Pressure Warning light/buzzer came on - Fiberglass RV


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Old 10-01-2007, 05:39 PM   #1
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My tire pressure warning light/buzzer came on the other day. I'm now the proud new owner of a tire pressure gauge (why, why, why did I not have one before??? ) Anyway, the tire pressure on the sticker calls for 35 psi for front and rear. All tires were down (probably from weather changes) but the front tires were only down about 2 psi , and the rear were down 7 psi.

So my question - did the dealer put +/- 5 psi lower pressure in the rear tires the last time they had it in the shop, or did the rear tires lose more air for some reason? (Towing?)
Is there a reason why the dealer might have put more air in the front than the rear?
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Old 10-01-2007, 05:47 PM   #2
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My tire pressure warning light/buzzer came on the other day. I'm now the proud new owner of a tire pressure gauge (why, why, why did I not have one before??? ) Anyway, the tire pressure on the sticker calls for 35 psi for front and rear. All tires were down (probably from weather changes) but the front tires were only down about 2 psi , and the rear were down 7 psi.
So my question - did the dealer put +/- 5 psi lower pressure in the rear tires the last time they had it in the shop, or did the rear tires lose more air for some reason? (Towing?)
Is there a reason why the dealer might have put more air in the front than the rear?
If my assumption is correct that you have some sort of tire pressure warning system with things attached to the valve stems of tires then you're going to have the warning system indicate a low pressure situation from time to time. There's no real good way of really sealing anything attached to the end of a tire valve system. Air is always trying to open the seal. The Schrader valve that's in the stem is designed so that the more pressure inside the tire the tighter the seal. No way to do that with stuff on the of the stem.
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Old 10-02-2007, 09:45 AM   #3
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Having seen the tire pressure monitors which are installed on the valves, I have wondered about leakage myself. If the monitoring system is original equipment, then it will not have this type of sensor; instead, it will use sensors mounted to the wheel inside the tire, or it will just compare wheel speeds - neither of those systems will cause leakage.

I would not expect the extra load of towing to cause faster air leakage.

The consistency - rear tires lower than front tires - is interesting, but I can't think of any physical reason why the front and rear tires should loose air at different rates.

The dealership tech, on the other hand, could have any reason for picking inflation pressures. What does the sticker on the vehicle (usually on the driver's door jamb or inside the glove compartment) say the pressures should be?
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Old 10-03-2007, 09:30 AM   #4
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If the monitoring system original equipment
Yes, it is the Factory installed tire pressure monitoring system we're talking about here.

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The dealership tech, on the other hand, could have any reason for picking inflation pressures. What does the sticker on the vehicle (usually on the driver's door jamb or inside the glove compartment) say the pressures should be?
The sticker calls for 35 psi on all tires, front and rear.

My assumption is that the dealer tech put 5psi less in the rear tires.
If it matters, the truck is RWD when not running in 4WD mode.
Is there any benifit to running with a lower pressure on the rear tires?
Any guess as to what will that do to my gas mileage? I'm watching now that I've got all 4 at 35psi to see if I notice any difference and hoping for some improvement.
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Old 10-03-2007, 11:04 AM   #5
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The sticker calls for 35 psi on all tires, front and rear.
If that's right at the maximum pressure shown on the tire sidewall, it's possible that the ideal inflation pressure at full load would be even higher if suitably rated tires were used... that's the situation for my Sienna.

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Is there any benifit to running with a lower pressure on the rear tires?
Yes, because the rears carry less load when there's nothing in the box. Matching pressure to load provides the best ride and handling. I assume that the factory setting are chosen to be appropriate with a full load; using lower pressures when not loaded would probably be better, but risks underinflation if you forget to pump them up when you carry stuff or tow.

Underinflation is bad for traction, stability (especially important for the rears when towing), and reliability. I'd rather risk being higher than ideal than being too low.

Since most people don't use their pickups as trucks, I would not be surprised if the dealer techs routinely set the rears lower for ride comfort... a dangerous thing to do without educating the owners.

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Any guess as to what will that do to my gas mileage? I'm watching now that I've got all 4 at 35psi to see if I notice any difference and hoping for some improvement.
It should make a difference, but I don't know if you'll notice it. I won't even guess at a specific number.
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Old 10-03-2007, 12:21 PM   #6
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My Subaru Legacy wagon's sticker calls for 32 PSI in front & 30 PSI in the rear - interesting as one would expect a wagon to be carrying passengers/cargo and need as much in the rear as front. It is all-wheel drive of course, so I don't imagine any advantage to more pressure on front as you might want with front wheel drive?
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Old 10-03-2007, 01:02 PM   #7
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My Subaru Legacy wagon's sticker calls for 32 PSI in front & 30 PSI in the rear - interesting as one would expect a wagon to be carrying passengers/cargo and need as much in the rear as front. It is all-wheel drive of course, so I don't imagine any advantage to more pressure on front as you might want with front wheel drive?
I think this is very much like Lainey's truck: front-heavy unless fully loaded. The recommended front/rear difference is quite small.

I don't think which wheels are driven really matters. You want the best lateral and braking traction, stability, ride, and durability for each tire (and must compromise between those) regardless of whether or not drive traction is needed. Slight adjustments from ideal are used to adjust the front/rear balance of the handling, and that may be a reason for the difference in the Subaru.
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Old 10-05-2007, 07:44 PM   #8
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My '98 Ranger pickup is the other way around. The Ford sticker says 30psi in front and 35psi in rear.
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Old 10-06-2007, 10:03 AM   #9
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My '98 Ranger pickup is the other way around. The Ford sticker says 30psi in front and 35psi in rear.
Since pickups commonly have a higher axle capacity in the rear than the front, this makes sense to me... the higher rear pressure may be required for the tires to have sufficient load capacity.
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Old 10-06-2007, 11:09 AM   #10
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Some reasons for tire pressure differences,

Many tire techs don't put the emphasis on precision tire pressure that we do as individuals.
Most tire pressure gauges don't even read the same, I have 3 of the pen type gauges and none of them read within 5 lbs of each other. When I lived in the mountains of Virginia I put (by a Dial type gage) 3 or 4 lbs more than recommended because of the switch backs and curves in the road to keep the edges of my tires from wearing, worked very well, when I tow my Casita or have a heavy load I add 5-7 lbs to the rear wheels of my truck, that also works well for me, I don't use a wdh. On the Casita I use the max recommended pressure. These are done with ths same gauge whether its properly calibrated I know not, but I try not to get all bent out of shape over a pound or two. When I towed 4 wheel trailers I kept the pressure the same on all 4 tires. In a front wheel drive van with all the weight in front the manufacturers probably figure on most folks normally driving with minimum weight in back. I would still keep all tires the same pressure (with front specs being benchmark) The vans (fwd) would normally be towing with a wdh I would think which would put more weight on each of the wheels I think I would try 2 or 3 pounds more in each tire, It would take some pressure off the power steering and also might add to your mileage. All just my opinions but worth a try
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Old 10-26-2007, 04:16 AM   #11
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Unfortunately, tire pressure is a highly neglected part of a vehicle. I'm guessing that the 'dealer" didn't pay any attention to the tire pressure on your vehicle and the rear tires should not go down more simply because you tow a trailer. Be advised that the tire pressure shown on your tires is the maximum pressure your tire should have when carrying the maximum load, not the pressure you should use on a day to day basis. The pressure shown in your owners manual or on the vehicle drivers door is actually the recommended pressure your vehicle should have for day to day driving. Ron
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