Scary tyre pressures.

[Thingy]

As I get ready to tow with the Shogun for the first time, I have to say Im a little bit taken aback by the tyre pressures.

This is the first true 4x4 I have owned, previous has been Volvo XC70 preceeded by two xTrails. When I look at the tyre pressures for this vehicle, I find three sets rather than the standard two and are as follows:

Bar with 5 people up 2.2f and 2.4r
Bar with 7 people or full load 2.4f and 2.8r
Bar towing with AT, 3.2 f and 3.5 rear.
As best as I can convert this into real money it gives in PSI
32f and 34/5 r
34/5f and 40r
these I can live with, but
46f and 50r seems awfully high to me. The non Euro4 engine is substantially lower. Tyres are 265 60 r18.

Just wondering what you experts think about pressures this high. Kerb weight is 2300kg, max load 3000kg, with a towing capacity of 3500kg. I understand these figures are correct, but they seem very high to me.

 

[ProfJohnL]

Hello Thingy,

It makes perfect sense that as you load a vehicle for the tyres to maintain the desired footprint and side wall support form, you need correspondingly increase the tyre pressure.

Especially with many 4x4 tyres the side wall is quite tall and will flex more under cornering and braking etc, When towing these forces are substantially increased so higher tyre pressure will help reduce the side to side shimmy that might other wise occur.

There are some members of the forum who will tell you the car manufactures don't seem to know what the're talking about when it comes to recommended pressures, but the're not going to be a mile out unless its a misprint in the vehicle hand book.

There are tyre pressure charts which will allow you to select a finer incremental pressure dependant on the actual axle load, but not many of us have access to axle load indicators to be able to make these changes on a journey by journey basis.

The other factor is you must check the tyres you have fitted are rated to these higher pressures.

 

[Thingy]

Hi Prof

totally with you on all points, just thought that 50psi was a little excessive on the vehicle, but it must be correct. Never had a car with them that high before. Tyres were replaced last month and I used the manufacturers original fitted tyres, Dunlop GrandTrak AT2, but I will check that loading just in case.

It was interesting to note that the same vehicle with same wheels, non Euro4 engine, had tyre pressures 12 psi lower for toing.

 

[Dustydog]

Hi Thingy
What make of tyres do you have?
The car manufacturer and tyre maker spend many hours working out the best tyre pressures for a range of weights .
As pressures rise a lot of domestic pressure gauge and pumps become less accurate.
Most garage gauges are tested and calibrated annually so use one of them first and then see how your own gauge compares.

 

[Thingy]

I use ring equipment, both for the pump and seperate tyre pressure guage. Tyres are Dunlop Grandtrek AT2 on 265 60 r18 H110, more than capable of taking the tyre pressures.

Being a Shogun, superb offroad but harsh on it, I reckon at 50psi Im going to feel every little bump in the road.

I had better load the beer in the caravan, not the car.

 

[Gagakev]

Hi Thingy, I was surprised as you were.
Last Shogun Sport model on 28 front and 30 rear
This one on 265/65 R17 @ 38 front and 43 rear
So as you have the 18 inch works out about the same I suppose (Thats a guess )
Dont find it a hard ride at all, hope your first tow goes well.

 

[Thingy]

Im going to keep an eye on the tyres at those pressures and make sure they arent getting warm, but Im going to try them at 46f and 50r.

If the Shoggy is half as good as the XC70 I had last, I will be delighted, that was a highly recommened tug, loved it to bits.

Its going to be interesting to see the fuel economy or lack of it. Im running fully laden (away for a month) from Derbyshire to Kenford (Exeter) and then on into West Cornwall.

 

[Gagakev]

Im going to keep an eye on the tyres at those pressures and make sure they arent getting warm, but Im going to try them at 46f and 50r.

If the Shoggy is half as good as the XC70 I had last, I will be delighted, that was a highly recommened tug, loved it to bits.

Its going to be interesting to see the fuel economy or lack of it. Im running fully laden (away for a month) from Derbyshire to Kenford (Exeter) and then on into West Cornwall.

