RE: Adjusting tire pressure for load
http://www.goodyeartrucktires.com/pdf/resources/publications/2010_loadinflation.pdf
The source is the Tire and Rim Association, so it should apply to all manufacturers.
I already stumbled on this article, and it shows at the bottom of page 1 that the pressure most think is the maximum is in fact the minimum required presure for the maximum load.
TRA allows even 10 psi for LT tires above that, and for truck tires even 20 psi above that maxloadpressure as I saw it called also.
so dont be afraid to go over the fi 80 psi if that is the pressure printed on the sidewall ( E-load/10plyrating).
for topic starter this all is not the issue.
Page 2 even gives at lower speed 9% addition above maximum load without highening up the pressure.
RE: Adjusting tire pressure for load
Using my spreadsheet i come to 64F and 49 back, and I use my own formula that gives a bit lower pressure then linear math. This is higher then your linear math because I add 10% reserve to the load first.
These pressures wont give damage to the tires, assuming your given weights are right, and thats the tricky point here, but you realise that , I make of your story.
The tires stability is yust how you feel it, a little swaying wont say that the car is dangerously unstable, is my opinion.
Nowadays cars are made that stiff, that we have gotten used to the discomfort, wich a stiffer tire gives, but before 2000 the tiremakers also gave minimum advices.
Here a picture of the spreadsheet but will also give the link to the map where you can download the spreadsheet, search for 4xMike,
Then you can chanche things or add in dark blue the GAWR's and to use reserve % , wich is now set on 10% standard.
https://x3mzhq.blu.livefilestore.com/y2pkEUtJsB40BW4dhcYIkaoO9U8HHZVZGek2dSF5iW6xfolemqtSLEJJVr2e1HvsFunMQheCckGuswLuyZLJZ5CTbxBm_mgx5gc51C-cjqFHJzevcZN4B2TLhqkzHjswdhy/4xMikeRVTPC.GIF?psid=1
Now the link to the map.
The examples map with the spreadsheet 4XmikeRVetc.
See what you can do with it.
RE: Wandering Nightmare
Once read somewhere that you must have at minimum 30% of the total load at the front wheels, so if you ever weigh, calculate if it is below or above that.
With that large overhang I expect mayby even much lower then 30% on front, so it sertainly can explain the complaints you have.
Also with that large overhang , mind that things behind the rear-axle give more weight on the rear axle then the weight that is placed because of the leaver-effect, and lifts up the front.
What you can try , if weighing prooves this all, is to replace some heavy things like watertank if possible , beween the axles as much to the front as possible.
Also mind the tire-pressures, high at back and low at front
Back even higher then the maxloadpressure printed on sidewall.
TRA allows 10psi higher for LT tires and 20psi higher for truck tires.
So if the pressure yyy in "maximum load xxxx lbs AT yyy psi(cold)"is fi 80 psi then you may fill to 90 psi, and it is supported by the tire-makers, they cant sew you for it. At lower speed even more then maximum load of tire is supported by the TRA.
My advice is also to weigh , then you will be surprised of the overloading of the rear-axle and low load on front, is my prediction.
RE: tire pressure for towing 2008 dutchmen colorao FW
You have a dutchmen but I am a dutchman so explain what FW stands for ( Folding Wagon mayby).
And what does the 0.1/10 means.
ST ( special trailer) tires are kept to that 80 psi for E-load/ 10plyrated for the next reasons.
They are calculated in their maximum load for a lower speed, so the tire is allowed more deflection, wich gives a larger surface on the ground.
Second is , and that is my own conclusion, because they often have other profile, large profile blocks that cover a part of the sidewall, wich shorten the free flexible part of that sidewall,so less deflection is save for the tire, wich leads to lower maximum load then the tire-maker calculated, because they assumed more deflection.
First reason is often used, but this makes the reserves above given maximum load marginal.
Second reason means that you have to substract about 20% of the maximum load, before calculating the tire-pressure, to bring back the reserves a normal car tire has.
