I LOVE love love this site!Quick question: I went to Discount Tire (they are always very helpful) to replace the tires on my 2H straightload trailer, wt-2600 lb. It has "ST225/75D-15 (H78-15ST) CARAVAN" printed on the tires, D=bias, the sidewall says, "Never to exceed 40psi when seating beads."Discount Tire said they would have to order these tires and the cost would be $74. They said they could get ST225/75R-15/C1 easier and the cost would be a little less, $69, and the "C" rating would just mean more psi, stronger tire, no reason not to use these.My questions: -Does this matter: 75R=radial? rather than D=bias?-Will these tires make the ride rougher? (I only haul one horse but I move the divider over to give him a slant ride and sometimes I do feel him shift his weight to one side).-And, is there any reason I should not use these tires?THANK YOU!!!! karla
Posted 2005-08-26 6:19 PM (#29643 - in reply to #29638) Subject: RE: trailer tires
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Originally written by AppyRider on 2005-08-26 2:04 PM
I LOVE love love this site!Quick question: I went to Discount Tire (they are always very helpful) to replace the tires on my 2H straightload trailer, wt-2600 lb. It has "ST225/75D-15 (H78-15ST) CARAVAN" printed on the tires, D=bias, the sidewall says, "Never to exceed 40psi when seating beads."Discount Tire said they would have to order these tires and the cost would be $74. They said they could get ST225/75R-15/C1 easier and the cost would be a little less, $69, and the "C" rating would just mean more psi, stronger tire, no reason not to use these.My questions: -Does this matter: 75R=radial? rather than D=bias?-Will these tires make the ride rougher? (I only haul one horse but I move the divider over to give him a slant ride and sometimes I do feel him shift his weight to one side).-And, is there any reason I should not use these tires?THANK YOU!!!! karla
Wadda coincidence (-:
Following a dramatic blow out due to some road debris I just replaced this size. Check again, be sure about the D meaning bias ply, non-radial. It could be the load range. I had trouble finding a load range C in this size, so I went to a load range D - which hurt since it is for a never_to_be_used_spare. I got the Goodyear Marathon, they had it in stock but not on a 5 stud rim. $50 for the rim, $85 for the tire, $6.75 mass sales tax, $6 freight because they had to buy in the rim = $147.75, I had been quoted as much as $220 at marinas and (horse) trailer places.
This was at a Utility trailer and welding place - for Mass residents' interest Welch Welding in North Chelmsford - I have no commercial connection to them,,,, etc.
No, the pressure for a given load on a given tire size doesn't vary by load rating.
Yeah, I know this will draw flak, but the pressure is the SAME for a given load on a given tire size. What is DIFFERENT is that the higher rated tire can take a higher load at a higher pressure, e.g. a D rated tire is inflated to the same pressures for the same loads as the C rated tire at every load point in the C rated tire's range. The higher the load range the stiffer the side walls and the harsher the ride, though slight for a one letter load range difference.
Posted 2005-08-27 12:10 AM (#29655 - in reply to #29638) Subject: RE: trailer tires
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Posts: 26 Location: Ontario, Canada
If you read the 'fine print' on the sidewall fo the tire, it will tell you the maximum load rating for the tire, maximum pressure (usually given at a certain temperature), the number of plies (sidewall and tread may be different numbers too), the load range, and lots of other stuff too.
One of the main things to watch for is that some places don't always pay attention to the trailer designation, make sure that it's a trailer tire you're getting!! Car and truck tires will fit, but aren't designed for the application of a trailer. (The 'ST' at the beginning is 'special trailer', p is passenger car, LT is light trucks (pickups, some SUV's, full size vans, some mini vans, etc....)
A 1/2 ton pickup I bought several years ago had 'P' tires on it, gave a softer ride and such, but they were too soft for carrying loads. I believe the fellow I bought it from put them on for a softer ride. (He didn't use it as a truck very often.)
Posted 2005-08-28 3:11 AM (#29670 - in reply to #29643) Subject: RE: trailer tires
Location: Del Mar, CA
Thanks for the input! Reg - do I have this right?-a tire with a D load range of 2540lb (65psi) can be filled to only 50 psi to carry a load rated in the C range of 2150 lb?
The 75D on my old tires indicates Diagonal Bias (B=Belted Bias, R=Radial) I read that the stiffer Bias sidewall helped reduce trailer sway. But would the ST Radials give the horse an easier ride? Thanks for your help! karla
Posted 2005-08-28 6:11 AM (#29671 - in reply to #29670) Subject: RE: trailer tires
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Originally written by AppyRider on 2005-08-28 3:11 AM
Thanks for the input! Reg - do I have this right?-a tire with a D load range of 2540lb (65psi) can be filled to only 50 psi to carry a load rated in the C range of 2150 lb?
