Silly Tyre Pressure Question

Skilid

Skilid

Skilid

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Feel like an idiot for asking, but I'm going on a 1,000 mile round trip this weekend in my 2 series and the car will be fully loaded (4 people and luggage).

Tyre pressures recommended for 2 people is 32 psi all round. When fully loaded it recommends 36 front and 44 rear. This seems like a big jump. However, my question is do I actually need to load the car up first before I set the pressures, or do I set the pressures before you load up?

Is it even worth bothering with?
 
One thing I would say 44 is quite high for most tyres - inflating it to that loaded (won't make much difference loaded vs unloaded usually) and a long trip getting some warmth into the tyres and a summer day could see the pressure rise beyond the max recommended for the tyre.

Personally I've rarely bothered with the fully loaded specs unless really pushing it - normally with 4 people and luggage I'll just go up a couple of PSI or so - I find going much beyond that the steering starts to feel a bit vague once you've got some heat in the tyres from driving. If carrying a fair weight of luggage a couple of extra PSI rear vs front will help to balance out comfort and steering response.
 
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Armageus said:
Seems like a huge jump for the rear - are you sure your reading the sticker correctly, or does you car have different staggered tyre sizes?
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They are staggered. 225/40/18 on front and 245/35/18 on rear. Definitely reading sticker correctly.

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I can't find the exact door placard from a quick Google but similar BMW cars have a loaded section divided between speeds under and over 100MPH loaded (assumedly due to Autobahn) usually ~39 max for sub 100MPH use and 42-44 for >100MPH.
 
I'd just follow the recommendation from BMW on the sticker? It's the rear that will need inflating because that's where all the additional weight is going to be going (2 blokes on the rear seats and a 4 suitcases in the boot!)
 
Pump them up before hand, you'll not notice a difference i'll bet, you may have slightly reduced grip when its unladen but the reality is it'll be totally fine.

Van's can have their tyres at over 75psi so don't overthink it, just do as the sticker says.
 
sovietspybob said:
Pump them up before hand, you'll not notice a difference i'll bet, you may have slightly reduced grip when its unladen but the reality is it'll be totally fine.

Van's can have their tyres at over 75psi so don't overthink it, just do as the sticker says.
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Van tyres are a different kettle of fish again (usually rated for 10-20 PSI higher than your average car tyre), at least if you are running the correct tyres. The door sticker/placard is usually rated for the range of factory fitted tyres and not necessarily correct if you are using other tyres though still indicative. I would not recommend going to the max loaded values unless you really are maxing out the axel weight as it will compromise ride comfort, steering and braking especially when the heat from driving increases it. For 4 people and luggage you'll probably find the best results around 2-3 PSI over the normal values and another 2-3 on top of that on the rear if you've got some weighty humans/luggage.
 
I always follow the recommended tyre pressure's stamped on the plate inside the drivers door. However I run those pressures when the tyres are warm, as like others have said, if you set that pressure when the tyres are cold they'll go up even more once you get some heat in them. Having said that, I do monitor my tyre wear, and if the outside edges start wearing more than the middle, I'll add a bit more pressure in there to even them out.
 
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DJ_Bucho said:
However I run those pressures when the tyres are warm, as like others have said, if you set that pressure when the tyres are cold they'll go up even more once you get some heat in them.
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Just do it as per the manual, they do think of this sort of thing :p

The manual for my BMW for example, specifically references this:

Tyres heat up while driving and with the temperature of the tyre, the tyre inflation pressure increases. The tyre inflation pressure data relate to cold tyres or tyres at ambient temperature. Only check the tyre inflation pressure when the tyres are cold.
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What's your internal logic for why you might need to load the car up first? :)
It doesn't matter either way, load does not significantly affect tyre pressure.
 
EvilRob said:
What's your internal logic for why you might need to load the car up first? :)
It doesn't matter either way, load does not significantly affect tyre pressure.
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Tyre pressures increase on their own when the car is loaded, as the tyre gets squashed. I have no idea how much by though, so thought it safer to ask. I've never really needed to adjust tyre pressures for load before as I've normally only done short trips.
 
Skilid said:
Tyre pressures increase on their own when the car is loaded, as the tyre gets squashed. I have no idea how much by though, so thought it safer to ask. I've never really needed to adjust tyre pressures for load before as I've normally only done short trips.
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No the pressures will only increase by a very small amount.
 
Be very wary of a long trip loaded up with pressures too low, this is where the tyre will suffer and any weakness's rear it's ugly head.

I was chatting to our tyre fitter at work the other day and he said the vast majority of blowouts are caused by running too much weight for the given tyre pressure on both cars and commercial vehicles.
 
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