Tire Pressure

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Tire Pressure

Post by nubrocket on Tue Dec 11, 2012 1:19 pm

The topic of tire pressure has come up in lobbies recently, which of course is too late for me to do anything about it. I've tinkered with it before, but until recently I didn't realize how much I didn't understand about it.

The GUI in Forza says "Decrease pressure to increase grip and oversteer at the cost of top speed, and increase pressure to go faster but also increase understeer. Oh, and a little change can have a huge impact so be careful with this". Well, more or less it says that.

As a result I've run more cars with less psi than more. For the few cars I've tweaked, I usually land around 28.5 to 29. Well, after our Road Atlanta run last week where Lou gave me learnin' about how tires can wtf melt and become "gummy", and Beef's comments about how he's running different pressures in front and back, I'm now here asking for info and advice.

What are y'all running for the December series? Do you change pressures depending on the track? Where are your comfort zones, if'n you have any?

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Re: Tire Pressure

Post by joekorn on Tue Dec 11, 2012 2:46 pm

RWD: I almost always run 29 in front, 28 in back. Seemed to work well on the Corvette, not at all for the 370Z. Those are pretty conservative settings, but I tend to sacrifice speed for grip. Makes me a consistent driver, but not the fastest.

FWD: Just the opposite of RWD, I typically go with 28 front, 29 rear.

AWD: Usually run 28.5 on both.

These are just my personal preferences though, haven't really put any time into looking at the metrics. Will be nice to hear from those who have spent time actually testing pressures. I'd like to learn more about it too since it can make a fairly big difference.

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Re: Tire Pressure

Post by marmuttlebow on Tue Dec 11, 2012 2:54 pm

Just watch your tire temps?

Perhaps it's cuz I'm not much of a tuner.

I know that I can't drive Lou's tune's fast. They don't suit my style (apparently I like it a little looser). So I think it's more a personal thing as to how to dial in your car and to have it handle the way you like it to.

Set the tire pressure the way you like (and I just have 'em at 28 or 29 across the board) and go with it. Keep an eye on your tire temps and adjust according to that.
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Re: Tire Pressure

Post by nubrocket on Tue Dec 11, 2012 3:02 pm

marmuttlebow wrote:Just watch your tire temps?

I was going to ask about this but then I asked Bing instead.

I found this.

I r will reads it.


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Re: Tire Pressure

Post by marmuttlebow on Tue Dec 11, 2012 3:12 pm

I can tell you how I tune (although it doesn't really come into play here):


Drive it, play with a few things.  Repeat.  It helps to be somewhat consistent on a lap to lap basis and how you take turns (for that, perhaps a shorter track is a good place to start tuning).  The reason is because then you compare apples to apples.  You can see if the car is plowing through the corners or feel the back end wanting to swap ends.  Etc. 


Once that's done, then you can do some fine tuning.  Read the tire temps and tweak things accordingly.  Check suspension travel, etc.  Basically, watch the "live loads" as you drive and see what needs to be tweaked.


That's the extent of my tuning.  Not that it's passing the muster (or is it Mustard?) these days.

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Re: Tire Pressure

Post by nubrocket on Tue Dec 11, 2012 3:33 pm

I think that article I linked is explaining something backwards.


If front tires are hotter than rear tires, your car will under steer. This is because, too much front spring/sway bar, not enough rear spring/sway bar, or front pressure is too high or front tires are too narrow or rear tires are too wide. In this case, soften up front spring and sway bar, stiffen up rear spring and sway bar, decrease front pressure or increase rear pressure.

If rear tires are hotter than front tires, your car will over steer. This is because, too much rear spring/sway bar, not enough front spring/sway bar, rear pressure is too high, front pressure is too low, rear tires are too narrow or front tires are too wide. In this case, soften up rear springs and sway bar, stiffen up front spring and sway bar, decrease rear pressure or increase front pressure.


That sound wrong to anyone else?

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Re: Tire Pressure

Post by beefsupreme42 on Tue Dec 11, 2012 11:15 pm

as I said earlier, I have the corvette at 31 in the front and 30.5 in the back. I noticed that with the stock (30 PSI) tire pressure, the tire temperatures were getting very close to 210 degrees. Keep in mind that you generally want the tires to be between 180 and 210 degrees - too hot and they will get gummy and you will just slide all over the place, too cold and there isn't enough temperature to stick to the track. This leads into multiple tips:

1. if your tires are too hot, bring the temperature up. It they are too cold, bring it down. I usually start with 28.5

2. If upgraded, you can adjust the roll bars to help get optimal tire temperatures. I believe that increasing stiffness increases temperature and decreasing stiffness decreases tempertature.

3. if upgraded, adjusting the springs can act as a sort of "multiplier" (I guess is the word for it) to the settings from the roll bars and the tire pressure. higher stiffness = higher temps, lower stiffness = lower temps.

