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Track prepping a road car

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Track prepping a road car

Post by junkie on Sun Apr 26, 2009 2:13 pm

To be able to enjoy to the maximum a track day using your road car it pays to spend some time in basic preparation. I will try and break down some of the simple checks and changes you can make to your car to enable you to get the most time on track during the day and to stay safe whilst driving harder than you would do on a public road. Interior

Remove all loose objects from the car interior. If you have a fury dice or air freshener hanging from your coat hooks/mirror take it out. Empty your glove box of all unnecessary clutter and remove all the floor mats, especially the driver’s side floor mat and vacuum the floor to remove any small stones etc.
Remove anything that will slide around under cornering loads and will distract your attention from driving the car. At the track remove the spare wheel and store it in a secure location. If you plan to remove items at the track make sure you arrange for a permanently manned area for storage or a friends car boot, it is not uncommon for scum to be wandering around the paddock looking for an opportunity to make a quick profit.

Brakes

The brakes on your road car are likely to be the most inadequate area of the car when you drive on track. During your everyday road driving you will only use the brakes at working temperature for about 1% of the time on a motorway, 15% of the time commuting and 25% of the time cross country driving. When on track this pattern changes dramatically, you will have the brakes upto full working temperature for at least 85% of the lap time. This is a huge change in use from that the car designers envisaged and should you decide to use the car in standard set-up you will quickly realise that after 2 laps of most circuits you will have to slow down to allow the brakes to recover.

There are 3 main areas you can tackle to improve the situation dramatically, they are listed in no particular order, as all three are important.

1. Brake Pad Material.
2. Brake Fluid Type
3. Brake Disk Cooling

Brake Pad Material

The brake pads fitted to your road car are designed to do the following jobs. Work from cold, produce minimal dust and last longer than the service interval of the vehicle. The pads fitted to your road car in this application are perfectly adequate for the job intended however as soon as you take your car onto a race circuit they will quickly fail to cope with the demands put upon them. You have 3 choices as to how you tackle this problem. First you can choose to ignore the problem and limit the number of continuous laps you drive on track, a rather frustrating approach in my book. Secondly you can choose to use a compromise brake pad that works well on both road and track, such as a fast road brake pad. Finally you can choose to use a full race brake pad and fit these on arrival at the track and remove them at the end of the day before driving home on public roads.
If you are looking for the maximum performance from your car on track then the full race pad option is the one for you. If you want to be able to stay on track for a prolonged period of time and are happy to give away some performance for a lack of mechanical work at the track then the fast road pad is your best option. Normal road pads on track in my opinion should never be used, the main reason is that after overheating them on track (which you will do), they never work at 100% of there original performance again and quite often suffer from cracking which could lead to brake failure in the future.

The other major area to bear in mind is the life of the pad. A fast road pad on an average weight road car will last about 100 miles on track before wearing to the minimum pad thickness, on the road this same pad will last about 7000 miles.


Brake Fluid Type

When was the last time you replaced your brake fluid? Why did I ask the question?
Most brake fluid’s are hydroscopic, this means the brake fluid absorbs water from the atmosphere, which reduces its boiling temperature. It is unlikely you will ever boil the brake fluid when driving on the road and yet it is a main service replacement task at least every 3 years. I suggest you have your brake fluid replaced with a DOT 5.1 or better fluid when you plan to do a track day and then have it changed every year to keep the boiling point as high as possible.
Avoid using full race fluids as they tend to be more effected by water absorption and are designed to be replaced far more regularly than a road car fluid. They do usually work at a higher initial temperature however this drops off far more rapidly than a road spec fluid.


Brake Disk Cooling

Ventilated brake disks cool by acting as a centrifuge, forcing air from the centre of the disk out through the vanes and into the wheel rim area. Race spec disks are handed and have a spiral design to the internal vanes to improve the centrifuge effect. If you have upgraded brakes with race spec disks make sure they are on the correct side, it always amazes me how many people fit them on the wrong side, racing teams included. The easiest way of improving cooling to your road car brakes is to do a temporary fix at the racetrack. Buy some 3” diameter tube and tie it to the underside of the car with the front pointing directly forward and the rear pointing into the centre of the disk eye. Once fitted do a check to ensure the pipe is not fouling on any of the steering/suspension under all movement. This simple bodge could be the difference between having 100% useful brakes and suffering from brake fade or boiling fluid, it is worth the effort if you have marginal brakes in particular.

