General Grabber Pressures

[T6Chas]

Our 2023 T32 4 Motion is fitted with 235/55 R18 XL (104) tyres.

It has a full camper conversion and removable towbar.

Before our recent trip I put it on a weigh bridge and with a full tank of diesel, gas, tools but without driver or passenger it weighed 2,600Kg.

Therefore I guess with driver, passenger, dog and gear it’s going to be in the region of 2,900Kg.

The tyres are rated at 900Kg at 51PSI. Iknow I should have weighed front and rear axles separately…….next time.

In the meanwhile I’m finding 41PSI on the front tyres and 38 on the rears seem to give a reasonable quality ride.

I’d be very interested in anyone’s useful comments.

 

[Green Giant]

Our van, same spec as yours weighs 2640 with full fuel, driver and passenger, tailgate bike rack Thule awning, etc etc, 235 65 17 GG AT3 tyres.
When loaded up for a 4week trip, with all the holiday kit we weighed in at 2880,, that’s loaded with 4weeks food and drink, 100 kg probably, (went to Norway) spare gas bottle, water, and all the camping kit, I keep our pressure around 47/48, I can’t ever see us taking more kit, we took too much on that trip anyway…maybe not drink..
We have changed the shocks out for better comfort and control

 

[AeonMach]

And

Our 2023 T32 4 Motion is fitted with 235/55 R18 XL (104) tyres.

It has a full camper conversion and removable towbar.

Before our recent trip I put it on a weigh bridge and with a full tank of diesel, gas, tools but without driver or passenger it weighed 2,600Kg.

Therefore I guess with driver, passenger, dog and gear it’s going to be in the region of 2,900Kg.

The tyres are rated at 900Kg at 51PSI. Iknow I should have weighed front and rear axles separately…….next time.

In the meanwhile I’m finding 41PSI on the front tyres and 38 on the rears seem to give a reasonable quality ride.

I’d be very interested in anyone’s useful comments.

Woah, wait on: some misconceptions here (and there seem to be a shit-load about this subject generally so it’s not surprising… the industry have tried to dumb it down to keep it really simple but the result has been a confusing lack of info if you vary from the standard OEM door jamb recommended sizes!).

Our 2023 T32 4 Motion is fitted with 235/55 R18 XL (104) tyres.
…

The tyres are rated at 900Kg at 51PSI.

Look carefully at the sidewall: I’m pretty sure that is the US-only spec (although that doesn’t mean it’s irrelevant since we don’t have different laws of physics from them… whatever MAGA types might think )…

…but more importantly while this is sorta true it’s also a really misleading statement: you have max 900kg load AND **separately** a MAX PRESSURE of 50psi.
Yes at 50psi you will have a load capacity of 900kg BUT you will achieve this max load rating at much lower load pressures (and won’t be so likely to blow a tyre due to overflation at high speed and in hot weather!!).

The ERTRO sets the standards for these Euro metric tyre sizes and the load ratings associated with them, and they and tyre manufacturers publish standard tables showing tables of load vs pressure. Except they are not well publicised and hard to get hold of… and I’ve not really seen anyone refer to the here; merely continue to pass on word of mouth recommendations of what-seems-to-work!!

But you can find them because they are standards based it doesn’t matter that you have a tyre from a different manufacturer!
So here’s Continental’s documentation:
https://www.continental-tires.com/c...nload-technical-databook.pdf.coredownload.pdf

See page 106 for tables for XL tyres and reference your load rating.
You will see that for a 104 load rated tyre you achieve max load rating at 2.9bar/42psi!!
The load capacity does NOT increase at higher pressures.
A bit higher pressure might be needed for speed but one shouldn’t be pushing the max pressure since you need to allow for heating!!

Bear in mind that even if you are at your full 3.2T then (simplifying slightly and assuming equal axle loading) then you only have 1.6T per axle and therefore 800kg per tyre.
And that load is achieved at 2.5bar/36psi!

So in short (based on some actual standards and data rather than word-of-mouth ) yes 41/38 seems very appropriate.

PS I’m also running a LWB 4Mo weighing 2.7T. Different tyres but same size (235/55/R18s XL) and 104 load rating - and load ratings are load ratings!
I run 40/38 or sometimes just 40 all-round.


