Tyre/Tire Pressures. What do you run? (MERGED)

Ben Up North

Ben Up North

can only hope to improve
Joined
Oct 1, 2017
Messages
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Location
FNQ
Car Year
2004 | 1992
Car Model
SG Forester X MY05 | 92 SVX
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5MT D/R | 4EAT
In an effort to try and find out what's recommended, I've started this one thread fits all thread about tyre pressures.

2 days ago I had some Dueler A/Ts fitted, 215R65/16C.
Bridgestone put them on at 38psi (that's whata it was when I got the car home, so would have been warm.
Went for a little drive to see how they felt yesterday. Noticeably more feel on the road which was to be expected.
Got to the start of the dirt, deflated them down to 30psi. Made the corrugations quite bearable.
When I got to the rough stuff, I deflated to 25psi.
Very smooth on the whole.

Problem is, I've really got no idea what I should be running them at.
I've read in various threads that people go down to 22PSI off road, below 20 for sand.
For on road use, discussion seems to be fairly even between what the tyre dealers inflate to (high 30s) and what the vehicle manufacturer recommends (about 28-30 on the SG)

Currently I've inflated back to 35 when warm for road use to spllt the difference but would appreciate input.

What do you run your pressures at?
a format of:
Tyre
Tyre Use | Pressure
would make things nice and clear for readers :)

So to start..

Bridgestone Dueler A/T 215/65R16C
Road | 35psi
Dirt | 30psi
Offroad | 25psi
 
BFG TA KO2:

Road: 39 cold
Dirt road: 28 hot
4x4 trail: 21 hot or 18 hot, if anticipating more traction challenges
sand: as needed

Geolander ATS or COntinental AT or any other non-LT tire:
Paved road: 35 (ATS), 32/30 (Conti AT)
Dirt road: see paved road
4x4 trail: 28 (ATS), see paved road (if the Conti AT ever go on 4x4 trail).
sand: as needed

There is no point airing down from 35 to 30 for dirt. You could go 35 for around town or long road trips but once you start your unpaved adventure, just stay at the door pressures on and off road. There is absolutely no appreciable traction benefit at 30 vs 35 and ride quality should not be an issue with a Subaru wearing P-metric tires.

If you are short on traction, then you will want lower pressures, specifically 20 and lower. Subaru AWD is pretty poor in rock so that is where lower pressures come into play (sand aside). In turn, this requires strong sidewalls, hence 3-ply sidewall, LT tires. But if you only deal with generic rock on dirt roads, then the LT tires are an annoying overkill. Having to air down for any dirt road to keep the ride smooth is, in itself, a good enough reason for me to use the KO2s only for trips that involve actual 4x4 trails.
 
MiddleAgeSubie said:
BFG TA KO2:

There is no point airing down from 35 to 30 for dirt. You could go 35 for around town or long road trips but once you start your unpaved adventure, just stay at the door pressures on and off road. There is absolutely no appreciable traction benefit at 30 vs 35 and ride quality should not be an issue with a Subaru wearing P-metric tires.
Click to expand...

Thanks for the info, The tyres were at 38 originally. Dropping them to 30 certainly seemed to take the sting out of the corrugations compared to running a road tyre, but then I hadn't really tried the Duelers on corrugations before, so it could be that they'd be as comfortable at full pressure.

Door pressure for the SG is apparently 29 at all times on the front, 28 (unladen) to 40 (towing) on the rear

I guess my biggest concern is getting a decent life out of the tyre without uneven wear due to over/underinflation.

It's so confusing.
 
If they are P-metric, they should wear well at door pressures or a bit higher. Use IR termometer to see if center heats up as much as the edges.

You will NOT get good life from any tires actually used in harsh terrain. It comes with the territory. But forum members from Australia will give you better idea about what you can expect.
 
MiddleAgeSubie said:
If they are P-metric, they should wear well at door pressures or a bit higher. Use IR termometer to see if center heats up as much as the edges.
Click to expand...
Hmm.. now I've got to get an IR thermometer!:p

You will NOT get good life from any tires actually used in harsh terrain. It comes with the territory.
Click to expand...

I learnt a long time ago that good (or decent) is a very relative thing. :ebiggrin:
 
Good idea for a thread.

