| Mind | 09-11-2006 09:36 PM |
Tire Pressure Question
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Hey, got a question about when you guys set/report tire pressures at AutoX or track or wherever... are you guys reporting cold pressures or pressures during the actual race/event?
Here is my method of setting tire pressures... usually I have to drive about an hour to an autocross. I'll note the baseline tire pressure and ambient temperature in the morning before I leave. Once I get to the event, I'll adjust the baseline tire pressure for whatever the temperature happens to be, and then calculate how much more PSI I need to get to my target PSI. Whatever this difference is, I'll add to the current pressure reading.
Example -
leave at 7 am, 36 psi, 60 deg, baseline
arrive at event, it is 80 deg, so I add 2 psi to my baseline->38 PSI
Target psi is 43, 5 higher than baseline
Current measured psi is 41, so add 5 psi to tire to get a measured 46 psi
I know usually tire pressure is all cold... just wondering if you motorsports guys report cold or actual pressures... since it seems like getting the cold takes some calculation...
Here is my method of setting tire pressures... usually I have to drive about an hour to an autocross. I'll note the baseline tire pressure and ambient temperature in the morning before I leave. Once I get to the event, I'll adjust the baseline tire pressure for whatever the temperature happens to be, and then calculate how much more PSI I need to get to my target PSI. Whatever this difference is, I'll add to the current pressure reading.
Example -
leave at 7 am, 36 psi, 60 deg, baseline
arrive at event, it is 80 deg, so I add 2 psi to my baseline->38 PSI
Target psi is 43, 5 higher than baseline
Current measured psi is 41, so add 5 psi to tire to get a measured 46 psi
I know usually tire pressure is all cold... just wondering if you motorsports guys report cold or actual pressures... since it seems like getting the cold takes some calculation...
| leecea | 09-11-2006 10:06 PM |
All I can offer is my method of setting tire pressure:
- Pump tires up to target pressure.
- Before each run, check pressures and let air out until all tires are at target pressure.
BTW: Were you at Warminster on Sun? What class? Just curious - I'm in DS.
- Pump tires up to target pressure.
- Before each run, check pressures and let air out until all tires are at target pressure.
BTW: Were you at Warminster on Sun? What class? Just curious - I'm in DS.
| Mind | 09-11-2006 10:21 PM |
So, then you go by 'hot' pressures... if that's what most people are reporting here, then I think I'm seriously over-inflating my tires...
Yeah, I was at Warminster, in STU... were you the non-06 black sedan? It was a fun course. Wish we could have had one more run though...
Yeah, I was at Warminster, in STU... were you the non-06 black sedan? It was a fun course. Wish we could have had one more run though...
| leecea | 09-11-2006 10:58 PM |
Well, when I first inflate them, they are cold. Then I guess they are hot pressures after each run, but the pressure usually needs adjusting a bit each time. My goal is just to keep the same starting pressure for reach run. Not sure if that's what others do.
I was the silver 03 WRX in DS. Yes, it was a fun course. I don't mind three runs - it seems to focus me!
I was the silver 03 WRX in DS. Yes, it was a fun course. I don't mind three runs - it seems to focus me!
| waktasz | 09-12-2006 12:32 AM |
I'm here to add nothing to the conversation other than to say hi. I was in STU also.
| Mind | 09-12-2006 04:44 PM |
Hey wak, I guess you're the '06 with the bat on back? I'll come over and say hi at the next event. How do you manage your pressures?
Would either of you object to ride-alongs? I thought it would be a good opportunity to feel your other suspension setups/driving style and maybe even become a little more familiar with the course. If not, I completely understand, for weight or focus or whatever issues... but I thought I'd throw the idea out there. You're welcome to ride along with me, although my driving isn't that inspiring...
Would either of you object to ride-alongs? I thought it would be a good opportunity to feel your other suspension setups/driving style and maybe even become a little more familiar with the course. If not, I completely understand, for weight or focus or whatever issues... but I thought I'd throw the idea out there. You're welcome to ride along with me, although my driving isn't that inspiring...
| chimchimm5 | 09-12-2006 05:00 PM |
From the language I've read everywhere, it sounds like people are talking about warmed up pressures.
For example, when people pyrometer their tires and "then adjust pressure accordingly", it has to be a hot pressure.
For example, when people pyrometer their tires and "then adjust pressure accordingly", it has to be a hot pressure.
| waktasz | 09-12-2006 05:07 PM |
[QUOTE=Mind;15221061]Hey wak, I guess you're the '06 with the bat on back? I'll come over and say hi at the next event. How do you manage your pressures?