With #2 and 3, you want to make sure that you get the right balance of stiffness and tire temperature. If you have to bring the roll bars under 12 or the springs under 20% of the highest possible setting to get the temperatures low enough, then you should probably go back to step one and adjust your tire pressure to make it work. It will take a while at first, but you should get the hang of it rather quickly

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Re: Tire Pressure

Post by BiggLou55 on Wed Dec 12, 2012 12:12 pm

Do this....

Run 5 laps in a HotLap session and view the replay at the end of the session. Skip to lap #4 and watch your tire temps in telemetry (the tire temp screen with inside middle and outside temps for each tire)... Switch back and forth between the tire temp and suspension stats (camber, tow, temp, pressure, etc) making note of the tire pressure here and there...

If your average tire temp is between 180 and 210 degrees F, then you are fine... You may see spikes over 210 in heavier cars, but as long as the temp comes right back to "normal", it will be fine. Temp spikes happen in tight corners, wheel spin and slides... Those events will spike pressure, but it will return to normal....

For FWD cars, just set the rear tire pressure to 25-28 PSI and forget it. You will never be able to get the temps up on the rear tires of FWD cars... It's not a big deal..

Two of the most overlooked adjustments when it comes to tire pressure is Aero and Ride height (both ways)...
Too much aero, and you may heat your tires up too much... too little and they will heat up from sliding.
Ride height is one of the most important suspension adjustments and can completely change the handling of a car with just one click in either direction...

Finally... SAVE YOUR TUNES OFTEN... I can't tell you how many times I've adjusted a great tune into oblivion only to find I forgot to save it when it was working pretty well... It doesn't have to be perfect to save, so SAVE SAVE SAVE and PLAY PLAY PLAY!!! Wink


Last edited by BiggLou55 on Wed Dec 12, 2012 3:10 pm; edited 1 time in total

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Re: Tire Pressure

Post by U2SCDoli on Wed Dec 12, 2012 12:51 pm

if you're not a master tuner and you only wanna get ideal grip from your tires without adjusting everything else, just get the tires to stay green, like lou said, between 180F and 210F. do about three warm up laps, then check the temps and adjust accordingly.

higher PSI = lower temp
lower PSI = higher temp

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Re: Tire Pressure

Post by nubrocket on Wed Dec 12, 2012 12:53 pm

This is great info, thanks guys! I had only seen the little car picture with colored tires before which I didn't feel really told me anything. I assumed it was a temp thing but wasn't sure.

What this is telling me though is that for the Dec series, which is a spec series, our tire pressure choices should end up close to each other, right?

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Re: Tire Pressure

Post by BiggLou55 on Wed Dec 12, 2012 3:11 pm

For the most part, yes... Wink

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Re: Tire Pressure

Post by xraydash on Wed Dec 12, 2012 4:42 pm

beefsupreme42 wrote:as I said earlier, I have the corvette at 31 in the front and 30.5 in the back.

What do you have the 370 set to? Anyone else gonna be a bro and tell us your settings? I'll be honest- I just like to drive and have no interest in figuring anything out for myself. Razz
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Re: Tire Pressure

Post by BiggLou55 on Wed Dec 12, 2012 5:55 pm

I'll send you what I'm running... Just can't remember off the top of my head....

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Re: Tire Pressure

Post by beefsupreme42 on Wed Dec 12, 2012 6:13 pm

xraydash wrote:
beefsupreme42 wrote:as I said earlier, I have the corvette at 31 in the front and 30.5 in the back.

What do you have the 370 set to? Anyone else gonna be a bro and tell us your settings? I'll be honest- I just like to drive and have no interest in figuring anything out for myself. Razz
I haven't adjusted that yet (probably why I was spinning the tires so much) so I will probably tune it some time this week and send it to you

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Re: Tire Pressure

Post by xraydash on Wed Dec 12, 2012 6:15 pm

BiggLou55 wrote:I'll send you what I'm running... Just can't remember off the top of my head....
Thanks, Lou! Always appreciate it.
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Re: Tire Pressure

Post by BiggLou55 on Wed Dec 12, 2012 7:25 pm

xraydash wrote:
BiggLou55 wrote:I'll send you what I'm running... Just can't remember off the top of my head....
Thanks, Lou! Always appreciate it.

Anything that you do set you will need at least 2 laps to get up to full grip... The first lap will be quite sketchy no matter what you try... Wink

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Re: Tire Pressure

Post by nubrocket on Thu Dec 13, 2012 3:42 pm

Forza should just implement these.

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Re: Tire Pressure

Post by marmuttlebow on Thu Dec 13, 2012 5:10 pm

Last night's race at 28.5 for all cars yielded my left front outer always in the yellow.

Gonna be similar for next week.
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Re: Tire Pressure

Post by xraydash on Thu Dec 13, 2012 6:09 pm

I used Lou's garage cars, whatever those are set at.
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