[aerobod]

Originally Posted by ftjack

I know people warm up tires on track and lower the pressure to recommended value (i.e. 32 psi hot instead of cold). Many of them lower it even more. Low tire pressure gives you more contact area with track surface and improves handling.

There is an optimum for a given car on a given track with a given tyre. The pressure could be lower or higher depending on tyre compound, suspension geometry (especially camber) and the way the tyre sidewall and belts distort. The lowering of pressure from initial cold setting to final hot setting while at the track is normal, to reach the optimum hot pressure for the tyre compound.

Street tyres such as the MPS4S will often give optimum grip at hot pressures in the low to mid 40s on a car the weight of the G87 at tyre temperature of 60C or so. A more track orientated tyre such as the AR-1 will need to be at 80C with more of a pressure rise. With AR-1s on my Caterham (which weighs 620kg with me in it), on the track I tried cold pressures all the way from 14PSI to 24PSI (18PSI optimum for the road) and 21PSI cold pressure gave the best grip and most even tyre wear at the optimum 28PSI hot pressure.

[c1pher]

Originally Posted by RockCrusher

BMW sets the tire pressures based on max speed, load, and package and wheel/tire combinations. I'm sure BMW receives some input from the tire makers and does some field testing: track and road; to ensure the tires do not manifest any abnormal (side wall or center) wear under varying speeds and load conditions.

32psi is not low for those of us owners that have the tire/wheel setup for which 32psi is the recommended pressure. Oh, and keep the speed below 100mph...

40/45 is way high unless you are carrying the Olympics weight lifting team on a run around the 'ring...

Or you have the M package and are running 285/30 20" and 295/20 21" tires. At >100mph the manual calls for these to be inflated to 44psi and 48psi respectively.

My car doesn't have the M package and has the 19"/20" tire combo and I don't but very seldom and then not for but just a brief instant or two take the car above 100mph.

Thus I follow the owners manual -- which someone has already posted -- and for my car/tires it is 32psi "cold" provided 100mph is not exceeded. (If I drove my car fully loaded or tracked my car I'd certainly check the owners manual for how much pressure to run fully loaded or if I exceeded 100mph for any significant time.)

With 32psi is the tires I don't notice any issues. Gas mileage is reasonable. Really though the tires would have to be considerably under inflated to affect gas mileage. Far and away the biggest factor in gas mileage is vehicle usage.

The ride is firm but not jarring or harsh and the tires even when I press the car on curvy roads manifest considerable grip.

Unless you are running tires for which BMW calls for higher inflation pressures and the pressures you have selected are within BMW's recommended pressure with the tires inflated as high as you have then inflated I would expect sub-par contact of the tread to the road. And I would expect after awhile the tires to show excessive wear in the center of the tread.

This is confusing to me, don't all M2s have the same OEM wheel/tire sizes?

[M_Power Rob]

Originally Posted by RockCrusher

BMW sets the tire pressures based on max speed, load, and package and wheel/tire combinations. I'm sure BMW receives some input from the tire makers and does some field testing: track and road; to ensure the tires do not manifest any abnormal (side wall or center) wear under varying speeds and load conditions.

32psi is not low for those of us owners that have the tire/wheel setup for which 32psi is the recommended pressure. Oh, and keep the speed below 100mph...

40/45 is way high unless you are carrying the Olympics weight lifting team on a run around the 'ring...

Or you have the M package and are running 285/30 20" and 295/20 21" tires. At >100mph the manual calls for these to be inflated to 44psi and 48psi respectively.

My car doesn't have the M package and has the 19"/20" tire combo and I don't but very seldom and then not for but just a brief instant or two take the car above 100mph.

Thus I follow the owners manual -- which someone has already posted -- and for my car/tires it is 32psi "cold" provided 100mph is not exceeded. (If I drove my car fully loaded or tracked my car I'd certainly check the owners manual for how much pressure to run fully loaded or if I exceeded 100mph for any significant time.)

With 32psi is the tires I don't notice any issues. Gas mileage is reasonable. Really though the tires would have to be considerably under inflated to affect gas mileage. Far and away the biggest factor in gas mileage is vehicle usage.

The ride is firm but not jarring or harsh and the tires even when I press the car on curvy roads manifest considerable grip.

Unless you are running tires for which BMW calls for higher inflation pressures and the pressures you have selected are within BMW's recommended pressure with the tires inflated as high as you have then inflated I would expect sub-par contact of the tread to the road. And I would expect after awhile the tires to show excessive wear in the center of the tread.

The one item I find confusing (or even lacking clarification) is the refer to the "M Package" which I assume is just the higher top end mph (limiter removed/adjusted). If so, as most driving would not be at that speed, would one really want to adjust for that figure?

[RandomBro]

Originally Posted by M_Power Rob

The one item I find confusing (or even lacking clarification) is the refer to the "M Package" which I assume is just the higher top end mph (limiter removed/adjusted). If so, as most driving would not be at that speed, would one really want to adjust for that figure?

I would assume this would be more the case for autobahn drivers. The rest of us would we put in jail, even attempting the M Driver Pack speeds on our highways. 2nd would be track usage, which u would be adjusting for pre and post.

[M2siast]

Originally Posted by c1pher

My door placard says 32 psi. What are you referencing to get 39/44? With that said, I noticed my tires from the dealer were set to 36 all the way around.

As mentioned, the manual (which is what the placard tells us to do).
The placard in the M2 is the least informative of all BMWs, it just says “read the manual, or 32”. Other BMWs had the tire pressures on the placard too.

Aerobod posted the image of the manual for reference on page 1, if not handy.

[sacowich]

I drive 32/32 cold start.

