Boyle's law - tyres

[FastFred]

No not Susan Boyle....

Went for a ride this morning and set tyres to just over 2.2 front 2.5 rear for solo riding. Temperature was about 5 degrees C probably. After riding ten miles I checked the tyre pressure monitor and it showed 2.4F and 2.8Rear (bar). Obviously this is because the reference temp is 20deg C. Does anyone know what typical volumes are in the front and rear tyres I can calculate what the onbike computer should be over-reading when the temp is colder than 20deg C? Guess I should read it as soon as I set off and just note the difference is the answer.
Does anyone use this tyre check function regular?

 

[RickG]

Mate, you're not serious really??

The tyre pressue is set cold-ish and as you've noted, increases as it gets hot, but it depends how hot which will vary on how hard you ride. And solo means one person fat? or skinny? full tank or empty..in other words it's not THAT important.

However:

Volume =[1/4]pi squared x (R+r)(R−r)squared, where R is the outer radius and r is the inner radius of a torus (the tyre)

Or use nitrogen.

This is a wind-up though?

 

[Blackal]

Are you sure that the volume will be changing appreciably for the difference in pressure and temperature?

P1/T1 = P2/T2 should about do it.

Al

 

[AberdeenAngus]

volume stays the same and as temperature is in Kelvin, its only going to change about 1%.
You'll see a small change in tyre pressure but not much.

Maybe you should get out on your bike a bit more and try not to worry about it.

 

[Giles]

Mate, you're not serious really??

The tyre pressue is set cold-ish and as you've noted, increases as it gets hot, but it depends how hot which will vary on how hard you ride.

Fred, this is why on track days (on a sports bike) you drop your tyre pressures down to about 28 .......

 

[swissrob]

Mate, you're not serious really??

The tyre pressue is set cold-ish and as you've noted, increases as it gets hot, but it depends how hot which will vary on how hard you ride. And solo means one person fat? or skinny? full tank or empty..in other words it's not THAT important.

However:

Volume =[1/4]pi squared x (R+r)(R−r)squared, where R is the outer radius and r is the inner radius of a torus (the tyre)

Or use nitrogen.

This is a wind-up though?

what difference is nitrogen going to make - it still heats up.

 

[AberdeenAngus]

Couple of petrol heads at my work were banging on about the benefits of replacing the air in their tyres with pure Nitrogen.

They had actually paid a guy to do it.

Pissed myself laughing.

Mr Barnum would have been proud of that one.

 

[FastFred]

Well I was serious actually so chill a bit.

I used to race a TZ350 so I know all about the lower pressure rules although it's a bit more exact than dropping to 28psi. There is a 10/20 rule for that.

Bike tyres have 2 small contact areas and pressure is very important. A mate was killed after not checking his tyres. The bike had been stored for months. He got on the bike stored in his mates garage and rode up the first long long straight. The bike went into a speed wobble and killed him. Whilst they don't have to be exactly spot on some people do like understanding and calclulating things. That's exactly we are all riding very sophisticated motorbikes and why man got to the moon and back whilst your average punter can barely calculate a percentage these days.

Enjoy. I'll work it out anyway. You stick with the slide rule

 

[Deleted account 211025001]

I still race

I lower my pressures..................I still fall off

Andres

 

[peterh]

What you want to know is under "Engineering Details" in the handbook. At least it is in the RT version ....

 

[cookie]

use helium - lower unsprung weight

 

[Owen Snell]

The pressure will always increase when riding a bike or driving a car. The reference is to check tyres when cold, so check them when you start in the morning and don't worry about it.

I am not sure why Nitrogen, as the biggest factor in pressure change when tyres are hot is water content, because the condensed water in the cold tyre will evaporate to vapour. Dry air is just as good as dry Nitrogen.

 

[(RIP) Bin Ridin]

N2 molecule bigger and leaks less than O2 molecule so pressure loss is slower - as well as the dry part. I am usually a septic but I beleive in this.

 

[Balders1450]

Pressure Guages

I just picked up my new GSA, it came with Bridgestone Battlewings, love em, I had 3 sets on my 08, and Bridgestone tell you to run at F 2.5, R 2.9 one up, two up loaded whatever!

My dealer didn't know this, so they took it back in workshop to adjust pressures. Their tyre guage had just been calibrated ( all guages in dealerships and garages should be checked every so often ) and is now 99.9% accurate. After inflating to 2.5 and 2.9 cold, the bike TPC read 2.7 and 3.1, so the TPC isn't 100%. So in future when I check my pressures cold, all I have to do is make sure the onboard TPC reads 2.7 and 3.1. When hot they go up even more.....2.8 and 3.2....Simples!

.2 isn't going to make much difference really, as Swissrob quoted, "fat thin full tank" etc. I bought a 2nd hand GSXR1100 once, didn't check pressures, just got on and rode it home, furkin scared the hell out of me, handling was SCAREY, checked tyres when I got to work ( work in motor trade ) 12psi in rear tyre. You only do it once, now I check them every time I ride, well it's easy with a GSA.

 

[AberdeenAngus]

N2 molecule bigger and leaks less than O2 molecule so pressure loss is slower - as well as the dry part. I am usually a septic but I believe in this.

Only about 3% bigger so its not going to make any noticeable difference.
Don't forget that air is 80% Nitrogen, 20% Oxygen anyway.
So by replacing air with nitrogen you will get a 3% x 20% = 0.6% reduction in the rate of pressure loss - which is tiny anyway.

Sorry, the N2 thing is pure snake oil.

 

[Rod Souter]

Nitrogen molecule is 109.76pm long, whilst Oxygen is 120.74pm.

Rod

 

[E. Buygum]

Moving from 5 to 20C would result in around a 5.4% increase in pressure at constant volume (293/278) taking 36/42 PSI types to about 38/44. However, that's in an ideal gas and the effect could be more in moist air where evaporation/ condensation would exaggerate the effect. (Nitrogen is dry). Although only marginally smaller, the O2 molecule permeates significantly faster than N2 through rubber in the same way that a small percentage difference in grain size could make a massive difference to the rate at which sand passes through a mesh. (So even though air is only 18% O2, it can make a measurable difference). Net result is that N2 gives you a more stable and predictable pressure in a tyre. Completely irrelevant for day to day motorcycling, of course, but if there wasn't something in it, I suspect airlines and F1 teams wouldn't bother with it (as many do).

 

[E. Buygum]

Nitrogen molecule is 109.76pm long, whilst Oxygen is 120.74pm.

Rod

Don't know exact values but Kinetic diameter of O2 (which is what counts when you are looking at permeability) is about 5% less than that that of N2, despite it being the heavier molecule. Some industrial production of Nitrogen relies on this as the bigger Nitrogen molecules are just "sieved out"/separated from the oxygen in compressed air.

 

[mechcanico lee]

Jesus....kinetic molecules,evaporation of constant nitrogen effect e=mc2

check ya pressure and ride the bike !!!!!!!!

 

[E. Buygum]

Jesus....kinetic molecules,evaporation of constant nitrogen effect e=mc2

check ya pressure and ride the bike !!!!!!!!

Couldn't agree more.