When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
There is what people anecdotally find works for them, and there is what Michelin/Porsche recommends. Michelin and Porsche recommend 29 front and 33 rear, regardless of operating temperature. The N1 compound is designed for this car and those pressures. Other tyres that aren't factory homologated will probably differ from this but they are quite specific about it. Our race team has had a direct conversation with Goodyear on our GT2 RS rally car, their tyres are factory homologated as well and they have told us the same thing. Nameplate pressures regardless of operating temperature is what you want to aim for.
My own personal anecdote is that all of my fastest laps have been set when the tyres were closest to 29/33. Best outcomes have been generally for me to aim for them to come up to 29/33 for the fastest lap, typically 3-4 laps into a session, then they will finish the session slightly higher than this. If you are doing a full race you want them to stabilize at 29/33, a short autox would probably start with them at those pressures.
My track experience has been the same - adjust until the pressures stabilize at the target. But I have two concerns - first, I'm starting pretty low and that probably means I need to bring them up to pressure gently over a couple laps - and, second, tire life will be shortened by the high (over 200) operating temps resulting from low pressures, especially in warm weather. Do you agree? Thanks.
My track experience has been the same - adjust until the pressures stabilize at the target. But I have two concerns - first, I'm starting pretty low and that probably means I need to bring them up to pressure gently over a couple laps - and, second, tire life will be shortened by the high (over 200) operating temps resulting from low pressures, especially in warm weather. Do you agree? Thanks.
Yeah, you don't want to start too low in pressure or you can damage the sidewalls (and same goes with driving too hard before warming gently).
There is what people anecdotally find works for them, and there is what Michelin/Porsche recommends. Michelin and Porsche recommend 29 front and 33 rear, regardless of operating temperature. The N1 compound is designed for this car and those pressures. Other tyres that aren't factory homologated will probably differ from this but they are quite specific about it. Our race team has had a direct conversation with Goodyear on our GT2 RS rally car, their tyres are factory homologated as well and they have told us the same thing. Nameplate pressures regardless of operating temperature is what you want to aim for.
My own personal anecdote is that all of my fastest laps have been set when the tyres were closest to 29/33. Best outcomes have been generally for me to aim for them to come up to 29/33 for the fastest lap, typically 3-4 laps into a session, then they will finish the session slightly higher than this. If you are doing a full race you want them to stabilize at 29/33, a short autox would probably start with them at those pressures.
I disagree. 29/33 are the recommended cold pressures and not the hot ones. I've seen pressure rises of 10 psi in a session. To arrive at the values you stated means throwing away numerous sessions and/or starting with way too low starting pressures,throwing away several laps. Best way to start is with square pressure and bleed down. This chassis works well with 32 F and 34 R.
My track experience has been the same - adjust until the pressures stabilize at the target. But I have two concerns - first, I'm starting pretty low and that probably means I need to bring them up to pressure gently over a couple laps - and, second, tire life will be shortened by the high (over 200) operating temps resulting from low pressures, especially in warm weather. Do you agree? Thanks.
Yes that is a constant battle, I was at a track night last week and when we stopped for a dinner break my pressures dropped to the point where the TPMS was throwing errors. It's quite annoying and needs to be balanced.
If you are going for optimal lap times you want to aim for the pressures to come up to 29/33 after about 2 warmup laps, then maybe 2 hot laps at optimum, then after that the tyres will be overheating and overpressured.
I am not competing with anyone and I personally like to get as many laps in as possible, so I keep my pressures a bit lower so they stabilise at 29/33 and just do bulk laps with overheated tyres, but at least they are at the right pressure.
I disagree. 29/33 are the recommended cold pressures and not the hot ones. I've seen pressure rises of 10 psi in a session. To arrive at the values you stated means throwing away numerous sessions and/or starting with way too low starting pressures,throwing away several laps. Best way to start is with square pressure and bleed down. This chassis works well with 32 F and 34 R.
You might disagree, but that doesn't mean you are correct.
I too was unclear on exactly what 29/33 meant until my race team held a conference call with Goodyears engineering team (Who designed the F1 Supersport R, equivalent to Michelin Cup 2). We race a Goodyear sponsored GT2 RS in tarmac rallies and they told us in no uncertain terms that the nameplate pressures are the target pressures to aim for regardless of whatever your operating temperature settles at for a factory homologated tyre (Of which both the Michelin and Goodyears are). There is no ambiguity to me anymore. The 4psi split front/rear is the singular most important part for handling balance but the overall pressure recommendation still remains, and those are HOT pressures. Reminding you that this was confirmed on a video conference call on which this guy was dialled into:
The only thing that could change my stance is if you got hold of his equivalent at Michelin to tell you something different but our conversation was very specific to these points.
My experience in my GT4 is anything over 30psi on the front axle is not good. The rear is a bit less sensitive but it's a bold call to think you know better than all the engineering teams of Michelin, Goodyear and Porsche combined.
The one thing you are right about is not wanting to drop pressures too low. That is a constant struggle. But it is also the reason why race track mode in your TPMS allows you to drop the pressures a lot lower before throwing errors.
On a typical day I will set fronts to 26 and rears to 29 for the first session, they come up well over and I will bleed them back and hopefully have them set for the rest of the day as the car retains residual heat between sessions. Circuit style, ambient temps, session length and spacing makes a huge difference there.
Most days I go to are 15 minute sessions about once per hour but others are open pit lane, some of them turn around so quickly the car doesn't even get a chance to cool down in between and they all have very different set points to aim for.
Also another interesting myth that the tyre engineers dispelled for us, was nitrogen filled tyres. Nitrogen is of minimal benefit, what actually matters is that whatever is going in the tyres is as dry as possible. Moisture is what causes huge pressure growth when water starts to turn into steam.
