Tire pressures--newbie questions!

[jillhop]

I recently purchased my first RV (1998 Coachmen Catalina 22RK, Ford E350) and immediately replaced the 10 year old tires with new ones (Aeolus CrossAce HT AS02 LT225/75/R16). I've done a lot of reading about proper inflation pressures, but I have not been able to locate a weight/inflation chart for these particular tires. Can I use one from a different manufacturer?

Last weekend I loaded 'er up and had a shakedown overnight camping trip in a friend's driveway (went well, boondocked and used all systems successfully). On the way there, I stopped at the CAT Scale and got weighed. I only have axel weights, as I have not been able to find anyplace to get 4 wheel weights ...

Here's the info from my door sticker:

GAWR-- Front: 4200 PSI 65
Rear: 7800 PSI 60

GVWR: 11,500

Weights from the CAT Scale:

Front: 3480
Rear: 7680

Gross Weight: 11,160

This weight was with all occupants, full gas/LP, 3/4 tank of fresh water, about 1/4 full gray/black tanks, and all gear.

So, I feel like I'm doing pretty well in the weight department, and I'm going to move some heavy stuff (drinking water) to the front passenger area (I travel alone with three dogs to dog events). Right now, the tires have 72psi. Can someone point me where to go to determine what the tire pressure should be at this weight?

Oh, and do I need the weight in the rig when I check/fill the tires (should I fill the fresh water tank back up)?

I'm heading out on my first big trip in 10 days (650 miles each way) so trying to get all my ducks in a row!

Oh, and this is a great forum!!!

[jillhop]

Reporting back after my first trip, 1300 miles round trip to a dog event in Williamsburg, VA. I considered everyone's advice, and set the tire pressures at 65 rear, 62 front. Boy, what a difference in the handling! Steering MUCH improved, hardly any wandering, little reaction to passing big trucks. It was quite windy on the return trip, so had to take it slow, but otherwise no issues. I kept track of gas mileage on the trip and was pleased to get just over 10mpg.

I rearranged some stuff inside, and was loaded a little lighter than my worst-case scenario previous weight. I weighed the rig again on the way out on the trip, and got 3540 front, 7460 rear, 11000 total (previous weight was 3480/7680/11160). Better weight distribution probably helped too. I'm taking another trip this coming weekend (shorter, about 5 hour drive each way) and after that I will probably have the alignment checked.

The camping part went well, too--dry camped in a friend's driveway going and coming home, two days with power/water hookups at the event. I'm hooked! Plus, one of my dogs was a BIG winner, and I came home with the most gigantic winner's rosette I've ever seen (fortunately, for all it's impressive bling, it didn't weigh much).

Thanks for all the help on this forum!

[jillhop]

I spoke with my local repair guy, and he does truck alignments. I will bring him Harvard's essay on "caster" and have him check it out. 🙂

[Calisdad]

Great topic, especially the responses for those of us who are trying to fully understand tire inflation charts.

Regarding 'Bow wave', my E350 based 21' RV used to get pushed around quite a bit by passing semis. I installed the Hellwig rear sway bar and 90% of the issue disappeared. I imagine if I upgrade the front sway bar it will improve even more.

[Harvard]

Butch50 wrote:
.... This is a normal thing it just depends on how your MH handles as to how much you feel it....

Yes, I agree, and you gotta own or drive a E350/E450 with only +3 degrees of caster to fully appreciate how much increasing the caster to 5+ adds to the stability under such conditions. IMHO

[Butch50]

What you are feeling when a semi passes you is called bow wave. When the truck approaches you they are pushing a wave of air in front of them. This causes the wind to push you away from the truck then after they get by you there is a draft behind them that has a tendency to pull you towards them. This is a normal thing it just depends on how your MH handles as to how much you feel it.

[Harvey51]

I have an E350 with the same 65/60 psi on the door plate. My house is a little smaller and lighter than yours. The tire shop I use, a particularly good Costco one, said I should just go with the 65/60, never mind the Michelin chart. I dropped to 60 on the front because my compressor is very slow getting over 60. That 60/60 seems to work fine. Since 2008.

[Harvard]

jillhop wrote:
... What I notice about the handling is that if it starts to sway (like a big truck goes by, or a big gust of wind) I have to be careful not to get into an back and forth over-steer pattern (not sure what you'd call this, but maybe you get the picture). ....

Here is a link to my handling story and +caster, circa 2010

Here is a link that ties +caster (trail) and tire inflation pressures.

[jillhop]

Oh, and my fresh water tank is under the couch on the left side, so with that full (or fairly so) it is really loading up that side of the rig (which I think your factory sticker already said was the heavier side). I will move everything I can forward and to the right ...

[jillhop]

Thanks for the link, Mich! As far as the floorplans go, the 1997 and 1998 220RK are identical. No hurry on getting the tank capacities--I'm mostly just curious, and like statistics. 🙂 I am definitely going to reduce the tire pressures and hope that improves ride and handling. I really appreciate all the advice and information!

Does your 1997 model have the etched glass on the cabinet doors over the couch? At first I thought they were palm trees, but now I've decided it's waving seaweed ... I guess a reference to the glass bottom boats off Catalina Island off southern California ...

[Mich_F]

jillhop sorry that I couldn't get the tank capacities for you today. Should be able to get them tomorrow. I think if you dropped your front tire psi to 60# that would give you plenty of cushion over the weight you are carrying on the front axle and be at 75% of the max 80# psi of your tires, assuming you have load range E tires, and it should improve your ride.
I just found this online for the 1997. Not sure if everything is accurate. I know my son told me the water tank is listed on mine as 43 gal, but on the specs. here it's 37 gal ?
1997 Coachmen Specs

[jillhop]

I don't know the wheelbase (but I could measure tomorrow with a tape measure), but I did measure the vehicle bumper-to-bumper, and it's about 24 feet.

When I had it weighed this past weekend, I drove it full to the scales, and then continued on (about 70 miles) to a friend's house for a night of driveway camping. In the morning I emptied out the fresh water (I probably had 25-30 gallons) before I left to drive home. The handling was noticeably improved on the way home with the lighter load (although there was also less wind). Had the stuff on the rear hitch carrier both ways. What I notice about the handling is that if it starts to sway (like a big truck goes by, or a big gust of wind) I have to be careful not to get into an back and forth over-steer pattern (not sure what you'd call this, but maybe you get the picture). I am getting better at driving it, however, but I do sometimes feel like I'm herding it around when I'm on the interstate.

I've been warned that carrying ex-pens on the front of the vehicle is not a good idea, because it would decrease air flow to the radiator.

[Mich_F]

J-d
The 220RK is the same length and wheelbase as your MH.

[j-d]

For these 22RK's, what is the Wheelbase and the actual vehicle Length?

I saw what might've been one of those, had a Motorcycle Rack on the rear. Not One, but TWO motorcycles. They weren't big bikes, but still, yeesh! I asked the owner how it handled and he said "Like it two motorcycles on the back."

As I mentioned earlier, the short C's don't seem to have so many handling problems. I know our 24-ft Holiday was pretty agreeable once I fixed a couple front end problems. And wheelbase was only 158".

You could get a Front-mounted hitch receiver and shift that cargo carrier weight from Rear to Front...

[jillhop]

Thanks, Mich. Much appreciated!!