Posted 2005-09-12 9:55 AM (#30213) Subject: trailer tire presssure?
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Posts: 17
i checked the tire pressure in my new trailer and it was 20 psi's. the tag on the trailer says it's supposed to be 50 psi's. the tires say 50 psi's max. so i filled them up to 50 psi's but now i'm having second thoughts about it. am i supposed to fill them up to what's on the tag? less? depending on load?
i'm hauling 1 small horse and this is a 2 horse stock, so i am definitely way under the max capacity here. yet, i don't think that i've seen people change the tire pressure in their trailer tires every time their load changes.
please help!
Posted 2005-09-12 12:36 PM (#30222 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 2953 Location: North Carolina
From what you've posted 50 PSI is good. The psi should be checked with the tires cold. You will have more trouble with under inflated tires than max inflated tires.
Check the tires again in a week. Potential trouble at 50 psi and a light load is a rough ride and tire wear in the center of the tread. Under inflation potential troubles are blow out and poor gas mileage. Someone posted before about a pressure reduction for part loads. Do a search of the forum. you get to pick.
Posted 2005-09-12 12:58 PM (#30224 - in reply to #30213) Subject: RE: trailer tire presssure?
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Originally written by mnk on 2005-09-12 9:55 AM
i checked the tire pressure in my new trailer and it was 20 psi's. the tag on the trailer says it's supposed to be 50 psi's. the tires say 50 psi's max. so i filled them up to 50 psi's but now i'm having second thoughts about it. am i supposed to fill them up to what's on the tag? less? depending on load?
i'm hauling 1 small horse and this is a 2 horse stock, so i am definitely way under the max capacity here. yet, i don't think that i've seen people change the tire pressure in their trailer tires every time their load changes.
please help!
Tires are rated for the MAXIMUM that they can carry continously (with some safety margin). The tire manufacturers don't know every application that the tire will be used in. The trailer builder SHOULD select a tire that has adequate capacity - plus a little extra.
My guess is that the tires on your trailer are marginal for the trailer's rated load, but since you're not loading it fully you should/might be OK.
See other threads on exactly this topic, find the link that I posted to the Goodyear web site.
BTW, if these are ST225/75R15 tires on 3500 lb axles, 7,000 GVW...
Well, you have the usual 2 horse bumper pull.
Posted 2005-09-12 1:34 PM (#30225 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 17
reg,
are you intentionally trying to confuse me?;)
seriously now, marginally suitable? and what's that unfinished sentence at the end? come on, don't leave me hanging.
i will search the topics for your prior post.
these tires look great but are 4 years old so i will probably want to replace them next year. sounds like i should be looking for something more suitable but how do i know what?
Posted 2005-09-12 3:06 PM (#30230 - in reply to #30213) Subject: RE: trailer tire presssure?
Extreme Veteran
Posts: 366 Location: Albany, Oregon
mnk, You are fine! When in doubt inflate to the max. cold psi stated on the tire. If you are doing a long haul empty let a bit out....maybe 45ish. The 20 psi the tire had when you checked is really dangerous on a hot long haul! The same goes for the tow vehicle tires! Oh and you might check your trailer lug nuts if you haven't lately.
Posted 2005-09-12 6:51 PM (#30244 - in reply to #30225) Subject: RE: trailer tire presssure?
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Originally written by mnk on 2005-09-12 1:34 PM
reg,
are you intentionally trying to confuse me?;)
seriously now, marginally suitable? and what's that unfinished sentence at the end? come on, don't leave me hanging.
i will search the topics for your prior post.
these tires look great but are 4 years old so i will probably want to replace them next year. sounds like i should be looking for something more suitable but how do i know what?
Nope, tires are designed for a maximum load, pressure should be set to match the ACTUAL load. If your manufacturer has selected a tire (size and profile) that needs to be inflated to it's maximum pressure to carry that trailer's load... the tire is at it's max load. As a matter of "opinion" this could be considered a "marginal" application of the tire or selection by the trailer manufacturer.
errr, QED or somesuch.
Please tell us about your trailer's GVW and tire size ?
I was just GUESSING ST225/75R15 on 3500 lb axles and 7,000, but it is typical for contemporary 2 horse trailers.
Tires inflated to their maximum pressure will typically be skippy and give a harsh ride - unless loaded to their max load.
