Hot tires!

[EngineerMike]

Sounds like underinflation can be ruled out entirely (I'd run a manual guage check on the VMS reading if you haven't which is unlikely). The rears at least are overinflated, but sounds like both, and that should mitigate unreasonable tire heat gains. Overinflation shouldn't hurt you while completing the diagnosis on this; it'll mean that the contact patch is smaller than optimum for steering, but sidewall support (to avoid tire damage) is OK or better. The contact patch thing won't matter till you need to make a sharp, somewhat high speed turn (the kind that sends your dishes flying), except in how it matters to the ride.

Sounds too like the tires themselves are not actually overly hot. The VMS is showing a 10psi gain to stady-state rolling temps & therefore pressures. My guess is that the tire pressure gain is a lot more indicative of the temp gain than the temp reading (which seems good for wheel temp gain). IIWY I'd, till you get next to infra-red readings to match to the VMS, assume tire temp equal to half way between ambient & wheel temp, or maybe ambient plus 60% of the diff. If change in pressure is proportional to change in temp, assuming starting temp of 80F, the 8% increase in front tire pressure (10psig/(110psig + 15psia)) equates to air-inside-the-tire temp of about 123F (won't bother here w/the math converting to degrees absolute), which is near the 60% mark from your earlier posts. Of course that doesn't account for the differences in heat gains/losses between tire & wheel & outside air/pavement. But it still seems to show that the alarm condition is not really indicative of a tire heat problem.

Related subject- you said in your earlier post that the wheel temp guages were an "option" that was new on the 06; were you saying it is newly standard on the 06, or that you paid extra to to oder it as an option? Thanks, (I'm wondering how mine will come). Mike

[Audrey & John]

We did indeed run a manual check on the pressure to see if it matched the VMS readings - within a few PSI - definitely close enough. At least we verified 4 of the six - we are missing the extensions to get to the inner duals.

At this point both our dealer and WRV are looking into the issue and will get back to us. We don't have to drive anywhere for a while, so we've got time to get this figured out. We'd really like to be sure that nothing is wrong with our wheels either.

The tire temp sensors are a published option for the 2006. The VMS system itself is standard in the 2006 (i.e. included in the base price), the tire temp/pressure sensors option is $1,798.

So - if you want that option, see it's not too late to add it to your order. They put the wheels on pretty early in the build process (part of the chassis assembly). It appears that their wheel subcontractor (Les Schwab) sends them the wheels with the sensors already installed according to some of the documents we got for the coach.

Audrey

[Wayne R]

Today I made another trek to Springdale AR to get my batteries replaced due to the float issue. On the way back it was 98 degrees and I experienced some high tire temps. The left inside dual got up to 160 degrees causing a yellow condition and the right outside dual got up to 158 just 2 degrees from a yellow alert, the left front hit 153 the rest were in the 140's. My toad was also showing high temps both front tires were at 136 and the rears were at 126 and 122.

When I got back to the resort I dug out my IR thermometer and found the blacktop to be 137 degrees. I also checked my 2 hottest tires and they were 133 degrees at the sidewall and the rims were 112 everywhere I checked. Pressures were up 15-18 PSI from cold, varying by temp. The hottest 2 gaining 18PSI and the coolest 15. There was about 10 minute delay after parking so the tires and rims had time to cool down

I intentionally used very little brake and relied on the Jake brake. I am just sharing data I am not convinced there was a problem. I had not seen any updates recently and assumed that Audrey and John were satisfied everything was OK. I previously had never seen these temps, which were similar to what Audrey and John had seen. My red alarm is set at 180 degrees but would have probably pulled over at 165. After making a stop at a stop sign the tire at 160 cooled down and went green for about 5 minutes then hit 160 again.

[Tom and Patty]

I don't have the Smart Tire System but you guys got me curious.

