what is over the axle weight of the E90?

[GrumpyBimmerFan]

My tire shop wants to put precise pressure in my tires. Once they have the weight, then they can send it to tire manufacturer (Conti), and get the recommended tire pressure. I often get up to 190-200mph, so this is important.

[tibra1]

You are willing to go this lenght of accuracy yet you dont want to go with a better tire than Contis..especially at those speeds..

[DARK_M3]

Originally Posted by kotik

My tire shop wants to put precise pressure in my tires. Once they have the weight, then they can send it to tire manufacturer (Conti), and get the recommended tire pressure. I often get up to 190-200mph, so this is important.

In a jet?

[DARK_M3]

You need to get the car on a corner balancing scale (with you sitting in the car) to get an accurate assesment of exactly how much weight is over each tire.

[GrumpyBimmerFan]

:/ trying to get this done before this track weekend. I live in a country side, so it's hard to find scales.

on the autobahn...


What's wrong with Conti's? As far as I've seen there are only 3 tires that are rated for 190+: PS2's, Conti 5P's, and yokohama. Coming from PS2's, I have to say that I like conti's better.

[jadatis]

The tire-maker calculates this pressure with a formula first introduced in 1928 and about 1970 adapted for radial tires. This different in America and Europe.
Only in 2006 America stept over to the better European calculation.
I once got hold of this European calculation and its extra's for higher speed and camber-angle .
Working this all out , I discovered a lot about tire-pressure.
Latest conclusion I drew out of this is that tires with low aspect ratio ( the 40 in 225/40ZR18 for instance) are calculated to high in their maximum load.
This could be compensated by putting higher pressure on the tires.
This all is done for savety of the tires , so you wont get a blew-out.
Gripp and comfort is long gone then , but savety first.
so the pressure that is given for your tires , because I expect them low AR tires, will be to low for savety of the tires at the higher speed.
But if you trust these advices, you can calculate it your selfes with spreadsheet I made, in wich I use the same formula as the tire-makers.
https://skydrive.live.com/?cid=a526e...E092E6DC%21235
follow this link , it leads to a map on my skydrive of hotmail adress with the spreadsheets and examples.
The GAWR's you can find on a plate on the car ( in Europe it is called a VIN-plate and has to be on the car somewhere by law since about 1980).
And if you cant work it out , give me the needed data, and I will do it for you.

[tibra1]

Originally Posted by kotik

What's wrong with Conti's?

Nothing really wrong with them.. I just think a Z rated tire is more suited for those speeds..Contis are Y rated

[jadatis]

@tibra1
with Z tires you probably mean the ZR in for instance 225/40ZR 18 92Y.
Then the tire-maker did something out of the protocol with the tire.
Then they have to give the borders and amount of highening up the referencepressure for higher speed themselfes. But mostly they print as in the Example the Y on the tire, and then you can use that Y system for highening up the refencepressure . To give you an idea for Y rated tires, but then in kPa and km/h .
Up to 220km/h use referencepressure of mostly 250 kPa or XL 290kpa for European metric tires.
Every km/h more use 1 kPa higher pressure then the referencepressure.
So at 270 km/h use 250kPa+50*1kpa=300kpa=44psi=3 bar.
Above 270 for every km/h lower the maximum load with 0,5% , so at 300km, 300-270=30km/h*0,5%=15% less maximum load .
And so the system is a bit diferent for W,V,H,T.S speedrated tires.

[GrumpyBimmerFan]

Originally Posted by jadatis

@tibra1
with Z tires you probably mean the ZR in for instance 225/40ZR 18 92Y.
Then the tire-maker did something out of the protocol with the tire.
Then they have to give the borders and amount of highening up the referencepressure for higher speed themselfes. But mostly they print as in the Example the Y on the tire, and then you can use that Y system for highening up the refencepressure . To give you an idea for Y rated tires, but then in kPa and km/h .
Up to 220km/h use referencepressure of mostly 250 kPa or XL 290kpa for European metric tires.
Every km/h more use 1 kPa higher pressure then the referencepressure.
So at 270 km/h use 250kPa+50*1kpa=300kpa=44psi=3 bar.
Above 270 for every km/h lower the maximum load with 0,5% , so at 300km, 300-270=30km/h*0,5%=15% less maximum load .
And so the system is a bit diferent for W,V,H,T.S speedrated tires.

so what would you recommend for 255/35/19 front (Y) and 285/30/19 (Y) rear? I do both track and highspeed daily driving. I had the shop set me up with 2.6 front and 3.0 back (bar).

