them all back with lateral G's to keep the total constant. Milliken, in his great book Race Car Vehicle Dynamics, talks about this in more detail. I tried putting in html code with a link to amazon, but it didn't work. Here's the link text:

http://www.amazon.com/gp/product/15...104-1527816-1363128?s=books&v=glance&n=283155

This is an interesting topic. I have sometimes wondered whether the grip properties of the tyres themselves change with speed. I remember reading a tyre manufacturer’s literature explaining that grip was not purely a function of the coefficient of friction, but also of the slip properties of the tyre. According to this literature, a tyre does not slip across the road surface at a constant rate, but instead does a grip-release-grip-release dance (which is what causes a tyre to screech), the lower the frequency of this dance, the greater the grip. On that basis, a fast spinning tyre would reduce the time that a section of the tyre spends on the contact patch, and therefore might “release” more often than would be the case of a slow spinning tyre. A check I guess would be to see if a road tyre screeches at a higher frequency in a high speed corner compared to a low speed corner. Any thoughts?

Malcom

Do it the easy way

Get the data logs from the last owner who ran it in the competitions.

You then have data to aim at and also know how cnsistant the tyres etc. are.

Or give the car to "the Stig" for a couple of laps and then see what data he gets

Best thig just go, drive and have FUN

Ian

The car in question is pictured at the bottom of this article I wrote about my experiences at VIR with Ron last year. I tried making a link but failed so if you look at the thread in The Track section of the forum about Viginia International Raceway Adventures with RTP Racing, and either read it or scroll down to the last page, the picture is there.

As you can see it has front splitters and canard wings, a 6 ft rear wing plus 2 gurney flaps, one adjustable. The underside of the car is completely flat. But no venturi or skirts.

The tyres are 17 inch radial slicks ie modern racing tyres. The car is bigger than a GT40, both width and lenght but weighs over 400 KG less!

I am sure that grip is not a purely linear action but will vary with different speeds and corner radii. BUt by how much is it likely to change? Enough for my G force analysis suggestion to be invalid? At our level of motorsport can these vairances be ignored for a simple driver aid diagnostic? Or as Mark W says, the faster this car goes the more downforce I get therefore I should be able to exceed the 1.5G figure?

What I do know is that driving this car is a blast! A while back, I used to run slicks on my GTD and that raised grip levels massively. Especially under braking. What I need to do is get used to the feel of the higher G force corners so that I can feel when the car is approaching its limit. It is a new feeling at the moment so one I have to gently build up to. The same would apply to someone going out in thier GT40 replica for the first time I guess.

The first go I had in this car was in the torrential rain and it wasn't huge fun but I needed to check all the gears in the gearbox were there and worked. Even then the G forces recorded on full wets read up to 1.45G! That was on only my 3rd lap! In the dry my first thought was that the G forces would be much higher than this but so far my highest recorded cornering G force is 1.63G. So far. So maybe that implies the wings etc on the car do give quite a lot of downforce.

If you read up about trail braking, a tyre only has 100% grip available to it. If you go over 100% you are skidding or sliding or wheelspinning. Under and you are not at the maximum grip level of the tyre. It is up to the driver to use this available amount of grip how they want to ie for acceleration, deceleration or cornering, or a combination of any of these three actions. There are statements out there that say that optimum acceleration requires some slip of the tyre and likewise under braking optimum braking is acheived with a different road speed to wheel rotation speed.

The other interesting aspect of my first couple of runs out with the car relate to the camber of the tyres. It runs 2.5 degrees negative at the front and 2 degrees negative at the rear. These high numbers are needed to generate tyre heat I am told. I need to measure the tyre temps to see if they are equal across the tyres but so far haven't been organised enough yet to do so. However just looking at the tyre wear patterns and marble pick up show that I am not leaning enough on the tyres in corners.

I guess the only true answer is to keep on being out there drving the car and learning the limit. Fortunately that is also the fun way of findining out the answer to my original question!

I believe the traction circle as explained well by you guys gives the correct information. As we know traction is traded between braking, accelerating and lateral grip. So you wouldn't want to maintain heavy braking when you turn in to a corner for example.I've had plenty of 'oh shit' moments with the forty now and some have been caused by track surface changes or bad suspension changes, while others simply by me. I will warn you guys to watch out for one in particular. I was watching the latest "Top Gear" last night and the Stig went off the track while driving the latest Koenesigg (I think that's how you spell it). whilst taking a corner the car broke into oversteer, which he quickly corrected with opposite lock but the car ran off the track and he couldn't recover. I believe this is why oversteer is so dangerous as after the steering correction that counters it, your line is heading off the track and you have no time or track left to do anything but either slam on the brakes or or hold the steering straight, while hoping it will stop before the solid bits arrive.The Stig ran off onto grass and you have to keep steering input to a minimum when on grass, and it can take a long time to stop, as even with the brakes locked grass cannot provide the traction asphalt does. Our cars with mid engines do have a high cornering capability but there is a limit and race drivers have to flirt with it don't they!

