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Doh!!! Tire Pressure


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25 replies to this topic

#1 OFFLINE   Kelleytoons

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Posted 01 October 2014 - 09:05 AM

Well, I had another Homer moment today but in the hopes it might help someone else in the same position I thought I'd share.

 

We have a little over 2K worth of miles on Maximis, at a little over two months of ownership.  In that time I haven't checked the tire pressure... at all.  

 

I've put air in our Durango twice during that period of time and in my defense this new technology stuff is still confusing this old man.  For some reason I thought that, just like I didn't need to worry about oil changes for quite some time, that Maximis would tell me when I needed to put air in.  I could have sworn I read something like that.

 

Except -- in putting air today in the Durango I took a quick look at the manual for the C-Max and see that it only *warns* you when the pressure is very low.  Not when you should be putting it in as usual.  Doh!  Okay, so I measure it and it seems *really* low to me (about 30 psi cold).  The tires are all rated at 51 psi max, so I figure I had better put at least 45 in them, which I do.

 

Then I drive to my usual location and back, a round trip of 24 miles I make at least twice a week (so I'm *real* familiar with the mpg I should be getting).  Normally I get around 45 (it's a mix of city/highway, with the emphasis on the highway) and, of course, it always starts from a cold engine both ways (before and after tennis <g>).  Today I get 56 mpg.

 

Now -- it's a bit cooler than usual (near 80 degrees when it's been in the mid to high 80's) so perhaps the A/C (which I always have set for 73) is working less, but I also have to think that at least some of that was due to the tire pressure.  If that's true, the tires have mostly been low since we've got it (because I noticed how different the ride is right away -- a bit rougher but not at all unpleasant).  

 

I'm going to start paying closer attention to tire pressure.


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#2 OFFLINE   Jus-A-CMax

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Posted 01 October 2014 - 09:31 AM

Ssshh...don't tell anyone else Kellytoons but most hypermilers (moi included) run the tires at the max psi. yes, we are sacrificing some road comfort for the MPG as we screech around the corners... ;)

 

Add a center grill cover and the gas pods and we'll see you in the 700 Bar club  :rockon:


Edited by Jus-A-CMax, 01 October 2014 - 09:32 AM.

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#3 OFFLINE   RockwallRick

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Posted 01 October 2014 - 09:57 AM

Tire pressure is very important for mileage as well as tread wear. For those that can't seem to remember to check their tire pressure you can have your tires filled with nitrogen. :rockon:


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#4 ONLINE   ptjones

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Posted 01 October 2014 - 10:02 AM

I'm thinking pressure is worth about 1mpg improvement well worth doing. :)

 

Paul


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#5 OFFLINE   C-MaxSea

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Posted 01 October 2014 - 10:17 AM

Good reminder Kelleytoons, always good to maintain appropriate tire pressure.  We are sticking with 45 psi cold for now - comfortable & efficient.

 

and BTW, you will find 700 mile tanks require no mods or super techniques to achieve - just careful, safe & sane driving ("Common Sense Driving" as you so appropriately coined)  :).  If your routes are predominantly urban/suburban arterial or rural roads 700 is like falling off a log (for you at least given the opportunity).  Scuba leads the way for you on that in Florida.  Unfortunately for us, we are on the freeway most of our miles (roughly 70%); so no 700s yet (but we are still 'breaking the car in').

 

EV when you can, ICE when you must, and never pass up free float/free HVB charge miles,

Nick


Edited by C-MaxSea, 01 October 2014 - 10:58 AM.

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#6 OFFLINE   Jus-A-CMax

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Posted 01 October 2014 - 10:24 AM

Nick is right, mid 600s is there is 50% freeway but -it is- possible to break the 700 to low 700s even with some freeway, jus have to be judicious with the city portion. 800s are tough with any freeway involved - especially with a wifey who insist on the freeway and AC on... :doh:


Edited by Jus-A-CMax, 01 October 2014 - 10:25 AM.

