Change wheel size for better tires?

[MichaelOverfield]

GAmes, We agree on much more that we disagree.. I have validated first hand that you are 100% correct on the RV trailers being built with the cheapest components possible, at this point I'm just about 100% rebuilt on mine and have seen the cheapness first hand. Tires are garbage, brakes are marginal... mine developed an internal short in the axle tube, I had to 100% re-wire, and the original wire was not adequate for the current demands of electric brakes.. I really considered going with the hydraulic disc brakes at the time. Now having a broken spring of all things, but this seems to clearly be related to odd shaped tire, so at least I should not have to think broken springs are that common, just the same I increased the capacity of the spring for all 4 while at it and will replace all the hardware, and add shocks.
I guess I should add, by axle capacity, my rig is no where close to what it is rated for, and I'm convinced now that one needs a large buffer where components are rated well ABOVE typical loads..
When I first got the trailer, I hauled it with a 1/2 ton gas pick-up, and with that rig, 60MPH was the fastest speed, in some cases most it could do period, but from a safety perspective the truck and trailer were of similar weights, making it much less stable..
That said, now I tow with a 3500 Dodge, long bed, crew cab.. it is VERY stable.. I have to check to make sure it has not come off, because it is so well under what the truck can tow it is not even 1/3.. with this particular rig I can get up to 70 -75 and be very stable, I rarely even notice a cross-wind, nor have any sway at all, I've tried to induce it to be sure, I can swerve and it goes as straight as an arrow, no issues.. the point we all need to realize is that each combination of tow vehicle and trailer and loading pattern will have considerable effects on stability and safe tow speed, the prudent and safe driver will diligently assess this for their particular rig. There is no one size fits all safe speed for all combinations of trailers.
And yes, I'm aware of the California limits, and I've often done 62 going through, but get tired of constantly being passed by 18wheelers.. so I adjust accordingly, most rigs seem to do about 65-67 in Cali.
Having said all that, whenever possible, and not in a tight schedule, I've come to prefer US roads and back roads where speeds are closer to 55-60 MPH, the views are better, less stress in most cases, better things to see.. but can't always do this, and as you correctly point out, much, much better MPG, in mine it is from about 11 to about 14, and as a percentage, that is HUGE.

 

[MichaelOverfield]

Getting back to the tire discussion.. Here is what I'm doing with my situation... and I'll post follow-up once it is all installed and see how it goes.

From here and other looking I did I found the in MOST cases ST tires are 65MPH speed rated, but I found some at e-trailer that were M rated, for 81MPH, I almost went that route, they did have LR D in 14 inch rims... $114 ea, Taskmaster tires (http://www.etrailer.com/Tires-and-Wheels/Taskmaster/TTWA21514RTM45WS.html) (on nationwide backorder, go figure.. likely many are finding out how cheap and poorly rated trailer tires really are!).. so I could just bolt those on and be done, but I'd like to have the option of using LT type tires, and you won't get them in 14" rims....

So, I'd have to go with 15" or maybe better 16" rims to so do this.. now at some point I'd have to rotate my axles and raise the trailer, but it is very low as it is, so adding a few inches might actually help in some ways. So I did not rule out that, and beside it is already jacked up with all the tires off to fix this latest and to replace the springs, all of them.. these are a pair of 3500# axles, I increased the springs to 4800# (http://www.etrailer.com/Trailer-Suspension/Redline/PR4.html), at e-trailer they are exact size, and same price as the 3500# springs, about $25 ea... I don't mind a bit less give in the suspension.. besides I'm going to also add a pair of shocks, that kit is about $130 and seems to be pretty straight forward to install (http://www.etrailer.com/Trailer-Suspension/Lippert-Components/LC281255.html) , but I'll report back once I get there...

I ended up going with 15" rims, but 6" wide (Most LT tires need at least a 6" wide rim), this did open up many LT type tire options.. keeping in mind the original load range was C / 1760#, I wanted something like a LR D, 2000 or better, which many LT tires will have.. I could not go 16" unless I also replaced hubs.. mine are 5 on 4.5", and I can get 15" with that bolt pattern, but to get 16" I have to have 6 on 5.5" hubs.. they don't have 16" rims on my bolt pattern, and I did look..

The other thing interesting in all of this, one item I originally found was a 14" LR D tire, but the rim had a 1760# rating for a 2200# tire.. probably OK, but seemed to me I'd like to not be under on ANY part of the suspension.

