Trackday wisdom required.

Equipment that may be needed plus general information on track days.
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Nerdstrike
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Trackday wisdom required.

Post by Nerdstrike »

As a novice at trackdays, I've still got lots to learn about taking a car to the limit and keeping it there, so I've come for some advice.

Last time out I got my front tyres (Vredestein Sessantas) rather toasty and howling in the corners and they've never been quite the same since. I conclude that they either got too much pressure in them or the rubber overheated through "overdriving the car", but I don't know how to tell. I was only out for four laps at a time, but I was doing my best to get corner speeds up. My previous effort with some Bridgestones on the front didn't exhibit the same issue (but I was probably braking more).

a) What is overdriving the car. How does one manage tyre condition? For sake of argument, let's say it is a nice warm and dry day.

b) What are the signs of needing to adjust tyre pressures?

I realise this topic is tricky to do as book learning, but I'm trying to establish whether I need to adjust my style to better maintain both speed and car endurance. Any thoughts welcome, any related questions also welcome.
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Re: Trackday wisdom required.

Post by stewartm »

I'll steer clear of the specifics of driving as I am no expert, just an enthusiastic amateur :) other than to say, if you can get it booked, always get some time with an instructor. It is getting to be a massive cliche now, but there is no cheaper modifcation/upgrade for your car to improve laptimes. Other than the usual guidance with lines, they will also concentrate on ensuring that you set the car up for each corner as you approach, which will have a massive bearing on tyre performance and condition.

As for pressures, I don't think there is established approach amongst the regulars. Most people run their cold pressures a few PSI below the recommended, with the intention that hot pressures will be 32PSI. It is quite hard to judge tho, as you need to check the hot pressures as soon as you come in, and likely after one or more cooling down laps. Casey has a pretty cool real time pressure monitor that he was running at the last track day I went to. The sensors are in special valve caps, that transmit to a wireless monitor in the car and give you real time readouts (I think they update every 5s). I think he was quite surprised at the amount of pressure he needed to run and how different it was at each corner.

Hopefully he will be on in a bit and will be able to give a bit more info.
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Re: Trackday wisdom required.

Post by Nerdstrike »

Obviously instruction is one way to get things on track (see what I did there?), but I'm a thinker and you don't get much thinking time when you're out on circuit. Wil and Malcolm did a grand job of co-piloting for me on my first outing, for which I am very thankful.
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Re: Trackday wisdom required.

Post by macgtech »

The harder the pressures, the more stress you will put into the tyre tread rather than the sidewall, so you will see the tyres getting hotter on the tread surface. If the tread looks like it is melting at the edges, try dropping the pressure a bit. New tyres will also suffer more from older ones, as you will have more tread which is more prone to moving around, and heating up.

This is why wet tyres burn up quickly when it is dry, as the individual tread blocks move around and heat up far more than a slick tyre with a 'solid' surface. Without the water to cool them they suffer. The same applies to treaded road tyres to some extent, but much less so as they are a LOT harder.

As stated by others above, you should aim for a sensible pressure when the tyre is hot, so starting a few psi down (say 4-5 psi) from standard is a good place to start. You don't need to check the pressure the second you get into the pits - the tread block temperature will drop very quickly (already lost a lot of heat during your in/cooling down lap) but the pressure increase due to the heat will be lost far more slowly. We can see a 10 psi rise (from 18 cold to 28 hot) on slicks.

The key to speed is being smooth. The classic novice mistake, apart from the obvious lines etc, is to try to be quick. Try being smooth instead, and the speed will come naturally.
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Re: Trackday wisdom required.

Post by Nerdstrike »

Ok, good to get some ballpark numbers and explanation, thanks MacG. My tyres were tacky all over but had some sticky ridges on the tread so they were probably a bit high and generally too hot.

Sometimes impetuousness overcomes the smooth thing!
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Re: Trackday wisdom required.

Post by casey »

Hi Nerdstrike :D

I will preface this by saying I'm also just an enthusiastic amateur, so don't approach my trackdays with huge amounts of science! However....

I try to drive as smoothly as possible (people often comment on my smooth style), but always look to use the entire width of track (including "benign" kerbs :D ) and seek corner entry and line to maximise speed OUT of the corners. This approach, at least for me, leads to quicker lap times. By doing this at Snetterton earlier this week, I was getting ~2m30s laps when running 31psi tyre cool temp to start the day. However, my pressure monitor on each tyre (excellent tool by Tyrepal, £99 for the whole set) showed temps of 36-38psi when hot. The front right being the hottest, as this is a Clockwise circuit, punishing that tyre most. I dropped the temps to 32psi all round when hot (so would have been slightly uneven when cold) and managed 2m27.5s in later laps. The tyres also seemed to understeer less with the pressure drop. So, as above, dropping the psi by 5-6 to start the day and making sure you warm up the tyres before going fat out is likely to get you the best results, and look after the tyres better.

