15 inch tires on 14 inch axle

[RockyMtnRay]

Originally Posted by Bill

Ray, what am I gonna do with you? The article reports the results of testing the new improved magic hypower brake against standard electric brakes DRIVEN BY AN ANCIENT TIME CYCLE CONTROLLER. The description in the article's Introduction is laughable - this controller doesn't even activate until the tow vehicle noses over enough to activate a mercury switch! And only then does it begin to slowly ramp up the brake current. Over the past couple years, you and I have competed for King of the Time Cycle Controller Bashers. This one of the reasons. Let's not stop now.

After describing the time cycle controller, the article continues by saying "the HD3000 is intended to use the same dashboard controller" - but then they say that activation "instantly forces the brake pads against the rotor." Instantly? With a time cycle controller? How did that happen? Well, a little later on, we see casual mention of a new master cylinder sensor that actually sends current to the disk brakes. Doesn't sound to me like they actually used the same controller at all.

Let's step back from this particular article, and look at the bigger picture. If one braking system can provide 3:1 or 4:1 improvement over another, then there is something wrong (or grossly lacking) in the first one. So the first question has to be, what is it that is wrong? There are only two parts to a trailer braking system - the brakes, and the controller - so the difference has to be in one or the other.

Is it in the brakes? Now, it is clear that disk brakes have some very real advantages over drums (fade resistance and wet braking being chief among them). But raw braking power, the supposed subject of this test, is not one of them. Despite the hype of the automotive industry since disk brakes were popularized 20-30 years ago, discs are no better than drums in raw braking power. Both respond instantly, both give you fine-grain control of braking power, and both can lock up your wheel if you ask them to. Assuming that the drum brakes in this test met these basic criteria, and were properly adjusted, the brakes themselves would show only the most minor of differences in the tests. All else being equal, changing over to disks will NOT produce a big improvement. Repeat - despite the hype, DISK BRAKES ARE NOT MAGIC!

So that leaves the controller. And voila, they have set up the most laughable comparison you can imagine. It demonstrates the power of advertising dollars. There is no way that you, or I, or any mechanically savvy reporter for Trailer Life, would have accepted these test conditions and printed this article. The testers (who also build the brakes, surprisingly enough) clearly bought advertising space in the guise of "unbiased testing". The biggest laugh is that the article is probably printed right next to an ad for a decent modern brake controller like the Prodigy. Now there is a test I would like to see.

I just love these technical discussions ...

Bill

Oh yeah, I took due note of the type of controller (or perhaps controllers) that were used. And yes, that definitely made some contribution to the stopping distance. And yes, a time delay controller is slower than molasses about getting up to full braking voltage. But it does eventually get there...and will eventually induce as much stopping power as the brakes can provide.

However, I also noted the circumstantial side effects of the disc brakes...like objects being pulled loose from their moorings due to much greater braking force.

I've reviewed a lot of commentary RV.NET about electrohydraulic disc brakes and it's uniformly positive...basically once you try them there's no going back to electromagnetic drums.

And I also considered the ho-hum braking I'm getting at speed from the electromagnetic drums on my own trailer...I'm meticulous about their adjustment and they are more than capable of locking solid at very low speed (under about 5 mph). In fact I use them as temporary parking brakes on my 20% grade driveway while I'm chocking the tires.

But even with the Prodigy at max gain, there's no way I can get tire lockup out of them (with the trailer loaded) at speeds over about 15 mph. If they were hydraulically actuated drum brakes, yes, then I'd agree with your statement that a drum brake can equal a disc brake in braking effectiveness. But I have real doubts about just how much braking can be gotten out of an electromagnetic drum brake even if it was getting 14 volts directly from the TV. The difference in performance between electrohydraulic and electromagnetic brakes is not so much from the difference between disc and drum brakes themselves but rather from the much greater braking power the electrohydraulic actuator can produce versus the limited friction induced braking force the electromagnet can produce. Or, IOW, it's the difference in actuator technology and not brake technology that makes the huge difference.