PPS to give some more confidence, here’s tiresize.com’s pressure calculator using the OEM door jamb pressure recommendations based on the stock Sportline
255/44/R18s 48psi loaded pressure… and for our 235/55/R18s it recommends 41psi

 

[Green Giant]

Checked my GG AT3 tyres are 108 load so are 1000kg,

 

[AeonMach]

Checked my GG AT3 tyres are 108 load so are 1000kg,

They’re beasts!

But if you follow my points above and reference the table for your 108 load rating then you will still see that they also still achieve that max load rating at 2.9bar/42psi!!
…and you don’t need the load rating that high either cos the rest of your 3.2T capacity means -> 1.6T axle (simplifying) -> 800kg per tyre!

So your pressures (you said 47/48?) seem a little high possibly…
Does it state a max pressure? If it’s 50 then I think you’re running pressure too high… drive fast and with warm temps and that cold static pressure will be higher than 50 very quickly!!

PS I’ve run the numbers (using the OEM Sportline 245/55/R18s door jamb 48psi recommendation and converting for your 235/65/R17s and yes I think you’re running your pressure WAY too high!!

 

[T6Chas]

Thank you. Your are quite right I assumed that maximum load went with maximum pressure. Looking again at the tyre sidewall it does indeed state maximum load 900Kg, maximum pressure 51psi without linking the two.

We had a relatively high speed run down from Cumbria to London yesterday. I set the ACC at 75mph and for the first two hours had very little traffic. I checked the temperatures when we stopped for coffee and they were no more than vaguely warm. Given the impact of speed on fuel consumption I don’t think we will ever travel faster than that.

 

[Green Giant]

They’re beasts!

But if you follow my points above and reference the table for your 108 load rating then you will still see that they also still achieve that max load rating at 2.9bar/42psi!!
…and you don’t need the load rating that high either cos the rest of your 3.2T capacity means -> 1.6T axle (simplifying) -> 800kg per tyre!

So your pressures (you said 47/48?) seem a little high possibly…
Does it state a max pressure? If it’s 50 then I think you’re running pressure too high… drive fast and with warm temps and that cold static pressure will be higher than 50 very quickly!!

PS I’ve run the numbers (using the OEM Sportline 245/55/R18s door jamb 48psi recommendation and converting for your 235/65/R17s and yes I think you’re running your pressure WAY too high!!
View attachment 278317

Yes taken your info on board and will lower them and see how I get on for a while

 

[AeonMach]

Thank you. Your are quite right I assumed that maximum load went with maximum pressure. Looking again at the tyre sidewall it does indeed state maximum load 900Kg, maximum pressure 51psi without linking the two.

We had a relatively high speed run down from Cumbria to London yesterday. I set the ACC at 75mph and for the first two hours had very little traffic. I checked the temperatures when we stopped for coffee and they were no more than vaguely warm. Given the impact of speed on fuel consumption I don’t think we will ever travel faster than that.

View attachment 278325

Yes I think you’ve got your pressures spot on… and your nice checking of the running temps is a good sign.

 

[Ricardo T]

I run GG’s on my panel van, albeit 17”. There was a bit of a discussion about my pressures ( thread ‘ Swamper tyre pressures’) F 57 R 48 psi as set up by Bognor Motors who are the so called ‘specialists’ in all things relating to mods on T6’s. My tpms was duly changed and set up to those pressures, by them, when they fitted the wheels and tyres over two years ago now. At the time I did think the pressures were a bit high but I didn’t challenge it, maybe I should have.
Those pressures gave a comfortable ride and are wearing evenly across the tread.
After the discussion on that thread I thought I best check the maximum pressure of those tyres….51psi !!!…..Lost for words.
Have spoken to them since and they said that those were the pressures they were told at the time, wtf, and that they should in fact be 45psi all round.
I’ve now got to arrange for someone who knows what they are doing and that I trust to change the whole set up on the tpms to 45, which to be fair Bognor have said they will pay for.
Not what I was expecting from a highly regarded mods specialist, so very disappointed.
I think the general consensus with most of these all terrain tyres is around the 45 mark it would seem, but I’m finding the pressures can vary by as much as 8-9 psi depending on weather and tyre temperature, that’s what my tpms is telling me anyway!