Geolander G012 205/75/15
Kumho Road Venture KL71 muddy 215/75/15
Road 34psi
Dirt 25psi
4wd tracks 20psi
Sand/difficult tracks 16psi
Soft sand 12psi

You can go down to 8psi to get out of a very soft section of sand but air back up to 12psi when you can.
Be careful turning on 12psi, it's easy to roll a bead
 
Ben Up North said:
Hmm.. now I've got to get an IR thermometer!
Click to expand...

I've got one; it's my palm and "I Reckon" it's about right! :lol:

BFG TA KO AT 21575R15

My pressure depends on loaded / unloaded / road conditions / on-road / off-road / mud / sand / rocky / etc but in general:

Road 34-36 psi
Dirt 28-32 psi
4wd tracks 22-25psi
Sand/difficult tracks 18psi initially
Soft sand 14psi (drop to 10 if necessary)

Good idea Ben, I've stuck the thread
 
Road Used to always run 34, now 38 on advice from tyre dealer and no problems re being too harsh.
Dirt To date, haven't gone on extended dirt tracks so I just leave pressure as is and never had a problem.
4wd tracks I will have to let you know! My off-roading of any significance has all been on sand!
Sand I've always run at 18psi and only went down to 10psa at Ngkala Rocks at Fraser Island in very soft sand. I might have made it at a higher pressure so maybe I will try again and see another time! So, other than dropping to 10psi at Ngkala Rocks I have done Fraser, Moreton and North Stradbroke Island at 18psi without problem so feel confident that this is a good starting point.
 
Proper inflation of LT metric tires for my Outback was about 44 psi. They were unbearable at 44 so I ran them at 39 which was fine when loaded on trips. They were unbearable on dirt at 39 requiring airing down for every single dirt road or grinding it out. They did great at 20 psi offroad.

I don't think anybody runs LT tires on lighter vehicles at proper pressures, but 30 psi is extremely low for street use. It is dangerous because sidewalls overheat constantly at that psi and street speeds. Not everyone gets a blowout, but it can happen. Even when it does not happen, you lose about 25% of tire life. There is a Nitto file on Google search that shows the sidewall temps at 30 vs proper psi on LT tires. There are also good tables made that show how drastically LT tires lose payload capacity under 35 psi.

Lots of people do the wrong thing and get away with it, it does not mean it will always be so.
 
No wonder the BFG were unbearable at that pressure in a lighter vehicle - 44 PSI (cold) is what I use for my ute when fully loaded; approx 3 ton.
 
I run D697 LT tyres at 40 psi unladen because that’s what Bridgestone recommend. Fully laden at 3.5 tonne it will be 44 psi, same as Kevin. Bridgestone wouldn’t recommend a pressure for off roading, but said as a guide for mud, rock and gravel to use 75% of highway pressures, and soft sand 33%. I think it’s significant Bridgestone are vague about tyre pressures for off road use and perhaps suggests not to go too low even at the expense of traction.
 
I have found that very few manufacturers will recommend lowering tyre pressures for off road use. The reason for this is legal liability should there be a tyre failure, particularly one that results in a serious vehicle accident. A key component of this legal liability is the tendency for many people to neglect to reinflate their tyres when leaving the dirt, either due to laziness or forgetfulness. This does not mean that the tyres are not capable of operating at lower pressures off road but it does mean that safety margins are reduced.
 
Rally said:
I run D697 LT tyres at 40 psi unladen because that’s what Bridgestone recommend. Fully laden at 3.5 tonne it will be 44 psi, same as Kevin. Bridgestone wouldn’t recommend a pressure for off roading, but said as a guide for mud, rock and gravel to use 75% of highway pressures, and soft sand 33%. I think it’s significant Bridgestone are vague about tyre pressures for off road use and perhaps suggests not to go too low even at the expense of traction.
Click to expand...


That's good and unusual info, thanks for sharing it.


Beachworm said:
I have found that very few manufacturers will recommend lowering tyre pressures for off road use. The reason for this is legal liability should there be a tyre failure, particularly one that results in a serious vehicle accident. A key component of this legal liability is the tendency for many people to neglect to reinflate their tyres when leaving the dirt, either due to laziness or forgetfulness. This does not mean that the tyres are not capable of operating at lower pressures off road but it does mean that safety margins are reduced.
Click to expand...


I could not agree more.
 