This together makes that the load on the tires comes close to the maximum load the tires may have to laws of nature, especially when you are unequally loaded R/L ( for 1 tire then)
This does not mean that if the tires are oversised, and you have a verry light trailer, you have to keep to 80 psi.
But also if your loads are at the max, you may even go over the 80psi, TRA allows 10 psi , but does not support higher loads for that.
What I need is the GVWR ( gross vehicle weight rating) of your FW, and the number of tires on the ground when driving ( so not the spare), and the number of axles. your tires I could not find with google, so look on the sidewal what the maximum load is, searching saw the rimm-sise of 11 ,pooh thats small, but means that the maximum load will be low. Or could it be you miswrote the rimm-sise, again googling a picture I saw your colorao is a verry large 5thwheeler with tandem-axles.
If you give me that I will calculate a pressure that is save for the tires, including all the factors I described.
Estimate that the advice will be above 80 psi, because your FW has low weight , but the maximum load of the tires is also low.
Edit: here I found maxis tires and the only trailer tire with 235/80 was a 16 inch rimm with Loadindex of 124 wich stands for 1600kg/3527lbs maximum load. so this is know , if its richt, check it.
then I only need the vehicle specifications, if you ever weighed per axle or beter per wheel, those loads and tonge-weigt .
Saw other mis-writing I think Colorao must be Colorado I think.
RE: Max tire pressure vs Load on tires
I always follow the tire load chart. The tough part is knowing the load on my cargo trailers.
I may have to make a chart of spring sag vs load so I know the load at any time. Like a Plimsoll line on a boat.
You could also use the deflection of the tire.
Idea is that the sidewall may deflect maximum 20% of the free flexible part of it . This is for a 80% hight/width (aspect ratio=AR).
Only thing you need is a perfect flat and water-leveled underground, and that is hard to find.
If you look in a tire load chart , then look in the list I made, so you dont loose a part of the carrefully deterimined reserve, by the to high given loadcapacity in the lower pressures on the american charts.
RE: Max tire pressure vs Load on tires
Inflate to what is indicated on the sidewalls. If the weight on the tires is more than what the tires are designed for then you are overloaded.
Amd if you are overloaded, what do you have to do then, stop driving and leave it standing?
Practice is that a little overloading easyly happens at RV's.
If then you yust highen up the pressure within the limits that are allowed , you can savely drive with a lower speed.
RE: Max tire pressure vs Load on tires
When you weighed per wheel, you can use part 3 of my camperRVtyrepressurecalculator. In that I use formula that leads to even higher pressure then the European calculation of the tyre makers.
In next map on my skydrive of hotmail adress, you can find it, always take the newest version and they are in xlsx and xls so also for older Excell to use.
Download by RIGHTclicking on it and choose download in the dropdownbox.
After eventual viruscheck, open in Excell or OO Calc to use it.
Mind to check the weight kinds.
RV tire pressure calculators
But mind that if they are trailer-tires they are as already written here, calculated for lower speed, so allowed more deflection, and have no reserve built in. If then the profile is of an off-road kind and covers a part of the sidewall, that sidewall may flex less then the tire-makers used for their calculation of the maximum load, wich makes the needed pressure even higher.
So if you have them you can substract even up to 20% of the maximum load beforre filling in.
In part 3 of that spreadsheet I go from same pressure R/L and lowest use of the loadcapacity for the pressure of 85% and highest of 95%, so with some reserve still for , pressure-loss in time, loadshifting during vacation,misreadings of load and pressure scales.
But if you rather use a list to look back in you can find it in next map on my skydrive.
They are in PDF so can be left-clicked too. you can choose the right PDF by the name of it, beginning with the maxloadpressure wich is not the maximum pressure of the tire. AT the end pick "tire" for given per tire, "Axlesingle" for given per single axle so 2 tires , and " AxleDual" for given per dual-axle so 4 tires , so you dont have to do that calculation yourselfes. determining the right loads to search back is your own responcibility, but this is also the case in the first spreadsheetsmap.