Getting around 18 to gallon on mine (last one petrol model around 10 to 12)
Be interesting to see what you get as mostly motorway mine was mostly done on dual carriageway with lots of roundabouts.
Weather down here, 15 miles from Kenford...... glorious enjoy your time away,

 

[Thingy]

Didnt realise you were down there. We always stay over at Kenford, microclimate up there always good for a laugh.

Around here, solo, Im getting between 19 and 21 around town, and just into the low to mid 30's on the motorway. I find mine is most economical in sequential rather than drive and stick the cruise control on. Im guessing towing should still be around the 19 - 20 mark.

 

[otherclive]

A rule of thumb used to be to drive for 20-30 minutes and recheck pressures. If they have gone up by 4psi then the 'cold' pressure is right for the load. My Pajero rides on 265/70/15 AT tyres and seems to conform to the RoT. But our old Sorento was 35psi (from
Memory) irrespective of load. And the current Subaru Forester varies very little with load also. I always go by the makers figures which as said above will be arrived at through a pretty comprehensive development programme.

 

[JonnyG]

Hello Thingy,

It makes perfect sense that as you load a vehicle for the tyres to maintain the desired footprint and side wall support form, you need correspondingly increase the tyre pressure.

Especially with many 4x4 tyres the side wall is quite tall and will flex more under cornering and braking etc, When towing these forces are substantially increased so higher tyre pressure will help reduce the side to side shimmy that might other wise occur.

There are some members of the forum who will tell you the car manufactures don't seem to know what the're talking about when it comes to recommended pressures, but the're not going to be a mile out unless its a misprint in the vehicle hand book.

There are tyre pressure charts which will allow you to select a finer incremental pressure dependant on the actual axle load, but not many of us have access to axle load indicators to be able to make these changes on a journey by journey basis.

The other factor is you must check the tyres you have fitted are rated to these higher pressures.

not some prof i believe you are referring to my persons.! and yet again using poetic licence for what point i don't know.. bit like your knowledge of tyres! as nobody but you has ever used the words "There are some members of the forum who will tell you the car manufactures don't seem to know what the're talking about when it comes to recommended pressures" do what you do best stick to book facts which you know and don't go making statement up merely because you have reach your limited limitation on a specific subject!!!!

 

[otherclive]

I haven't been on the Forum for neigh on 3 months but sad to see that some correspondents are still as impolite as ever.

 

[seth1]

I wonder if people notice how much of a slow forum this has turned into compared to how it used to be.Its like being sat in a court room at times.The asking of one question then turns into the answer for an assumption that wasnt asked for or made and lets not forget clive some of your replies have been rather short on occasion.

 

[JonnyG]

in polite? in polite is hiding behind or making statements that infer an untruth or the twisting of someone's words for some sort of gratuitous effect, who know it could all be down to trying to hold an authoritarian position ....
Now in your case Clive as you posted on said tyre topic last year and have no doubt forgotten it I'd suggest you re read it then read the prod post, then call me in polite. unless that is you have the Uruguay syndrome..err thats where to some one cannot do wrong..!

 

[ProfJohnL]

For anyone who wants to see the thread Jonny G refers to you will find it here.

http://www.practicalcaravan.com/forum/towing-driving-and-safety/48090-car-tyre-pressures?start=0
Please make up your own minds.

 

[otherclive]

I don't disagree that I contributed to an earlier thread on tyre pressure, but my comments relating to 'in polite' (sic) are in regard to this thread on Scary Tyre Pressures. Over and out

 

[Damian]

This topic has been reported to me for "Flaming", the strange bit is, it is the "Flamer" who reported it.
Now, having shot themselves in the foot I suggest that it stops now or I may just hit the Ban button.
Bringing up topics that are as old as the one brought up does nothing but reinforce my feelings that there is a bit of drastic action waiting to happen.

As for Seths' post, yes it is becoming quiet and people seem to be afraid to ask a simple question and get a simple answer, it ends up chapter and verse about the intricacies of almost everything , which is very frustrating, and to the average vanner way over the top and lost in space.

 

[JonnyG]

Im going to keep an eye on the tyres at those pressures and make sure they arent getting warm, but Im going to try them at 46f and 50r.

If the Shoggy is half as good as the XC70 I had last, I will be delighted, that was a highly recommened tug, loved it to bits.