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#7 OFFLINE   Kelleytoons

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Posted 01 October 2014 - 10:48 AM

I'm getting *real* excited now to see just how much better I can do, both with the higher tire pressure as well as the coming cooler temps (which for us in Florida means no heating or cooling, but just ventilation and perhaps even some open window driving around town).  700 does seem achievable (particularly since our "highway" speeds are not more than about 55 mph the way this old man drives).


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#8 OFFLINE   Jus-A-CMax

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Posted 01 October 2014 - 11:05 AM

...Jus do it  ;)



#9 OFFLINE   scottwood2

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Posted 02 October 2014 - 11:51 AM

I wonder about the value in these systems too.  My 08 truck has them and the sensors need to be replaced.  It is $240 for the 4 sensors.  I am having a tough time deciding on wither I should replace these or not.  My other half drive this and I don't know how many times I have been told, "oh BTW the light is on for low tire pressure".  When I ask how long I usually here "oh I don't know at least a few weeks now".  I have many times noticed this by looking by eye at the tires and find out that the warning has been on but I did not know about it. 

 

Then there was another time that the dash told me that the rear tires were low.  I filled them up and it still said that it was low so we thought something was wrong and just lived with it.  Some time later I decided to check the front tires with a gauge because they looked kind of low.  Sure enough, they were low and when I filled them up the rear pressure warning went away.   When they rotated the tires they did not reprogram the sensors. 

 

Guess it would be good to have everything working again but this seems like a lot of money to replace these for another 6 to 8 years.  It is kind of nice though that the truck actually tells me the pressure in each tire.  The idea is to save fuel by having these but I wonder how many people ride around with these lights on because they still don't bother to fill up the tires. 

 

I think I will check my tires on the Max tonight as well.  Thx for the post.



#10 OFFLINE   Kelleytoons

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Posted 02 October 2014 - 12:17 PM

Since my tires were at 30 psi cold (which I do believe is *really* low) I have to question how low they would have to go before a light would come on.  

 

I also think that it's not too much to just check once a month -- that's why I have a tire inflator in the garage and what I've done for, oh, the last half century or so on all my vehicles.  Yep, I'm a lot older, but I think I'd have to be near death before I couldn't perform this simple check (and then fill as needed).  So a light to tell me?  Um, perhaps not so much.

 

The oil change light is another thing entirely -- again, when I was changing oil every 3000 miles or so (as I still do with the Durango, although I've started letting it go longer) it wasn't needed, but I'm not so sure I'd remember the changes with Maximis being so seldom.  But we'll see.



#11 OFFLINE   kostby

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Posted 02 October 2014 - 12:28 PM

In spite of the text in the manual that says 'one or more', I truly believe the TPMS system ls primarily designed to alert you when there is ONE low tire.

As long as all of them are nearly the same pressure, the TPMS is not going to warn you. 

Attached File  Screen Shot 2014-10-02 at 1.25.55 PM.png   77.29KB   0 downloads

 

Our car was delivered with all tires at ~32psi! I checked tire pressure after the first time I drove it on the highway, because the handling felt 'squishy', as if the tires were filled with jello, likely from sidewall flex. My other daily driver has always been shod with H-rated or V-rated tires, so I'm used to crisp handling. Adding 13psi  ~45psi cold improved the handling significantly, and probably bumped gas mileage up a couple of mpgs too. I haven't tried the sidewall-indicated max of 51psi yet.


Edited by kostby, 02 October 2014 - 12:36 PM.


#12 OFFLINE   Plus 3 Golfer

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Posted 02 October 2014 - 02:21 PM

The service manual indicates each tire is monitored and " the TPMS warning indicator and the message center displays a message when a fault is present or when the tire pressure falls below the low pressure limit."  I don't know what the threshold is but when I had a screw in one of my tires on my C-Max, the indicator came on and the pressure in that tire was down to IIRC around 22- 24 psi.  The other 3 tires were at 44 psi +-.

