Optimum Track Conditions?
10-02-2017, 12:42 AM
#1
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Optimum Track Conditions?
Our little cars seem very sensitive to ambient and track temperature / conditions. Sure makes finding the last couple of tenths when testing very hard. Seems to me cooler air is best, with times varying up to around 2%, but more often around 1% from best. What temperatures (air / track) have you found to be optimum? How much variance have you seen?
I am NA, turbo would be even more dramatic I imagine.
I am NA, turbo would be even more dramatic I imagine.
Last edited by Neddy; 10-02-2017 at 04:21 AM.
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10-02-2017, 09:11 AM
#3
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I'm all about 100* days, direct sun, exhausted driver. If the oil and coolant temps stay in check, sensors don't heat soak or loose sync, shock valving remains consistent, and the tires survive for over 2 hours of track time, I'm happy with times close to upper tier SM times.
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10-02-2017, 03:26 PM
#5
Fast weather
Optimum conditions for lowest lap times vary depend on the engine setup, tune and tire being used. The Miata is nor more sensitive to temps than any other car.
Grip
Track surface temps are usually the most critical as they dictate what temp the tire operates and thus, the grip that is generated. Street tires seem to want 60-70°, race tires 70-80°. To get track temps in this range usually means ambient temps 15-30° cooler. Early morning session can have the ambient (air) temps in the right window but if it was cold overnight, the track may actually bee below ambient temp. When the sun is at a low angle on cold days, it impinges too indirectly to raise track temps into the best window. So on a hot day, when it has been warm overnight, you want that first morning session before the ambient or surface temps get too hot. Here in SoCal late summer, sometimes even first session is well beyond optimum, the track just getting slower from there. In the winter, the best session is usually mid morning when the sun is high enough to heat the track into the right temp window but the air is still cold.
A standard Time Trial hack is to pay close attention to weather reports and your recorded tire data to see which session will have the best track temps for the tires you are using. Save your best tires, fuel, redline for that session. A little local knowledge helps but simply looking at the previous data you have and a smartphone can pay big dividends.
Power
Best temps for power are simply cold. The colder the better. No lower limit until your radiator or oil cooler are over cooling. Power gains are linear but still modest for an N/A engine. Gains for forced induction engines are greater. Even so, the gains from grip at slightly higher temps outweigh the gains from power at lower temps. When it's say 40° out, the track is usually too cold for the tire to work properly. At 40° you lose more time from cold tires than you gain from the extra power.
Aero
Wind is the enemy to low lap times no matter which direction or what aero you do or do not have. More wind is always slower. One might think that a tail wind on a certain part of a given track might outweigh the extra drag on the other sections. It doesn't, ever. Drivers experiencing big aero for the first time on a windy day can very easily be caught out by sudden, unpredictable and sometime violent shifts in balance in fast turns. Be cautious on windy days on fast turns with big wings.
Grip
Track surface temps are usually the most critical as they dictate what temp the tire operates and thus, the grip that is generated. Street tires seem to want 60-70°, race tires 70-80°. To get track temps in this range usually means ambient temps 15-30° cooler. Early morning session can have the ambient (air) temps in the right window but if it was cold overnight, the track may actually bee below ambient temp. When the sun is at a low angle on cold days, it impinges too indirectly to raise track temps into the best window. So on a hot day, when it has been warm overnight, you want that first morning session before the ambient or surface temps get too hot. Here in SoCal late summer, sometimes even first session is well beyond optimum, the track just getting slower from there. In the winter, the best session is usually mid morning when the sun is high enough to heat the track into the right temp window but the air is still cold.
A standard Time Trial hack is to pay close attention to weather reports and your recorded tire data to see which session will have the best track temps for the tires you are using. Save your best tires, fuel, redline for that session. A little local knowledge helps but simply looking at the previous data you have and a smartphone can pay big dividends.
Power
Best temps for power are simply cold. The colder the better. No lower limit until your radiator or oil cooler are over cooling. Power gains are linear but still modest for an N/A engine. Gains for forced induction engines are greater. Even so, the gains from grip at slightly higher temps outweigh the gains from power at lower temps. When it's say 40° out, the track is usually too cold for the tire to work properly. At 40° you lose more time from cold tires than you gain from the extra power.
Aero
Wind is the enemy to low lap times no matter which direction or what aero you do or do not have. More wind is always slower. One might think that a tail wind on a certain part of a given track might outweigh the extra drag on the other sections. It doesn't, ever. Drivers experiencing big aero for the first time on a windy day can very easily be caught out by sudden, unpredictable and sometime violent shifts in balance in fast turns. Be cautious on windy days on fast turns with big wings.
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10-02-2017, 04:34 PM
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cheers. poscats given. Agree regarding the morning sessions, although we have sometimes set the best time last session on a clear winters day when the ambient temp has started dropping quickly but track is still warm. Appreciate the numbers to back up the discussion. I am going to have to record more info in my track notebook...
interesting regarding wind.
hornet raises a good point about track rubber conditions in addition to ambient / track temps.
Any comments on what the variation between an optimum and best lap on a slow day could be? From trawling through my numbers it appears to be around 2%. I realize that may be a can of worms as many factors are at play.
interesting regarding wind.
hornet raises a good point about track rubber conditions in addition to ambient / track temps.
Any comments on what the variation between an optimum and best lap on a slow day could be? From trawling through my numbers it appears to be around 2%. I realize that may be a can of worms as many factors are at play.
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10-02-2017, 05:42 PM
#8
Yup. I didn't get into the rubbering in factor. If the track is green, no rubber on it and the temp stays fairly constant then it can get faster as the days goes on. If it's well rubbered in to begin with and you go faster as it heats up then you're just driving better.
When we did a lot of enduros in the summer, the track would always get a bunch faster right at sunset. Those that either had little night driving experience, bad lighting or weren't super familiar with the track would slow down. We always had good lights, knew the track intimately and knew how to race at night. We won many an enduro by suddenly gaining a lap right after the sun went down. In the Thunderhill 25 hrs, they call the hour or so just before sunrise "magic hour". Air is still cold, just enough sun hitting the track to let tires start working. Fastest laps are almost always during that hour.
When we did a lot of enduros in the summer, the track would always get a bunch faster right at sunset. Those that either had little night driving experience, bad lighting or weren't super familiar with the track would slow down. We always had good lights, knew the track intimately and knew how to race at night. We won many an enduro by suddenly gaining a lap right after the sun went down. In the Thunderhill 25 hrs, they call the hour or so just before sunrise "magic hour". Air is still cold, just enough sun hitting the track to let tires start working. Fastest laps are almost always during that hour.
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10-03-2017, 08:34 PM
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cheers. poscats given. Agree regarding the morning sessions, although we have sometimes set the best time last session on a clear winters day when the ambient temp has started dropping quickly but track is still warm. Appreciate the numbers to back up the discussion. I am going to have to record more info in my track notebook...
interesting regarding wind.
hornet raises a good point about track rubber conditions in addition to ambient / track temps.
Any comments on what the variation between an optimum and best lap on a slow day could be? From trawling through my numbers it appears to be around 2%. I realize that may be a can of worms as many factors are at play.
interesting regarding wind.
hornet raises a good point about track rubber conditions in addition to ambient / track temps.
Any comments on what the variation between an optimum and best lap on a slow day could be? From trawling through my numbers it appears to be around 2%. I realize that may be a can of worms as many factors are at play.
Track record of 1:29.6 is only beatable in September (usually freezes in October so no track days) 10°C no wind and sunny 10-11am session is where its at in a Spec Miata here.
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