Extasave pressure/loadcapacity-lists
The lists are made with my own formula that leads to lower loadcapacity for the pressure then the American way and even the European way of calculating, and to my opinion takes care that the deflection of the tire stays the same over the whole pressure/loadcapacity-range.
Also higher then maxloadpressure is given , because you may go over that "maximum load xxxx lbs AT yyy PSI ( cold)" in wich yyy is the maxloadpressure, called reference-pressure in the official formula. So if the outcome is 10 psi higher it is allowed by TRA for LT and trailer tires.
But if you cant work it out, give me the tire-loads and maxload and maxloadpressure of the tire, and I will do it for you.
RE: Need a little advice.
@ AZ T&T your 115 lbs is about the same as used in Europe 110 to 120 Nm. Coincidence??
For the tire-pressure you could use spreadsheet I made, if you have Excell or Open Office Calc on your computer.
Otherwise give the GAWR's ( Gross Axle Weight Ratings) front and back.
Beter would be, if you weighed fully loaded, those axle, or better seperate wheel weights.
And from the tires the maximum load , the 80 psi is already given, is called the reference Pressure and is not the maximum pressure.
You may even go over that , for LT tires 10 psi and truck-tires 20 psi.
No extra load is supported though by the tire-makers, only for low speed.
When you search on the sidewall for the maximum load or loadindex, also see if there is an additional loadindex with a lower speedcode letter.
Then the tire-maker even supports that higher load with the same pressure, but only for that lower speed the letter stands for.
Speedcode N= 140km/85m/h and J=100km/60 to 65m/h
If you want to do it yourselfes, here the link to the map.
RV tire pressure calculator
Always pick the newest version, and they are given in XLS( older versions of Excell) and XLSX.
Click right( so not left) and choose download from the dropdownbox.
After download and eventual virus-check, open in Excell or OOC .
Mostly if you yust click on it , it is automatically openend in Excell, if you have it on the computer.
If you rather look it up in a list, use those in next map.
The loadcapacity there is lower then the American lists give, and even lower then the European lists for larger tires.
To my opinion , my calculation takes care that the deflection of the tire stays the same over the whole range of pressure/loadcapacity range, wich is the goal of all the different calculations.
If your loadindex/maximum load is not in the list, write it here , and a make a new one.
Pressure/Loadcapacity-lists
You can see wich list to use by the name of it beginning with the referencepressure then loadindexes and last for tire/axle single and axle dual. In America it is always give per tire, but the for the axles the times 2 and 4 is done for you. You would need the 80psi100li143axlesingle.
Mind to add a reserve to the loads you weighed ,I advice 10% extra but up to 18% wont even give bumping ( my conclusion so discussable)and gives maximum reserve for ,, pressure-loss in time, unequall loading R/L, misreadings of load and pressure-scales, what I might have forgotten.
If you use the list the determination of the right load is your responcibility.
RE: Air pressure...what's the correct amount?
If the tires are load rated at 80 PSI I would run them at 80 PSI for all the load bearing tires (trailer tires and truck's rear tires). You will get the least sidewall flexing and they will run cooler and last longer and provide better handling.
It is a mistake to go by the manufacturers' charts to determine the proper air pressure to use. If a truck's manufacturer puts on load range E tires and the truck manufacturer recommends 65/80 that is what you should use with that type of tire.
At lower pressures there will not be even contact with the road surface and the tires will wear faster at the edges. There will also be more tire flexing and this also shortens tread life and makes the tires run hotter and increase the odds for a blowout.
This is in effect what happened with the Bridgestone tires on the Ford Explorers where Ford's engineers changed the recommended inflation for the tires to compenstate for suspension design flaws and so people were driving the SUV's with underinflatted tires and the end result was a great many blowouts that often result in the deaths of the SUV's occupants.
About the Bridgestone tires on the Ford Explorer, the story is a little different. also for those tires a lower pressure then written on the sidewall was allowed.
At first I thougt the calculation was wrong, and it was, but was repeared by substracting 10 of the maximum load.