 

TPMS systems that do not use pressure sensor but the ABS wheel speed sensors to indicate a tire issue are based on wheel speed differences not pressure. So a fault is triggered when one wheel spins faster than the others and a threshold is reached regardless of pressure.  I don't recall what the speed sensing TPMS algorithms generally use for a differential speed and what that equates to in a tire pressure difference.  But it is probably a fairly large pressure difference.  Also, different size tires / wheels say on rear wheels vs front wheels can trigger a fault with TPMS speed sensing system. Obviously, the advantage using the ABS speed sensors is lower cost as TPMS pressure sensors aren't needed. 


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#13 OFFLINE   jdbob

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Posted 02 October 2014 - 04:14 PM

TPMS systems that do not use pressure sensor but the ABS wheel speed sensors to indicate a tire issue are based on wheel speed differences not pressure. So a fault is triggered when one wheel spins faster than the others and a threshold is reached regardless of pressure.  I don't recall what the speed sensing TPMS algorithms generally use for a differential speed and what that equates to in a tire pressure difference.  But it is probably a fairly large pressure difference.  Also, different size tires / wheels say on rear wheels vs front wheels can trigger a fault with TPMS speed sensing system. Obviously, the advantage using the ABS speed sensors is lower cost as TPMS pressure sensors aren't needed. 

 

That's what is called an "indirect" measurement, and our cars do not do that.

 

Our cars use a "direct" measurement so there is indeed a battery operated pressure sensor (and radio transmitter) in each tire. That's why they cost $50 or so each.



#14 OFFLINE   ScubaDadMiami

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Posted 02 October 2014 - 04:33 PM

I no longer trust the dealer to monitor the tire pressures. Like Kelleytoons, I never bothered to check my pressures, and I did this during the entire first year of driving. So, Kelleytoons, it could be worse. Think of how you would feel after letting a year and 12,000+ miles go by with low pressures. Luckily, even with this, I still made my 600, 700 and 800 mile tanks. :)

 

I never bothered to check, because I went to the dealer to get The Works at 5,000 miles, and then I got the 10,000 mile service done at just over 9,000. At the 9,000 service, done just before my 5,400+ mile trip to New England and back, I paid extra for rotation and balance, and I requested fill pressures of 38 PSI. So, the dealer had at least two chances to fill my tires during its first year. From what I can tell, they never did it, and it looks like they only did the rotations and balancing. The TPMS light came on in just a few weeks after my service, although I had driven about 2,000 miles on the car by then.

 

My recollection is that the TPMS light to comes on at 34 PSI. When I was driving from Miami to New England and back, my light came on just as I crossed the border into New Hampshire. I got out, and everything looked fine (no flat or obvious signs). I topped off the next day, and the light went off. I've not had problems since then. There was nothing found on the tire that caused leaks, and I've not had a leak since topping off, so I can only conclude that nobody ever topped off the tires properly when getting service done.


Edited by ScubaDadMiami, 03 October 2014 - 01:30 PM.


#15 OFFLINE   Plus 3 Golfer

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Posted 02 October 2014 - 07:12 PM

That's what is called an "indirect" measurement, and our cars do not do that.

 

Our cars use a "direct" measurement so there is indeed a battery operated pressure sensor (and radio transmitter) in each tire. That's why they cost $50 or so each.

Correct my response was to set the record straight on Kotsby's comment about our C-Max - "As long as all of them are nearly the same pressure, the TPMS is not going to warn you."  That is not correct for our C-Max as if one or more of the tires drop below the threshold pressure a TPMS fault will be indicated.   After a quick search I believe the final rule of TPMS threshold activation level is the greater of 75% of the placard pressure which for our C-Max would be 28.5 psi or a table based on type of tire which is lower than the 28.5 psi.

