LT Tyre Deflation

Submitted: Tuesday, Mar 09, 2010 at 08:08
ThreadID: 76697 Views:3064 Replies:6 FollowUps:19
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Hi Guys,

i have been running Bridgstone Dueler A/T 693's and am quite cofortable with the various tyre pressures for different applications however in a couple of weeks i will be putting a set of Dueler A/T 694 LT's on and having never run LT's before i was wondering if somone could give me some hints on what pressures for gravel, rock and sand. I believe with the LT's the road pressures are higher due to the chunkier side walls so i presume the lowering pressure will also be higher but a search on here and other sites hasnt gleaned much info for LT's. Thanks in advance.

Tony.
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Reply By: Member - Oldplodder (QLD) - Tuesday, Mar 09, 2010 at 08:54

Tuesday, Mar 09, 2010 at 08:54
Your DMax most probably is about the same weight as my pajero.
As you know , also depends what load you are carrying :o)

My '10 ply' LTs are rated to 80 psi max, around town and on the highway lightly loaded I run about 36 to 38 psi.

Heavy load, might put the rears up to 45.
Any higher and I start getting centre tread wear, but have used 50 psi on some makes of tyres.

Usual 35 to 28 for tracks, depending on speed and conditions.

And 25 to 18 for sand.

AnswerID: 407999

Follow Up By: Member - TonBon (NSW) - Tuesday, Mar 09, 2010 at 09:13

Tuesday, Mar 09, 2010 at 09:13
Good stuff, thanks Oldplodder. Planning an extended trip in July accross the Great Sandy desert heading East from Eighty Mile and working accross from there to Uluru and then onto Oddnadatta and Cameron Corner so i will be pretty much loaded up to capacity. This is good info, cheers.
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Reply By: Member - Stephen L (Clare SA) - Tuesday, Mar 09, 2010 at 08:58

Tuesday, Mar 09, 2010 at 08:58
Hi Tony
I have the 694 LT's and for Highway work run 32 psi and work on the 20% rule when on dirt, dropping down to 24 psi, as you will also be dropping your speed accordingly. For sand start at 18 psi and work from there. The above figures work well for me, but other may not agree with my pressure figures.


Cheers


Stephen
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Follow Up By: Member - TonBon (NSW) - Tuesday, Mar 09, 2010 at 09:15

Tuesday, Mar 09, 2010 at 09:15
Great stuff Stephen, gices me a good starting point for the trip in July. Are you happy with the tyres? i have researched for 12 months and finally decided on these as the current 693's performed well.

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Follow Up By: Tenpounder (SA) - Tuesday, Mar 09, 2010 at 09:19

Tuesday, Mar 09, 2010 at 09:19
Hi there. I run Cooper LT tyres (no rude remarks) and I am aware Coopers suggest that low pressures should only be used with LT construction tyres The exact wording is "All pressures stated are suggested for light truck construction tyres only, and should not be advised to any person driving on passenger construction tyres."
I am with Stephen L as to the pressures he recommends, when using LT tyres.
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Follow Up By: Ozrover - Tuesday, Mar 09, 2010 at 10:01

Tuesday, Mar 09, 2010 at 10:01
Stephen,

Spot on with the pressures you suggested, I have had Dueller's, Goodyear A/T's & MTR's, Firestone as well as Coopers & run them all on the pressures that you quoted with no problems.

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Follow Up By: Member - Stephen L (Clare SA) - Tuesday, Mar 09, 2010 at 14:24

Tuesday, Mar 09, 2010 at 14:24
Hi Tony
So far I am happy, but this years trip will be the telling factor. They have handled very well, very quite on the road and have had no problems on the Great Central, Abandoned Gunbarrel, David Carnegie Road, Connie Sue, Sydney Yeo Track, Plumridge Lakes Road and the Lake Rason Road, These were all on well formed and marked tracks with the exception of the Sydney Yeo Track. This years trip is a little different with about 5 days of true cross country work in the Great Victoria Desert, where any track will be a premium.

From past experience on this type of cross country work, tyres get a real work out and ANY tyre can suffer from side wall stakes. But like I said, I will have a better idea of how they went by the end of August.


Cheers

Stephen
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Follow Up By: Member - TonBon (NSW) - Wednesday, Mar 10, 2010 at 05:35

Wednesday, Mar 10, 2010 at 05:35
Thanks Stephen, sounds like you have a big trip planned. Hope all goes well, stay safe and enjoy.

Tony
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Reply By: Notso - Tuesday, Mar 09, 2010 at 09:01

Tuesday, Mar 09, 2010 at 09:01
The 693 LTs I had on the old Patrol recommended pressure from the tyre service was 30psi all round light load and 30 front 35 rear for towing.

This was pretty close to the manufacturers specs for the 693 non LTs.