The 75D on my old tires indicates Diagonal Bias (B=Belted Bias, R=Radial) I read that the stiffer Bias sidewall helped reduce trailer sway. But would the ST Radials give the horse an easier ride? Thanks for your help! karla
YES, you should only put in the pressure for the load the tire will be carrying, NOT the highest pressure that the tire is rated for. If you are using a D rated tire for a load in the C range you should inflate it to the same pressure as you would for that load in the C rated tire. If you get a load/pressure table you'll see this very clearly, the D rated tire just goes up higher. BTW, it is almost certainly a lot more tire than your axles are rated for (3500 at a guess).
I'm a bit curious about the age of your trailer, I know radials took a LONG time to catch on in the US, at first on sporty cars, then sedans, eventually on trucks and I think trailers were last. Do you know if radials were on there originally, or if a previous owner might have down graded to bias ply ? The OLD arguement against radials was that the sidewalls were too soft and if the rest of the suspension system wasn't designed to take this into account there would be handling problems. The trailer version of this was "SWAY", but I think the reality was resistance to the French way (-:
It could just be that the ST is the stiff sidewall radial that is sway resistant.
Posted 2005-08-29 4:16 AM (#29701 - in reply to #29671) Subject: RE: trailer tires
Location: Del Mar, CA
Hi!! My trailer is a 1989 CircleJ 2H str-load 2560 lb. I bought it in 2000 from an individual who said he'd just put new Caravan ST225/75D-15 tires on it (he'd kept it covered and had all maint records so I assumed he knew what he was doing). What I've discovered in all this "Tires 101" I've been doing is that the H78-15ST also printed on the tire stands for H=130mph max, the 78 is the load index(vertical wt), not load range(horizontal/everyway wt), and two charts I found on the web show that a load index of 78 is rated for 937 lb !!! that's 3748 total !! with just one horse and some gear I'm already at 4000 lb. I don't remember who told me to inflate them to 33-35 lb, the sidewall says not to exceed 40 psi when "seating beads," there's no indication of a "load range." The tires Discount Tire have are "C" load range (2150) with a psi of 50. I don't know how much air I should actually use in them??? even with two horses the total wouldn't go over about 5000 lb. Oh, I originally started checking why I had to have a more expensive, stiffer sidewall because I was told that this was necessary in case a horse suddenly shifted all his weight to one side - it could blow out a regular sidewall ??? THANKS again for your help! karla
Posted 2005-08-29 6:16 AM (#29702 - in reply to #29638) Subject: RE: trailer tires
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Posts: 2689
I have a '90 boat trailer with the same size (& lettering) tires, so I'm guessing that trailers didn't "go radial" until some time later in the 90s.
This is a SINGLE axle trailer, but is rated at 4,000 lbs., so even in '90 on a boat trailer the H78-15ST would probably have been good for a GVWR of 7,000 on a two axle trailer.
I know, boats ain't hossies, but tires are tires and I think the ST225/75R15 is an ADEQUATE replacement for the H78-15ST, in fact an upgrade. BTW, 937 * 2.2 = 2061.4 so you might have some kilos and pounds mixed up somewhere.
Having checked that trailer's tires JUST NOW - DANGITT ! I have sidewall cracks. I s'pose after 15 years I'm due for tires. Since the D rating is easier to get around here I'll probably go with those. Nice that I'll only need TWO (-:
Posted 2005-08-29 6:30 AM (#29703 - in reply to #29638) Subject: RE: trailer tires
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Posts: 1416 Location: sc
here comes my 2 cents........ST tires are what come on most new trailers. ST tires are designed to meet the harsher requirments for a trailer tire. trailer tires lead a difficult life, often loaded heavy, hitting curbs, tight sidewall scraping u turns, and trailer suspensions are not up to automotive technology causing the trailer tire sidewall to flex and absorb more abuse causing heat that will blowout a P tire.
that being said, get the ST tires from discount tire. as for the inflation, since youll have a known weight riding on the tire here is what a "good" tire dealer/manufacturer will tell you.......take the GVW lets say 5000#(just guessing here on your loaded 2h BP) and divide by 3, (that way if you have a blowout the other 3 tires will not be overloaded) and then check the inflation chat. now here is where reg will probably disagree.
so checking the chart 5000/3=1666 that would appear to need just over 30psi to meet that requirment, however depending on who you talk to no one will recommend running a tire at less than 35 or 40 psi. now there are 2 options, change the tire size to get a load rating that would be in the appropriate psi range or just run the 225/75/15 at the 40 psi.
Posted 2005-08-29 8:32 AM (#29705 - in reply to #29703) Subject: RE: trailer tires
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OK, I'll disagree (-:
I don't know the origin of THAT rule of 1/3rd, but it looks suspicious.