The 15" rims I got from e-trailer were each rated at 2600#, so that checks out, and only $32 ea. (http://www.etrailer.com/p-AM20545.html)

Next to tires.. I searched many, TireRack.com, Amazon, Walmart... and I found some I'm going to try, at Walmart, These are Light Truck tires (Hankook).. with a rated load of 2200#! They are H724 235/75R15 XL 108S (http://smile.amazon.com/Hankook-Opt...sim_293_2?ie=UTF8&refRID=1YGM3X1XTD3JBMV10W8A) , and came in at $67/each (Walmart), so for about $104 per wheel (tire and rim), even cheaper than most truly cheap ST tires out there, but rated well over my trailer's weight, and speed rated well over any realistic speed... so should be a good fit. My diameter goes from 27" to 29" overall, so I'm looking at 1" less fender clearance.. but I may change the spring mounting on the axles from below to above.. I can weld it if needed, and if I do that opens up about 3-5" more in clearance.. my RV is a low profile, perhaps one of the reasons it tows so well.. but I often worry about dragging the bumper at its current height in some not so groomed trails and roads, and my caster wheels back there have seen contact on occasion...so raising it up may be worthwhile anyway...

Once I get this all put together I'll update on how it goes... Any thoughts or feedback, please send it! (also if you want any details or links.. )

 

[RUSSELL5000]

MichaelOverfield,

It seems like you are going through the same observation of pathetic RV trailer suspension adequacy that I did. I started by trying to map out a suspension that would be working at 70% to 80% of rated capacity. I found the same challenge with 3500 lb axles and 15 inch tires that you have.

Since you are replacing springs, I suggest you also consider bronze bushings in the spring eyes, greasable "wet bolts" in the spring eyes, the thicker shackles, a better equalizer, and the shock kit (already on your list). I think all of these are available at eTrailer. This is pretty much where I am at now, and all but one aspect of my rig, from truck to trailer, is at 80% or less of paper specification (the one aspect that is not is truck payload - the trailer weight, bed full of stuff, full fuel tank, family of four and two dogs in the cab pretty wheel uses up the 2500 payload - I think you would still have plenty of capacity with a dually). I have one more enhancement in mind and that is to change from electric drum brakes to disc brakes with electric over hydraulic control. Then the trailer suspension would at least be somewhat "modern".

I have gone a more costly route as I replaced the axles. I went up in axle rating which gave me the bolt pattern required for a 16 inch wheel; I think if you go from 3500 lb to 4400 lb axles you get the desired hub for 16 inch wheels. If you were to swap axles with the flip you mentioned then you would be in the realm of the 16 inch wheel and the wide choice of high-quality LT tires. That is NOT a cheap date. However, if you are contemplating towing at speeds up to 85 mph then it may be worthwhile - it is worthwhile to me and I only ever do between 60 mph and 65 mph (where fuel economy is best).

 

[MichaelOverfield]

Russell,
Thanks for the feedback, I did get the wet bolts, and bronze bushings also.. forgot to mention in the list before.. I also found I could mitigate some of the near 6 inch rise changing the side of axle where the spring mounts by changing the equalizer from a 4 inch height to a 2 inch, and use the Dexter rubber version to further cushion the stress on the suspension, with that and shocks it will likely have a better ride by far than the truck! Here is that Dexter unit, this comes with the wet bolts, but I got just the center part as I have the wet bolts already from a previous order... http://www.etrailer.com/Trailer-Suspension/Dexter/K71-652-00.html

My current equalizer is rated way above the trailer weight (can't recall the brand, but it is quite good), and I have a Tru-Center (Blue Ox) gas piston anti-sway bar (last I looked they don't make them anymore, which is sad, it works great)... It is really nice unit, not so critical to the current tow vehicle, but vital to the previous lighter vehicle.

E-trailer has a nice kit to covert to the electric over hydraulic/disk brakes.. almost did it, but I'd need a new brake controller also, as only the newest Prodigy can work with that unit.. so I had to factor in that cost as well, and I was hard to justify, particularly as my trailer sticker weight is 4300 empty, 5500 loaded.. One of these days I need to get it on a scale to see what it really is.. I suspect it is closer to the 5500, or a bit more, but with 7000 axles it should not be an issue.. better with new springs.. I can't imagine getting 2700 lbs of stuff in there, that is darn close to the 1 ton truck payload!
Best part of a light trailer with respect to the tow vehicle is that the trailer brakes are less critical, that said, I do like mine to work, and work well. With the new wiring from plug to magnet, and proper if not oversized gauge of wire.. they now work pretty well.

My trailer (Outback 21RS), when rear slide is in for towing is only 21 feet, so much less cross wind surface area.. that helps too.

