Outer Limits 4x4 Board

g'day all. not too sure what's wrong with my tyre pressures. they are the bfg km2 and i've been checking the pressures every week and it seem to drop couple of psi. i usually have em' at 36 but it drops to 34 and sometimes to 32. any reason why ?

puncture, faulty/incorrectly fitted valve, crap in the bead - go back to who ever fitted them and get them checked

- Leaking inner valve
- Leaking valve on wheel surface
- Cracked/leaking rims (not likely)

As said - take them back.

Also make sure you're checking them at the same temperature. If you're checking them cold one time and then after driving for 4 hours they will read a different pressure. We had a 2PSI variance on tyres from one side of a vehicle to the other and they hadn't been driven on... it was the fact that the morning sun was directly on two.

Cheers,
Ryano

that's a really stupid question. SORRY

DR Frankenstine wrote:that's a really stupid question. SORRY

X 2

DR Frankenstine wrote:that's a really stupid question. SORRY

maybe it's a really stupid question for someone who knows a lot about cars and fourbies and tyres and all that technical shizz. it's a really genuine and perplexing question for someone who is less well schooled in these things. if you don't have anything constructive to say, why say anything at all?

there are many reasons why air may leak or appear to leak from tyres. some are easier to diagnose than others. I'm wiling to bet a dollar that even you in all your great and glorious extensive automotive wisdom do not know of all possible ways in which a tyre might lose pressure, so how about we all sit back and share the knowledge, you never know, you might even learn something.

feel the love.

XXXOOO DD

chicken wrote:
X 2

for frankenstye I have the courtesy to bother with an explanation - for you, johnny come lately, I say

STFU NOOB!

are you using the same tyre gauge each time? Because if you are checking on different gauges that could be the problem

grimbo wrote:are you using the same tyre gauge each time? Because if you are checking on different gauges that could be the problem

And servo guages are usually up the shit too (i've seen 13psi error) . I normally use my own small digital gauge.

As soon as I read "BFG" I automatically thought crap in the bead. I think they fixed the issue on the KM2s though?

Driven through mud lately?

Do you have valve caps, preferably metal ones with seals inside. Valves can leak very slowly. Check it with a drop of spit.

chicken wrote:

DR Frankenstine wrote:that's a really stupid question. SORRY

X 2

As the saying goes, There are no stupid questions, only stupid answers.
As you both have proved, stupids!

Anyway, one of my tyres, BFG also loses about 10psi a week! I know what it is too, crap in the bead. Just too lazy to fix it.

Mike

^^ My apologies. Didn't realise you were from Tazzie till now.

cheeeers fellas for the suggestions....

grimbo wrote:

are you using the same tyre gauge each time? Because if you are checking on different gauges that could be the problem

---yeah, i've been using the same gauge.

v840 wrote:

As soon as I read "BFG" I automatically thought crap in the bead. I think they fixed the issue on the KM2s though?

Driven through mud lately?

---> yeah. had a 4wd training with a club. very muddy conditions when we were driving . didn't really washed the tyres. i just did then .

BundyRumandCoke wrote:

Do you have valve caps, preferably metal ones with seals inside. Valves can leak very slowly. Check it with a drop of spit.

----> not sure what u meant by that? i have metal caps. the instructor for that training session removed all 4 thin cylinders that was located just below the thread. that cylinder prevented the air compressor head from fully engaging itself into the valve .. sorry i just don't know how to explain it better



----. so i've checked the psi again today at abt 130pm. really sunny. the psi read 36 on all tyres. and just checked it just now . so it's cold. reads 34 on the left front & rear, 36 on the right front & rear . and i just realised that the recommended tyre pressure 4 the KM2 are 35

--- anyway i did asked another bloke at another forum for his opinion and he emphasised the 4psi rule. and he did enquire abt the weight of my rig and the type of driving im doing at the moment.

so my rig alone weighs abt 1.4 ton. im driving up to lake mungo and painted desert for abt 4-6 weeks. will be doing sealed and unsealed roads. the tray is loaded up with camping gear, 2 spare tyres, and spare fuel , water.

and this was his suggestion .

