Tire pressure

[GolforRide]

 
Just returned from a 1700 KM 4 day ride noticed  the rear tire fluctuated  by 6-7 psi over the day 42 cold to 48-49  on the rear whereas the front only changet by 2 36-38
Is this normal
First time I have ridden with luggage  and tailbox loaded

Thanks

[dsinned]

That is quite a difference . . . more than I would have expected, but perhaps "normal" with a full load of cargo x3. 

While riding mine, without any cargo, and no rear pillion rider, the heated up vs. cold tire pressures are about the same front to back; about +4 to +6 psi max after ~30 miles per TPMS readouts on the center LCD.  Cold tire pressure readings are dead on compared to checking with a digital (highly accurate) tire pressure gauge at 36 and 42psi respectively.

[Travelling2bob]

Depending on warmer ambient temperature sounds about right loaded top box and panniers.

[Ernest T]

That's about normal for Texas in summer. I can start with 42 in the rear and it'll hit 50 by mid afternoon when the temps are ~100.     That's one up, unloaded riding at 80-85.

[john348]

Of course the front won't heat up if it is in the air  Sounds about right for the rear one up not much luggage in top box (laptop) then both front and back track about the same.  Depending on type of roads they will vary a bit between them.

[GarminDave]

Perfectly normal in my view something to do with Boyles Law I believe.

Later

Dave

[w8d4it]

Hate to go against the crowd here but I say  it is not normal.  Yes the amount of pressure changes in the rear tire are absolutely normal.  A 5-7 pound increase from cold to fully hot is completely expected.  However you say your front tire showed only a 2 pound increase and that is not normal.  GarminDave mentioned Boyle's law and he is absolutely correct.  Keeping volume the same, pressure will increase as temperature increases.  You can't get around it.  So if your front tire pressure read 36 cold and only 38 hot, then something is wrong.  And it can't be a deviation from Boyle's law.  Therefore if your observations are correct then I say there is something wrong with your front tire sensor.  On the other hand if you didn't correctly notice your cold pressure on the front I would say your front tire is low. 

[Volfy]

Several factors could have contributed to the F-R difference.

1. Rear tire had much more moist air in it.  Vapor pressure can rise with temperature faster than dry air.

2. Loading on the rear tire was significantly greater.  This appeared to be the case, based on OP's description, though I dunno how heavily loaded the bike was.

3. Sun was hitting the rear tire more than the front.  I've noticed with my cars that have TPMS readouts, that the side the sun is hitting on will have significant higher tire pressure than the other side.

4. Rear tire was warmed by the engine waste heat, so as to have higher temp than front, which saw nothing but cool air.

What's "normal" depends on your POV.  Some or all of the above could have conspired to produce what OP observed, but I would hesitate to call any of them "abnormal".