Another possibility is that your trailer manufacturer just doesn't KNOW about tires and just copied the numbers off the sidewall of the tires - wouldn't be the first and only time (don't say "rollover") (-:
Posted 2005-09-13 9:06 AM (#30269 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 17
reg,
from what i recall right now, it's max capacity is 7000 lbs, i think 3500 lbs per axle and the tires are 15's but i don't recall the other codes on the tires. sounds like you were guessing right. i would hope that the trailer mfr gave this info a little more thought than just copying it off the tire walls...
anyway, so if max is 7000 lbs then the 50 psi is suggested for the max? so then if i'm hauling a single horse (trailer weighs 1900lbs) then how much do you suggest i lower the pressure?
Posted 2005-09-13 1:20 PM (#30290 - in reply to #30269) Subject: RE: trailer tire presssure?
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Originally written by mnk on 2005-09-13 9:06 AM
reg,
from what i recall right now, it's max capacity is 7000 lbs, i think 3500 lbs per axle and the tires are 15's but i don't recall the other codes on the tires. sounds like you were guessing right. i would hope that the trailer mfr gave this info a little more thought than just copying it off the tire walls...
anyway, so if max is 7000 lbs then the 50 psi is suggested for the max? so then if i'm hauling a single horse (trailer weighs 1900lbs) then how much do you suggest i lower the pressure?
That really DOES depend on the tire size and profile.
To do it RIGHT weigh each axle when loaded, divide by two, find the presure from the table on the goodyear web site referenced above. Get to page 9 before you fall asleep. Close enough is to add it all up and divide by 4.
ST225/75R15s at 50 psi would be good for 8600 lbs - and definitely harsh and skippy at the load you propose.
Posted 2005-09-13 2:26 PM (#30298 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 17
so 50 psi bad, can you give me an estimate on what in your experience would be appropriate for that load? 45? 40?
i really don't see myself getting through the calculations you propose
Posted 2005-09-13 4:56 PM (#30337 - in reply to #30298) Subject: RE: trailer tire presssure?
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Originally written by mnk on 2005-09-13 2:26 PM
so 50 psi bad, can you give me an estimate on what in your experience would be appropriate for that load? 45? 40?
i really don't see myself getting through the calculations you propose
I can't figure that without the tire size and profile.
You really DO have to get that off the tire's sidewall.
Then look it up in the table.
Posted 2005-09-13 7:07 PM (#30338 - in reply to #30213) Subject: RE: trailer tire presssure?
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Location: Tucson, Arizona Territory
mnk,
If your trailer says 50 psi and your tires say 50 psi how can you go wrong at 50psi? It won't be dangerious to tow at that pressure so maybe you should go with the factory recommendation. Then after you put some miles on your rig you will be better able to to make a decision. With all the liability issues that could arise I doubt whether the trailer manufacturer would put 50 psi tire pressure on their trailer placard without engineering studies to back it up. Good luck
Posted 2005-09-14 5:53 AM (#30348 - in reply to #30338) Subject: RE: trailer tire presssure?
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Originally written by Saddlemaker on 2005-09-13 7:07 PM
mnk,
If your trailer says 50 psi and your tires say 50 psi how can you go wrong at 50psi? It won't be dangerious to tow at that pressure so maybe you should go with the factory recommendation. Then after you put some miles on your rig you will be better able to to make a decision. With all the liability issues that could arise I doubt whether the trailer manufacturer would put 50 psi tire pressure on their trailer placard without engineering studies to back it up. Good luck
You might have to think about what maximum means.
The only sense in which it could be dangerous is that tires are typically very HARD at their maximum pressure, resulting in poor road holding capability if they're not carrying that maximum load (or something fairly close to it), i.e. "skippyness".
See other forums on the dangers of inflating light aircraft nose wheels beyond their proper load pressure. Basically there is NO steering with a nose wheel tire at it's max rated load pressure, it spends far too little time actually in contact with the ground..
