I was on interstate 24 driving about 75 when I noticed a previous generation Mitsubishi Eclipse that was tailing me. I wasn't in the mood to be provoked by him so I signaled a right lane change so that he could pass. After about 20 minutes I noticed headlights approaching me quickly and was passed by the same Eclipse closely trailing a new Nissan Altima 3.5SE. I estimated they were going about 100mph. They must have gotten about 200 yards ahead of me when I decided to floor it and reached 130+ and caught up side by side with the Altima. From that point on it was no turning back. For the next 20 to 30 minutes I was locked in an unrelenting race with the two cars with speeds ranging from 80 to 130+. We had to slow to negotiate traffic.

I truly only considered the Nissan to be competitive with the 330i. The we reached a mountainous 8 to 10 mile stretch of highway (2 to 4 lanes wide) and I basically left the altima and eclpse back. First of all, my impression was that the Eclipse didn't have the accleration that I did with the 330i at speeds of 90+, so he was left for that reason alone. As for the altima, I wasn't as sure. I was making turns at 110 to 120 and the altima still didn't gain on me. In fact he was losing ground. It was only when we came out of the mountains, that he caught up after I slowed to 80's. The surprising thing was several times I accelarted to beyond 130 and up to a max of 137 on my speedometer on flat sections (I wasn't expecting for these speeds to be reached since I thought that the speed-govenor on the 330i is 130). AnywayMy speedometer read 137 and I was weaving from left to right lanes on a 2 lane interstate to pass cars. Risky, I know. But the car felt stable at that speed. My main fear was of something failing in the car like a tire blowing or whatever.:az:

It's that rush of adrenaline that makes it so tempting to drive hard and fast, even though your head knows better. It's also the same shit that causes fools to run from the cops and cause fatal accidents. I wonder what I would do if I were clocked at 125MPH, and I had any thought that I could run away. Scary. :devillook


But anyway...

It is always best to run extra pressure in the tires. I have 16" wheels with 225/50/16 Pirellis on my E28 M5. Due to the weight and occasional high-speed interlude, I like to keep them at 34-37psi cold. This will increase the lateral stability of the tire and improves handling greatly versus lower pressures that maximize tire wear. If you never corner hard, 36psi will wear out the center of the tread. Since I do corner aggressively, I use more of the outer areas of the tread, so the wear evens out. Also, you MUST increase pressure for high-speeds. BMW recommends 4psi+ for cruising over 100MPH. A higher pressure will prevent excessive tire flex and keep the tire temp lower. If the tire gets too hot, BOOM, at the worst time possible.

It's also VERY hard to maximize tire wear by adjusting camber, alignment, and pressure AND get the best grip at the same time.

JamesM

I think BMW speedo exagerate speeds.

My father's Lexus RX shows 80 going side by side with my wife's car - the 7 - and the 7 shows 86. As we increased to 85, the speedo showed 93.

So using that extrapolation - you were probably going 120-128 - which would probably be beyond the speed limiter of the 3.5SE (just guessing don't know, don't care) and the Eclipse well...no idea there...

JamesM3M5,

I suspect that running at high speeds will heat up the tires more than at lower speeds resulting in higher air pressures in the tires. If you start with a slightly higher psi for high speeds, then you'll get tire pressures that may exceed a safe limit. I understand about maximizing sidewall rigidity to stabilize cornering forces, but with the sport package tires that have low profile sidewalls, it can't seem to figure that 3 or 4 psi additional will make that much of a difference once you reach the recommended pressures of the mid-30's. Camber and spring stiffness must contribute much more to cornering performance.

Originally posted by aust95x
JamesM3M5,

I suspect that running at high speeds will heat up the tires more than at lower speeds resulting in higher air pressures in the tires. If you start with a slightly higher psi for high speeds, then you'll get tire pressures that may exceed a safe limit. I understand about maximizing sidewall rigidity to stabilize cornering forces, but with the sport package tires that have low profile sidewalls, it can't seem to figure that 3 or 4 psi additional will make that much of a difference once you reach the recommended pressures of the mid-30's. Camber and spring stiffness must contribute much more to cornering performance.

This is a false notion. Additional pressure is required for continous high speed running. All the German marques suggest about 4psi additional for sustained 100mph running. DO NOT decrease pressures on the assumption that additional speed will cause heat that will increase the pressure for you. The manufacturer is talking about COLD pressure. And not just for cornering performance, but overall high-speed safety. High performance tires can take at least 44psi COLD, so don't worry about setting it higher for high speed running. COLD. Ignore potential pressure increases due to heat. V, Z, etc. rated tires have that engineered into them.

Check your cold pressure, and adjust it up 4psi for high speed running. Been on a race track? 4psi can make a difference.

Never assume that 45-series tires somehow compensate for incorrect tire pressures. Not true.

Us North Americans get VERY few chances for sustained (we're talking about more than a burst) running at 100mph or more, and for 99.99% of us, the suggested pressures will do just fine.

Originally posted by aust95x
JamesM3M5,

I suspect that running at high speeds will heat up the tires more than at lower speeds resulting in higher air pressures in the tires. If you start with a slightly higher psi for high speeds, then you'll get tire pressures that may exceed a safe limit.

You should set the pressure in the tire when stone cold, like "2002tii" said.

The reason you need extra pressure is because the tire is harder to flex with more pressure in it. The tire heats up because of flex. If you do not increase the pressure when travelling at very high speeds, the tire will flex more and faster. This will increase pressure in the tire somewhat, but not as much as needed. This will also overheat the tire carcass.

The recommended pressures are merely a suggestion. Proper pressure varies according to load, tire brand, construction, size, and driving style. Check your tires often, rotate accordingly, and keep the pressure higher than recommended if it doesn't cause funky wear patterns on the tire. I run 36-37psi in my 225/50/16s on a 3500lb M5 and 36psi in 225/45/16s on my 2800lb M3. I've run 41psi in 225/55/16 Dunlop street tires (D40 M2) at the track before. They wore perfectly even and got hot enough to pick up gravel in the paddock area at Roebling Road. Outside temp was 95F both days. I drove them until they corded.

JamesM