Towmax by Power King – Facts

[tireman9]

Re: Towmax by Power King – Facts

The Michellin XPS Ribs have a Speed Rating Q (120 MPH). Not trying to sell them to anyone, but IMO this means there is a lot of safety margin when driving 65, plus the fact that they are rated as a LT tire which assumes they will be carrying passengers. Any ST tire rated for 65 mph will be running at or near it's maximum speed rating, guaranteed. Would you purchase a set of tires for you vehicle that were rated for 70 mph, and assume you will never drive faster than that?

Yes the tire might be "Q" rated but have you looked up your tire in the Michelin RV Data book? I think you will see they state 75MPH max in RV application.

Let us know what you learn.

 

[tireman9]

Re: Towmax by Power King – Facts

The RST designation fooled me too. It's not the same type of designation as ST or LT. It's a marketing designation that stands for something like "Regional Service Tire" (Regional versus Long Haul). Goodyear's documentation shows the G614 as having been designed for demanding trailer applications, but they've tested and certified it as an LT tire. That's why it carries the LT235/85R16 designation. Unlike most ST or LT tires, it's supposed to have steel belts that go from bead to bead, strengthening and protecting the sidewalls.

It's designed to shed heat up to 75mph whereas most ST tires are only designed to shed heat up to 65mph.

I suggest you read the tire sidewall. It will tell you the number of layers in the tread and in the sidewall. Also the material.(Steel, Polyester, Aramid etc)
"Belts" are in the tread area only and you will have 2 or maybe 3.
Body ply or Layers run bead to bead and you will have 1, 2 or possibly 3.
NOTE the total number in the tread includes the number of body ply PLUS the number of Belts.


We all would be interested to know what your tire says.

 

[Miltp920]

I appreciate your feedback. I have learned ALOT about tires and NOT taking anything for granted on this website, and owners forum. THANKS to all those who help keep us informed. Can you recommend an add on tire pressure monitoring system. I do not recall even seeing this as an option when I ordered the 3100 Cyclone, 2axle. I just saw the add for the TPMS. On your blog. Looks like a good insurance policy. THANKS AGAIN TIREMAN. Does anyone recommend putting TPMS on both tow vehicle and 5th wheel? OR typically just put on 5th wheel?

 

[pegmikef]

i appreciate your feedback. I have learned alot about tires and not taking anything for granted on this website, and owners forum. Thanks to all those who help keep us informed. Can you recommend an add on tire pressure monitoring system. I do not recall even seeing this as an option when i ordered the 3100 cyclone, 2axle.

tst 507

 

[guyc66]

Thanks Dan.....that makes sense. I just wanted to be sure I wasn't damaging my tires if/when I tow my rig over 65 MPH. I don't make it a habit to go that fast, but sometimes when passing a much slower vehicle on the Interstate it may become a necessity since I don't have a whole lot of patience.

Do you also only exceed engine Red-Line "sometimes" ? If so do you expect to get 100,000 miles on the engine?

I have never found it necessary to redline my engine to go from 65 MPH to 70 MPH just to pass someone on the Interstate for that short span of time it takes to get around them. Besides what does red-lining an engine have to do with me going over 65MPH for short distances as long as I keep it below the 75 MPH rating of my tires?

 

[scottyb]

Yes the tire might be "Q" rated but have you looked up your tire in the Michelin RV Data book? I think you will see they state 75MPH max in RV application.

Let us know what you learn.

You are correct. Can you tell us why that is? I mean, if they are rated to carry up to 3042 lbs with passengers @ 120, why would they be re rated to carry the same weight w/o passengers at only 75? Just curious. Bear in mind, I never intend to hit 75 w trailer, nor do I have any intentions of getting any where near 120 w/o trailer.

 

[TravelTiger]

Tire pressure monitor: TST 507 here, we started with just the trailer and added the truck tires (dually) later. We wanted them because it's hard to check the air in the rear tires without removing the hubcap/inserts, a real pain. We've had a few low tires on the truck over our towing experience, so it was a worthwhile investment.


Sent from my iPhone using Tapatalk

 

[JohnD]

My car has TPMS . . . GM factory install!

Not sure how much I trust it!

They are usually off by at least 5 PSI per tire . . . and that is when they are cold.

And of my three tire pressure gauges . . . none of them match the dashboard readouts, nor do they match those at my local tire shop, either.

Once on the road . . . all bets are off as to how accurate the readings are!

Funny . . . when the tires are cold the dash reads all of the tires at the same pressure, but once on the road, one is usually showing 5-7 PSI more than two of the other three, and generally 8-10 PSI higher than the last tire (which is the same tire I write about in the next sentence).

And one of the tires has been setting off a 'SERVICE TIRE MONITOR' alarm a couple of times per week since the car was new (now three years old).

I brought it up every time I took it in for service at the dealership . . . and they would tell me that it was dirty and needed to be cleaned.

Well . . . since it was in under warranty I asked them several times to clean it as they suggested . . . they never did.

When I was at the tire shop a couple of weeks ago it had just gone off again . . . they told me I needed to replace the module at a cost of around $350.

I think I might just pull the fuse instead . . .