Its going to be interesting to see the fuel economy or lack of it. Im running fully laden (away for a month) from Derbyshire to Kenford (Exeter) and then on into West Cornwall.

one should always keep an eye on tyres but why are you worried about them getting warm at those pressure? tyres get too warm when they are under inflated as opposed to max pressures...

 

[Dustydog]

Cutting the chase the banter and referral to an an old thread is IMO warranted and does provide some interesting thoughts.
Please don't hit the button Damain. This is a healthy scientific debate.

Lutz statement is very relevant and should not be dismissed"

Sir Gafferbill clearly pointed out the most important factor for any driver. Make sure your tyres are correctly inflated. Under inflation is the cause of most overheating issues.
My Sorento runs at 35 psi all conditions.
I am sure Kia liaised with more than one tyre manufacturer in reaching that conclusion.
The rest of the posts are opinions and do provide fodder for a healthy debate even if lively at times. I like the debates!

 

[JonnyG]

Cutting the chase the banter and referral to an an old thread is IMO warranted and does provide some interesting thoughts.
Please don't hit the button Damain. This is a healthy scientific debate.

Lutz statement is very relevant and should not be dismissed"

Sir Gafferbill clearly pointed out the most important factor for any driver. Make sure your tyres are correctly inflated. Under inflation is the cause of most overheating issues.
My Sorento runs at 35 psi all conditions.
I am sure Kia liaised with more than one tyre manufacturer in reaching that conclusion.
The rest of the posts are opinions and do provide fodder for a healthy debate even if lively at times. I like the debates!

hi dustydog, when you say" you are sure Kia liaised with more than one tyre manufacturer" are you sure or just assuming? or do Kia use more than one make of tyre for the same model of car as standard?.. and indeed under inflated tyres are a safety issue, my point? is simple enough. when is a tyre an under inflated tyre? purely from a scientific, nay safety point of view? anyone? its not a pedantic question just wondering under inflated is merely a couple of word to describe a scenario, put into action does anyone know at what bar or psi their vehicle has under inflated un safe and illegal tyres?

 

[Dustydog]

Hi Johnny.
I know for fact Kia fitted Hankooks on all mk1 Soentos.
latterly on the Sorrento Titans ome was Goodyear Wranglers.
We all agree under inflation is a safety issue.

 

[Damian]

Quote " The rest of the posts are opinions and do provide fodder for a healthy debate even if lively at times. I like the debates! "

Healthy debate is fine as long as it stays on topic and relevant and statements which are made are verifiable and safe.
What is NOT acceptable is personal attacks on other posters and snide remarks about other posters.
There is no need for those and they will not be tolerated, neither will the poster of such remarks be tolerated and can expect a lengthy ban.

 

[JonnyG]

Hi Johnny.
I know for fact Kia fitted Hankooks on all mk1 Soentos.
latterly on the Sorrento Titans ome was Goodyear Wranglers.
We all agree under inflation is a safety issue.

agreed but does anyone actually know at what point there vehicle has under inflated tyres? or do we merely go by manufacturer recommendations and assume 1 psi or 2 psi or even 10 psi under their recommendation is under inflated un safe and illegal?

 

[seth1]

An under inflated tyre wont fail mot as long as a brake test can still be performed.Make your own mind up.I have no opinion either way.I do mine the simple way-of the hand book.I know for a fact ive ran tyres under inflated by probably 10 psi,never had an issue.

 

[Damian]

Taken from TyreRack website:

Disadvantages of Underinflation

An underinflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle’s tires are underinflated by only 6 psi it could lead to tire failure. Additionally, the tire’s tread life could be reduced by as much as 25%. Lower inflation pressure will allow the tire to deflect (bend) more as it rolls. This will build up internal heat, increase rolling resistance and cause a reduction in fuel economy of up to 5%. You would experience a significant loss of steering precision and cornering stability. While 6 psi doesn’t seem excessively low, remember, it usually represents about 20% of the tire’s recommended pressure.

Disadvantages of Overinflation

An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when running over potholes or debris in the road. Higher inflated tires cannot isolate road irregularities well, causing them to ride harsher. However, higher inflation pressures usually provide an improvement in steering response and cornering stability up to a point. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures. The pressure must be checked with a quality air gauge as the inflation pressure cannot be accurately estimated through visual inspection