Would either of you object to ride-alongs? I thought it would be a good opportunity to feel your other suspension setups/driving style and maybe even become a little more familiar with the course. If not, I completely understand, for weight or focus or whatever issues... but I thought I'd throw the idea out there. You're welcome to ride along with me, although my driving isn't that inspiring...[/QUOTE]
Yep, that's me.
Usually I go by the set it and forget it philosophy, with some water spraying down between runs. I JUST got new tires (hopefully that explains why I did so bad this weekend after a few 2nd in classes at previous events) and didn't play with pressures much at all, aside from lowering the rear A LOT after the first run. I was just trying to get used to them at this event.
Would either of you object to ride-alongs? I thought it would be a good opportunity to feel your other suspension setups/driving style and maybe even become a little more familiar with the course. If not, I completely understand, for weight or focus or whatever issues... but I thought I'd throw the idea out there. You're welcome to ride along with me, although my driving isn't that inspiring...[/QUOTE]
Yep, that's me.
Usually I go by the set it and forget it philosophy, with some water spraying down between runs. I JUST got new tires (hopefully that explains why I did so bad this weekend after a few 2nd in classes at previous events) and didn't play with pressures much at all, aside from lowering the rear A LOT after the first run. I was just trying to get used to them at this event.
| Yoo Shin | 09-12-2006 05:13 PM |
[QUOTE=leecea;15210865]Well, when I first inflate them, they are cold. Then I guess they are hot pressures after each run, but the pressure usually needs adjusting a bit each time. My goal is just to keep the same starting pressure for reach run. Not sure if that's what others do.
I was the silver 03 WRX in DS. Yes, it was a fun course. I don't mind three runs - it seems to focus me![/QUOTE]
That's what I do and even in south Texas summer heat, the fluctuation is only 2-3 psi at the most (Falken FK451s for the record <- also, not an autox tire for the record :D )
I was the silver 03 WRX in DS. Yes, it was a fun course. I don't mind three runs - it seems to focus me![/QUOTE]
That's what I do and even in south Texas summer heat, the fluctuation is only 2-3 psi at the most (Falken FK451s for the record <- also, not an autox tire for the record :D )
| leecea | 09-12-2006 09:43 PM |
[QUOTE=Mind;15221061]Would either of you object to ride-alongs? I thought it would be a good opportunity to feel your other suspension setups/driving style and maybe even become a little more familiar with the course. If not, I completely understand, for weight or focus or whatever issues... but I thought I'd throw the idea out there. You're welcome to ride along with me, although my driving isn't that inspiring...[/QUOTE]
Sure. I have no problem with ride-alongs. This year my daughter has joined me at some events, so I'm used to having ballast in the car :) Just come over next time you see me (29 DS).
Andy.
EDIT: actually, I should add that I'd rather not have a ride-along at the Subaru challenge this weekend, in case you're there. I'm hoping for a decent result, so I've banned my daughter from the passenger seat. At Philly events I have no chance, so I'll take anyone along!
Sure. I have no problem with ride-alongs. This year my daughter has joined me at some events, so I'm used to having ballast in the car :) Just come over next time you see me (29 DS).
Andy.
EDIT: actually, I should add that I'd rather not have a ride-along at the Subaru challenge this weekend, in case you're there. I'm hoping for a decent result, so I've banned my daughter from the passenger seat. At Philly events I have no chance, so I'll take anyone along!
| Mind | 09-12-2006 11:39 PM |
I won't be at the Subaru Challenge this weekend (unfortunately). But maybe at Boeing I'll take you up on the offer, unless your daughter is there, of course.
DS is pretty competitive in Philly region... Bimmerworks and Otto's run some pretty fast times :eek:
DS is pretty competitive in Philly region... Bimmerworks and Otto's run some pretty fast times :eek:
| leecea | 09-13-2006 09:57 AM |
I won't be at Boeing. Oct 22nd at Ripken is the next Philly event I'll try to attend. Maybe I'll see you there or at the last Warminster event in Nov.
| solo-x | 09-13-2006 01:10 PM |
one quick point. for your first run, start out a couple of pounds lower then your target warm pressure. you're going to see a huge buildup in pressure on your first run relative to the others. start a little lower and you'll be closer to your target pressure for more of the run. after that, bleed down to target pressure between runs, and be aware that your front brakes are likely still adding heat to the front tires and subsequently building pressure while you wait to run again.
| goto_racing | 09-13-2006 02:01 PM |
That's interesting. I never thought that in terms of AutoX your tires won't heat up that much because the runs are so sort, but that at the same time there is temp/pressure diff between the begining and end of a run. It's like every lap is a first lap. What an interesting twist on AutoX tuning.
