Agentorange

I keep my tire pressure at 33front and 38rear according to the tire pressure monitor system on 14’ TTS. When I hit 170mph a low tire pressure light came on!
Do I need the tire pressure higher to go faster?
Anyone ever take their 991 TTS to max speed?

jennifer911

Agentorange, if you check your manual you will note that heavy loads and extended high speeds need a tire pressure of 36 front / 44 rear. With a casual glance at your tire it will look to be perfectly round. However, if you get down on the ground for an earthworm’s view, you will see that contact patch is an area about 3 to 4 inches that sits flat on the road. As the tire rolls along the tire casing and tread plies must constantly flex to maintain this flat contact patch, With a stiff ultra high-performance tire this will generate enough heat that may destroy the tires. the tire pressure monitor is just trying to save the car from a fiery crash. Oh yeah, saving your life is simply an added benefit.

Jean

Agentorange you must have a leak in one of the tires or sensor error. Pressures increase with speed, you pressure readings are ok but could benefit a bit from slightly higher pressure at the front if you're after straight line speeds. We reach consistently higher than those speeds at the racetrack's straight line without issues.

hcvone

I have Forgeline CF201's and Michelin pilot super sports, I run 32/38 cold, that gets me 36 to 38 fronts hot and 43 to 45 rears hot, above 150 mph the pressure gets to 40 fronts and 50 rears in the summer, been way faster many times, zero warnings.

jadatis

Can be that your TMPS corrects the pressure for temperature. Then you see the same pressure every time and no warning in the morning on cold days.
But also the sustem can worn you when inside tire temp gets to hot. This happens when to much heat is produced, as happens at your absurd high speed.
I am able to calculate a safe pressure for higher speed with safer formula and system then the officially used, wich I once got hold of, and went running with.
Need weights on tires and speed, and 3 tgings of tires
1 maxload or loadindex
2 kind of tire , if XL/ reinforced/ extraload, then 42 psi is needed in the formula, otherwise 36 psi.
3. Speedcode, if ZR , also speedcide Y or W is given mostly, but in my system not important, so can do without. Some ZR dont have speedcode given.

Randyc151

You didn't mention what tires you are using, so this is a general response. Let's assume you are using Cup2 tires. Yep, that warning comes on at 165mph when the tires (TPMS) are set to "Summer Tires and Comfort pressure". I've seen that warning thousands of times. As mentioned above, the car has different tire pressure settings for different situations. For briefly hitting 170mph on track before a turn, you are fine with much lower pressures. I like 30-32 hot. If you fill the car full with passengers and luggage, then go on a blast down the Autobahn for half an hour, you should raise the tire pressure accordingly.

Agentorange

Wow thanks for all the good info ladies and gents. I’m running Michelin pilot sport 4s. I’ll bump up the pressure and try again.

worf928

This ...
... and this.
OP, check your TPMS settings. Comfort pressure setting will cause the warning.

Agentorange

OP, check your TPMS settings. Comfort pressure setting will cause the warning.[/QUOTE]
Copy that. I’ll bump the psi up to “high speed” psi.

Paliknight

There’s tpms settings?

longboarder

No. I was running 20psi on rear r888's and now 25psi on your same tires. I run low tire pressure because my Turbo S is running 68mm turbos lots of meth with a custom ES tune and can spin the tires easy even on roll hits. I run 175+ in the half mile and on desolate highways in Mexico well above that number with no issue with these tire pressures. Yes my tmps sensor is always on and yes it is better to run higher pressures however I have not had any issue running these low pressures for hundreds of high speed runs so you are just fine nothing to worry about at 38psi.

Randyc151

Agreed - I would not worry about increasing pressure, just knowing that the monitor will come on at high speeds, and go back off when you slow down. Porsche is just trying to limit their own liability for the tires. (Read the story about Ford and Firestone tires from the 90s. Ever since then, manufacturers have raised their recommended pressures to avoid lawsuits, even though tire design is vastly improved today)

worf928

This -^

m33ufo

I’ve got an air leak from one of my sensors. Is this likely to be the sensor itself or just the seal?

2fcknfst

Reminds me of going into my Subaru dealer in 2003 and complaining that Cruise Control would not engage in my STI over 100mph... and the looks of shock and bewilderment that followed.

Tough problems we have indeed; mind you, I don't think I'd like my tyres to de-laminate at 170mph...