205/55/15 R888 pressures?

[sammydickie]

Running nitrogen any ideas on what ideal hot pressures should be? Started at 32 psi cold they went up to 36. Then dropped them to 26 psi and they went up to 29. Went out at 29psi fronts and 26psi rears they seemed to stay at this pressure through out the next session. The car is stripped and caged but not sure on wait it has m20 6 cyl engine. Thanks for any advice!

[Black_Potato]

30-31 PSI hot. You shouldn't be getting that range on dry nitrogen though. 24-31 is expected with average humidity.

[Demlotcrew]

Running nitrogen any ideas on what ideal hot pressures should be? Started at 32 psi cold they went up to 36. Then dropped them to 26 psi and they went up to 29. Went out at 29psi fronts and 26psi rears they seemed to stay at this pressure through out the next session. The car is stripped and caged but not sure on wait it has m20 6 cyl engine. Thanks for any advice!

Like you said it all depends on weight!

Did you see the tyre fitter change the air? It takes about three to four complete cycles to fill a tyre with a higher percentage of nitrogen gas. (not cheap). It might be more financially viable to use dried air instead.

You should also slightly over inflate the load tyre (to get even wear).

36 hot on the weight of your car is a good target or 28 front and 26 rear cold.

What are your camber settings?

[DanThe]

The PBMW lot reckon on 31 hot for the 888's

[Demlotcrew]

They all must be running < 1000kg cars!

[Black_Potato]

The PBMW cars running 6 pots will be aprox 1170kg.

Within reason the weight will have little effect (+-200kg), its more to do with heat and air expansion and getting the tyre to the right temp across its contact patch. If anything more weight will mean more heat so starting at the same pressure, say 24psi they will end up high, say 33-34 PSI if you are running 1400kg.

If you really want to check get a pyrometer and check across the tread to see its even. They will probably be 90-100 degrees a few mm below the surface.

[DanThe]

I was using an infra red thermometer at the last track day, the centre of the tread was always a fair bit cooler, had 11° difference inner to outer to start with so took some camber out got it down to 3-4° difference and it was much better

[Black_Potato]

Its a very usefull approach that gives you some facts to work with, however its worth getting one that penetrates the surface if you can as that will give you more realistic numbers. It also helps if you can get a mate to do it, do some hot laps, roll through the pits with hot tyres (no cool down lap) and then go back out to cool down if required.

[Demlotcrew]

Within reason the weight will have little effect (+-200kg), its more to do with heat and air expansion and getting the tyre to the right temp across its contact patch. If anything more weight will mean more heat so starting at the same pressure, say 24psi they will end up high, say 33-34 PSI if you are running 1400kg.

If you really want to check get a pyrometer and check across the tread to see its even. They will probably be 90-100 degrees a few mm below the surface.

This goes against everything i have ever been told/Experienced.

I think you are confusing two issues.

1. Wet Air expansion due to temperature increase (basic physics).
2. Maximising grip by running optimum tyre pressures.

In your first point you say that weight has no effect +-200kg then you go on to say that it does have an effect and if you add 200kg to a 1170kg PBMW car the tyres will generate more heat and this results in higher pressures.

My recommendations was based on the use of Nitrogen and weight has everything to do with hot target temps.

Dan, I have one too, I was seeing 120° across the tyres on my last day out.

[Black_Potato]

OK.. too try and be clearer.

Toyo's in GG in a profile like 195/50/15, 205/50/16 etc... for a car between say 1100 & 1300 seem to work best at aprox 31PSI hot which in turn give a good shape to the tyre and as a result constant contact patch and temp.

Having run these tyres on a 318i or 950kg, 320i's around 1150kg and M3/320is of up to 1300kg I have found no significant change in starting or ending pressures to reach the ideal performance. But where there is a difference its generally in getting heat into the tyres and stopping them going off. i.e. in the heavier car the tyre needs to do more work so it will heat up or go off more quickly.

Running R888 a few PSI higher will help when you 1st go out but within 5 laps or so they will be overheating and grip will tail off.