Posted 2005-09-14 2:41 PM (#30382 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 366 Location: Albany, Oregon
Hmmm.....food for thought.... I just offloaded an 18 wheeler & read the tire pressure info on the side. 100psi @ 6200# single 6000# dual cold. Trucks run millions of miles with full loads and empty loads. I have never seen a driver let air out after I unloaded 50,000#'s yet! Have any of you? They all run max psi.. They never know what the weight is going to be. But when they beat that tire with an iron they are looking for under inflated tire not max psi. Under inflated will get dangerous big time! Ask the Ford Explorer guys. Max PSI not! Think about it the next time you pass a loaded 80,000#er and then an empty flatbed bouncing down the road. I agree 100% there is a correct inflation preasure for a paticular tire for the load being carried but that can be a big variable. A camp trailer or your car is a more consistant load but horse trailers and equipment trailer arn't. So if somone asks me how many PSI they should put in some tire on some trailer I have a standard answer. Look at the side of the tire! That all folks!
Posted 2005-09-14 11:22 PM (#30395 - in reply to #30382) Subject: RE: trailer tire presssure?
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Originally written by xyzer on 2005-09-14 2:41 PM
Hmmm.....food for thought.... I just offloaded an 18 wheeler & read the tire pressure info on the side. 100psi @ 6200# single 6000# dual cold. Trucks run millions of miles with full loads and empty loads. I have never seen a driver let air out after I unloaded 50,000#'s yet! Have any of you? They all run max psi.. They never know what the weight is going to be. But when they beat that tire with an iron they are looking for under inflated tire not max psi. Under inflated will get dangerous big time! Ask the Ford Explorer guys. Max PSI not! Think about it the next time you pass a loaded 80,000#er and then an empty flatbed bouncing down the road. I agree 100% there is a correct inflation preasure for a paticular tire for the load being carried but that can be a big variable. A camp trailer or your car is a more consistant load but horse trailers and equipment trailer arn't. So if somone asks me how many PSI they should put in some tire on some trailer I have a standard answer. Look at the side of the tire! That all folks!
As you say, "an empty flatbed bouncing down the road".
Part of trucker training is to understand how reduced their braking is with light loads, though I don't know that all of them appreciate WHY their wheels hop so much. Part of it is stiff springs, but another part is certainly due to tires that are a lot harder than they need to be.
I know what my trailer axle loads are at empty, 1, 2, 3, 4, 5 horses with tack. I don't always change pressures for a 1 horse difference, though I usually do for 2 or more (figuring it to be more than a ton, 500 per tire).
I'm more often "over" than "under", which is in agreement with your approach.
It really doesn't matter THAT much to me who does this right or wrong, I'm just answering a question as accurately as I know how and trying to keep any of my lax ways out of it.
I believe your "Look at the side of the tire" answer is bad advice and in most cases wrong for the reasons I've stated in other posts.
Posted 2005-09-15 8:43 AM (#30407 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 17
o.k. reg, got the code off the tires, they're ST205/75R15. i'm looking at that chart and of course, i don't know exactly what the load is on each axle, but if the trailer weighs 1900 lbs and the horse weighs 1000 lbs (probably a little less), so we're talking 2900 lbs, round it up to 3000 lbs. so i divide that by 2 and then look up the pressure in the chart? so it's somewhere between 35 and 40 psi, right? or am i doing this wrong?
Posted 2005-09-15 9:50 AM (#30410 - in reply to #30407) Subject: RE: trailer tire presssure?
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Originally written by mnk on 2005-09-15 8:43 AM
o.k. reg, got the code off the tires, they're ST205/75R15. i'm looking at that chart and of course, i don't know exactly what the load is on each axle, but if the trailer weighs 1900 lbs and the horse weighs 1000 lbs (probably a little less), so we're talking 2900 lbs, round it up to 3000 lbs. so i divide that by 2 and then look up the pressure in the chart? so it's somewhere between 35 and 40 psi, right? or am i doing this wrong?
Posted 2005-09-15 11:49 AM (#30416 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 17
yes, 2 axles. so you divide by number of tires, not the number of axles?
that would mean 15 psi? are you sure about this? that's less than i had in there...
Posted 2005-09-15 1:44 PM (#30421 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 1416 Location: sc
well reg i know we have slight differences in opinion on tire inflation, but ive been waiting for this conclusion to this situation. im resonably sure you will agree running 15psi at highway speeds is undesirable to say the least, no matter what the load. even the "dividing by 3" theory does not help here. i am curious as to the correct answer to this situation.
to the OP, my trailer empty is 3500# (225/75/15 tires and 2 3500# axles)and when the tires are inflated to 50psi it does have noticable bounce to it. however in my experiance lowering the tire pressure does not have "much" effect on the "ride" as i belive the unloaded suspension is the larger part of the problem. i would be very careful running highway speed with less than 35-40psi, unless confirmed by the tire manufactuer.