[jadatis]

For that I need the actual weigt on the axles to.
For the advices of the factory the GAWR's are used mostly.
GAWR means Gross Axle Weigt Ratings, and is the maximum the axles may have by law. That these are not the weights the axles have in normal use, is another thing. If you ever weigh the axles in the loadconditions you use, then these weights can be used.
If you give me those GAWR's I have all the needed details, and I will do the calculations 2 ways . One exactly according to the system of the manufacturers, and my own way with the mildest extra , so the minimum to use.
But again , gripp and comfort is probably totally gone then , only for savety of the tires, and longer tire-live.

[GrumpyBimmerFan]

can you give me a ball park figure (approximate?)? I'm E90, lots of highspeed driving, and occasional track use. I put nitrogen, so I need something in between.

[jadatis]

For that I had to Google your tires for the loadindex.
I made 3 calculations for front and rear wiht a list of pressures with their load-capacity , with a spreadsheet I made.
1 is the way the factory will calculate it , asuming they are XL/extraload tires, which they most likely are, most low Aspect ratio tires ( AR= the 35 and 30% in your tires) are XL tires, but look at the side-wall.
2 with the pressure to use for up to 270kmkm/169m/h calculated the factory way. I think this speed is fast enaugh for you. above this speed the maximum load has to be substacted 0.5% / km/h, wich became to complicated for me to re-calculate in the 3th way. And my own calculation for lower then maximum load, wich comes to my opinion the closest to the ever to be constructed ideal formula. Diferences are small for Standard load and XL/Extraload/reinforced tires.
3. with the pressure for 270km/h but recalculated for less deflection.
For this I assumed the factory calculated the maximum load for a standard load tire with referencepressure( further Pr) of 36psi and gave it the name XL , so the Pr to use is 42 psi, to compensate for the to much deflection .
And then again calculated with my own formula with a construction load of 10% of the maximum load.
Put it in a word document wich I atached to this post.
Now you only have to detemine the loads on the axles and search them back in the word document. If you trust the tire-maker use the first line, I you trust my conclusions use the 3th line, but mind that this is still a mild calculation. If the tires maximum load are calculated with XL Pr then it even gets worse. And mind that you may not officially go over the maximum pressure of the tire of mostly 3,75bar/55psi?.
This pressure calculation is only for the savety of the tires, not for gripp and comfort. To low pressure gives better gripp and comfort, but you risk damaging the tires that much , so the blow before the treath is worn out.

[jadatis]

Another thing:
For track racing it depends if you have much curves and have to use the brakes often, or that you have less sharp curves where you dont have to use the brakes.
The heat of the brakes can drive the inside tire temperature up to about 90 dgr Celcius, converse it yourselves to Fahrenheit.
With that temperature-rise the pressure also rises.
Again I made a spreadsheet for that . Idea is to fill cold a lower pressure, so warm (90dgr C ) pressure is the same as normal warm pressure ( 45dgrC/112dgr F) , then you have to lower the pressure for more warm gripp and still save deflection of the tire. Going from my calculation.
If you want to fill one pressure for all, then you can use 2 calculations, 1 for lower speed on the road and one for on the track for higher speed but lowered for higher inside tire warm temperature. If you are lucky , they are about the same.
And on the road 220km/13? m/h is fast enaug, for this you use the referencepressure for Y tires of 42 psi ( or recalculated with my system for less saver deflection).

So you see that I still need more data , like speeds to use , axle-loads for the different conditions ( track 1 person, road maybe more + load), what kind of track racing.

You can though yust fill up with air, it wont bite the Nitrogen, and the moisture is that less that you wont spoil the effect of Nitrogen. Depending on the pressure in the tire, the oxigen part will be going to a sertain percentage, even if you fill with 100% Nitrogen, if you manage to do that. 44psi/ 5% O2. If inside percentage is lower there will be going O2 into the tire from the outside against the higher pressure . Has all to do with partial pressure .