In my first post I may have given the impression that I want to always tow at high speeds... actually I just want to know I can without issue, if needed, typically 65 is good, though there have been times where I could go 75MPH easily.. and I want to know I'm not going to have a broken spring, oval tire, or other disaster. Last year I replaced all the brakes, and hubs after a close call of losing a wheel due to bearing failure.. from bad grease seal, and cheap Russian bearings from the OEM.. put in all quality Timken bearings... It has been one thing after another it seems.. the good news was I caught the bearing failure before the wheel came off, and I carry plenty of tools, so in less than 4 hours of delay, mostly getting the parts, I was back together and down the road.. (now I carry spares!) but is was much too close for comfort.

 

[MichaelOverfield]

Duplicate due to computer glitch......

 

[Jeepr]

So, here is an interesting twist. First, I think I'm going to go with the Goodyear HT 215's...

But, I was at the trailer place today (had one of the backing plate and magnets replaced), and asked their opinion. She said unofficially, she would prefer LT tires. But, that she is aware of MO State Police having pulled people over (probably commercial people) and if they have other than ST tires on a trailer, ticketing them. WTH???

 

[MichaelOverfield]

SNOKING,
Great comment, I just watched that video and can call it propaganda as well from my experience and research. The guy says ST tires can dissipate heat better? If that were so, they would be rated at more than 65 MPH! Note he made no mention of their speed rating. He also carefully selected tires to make his case, In my looking I found several LT tires, and even some XL P type tires with HIGHER load ranges than similar size ST tires.. One does have to look to find this. Then there is the option to up you rim/tire size to go with LT type tires.. not addressed in this video.

I do not buy the sway with softer side walls.. LT and P tires have to deal with turning wheels, while trailers only see issues in slow speed maneuvers with lateral loads, not at speed. Sway issues are almost always too much load too far aft on the trailer, and ST won't save you from poor loading and sway!

The only thing I might grant on stiff sidewalls would be the occasional curb hit, but both P and LT tires see this too, with typical driving.. so not sure what the point is...

When I came upon many LT/XL P tires that were well less than the cheapest STs I could find, I also don't buy the comparable cost line either.

Having said that, I would not fully load to capacity either a LT or P type tire on a trailer (then again, it is quite clear that we should not do this with ST tires either!), because they typically are well under capacity on trucks and cars.. but in my case I'm putting 8800 capacity tires on a trailer that has 7000 axles, and a loaded rating of 5500.. that should be sufficient margin..

I'm quite surprised the ST tire propaganda has lasted so long, and people are OK with 2 years service on a tire, when they'd never accept that on a car or truck tire..

 

[AH64ID]

So, here is an interesting twist. First, I think I'm going to go with the Goodyear HT 215's...

But, I was at the trailer place today (had one of the backing plate and magnets replaced), and asked their opinion. She said unofficially, she would prefer LT tires. But, that she is aware of MO State Police having pulled people over (probably commercial people) and if they have other than ST tires on a trailer, ticketing them. WTH???

LT tires are OE on multiple trailers so I am going to call BS.

 

[MichaelOverfield]

Jeepr,
Interesting.... I doubt it, but check your MO DoT.. in WA, I just checked and it has the following for trailer tires: "Any tire marked “for mobile home use only,” “mobile home only,” “not street
legal,” or any marking indicating the tire is not legal on the vehicle presented for inspection will not pass inspection."

Now the last line could leave interpretation... LT and P or XL on the tire might be seen by some as defining the use of the tire to a vehicle... but you can put a P tire on a LT, in fact, many P tires specifically say they are for Light Trucks.. so I'm not sure how that can be held to mean "not legal on the vehicle presented" Keeping in mind the section I cited was for the inspection and registration of a new or homemade trailer...

Keeping you in a ST tire that might go 2-3 years at best could be a reason the trailer place want's you in a ST tire.

 

[RUSSELL5000]

MichaelOverfield,

I read through the posts again and it looks to me like you have it done. I like 8800 spec capacity on 5500 load - even if real load is more, you have it covered.

My tire capacity is roughly 10,700 for a trailer with GVWR of 9,250. My trailer tires always feel cool to the touch.

 

[MichaelOverfield]

I have to confess some errors on my original assessment on the failed tire... I read off the date code last eve as 3906, which is late 2006 production (2005 trailer, so the OEM were not even good for a year, and maybe 5000 miles, those were bias ply NANCO tires). I'm pretty sure the Goodyear Marathons ST 215/75 R14 were installed in early 2007. They are LR C, so 1760 each, which is well over the trailer weight. It appears they were good for over 10000 miles, maybe 15000. However, they are due for replacement by age alone, so I really can't complain about them too much, they did what they were supposed to do.. but the warning and lesson learned is to verify and monitor age by date code on tire (WKYY), week of production 1-52, and year YY. Going forward, at 6 years.. I'm looking at new tires, not matter how good they look, 3 of the 4 have plenty of tread, no dry rot, I store with weight off the wheels.. so age is the limiting factor in my case, and likely is also for most, unless you have the garbage OEM bias ply tire like the Nanco's that came with the Trailer.