Kevin said:
No wonder the BFG were unbearable at that pressure in a lighter vehicle - 44 PSI (cold) is what I use for my ute when fully loaded; approx 3 ton.
Click to expand...


Well, that's the thing, the load capacity equivalent to 32 psi P metric in that size was 44 for LT.

Now, there is a lot of margin built into the stock capacity and presumably this is why people get away with running LTs at much lower than recommended but under 35, the LT curve starts going down pretty quickly.

https://www.toyota-4runner.org/engi...s/110299-lt-tires-need-more-air-pressure.html
 
I don't know why there's so much confusion for offroad pressures, it's so simple:

general dirt/gravel roads 25psi
easy 4wd tracks & firm sand 20psi
medium 4wd tracks, soft sand 16psi
hard 4wd tracks, very soft sand 12psi
Get out of trouble 8psi

Subarus are not big heavy 4wds. We need to run at lower pressures offroad to get the same amount of bagging as a fat 4wd would get.
We can also run at lower pressure without needing beadlocks because we are so much lighter & don't put as much loading on the tyres

Completely ignore any advice about tyre pressures for 4wds, it is completely irrelevant for a Subaru that weighs only half as much with an AWD system & IFS/IRS

Ignore any advice from manufacturers! This is aimed towards 4wds...see above

Don't try to get fancy. Offroad tyre pressures are very simple for our Subarus, stick to the above & you will be fine in 99% of situations
 
NachaLuva said:
I don't know why there's so much confusion for offroad pressures, it's so simple:

general dirt/gravel roads 25psi
easy 4wd tracks & firm sand 20psi
medium 4wd tracks, soft sand 16psi
hard 4wd tracks, very soft sand 12psi
Get out of trouble 8psi
Click to expand...


There is no confusion, but it matters whether the tires are P or LT. I never ran under 28 my P-metric ones and never had issues (not talking sand).

But the LT-D had to be run at 20. Terrain difficulty did not matter. But P at lower pressures is really exposed in sharp rocks.
 
Tyre pressure is critical to offroad performance. Lift, drivetrain, tyre brand, driver, etc are useless if the tyre pressure is too high.

If the tyres are LT, you need to run them at lower pressures to get the same bagging as the sidewalls are stiffer.
At the same time, LT are able to cope with lower pressures.

The increase in grip as you lower tyre pressure is not linear, it's more exponential:
Running at 25psi has mild increase in grip over road pressures, the main difference is comfort, esp on corrugations
20psi has a moderate increase in grip over 25psi
16psi has a big increase in grip over 20psi
12psi has a huge increase in grip over 16psi
8psi is like having tracks!

By P-metric, do you mean normal passenger tyres? Use the table listed before.

Remember that tyres are like balloons, the higher the pressure the more likely you are to get a puncture. Reducing the pressure allows the sidewall to bend around the sharp rock or stick without being cut

Like I said, don't complicate it. Stick to the table listed & you will be fine in 99% of situations. If you're on a loose or slippery surface & are spinning tyres & want more grip, just drop 4psi & feel the difference
 
NachaLuva said:
I don't know why there's so much confusion for offroad pressures, it's so simple:

general dirt/gravel roads 25psi
easy 4wd tracks & firm sand 20psi
medium 4wd tracks, soft sand 16psi
hard 4wd tracks, very soft sand 12psi
Get out of trouble 8psi

Subarus are not big heavy 4wds. We need to run at lower pressures offroad to get the same amount of bagging as a fat 4wd would get.
We can also run at lower pressure without needing beadlocks because we are so much lighter & don't put as much loading on the tyres

Completely ignore any advice about tyre pressures for 4wds, it is completely irrelevant for a Subaru that weighs only half as much with an AWD system & IFS/IRS

Ignore any advice from manufacturers! This is aimed towards 4wds...see above

Don't try to get fancy. Offroad tyre pressures are very simple for our Subarus, stick to the above & you will be fine in 99% of situations
Click to expand...

I think with non LT tyres this is probably correct. I’m not so sure about LT tyres. With a substantially different construction, it may not necessarily follow that you can use the same pressures. By way of example, you use a lot less pressure in racing slicks than you would in street tyres on a race track. Perhaps to run those thick sidewalls of the LT you need more pressure. I don’t know. Thankfully for me it’s easy with my Forrie. 25 all round off road, 40 on. Sand is for mixing cement! 🤣
 
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