Reply With QuoteDoes tyre pressure vs tyre load (weight) work proportionally like you have done?
ChatterBox
I usually run 38psi, stone cold, checked in the morning before the sun shines on one side of the car before the other. I know their are those that like the front with less pressure than the rear for their own good reason but I personally like the handling with the same pressure F/R. I get more sidewall stability when pushing hard through corners.
I have just done a dumby run to the weight bridge with the vehicle loaded for camping and below is the weights.
There has been numerous posts on tyre pressure but one (I can't find) linked to a 20 plus page doco on what tyre pressure should be. This doco described many various theories on what tyre pressure should be given that manufactures only provide pressure at max load and most if not all people only run at part of max load.
I know about the 4psi rule and that's great for people that drive the same type of driving often. Most often I make a 20 minute drive to Darwin's industrial area buying stuff or it's a 5 minute run to work then on days off, I might run 200km plus out of town. The 4 psi requires 100km/one hours driving and then looking for a 4 psi increase over cold. I swear I'd wear out a set of tyres before I work out the best pressure and then which type of driving would that suit. I'd need a pressure for high way driving, a pressure for running to work and then another for general running around town.
My preferred method is to measure the tread wear every 10,000km when I rotate the tyres and aim for even wear across the tread. If the fronts are wearing on the shoulders, I increase the pressure, if the rears are wearing in the centres, I decrease the pressures.
This is all well and good if you have owned a vehicle and run the same tyre for a long enough time but I have less then 10,000km (just over 7000) on my 245/75-16 BFG KM2 tyres. So I will use the rule that says the pressure should be the percentage of max pressure relative to the max load. So BFG say I need 80psi for 2557 LBS, I have 1609 LBS on a single rear tyre which is 58 percent of the max load. So I will run 58 percent of 80psi which is 46.3psi. The front calculated out under what I run empty. I run more to stop the tyre rolling and wearing the shoulder but as most of the driving with the load on will be straight running, I'll stick with what I usually run.
............Total KG.....Total LBS.......Single KG........Single LBS.......LBS@80psi.......KG@80psi........LBS@1psi .........KG@1Psi........% of Max........Recommended PSI
Front ....1160.........2557 ............580................1279..............2 778...............1260...............34.7......... ......15.8...............46................36.8
Rear .....1460.........3219 ............730................1609..............2 778...............1260...............34.7......... ......15.8...............58................46.3
Just for those that wonder why I'd fully pack my Disco 2 just to weight it. I have everything in single units ie all my parts are in 2 milk crates, we have a box for food and a box for clothes etc. I need it easy to pack and unpack as 2 of us will sleep in the roof top tent and 2 will sleep in the back of the vehicle with everything unpacked into the annex.
Happy Days
ForumSage
Does tyre pressure vs tyre load (weight) work proportionally like you have done?
AT REST
I run the recommended tyre pressures on our D1 with 2.45/70/16 Bridgestone Dueler A/Ts 30lbs front 34 rear and have not had any wear problems over 30,000 klms and 35 front and rear on the fat footed 15s on the RRC
ChatterBox
Well the conclusion of this doco L/R 110 4x4 Regional Force Surveilance Vehicle (RFSV) . Says:Originally Posted by uninformed
The simple ratio method given by Equation 9 provides a slightly more conservative, but computationally simpler, method of developing a safe operating pressure for tires operating at less than maximum loads.
There is 12 different methods/equasions for caclulating inflation pressure at reduced loaded and the theory behind those methods/equasions, listed in the doco.
Equation 9 is what I used, that's the linear corolation of pressure/load.
Off Track seemed to understand it more than I did. He posted a bit here: http://www.aulro.com/afvb/1588421-post12.html
The other equations are a little difficult and a small miss measurement can throw out the whole equation. I think equation 9 being the simplest is the best starting point for me with my vehicle loaded.
Happy Days.
CTRL + V!
Subscriber
Goodness me, I just pump the beggers up, to around 35-40, and judge by the road surface, hard, sand or mud, if I should change it. Probably doing the wrong thing, but I'm too lazy to change. Bob
I’m pretty sure the dinosaurs died out when they stopped gathering food and started having meetings to discuss gathering food
A bookshop is one of the only pieces of evidence we have that people are still thinking
ChatterBox
Do you care if your tyres wear evenly and you get the longest wear you can from them? They're the reasons I check mine often and I make an effort to get them close to right.
I'm sure most know this but I believe tyre pressure accounts for a lot of tyre failures. It's also hard to judge people's comments on tyre life and failures when you don't really know how the tyre have been looked after.
High pressure will wear the centre and make the ride rougher than it needs to be. A rough tide can be hard on gear. Too higher pressure doesn't really serve much purpose at all, maybe just a little fuel saving.
Low pressure means extra flex that creates more heat than is necessary. That extra heat just wears out tyres because the rubber is softer when hot. That's fine for those that can afford the extra fuel, tyres and extra wear on the motor from the extra load.
Happy Days.
Master
Aren't there greater things in life to worry about?
If that's what floats your boat Joel, then all power to you. I'm with Bob though. Pump them up to certain psi for road, let them down to certain psi for whatever offroad situation presents. Rinse and repeat... If that means I'm not maximising my tyre life, then so be it.
Master
Personally Joel I think we can over think things in life at times, constantly adjusting tyre pressures will increase the life of the tyres there's no doubt in that but to what degree are these adjustments effected by the constant variables of everyday driving, examples that come to mind are different asphalt compounds, different turning radius and the speed the vehicle is doing at the turns, braking pressures etc.
Is the extended life of the tyre increased by a significant margin that makes it worthwhile? maybe. It would be hard to judge I would think.
The recommended pressures are brought about after consultation with tyre manufacturers and vehicle manufactures to give good all round comfort/handling/wear of the tyre. On my Mazda B2600 I have found the front wheel bearings need adjusting frequently, without this the tyres wear is increased. Each service we rotate and every third service we actually strip the tyres off the rims and swap to change rotational direction as I have found that with the lifted suspension the front tyres do get a slight "toe in" wear appearance. doing this has given an apparent increase in tyre life.
Personally and it is my opinion only, I think maintaining the pressures at a good average for the conditions is suffice along with ensuring the other parameters that affect wear addressed.
Then again a calculation is just that, if you can calculate an increase in tyre life by doing the adjustments like you suggest then yes you can justify it.... but measuring the increase in real life circumstance may be a little more difficult taking into account all the other variables.
Will be interesting to see the results down the track
ForumSage
All you need to do is chalk a line across your tyre, drive 100 meters on a smooth flat surface eg carpark, if the chalk is worn in the center tyres are overinflated, etc. Simple.
ForumSage
SupporterPushing hard through corners will wear the tread more than a couple of psi difference.I get more sidewall stability when pushing hard through corners.
Near enough is good enough.
1973 Series III LWB 1983 - 2006
1998 300 Tdi Defender Trayback 2006 - often fitted with a Trayon slide-on camper.
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