Tire construction and technology - lower pressures

Submitted: Monday, Mar 29, 2010 at 20:37
ThreadID: 77297 Views:2924 Replies:5 FollowUps:4
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OK I know the benefits of LT tires and lowering pressures. Specially on gravel roads where I have over many years ran or lower on gravel, travelling around 80km/hr

No my old man (he is over 80) often pull me up about that. He says that tires are simply not engineered to be so deflated.

I do not have the technical knowledge to give him an informed answer. I do know that he is probably right based on tires of 40 years ago, but can someone give me a simplistic answer to explain the difference to him and to convince him that lower pressures are indeed ok?

Thanks

CJ
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Reply By: Eric Experience - Monday, Mar 29, 2010 at 21:11

Monday, Mar 29, 2010 at 21:11
CJ.
Your father must be a mine of information. It is a shame that the young ones can not have the rich experience that he must have had over the years.
To answer your question, the old tyres where thicker and stiffer so they got very hot if run at low pressure, the modern tyre is designed to flex more in the side walls and less in the tread, this allows them to dissipate heat better. Eric
AnswerID: 410961

Follow Up By: Member - mazcan - Tuesday, Mar 30, 2010 at 11:05

Tuesday, Mar 30, 2010 at 11:05
hi cj
the old tyres were crossply conventional casing and sat up on the sides and were as mentioned quiet thick on the side walls with several plys and had a tube in every tyre ( and could be fixed with a criss/cross patch that stuck inside the conventional tyre over any splits to stop the the split from pinching the tubes ) and your old dad will know about these
the x/plys did't fit tight on the rims like
radials do with the safety beads built into the rim

they had rims with splits and locking ringson one side like toyota still use on a couple of basic models

where as today our tyres of are radial construction and have a totally different rolling action
with only 2 or 3ply in the side walls and generally dont have tubes as the flexing of the radial side wall with a tube inside causes too much heat build up and will eventually cause them to blow out
but i know we often put a tube in to get by when we are out in the back blocks when the radial casing wont hold air any more after several stakes
cheers
hope this helps and give your dad my best wishes
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Follow Up By: Member - mazcan - Tuesday, Mar 30, 2010 at 11:08

Tuesday, Mar 30, 2010 at 11:08
hi
just thought i'd mention that earlier radial tyres did have radial tubes when first on the market but were not used in later designs
cheers
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FollowupID: 681065

Reply By: Member - T N (Qld) - Monday, Mar 29, 2010 at 21:14

Monday, Mar 29, 2010 at 21:14
G'day CJ,
In Oz Tyres have a Y in them.
Guys are called blokes, unless you come from NSW where anything goes.




AnswerID: 410962

Reply By: CJ - Monday, Mar 29, 2010 at 21:29

Monday, Mar 29, 2010 at 21:29
;-) yes I am a Queenslander. I see the tires in any Coopers brochure is with a y, I guess it stuck. It is American I know

So the older tires were stiffer. Did they have a different reinforcement method?
AnswerID: 410968

Follow Up By: Member - Mark (Tamworth NSW) - Monday, Mar 29, 2010 at 22:19

Monday, Mar 29, 2010 at 22:19
Can't help you with old tyres, but........
LT Tyres are stiffer than passenger construction. One Qld tyre company engineer told me when flexing LT tyres generate more heat than a passenger construction tyre, hence you should not deflate as much as a passenger construction tyre as excess heat will destroy thye tyre.

But then Adam from the Pink Road House who knows infintely more than I ever will on tyres, says doesn't matter whether it's P or LT construction, as long as you aren't going too fast deflate to lower prressures off road.

Suggest you go to his web site or Mt Dare Hotel web site for better information than the dribble I'm trying to remember
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FollowupID: 681000

Reply By: Olsen's 4WD Tours and Training - Monday, Mar 29, 2010 at 22:55

Monday, Mar 29, 2010 at 22:55
The "simple" answer is deflate to avoid punctures. About 20% reduction is recommended on the worst gravel roads. This applies to LT since you start at a higher pressure, you will be at a higher pressure when deflated. This is one good reason to not pay attention to pressures recommended by others. The footprint measurement method is preferred by me and others who spend lots of time with lots of different vehicles starting at lots of different on road pressures. We suggest 180mm long footprint on road, 220 to 240 on gravel, 300 to 350mm on sand.

However if you start at the correct pressure as determined from the info on the side of the tyre using this calculation on road pressure = max pressure allowed x actual load per single/max load per single = 4psi. So for example 50% load = 50 % pressure plus 4 psi.

When you start at that pressure you can reduce 20% for gravel and 50% for sand.

When you do, you absolutely MUST slow down by at least the percentage reduction, so 100- 110 at road pressure, max 80 kph at gravel pressure and mx 50 kph at sand pressure, and NO aggressive steering.
AnswerID: 410983

Follow Up By: Olsen's 4WD Tours and Training - Monday, Mar 29, 2010 at 22:57

Monday, Mar 29, 2010 at 22:57
road pressure = max pressure allowed x actual load per single/max load per single + 4psi.


damn equals and plus keys trick me every time. Above is the corrected calc.
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Reply By: Member - Oldplodder (QLD) - Tuesday, Mar 30, 2010 at 08:39

Tuesday, Mar 30, 2010 at 08:39
If you are talking about tyres from 40 years ago they were most probably cross ply tyres.
Now they are radial construction, except for what Willem runs.
Cross plies got hotter a lot quicker with side wall flex.
Radials run cooler.
AnswerID: 411011

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