Being in the tire business for many years I've requested Bridgestone as to what temp reading would be too high? I've never discussed tire temp at any length, just pressures.
I'll also call their tech service tomorrow. If I get an answer I'll be sure to copy it and post it.

[Audrey & John]

SORRY! I've been so meaning to post because we DID get some satisfactory answers to our question. WRV looked into it quite a bit. We also talked to Toyo and Meritor (the makers of the wheels/axle assembly).

Based on our experience and documentation, WRV researched the issue further and is now setting the yellow alarm to be 180 and the red alarm to be 190 at the factory. Quite a difference!

Toyo said - well the tire next to the tread should not exceed 200 degrees. This is measured with a probe inserted 1 inch deep where the tread meets the tire wall. In this position the probe is close to the steel belts. They cannot comment on the temp at the wheel or of the air in the tire. They have no such data - does not compute.

Meritor said - the wheel lubricant doesn't start breaking down until the end of the hub reaches 250 degrees or 180 + ambient temp - whichever is lower. They were not at all concerned that the tire hub was very hot to the touch. As long as the end of the hub didn't exceed 250 degrees, it's OK.

Based on this we decided that the alarms were indeed set too low, and WRV came to the same conclusion with their own research.

We are setting our yellow to 160 and our red to 180. The reason for 160 is simply to wake us up if one of the tire temps starts changing quickly compared to the others indicating some potential failure.

We also have an infrared therm gun on order.

Wow - black top at 137 degrees. I'm not surprised. Those are the kind of conditions I think we were experiencing. I bet it's worse in TX now - it's simply been BRUTAL here heat wise.

John says that a infrared gun will not give an accurate reading on metal (in particular shiny metal). Asphalt, rubber, paper, any painted surface - reads OK. Metal - they recommend you paint with a flat black paint to get an accurate reading.

Audrey

[Wayne R]

Audrey, glad to here you got some good answers.

I have been running 160 yellow and 180 red from the beginning on recommendations from Dickman Tire's web site http://www.dickmantires.com/.

On my 200 Alpine I had the brake caliper hang up on the left front, the hub got so hot it blew the oil seal and melted the ABS sensor. Curiously the tire temp only hit 169. The alarm on the smart tire monitor got my attention before more serious damage occurred. Same thing happened on the other side a year latter. Don't everyone panic this was isolated to a few coaches and WRV replaced all 4 calipers at their expense off of warranty.

Great system not perfect but a good tool.

[Wayne R]

That may explain why my wheel was cooler than my tires per the IR thermometer

[Audrey & John]

Hi Wayne - yeah I remembered your settings of 160 and 180. Turns out to be a pretty good working choice it seems! We're just not comfortable setting our yellow as high as 180 and part of it was remembering your story. But mainly it's the - "Hey, one tire is acting funny" situation we want to recognize early. 150 was just too low and became a nuisance alarm.

We feel so much better now that we've educated ourselves on this subject.

Audrey

[Audrey & John]

Most IR guns have a fixed emissivity setting of 0.95; the more expensive guns have adjustable emissivity. Here is the link to Raytek's Emissivity of Most Common Materials and what to do if you can't adjust the emissivity setting on your IR gun.

John

[Wayne R]

Thanks, mine is a real cheap unit, no adjustments available. I bought it to check temps on my RC helicopter works fine for that.

I don't think I will be painting my wheels anytime soon but a piece of masking tape would be OK.

200 for red does seem high, if I approach 180 I will pull over and let things cool down for sure.

[SteveS]

John,
You are correct that most IR thermometers have fixed emissivity of .95, because that is the most common level of non-metalic or non-shiney surfaces. Regarding painting a surface, you will find that if you put masking tape on the object you want to measure it will be very accurate. Just give the tape a chance to get to temperature of the object...a few minutes. It is not necessary to paint it.

[Tom and Patty]

I got my answer from Bridgestone. Sounds like everyone is on the right track.

Here is my question and their answer.



<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> With air pressure and tire temp sensors installed in aluminum wheels, what kind of temperatures should be observed while driving in 90 to 100 degree temperatures?