 

There is debate about the indirect system vs the direct system but both meet the safety standards for a TPMS.  However, I think people mistakenly believe that a TPMS mitigates the need to check tire pressure regularly.  Obviously, given the threshold pressure level for triggering a fault and the inability to capture gradual pressure loss, one could be driving on under inflated tires for quite some time believing everything is fine if they solely rely on TPMS to alert them to a pressure issue.  


Edited by Plus 3 Golfer, 02 October 2014 - 07:52 PM.

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#16 OFFLINE   kostby

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Posted 03 October 2014 - 12:56 AM

Thanks for the amplifications and clarifications!

Either ABS or pressure-sensing implementation still results in a system that serves primarily to confirm that the loud noise you're hearing and the vibration you're feeling is your now-blown-out tire flapping around what's left of your expensive alloy rim.

 

Notifying me that any of my tires, manufacturer-labeled as capable of 51psi, have only 28psi remaining is way too little, too late IMHO.

 

A TRULY USEFUL TPMS system should let the driver set a higher minimum notification pressure, OR set a higher notification threshold percentor both.
 
Seems like a Catch-22 anyway:

If there is a small puncture, then the onboard tire mobility kit with pump equipped with stop-leak ensures that you'll need to replace the TPMS sensor.

If it's a sudden blowout, then the onboard pump and stop leak is useless, and the TPMS sensor might be the only thing salvageable as you pull to a stop on the now-ruined tire and rim.

 

The TREAD law mandating TPMS in the US was apparently a legislative response to the deaths and injuries resulting from mid-1990's Ford Explorers with OEM Firestone tires that suffered tread separations and blowouts leading to rollovers. http://en.wikipedia....umentation_Act 

http://www.forbes.co.../tireindex.html

 

Another government attempt to mandate a technological solution to a social problem:  Many people just don't take good care of their cars!

 

Many of us here are probably old enough to remember the days of the Full Service gas stations when station attendants would fill your car, clean your windshield, and offer to check the air in your tires.

Self-service gas refueling is still prohibited in a few communities in Massachusetts.

 


Edited by kostby, 03 October 2014 - 01:03 AM.


#17 OFFLINE   Kelleytoons

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Posted 03 October 2014 - 05:08 AM

Actually, all I really want is this ability for Maximis (well, the rockets would *also* be nice...)

 

https://www.youtube....AME9fAA-4#t=129



#18 OFFLINE   Plus 3 Golfer

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Posted 03 October 2014 - 06:52 AM

 

...

Notifying me that any of my tires, manufacturer-labeled as capable of 51psi, have only 28psi remaining is way too little, too late IMHO.

 

A TRULY USEFUL TPMS system should let the driver set a higher minimum notification pressure, OR set a higher notification threshold percentor both.
 
...

 

Agree, the pressure of each tire could be displayed to the driver with adjustable warning levels say on the hybrid power flow screen or in a ETM screen.  Why isn't it available? - probably because consumers are more interested in "convenience" tools like adjusting the automatic volume sensitivity level of the radio to speed than "safety / social" related tools (see EPA quote below) and manufacturers generally need someone with a "big stick" to force them to implement stuff that might improve safety and reduce social costs. 

 

Also, if we had the PID codes for the TPMS sensors, we could view the data via the OBDii port on the various apps like Torque App.  

 

"Check your tire pressure regularly. Under-inflation increases tire wear, reduces your fuel 
economy by up to 3 percent, and leads to increased emissions of greenhouse gases and 
air pollutants. If you don’t know the correct tire pressure for your vehicle, you can find it 
listed on the door to the glove compartment or on the driver’s side door pillar." -EPA

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#19 OFFLINE   ScubaDadMiami

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Posted 03 October 2014 - 01:33 PM

When my light came on, I checked the pressure before filling, and it was at 34 PSI, and I believe that the other three tires were at 36.



#20 OFFLINE   Kunari

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Posted 06 October 2014 - 11:19 AM

Thanks for the reminder not the trust the dealer to check your tire pressure.  I've got my Max in there today to get the splash-guards installed --I had the dealer include them *installed* as part of my purchase.








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