Ross

Actually Ross, I think with grossly excessive speed what you say may be correct but the situation would be no better with understeer, regardless of where the front wheels are pointing you are going to run out of track. However I didn't see the Top Gear program. At speeds that are less excessive, in oversteer the front wheels tend to follow the direction of the track, the advantage of understeer in something like a '40 though IMHO is that you can get the power on sooner coming out of a corner thus counteracting the understeer. It's better to have full throttle to combat the understeer than part throttle to combat the oversteer. Generally the less time you spend on the brakes and the more time you spend with the loud pedal hard to the wood the better. Just my 2cents.

Regards,

Russ

I saw that Top Gear too. A big off for the Stig but I thought the owners of the Koenesigg were top sports in saying they would come back having implemented Stigs suggested mod! A sodding great rear wing! Once they had retreived that tyre from the front of the car!

Understeer is safer for road users and oversteer is for Rally wannabe's. Circuit drivers aim for (but don't always get it) a balance that reduces both to the minimum. A true equal four wheel drift is a cool thing to watch and satisfying to occaisionally manage to pull off. But not so easy when on slicks compared to old cross ply racing tyres.

Another big difference between this car and my GTD is the front/rear weight bias. My GTD is roughly 45/55 but the Prosport is 40/60. It is the GTD however that is tail happy in corners and once gone, it is GONE. A lot of this is down to a high engine position in the chassis but with the engine in the Prosport being dry sumped and race engineered from day one it is very low in the chassis.

Ian, I am in contact with William Hewland who raced the car in Coupe form in the mid 90's to 2 championship wins. A different data logger onboard then and no set up sheets being handed out although I have an offer for him to join me for a day to assist in driver and car improvement. Once I know my way around the car more, I will take him up on it.

Ahh that magic balance between under-steer and over-steer… much more difficult to achieve on a mid-engined car (and differs between track car and road car).

Ideally, on a serious track car (and I emphasize “serious”) I would set up the car so that it has natural over-steer, then drive it so hard into a corner that it under-steers, then find the over-steer again with the throttle. If you get the balance right, then you will throttle-steer through the corner very fast. If you get it wrong, then you will find that the car will swap between under-steer and over-steer very quickly (caused by too much over-steer and is very unstable), or spear off the track in continued under-steer (caused by not enough over-steer so throttle just gives you more under-steer). In the past, I had managed to find that magic balance in a Toyota MR2 but I’ve yet to achieve it in the GT40 (still in early stages and currently getting the “swapping” effect).

Consequently, you will find that mid-engined cars are only really suitable for circuit racing and require far more courage and commitment to drive fast. This is because you not only need to get the balance right, but you also need to find that window of corner entry speeds that are faster than the over-steer point, but slower than the non-recoverable point.

Alternatively you could set your car up similar to a front-engined car and so make it safer and easier to drive on the track, but that will also make it slower than the equivalent front-engined car. This however, is how I would also set up a road car.

Just my 2cents.

Chris, I would not be confident of your theory working on a car with slicks unless it has monster power. My Cosworth FBE has about 320 bhp at the flywheel. But a Cobra or a 40 you stand a chance......

Malcolm,
If you want to go fast you need to look at the physics of what is happening. You can go around a small radius turn at a lesser speed than a large radius turn and generate more g forces. The formula F=WV(2) / g *r
W= mass vehicle kg or lbs, V= velocity m/s or fps, g=9,81 or 32.2, r=radius m or ft.
The centrifugal force generated (F) is reacted by the tyres. The reacting force Fr = Mw* coeff of friction. If F is greater than the Fr the vehicle will slide.The force F is acting through the centre of Mass, the force Fr is acting through the interface of each tyre with the surface. The mass Mw is the sum of the wheel masses. The individual Mw changes with mass transfer as the g increases and the body rolls around its roll axis due to the height of the centre of mass. Down force adds to this thereby increasing the force Fr. It is further complicated by the front to rear ratio of Fr and the tyre slip angles. Given the downforce generated at various speeds the base handling can be calculated. The driver then can make adjustments to suit his preference. That is in an ideal world where time and money are available to so do.

For a given vehicle where all of the data is not available,experimentation is the only way. In the event that your suspension is limited in its adjustment, then shocks, springs, anti roll bars, tyre pressures are all that you can play with. In the event that your suspension fully adjustable then bump/roll steer, caster can be played with F&R. roll steer can change the handling from under to over steer. Ask your tyre manufacturer for operating temps, too small a tyre may well overheat, too large a tyre may well not generate optimum temp.
When using the data logger and fiddling, compare corner to corner values, not one corner to another.
Trevor

Thanks everyone, that is a lot of useful info above.

Trevor, my data logger also gives me corner radius so your formula are useful indeed. In the notes I have the tyre temp is meant to be between 70 and 80 celcius.

Malc's Prosport

For those of you wondering what Malc's car looks like - here are a couple of pics of it at Silverstone, either side of a 'quiet and compact' saloon - NOT!!!

Malcolm,
What data logger are you using? I am finishing up a Race Technology DL1 install at the moment.

Mine is a 10 channel (ie small) Stack system SP8102. I am considering an upgrade to 18 channels plus the later software but it ain't cheap so I need to consider return on money invested as really it is a toy to me not a necessary tool.