Using Road Tyres

How do you choose which tyres to use? Is it OK to use the tyres already fitted to the car?

The tyres on your road car are going to suffer as much abuse as your brakes when driving your road car on a racing circuit. Road tyres have to work in a very wide band of applications from pouring rain to scorching hot public roads. They are designed to provide acceptable grip yet minimal noise and on average must last at least 20,000 miles. All of the above requirements are contradictory and tyre engineers do a remarkable job to achieve a usable compromise.

I will base the following comments on the assumption that the track is dry. Should you be driving on a wet track then a great deal of the problems seen with using road tyres does not materialise due to low lateral loading.

What happens to a tyre when driving on track?
The first thing to be aware of is that the work each tyre does on a racetrack is not uniform. The front left tyre always has the hardest life on a clockwise track (Most UK circuits). Unlike driving on the public road where you will be cornering with both directions equally, due to the nature of the track you will mainly be cornering in one direction (right hand corners). The effect of this is that the front left tyre heats up far quicker than the other three and will wear much quicker as well. I will cover how to monitor this and compensate for it later. The next most worked tyre will be the left rear tyre, which sees a great deal of loading on a fast sweeping circuit in particular.

There are two main reasons why a tyre heats up; the first is due to the sidewall deflection generating massive heat in the tyre carcass, which has the effect of heating up the gases inside the tyre. As we all know if you heat a gas it expands, this leads to an increase in tyre pressure as the heat builds. The other reason is due to the flexing of the tread block, the larger the tread block in surface area the less it moves and therefore the less it heats up, the deeper the tread block the more it moves and therefore the more it heats up. As you can see from this the best road tyre for use on track will be one with minimal tread depth (below the legal limit) and a very large block pattern, especially on the outside edges of the tread.

As you can see from the above it is much better to use a part worn tyre than your currently fitted legal road tyre, this means that ideally you should have two sets of wheels if you plan to do regular track day’s. It is not impossible to drive on track with your usual tyre/wheel combination, I did it myself at first, however the wear rate is so high that you are throwing good money away and running the risk of having to drive home on illegal tyres. Something which is very heavily penalised in the UK (3 points per tyre).

Some track days organise a dedicated tyre supplier to attend the day to swap tyres over at the start/end of the day or to supply new tyres to be fitted at the end of the day after you have destroyed your old set.
This is a superb service if you don’t wish to buy a second set of tyres and takes a great deal of the worry away from keeping your tyres in a legal state to drive home on.

Ideally you are also looking for a tyre that has a fairly hard compound; a tyre that works incredibly well on the road with massive grip will most likely be a soft compound. Take this same tyre onto a racetrack and after about 2 laps it will start to overheat the tread and start to slide around, as the rubber becomes more liquid. It is very common to see a high performance tyre destroy its outer edges of the tread pattern and have an angular wear pattern to all the tread blocks, with the outer edge of each block being worn down to the level of the underlying carcass. This effect is always worse on a newer tyre as the tread block is deeper and generates more heat compounding the problem. Sometimes the less well thought of road tyre is actually a better option on track due to its harder compound.



How do you set your tyre pressures when driving on track?

When setting your tyre pressures for your road car during your weekly car checks (you do this don’t you!) you should always set these when cold to give a static state of reference. As you drive your tyre pressures will always increase due to the heat generated as explained above.

When it comes to setting tyre pressures for the track this method has to be thrown out of the window. Due to the fact that all four tyres run at different temperatures on a racetrack you have to set each corner independently. Also it is advisable to run the tyres at a higher pressure than you would on the road, this is mainly to help the tyre to maintain its shape under hard cornering and support the sidewall. I usually suggest you run 4-6 PSI higher than you would on the road.


