Buzzlt Posted May 23, 2018 Report Share Posted May 23, 2018 Well after putting a few thousand miles on my Boxster the last couple of weeks Via the Monaco and Spa classic and a load of twisties thrown in this is my latest subject of curiosity. I have had a quick look through the tyre snobs topic bit dis not want to throw a spanner in the works. I have fitted some cheap tyre pressure monitors which also monotor the temperature of the tyres (about £45 from the rain forest/river). I set the pressures when I left 30 front and 37 rear although the weather was a bit cooler. For the record I have Pirellis at the front (OK) and Bridgestones at the back (not impressed as wear quickly and dont grip as well cold). I have found in this weather they heat up much more quickly to an operating temp of about 30deg and a couple of PSI more with normal driving. With spirited driving the pressures and temps increase to around 38 psi front and 45 psi rear and around 50deg C. This means that reducing the pressures a couple of psi when cold dramatically improves the grip when hot especially in the wet when the grip is unbelievable when warmed up. Just thought I would share my experience and open to comments in other peoples. Heres how it went around Spa (didn't teally know what I was doung but had a hoot). https://youtu.be/YN-ZSLy9IbE Link to comment Share on other sites More sharing options...
Simon_R Posted May 23, 2018 Report Share Posted May 23, 2018 Looks like you were having fun @ Spa. Great track, only driven it the once but it really is epic. Question, who was the TDO & was it overtaking on both sides? Oh & suggestion, try keeping both hands on the steering wheel unless changing gear, I used to do that & got knuckles rapped by an instructor for doing so. Link to comment Share on other sites More sharing options...
Gorsh Posted May 23, 2018 Report Share Posted May 23, 2018 That looked great fun Greg! I checked mine now and again on our warmer driving days and noticed the pressures went up by around 0.3 bar from cold. I think that is normal tbh and well within the operating pressures expected (no idea what the temps were though). Lowering the pressures some days and not others is a bit of a faff so some owners solve this by having them filled with nitrogen - think good tyre centres and some OPC's will do it for you. Really enjoyed the trip - I must do Spa as well next time! Link to comment Share on other sites More sharing options...
Buzzlt Posted May 23, 2018 Author Report Share Posted May 23, 2018 Hi Simon Lol only need two hands for a car with no power steering and yes I have been told that before but not had much experience. It was only ‘parade’ laps during the event and most people don’t even use their mirrors so there is no etiquette required ! Assume you mean Track day organiser - if so it was part of a package organised by Fasttracktours. At some point I will try and post some pictures of the other Boxsters etc that came along. Link to comment Share on other sites More sharing options...
Buzzlt Posted May 23, 2018 Author Report Share Posted May 23, 2018 15 minutes ago, Gorsh said: That looked great fun Greg! I checked mine now and again on our warmer driving days and noticed the pressures went up by around 0.3 bar from cold. I think that is normal tbh and well within the operating pressures expected (no idea what the temps were though). Lowering the pressures some days and not others is a bit of a faff so some owners solve this by having them filled with nitrogen - think good tyre centres and some OPC's will do it for you. Really enjoyed the trip - I must do Spa as well next time! Yep it was a fantastic trip and good to meet you. Have read a bit on Nitrogen but suspect that as you probably can’t get all the air out its a waste of time.....? I think we have some at work - hmmm.... Link to comment Share on other sites More sharing options...
Greenman Posted May 24, 2018 Report Share Posted May 24, 2018 Standard pressures for my 981 20” tyres is 2.3 bar (33psi) but I regularly see 2.6/2.7 when warm and that’s not even on track so would be even higher there. I do find it a bit strange that tyres should always be checked when cold, you would think the optimum hot pressure would be more important to get right especially on track use. i also find it somewhat strange that the 987 has much higher rear pressure than front, whereas 981 is same front and back. 10 hours ago, Gorsh said: Lowering the pressures some days and not others is a bit of a faff so some owners solve this by having them filled with nitrogen - think good tyre centres and some OPC's will do it for you. What?? I’ve seen plenty of (dubious) claims about the benefits of Nitrogen inflation but being immune to the effects of temperature isn’t one of them, physics is physics I’m afraid. Link to comment Share on other sites More sharing options...
911-32 Posted May 24, 2018 Report Share Posted May 24, 2018 BuzzIt - interesting real world feedback on pressures. Thanks I don't know why, but I have always found Porsche recommended tyres pressures to be rather high particularly rear pressures. Through my 25 years of 911 ownership and extensive track days I have always aimed for hot temps in the low 30s with front/rear differentials aimed at fine tuning the handling balance. In the real world you would be adding/bleeding air all the time which is impossible for the average owner, so I guess Porsche recommend something that works freezing cold and boiling hot. FWIW, I wouldn't be running a hot rear temp of 45psi by choice. I set my own cold pressures last week at 32/34psi and will likely drop further for roadtrip action. Cold pressures for track days have in the past been set as low as 20psi in order to aim for ~32psi hot - though that requires careful initial warming up laps. $0.02 Link to comment Share on other sites More sharing options...