So to conlude .. 31PSI hot is a good target. If you use plain old air or dried air then end temp/pressure will still be the same, you just vary the starting pressure. Its not just what I have found but a common view of a 100 or so people which compete in these cars with the tyres.

BTW... what tyres are you running, they arnt R888, maybe T1R or some kind of Khumo ?

[Demlotcrew]

Dont forget to add in min and max Camber settings for front and back.

Now im running Khumo v70's, i ran R888's I didnt think they were as good once to temp. Im also using the hardest compound and they are exceptional. (only down side is it takes quite a few laps to get heat in to them as they are stiff).

[Black_Potato]

Probably because you ran them too hot with too much pressure :p

Only kidding ;)


Camber, folks start off around 4d front and 1.5 rear but that should be tuned as a result of tyre temp. I run around .5 degree difference NS/OS as it helps with braking etc. But this discussion gets more subjective based on springs, dampers, ride height, driving style etc.

[DanThe]

Dan, I have one too, I was seeing 120° across the tyres on my last day out.

Where was the track day, Bahrain?

I think my max temp was about 54 just over a week ago and that was slicks

[Demlotcrew]

It was at Rockingham.

Dude slicks are barely working at 54! You must have not been on the limit much.

What are your camber settings?

[Demlotcrew]

Camber, folks start off around 4d front and 1.5 rear but that should be tuned as a result of tyre temp. I run around .5 degree difference NS/OS as it helps with braking etc. But this discussion gets more subjective based on springs, dampers, ride height, driving style etc.

-4° Camber, you must have a lot of roll to need that much?

R888's are well over rated, not that great.

[DanThe]

I am not hardcore like you S14 ists

Not measured yet, but the topmount cant go over anymore on the nearside, offside is about 3mm off max

[DanThe]

This is the top mount

[Demlotcrew]

Thanks for that Dan, i would have never guessed what it was!

Have you measured the camber at the Hub?

Ps, you are more hardcore than i am, "Best Car & Mod-Master Winner 2009"

I think you might need to move that turret a little bit forward, maybe thats what the problem is?

[DanThe]

Well, your guess is as good as mine

What should I be aiming for? 3.5 - 4 is what I think of?

Tell me how hot the slicks should be and I will try harder next time/february

[Demlotcrew]

Dan,

Camber really does depend on and is proportional to roll.

Im running -2.5° on the front, Like Mr Potato has said, the subject of camber is very subjective and what works for me may not be the optimal for your car.

When i tried -4° not only was braking hard on a straight line an issue my tyres were not wearing evenly on the outer edge. I have little roll and very high spring rates on the front.

Every tyre manufacturer has its own target temps so i would contact them first. My aim is for anything between 80° - 120° depending on track surface temps and weather conditions.

What track day are you doing in Feb? I might come along

[DanThe]

Oulton car club day

[Demlotcrew]

Hmmm, bit north for me, weather isnt great in Feb these days. Let see.

[Demlotcrew]

So to conlude .. 31PSI hot is a good target. If you use plain old air or dried air then end temp/pressure will still be the same, you just vary the starting pressure. Its not just what I have found but a common view of a 100 or so people which compete in these cars with the tyres.

Seems that others disagree.

http://www.e30zone.net/modules.php?name ... c&t=184501

Going by the numbers on this post, my first recommendation was pretty much spot on.

http://www.e30zone.net/modules.php?name ... 32#2021332

Andrew

[Mikey_Boy]

Well discussed this one...

I have found that my R888's work best at around 40psi HOT... But then I am only doing a few laps before I come in, not a full race distance..

[Black_Potato]

Life would be dull if we all agreed ;)

[sammydickie]

I was running 1 3/4 degrees front camber, on advice from the guy setting up the geometry for me. I was told to dial in as much as possible by the guy at gaz-shocks.
I have adjustment for a lot more. May try more at silverstone next sun. Ill keep the pressure around the 30-32 hot area and report back on my impressions and findings.
Thanks for the advice everyone!