I remain convinced that electrohydraulically actuated brakes (drum or disc) will provide much greater braking than an electromagnetically actuated brake and especially so at highway speeds. The only question in mind is whether or not I need/want that extra braking enough that I'm ready to spend $1500 to get it. I'll know by the end of this towing season.

[RockyMtnRay]

Originally Posted by hingarfi

Ray said
"FWIW, I may go quite a bit beyond just retrofitting oversize tires...I'm currently mulling over also swapping the 3.5K axles on my 2720SL for 5K axles"

I thinks Ray has the ultimate solution to pulling a 4000# 2720. When I researched the wheel situation, I think I discovered that the max wheel rating for 5 on 4.5" bolt pattern is 2150# which matches the tire rating at 50 PSI. I would assume that the 5K axle has 6 on 5.5 bolt pattern which gets one to 2500# loading.

The 2" lift seems to address the vertical clearance issue but the width issue may exist. If the 15" will fit, one could run at about 50-55 PSI and probably have a good tire margin (probably about 1900# loading for 4000# TM -- Notice that the SR215/75R14 is rated at 1820#).

Ray, are you interested in posing the width clearance question to TM ? You own a 2720 whereas I am a prospective owner. You probably have more clout with TM.

Called TM today...had a great discussion with Ed Lytle. Found he does read our board once in a while...and knew who I was. Anyhoo, he said they only use one size of wheelwell liner (my guess was right! ) and all models with 15 inch tires get the lift kit (that explains how they...and we...can use 15 inchers). Going on he said that the 15 inch wheels they use have a different bolt pattern than the 14 inch wheels and that would necessitate also retrofitting the 5K axle. He didn't have knowledge of aftermarket 15 inch wheels that would fit the smaller bolt pattern of the 3.5K axle.

I also asked about my idea of a full retrofit...5K axle, 15 inch wheels. He said should be doable...axle will run around $400, wheel/tire combo (from them) about $147 each (and 3 will be needed if the axle is changed)...total around 950 plus freight. Whee...as soon as I get some finalized weights on my trailer later this summer I may just do this retrofit for 2006!

One final caveat...he was going to run all this by Mike Hulsey tomorrow for an engineering validity check and would get back to me with the final TM view in the next day or so. So nobody run out and start making mods until we get the final word!

[Bill]

Well all right! Excellent work, Ray! And you're right, Ed Lytle at the factory is great - I've dealt with him on a couple occasions, always to my great satisfaction.

Now - what is the secondary market like for all these changed-out 3.5K axles!!?? Ebay, anyone? Pop-up Times?

Bill

Ray, thanks for the great info from Ed at TM. Ed seems like a real great guy from all the posts I have read. As I previously posted, there are 15 x 6 wheels with the 5 @ 4.5 bolt pattern which are rated 2150# That is the same rating as the 225/75R15 Marathon. Will be watching for the final go ahead from Mike Hulsey. Thanks to all for setting the record straight on this issue.

[Frenchy]

Originally Posted by RockyMtnRay

There's general consensus that travel trailers should only be equipped with "ST" (special trailer) series tires, not light truck tires ("LT" series), not commercial trailer tires ("C" series like the ones you bought), and not passenger car tires ("P" series). Certainly you often find higher load ratings in the same size tire if you use a "C", "LT", or "P" tire but these tires are designed for regular use and tend to deteriorate substantially if left unused but loaded for extended periods. By comparison ST tires are specifically designed to not deteriorate (internal oxidation) when left unused but loaded for months...a typical scenario for travel trailers that are left in storage for 6 months. Furthermore, ST tires are designed to better withstand the sidewall twisting and sideforces that happen when double or triple axle trailers are sharply turned (e.g. backing into a camping site).

So, yes, a commercial or "C" rated tire will do fine the first season it's mounted...probably better than an ST tire. But it may not be in very good shape at all by the beginning of the 2nd or 3rd season after it's been left unused for months at a time in a fully inflated state with the weight of the trailer on it. IOW, if you want that C rated tire to be still be good by the next towing season, you need to get all weight of the trailer off the tires during the winter and deflate the tires down to about 10 psi. And make sure the tires are completely protected from the weather (ideally inside).