Having said all that, the upgrade to 15 inch rims, and the Hankook P235/75 R15 108XL tires is still a cost effective option, the marathons are near $100/ea, while the Hankook tires ($67 Walmart), PLUS new rims ($32 e-trailer) came in at $104 each (after tax), and I go from 1760# to 2200# each, and speed rating is no longer an issue (next replacement I can go with just the tires, and be way less than ST tires). I compared the plys on the two tires, the video linked earlier makes the claim that ST had more side wall strength, so I checked and both the ST and the Hankooks are 2 ply side walls, the ST has a total of 6 plys on the radial, 2 steel, 4 poly, where the Hankook has total of 5, 2 Steel, 2 poly, and 1 nylon. Both have a 50psi pressure rating. The new tires have a larger area of road contact, since they are larger diameter, and wider, that is less stress, thus less heat.

Oh, the Hankooks I got for the trailer are Korea manufacture, the one's one my wife's Jetta OEM are China manufacture, but they are holding up well with about 43000 miles, so I can't complain about Hankook as a brand.

One other objective thing when evaluating tires.. look for weight. TireRack.com has excellent technical specifications, and I've ordered many tires from them over the years.. they list all the dimensions and weight. If the tire is higher load, it means more plys, higher pressure inflation, and heavier.. so that will tell you quite a bit. ST tires are typically on the heavy side, so are LT and the XL load range tires like the Hankooks I choose, but there are others in the same series with lower load range, so be aware of that. The "108S" is load and speed rating (the XL is Extra load, but it is not an industry standard, just something Hankook added to these). For a trailer you would need to stay above 105 for sure, higher is better, any LT or P tire is going to have a speed rating well above any ST tire, so no worries on that, I think S=100MPH if I recall correctly.

 

[AH64ID]

While the weight rating may increase I personally don't consider a P rated tire an increase over a ST LRC... just my 0.02.

P rated tires used in any application except passengar cars are only rated at 91% of their side wall, or 1986lbs. It is more than the 1760# but not as much as you thought. This reduction is due to the weak nature of P rated sidewalls and their ability to control taller loads without generating too much heat.

A 215/75R15 in LRD would be a MUCH better option than a P rated tire.

ST tires are on the light side not the heavy side when comparing to a LT of similar size. They are also light compared to similar size P rated tires especially when you consider load rating. 225/75R15 LRD Marathon's are 31lbs. P235/75R15 Hankook's are 30lbs.

The number of plys isn't as relevant as the strength of the plys. My LRG 4500lb rated tires have 1 sidewall ply.

Higher load does not mean more plys. Ply's are an old biased ply carryover and load range is a much better indication of rating. The reason a LRE is called 10PR is because it has a 10 Ply Rating, but it will probably not have 10 plys.

 

[MichaelOverfield]

AH64ID,

Thanks, good feedback.

I think you have a typo though, 31lbs on the marathons is more that 30lbs on the Hankook's... and the later is a increase in size, and that implies the ST is a thicker tire, thus its higher weight?

When I searched, I was comparing same size tires in the three groups, for same size, ST and LT are similar in weight and load, P is less load and weight for same size. I wanted a dedicated LT tire, but I can't see a problem with the Hankook tires, as they have similar load capacity as the LTs, but much lower cost. In my case I adjusted by an increase in tire size to get a higher load range, and that distinction is important. To do this and have fender clearance, I have to re-mount my axles from spring below, to spring above, and weld a new mount to do so (that's about 6 inches). I take the equalizer from a 4" to a 2" tall and get 3 inches, but the tires add about 1-2 inches, so I get about 3-4 overall). This level of work is likely beyond what most will want to do, or are capable of doing... As it turns out, I was short on clearance with the OEM tires too, yet another bit of data on the cheapness of the OEM components...

1986lbs is still over 200# per tire over what I had, and the cost is so much less.. and no limited speed concerns.. Thanks for the 91% data, I did not know that, but it is helpful.

I'll be reporting back on this project when complete, with on road testing of how it handles.. I'm raising the trailer about 3-4 inches, and it gets stiffer springs.. so it may be hard to nail down any change to the tires alone, as there will be several enhancements at the same time, including shocks..

 

[GAmes]

But, that she is aware of MO State Police having pulled people over (probably commercial people) and if they have other than ST tires on a trailer, ticketing them. WTH???