Set your tyre pressures evenly before you go on track for the first time 4PSI higher than your normal cold pressures. Go out on track and do one slow lap, one fast lap then one slow lap and come back into the pits. Check your tyre pressures again, you will find that they are all now different to each other with the front left being the highest. Reset your tyre pressures and this time go out and do one slow lap, 5 fast laps then one slow lap and come back into the pits. All four tyres will again have risen with the front left the highest again. Reset all the tyres to be 6PSI higher than you would use on the road and repeat the last exercise. You should now start to see all four tyres stabilising the pressures; you may have to drop the front left a little to even out the pressures. You should now be in a position to drive the car at will without much change in pressures being seen for the rest of the day. It is always a good idea to check your pressures after each run (not just before) to ensure you are not seeing a sudden drop off of pressure in one tyre as this is a good sign you are heading for a tyre failure on track.


Finally remember that if you are intending to drive home on these same tyres check the tread is still legal and check your tyre pressures after 10 miles of normal driving, they will be all over the place and will need resetting. Reset them again in the following morning as per your normal weekly checks.


A word of warning on using road tyres on track. Make sure you know the speed rating of the tyres fitted to your car and never exceed this speed whilst driving on track. As an example I never drive above 85MPH on the public road and yet I often drive faster than 150MPH on a racetrack. If you are going to drive this quickly make sure the tyres are rated for this speed, you do not want a tread failure at 150MPH, it would not be fun.



Using Slick Racing Tyres

The main benefits of using slick racing tyres on track days are that by definition you will not be wearing out your road tyres and you will be using a tyre designed specifically for the job.

You can set the tyre pressure in the same way as described above however you need to speak to your tyre supplier to get the optimum working pressure of the tyre. As an example on our lotus esprit racecar we run 22PSI front pressure hot and 18PSI rear pressure hot. These are using F3000 spec tyres on a 700Kg 420BHP racing car. Slick running pressures need to be very different to a road tyre and each type of slick construction has its own specific requirements, your tyre supplier is the best source of information on these requirements.



You will see much better wear characteristics using slick racing tyres and will generate incredibly high levels of cornering speed compared to people on road tyres. Taking 10 seconds a lap off your lap time is not uncommon with a skilled driver when going from road to slick racing tyres. There is a downside to this. Firstly, when the limit of the tyre is reached the breakaway characteristics are not as user friendly as a road tyre, especially when using radial slicks (crossply’s are still heavily used for slick tyres). When you do go over the limit of the tyre you will be travelling much faster than if you were on a road tyre, making the impending crash more severe. The brakes on your car will be worked much harder than when using road tyres as the speeds you are slowing from will be higher and the tyre will allow much harder braking before you see brake lockup. Finally and most importantly in my opinion the likelihood of seeing oil starvation on your engine (and gearbox, diff) will be massively increased which could lead to engine failure. With the increased cornering forces the oil in the engine sump will be forced up the outside edge of the engine block and out of the sump where the oil pump pickup pipe is located. This will starve the pump of any oil and your engine bearings will run dry, this only needs to happen for a few seconds to see total engine failure (rod out the side of the block is a good one). If you plan to drive on track with slick tyres an absolute minimum requirement is a baffled sump, ideally you should have the engine converted to a dry sump system to be 100% certain of permanent oil feed. Some modern high performance cars have a baffled sump fitted as standard, if you do plan to use slicks I suggest you do some homework to see if your particular car is safe and has a baffled sump.
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Re: Track prepping a road car

Post by dukest on Tue Apr 28, 2009 2:18 am

Good work

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Re: Track prepping a road car

Post by junkie on Tue Apr 28, 2009 11:36 am

What i find interesting the most is the tyres, you need a hard tyre and if using road tyres then below the legal limit is best as there is less tread block to go soft and hence stop sliding.
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Re: Track prepping a road car

Post by dukest on Tue Apr 28, 2009 1:38 pm

yes, especially since you hear that you should always put the tyres with the most tread on the back etc. etc.

obviously the dynamics of track use are different and you're looking for the most contact of the least flexible rubber with the track, possibly the quality of the rubber doesnt come into it until higher extremes of performance.

however under "normal" road use, perhaps the better rubber quality early in a tyre's life is meant to be more of a safety net for the unprepared driver about to lose grip than rubber that is worn out and has less immediate cold grip to give?

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