Posted 2005-09-15 2:22 PM (#30422 - in reply to #30421) Subject: RE: trailer tire presssure?
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Posts: 2953 Location: North Carolina
Originally written by chadsalt on 2005-09-15 12:44 PM
unloaded suspension is the larger part of the problem.
Chadsalt.. something we can agree on .. As the max tire pressure is 50 PSI if this were my trailer, I would run 45 to 50 psi cold. Most tire gauges will fall within this range for accuracy anyway. Having the upper range for the trailer tires is good for several reasons:
There may be a time when the trailer will be fully loaded. Unless one carries a compressor, the tires will be under inflated in that case.
There is/may be a pressure loss over time. Better to start high, than start low and leak to worse.
To recap... it is better to be at max tire inflation than under inflated.
Posted 2005-09-16 3:27 AM (#30449 - in reply to #30213) Subject: RE: trailer tire presssure?
Location: Del Mar, CA
My two-bits on tire pressure: I had my new ST225/75R-15/C1 tires put on my trailer yesterday. Today I pulled it empty and it felt like a giant beach ball, had a life of it's own back there. With my 1200 lb geld it still seemed to drift on the turns (and I drive really slow with horses). It pushed my truck a bit on bumps and uneven dirt road. The paperwork says the tires are "C1" taking a 50 psi, but Discount Tire mounted them with 65 psi, and the small print on the tire says "max 80 psi!!!!!!" So I don't know what they are, will be calling the tire shop first thing tomorrow. I've always loved my trailer because it tracked so well I'd forget it was back there, with one horse (total 4000lb)on bias tires with 35 psi it was so stable and smooth. So, if I am stuck with these tires I would opt for reducing the psi and seeing if that makes the trailer track better. I don't know how low I could go if these are "D" or "E" load range??? My max wt for 2H trailer is 7000lb so I'm guessing if they are "E" load range I should exchange them? k :))
Posted 2005-09-16 12:05 PM (#30464 - in reply to #30416) Subject: RE: trailer tire presssure?
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Originally written by mnk on 2005-09-15 11:49 AM
yes, 2 axles. so you divide by number of tires, not the number of axles?
that would mean 15 psi? are you sure about this? that's less than i had in there...
I don't now where you got the 15 psi figure from.
The Goodyear table for that tire size and profile only goes down to 25 psi.
Posted 2005-09-16 12:53 PM (#30467 - in reply to #30213) Subject: RE: trailer tire presssure?
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Posts: 17
i said 15 psi not 5 psi. i was looking at a different table, although also by goodyear. the table you posted a link to, doesn't even show psi for a load that low. the lowest there is 1200 lbs at 25 psi. my 3000 lbs divided by 4, would be around 750 lbs.
so i'm still confused.
Posted 2005-09-16 4:42 PM (#30485 - in reply to #30463) Subject: RE: trailer tire presssure?
Location: Del Mar, CA
xyzer-called Discount Tire and they said they put load range "E" on my 2600 lb trailer. They had originally said that Carlisle was slow in delivering, so maybe they just took what they could get. They said, yes it was way more tire than I needed but that it was OK because they would be safer, stronger as far as avoiding flats or accidentally running on low pressure. And that, no the heavier material would not be a rougher ride for the horse as long as I reduced the psi. They said I should reduce pressure to match the load and that it would not be a problem for the tire, that I could run them at 40-50 psi as if they were "C" load range. The trailer tracked so well with the bias tires at "B" load range of 35 psi, he said I could run these at 35 psi as well for my 4000 lb load, but put more pressure in for a higher load. The Goodyear chart shows that I could lower it to 25 psi @ 1430lb per tire X4= 5720 total load, still more than I need. Looks like, if I kept them at 35 psi (1760 X4=7040) I would not have to worry if someone borrowed the trailer and put two horses in it. Hope I'm figuring this corrrectly. k :))
trailer tire presssure?
