Tyre Pressures (again)
Submitted: Friday, Sep 23, 2005 at 11:34
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P.G. (Tas)
G'day all, Some thought provoking idea's on tyre pressures. I just changed from Bridgestone D693's to Cooper S/T's.
I formulated an equasion for working out cold tyre pressures as a starting point only (I'm sure others have worked it out before me) and it goes like this -
Weight on the axle divided by 2, times the maximum inflation pressure (at rated maximum load) divided by the maximum carrying capacity of the tyre plus
4psi for temp build up at highway speeds. Then monitor your tyres after an hours running on the hightway so that you get a
4psi increase.
The Bridgestones D693's (265/70R16) worked out to be 28psi front, 26psi rear using this formula.
Now with the Cooper S/T's (265/75R16) using the same formula, I am running 40psi front and 38 psi rear for the SAME axle weights and same driving conditions. These pressures are for MY VEHICLE.
It seems that a lot of advice is being bandied around about the RIGHT pressures for a certain type of vehicle, but I think it would pay everyone to do their own homework for their own particular vehicle, tyres, loading weights, and driving style to get the best out of their expensive black round things ;-)
Reply By: Member - Jeffrey - Friday, Sep 23, 2005 at 13:23
Friday, Sep 23, 2005 at 13:23
Hi P.G,
I think you have your presures back to front...my experience has always have the steer tyres slightly less than the drive..not meaning to be a smart A-----.but if this is the case for what reason when it seems to me most of the weight would be over the rear of the truck???.
All The Best In Health And Wealth
Jeffrey (AKA JD)
AnswerID:
131506
Follow Up By: Voxson (Adelaide) - Friday, Sep 23, 2005 at 14:06
Friday, Sep 23, 2005 at 14:06
I would expect the engine to weigh more than a set of drawers and cargo...
But maybe not..
FollowupID:
385842
Reply By: Member - Jeffrey - Friday, Sep 23, 2005 at 14:29
Friday, Sep 23, 2005 at 14:29
Hi Voxson,
If you had read the comment properly you would have seen that I stated I WAS NOT being a smart A now as soon as posted my last post I thought to myself but the engine is in the front..but I have always put less in the front tyres and everybody I talk to does the same something to do with better grip fpr the steer tyres.But make of it what you will..works for me!
All The In Health And Wealth
Jeffrey (AKA JD)
AnswerID:
131517
Follow Up By: P.G. (Tas) - Friday, Sep 23, 2005 at 16:21
Friday, Sep 23, 2005 at 16:21
Hey there, Jeffery, just a couple of points. As I stated, these figures are for my vehicle, which at the moment is just running backwards and forwards to work. empty.
Therefore in my vehicle the front is heavier than the rear. When I load up, I will re-weigh the vehicle axles and inevitably the rear will then be heavier, and I will adjust the tyre pressures accordingly then.
As far as getting better grip in any tyre, back or front, you have top get your starting pressures right first, otherwise you are just guessing.
Cheers
FollowupID:
385853
Reply By: Kiwi Kia - Friday, Sep 23, 2005 at 16:55
Friday, Sep 23, 2005 at 16:55
When running in two wheel drive on hard tarmac then use the manufactureres recomendation. Off road,
well thats up to you but be very aware that as you lower the pressure your side walls will flex more and (a) generate LOTS of heat, and, (b) the sagging side walls will be more exposed to stakeing and slashing by sharp rocks.
AnswerID:
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Follow Up By: P.G. (Tas) - Friday, Sep 23, 2005 at 17:41
Friday, Sep 23, 2005 at 17:41
Hey Kiwi, just remember, the manufacturers recommendation is only for OE tyres, and at best a compromise between comfort and load carrying.
Cheers.
FollowupID:
385867
Follow Up By: Kiwi Kia - Friday, Sep 23, 2005 at 19:49
Friday, Sep 23, 2005 at 19:49
Perhaps I should have indicated that I was refering to both the vehicle and the tyre manufacturer recomendations. Traveling at a lowered tyre pressure on a rough, slow speed track is very different to traveling the Tanamai at 80 - 100 kph.
FollowupID:
385896
Follow Up By: P.G. (Tas) - Saturday, Sep 24, 2005 at 08:15
Saturday, Sep 24, 2005 at 08:15
You are so right Kiwi, but as I said initially, this formula is for on road use and a starting point only, every vehicle/driving style/tyre combination is different.
What I'm trying to highlight is, what works in my vehicle won't work for anyone else's vehicle (be they the same or not), because there are SO many variables and everyone should do their own homework.
It just gives you the RIGHT starting point.
Cheers
FollowupID:
385976