Later I came to the conclusion, bij an article of Capri-Racer ,in wich a tipical cavity patern under the treath, that the maximum load of such a off-road-looking tire , with large profile-blocks that cover a part of the sidewall, was calculated to high by the tire-maker.
RE: Want to switch tires from ST to P
Been searching for a tilting caravan on youtube .
Came to a germain spoken film , but that does not matter, its only to show the tilting.
http://www.youtube.com/watch?v=uLJr7DB7eak
RE: Want to switch tires from ST to P
So I made a new picture again with the 2700 lbs, and came to 50psi exact.
So probably the blow out was yust because of a puncture.
Did you have many blow outs with the original tires?
For this topic I was searching for a reason for the blow out in to low advice-pressure or maximum load. But probably it was yust an accident.
But we became both wiser about the axle and tonge-weight.
https://jbh17w.bn1.livefilestore.com/y1poSDqbvj5VcZ9Zp5ilHrFmEYm_H9ulj7BfNRbik6WQWs6DMDIb6oT-phTXFWy4nX8STX4Q1k8Yh3_MXfwwRtZP3nZYB4FXymy/175R13SToriginaltires.GIF?psid=1 height=400 width=600
RE: Want to switch tires from ST to P
2 Propane tanks of only 7 liter at the front in the disselcompartiment ( probalby wrong word, the thing that is open at the front at the first picture).
then even a bicycle rack at the back with 2 bikes of total 90 to 100 lbs . Some have a bicycle rack on the front on the "Dissel"to get more weigth on the front. And nowadays we have electric bicycles of about 55 lbs each.
Whe had all the heavy stuff like outside tables and chairs on the roundsit wich we transformed to bed, Also to give the front more weight.
Think we had about 120 lbs on the hook, so if the 1300kg/2860 lbs was realy the weight it would have been a poor 5 % .
RE: Want to switch tires from ST to P
Asuming you weighed fully loaded, what maximum load and referencepressure( maxload xxxx lbs AT yyy psi(cold) did the original tires have and what pressure did you use.
ST tires are made with same referencepressure as normal car tires(35 psi) up to E load ( 80 psi). so wich where they.
Looked at the picture and yes the axle is more to the back.
Found a picture of my caravan, wich i sold last year to show the axle placement
https://jbii2a.bn1.livefilestore.com/y1pZ9DkDRk4NduvGlT0mVuD8nEj5RbfBCTY8L6MSS46fOaGeiceaJXLujEpnof4poHYLiUhVWAkwsivxjfJl6OrWExCuiRn4zzf/DSC00979.JPG?psid=1 height=200 width=300
and one from the front to show the length of the "dissel" as we call it.
The wheels are placed almost in the middle of the box.
Here the front
https://jbii2a.bn1.livefilestore.com/y1p9za9rj_ODbwjoKfk-w2WlfpWPNNICR_nG2RIxWi9mvpR20xAMhP6FzqJhsW4BI53nxk5lIZ8maQ90hVl8cdD2EmRw9CT-L_c/DSC00943.JPG?psid=1 height=200 width=300
RE: Want to switch tires from ST to P
@ Dannydimmit
They only give an lowest limit of 1% by law, but maximum is not given.
Fact in Europe is that the tow bar of cars are not allowed to carry more then 50kg/110lbs to maximum rarely 100kg /220lbs.
Must have something to do with the construction of modern cars, I think.
The construction of Caravans( so TT is travel-Trailer and not Tent-trailer , thanks for this correction)shal be made, so the tongweight does not get to high, in contrary to America.
We have a site called "caravantrekker" that gives advices about towing and car-TT combinations.
They advice minimum of 5% tong weight , thoug they say that above 10% would be more ideal. But also the hight of the gravity-point is important. If that is low placed, the TT gets more stabyle.
Well, on our little 2011 Ford Focus the hitch is rated 200 pounds
of tongue weight , and 2000 pounds gross trailer weight.