One thing I do know is that the only tire pressures that are important are the ones you have when you are out on the course in that important turn. We never get to know exactly what that is, but all our techniques should be aiming to have even and approrpiate pressures when the car is on track and being asked to perform. Starting and ending pressures are only relavant as tools to hit this target.
Chris Lock
One thing I do know is that the only tire pressures that are important are the ones you have when you are out on the course in that important turn. We never get to know exactly what that is, but all our techniques should be aiming to have even and approrpiate pressures when the car is on track and being asked to perform. Starting and ending pressures are only relavant as tools to hit this target.
Chris Lock
| Harry | 09-13-2006 02:35 PM |
Same car, same question
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[QUOTE=Mind;15209737]Hey, got a question about when you guys set/report tire pressures at AutoX or track or wherever... are you guys reporting cold pressures or pressures during the actual race/event?
Here is my method of setting tire pressures... usually I have to drive about an hour to an autocross. I'll note the baseline tire pressure and ambient temperature in the morning before I leave. Once I get to the event, I'll adjust the baseline tire pressure for whatever the temperature happens to be, and then calculate how much more PSI I need to get to my target PSI. Whatever this difference is, I'll add to the current pressure reading.
Example -
leave at 7 am, 36 psi, 60 deg, baseline
arrive at event, it is 80 deg, so I add 2 psi to my baseline->38 PSI
Target psi is 43, 5 higher than baseline
Current measured psi is 41, so add 5 psi to tire to get a measured 46 psi
I know usually tire pressure is all cold... just wondering if you motorsports guys report cold or actual pressures... since it seems like getting the cold takes some calculation...[/QUOTE]
I'm the slow driver in black 06 WRX wagon (#13 DS) :o .
I have been using actual pressures, set pre-first run, and then adjusting to maintain those pressures on the hot tires after runs. I have seen between 2 - 3 # increase on a run, but only if I am really pushing it and only on the fronts. Many of the runs at FedEX, I had no increase by the time I was back on grid. Probably why I'm slow. Even with rears 4 - 6 # over fronts, I'm still understeering big time. I hope a recent performance alignment by AndrewTech will help.
Are you on stock tires (I am) ? If so, the max is 51# (I had thought it was 44#, so I was running 38# front, 42 - 44# rear; both pre race). For the Subaru Challenge, I'm going to try 40 front, 44 rear to start, and go from there. Thoughts?
Here is my method of setting tire pressures... usually I have to drive about an hour to an autocross. I'll note the baseline tire pressure and ambient temperature in the morning before I leave. Once I get to the event, I'll adjust the baseline tire pressure for whatever the temperature happens to be, and then calculate how much more PSI I need to get to my target PSI. Whatever this difference is, I'll add to the current pressure reading.
Example -
leave at 7 am, 36 psi, 60 deg, baseline
arrive at event, it is 80 deg, so I add 2 psi to my baseline->38 PSI
Target psi is 43, 5 higher than baseline
Current measured psi is 41, so add 5 psi to tire to get a measured 46 psi
I know usually tire pressure is all cold... just wondering if you motorsports guys report cold or actual pressures... since it seems like getting the cold takes some calculation...[/QUOTE]
I'm the slow driver in black 06 WRX wagon (#13 DS) :o .
I have been using actual pressures, set pre-first run, and then adjusting to maintain those pressures on the hot tires after runs. I have seen between 2 - 3 # increase on a run, but only if I am really pushing it and only on the fronts. Many of the runs at FedEX, I had no increase by the time I was back on grid. Probably why I'm slow. Even with rears 4 - 6 # over fronts, I'm still understeering big time. I hope a recent performance alignment by AndrewTech will help.
Are you on stock tires (I am) ? If so, the max is 51# (I had thought it was 44#, so I was running 38# front, 42 - 44# rear; both pre race). For the Subaru Challenge, I'm going to try 40 front, 44 rear to start, and go from there. Thoughts?
| Student Driver | 09-13-2006 02:50 PM |
I report hot temps, but I qualify what I state with "hot". I typically get the tires, when cold, about 2 psi over what I run. However, I run a lot of negative camber in the front of my car with R-S2s, and use 37psi on asphalt and 39psi on concrete.
| Mind | 09-13-2006 09:27 PM |
[QUOTE=solo-x;15231205]one quick point. for your first run, start out a couple of pounds lower then your target warm pressure. you're going to see a huge buildup in pressure on your first run relative to the others. start a little lower and you'll be closer to your target pressure for more of the run. after that, bleed down to target pressure between runs, and be aware that your front brakes are likely still adding heat to the front tires and subsequently building pressure while you wait to run again.[/QUOTE]
Thanks for the tip... I guess I need to start managing my pressures differently. Makes sense that it would provide more consistent feel.