[KCuv]

mine fluctuates in the cold/heat from 36-40 all 4. car feels great. have the PZeros which I wasn't thrilled about, but it poured all weekend and the car handled it perfectly. Not sure if this helps lol.

[RockCrusher]

Originally Posted by M_Power Rob

The one item I find confusing (or even lacking clarification) is the refer to the "M Package" which I assume is just the higher top end mph (limiter removed/adjusted). If so, as most driving would not be at that speed, would one really want to adjust for that figure?

The manual lists tire pressures for all the factory sanctioned wheel/tire combos for speeds up to 100mph and for speeds over 100mph.

The M Package tires have the highest cold pressure setting for both up to 100mph and over 100mph.

[KC87ZB]

Interesting discussion. I don’t have the drivers pack and have standard Michelin tires, here is what my car is saying. It has been in the garage two weeks while traveling. Not sure how it determines it needs 33.1 psi.

[Zatellia]

Originally Posted by KC87ZB

Interesting discussion. I don’t have the drivers pack and have standard Michelin tires, here is what my car is saying. It has been in the garage two weeks while traveling. Not sure how it determines it needs 33.1 psi.

Yeah that's mine too, recommends 33.1 normally however I just checked it and now it recommends 33.9, but the weather is starting to get colder.

[nype]

Originally Posted by Zatellia

Yeah that's mine too, recommends 33.1 normally however I just checked it and now it recommends 33.9, but the weather is starting to get colder.

What do you have set for tire type in iDrive?

I was seeing a recommended pressure when iDrive was set to “auto” tire type. But now that I have selected “summer” the app no longer shows a recommended pressure.

[Zatellia]

Originally Posted by nype

What do you have set for tire type in iDrive?

I was seeing a recommended pressure when iDrive was set to “auto” tire type. But now that I have selected “summer” the app no longer shows a recommended pressure.

I cant recall what it says exactly but its set to summer tires and less then 100mph

[c1pher]

Originally Posted by KC87ZB

Interesting discussion. I don’t have the drivers pack and have standard Michelin tires, here is what my car is saying. It has been in the garage two weeks while traveling. Not sure how it determines it needs 33.1 psi.

I wonder the same. Mine says 33.9 front, 33.1 rear. I wonder what’s going on.

[M2siast]

Originally Posted by c1pher

I wonder the same. Mine says 33.9 front, 33.1 rear. I wonder what’s going on.

It’s based on temperature.
If it’s cold, it’ll recommend 32.1.
If tires are warmer, it’ll go 33+

[c1pher]

Originally Posted by M2siast

It’s based on temperature.
If it’s cold, it’ll recommend 32.1.
If tires are warmer, it’ll go 33+

Interesting the fronts are not the same exact pressure, although not a big difference.

[M2siast]

Originally Posted by c1pher

Interesting the fronts are not the same exact pressure, although not a big difference.

You’ve been a naughty burnouty/drifty boi?

Tires are always at different temperatures, I see what you see all the time.

What you can do to validate the pressures and system is wait until the tires cool down and go back in the car, turn it on so it reports the new values, and then look in the app later. Then it should read the same value all around.

[c1pher]

Originally Posted by M2siast

You’ve been a naughty burnouty/drifty boi?

Tires are always at different temperatures, I see what you see all the time.

What you can do to validate the pressures and system is wait until the tires cool down and go back in the car, turn it on so it reports the new values, and then look in the app later. Then it should read the same value all around.

Car is broken in

[baj_baj]

Originally Posted by aerobod

This is the info I have for the placard and owners manual:

Well that explains why my car was all over the place at 290km/h. The dealership pumped the tyres to 30psi and I never really looked at it until now

[Carefree]

In Arizona yesterday it was 28° when I left for hiking at 7AM- tire pressures were 30psi. Later in the day, as temperature rose, tire pressure increased to 32psi. My rule of thumb for all our cars is to set pressure at the average, most likely, normal, seasonal outside temperature or something like that. Pressure will vary, period.

That’s my story and I’m sticking to it.

[RockCrusher]

Originally Posted by Carefree

In Arizona yesterday it was 28° when I left for hiking at 7AM- tire pressures were 30psi. Later in the day, as temperature rose, tire pressure increased to 32psi. My rule of thumb for all our cars is to set pressure at the average, most likely, normal, seasonal outside temperature or something like that. Pressure will vary, period.

That’s my story and I’m sticking to it.

Think you need to ditch your rule of thumb...

The tire inflation pressure specifications in the tire inflation pressure table only relate to cold tires or tires at the same temperature as the ambient temperature.

Only check the tire inflation pressure levels when the tires are cold, i.e.:
▷ A distance traveled of max. 1.25 miles/2 km has not been exceeded.
▷ If the vehicle has not moved again for at least two hours after a trip.


You should set the tire pressures for the coldest ambient temperature. At 28F and 30psi the tires were under inflated.

[Carefree]

Originally Posted by RockCrusher

Think you need to ditch your rule of thumb...

The tire inflation pressure specifications in the tire inflation pressure table only relate to cold tires or tires at the same temperature as the ambient temperature.



Only check the tire inflation pressure levels when the tires are cold, i.e.:

▷ A distance traveled of max. 1.25 miles/2 km has not been exceeded.

▷ If the vehicle has not moved again for at least two hours after a trip.



You should set the tire pressures for the coldest ambient temperature. At 28F and 30psi the tires were under inflated.

With the huge temperature variation during an Arizona winter I’d be adjusting pressure perhaps daily.

Rule of thumb it is.

[kyrix1st]

Not only is 40/45 too high, it is also super-understeery setup. With more weight up front, you want square pressure or slightly higher front pressure to compensate for more weight and to get better turn-in response.