Jon61 Posted May 24, 2018 Report Share Posted May 24, 2018 There are several other threads that have mentioned this, but I think if you want to minimise the effect of temperature on tyre pressures, it's worth just using dry air (which is 78% nitrogen anyway) if you can get it rather than bothering with 100% nitrogen. I believe the water vapour in "normal" air makes more of a difference than the oxygen, CO2 etc (because water changes state at ordinary temperatures far more than the other components). And FWIW, for the 981 with 20" wheels (only), Porsche also list 'comfort' tyre pressures 3psi below the normal ones. Only usable up to 165mph though Link to comment Share on other sites More sharing options...
PaulQ Posted May 24, 2018 Report Share Posted May 24, 2018 2 hours ago, 911-32 said: I don't know why, but I have always found Porsche recommended tyres pressures to be rather high particularly rear pressures. I find my car is much nicer to drive with approx 30 psi all round, maybe a touch more on the rear, though I have a near square set up on relatively small tyres. Link to comment Share on other sites More sharing options...
Buzzlt Posted May 24, 2018 Author Report Share Posted May 24, 2018 Thanks for the useful feedback so far, I think I might try lowering the pressures a bit more maybe 2psi front and rear to see what gives. Had a quick search and can’t easily find any other topics specifically talking about the difference tyre pressure makes on this forum so would be greatful for any pointers as to what to put in as search criteria? Part of the reason for further reaseach is that a combination of suspension geometry and tyre pressures has caused the tyres both front and rear to wear on the inside edge. This means I will soon have to replace both sets but do not want the new ones going the same way so quickly. Yes I did get the geo checked and have replaced most of the suspension components but still a work (hobby) in progress. Link to comment Share on other sites More sharing options...
Jon61 Posted May 24, 2018 Report Share Posted May 24, 2018 2 hours ago, Jon61 said: There are several other threads that have mentioned this, but I think ... 1 hour ago, Buzzlt said: Had a quick search and can’t easily find any other topics specifically talking about the difference tyre pressure makes on this forum so would be greatful for any pointers as to what to put in as search criteria? The threads I was thinking of were mostly about the merits of nitrogen inflation, rather than pressures versus handling dynamics, but for the former you could have a look at these (I searched for Nitrogen):http://www.BoXa.net/forum/topic/76697-nitrogen-in-tyres/http://www.BoXa.net/forum/topic/59106-nitrogen-in-tyres/http://www.BoXa.net/forum/topic/69552-n-rated-tyres-and-warranty-insurance/http://www.BoXa.net/forum/topic/70801-fuel-for-the-well-fuel-debate/http://www.BoXa.net/forum/topic/42173-nitrogen-in-tyres/http://www.BoXa.net/forum/topic/57651-track-day-tyre-pressure/ PS I liked the Spa video btw. Link to comment Share on other sites More sharing options...
Buzzlt Posted May 24, 2018 Author Report Share Posted May 24, 2018 Great thanks @Jon61 I particularly liked the bit on the first link I think about the cat but at least there is some science to the rest. Glad you liked my terrible driving ! Link to comment Share on other sites More sharing options...
Willemite Posted May 29, 2018 Report Share Posted May 29, 2018 It is perhaps interesting that Porsche now insist all OPCs use nitrogen inflation routinely. I had new tyres at my OPC six months ago so they were filled with nitrogen (no extra cost either). They don’t feel any different (why would they?) but the tyre pressures have remained remarkably constant* and the pressures do not increase as much when they get very hot on track days. its my understanding that the main benefit is that the gas is dry; it’s the water vapour in normal air that cause the big rise in pressure when tyres get very hot. * if you allow for difference in ambient temperature. “Cold” pressure is actually pressure at 17°C - reduce tyre pressure by 0.01bar for every 1° below, and increase by 0.01 bar for every 1° above 17°c ambient temperature. Link to comment Share on other sites More sharing options...
rsmithinfo Posted June 3, 2018 Report Share Posted June 3, 2018 In the little bit of racing I’ve done on a 944 we used to get the tyres up to temperature with a few laps at the start of the day (one of the quali sessions or similar) and then bring them down by letting air out to I think 34psi and left them the rest of the day knowing that they’d come back up to that pressure during the race. Never thought much about it for the road but makes sense for more spirited driving. Link to comment Share on other sites More sharing options...
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