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04-07-2008, 08:27 AM | #1 |
El Presidente
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Guys with Aftermarket Tires.
For those of you with aftermarket tires, what psi are you filling your tires to? I put my 19's on this past weekend, and I followed what it said on the door, but I had my sensor go off this morning. What psi should I have my tires on?
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04-07-2008, 10:34 AM | #4 |
Major General
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30-36 PSI front back as suggested on the side sticker for 225/45/R17 tyre, for lightly loaded car.
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04-07-2008, 12:46 PM | #5 | |
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Look on the 19" tire itself and it will tell you the MAX Cold PSI the tires should be filled to. |
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04-07-2008, 09:58 PM | #7 |
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I'm running 39 psi all around but you may want to check this out. http://www.e90post.com/forums/showthread.php?t=100597
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04-08-2008, 12:13 AM | #9 |
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Read the sidewall of your tire... it should say something like "do not inflate past 40 psi".
I'd inflate em to 45psi... at least 5+ over. (As long as they're new and undamaged... cause over inflating used/damaged tires will just put stress on the existing wear and tear.) *For ex: If it's a Z rated tire.. capable of 149mph, that speed rating is only if the tire is inflated to max psi.
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04-08-2008, 12:37 AM | #11 |
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Just got a set of 189 and running 32F & 38R.
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04-08-2008, 02:42 AM | #12 |
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You can inflate the tire to max psi, but that doesn't mean it's the correct pressure for running that tire, on this car, with the type of suspension setup on the car. On mine, I'm running 39F, 42R on 235/265 19s. I used this pressure after a bunch of driving and considered it to be a good pressure to go with in terms of cornering and braking. An overinflated tire will corner a bit better due to less roll over but you lose a lot in braking too... something I'm not willing to sacrifice on the street. At the autocross I'll go higher, 44F 46R.
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04-08-2008, 07:52 AM | #13 | |
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04-08-2008, 09:11 AM | #14 |
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I ran 40 PSI all around for the 255/30/19 s.
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04-08-2008, 11:46 AM | #15 |
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I'm running 36psi Front and 38psi Rear.
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04-08-2008, 12:31 PM | #17 |
pew pew
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Hard to say, I'd have to drive your car for a while and try different pressures to really make a recommendation. Things can change quite drastically when you change out your suspension. I had to adjust my pressures drastically when I went with my Eibach / Bilstein setup. And again when I went to 19s and the offset in the rears made the track quite a bit wider. I think I'm happy where I'm at now though.
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04-08-2008, 08:07 PM | #18 | |
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You’re not “over inflating” your tires, you’re inflating them to the psi that gives you the best overall use of them, whether it be for performance OR safety. With max psi and above you have: 1. Stronger sidewall 2. Better contact patch 3. Longer Tread life 4. More contact/traction in wet weather. (The faster you go the better contact your tires will have with the roads opposed to using the manufacturer’s recommended psi.) 5. Better handling 6. The only downside to this is a harsher ride... thats all. I've learned from racing instructors and all, but taking a stunt driving course opened my eyes to all the little things about tires. I learned a lot about tires, and a lot about cars and handling in general, so I’m just throwing my 2 cents in. Obviously you can’t inflate your tires to 50psi and start doing stunts in your E90, but I took this course, learned a lot, and will ALWAYS keep my tires inflated to at least 5-10 above max psi.
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04-09-2008, 02:22 AM | #19 | |
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I have experienced many "over inflations" where the tire is inflated to the point that the contact patch is reduced because the tire starts to get ballooned. Try this... Inflate your tires to 10psi over the max stated rating on one side, and 5psi under the max rating on the other. Put a stripe of paint on the tread of all 4 tires, from inner edge to outer edge. Take a quick drive on the freeway (less than a mile), and take a look at the paint stripes on the tires. The ones which are inflated higher will have a lot of paint left on the insides and outsides of the tire due to the ballooning. The contact patch of the tire is reduced, and braking performance is worse. It is better to run slightly higher pressures tires in the rain, as it reduces the contact patch on the road, which reduces chances of hydroplaning. It's like driving on 315mm tires in the rain vs 225mm tires. Even though there's less contact patch, there's a huge reduction in hydroplaning because there's simply less surface area for hydroplaning. I also find better cornering performance with more pressure in the tires, up to a certain point. Once there's a lot of air and the tire is ballooned up too much, there's too little contact patch on the road for grip, even though there is hardly any rollover because there's a lot of air in there. I try hard to find the balance between the two conditions at the track. Since I'm usually autocrossing, braking performance is not quite as important as on the track so I don't mind sacrificing some braking and accelerating grip for cornering. Harsher ride and wear... true but not the most important to me. Performance and safety above all. A lot of stunt cars run very high PSI because they incur a lot more load than a typical car does. Driving on 2 wheels and jumps are some things I can think of. Also, if doing a lot of J-turns and drifts, it's best to inflate really high to minimize the tire from rolling over and scrubbing all the tread off the sides of the tires... They would wear VERY quickly if inflated normally. In the end, do what suits your driving style best. It's just in my experience, I have not had the best performance by inflating the tire so much.
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04-09-2008, 03:30 AM | #20 | |
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Tires don't balloon up like you think. I used to think that way until this past September when I took a stunt driving class. The instructor (Bobby Ore) gave us at least two hours of classroom time on tires, which pretty much covered everything here, then throughout the course he showed us more... One thing I was surprised to see were the tires on his truck with a maximum psi rating of 44 inflated to 100psi. They didn't balloon, up, or get distorted in any way. (BTW, all the cars we used were stock.. even the truck.) As far as wet weather traction goes... he explained how the faster you go, the middle part of the thread of a tire, bends upward into the tire. (Hard to explain half this stuff without him, or the tires/examples he used in class.) One example he gave was how he was working with a tire manufacturer and they'd have him drive over a piece of plexiglass with dye on it, and a high speed camera under it. At 70mph the tire inflated to a recommended psi would retain 70% of it's contact patch, where one inflated 5psi or so above max psi would retain 90%. (I don't know the exact #'s, but at each speed, the tire with recommended psi would retain significantly less contact than the one inflated higher, about a 20% difference.) Don't get me wrong, this may or may not be the best set up for autocross, but for daily driving and everything in between I think it is. The stunt driving school was the most thorough driving school I've been to yet, and I plan to do more, and attend some more racing schools in the future.
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04-09-2008, 03:55 AM | #21 |
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Front: 225/40-18 @ 2.7bar (~39psi)
Rear: 265/35-18 @ 2.9bar (~42psi)
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04-09-2008, 12:11 PM | #22 | |
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I understand what you mean with the center of the tire moving up from the ground. It's like if you look at the contact patch head on, it'll kinda be like the shape of a "W" where the center section of the contact patch is elevated, and the tire is riding on the insides and outsides. I encourage you to test on your car and see how things work for you. The stunt driving instructor may have his preferable settings, and you should try out the best for your car and your driving style.
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