Ray, I have been unable to verify your facts. Can you direct me to a site or literature that confirms what you say. You have me worried. I plan to travel to Alaska this summer on these tires so I will need to change them if they are deteriorated. All the information I've found on ST tires talks about stiffer side walls and shallower tread only. Nothing about special compounds. Thanks for any info.

But even with the Prodigy at max gain, there's no way I can get tire lockup out of them (with the trailer loaded) at speeds over about 15 mph. (Ray)

I've always understood that you Don't want your brakes to lock. The wheel that locks up is the one that wants to become the lead wheel! That's not good if you're going freeway speeds and your trailer wheels try to become the lead wheel! Wasn't that the whole idea of ABS brakes so no wheel would lock creating a skid? Skidding trailer tires create jack-knifing one of the greatest fears of a trucker. I almost had one of those on the freeway in Tacoma when this old lady slammed on her brakes for no apparent reason. It took an hour for my regular heart beat to return. She never knew how close she came to dying! Other than that, I agree about the excellent stopping ability of disc brakes - I have them on the rear of my Jimmy and they're great, but then they are controlled by a proportioning valve and ABS to prevent them from locking up.

[RockyMtnRay]

Originally Posted by Freedom

But even with the Prodigy at max gain, there's no way I can get tire lockup out of them (with the trailer loaded) at speeds over about 15 mph. (Ray)

I've always understood that you Don't want your brakes to lock. The wheel that locks up is the one that wants to become the lead wheel! That's not good if you're going freeway speeds and your trailer wheels try to become the lead wheel! Wasn't that the whole idea of ABS brakes so no wheel would lock creating a skid? Skidding trailer tires create jack-knifing one of the greatest fears of a trucker. I almost had one of those on the freeway in Tacoma when this old lady slammed on her brakes for no apparent reason. It took an hour for my regular heart beat to return. She never knew how close she came to dying! Other than that, I agree about the excellent stopping ability of disc brakes - I have them on the rear of my Jimmy and they're great, but then they are controlled by a proportioning valve and ABS to prevent them from locking up.

No argument. I'm well aware I don't want the tires to fully lockup during a panic stop as fully locked trailer tires have very little directional control and actually have less braking effectiveness than still rolling tires. That being said, maximum braking occurs just short of lockup.

And until I can get the tires to lock (or be very close to that) during testing, I won't be able to fine tune the brake controller to have the braking at just before lockup when they're really needed. So, for testing purposes at around 30 mph, I do want to be able to achieve lockup and my trailer's brakes aren't coming anywhere close to that now. It's not so much that they're drums but rather that the electromagnetic actuator simply doesn't exert enough force on the brake shoes.

Having grown up in Montana and lived in Colorado for the past 13 years, I have gobs of experience with driving on icy/snow packed roads. Plus, when I was young, Montana didn't have any highway speed limits and I routinely traveled at well over 100 mph (somtimes at around 140 mph) on the highways. I recall making the run from Great Falls to Miles City...~300 miles...in a little under 2 1/2 hours one Sunday morning. I also lived in Germany for 3 years and routinely drove at 200 kph (120 mph) or higher on the Autobahns. As you might expect, I've made more than a few panic stops from extremely high speeds.

So I know well the excitement that comes from having a locked tire...and I have lots of experience in keeping a tire just short of lockup during panic braking. ABS is nice but it kinda takes all the sport out of high speed or winter driving.

[RockyMtnRay]

Originally Posted by Frenchy

Ray, I have been unable to verify your facts. Can you direct me to a site or literature that confirms what you say. You have me worried. I plan to travel to Alaska this summer on these tires so I will need to change them if they are deteriorated. All the information I've found on ST tires talks about stiffer side walls and shallower tread only. Nothing about special compounds. Thanks for any info.

First the definition of the damage.