 

[Kind of Blue]

I run GG’s on my panel van, albeit 17”. There was a bit of a discussion about my pressures ( thread ‘ Swamper tyre pressures’) F 57 R 48 psi as set up by Bognor Motors who are the so called ‘specialists’ in all things relating to mods on T6’s. My tpms was duly changed and set up to those pressures, by them, when they fitted the wheels and tyres over two years ago now. At the time I did think the pressures were a bit high but I didn’t challenge it, maybe I should have.
Those pressures gave a comfortable ride and are wearing evenly across the tread.
After the discussion on that thread I thought I best check the maximum pressure of those tyres….51psi !!!…..Lost for words.
Have spoken to them since and they said that those were the pressures they were told at the time, wtf, and that they should in fact be 45psi all round.
I’ve now got to arrange for someone who knows what they are doing and that I trust to change the whole set up on the tpms to 45, which to be fair Bognor have said they will pay for.
Not what I was expecting from a highly regarded mods specialist, so very disappointed.
I think the general consensus with most of these all terrain tyres is around the 45 mark it would seem, but I’m finding the pressures can vary by as much as 8-9 psi depending on weather and tyre temperature, that’s what my tpms is telling me anyway!

Tyre pressures normally taken cold because the tyres heat up as we drive. The faster we drive, the bigger the load, perhaps we sprint between bends, screech around bends, hard acceleration and braking then we expect tyre temp to rise. As the temps rise therefore so do the tyre pressures. So if we set the tyres when hot they would be underinflated when cold and the other way. The pressures are manufacturers suggested pressures on the door but we have an obligation to mind them for the tyres they quote for. If someone is involved in a serious accident resulting in injury or death then one can expect vehicles will be inspected foe defect, habits from the ecu ect and tyre pressures ware, if the car has been maintained and so on. i am sure that they have a comprehensive list of things. The tyre pressure comparison tables on the posts above are similar to the tables that I use. So if using tyres different in size and structure to what suggested by the the manufacturer then just enter all the appropriate numbers and tyre designations letters asked and a new figure will be presented. So from the manufactures tyres and suggestion the in opposing table the new tyre numbers ect ect comparison site will calculate the new pressures Just as demonstrated above. One cannot assume that all all "All Terrain Tyres"run at 45PSI" because it depends on size rating load rating and so on people use different sizes size ratio and load ratings and so on. Mine run at much lower psi at low load much less that manufacturers figures because I use different lager size and greater load rating ect/

 

[AeonMach]

Tyre pressures normally taken cold because the tyres heat up as we drive. The faster we drive, the bigger the load, perhaps we sprint between bends, screech around bends, hard acceleration and braking then we expect tyre temp to rise. As the temps rise therefore so do the tyre pressures. So if we set the tyres when hot they would be underinflated when cold and the other way. The pressures are manufacturers suggested pressures on the door but we have an obligation to mind them for the tyres they quote for. If someone is involved in a serious accident resulting in injury or death then one can expect vehicles will be inspected foe defect, habits from the ecu ect and tyre pressures ware, if the car has been maintained and so on. i am sure that they have a comprehensive list of things. The tyre pressure comparison tables on the posts above are similar to the tables that I use. So if using tyres different in size and structure to what suggested by the the manufacturer then just enter all the appropriate numbers and tyre designations letters asked and a new figure will be presented. So from the manufactures tyres and suggestion the in opposing table the new tyre numbers ect ect comparison site will calculate the new pressures Just as demonstrated above. One cannot assume that all all "All Terrain Tyres"run at 45PSI" because it depends on size rating load rating and so on people use different sizes size ratio and load ratings and so on. Mine run at much lower psi at low load much less that manufacturers figures because I use different lager size and greater load rating ect/

Yes I agree: @Ricardo T I think your pressures are possibly STILL too high!
See my reply above to Green Giant who is also on 17” GGs…

…or run your numbers through tiresize.com’s pressure calculator yourself.
(You can use your door jamb recommendations to give a *known* starting wheel size and recommended prrsssures - using the laden pressures I would think.)