On our 2003 Dodge 2500 pickup the weights vary by a incredible amount depending on which type of hitch that is on the truck
Class I – 2000-lbs. GTW, 200-lbs. TW
Class II – 3500-lbs. GTW, 350-lbs. TW
Class III – 6000-lbs. GTW, 600-lbs. TW
Class IV & Class V – 18,000-lbs. GTW, 1800-lbs. TW (GTW = Gross Trailer Weight, TW= Tongue Weight)
of course a load distributing hitch with anti sway bars are almost always used with a larger travel trailer. but on bumper pulled lowboy type trailers that are used to haul farm tractors , machinery or building materials the weight distrusting hitch is almost never used .
The bigger the % of the gross trailer weight thats on the tongue equates to a better trailing trailer.
In my calculator, I just recently chached something in the tong-weight,
Made it , together with the weight and speed-kind , that change with the language , to change with that language, and made a new language called "American English" and putted this percentage to 9% for America and 4% for the other European languages.
But in the picture I gave in orange the fixed tonge weight of 150 for the last one, so overruled this part.
This can better be to low so there is more weight supposed on the axle, and gives a higher pressure advice, wich is never bad, better to high then to low. In the first advice for the P-tires I used 100lbs even and 36 psi reference-pressure wich is for European tyres ,for American it is 35 psi, but this also only gives higher pressure advice.
Also added again in orange a what if real weight is higher of 100 lbs, with the used pressure-advice. It gives 183lbs weightdifference L/R before tire-damage happens ( on the most loaded side).
A weigtdifference of 80kg/175lbs can easyly happen for TT, with for instance kitchen on one side.
So in case of daubt, always use the highest load, and reference-pressure( wich is not the maximum pressure) and the lowest maximum load.
Also for tandem axle, better use the maximum load for twinwheel axle for higher advice , thoug I never found any proove that it should be used.
But what I understand from your replie, is that the TT's for american marked have the axle further to the back, so it gives more % tonge-weight. But to what weight are the towbar restricted mostly in America? There must be a limit too.
So tonge-weight is always 10% of maximum to tow weight.
In Europe the car maker has to have the car tested, for a weight they themselves determine. The car -TT combination must drive away from standing still for 3 times on a roadpercentage of 12% ( uphil) to pass the test. This gives difference between brands. One brand calculates better and has higher towing weight approved then another who presents it on the low side to the test.
My car , a Seat Alhambra Diesel 2.0 ( nephew of Ford Galaxy)has a maximum allowed towing weight of 2000kg/4400 lbs, and the tow-barr has a plate with maximum of 80kg/175lbs. So this is about only 4% .
I towed a TT of 1300kg/2860lbs with it on the Frence toll roads, wich are high quallity asphalt roads with speeds of max 110km/little 70 m/h ( is allowed there)and had no problems, but felt the TT pulling when going besides trucks. In Holland since recently 90km/55m/h is allowed now only on the highroad, rest is as it was 80km/50m/h.
But also at 50m/h on the bad roads near Luik/Liege(Belgium) only had the top wheel fibrating to the ground, but no stability problems.
Also depends on the ratio car-TT wich was good for my combination.
The tow bar has a plate with the maximum to tow weight, though some go a bit over that for better balance. I dont know for shure but police can give a penalty for that , if you go over it.
But the construction of American Tow-bars must be much heavyer then that of European to carry that larger weight.
Edit: saw your correction after I placed my reply, but had puzzled it out already.
RE: Want to switch tires from ST to P
@ Dannydimmit
They only give an lowest limit of 1% by law, but maximum is not given.
Fact in Europe is that the tow bar of cars are not allowed to carry more then 50kg/110lbs to maximum rarely 100kg /220lbs.
Must have something to do with the construction of modern cars, I think.
The construction of Caravans( so TT is travel-Trailer and not Tent-trailer , thanks for this correction)shal be made, so the tongweight does not get to high, in contrary to America.
We have a site called "caravantrekker" that gives advices about towing and car-TT combinations.
They advice minimum of 5% tong weight , thoug they say that above 10% would be more ideal. But also the hight of the gravity-point is important. If that is low placed, the TT gets more stabyle.