What air temperature reading would be too high? We are using the Smart Tire system.



Thank you,

Tom Dietrich

Am-Pac Tire Dist., a BFS distributor in California.







Dear Tom,



Thank you for the opportunity to be of assistance.



The answer to your question depends on a number of factors, and quite frankly, there is not a hard and fast rule.



There are basically (3) types of tire temperature measurement

Probes inserted into the tire

Contained air temperature (which your system uses)

Tread (surface) temperature



A probe inserted into the tire – into either the belt edge or the bead area – the hottest points of the tire – is the most accurate method; however, it can only be performed under controlled conditions.



The contained air temperature method is the next most accurate, however, it is affected by the mounting system of the sensor – if the sensor is attached to the wheel, it will pick up heat from the wheel (which is picking up heat from the brake drum); and if it is attached to the tire interior, it will pick up heat from the casing.



Tread (surface) temperature is the least accurate, since measurement is normally performed by a hand held unit, thus hampering repeatability, plus the question of where do you measure? The ribs will be cooler than the grooves, and the center will be cooler than the shoulders, etc.



So, while all this has so far done little to answer your question, hopefully it has shed some light as to why I am being a bit reserved in my answer.



Now, what can I say to try to address your question?



While this is not set in stone: A very general rule of thumb is that a properly inflated/loaded tire, when up to operating temperature – one hour+ operation - will typically run about 60 degrees F. hotter than the ambient temperature. Anything above 200 degrees F. could lead to tire degradation and you need to investigate for a problem.





I hope this has answered your question to your satisfaction; if not, or if you have any other questions, please feel free to contact me. </div></BLOCKQUOTE>

[EngineerMike]

Now THAT was a very useful post. Thanks.

For those w/the tire temp monitor system, it would be a fairly simple thing to calibrate your alarm levels. First get an infrared thermometer. Then record cold temps tread/shoulder interface & wheel (on the metal). Then go for a country drive, stop at an offramp & repeat measurements, all six tires & wheels. Check against the "ambient + 60 degrees" and note the adjustment for your tires/wheels as applicable. Then reset alarms as needed.
E.g. if your my run ambient + 50, I'd set alarm @ 100 (allowing for a good hot day) + wheel/tire differential + 50 + however many degrees of comfort factor I figure prudent before needing the alarm. If wheels are 40 degrees hotter (where your sensors are), and you like a 10 degree spread to avoid nuisance alarms, that'd be 100 + 40 + 50 + 10, or 200 degrees, for a set-it & forget-it alarm. For tighter monitoring, substitute high ambient you expect during travel + 40 + 50 + 10, & reset when ambient expectations change. As a practical limit, anything below 150 sounds like an invitation to lotsa monkeying w/alarms.

Thanks Tom.

[EngineerMike]

Just drove from Reno to Auburn, mostly downhill. Stopped twice to check tire temps w/infrared. Ambient air ~78.
Tires varied by about 15 degrees, w/about +10 degrees on the sunny side. Inside rear duals wer about equal, and were the hottest @ 137. I measured @ the edge between sidewall & tread. Some variation (~8 degrees) from one spot to another along the circumference; I'd theorize either minor variations in tire construction or in rubber emmissivity, prefering the former but w/out any evidence to argue either way.
Temps in the field of the sidewall & tread were lower.
Wheel temps varied a lot depending on place taken. Nowhere was the shiny aluminum too hot to touch, & read about 110-125. Inside the fronts, between the beads was hottest @ ~160 (& matte surface so reading should be in the ballpark). Inside rear duals (painted steel wheels) were ~175 @ hottest.
Strange, but the flange lug-nutted to the wheel, where conduction would transfer brake heat, wasn't the hottest. Instead, the portion radially outward from the brake was hottest, indicating convection & transmission as primary routes of brake heat transfer.
Toyo 120Z's, 110psi.