They wore evenly and lasted me around 90,000ks
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Follow Up By: Member - TonBon (NSW) - Tuesday, Mar 09, 2010 at 09:16

Tuesday, Mar 09, 2010 at 09:16
Interesting stuff Notso, i didnt even realise the 693's came in an LT. Food for thought, cheers.
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Follow Up By: Notso - Tuesday, Mar 09, 2010 at 09:21

Tuesday, Mar 09, 2010 at 09:21
The were made over in South Australia, but no more. I had two sets of them on the patrol and never had a puncture, did the oodnadatta and Gibb River on the first set when they already had 70,000 on them.
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Follow Up By: Tenpounder (SA) - Tuesday, Mar 09, 2010 at 10:18

Tuesday, Mar 09, 2010 at 10:18
Well then: 100% agreement, no rude remarks (even about Coopers). What is this site coming to? Have a great day, everyone!
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Follow Up By: Member - Phil G (SA) - Tuesday, Mar 09, 2010 at 12:16

Tuesday, Mar 09, 2010 at 12:16
Chris, there was 100% agreement on the "Savero" tyre thread too! Everyone thought they were garbage :-))
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Reply By: Member - Mark (Tamworth NSW) - Tuesday, Mar 09, 2010 at 14:26

Tuesday, Mar 09, 2010 at 14:26
Tony

I had a similar query 12 months ago and fortunately scored a reply from Bridgestone engineer.
He said that as LTs have thicker and stiffer sidewalls, they generate more heat, and to never run LTs under 32psi as it will destroy them.

In fear of tyre punctures, in Central Oz I ignored his advice and listened to the advice of Adam at the Pink Roadhouse & let them down to 28psi when running @ 80km/hr or less on dirt.
I checked my tyres every now and then and they ever got hot.
I can only assume Bridgestone advice was based on 100km/hr + bitumen.

In other far more technically detailed threads, there were notes that you can let your tyres down well below 28psi, provided the tyres do not increase in temperature more than x degrees Celcius. I can't remember what x is, but as I don't have any monitors to measure temperature rise, I played safe.

Yes they recommended that LT tyres do run typically several psi higher.

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Follow Up By: Member - TonBon (NSW) - Wednesday, Mar 10, 2010 at 05:41

Wednesday, Mar 10, 2010 at 05:41
Great stuff, thanks Mark. It often seems to be the case that the guy selling the gear knows less about it than those that actually use it, like us and more to the point the people that live where we go. I once asked for a quote from a tyre dealer for a set of BF Goodrich tyres, explaining the intended outback use and the wuote i got back was for H/T's?!?! at a cost of close to $400 a tyre. Needless to say, he didnt get my business.
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Reply By: RobAck - Tuesday, Mar 09, 2010 at 19:42

Tuesday, Mar 09, 2010 at 19:42
we've been using 693 and 694 in AT and LT for neary eight years and averaging over 20,000km off bitumen every year. Our LT 694 are run at exactly the same pressures as the AT's and that means 26 psi for a fully loaded Prado (2950 kg) at 80-90 on outback tracks. We use 32-34 around town and for bitumen travel with no problems. We use a TPMS and laser pyrometer to check pressuers and temperatures and have never had a problem

LT tyres can actually be run at lower pressures due to their increased load carrying capacity. We are testing Goodyear MTR with Kevlar at the moment and running them at 30 psi for bitumen travel with no problems for the last 10000km

Regards

RobA
AnswerID: 408120

Follow Up By: Member - TonBon (NSW) - Wednesday, Mar 10, 2010 at 05:44

Wednesday, Mar 10, 2010 at 05:44
Great stuff RobA, 8 years is a long time and exactly the kind of feedback i was hoping for. Reassures me i am making the right decision. Be interesting to see how the Kevlar's go as i have heard some not so good reports about them. On saying that, i am a boat builder by trade and having used exotic fibres like Kevlar and Carbon, i know their strengths and limitations. Kevlar in tyres makes sense to me on a particular level but they would have to be managed well.
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Follow Up By: Andrew & Jen - Thursday, Mar 11, 2010 at 16:43

Thursday, Mar 11, 2010 at 16:43
RobA
What are the temp parameters you use?
Is it a measure of the tyre temp cf ambient temp or an absolute temp?
Thanks
Andrew
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Follow Up By: RobAck - Thursday, Mar 11, 2010 at 18:35

Thursday, Mar 11, 2010 at 18:35
Andrew that is a highly complex question and I cannot give a simple answer as it depends on what we are testng and for whom. But in the simplest sense we measure the following way
We capture data from the TPMS
We then measure using the pyrometer at 12 points around the tyre
We also measure ambient and surface temperature

So far the Bridgestone and Goodyear tyre engineers reckon we are capturing enough data for them to understand tyre performance

Regards

RobA
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Follow Up By: RobAck - Thursday, Mar 11, 2010 at 18:45

Thursday, Mar 11, 2010 at 18:45
TonBon I am interested in negative feedack on the MTR with Kevalr. Goodyear cannot get enough of them to Australia so there must be something going right.