 

[tireman9]

I have never found it necessary to redline my engine to go from 65 MPH to 70 MPH just to pass someone on the Interstate for that short span of time it takes to get around them. Besides what does red-lining an engine have to do with me going over 65MPH for short distances as long as I keep it below the 75 MPH rating of my tires?

Guy... Th engine "Red-Line" was an analogy to tire speed rating. You would probably never intentionally run your engine above its RPM "Red-Line" as you know that does damage to the engine. However it is still possible to run an engine above the speed limit.

Tires have a "Speed Rating". You should think of the tire speed rating just as you would the engine red-line. It is possible to run the tires faster than their speed rating but doing so is doing internal structural damage to the tire.

ST type tires are rated for 65 mph MAX Most LT and TBR (22.5 size) tires are rated for 75 mph MAX in RV application by the tire manufacturer. You can confirm the rating for RV application by reviewing the data books under the RV section from the tire company web site.

Hope this clears things up for you.

 

[tireman9]

You are correct. Can you tell us why that is? I mean, if they are rated to carry up to 3042 lbs with passengers @ 120, why would they be re rated to carry the same weight w/o passengers at only 75? Just curious. Bear in mind, I never intend to hit 75 w trailer, nor do I have any intentions of getting any where near 120 w/o trailer.

The "de-rating" of the tire speed limit is based on experience in RV application where a majority of RV owners have one or more tire in an overload condition (no matter what speed they are driving).

Basically it is heat that "kills" tires.
Cars & many pick-ups are running tires at only 50% to 75% of their rated load most of the time but RVs run at 95% to 110% or higher of their rated load most of the time. This load difference is the main reason for the heat damage.
Damage to tire structure is cumulative and tires do not repair the microscopic tears in their structure. These reasons are why many RVs only get a few years life from their tires while the vast majority of car owners can run the tires to wear-out with no failure.
Every mile you run overloaded or under inflated cuts many miles off the tires design normal life.
Heat generation is not an on-off switch. Lets say that if you run at 75 mph & 100% rated load, the tire structure might get to 100F above ambient temperature.
If you cut the speed to 65 it might only hit 80F above. If you also cut the load to 80% the temp might only get to +60F (all these are just an example just showing it is BOTH speed & Load that generate heat)

 

[tireman9]

My car has TPMS . . . GM factory install!

Not sure how much I trust it!

They are usually off by at least 5 PSI per tire . . . and that is when they are cold.

And of my three tire pressure gauges . . . none of them match the dashboard readouts, nor do they match those at my local tire shop, either.

Once on the road . . . all bets are off as to how accurate the readings are!

Funny . . . when the tires are cold the dash reads all of the tires at the same pressure, but once on the road, one is usually showing 5-7 PSI more than two of the other three, and generally 8-10 PSI higher than the last tire (which is the same tire I write about in the next sentence).

And one of the tires has been setting off a 'SERVICE TIRE MONITOR' alarm a couple of times per week since the car was new (now three years old).

I brought it up every time I took it in for service at the dealership . . . and they would tell me that it was dirty and needed to be cleaned.

Well . . . since it was in under warranty I asked them several times to clean it as they suggested . . . they never did.

When I was at the tire shop a couple of weeks ago it had just gone off again . . . they told me I needed to replace the module at a cost of around $350.

I think I might just pull the fuse instead . . .

Don't forget the TPMS is primarily an ail loss warning device and I am not aware of any being intended for primary use as a pressure measuring device.

RE pressure gauges. Have you had any checked against a "certified " gauge? I find that 10% to 15% of the gauges I have checked are off by 5 psi or more. You can learn more about gauges in THESE posts.

RE your GM dealer. Maybe you need to select a better dealer. "Dirty" sensor is not something I have heard much about except from people using "sand" balance stuff in the tires or who have wet & dirty air from their compressor.

Since the the TV system is now "old" I agree with pulling the fuse but I would STRONGLY suggest you get a good aftermarket TPMS with enough sensors to handle the TV & TT.

 

[tireman9]

Here's a question I wondered about. If I am doing 65 mph and my TV has 18" tires but my towed vehicle has 16" tires how fast are the towed vehicle tires going?

Mike

Grumpy. Well the way to arrive before you leave on a trip is to put the biggest tires on the trailer you can find.(Get some 30" tires if you wanna go real fast like a race driver) That way it will be goin 100 while you are drivn only 55.




Sorry to burst your bubble but wheel diameter difference doesn't change the speed of the TT.

 

[Ks.Kev]

Re: Towmax by Power King – Facts

Guy, keep in mind that the max speed rating assumes that none of the tires are carrying more than 3750 lbs and that they are inflated to 110psi at 70 degrees (F) when not in direct sun. Overloading or underinflating generates additional heat and if you're running at 75mph while overloaded or underinflated, you could damage the tire. Damage is cumulative, so the failure may not show up right away.

In theory none of your tires should be overloaded. But because weight is not evenly distributed, you could in practice have one tire carrying hundreds of pounds more than the others. That's why it's helpful to have the rig weighed with separate scales under each wheel. The first time we had our Landmark weighed, the rear off-door-side tire was carrying close to the limit. The others were well under.

