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Old 04-28-2015, 02:02 AM   #1
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Default Heat and tire pressures

We finally got out for a few days trip starting today, to see how some of the winter project stuff worked out, but mostly to check out the rear axle replacement.

The old semi-floater axle always would be very hot at the rear wheel and hub, usually 20-30 degrees F or more hotter than the front hubs. I took the temperature gun with us and checked the hub temps a few times after highway runs, with almost no braking heat. The rear hubs on the full floating replacement axle are running the same as the front hubs, with both front and rear testing at only about 20 degrees above ambient. The rear carries about 1000# more weight, so this is pretty good, I think.

We were also doing some tire pressure testing to see how handling was at lower pressures, so I also checked the tire pressures when hot by watching the TPMS. The rear tire pressures did not go up nearly as much as the did with the old axle. They went up only 2 psi, which was the same as the fronts, where in the past ,the rears would go up 4 to 5 psi. I checked the tire temps with the same temp gun, and the tire temps were nearly identical to the hubs, at 20 degrees above ambient, and the same front and rear. 10 degrees is normally will give 1 psi, so it all makes sense.

All of this brought back some comments that Photog had made in the handling and tire discussions. He was concerned about his rear tire pressures increasing too much. Higher capacity tires didn't help, IIRC, which seemed very odd. Based on what we saw today, it may be very possible that the pressure increase that Photog sees is coming from his rear axle running hot (he has the same one as we used to have) and heating the wheels and tires. It would be interesting to see if his axle runs as hot as ours did.

We all have seen increased pressure from heaving braking heat, but I never would have guessed that the rear axle/wheel bearing heat might also be able to do it. This may also help explain why Chevy owners often talk of harsh rear ride, which would only get worse if the rear tires are getting harder than they should.

All very interesting.
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Old 04-29-2015, 12:14 AM   #2
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Default Re: Heat and tire pressures

That is interesting. Maybe Photog will catch this topic and compare the front and rear on his van. I notice the temperature affect on the ride in the car this time of year. There can be a 50F degree swing in ambient temperature in a period of days.
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Old 05-01-2015, 02:34 AM   #3
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Default Re: Heat and tire pressures

Just go home, after 400+ miles on the replacement axle. Temperature comparisons above were typical. Front and rear hubs running the same temp at about 20* above ambient, with the tires about the same temp. This is in 60* ambient type temps. I did shoot the temp of the cover on the differential, which should be just about the oil temp, and it was at 140*.

I had figured that the higher capacity axle would do better, but I am very surprised by how much. I think that says more about how over stressed the original was, than how wonderful the replacement is (it is a plain old full floater axle like they have used for decades). Getting the significantly lower rear tire temps is a huge plus, I think.
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Old 05-01-2015, 02:49 AM   #4
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Default Re: Heat and tire pressures

Sounds like we should change our semi-floating differential fluid more frequently on our heavy B's. I just changed mine at 60,000 miles, but should do more frequently in the future.

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Old 05-01-2015, 03:27 AM   #5
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Default Re: Heat and tire pressures

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Originally Posted by peteco
Sounds like we should change our semi-floating differential fluid more frequently on our heavy B's. I just changed mine at 60,000 miles, but should do more frequently in the future.

Pete
2006 Roadtrek 210P
I certainly would agree with the assessment! You might also consider overfilling it by a bit. I read a few places about filling it with the nose down, as only the rear jacked up, to get a bit higher level. That will let more oil down the tubes to the wheel bearings. They also do the same in very heavy towing with the full floaters.
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Old 10-04-2015, 02:53 AM   #6
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I figured I would bring this one back up now that we have a lot more information. We just got back from about 5K miles in temps from 35* to 98* in and around the Rockies. I took quite a few readings of hub and tire temps along the way. We had the tires, which are oversized, at 62/76 psi instead of the standard 65/80, at 70* ambient and never changed it, so we had a wide range of base pressures which didn't really make any difference in handling.

Bottom line is that the the rear hubs are now always equal or cooler than the fronts, usually 20-30* above ambient. The tires run just about at hub temps, except when it is quite cool (under 45*) when the tires are 5-10* hotter than the hubs. The side of the van that the sun is on makes the tires on that side run 5-10* hotter than the shaded side.

We have never had the rear tires run that cool, or even close to it, and never have heard of it on other's Roadtreks either. The tires had to be getting the heat from the rear axle outboard bearings. Very surprising, especially with 1000# more weight on the rears.

