As I stated in All that (air) pressure I spent the past weekend with my brother in Charlottesville, VA and got to spend some time relaxing. For this trip, I had driven my motorcycle out while my wife had driven with my son in our truck. It was a wonderful ride out and I got to enjoy some Appalachian mountain riding during the weekend.
Upon returning home, I had left my motorcycle out over night so that I could take it to work the next day. Just because I was going back to work didn’t mean I couldn’t enjoy the drive in. So, I woke up early put on my motorcycle gear and headed out onto my bike. It had significantly cooled off through the night, and it gave me pause as I walked outside as I tried to decide it would really be worth braving the cold.
At 35 degrees Fahrenheit, it was indeed very cold for Virginia. However, since I only moved here 3 years ago from WI, it actually seemed fairly pleasant. Therefore, I decided just to put on an extra layer and go for it. I got on the motorcycle and it seemed to hesitate as I tried to start it, but it finally got going.
I started driving down the road, and, as the wind begin to hit me, the joy of the wind hitting me as I got in a morning ride filled me up. As I got a little further down the road I leaned into a turn, but something felt a little off. As I was analyzing the feeling of the bike, I realized the tires had rolled a little under me as I had taken the turn. When I leaned into my next turn, the same thing happened again. I then stopped and looked at my bike. The tires were flat.
Awesome, I had just gone through this tire thing two days earlier with my truck, I really didn’t want to have to deal with it all over again, so I turned around and headed home. I dropped off my motorcycle and my gear and ended up taking the truck to work.
At work yesterday, I had an exam scheduled. During the exam, I was really just looking over people to try to keep them from cheating, so I started to think about my bike. I hadn’t hit anything, I was pretty sure I hadn’t run over anything that would pop the tire, so why would the tire be flat?
While, it is still possible that I ran over something I didn’t know about, or that the tire needed to be replaced, I realized that the temperature had dropped significantly since I filled them up on Wednesday afternoon. At that time, it was about 70 degrees Fahrenheit. Could it be that the change in temperature caused them to go low?
Well, since pressure and temperature are proportional, given a fixed volume, we should have that pressure divided by temperature is constant. However, this only works if we are using an absolute temperature measurement. That is, if we use Fahrenheit, the pressure and volume would be related linearly, but wouldn’t be directly proportional. As such, we would convert these to Kelvin to get 35 F~ 274.8K and 70 F~ 294.3K.
Now, noting that I filled the tires up to 30 psi on Wednesday, this means that P/T=30/294.3~.1019. This would then imply that the pressure in my tires on Monday morning would be approximately 28 psi. Well, that’s sad. I wouldn’t likely notice a drop in pressure of 2 psi, so there is probably something else wrong with my tires. For now, I’ll just inflate them and see what happens. I’ll keep you updated on how that goes.
If you enjoyed the story, or found it helpful in planning a lecture on pressure or in paying attention to your own tire pressure, let me know by liking the post below, on Facebook or Twitter. Otherwise, leave a comment if you’ve ever woken up to a flat tire, especially if it kept you from getting in a motorcycle ride.