"If your pressures are dropping overnight, it could be any of the above OR just the cold weather (has it been cold?)

Re the cold weather, if you set your tyres to 36 during the middle of the day when the temp is in or above about the mid 20's, or even just if the car's been sitting in the sun for a couple of hours & the internal tyre air temp is up around or over the mid 20's, then when the ambient air temp is dropping overnight down to anywhere below about 18 will cause pressure drops like those you are experiencing. To counter that, set your tyre pressures first thing in the morning, preferably BEFORE the sun gets on them, and before the ambient air temp gets up over about 18 deg C. Then you need to look for that 4psi pressure increase after 1 hours worth (or there-abouts) of driving on whatever surface & at whatever speed you normally use.

BUT, if your tyres are still losing pressure overnight after trying that, it is most likely one of the other problems you've already been told about. What size & sort of tyres are they? Make, size, and type can make them a bit more prone to one or the other of those problems, for instance, BFG's (KO's & KM's in particular) are renowned for getting crap in the bead if you use low pressures & the later KM's & KM2's are pretty well prone to slow punctures; Maxxis and some of the other cheaper brands tend to just become a bit porous to air as they age - resulting in slow pressure losses; and even your rim type can contribute - Speedy rims are very prone to rim leaks, they are a cheaply made rim with less quality control than the more expensive brands, and often it's only the paint on them that covers little cracks that eventually leak.

Then again, if you are setting your tyres at 36 psi during the day AFTER driving on them for a while, that reduction to 32 overnight is pretty much EXACTLY what you are looking for - 32 psi cold that reaches 36 psi after the tyres have warmed up (that hours worth of driving) means that for what you are doing, they are at the right temperature.

Lastly, without knowing more about your vehicle, it's weight, your driving style, the tyres make, type & size; it is a fairly well accepted generaliseation in the realm of specialist tyre users that MOST normal car drivers tend to run their tyre pressures a bit low, and MANY 4WDers run their tyre pressures a fair bit high. For example, ATM I'm in Bega NSW, probly pretty much the same sort of climate as Melb, altho maybe just a little colder, and for my fairly heavily laden Patrol running 33x12.50LT15 STT's, driving relatively short distances on bitumen (30km's) but at a reasonable sort of speed (80-100kph), I run the fronts at about 26psi and the rears at about 28psi. Longer trips (0ver 300km) see the fronts working best at about 28 psi & the rears at 32psi. Any more than that and I never get the 4psi increase in pressure; and I've already done 80,000km on these tyres & expect to reach 100,000km easily, so those pressures are working well for me. Alright, driving style can make a big difference, but I'd suggest that you spend at least a few weeks checking your tyre pressures EVERY MORNING, before you start driving, and then check them again after each hour of driving. I'm pretty sure that you will be quite surprised about exactly what your tyre pressures are doing, and even if nothing else, you'll be able to determine for sure if you have a slow leak or bad valve (not all that likely if it's all 4 tyres tho!!) "

dumbdunce wrote:

DR Frankenstine wrote:that's a really stupid question. SORRY

maybe it's a really stupid question for someone who knows a lot about cars and fourbies and tyres and all that technical shizz. it's a really genuine and perplexing question for someone who is less well schooled in these things. if you don't have anything constructive to say, why say anything at all?

there are many reasons why air may leak or appear to leak from tyres. some are easier to diagnose than others. I'm wiling to bet a dollar that even you in all your great and glorious extensive automotive wisdom do not know of all possible ways in which a tyre might lose pressure, so how about we all sit back and share the knowledge, you never know, you might even learn something.

feel the love.

XXXOOO DD

you're right and sorry for the stupid reply.

DR Frankenstine wrote:

dumbdunce wrote:

DR Frankenstine wrote:that's a really stupid question. SORRY

maybe it's a really stupid question for someone who knows a lot about cars and fourbies and tyres and all that technical shizz. it's a really genuine and perplexing question for someone who is less well schooled in these things. if you don't have anything constructive to say, why say anything at all?

there are many reasons why air may leak or appear to leak from tyres. some are easier to diagnose than others. I'm wiling to bet a dollar that even you in all your great and glorious extensive automotive wisdom do not know of all possible ways in which a tyre might lose pressure, so how about we all sit back and share the knowledge, you never know, you might even learn something.

feel the love.