In the event of a blow out you'll come to a stand still pretty damned quickly, you won't be "running on" 3 for more than a few hundred yards, I don't think the tire selection equation needs to account for it.
If you DO expect to run with a flat then 1/2 the load, the left or right side, would be riding on ONE inflated tire... seems you'd need a "rule of 1/4th". and you'd be over the axle rating anyway. It may be that there is enough margin for SHORT distances, but I'm back to carrying a ($147.75) spare (-:
I have memory fragments that suggest the H was a width designation, I think there was a halfie halfie lettering system for a while, then after years of resistance the feared metric system ALMOST came in. Rim diameter is still in inches, though I think I've seen Michelins here with 380 diameter (musta snuck across the frost border under cover of darkness).
Posted 2005-08-29 9:17 AM (#29707 - in reply to #29638) Subject: RE: trailer tires
Elite Veteran
Posts: 800 Location: Tenn/Ala.
Just a note from an old tire guy... The "H" on the end of the service description is indeed a speed rating of 130 MPH. In this application, where it is at the front, it is the actual size. This method was used until being phased out by P-Metric standards starting in the 80's. But the old sizes still exist. So an H78-13 is not rated for 130 MPH.
Posted 2005-08-29 10:11 AM (#29712 - in reply to #29707) Subject: RE: trailer tires
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Originally written by RTSmith on 2005-08-29 9:17 AM
Just a note from an old tire guy... The "H" on the end of the service description is indeed a speed rating of 130 MPH. In this application, where it is at the front, it is the actual size. This method was used until being phased out by P-Metric standards starting in the 80's. But the old sizes still exist. So an H78-13 is not rated for 130 MPH.
RTSmith
Oh yessssss, S, H, V, speed ratings at the END of the descriptions, WIDTH letters at the beginning. I've probably been subconsciously trying to forget that stuff, it WAS a MESS.
Posted 2005-08-29 11:39 AM (#29714 - in reply to #29638) Subject: RE: trailer tires
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Posts: 40 Location: Maryland
I just replaced the tires on my Exiss It had 7.50 16lt on it a bias tire I purchased a ST23580R16 10ply Which are radials. I was told by the tire guy that the bias will run hotter and dry rot quicker plus I would have a smoother pull with radials. I have them on my smaller trailer and have had no problems at all. The radials were about 140 $ cheaper versus the bias tire
Posted 2005-08-29 12:58 PM (#29719 - in reply to #29705) Subject: RE: trailer tires
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Posts: 1416 Location: sc
Originally written by Reg on 2005-08-29 9:32 AM
OK, I'll disagree (-:I don't know the origin of THAT rule of 1/3rd, but it looks suspicious.
got to love 2 points of view. but in your scenario wouldnt it be "rule of 1/2"? and of course both of these situations assume perfect load distribution on the trailer.
Posted 2005-08-30 10:01 AM (#29757 - in reply to #29719) Subject: RE: trailer tires
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Originally written by chadsalt on 2005-08-29 12:58 PM
Originally written by Reg on 2005-08-29 9:32 AM
OK, I'll disagree (-:I don't know the origin of THAT rule of 1/3rd, but it looks suspicious.
got to love 2 points of view. but in your scenario wouldnt it be "rule of 1/2"? and of course both of these situations assume perfect load distribution on the trailer.
Well, it isn't MY scenario (-:
I really think that running flat (to a stop) is an exception that the margin/safety factor can absorb. The other axle can handle it, the other good tire on that side can handle it, etc. If it is more than a few hundred yards I'd be surprised and I don't think (I'd) be worrying very much about heat build-up in 1/4 mile or so. The tire load/pressure/ratings are for SUSTAINED TRAVEL, which is something (I) wouldn't do on 3 wheels.
Again, I think the GWVR/3 rule is hokey. If it happens to coincide with reality and "practice" in a few cases, that is a coincidence. I wouldn't depend on it as a rule to work FROM.
24 hours in a day, 24 beers in a case, coincidence ?
Posted 2005-08-30 4:36 PM (#29796 - in reply to #29757) Subject: RE: trailer tires
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Posts: 1416 Location: sc
Originally written by Reg on 2005-08-30 11:01 AM
Again, I think the GWVR/3 rule is hokey. If it happens to coincide with reality and "practice" in a few cases, that is a coincidence. I wouldn't depend on it as a rule to work FROM. 24 hours in a day, 24 beers in a case, coincidence ? Correlation doesn't indicate causation, etc.
well it may be crap, but there is some logic to it, and it certainly wouldnt be the strangest thing ive come across. im just passing on what ive been told from the "horses mouth", so to speak. the manuf. "should" know better than us.
as for the 24 beer in a case/24 hours in a day, i call that convenient.
trailer tires