Thanks for the tip... I guess I need to start managing my pressures differently. Makes sense that it would provide more consistent feel.
| Mind | 09-13-2006 09:32 PM |
[QUOTE=Harry;15232566]I'm the slow driver in black 06 WRX wagon (#13 DS) :o .
I have been using actual pressures, set pre-first run, and then adjusting to maintain those pressures on the hot tires after runs. I have seen between 2 - 3 # increase on a run, but only if I am really pushing it and only on the fronts. Many of the runs at FedEX, I had no increase by the time I was back on grid. Probably why I'm slow. Even with rears 4 - 6 # over fronts, I'm still understeering big time. I hope a recent performance alignment by AndrewTech will help.
Are you on stock tires (I am) ? If so, the max is 51# (I had thought it was 44#, so I was running 38# front, 42 - 44# rear; both pre race). For the Subaru Challenge, I'm going to try 40 front, 44 rear to start, and go from there. Thoughts?[/QUOTE]
Is your pressure bias backwards? I think running lower pressure in rear than in the front should reduce your understeer... you should reverse the bias...
I have been using actual pressures, set pre-first run, and then adjusting to maintain those pressures on the hot tires after runs. I have seen between 2 - 3 # increase on a run, but only if I am really pushing it and only on the fronts. Many of the runs at FedEX, I had no increase by the time I was back on grid. Probably why I'm slow. Even with rears 4 - 6 # over fronts, I'm still understeering big time. I hope a recent performance alignment by AndrewTech will help.
Are you on stock tires (I am) ? If so, the max is 51# (I had thought it was 44#, so I was running 38# front, 42 - 44# rear; both pre race). For the Subaru Challenge, I'm going to try 40 front, 44 rear to start, and go from there. Thoughts?[/QUOTE]
Is your pressure bias backwards? I think running lower pressure in rear than in the front should reduce your understeer... you should reverse the bias...
| Harry | 09-13-2006 09:55 PM |
Yes!
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[QUOTE=Mind;15238016]Is your pressure bias backwards? I think running lower pressure in rear than in the front should reduce your understeer... you should reverse the bias...[/QUOTE]
Sorry, brain dead noob - misread the FAQ on which way to bias the pressures. Probably explains the understeer, huh?
Oh well, I'll try it the right way (FRONT higher than rear) this weekend!
Sorry, brain dead noob - misread the FAQ on which way to bias the pressures. Probably explains the understeer, huh?
Oh well, I'll try it the right way (FRONT higher than rear) this weekend!
| Mind | 09-13-2006 10:15 PM |
^:lol:
That [I]could[/I] explain the understeer... stock, mine understeered a good bit, but I can only imagine what you were experiencing with the tire pressures!
That [I]could[/I] explain the understeer... stock, mine understeered a good bit, but I can only imagine what you were experiencing with the tire pressures!
| Harry | 09-13-2006 10:32 PM |
but ...
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After re-reading the FAQ (for the billionth time), recent posts debated whether the FRONT higher bias was right or not, so maybe I'm only partially clueless.
That said, I remember being confused on the bias for my 02 wagon, thinking that higher in the rear would reduce the size of the contact patch (which it does), reducing the traction at the rear and improving rotation (nope, see FAQ). After reading the FAQ back then, I finally settled on FRONT at +2 over stock, rear at stock, for street use. Not sure why I forgot that now that I have the 06 wagon. Probably old age :(
That said, I remember being confused on the bias for my 02 wagon, thinking that higher in the rear would reduce the size of the contact patch (which it does), reducing the traction at the rear and improving rotation (nope, see FAQ). After reading the FAQ back then, I finally settled on FRONT at +2 over stock, rear at stock, for street use. Not sure why I forgot that now that I have the 06 wagon. Probably old age :(
| solo-x | 09-14-2006 08:07 AM |
the tires will make their most grip at one pressure. higher or lower then that decreases the grip. so you could go to a high rear bias or low rear bias. keep in mind though that tires have a spring rate too, and when you put a two springs in series the actual rate is lower then the softer spring. the tire spring rate is affected by tire pressure, so running a high rear tire pressure vs. a low would affectively increase your rear spring rate.
| Harry | 09-14-2006 09:17 AM |
[QUOTE=solo-x;15241588]the tires will make their most grip at one pressure. higher or lower then that decreases the grip. so you could go to a high rear bias or low rear bias. keep in mind though that tires have a spring rate too, and when you put a two springs in series the actual rate is lower then the softer spring. the tire spring rate is affected by tire pressure, so running a high rear tire pressure vs. a low would affectively increase your rear spring rate.[/QUOTE]
So what pressure do you think I should start with? The wagon is stock, with RE 92 on stock 17 x 7 wheels, everything else is stock except the alignment, with -0.5 camber front; -1.5 rear)
I was thinking 40 - 42 FRONT (;) ), maybe 38 rear?