XXXOOO DD

you're right and sorry for the stupid reply.

MAN HUGS!

Sounds like you had some bling bling chrome valve stem covers. Now removed by your pic.

Have a look inside your metal valve caps. There should be a rubber or plastic seal. This helps prevent air loss through the valve stem if the inner valve core is leaking a bit. The black plastic valve caps dont do as good a job, and are more easily damaged off road.

jezzat wrote: i have metal caps. the instructor for that training session removed all 4 thin cylinders that was located just below the thread. that cylinder prevented the air compressor head from fully engaging itself into the valve .. sorry i just don't know how to explain it better

Did the "cylinder" look something like this?


If so then he removed the valve core and probably didn't tighten it all the way up upon refitting. Check each one by removing the dust cover (the screw on cap - it really is only a dust cover, not a secondary pressure cap if the valve leaks...^^^). Put a bit of spit on the end of the valve to cover the opening and check for bubbles (feel free to use some soapy water instead if the idea of spitting on your finger disgusts you). If you get bubbles you'll need to find a valve tool to tighten the valve up. Supercheap etc will sell them. Engage the tool onto the head of the valve and righty tighty, lefty loosey.

From personal experience the BFGs shot them selves in the foot putting the so called rim protectors on, every time I went off road and aired them down a bit I would get flat tyres (usually the next day) sold them a couple of months after buying them and bought better tyres! Believe the new design has gone away from the rim protector idea and with good reason!
If you want an expense all round tyre that you can only run on road or get flats buy them otherwise stay clear of them IMO
I'm not biased toward them as ran the originals and had good run out of them, decided to upgrade and the flats put me off them. If I was feeling rich enough and wanted an all rounder I'd seriously look at the new design BFGs for sure!
I'd rather have road tyres (currently 33 Maxxis Bravos 751s and separate play tyres 36 Swampers)

36 psi in the tyres on a vehicle that weighs 1.4 tonnes ... (what sort of vehicle do you have)

Lower your tyre pressures 10psi and enjoy a FAR more comfortable ride.

RAY185 wrote:

Put a bit of spit on the end of the valve to cover the opening and check for bubbles (feel free to use some soapy water instead if the idea of spitting on your finger disgusts you). If you get bubbles you'll need to find a valve tool to tighten the valve up.

--- i did check it on the weekend. no bubbles.

love_mud wrote:

36 psi in the tyres on a vehicle that weighs 1.4 tonnes ... (what sort of vehicle do you have)

Lower your tyre pressures 10psi and enjoy a FAR more comfortable ride.

----> it' sitting at 35 psi now. thats the recommended pressure for the km2. i'm driving an 84 hilux ute. dropping it down by 10psi on bitumen will not be cmfortable unless it's off road yeah ? at the moment it's more bitumen driving. or should i drop it?

----> so i've been driving around and checking the psi. and trying to follow the 4 psi rule. on cold mornings or nights, they drop to 34. did some driving and it went up to 36. i had a read of the 4psi rule from the coopers tyre guide - it suggested that if it goes up by 4psi from the cold reading, i need to add more air. less than 4, cold pressure too high.

and they suggested for LT, use a 6psi guide. will do more test in the next few days.

Have you checked the tread for nails/screws.

A nail usually won't drop a tire straight away, it'll stay in the tread and simply allow a tiny leak of air.

You might not see a nail in the tire if they are the thin type nails, usually get them when driving around building sites/building site gutters and then driving in the shulder of roads or painted traffic islands on the roads as the crap goes there and doesn't move.

if you drive slowly on concrete and you hear tings as the tire go around then you'll have a nail or screw in the tire.

36 PSI will be the pressure you run when carrying a full load. of almost the vehicles weight again.
Dropping your tyre pressure (to a reasonabel level) will improve your ride comfort, and traction on and off road (you run lower pressures offroad than on of course)