2004-2007 Cadillac CTS-V Performance Mods Discussion, Best "Bang-for-your-Buck" Road Course Mods? in Cadillac CTS-V Series Forum - 2004 - 2007; You could easily run the R888s "backwards" (or any other tire, for that matter) if the weather is dry.
You could easily run the R888s "backwards" (or any other tire, for that matter) if the weather is dry.
Low 40s for pressure may be too high. Both the NT01s I ran before and the Z214s I'm running now seem happy in the mid 30s. I would say the same is true of the various R-comps I've run on my Subie over the years. It may be that you were getting the tires outside their comfort zone, which increased the wear rate. R888s have a reputation for being a durable tire (albeit not as durable as the older RA-1s), so 3 days definitely seems unusual.
The R888s are streetable, I ran them on my V for over a year (they didn't last long, but that was completely expected). Yes they were loud on concrete, but my exhaust drowned out most of the noise.
I agree that they probably aren't the perfect tire for the V, but I personally have had great luck with them @ 2 track days and I had a chance to get a good deal on used scrubs, so I took it. Also, this June I will be competing in a Hill Climb event (Spectre 341 Challenge) and one of the only rules for the event was you have to use a tire with a treadwear rating of 100 or more. The R888s are 100.
As for starting/ending track PSI: I think I usually start about 30-32 psi and get to 40-42 psi by the end of a session.
As far as starting at 24 and ending up at 33, I would be worried about rolling the sidewall. I guess it depends on the specific tire.
Actually, due to thermodynamics, the nitrogen filled tires have less of a change in pressure from the heat. I have run regular air and nitrogen filled and found it to be true.
With regards to final tire pressure when hot, it depends on the tread compound. I ran some Hankook R-comps that liked to be at 35 psi. I now have a set of Hoosier Grand Am Rolex GT Series R-comps that prefer about 40 psi. I call the tire manufacturer and get their recommendation before I run a set of tires.
I certainly would NOT start out at 24 psi, ever. And ending at 33 psi on our cars is way too low. Even if you're on street tires, it should be around 35-37.
Still, for whatever reason, I only get a fluctuation of about 6-8psi with nitro and much more with compressed air. I don't care what the reason is, but it's that way.
Again, I haven't run the V on the track yet. Just got it like two weeks ago. In sports cars, I'll start out way low on the psi so that it sits in the low 30s. Sorry if that was bad advice for these cars.
Let the middle school science class nostalgia begin. Dry air (the stuff we breathe) actually consists of 78.09% nitrogen, and 20.95% oxygen. Therefore, ‘the free stuff’ that air compressors blow into your tires is already roughly 78% nitrogen. In other words, you’re already getting 78% of the total benefit being sold to you for free with regular air. Wow, I feel so lucky to ‘nitronize’ my lungs for free!
According to Consumer Reports, the nitrogen consistency in the air produced by a nitrogen tank is about 95% nitrogen (and the recommended tire level is 93%). So, you’re really looking at only an 15% difference in added nitrogen.
But wait, according to the same Consumer Reports article, the person filling the tires would actually need to completely purge and refill the tire 3 times to get a 95% nitrogen consistency. Do you trust that the guy in the back is really doing that and rigorously measuring your tire’s nitrogen consistency? My guess is that he’s filling the tire to the spec PSI and calling it a day.
Do Nitrogen Tires Retain PSI Better than Air Filled Tires?
In the aforementioned Consumer Reports test, 31 pairs of tires were filled to 30 psi and then measured one year later. The results show “nitrogen does reduce pressure loss over time, but the reduction is only a 1.3 psi difference from air-filled tires. The average loss of air-filled tires was just 3.5 psi from the initial 30 pressure setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial 30 psi setting.”
So, over the course of a year, there was only a 1.3 (or about 3%) improvement in psi retention in nitrogen filled tires vs. air filled tires. And that is with 95% nitrogen filled tires – not what you are most likely getting from your local tire shop.
The real issue that we run into with the pressure increase when we heat up the tires has to due with the moisture content in the air. Most air compressors actually increase the amount of water vapor in the compressed air. Most nitrogen extractors attempt to scrub water vapor from the nitrogen. Ideally we would go with any inert gas, as long as it was "dry". Nitrogen is probably the cheapest to manufacturer because of it's abundance in air.
So what did we come up with for starting pressures on R888's ? Was my initial pressure too high, leading to bubbling ?
Agreed, nitrogen is probably more predictable for pressure increases mainly because the moisture content of air can vary so much. I'm just not convinced that it actually runs significantly cooler. Nitrogen is not all that convenient to carry around with you.