Apart from that we consider them a major improvement over the old MTR and have a commercial client who is now changing over with excellent feedback. These guys operate a coal mine in remote country and I can assure you it's a tough environment for vehicles and tyres. The improvement in grip is significant and I get the chance to bacak to back test so am very comfortable making a statement I can support with ease

We have tested the tyres at very low pressures in rocky country with no adverse results. We were at pressures you would not normally use unless on beadlockers but we were testing so its all part of the process. Very impressive grip. In quite soft sand the same result.

But if you want an all round tyre and use your 4WD for day to day driving then there are other tyres around and we normally lean to our D694 LT as the best all rounder. Although we have a set of Silent Armour on test as well and they are darned good as well.

Regards

RobA
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Follow Up By: Andrew & Jen - Thursday, Mar 11, 2010 at 20:45

Thursday, Mar 11, 2010 at 20:45
RobA
Hmm.... I don't think I am any the wiser :-)
Is there a max (or desirable) temp that I should not exceed?
[I have a non contact temp instrument that I specifically bought for this purpose]
Regards
Andrew
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Follow Up By: RobAck - Thursday, Mar 11, 2010 at 21:01

Thursday, Mar 11, 2010 at 21:01
Is there a max (or desirable) temp that I should not exceed?

That question is not easy to answer as there are too many variables. But at best I can say that a punctured tyre, say a sidewall failure is around 90C or thereabouts once we get to measure it.

So we set our TPMS maximum temperature at 75C and then if the alarm goes off get out and have a look at whats going on

You are asking a linear question which cannot be directly answered as temperature has a direct correlation to pressure and speed. So temperature is simply an indicator, albeit a very good one of impending tyre failure and more so than pressure. The reason for this is that pressure can be maintained, for a short period of time, whilst the tyre is deflating. The reason for this is that as the pressure "slowly" lowers then the additional friction created caused the tyre to be maintained for a while. Then we get to critical mass, low pressure and high temperature and the whole thing falls apart very quickly generally.

So temperature is a single/linear issue. You cannot rely on that single piece of data without other inputs such as pressure and speed etc. Hence the reason why we always recommend TPMS and to monitor temperature more than pressure but always both

Sadly there is no silver bullet for this. Our simple rule is lower your tyre pressurs to suit the track conditions, slow down to suit and drive to the conditions. Oh and there's no such thing as a puncture proof tyre

Regards

RobA
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Follow Up By: Andrew & Jen - Friday, Mar 12, 2010 at 09:09

Friday, Mar 12, 2010 at 09:09
RobA
Thanks for that comprehensive reply - much appreciated.
I monitor tyre (694 LTs) pressure pretty closely, particularly (but not only) when I deflate the tyres. Up until now I have used the "4 psi" rule which is a surrogate for temperature build up. However, I have recently bought a non-contact temp gauge and intend to use this as well as pressure - hence the question re expected "normal operational" running temps and a max that should not be exceeded.
Regards
Andrew
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Reply By: Member - Tony Z (NSW) - Tuesday, Mar 09, 2010 at 21:35

Tuesday, Mar 09, 2010 at 21:35
Tony, in reply to your Question. I was told on a outback trip by a elderly person to apply the 4psi rule: It is, you set the tyre pres. when cold and then drive for at least 1 hr (at road speed)to heat the tyres up then check pres. again. If hot tyre pres. has raised by more than 4psi, then the cold pres. was to low. Repeat cold pres. check again after adding a few more psi then do hot check again , repeat till correct. This is the same for Hwy and Dirt as kph is adjusted for dirt driving
This has worked for me I drive a 09 Paj with 694's LT rotated every 5000km(30,000km on them) and still plenty of tread left with good alll over tread wear. Tyre pres. of 39/40 psi hwy and 24/26 dirt
He also said this will apply to all tyre's be they AT's or just your wife's street car
AnswerID: 408144

Follow Up By: Member - TonBon (NSW) - Wednesday, Mar 10, 2010 at 05:47

Wednesday, Mar 10, 2010 at 05:47
Thanks Tony, interesting. I have been running 693's for 36'000Km now and they are just about at end of life so your figures for the LT's give me some confidence they will last longer. I run 36PSI on Bitumen, 26 on dirt/gravel and down to 16 on sand so i am confidant i was looking after them. I take it easy on the road anyway, no hooning but still the 693's just didnt last. Note to self, check wifes tyres lol.
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