Achieving proper tire temperature and pressure

[Peter Parts]

As I poorly understand it, there are two factors that need to be right for tires to behave right.

 

1. Air pressure: the lowest possible pressure below which the squigglies start. (Aiming for the lowest means the comfort is the highest possible, consistent with good handling.)

 

2. Rubber temperature: the lowest possible temperature at which the rubber has adequate stickiness. (Aiming for the lowest means the longest life consistent with stickiness.)

 

Most riders have favorite cold air pressures (which vary a bit with load and road type) and these are used year-round to get reasonable performance.

 

Is that the best way to do it?

 

I hope the folks who ride with tire pressure monitors have new info.

 

Ben

 

PS. I hope nobody will mention the meaningless "10% rule."

[jjg3]

I have a TPMS that measures temp, but am afraid I don't evaluate it quite so intimately. The pressures increase about 5-8 psi while riding, and the rear tire gets hotter by several degrees over the front. I assume this is a function of location with the front being in the air and the rear just aft of the cat. Am also taken to understand that lower pressure results in higher temps. I prefer pressure on the high side only because I've heard higher pressure results in longer tread life and I'm cheap.

[Peter Parts]

Bike model? Starting pressures? Tire model? Other pertinent?

[tallman]

I use a laser temperature sensor to read tarmac and tire surface temps.

Adjustments made for different road surfaces and when riding on the shady side of the mountains.

Mandatory adjustment when riding in rain with the same for night riding.

Around here seasonal changes can have a 90 - 120 degree difference in road surface temp.

Unfortunately my data won't do much good if you're in Canada.

[jjg3]

Bike model? Starting pressures? Tire model? Other pertinent?

 

R1100RT. Pressures start at 35 front and 40 rear on PR2's. Will check the temps next time out and try to remember to report back here. As the wx has been good the DR650 has been the commuter. The call is for rain tomorrow so the RT will get the call. But wet roads tend to cool the tires. Still, will try to remember to note temps.

 

I would recommend the TireGard TPMS as it provides the information you seek at a glance, provides low pressure warning, and is not overly expensive.

[g_frey]

I have found that the pressures need to be above what is recommended in the manual, at room temperature, just to prevent cupping of the front tire. Cupping will wear out your tires fast! As for comfort??? I don't know if I could tell the difference??? By the way, I dislike tire pressure monitors for providing me with another thing to worry about. So far, I have never been more than 2 psi low with any TPM warning. Basically that is the difference between a cold morning and a normal morning weatherwise. Every cold morning I will have at least one TPM warning which goes away 10 miles down the road. Since I check the tire pressure "religiously" it seems a waste. I do add a psi or two when two up with camping gear.

[Peter Parts]

+1, me too on all points.

 

I always laugh when people say "Follow the manufacturer's recommendation for tire pressure." For bikes, proper pressures have gone up as long as I can remember (due to changes in tires) while the little sticker under the seat hasn't ever changed. Nor have bike manufacturers have ever thought their customers deserved updates.

 

Which brings me back to the thread question.

 

Footnote: The real issue for sophisticated riders is how to change your suspension to adjust for the stiffer-pressure in the tires. You don't see that discussed but it is implicit in the immoderate enthusiasm you hear about aftermarket shocks.

 

Ben

[jjg3]

From a cool, wet day.

Ambient 56f this morning, 55f this afternoon, rain all day.

38.5 psi 64f front, 41psi 66f rear

15 highway miles (about 75 mph) later

41 psi 66f front, 42.5 66f rear

 

this afternoon

39psi 73f front, 41.5psi 73f rear

same miles maybe slight faster

40psi 59f front, 42psi 64f rear

 

Don't have the baseline pressure difference I thought I had.

The front tire is closer to the door in my unheated garage. The parking at work is enclosed, heated office basement which I suspect accounts for the starting temp differences.

 

It appears cool, wet days are good for tires.

Wed/Thur are suppose to be in the low 70s. Will see how different it is.

 

As for false alerts, the TireGard TPMS has adjustable warning levels, and based on my inputs, the tires would have to be quite a bit up (50 something) or down (20 something), or very hot to alert.

 

ps... curious, what is the meaningless 10% rule?

[Paco]

I will try to answer John's (jjg3) question, "What is the meaningless 10% rule."

 

I believe this refers to the recommendation that if a tire has been inflated initially to the proper inflation pressure when cold, there should be a 10% pressure rise after the tire has been run to a stabilized operating temp. That is to say that if the pressure rise was less than 10%, the tire was initially over-inflated, and if the pressure rise exceeded 10%, the tire was under-inflated.

 

This recommendation was supported by a Dunlop field engineer here in the US before radial motorcycle tires were so widely available.

 

I have no idea if this 10% recommendation is still valid due to the significant changes in motorcycle tire technology.

[Peter Parts]

It is fair to say that a properly inflated and warmed tire after 5 miles will have a pressure a few lbs (possible Gauss' or Pascal's or something too) that is higher than the cold morning temperature.

 

It is also fair to say that once in a while, under the conditions of that day, the difference might sort of look like 10% for one or the other of your tires.

 

It is also fair to say nobody has air gauges or filler necks or can work fast enough at gas station or has lab equipment suitable to get numbers (such as "3.85 lbs/sq in") to find the 10% rule any more helpful than the general poop in the first paragraph. And the act of measuring once will lower the psi way off the 10%-one-decimal-place accuracy too.

 

And at that, it is only a rough approximation anyway that just might get you the kind of feel that that legendary engineer from Dunlop happens to like for the kind of riding he or she likes to do.

 

Find the rule helpful? It gets repeated all the time so maybe some people do. Not me.

 

Ben

 

Footnote: set the front for 35 and the rear for 40 and adjust from there. Good numbers? Can't be less helpful than somebody whispering the 10% rule in your ear.

[tallman]

My car does more than 10% differential this time of year.

50-60's at start and @90 going home for ambient.

35 drops to 32 if I don't drive it a couple of days and goes up to 37-38 on the way home.

Greater volume of air obviously, but mc's tires follow the same rules of physics.

Total variation may not be in the 10% w/modern tires, but it would take a lot of data to get the range +/- %.