OK, back to the rule of 4 psi. I’ve only ever been able to come close to the 4 psi rule on the track. The increase in pressure is often down to what tire type, what spring rate and compression, static sag, and rebound damping I’m using to keep optimal grip. Track temperature and surface type play into that. Even so, I judge the correct warm pressure by reading the graining pattern and feel, setting the pressure relative to the hot tire. I’d start the day assuming approximately the rule of X psi, depending upon whether it’s slicks or road/race tires, but then go measuring pressure by how it’s working when hot after a session. Reading a tire by graining and chunking is a factor of many, many things in addition to pressure. It’s all a balance and a compromise. Compression and rebound damping can change things almost as much as tire pressures. I’ve fallen off too many times to even do track days at my age any more, but I still help the youngsters that do. I wish I could read tires like Dave Moss though. That man’s a genius.
Where my Spyder usually runs is from the base of the Wasatch mountains to the High Uinta mountains wherethe road surface is too poor and the road temperature too low to get enough temperature into the tire to bring them up by 4 psi. I’m running 4,500 feet to 10,000 feet so everything is a compromise due to large road temperature changes and the factor of exposed thousand or more foot drops with no guard rail that makes you think twice about what you consider hard riding. No matter what pressure you run cold, getting enough heat in them to go up by 4 psi is hard. I start cold (which in summer is far from cold) at 18/28 psi. On a trip with much freeway I admit I run the 20/28 psi set cold for better cruise stability. If I have full luggage I’ll run 20/30 psi. I always ride two up.
So, for me, the rule of 4 psi depends upon so many factors these days I think it’s only dependable as a starting point and really best applies to sports bikes on setup for the first session on track days in my opinion. Tire type, construction and technology, vehicle weight, spring rates, damping rates, road temperature and initial pressure are so many factors affecting such a simple rule that it probably only applies best to passenger cars on average tires and an average ambient road temperature and perhaps where longevity counts for more than feel or handling?
My suspicion is my riding conditions are only typical for someone living at altitude and riding mostly in the mountains. Your mileage may vary, and most probably will.
I also don’t have to consider riding over rabbits.