Anyway, all that to say that driving at less than the max speed rating is a good idea because it leaves you a little margin to compensate for the other variables.

Need to ask..... since I'm a newbie here....how does a person weigh each tire separately? Thanks for any info on this!

 

[danemayer]

Re: Towmax by Power King – Facts

Need to ask..... since I'm a newbie here....how does a person weigh each tire separately? Thanks for any info on this!

Kevin,

The simplest way is to go to the Heartland North American Rally. They arrange with RVSEF to do weigh-ins which put a scale under each wheel.

If that's not in the cards, let me point you to Fifth Wheel Safe Towing. They have a list of providers. Here's a link.

 

[Ks.Kev]

Re: Towmax by Power King – Facts

Thanks Danemayer. I'm getting ready to join, then I will be looking into which Heartland North American Rally to go to.

 

[danemayer]

Here's a link to this year's North American Rally. It's currently sold out, but if you put your name on the waiting list, there's a pretty good chance a spot will open up.

 

[tireman9]

Re: Towmax by Power King – Facts

Guy, keep in mind that the max speed rating assumes that none of the tires are carrying more than 3750 lbs and that they are inflated to 110psi at 70 degrees (F) when not in direct sun. Overloading or underinflating generates additional heat and if you're running at 75mph while overloaded or underinflated, you could damage the tire. Damage is cumulative, so the failure may not show up right away.

In theory none of your tires should be overloaded. But because weight is not evenly distributed, you could in practice have one tire carrying hundreds of pounds more than the others. That's why it's helpful to have the rig weighed with separate scales under each wheel. The first time we had our Landmark weighed, the rear off-door-side tire was carrying close to the limit. The others were well under.

Anyway, all that to say that driving at less than the max speed rating is a good idea because it leaves you a little margin to compensate for the other variables.

Missed the part "inflated to 110psi at 70 degrees (F) in my first reading. Please do not confuse "Ambient" with some Laboratory standard. If you check the publications from the tire companies you will not see any standard temperature is involved when setting tire pressure. The issue is the the tires should not be hot or warm from being driven on (usually 2 - 3 hours are needed to completely cool the tire) and not having been in the sun. Tires can be 30F to 50F hotter than Ambient. The Load & Inflation tables are based on tires being at whatever the air temperature is.

You are spot on about running a bit slower than the tire max rating (65 for ST type tires and 75 for most others). Only other comment is that with multi-axle trailers you want to run the tire max as that will lower the internal structural stresses.

 

[BobX2]

I think that is a great question by Grumpy, and a total lack of an answer to it. While I agree that the wheel diameter has nothing to do with it, the tire diameter would make a big difference. A taller tire is turning fewer rpm's than a shorter tire, while traveling at the same speed. Typically, the larger the wheel, the taller the tire is that is mounted on it. So a shorter tire mounted on a, lets say 14" wheel, is turning far more rpm's than taller tire mounted on a larger wheel, while both traveling at 65 mph. This whole 65 mph rating has to be directly related to how fast a tire is spinning, does it not? It would then seem that the shorter the tire, the lower the max mph should be. Anyone else confused about this? No way that one size fits all in this application of the 65 mph max speed ratings for ST tires. I'm not one to drive fast, but I sure would like to hear an explanation on this.

 

[danemayer]

Re: Towmax by Power King – Facts

Bob,

Let say you switched from the Towmax 235/80R16 to the 235/85R16, which would change the outer diameter of the tire from 30.8 to 31.7". That's about a 3% change. But I noticed that the larger tire carries a slightly higher load rating - close to a 3% increase - so perhaps the increased tolerance to heat buildup was assigned to the load spec rather than to the speed rating.

 

[tireman9]

Danemayer & Bobx2
Sorry I guess my attempt at humor fell flat on its face. I will try again w/no smart alic reply

We need to separate tire revolutions per minute (RPM) and vehicle traveling speed (MPH.)
While there is a relationship they are not interchangeable.

Grumpy asked "If I am doing 65 mph and my TV has 18" tires but my towed vehicle has 16" tires how fast are the towed vehicle tires going?" I assumed he was asking what MPH would the 16" tires be traveling. Since he didn't provide the details of exactly what tire size he was thinking of, there is no way to answer that question.

This question mixes vehicle speed (65 mph) with two different wheel diameters.
If the TV is going 65 MPH so is the TT and the wheel or tire diameter doesn't make any difference to the MPH of either vehicle
BUT clearly the tire RPM will be different depending on the OD of the tires we are talking about.

NOTE Wheel diameter can be different but a low aspect ratio tire (maybe 45 or 50) on a 18" dia wheel can have the same OD as a high Aspect ratio (maybe 75 or 85) tire on a 16" wheel, but we need to talk specific tire size to answer the question.

Now when a tire is given a "speed rating" or max speed, it is not stated as RPM but as MPH. A Large OD tire will turn fewer revolutions per mile than a small OD tire does.

Tires are normally tested to a MPH spec not an RPM spec, so we need to stick to just one measure of speed.

Hope this clears up everyone's question on this topic.