In my calculator, I just recently chached something in the tong-weight,
Made it , together with the weight and speed-kind , that change with the language , to change with that language, and made a new language called "American English" and putted this percentage to 9% for America and 4% for the other European languages.
But in the picture I gave in orange the fixed tonge weight of 150 for the last one, so overruled this part.
This can better be to low so there is more weight supposed on the axle, and gives a higher pressure advice, wich is never bad, better to high then to low. In the first advice for the P-tires I used 100lbs even and 36 psi reference-pressure wich is for European tyres ,for American it is 35 psi, but this also only gives higher pressure advice.
Also added again in orange a what if real weight is higher of 100 lbs, with the used pressure-advice. It gives 183lbs weightdifference L/R before tire-damage happens ( on the most loaded side).
A weigtdifference of 80kg/175lbs can easyly happen for TT, with for instance kitchen on one side.
So in case of daubt, always use the highest load, and reference-pressure( wich is not the maximum pressure) and the lowest maximum load.
Also for tandem axle, better use the maximum load for twinwheel axle for higher advice , thoug I never found any proove that it should be used.
But what I understand from your replie, is that the TT's for american marked have the axle further to the back, so it gives more % tonge-weight. But to what weight are the towbar restricted mostly in America? There must be a limit too.
RE: Want to switch tires from ST to P
My first choice tire right now is a Continental Vanco4Season size 195/70R15C.
Load index 104 - 1984lbs, 65PSI max
The type seems to be Commercial and/or Cargo and not ST, P, or LT.
If anyone would like to take another shot at the inflation pressure, what would it be at the 2700 GVWR with 300 tongue weight and 1200 per tire?
I have not had any sway problems to date. The ground clearance is only going to be 19in so it won't really be a high rider. I don't use WDH or sway controls.
HTH;
John
Here the new picture. Pigheaded as I am I lowered the tong weight because I daubt if you get to that. In Europe the maximum load on the towing bar is 80kg/175lbs for a bigger car.
But make me wiser about how it is in America, also about the TT = Tent-trailer.
As you see the C-tire ( you are right stands for Comercial and is yust the european notation for LT)needs a higher pressure for the same load then the P-tire, goes from 36 to 46, but part of it is because of the other sises.
So with these tires you will come close to the 50 psi that Capri-racer adviced.
https://jbh17w.bn1.livefilestore.com/y1p561tjv-572oj3GEwBhb1JTHTtyL8k-e7UggJbG7VZZjGEIHyfozvdc7Ijy7aoFg0lYlde9JL_57Wx-AQ1_5uQSKFfnwka3We/TTadvice195ar70R15C.GIF?psid=1
RE: Want to switch tires from ST to P
The rims are from cargo trailers at a trailer dealer. I'll check for zero offset.
The tires are P 215/60R15. A diameter change of 25.16 - 24.02 = 1.14 diameter change and would only have a 1.14/2 = 0.57in increase in height. The axle flip added 5in in comparison. I don't want to go higher but I would consider a P 215/65R15 at 25.5in.
For braking, the total weight of the TT is 2250 and the TV has a tow rating of 5000lbs and 10,000 GCVWR. The TT's GVWR is 2700.
Even if the tires are derated to 1329, I will still have a ~20% safety factor. Are you sure this 10% rule is meant for a 2060lb weight on a 3500lb rated axle?
The tires are 44psi. I run the 13s at 50psi. Is that a big difference?
Is there a 15in LT tire with a smaller diameter than 25.16in?
Thanks for the comments;
John
I filled in my caravan/trailer tirepressure calculator.
Not so familiar with the terms in America , but TT is probably Tent-Trailer so is pretty equally loaded R/L ( correct me if I am wrong.
and I asume the new tires to be realy P-tires and not XL .
Then save advice would be 36 psi . You weighed it and the TT was much lighter then the GVWR of 2700lbs so overloading is not the case.
https://jbh17w.bn1.livefilestore.com/y1p6O9sBPOy3c89fj-Xyu6oNE8fnE6WZOfb3jbHY_pAWSU_ksarmcUhRziiN6eg6YZri-nSMdh8dOswF4a51sOWoJtM5Cgj2U6o/TTadvice215ar60R15.GIF?psid=1
So 50 psi as Capri Racer advices , would be exagerated to my opinion.