You might disagree, but that doesn't mean you are correct.
I too was unclear on exactly what 29/33 meant until my race team held a conference call with Goodyears engineering team (Who designed the F1 Supersport R, equivalent to Michelin Cup 2). We race a Goodyear sponsored GT2 RS in tarmac rallies and they told us in no uncertain terms that the nameplate pressures are the target pressures to aim for regardless of whatever your operating temperature settles at for a factory homologated tyre (Of which both the Michelin and Goodyears are). There is no ambiguity to me anymore. The 4psi split front/rear is the singular most important part for handling balance but the overall pressure recommendation still remains, and those are HOT pressures. Reminding you that this was confirmed on a video conference call on which this guy was dialled into:
The only thing that could change my stance is if you got hold of his equivalent at Michelin to tell you something different but our conversation was very specific to these points.
From the Porsche GTK app:
The std and comfort tire pressures indicated here apply only to the tire makes and types approved by Porsche in case of cold tires (68 deg F(20 deg C))
Regarding your 'tarmac rallye', its not done in the US where most tracks are between 2 and 3 miles. Different rules apply for both event types.
Here is a comment from Michelin:
General Guidelines
Check the pressure of all your tires monthly, including the spare. Even if you don’t see any damage, tires can lose up to 1 psi - pounds per square inch - every month. This can be accelerated by air leaks due to accidental puncture, leaks in the valve or valve cap, or by wheel malfunction.
Check your tire pressure before making a long trip.
For best results, check your tire pressure when tires are cool– before driving the car or if it has covered less than 3 miles at low speed.
If the tire is hot, add 4-5 psi to the car manufacturer's recommended pressure value (0.3 bar) or wait until it has cooled down, which is an average of three hours after parking the car.
Never deflate a hot tire.
Tried to upload the GY trackday pdf which explains tire pressures, etc but its too large
My experience in my GT4 is anything over 30psi on the front axle is not good. The rear is a bit less sensitive but it's a bold call to think you know better than all the engineering teams of Michelin, Goodyear and Porsche combined.
The one thing you are right about is not wanting to drop pressures too low. That is a constant struggle. But it is also the reason why race track mode in your TPMS allows you to drop the pressures a lot lower before throwing errors.
On a typical day I will set fronts to 26 and rears to 29 for the first session, they come up well over and I will bleed them back and hopefully have them set for the rest of the day as the car retains residual heat between sessions. Circuit style, ambient temps, session length and spacing makes a huge difference there.
Most days I go to are 15 minute sessions about once per hour but others are open pit lane, some of them turn around so quickly the car doesn't even get a chance to cool down in between and they all have very different set points to aim for.
Also another interesting myth that the tyre engineers dispelled for us, was nitrogen filled tyres. Nitrogen is of minimal benefit, what actually matters is that whatever is going in the tyres is as dry as possible. Moisture is what causes huge pressure growth when water starts to turn into steam.
Originally Posted by wch
Interesting to hear about nitrogen. I suppose one could try to use tire warmers to maintain heat - too much hassle for me as I'm no longer racing.
We actually agree on something, wow. Yes, the tire pressures on the door jam are COLD pressures. If one tried to run 29/33 HOT, there is not enough sidewall stiffness and the car feels sloppy in the lateral plain.
For those saying it should be 29/33 HOT, I suggest you go back and re-read the owners manual. Every car MFG.'s recommended pressures on the door jam are those pressures when the tires are COLD
Well next time you go to a track day, go and find the guy who is 2-3 seconds faster than you are in the same car and ask him what tyre pressures he’s running.
Any track day tyre in this category is typically run at around 30psi hot. Trofeos, cup 2’s, Bridgestones and Yokohamas are all roughly similar, and everyone at the front of the field will tell you the same thing. 29psi on the front axle makes complete sense when the weight is in the back of a Porsche.
Another related question: There is an image of Bibendum (aka The Michelin Man) pointing outwards on the sidewalls of the Sport Cup 2s near the tread. This icon points towards the location of the wear bars on the tires. I can find this documented.
But is it also an indicator of how far the tire should roll over on its shoulder? When washing the car previously, I had noticed both my front and rear tires were worn exactly to the tip of his fingers. However, recently I scrubbed the icon completely off the rear tire somewhere, probably that last autocross where I suspected I deflated the tires too far.
Does anyone know if this indicator is also used to indicate desired rollover? I've found questions about it in online searches but can't find a definitive answer.
In the first photo you can see the indicator showing wear right at its fingertip (the darkness on the tread is water from where I was just washing the car). The second photo shows where the icon should be, but now it is missing. You can also see the wear extends to the edge of the tread on the rear. Thoughts?
EDIT: Well now that I posted this question, I find an article where Andy Hollis says this icon (or the triangle on other brands) does indicate where wear should stop. See https://www.tracknightinamerica.com/...under-pressure
@StormRune man, I figured you were on to the triangle; Bill taught it in his Driveway classes. Yep, use it for monitoring my wear, rule of thumb is wear to the top of the indicator. Muddying things are IIRC my last set had different indicators with three locations... though they were all pretty close to one another.
Where is that extract from? Is it N1 specific or is that a generic Cup 2 recommendation? I found with non OE stamped tyres that about 32-34 was a sweet spot but the N1's on a GT4 are a bit different to the generic ones.
For what it's worth, Manthey Racing recommend 1.9bar front and 2.0 rear, HOT. That's 27.5/29psi. That's even lower than I have been advocating but far as I'm concerned that's damn near the end of this argument for people doing track days.
Now I know this thread is about what Michelin recommend but there's what Michelin recommend based off their design parameters, and then there's what's fastest in the real world. My own experience is anything higher than 29/33psi produces much, much slower lap times.
08-19-2022, 12:50 AM