I too call BS. What was she trying to sell you? MO (or any other DOT) State police could not care less if a person is using LT tires on a trailer. As AH-64D said, many RVs come from the factory with LT tires.

 

[RustyJC]

Further to the above, the 3750 lb rated Goodyear G614 RST is specified for trailer use only, is standard equipment on many 5th wheels and comes in one size - LT235/85R16G.

Rusty

 

[RUSSELL5000]

AH64ID,

Not sure I get your point. My understanding is that LT rated tires have a stiffer sidewall than P rated tires. But he has a trailer with GVWR of 5,500 lb (say 6,000 to be on safe side), 7,000 lb of axle capacity, and roughly 8,000 lb of tire capacity (continuing your point on the sidewall rating).

Those seem like quite comfortable margins to me - wouldn't you expect his tires to run cool and last long?

What am I missing?

 

[AH64ID]

P tires are Passengar car tires and have weaker sidewalls for improved ride, which is the reason that on anything but a car they are only rated to 91% of their sidewall rating.

If we are talking plys they have a PR of 4. I personally wouldn't put a 4 PR tire on a trailer with the service and abuse trailer tires get.

Yes they have the load rating, but then again so do ST's....

 

[MichaelOverfield]

When I get the chance, I'll see if I can cut cross sections from the OEM bias ply ST tire, the GY Marathon Radial ST tire, and some P series tires I have (much smaller size, old car tires).. from the cross sections I will take some measurements and see how they really compare. From what I've found, there is a WIDE range in what comes under the "P" category.. just doing an unofficial survey yesterday walking past several heavy vans I noted some had LT type, some the XL P type tires, same vehicle type.. large 15 pax vans. From my initial flex test on the Hankooks, they seem as stiff as the ST tires.. they are also 50 PSI.. I think inflation pressure is going to dictate ride far more than side wall stiffness in any case (we all know that for passenger tires, OEM almost ALWAYS specifies lower pressure than what is on the tire, for the softer ride, so the pressure will have more effect than sidewall, unless the side wall is insanely thick) .. if I had P rated tires with 44 psi or less, I think they would be noticeably softer ride, but the ones I got are 50 PSI tires, same as the LR C ST or LT tires..

 

[RUSSELL5000]

MichaelOverfield,

I would be interested in the results of your cross section cuts.

When I chose my trailer tires I got Firestone TransForce HT, but only because the truck had those tires and the guys at the shop liked them. I did some looking at Tirerack.com and noticed that my tires weigh 38 lbs, the Michelin XPS Ribs weigh 49 lbs, and the Bridgestone Duravis 250s weigh 53 lbs. They are all load range E. But, there must be something different in the construction because the weights are so different. There are probably folks here on the forum that understand tire construction.

When I have read posts regarding trailer tire failures, here and on my RV forum, it seems that the failures occur when the tires are pushed to specified capacity or beyond/ or are older.

 

[MichaelOverfield]

Here is a great article I found on topic: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=219

In here they do mention the 91% referred to by AH64ID. This is very good to consider, and I'm glad it was pointed out in this discussion.

Note however in the article they compare tires of the same size, and this also notes the inflation pressure is a big factor. In my case I'm going up size, a ST 215/75 R14 LR C (50psi) to a P235/75 R15 108S XL (50psi). Both larger diameter, and profile, same pressure. All P-tires of the same size will have lower psi, and load capacity, and hence the general advice to not use them on a trailer. LT tires on the other hand of the same size are more closely matched, and use the Load Range letters, just like ST, so an easier match indeed.

In my case, on engineering alone, with a same PSI, over a larger surface area (bigger tires), I can expect less flex in the lager P-tires over the smaller STs, now no doubt same size P tires as the old STs would be a poor choice and very ill-advised.

The side wall point is interesting.. I'll try to do some cross-section cuts in the coming days.. and perhaps some side load tests with a scale and press.. see just how much the side wall stiffness affects the flexing of the side wall, I have to assume, compared to inflation pressure, it has to be a very small factor. The force of the pressure in the tire has to be much, much more than the bending resistance of the side walls in all but a near solid tire. A simple way to see this, is when deflating a tire under load, does the side wall matter, no.. it goes flat, the weight is held by the inflation pressure and we can see this in the increased pressures associated with the higher load tires (LR C= 50psi, LR D= 65 psi, LR E= 80 psi and so on (truck has OEM Michelins in LR E))

I don't know if I mentioned earlier, but I would have gone LT if I found a suitable 15" tire at a good price, there were some, but cost was up there quite a bit, and these I found at a mere $67/ea, well that is hard to pass up!