RE: Air pressure...what's the correct amount?
Weighing , and then left and right would be the best way to know for shure. If you havent weighed, you have to do with the GAWR or GVWR, mostly on the same plate written as the advice-pressures.
Then the kind of tire is also important, if you have a ST -tire ( special trailer tire) you have to be carrefull and take as much reserve as posible. But if they are LT tires with a normal profile, you may go lower.
So give the exact specifications of the tires like maximum load and AT pressure,the number of tires and if they are dual load or single load, and from the trailer the GVWR and or the GAWRs of the both axles, and I can give you a save advice using spreadsheet I made , in wich I use a saver formula then the tire-makers use.
Mostly this advice is lower then the AT-pressure ( reference-pressure, maxloadpressure and is not the maximum pressure).
But if the needed pressure is above the AT- pressure It is even allowed and supported by the TRA up to 10 psi higher. In some cases, ( low speed) they even support higher maximum load of the tires.
RE: Tire Pressure & TPMS Questions
used my spreadsheet to see if the temperaturechanche mached the pressure-change and it didn't.
To a pressure rise from 85 at 50degrF , to 104 psi would give a temperature of 147 degr Fahrenheit.
So one of the 2 is inacurate and I think the pressure-accuracy of your TMPS is bad.
here a picture of the calculation.
https://x3mzhq.bn1.livefilestore.com/y1p_aRQ2GUlfVh-_eEWN8B4Y4TTSxaIPPgCi-gj0G4mR2afwkL5xKz9CKqTkLDcJl1hVS-d1S_faGLq1vK-yVKhoQyfVO139Zk1/TPMSexample.GIF?psid=1
RE: Tire Pressure Question
Can you help me understand the formula you used? Thanks
The general rule with tire pressure is: for every 10 deg F the ambient temperature around your vehicle rises or falls, your tires will gain/lose 1.5 to 2 LBS PSI. If you are operating a truck with tire pressures in the 80-LBS + range (LR-E, LR-G, LR-H, etc...), the drop or rise may not seem significant; however, if you are operating passenger (or, P rated) tires, that rise/drop could be very significant in many ways...
This a general rule wich does not go for higher cold pressure.
I already wrote that from 18dgrC/60dgrF to 45dgrC/112dgr F wich is average normal cold and warm pressure, the normal car with 40 psi filled rises about 0,3bar/4 psi, and the 80 psi filled tire cold rises about 0,5bar/7 psi.
can be a bit wrong with the Fahrenheit, conversed it from Celcius which we use in Holland.
But use my speadsheet,from my last reaction here , to get the excact chanches. You can even fill a lower outsidetire-pressure for in the high mountains for instance.
Posted By: Reddog1 on 02/26/13 09:29am
I will throw a fly in the ointment. Can you tell a difference in MPG with higher air pressures?
A higher pressure then needed for the load, gives lesser deflection of the tire. At a sertain deflection the tire bares a part of the load on its construction. half of the deflection , I asume, gives half of the load that is wore by the construction.
The relation between deflection and surface on the road is about surface 1/ surface 2 =square(deflection 1/deflection 2)
So if surface on ground gets 0,8 times as low the deflection gets about 0,8 * 0,8= 0,64 times as low.
The rolling resistance can be related to construction load .
The pressure can be related to the surface on the ground.
I found somewere on the internet that rolingresistance is about 10% of power , and stays 10% at higher speed.
Putting 25% extra pressure then needed, makes surface on ground 0,8 times as high, so deflection 0,64 times as high, so construction load also 0,64 times as high, so rolingresistance also 0,64 times as high, so 0,64 times 10%= 6,4%.
The air-resistance is at 2 times higher speed 4 times as high.
So at higher speed the rolling resistance, is yust a little portion of the air-resistance. Sertainly for RV's wich are square boxes on wheels.