We also ran into a couple that has a 2007/2008 C190P that looks to have been produced right after ours was since it had the maple interior. They bought it new and had the rear differential fail at 4K miles, and again at 9K miles. The first time it was rebuilt, the second time they didn't know what Chevy did, but they had the van a week+ waiting for parts, so they most likely must have put in a complete replacement. They are now over 70K miles without any more issues. Further data to indicate a bad run of axles in 2007, I would say.
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Old 10-04-2015, 05:09 AM   #7
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tire pressure will vary will temperature and also the density of the surrounding air ( altitude).

"air" will swing all over the place


a full nitrogen will be much more stable- and teh larger molecules take longer to migrate through rubber, so stays at spec longer.

"air" is about 78% nitrogen already- the remaining 22% can really have an effect on wear, handling and ride.

most costcos are using nitrogen now.

when I took our van in for a new spare they pulled, rotated and refilled the other 4 tires with nitrogen, although they had come on our used van

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Old 10-04-2015, 01:08 PM   #8
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I saw a GM 14 bolt full float rear end listed in used ads recently and thought of your swap out. Year, ratio not listed. Price was $250 iirc. Drum brakes.
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Old 10-04-2015, 02:06 PM   #9
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[QUOTE=markopolo;33981]I saw a GM 14 bolt full float rear end listed in used ads recently and thought of your swap out. Year, ratio not listed. Price was $250 iirc. Drum brakes.[/QUOTE

If it was a van one, I think that would be the previous to ours version, probably like the one you have in your van. Does yours have rear drums? Very good price if reasonable miles.
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Old 10-04-2015, 03:14 PM   #10
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Mileage not mentioned in the ad either.
Yes, rear drum brakes on mine.
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Old 10-12-2016, 08:42 PM   #11
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Quote:
Originally Posted by markopolo View Post
That is interesting. Maybe Photog will catch this topic and compare the front and rear on his van. I notice the temperature affect on the ride in the car this time of year. There can be a 50F degree swing in ambient temperature in a period of days.
I have been out of the loop for a while. I will try to stay ion touch better.

We will be out on a trip in a couple weeks. I will record temperatures for the ambient air, tires, hub and diff. This should be interesting.

I would never have though the hub temps would rise high enough to push heat out to the tires enough to raise tire pressure.
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Old 10-13-2016, 12:59 AM   #12
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My van doesn't have the tire monitoring system like my car does but I have found I get better mpg when I run the tires on the upper end that is recommended. Since I do not get out rving as much as I would like, my tires would dry rot before they wear out. So, before any trip I top off the tires and get the better MPG.
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Old 10-13-2016, 01:28 AM   #13
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It will be interesting to see what Photog comes up with for temps particularly in the rear, as he has the semi floater axle but higher capacity tires. IIRC in another thread he had mentioned that he was getting a lot more pressure increase in his rear tires than he thought he should, with the stock size tires, so we should see if it is tires only making less heat, or if the axle is contributing to it also.

We have noticed with our setup, now that the fronts and rears gain about the same pressure, due to the same temp rise, that the handling stays more consistent over the day's drive. I would guess that is mostly to do with the fact that the front to rear tire pressure difference stays the same all day.
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Old 10-25-2016, 09:50 PM   #14
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Incomplete testing, but I did get tire and hub temps, front & rear.

Front temps 71-72 degrees F
Rear temps 81-83 degrees F

Ambient 62 degrees F

About 10 degrees difference, front-to-rear.

I run about 5psi more in the rear than the front tires, due to higher load. I am not at maximum cold-pressure yet, at the rear; but the load it not near maximum either, for these tires.

I am keeping my radar up, for a "Tow Package" disc brake, full float axle.
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Old 10-25-2016, 10:16 PM   #15
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Quote:
Originally Posted by Photog View Post
Incomplete testing, but I did get tire and hub temps, front & rear.

Front temps 71-72 degrees F
Rear temps 81-83 degrees F

Ambient 62 degrees F

About 10 degrees difference, front-to-rear.

I run about 5psi more in the rear than the front tires, due to higher load. I am not at maximum cold-pressure yet, at the rear; but the load it not near maximum either, for these tires.

I am keeping my radar up, for a "Tow Package" disc brake, full float axle.
Am I reading right that the hubs and tires were same temp? Ours were in nearly every test.
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Old 10-25-2016, 10:59 PM   #16
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Quote:
Originally Posted by booster View Post
Am I reading right that the hubs and tires were same temp? Ours were in nearly every test.
I couldn't actually measure the hub directly, as there is a plastic hub-cover. I measured the lug nut and center of the wheel, to estimate the hub temps.

They were within a 1 degree of the tires.
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