From the RV America webpage regarding RV tires. "According to Doug Jones, Michelin Tire Product Engineer, ozone is the principal enemy of uncovered tires. One of the ways tire manufacturers combat ozone is by blending ozone resistant rubber compounds during the making of the tire. These special waxes forma protective barrier against the ozone, but in order to keep up the battle, the waxes must be constantly brought to the surface of the tire. This is accomplished naturally by simply putting the tire to use. During the flexing and moving of a tire while you travel, a fresh layer of combative waxes is kept at the surface. Unused tires on stored vehicles do not receive enough exercise to allow the waxes to migrate to the surface and the ozone has a virtual picnic on any exposed area, especially the vulnerable sidewalls."

As you might expect, this ozone attack will be worst in the tire bulge area because the tire is deformed most here. Furthermore, the problem isn't just on the outside of the tire...ozone within the air inside the tire also attacks the rubber. Accordingly Goodyear's tire care recommends moving the vehicle at least every three months to put the bulge into a different area of the sidewall...or (1) avoiding the bulge by lifting vehicle's weight off the tires and (2) reducing tire pressure to 10 psi (which limits the migration of oxygen/ozone into the the tire's inner structure).

As for why ST tires are superior to all other types for this problem:

Let's start with this article from TrailerLife regarding tire safety. Among other comments about ST tires it says "ST tires also have the advantage of rubber compounds that are specifically designed to resist deterioration from the elements, including sunlight and ozone, during extended storage."

And from the Maxxis trailer tire webpage: "Specially formulated rubber compound reduces ozone deterioration while increasing tread life."

And from the Auto-RV website : "The The ST does indeed mean something. Many trailer tires don't travel a lot of miles per year, so it's likely the tires may fail due to old age instead of wearing too thin. Tires designated as ST models have a special rubber compound that's made to resist ozone deterioration and weathering to provide a longer "non use" or storage life than the average tire."

Since you don't have these long term storage advantages of the ST tires, that's why I advised (1) get your trailer's weight off the tires to avoid the tire bulge, (2) reduce the tire pressure (to reduce migration of oxygen/ozone into the interior of the tire) and (3) either fully protect or remove/store inside these tires to reduce exposure to UV and ozone.

Depending on how you've stored your C series tires this winter, you'll probably be still OK for this coming summer. But they could be really iffy by the summer of 2006.

[RockyMtnRay]

Originally Posted by hingarfi

Ray, thanks for the great info from Ed at TM. Ed seems like a real great guy from all the posts I have read. As I previously posted, there are 15 x 6 wheels with the 5 @ 4.5 bolt pattern which are rated 2150# That is the same rating as the 225/75R15 Marathon. Will be watching for the final go ahead from Mike Hulsey. Thanks to all for setting the record straight on this issue.

Ed called back this morning and said that Mike saw no problems with this kind of retrofit. The one caveat is they are basically limiting their OK to using the larger bolt pattern 15 inch wheels which in turn will necessitate the 5K axle. In other words...and quite reasonably...they're not giving a blanket OK to use any old 15 inch rim (including those that will fit the 3.5K axle bolt pattern) that they've never evaluated.

Apparently one TM dealer was/is inquiring about how much the 15 inch tire option will raise a 2720 over stock...Ed and I mutually agreed that it would be around 4 to 4.5 inches...2.5 from the mandatory lift spacer plus about .8 for the larger wheel/tire radius plus about another inch from the less-compressed suspension in the 5K axle.

Anyhoo, I'm expecting to get my trailer weighed again one last time at an RVSEF weigh-in on July 29...and I'll have it loaded as if for a 2 week no-resupply expedition (i.e. HEAVY). With those numbers in hand, I'll be asking my TM dealer (The Car Show) sometime in August/early Sept to order in the 5K axle and three 15 inch wheel/tire sets from TM. And then in Oct, I'll just have them do it as they know the trailer well, it's not a busy time, and I won't have to worry about the hassles of disposing of the used axle and wheels/tires.

Told Ed I'll be happy to be the guinea-pig for this retrofit.

What happened to the discussion about 15" tires? All of a sudden we're talking about brake controls.
I'd like to hear more about switching to 15' rims.

Jack