Tire Pressure Growth Questions

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SkiRideDrive

New Member
I have read through some of the posts and have some looming questions for the tire gurus. Full disclosure, I have not yet joined you guys on the track yet but am looking forward to doing so.

1. I spent some time racing/engineering on four wheels and find it hard to believe that the pressures only grow two pounds from cold to hot on a bike. (see Dunlop pressure recommendations - link) The recommendations only show a 2 psi difference for hot and cold recommended pressures. Unless the growth is only two psi from heating the tire on track the only explanation I can come up with is that the cold pressure is actually a warm pressure set after warmed by the tire warmers. Anyone care to comment? Anyone have any experience measuring the difference in pressures between cold (ambient) tires and right after pitting?

2. Especially in reference to my question above, I am very interested in the reasoning behind the vast difference in recommended pressures for the track vs. the street. At least in reference to Q2's it seems the consensus for on track cold temps is around 30f/30r. Yet the recommendation for the street seems to be 36f/42r. Are these vast differences to account for pressure growth of 6 to 12 psi due to heat (completely disagreeing with the recommended pressures discussed above), or do they just recommend a higher than optimal pressure setting for tire wear and puncture resistance? I was also curious about the front to rear discrepancy as well, but I'm guessing this is due to the potential of carrying a passenger and the higher pressure in the rear is to account for the higher load capacity.

3. Just curious about one other figure while I'm thinking about all of this. Anyone have any data on how hot tires get out on the track, either surface or core temperature would be useful.

Sorry for the length, I'm just really curious about this stuff and it helps me understand how it effects my bike.

Thank you!
 
DUNLOP-RTS

DUNLOP-RTS

New Member
SkiRideDrive;231392 wrote: I have read through some of the posts and have some looming questions for the tire gurus. Full disclosure, I have not yet joined you guys on the track yet but am looking forward to doing so.

1. I spent some time racing/engineering on four wheels and find it hard to believe that the pressures only grow two pounds from cold to hot on a bike. (see Dunlop pressure recommendations - link) The recommendations only show a 2 psi difference for hot and cold recommended pressures. Unless the growth is only two psi from heating the tire on track the only explanation I can come up with is that the cold pressure is actually a warm pressure set after warmed by the tire warmers. Anyone care to comment? Anyone have any experience measuring the difference in pressures between cold (ambient) tires and right after pitting?

2. Especially in reference to my question above, I am very interested in the reasoning behind the vast difference in recommended pressures for the track vs. the street. At least in reference to Q2's it seems the consensus for on track cold temps is around 30f/30r. Yet the recommendation for the street seems to be 36f/42r. Are these vast differences to account for pressure growth of 6 to 12 psi due to heat (completely disagreeing with the recommended pressures discussed above), or do they just recommend a higher than optimal pressure setting for tire wear and puncture resistance? I was also curious about the front to rear discrepancy as well, but I'm guessing this is due to the potential of carrying a passenger and the higher pressure in the rear is to account for the higher load capacity.

3. Just curious about one other figure while I'm thinking about all of this. Anyone have any data on how hot tires get out on the track, either surface or core temperature would be useful.

Sorry for the length, I'm just really curious about this stuff and it helps me understand how it effects my bike.

Thank you!
Click to expand...
I'll bit on this one.

Answering #1, First off you have basic misunderstanding of cold and hot definitions.

Cold is the cold pressure setting at room temperature. This could be a 40 degree morning or a 90 degree morning. Since the room temp (outside temp) can widely vary, we don't like to use this simply because its a variable that is hard to control as every day is different.

Hot temp is the "off the warmers" temperature. this is NOT the "off the track temp". The recommended, is to set the pressure hot on the warmers. Certainly the pressure is going to increase as the tire is used on the track and is made even hotter while fast laps are achieved. It would not be out of range for pressure to raise several PSI from hot of the warmers to hot off the track.

If you have warmers, you use the hot off the warmers recommended PSI. If you don't have warmers, use the cold recommended PSI. You would not check them cold, then check them hot and try to get a 2 PIS change. That would be a waste of your time, (remembering that the cold PSI is a big variable, while the warmers will always go to the same temp and thus give you a solid baseline to check your pressure hot off the warmers.

Growth has nothing to do with it, mostly because N-Tec tires are zero growth tires.

Answering #2. Don't try to correlate the recommended pressure for Q2 for the street and the track. recommendations are given to achieve different results for each. The pressure for the street is targeted to give greater stability, while pressure4 for the track will sacrifice stability for increased traction. Keeping in mind the surface on the road has much more irregularities and thus needs more stability. If you are riding on the street use the street recommendations, if on the track use the track recommendations. Don't over think this.

Answering #3. NO, there is not an absolute temperature you are trying to achieve. The tire will get as hot as it gets. If you go faster it gets hotter, slower its less hot. its a constantly changing variable and you are not trying to "Target" for a specific temperature. I highly recommend you take your temp gauge and place it in the bottom drawer of your tool box and leave it there. you have long way to go before that tool even remotely becomes useful at a track day.

Last note, if you are an engineer or trying to engineer something in this area, you need to get off this forum for data. You need to go into the field and take readings yourself. Get first hand data and observations yourself. Doing so you would observe the 2 PSI rise noted on the spec sheet from Dunlop.
 
S

SkiRideDrive

New Member
Steve,

Thanks so much for replying. I was just trying to get a baseline understanding of motorcycle tires. The fact that hot is off the warmers clears a lot of things up for me. I appreciate that. I also agree cold temps are a very unreliable way to set pressures. I did not have warmers either in the four wheel world, but instead developed a chart including temperature and humidity to account for irregularities on the initial cold pressure setting. It is difficult to take pressure readings on the street but when I get to the track I look forward to keeping records of pressure throughout the day just for reference.

Best regards and thanks again,

Kevin
 
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