I pretty much always get sticky build up on tread edges in the centre part of the tyre. Biggest problem is that the outer shoulder of the tyres on the front take a heck of a pounding :D

I stress I NEVER have any live lap timing viewable in the car on trackdays. All timings are via post session analysis :D
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Re: Trackday wisdom required.

Post by macgtech »

Getting the tyres hot then adjusting them down as Casey did is the best and easiest approach, just remember to re-adjust for the road again when cool. It could take a while for them to cool completely. You will more than likely have uneven temperature left to right and front to back.
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Re: Trackday wisdom required.

Post by casey »

Yep, I always have a problem at the end of a trackday in getting the psi right to drive home. I get them roughly right and then check them a day or so after I get home. The car isn't a daily and my normal "post trackday" routine, as soon as I can, is to remove the front tyres to clean the wheels and calipers of dust, check the pads, tyre treads and also check pressures all the way round. I also visually check the rear pads and tyres and may remove them too for a good clean and closer check.

I have a big brake kit on the front and I find (whilst the wheel is off anyway) bleeding ~50ml of fluid from each of the 4 bleed nipples hardens the pedal up as it goes a little soft during a trackday. I find the first 25ml of fluid out is pretty nasty (blackish), but then it comes through clean. Almost as though the fluid (DOT5.1) in the caliper itself gets "cooked" during the day? I never suffer brake fade or other brake issues, other then the pedal action "softening" during the trackday.

As I do quite a few trackdays, I change my oil at ~2-3k. If the oil looks reasonable I may change the filter every 2nd change (so 4-6k).

My biggest tip for trackdays is to make sure the oil level is ~3/4 on the dipstick. Don't fill more than this, to reduce the chance of oil "blow back" and check the level regularly throughout the day. I typically use 1/2- 1 litre of oil on a trackday, filling up twice during the day and on leaving the track. Don't let the oil level drop too far below 1/2 on the dipstick as, on a very hot day, you will be losing a lot of cooling capacity with the reduced volume of oil. I've found this out a couple of times on very hot days (ambients of 25 C plus); if the oil level drops too far I will get oil and water temps touching 110 C, where my after market gauge warnings are set. I'm happy to see up to 110, but not higher. Dropping off the gas pedal for a matter of 15 seconds is enough to cool things down though.
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Re: Trackday wisdom required.

Post by macgtech »

casey wrote: I have a big brake kit on the front and I find (whilst the wheel is off anyway) bleeding ~50ml of fluid from each of the 4 bleed nipples hardens the pedal up as it goes a little soft during a trackday. I find the first 25ml of fluid out is pretty nasty (blackish), but then it comes through clean. Almost as though the fluid (DOT5.1) in the caliper itself gets "cooked" during the day? I never suffer brake fade or other brake issues, other then the pedal action "softening" during the trackday.
The DOT rating of the brake fluid is a bit misleading, the thing you need to look for is the wet boiling point, which is the boiling point once it has absorbed a set % of moisture (as brake fluids are hygroscopic meaning that they absorb moisture from the air). If you are tracking the car regularly you should use a fluid with a dry boiling point of circa 600 deg C, such as Motul RBF 600 or AP 600. This will correspond to a higher wet boiling point too. These will be slightly more expensive than the 'performance' brake fluids but are much, much better.

Should solve your problems. Do you have braided lines too?
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Re: Trackday wisdom required.

Post by casey »

Yep, braided lines. The fluid is that recommended by Clive at MRP for track applications. I will check the specs....
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Re: Trackday wisdom required.

Post by Conan »

Hi Nerdstrike,
This is just a total guess of course :)
Your holding the steering on too much and not picking up the back end of the car with the throttle at the right time whilst unwinding to keep the car ballanced through the corner.
This is why your working the front end much harder than the back.
The vredisteins have very large rain chanels which make them a great all year tyre.
They do increase in pressure quite a bit which is why I recomend Nitogen for the track and 32 psi is fine. They work better than you would expect on a dry track and are very good for teaching people to ballance the car. I tested these tyres at Brands a couple of years ago and there is a video of me following Ray for some time (about 20 mins I think) which is past the 15 mins I always do. You can hear the tyres are in the high pitched sqeal for most of the lap, once you go past this high pitch you just damage the tyres and don't go faster. All tyres will move some rubber across when there working hard but if driven correctly will last a season and road miles easy.
Hope you can understand what I'm trying to say :)
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Pete

PS: I assume your running 235x40 tyres?
Have you done anything else to the car from standard?
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Re: Trackday wisdom required.

Post by Nerdstrike »

Thanks Pete, Malcolm, MacG.

My car is stock bar some coils, braided lines, pads and back box. I now feel a bit more informed!
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