So what pressure do you think I should start with? The wagon is stock, with RE 92 on stock 17 x 7 wheels, everything else is stock except the alignment, with -0.5 camber front; -1.5 rear)
I was thinking 40 - 42 FRONT (;) ), maybe 38 rear?
| leecea | 09-14-2006 12:54 PM |
Have you tried the rollover test with chalk on the sidewalls? I think that is supposed to be useful with street tires. At least it minimizes the tire damage!
| solo-x | 09-14-2006 02:17 PM |
[QUOTE=leecea;15244982]Have you tried the rollover test with chalk on the sidewalls? I think that is supposed to be useful with street tires. At least it minimizes the tire damage![/QUOTE]
minimizes tire damage, but nearly useless after that.
where should you start? first, ignore the max inflation pressure thing on the tire. that means diddly squat. don't go tom cruise crazy with them though. i just wouldn't be afraid of 50-55psi in the rear tires. for the fronts maybe mid/high 40's? you gotta kinda play around with it if you don't have the tools to quantify a pressure change. (and no, a pyrometer alone is not enough to accomplish that either). 48/55 doesn't sound outrageous considering stock tires and a crappy alignment. (no front camber) search around a bit. i'm POSITIVE there are at least 10 threads with tire pressure recommendations for the re92's.
minimizes tire damage, but nearly useless after that.
where should you start? first, ignore the max inflation pressure thing on the tire. that means diddly squat. don't go tom cruise crazy with them though. i just wouldn't be afraid of 50-55psi in the rear tires. for the fronts maybe mid/high 40's? you gotta kinda play around with it if you don't have the tools to quantify a pressure change. (and no, a pyrometer alone is not enough to accomplish that either). 48/55 doesn't sound outrageous considering stock tires and a crappy alignment. (no front camber) search around a bit. i'm POSITIVE there are at least 10 threads with tire pressure recommendations for the re92's.
| Scooby921 | 09-15-2006 08:55 AM |
[QUOTE=Mind;15238016]Is your pressure bias backwards? I think running lower pressure in rear than in the front should reduce your understeer... you should reverse the bias...[/QUOTE]
You do not always need higher pressure in the front. It is really tire and suspension dependent. On my WRX with R-S2's I run higher rear pressures. The fronts are done such that the tires rolls as much as it should...but not to the sidewall or too far down the side of the treadblocks. The rear pressure is adjusted until the rear end likes to rotate around corners without being too loose and unpredictable. But this is for my particular setup. Someone with a bigger RSB or stiffer rear springs might use a little lower tire pressure since their suspension is what gets the rear end happy.
A friend runs a 2.5RS in STS. With the 'kooks he runs higher rear pressure. On the same car with the same suspension setup he runs higher front pressure with Falken RT-215's.
The same goes for another friend running STX. He runs Advan Neova's at higher front pressure than rear, but ran higher rear pressures when he used to use the R-S2's.
So you need to look at your alignment, suspension setup, and tires before you start assuming what might be causing a problem. What works for one doesn't necessarily work for another. There are too many variables.
You do not always need higher pressure in the front. It is really tire and suspension dependent. On my WRX with R-S2's I run higher rear pressures. The fronts are done such that the tires rolls as much as it should...but not to the sidewall or too far down the side of the treadblocks. The rear pressure is adjusted until the rear end likes to rotate around corners without being too loose and unpredictable. But this is for my particular setup. Someone with a bigger RSB or stiffer rear springs might use a little lower tire pressure since their suspension is what gets the rear end happy.
A friend runs a 2.5RS in STS. With the 'kooks he runs higher rear pressure. On the same car with the same suspension setup he runs higher front pressure with Falken RT-215's.
The same goes for another friend running STX. He runs Advan Neova's at higher front pressure than rear, but ran higher rear pressures when he used to use the R-S2's.
So you need to look at your alignment, suspension setup, and tires before you start assuming what might be causing a problem. What works for one doesn't necessarily work for another. There are too many variables.
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