The right tire pressure - WOW!

[PushedAround]

Originally Posted by deandec

I understand that on a DP, the drive shaft is affected by incorrect ride height. Just something else to consider when adjusting away from the manufacturer settings.

I was not advocating moving away from manufactures settings, just properly setting the corner weights within their tolerance.

[SarahW]

Originally Posted by Musikboy

Two Newbie Questions:

- How does someone get their coach weighed?
- Once I get the coach axles and individual wheels weighed, how do I know exactly what tire pressure to use for each wheel?

If you are anywhere near any of the Escapees Smart Weigh locations, I highly recommend them. They will do the 4-corner weigh of your rig and your toad, then review the results and make recommendations for you. Best $45 we ever spent. SmartWeigh_Default

[Dr4Film]

Originally Posted by Musikboy

Two Newbie Questions:

- How does someone get their coach weighed?
- Once I get the coach axles and individual wheels weighed, how do I know exactly what tire pressure to use for each wheel?

I use Certified CAT Scales located at various truck stops all over the country. Junk yards have scales, moving van company's have them also.

The attached form plus the inflation charts off the Internet for your specific brand and model tires will get you to your proper tire inflation goal.

Dr4Film ----- Richard

[Musikboy]

Originally Posted by Dr4Film

I use Certified CAT Scales located at various truck stops all over the country. Junk yards have scales, moving van company's have them also.

The attached form plus the inflation charts off the Internet for your specific brand and model tires will get you to your proper tire inflation goal.

Dr4Film ----- Richard

Perfect! Thank you.

[Sleepy]

The best and most accurate way is to weigh each corner individually. Then inflate according the the heaviest side from the Michelin tire inflation guide. It also shows if you are evenly loaded side-to-side. My rig weighs in at 30K total and my tires are 100 psi fronts and 90 psi rears, after weighing each corner fully loaded with fuel, propane, and my 110 lb. wife! I weighed at a grain coop in Iowa [no charge]
My final suggestions is, absolutely have a tire-pressure monitoring system. My has alarmed twice in 7 years and saved me from a slow-leak pressure loss...wouldn't be without it. Good luck!

[Dr4Film]

Originally Posted by PushedAround

Richard, what I mean by cross weights is the difference between the left front plus the right rear vs the right front plus the left rear. Cross weights are more important than having specific ride heights. If you have a diagonal imbalance , it is just like having a chair with one short leg, and like the chair, your coach will teter-toter.

I have 40 years of race car suspension "engineering" and modification experience and from what I am seeing, these beasts are no different, just heavier. The side to side imbalance may be less noticeable on a big old truck chassis than in a stiffly sprung Porsche, but the effects are still the same. In my experience, you should get a median ride height for the front and back, and then adjust a specific corner up or down to get the cross weights right and the ride height close.

I sorta thought that's what you meant but I wasn't 100% sure.

If that's true, then how would you correct for my current cross-weights which are:

Total full weight of the coach.

Front = 13,200 lbs. With people and dog.
Rear = 23,200 lbs.

After doing the math here are my corner weights.

Left front = 6,500 lbs.
Right front = 6,700 lbs.
Left rear = 11,640 lbs.
Right rear = 11560 lbs.

LF to RR difference = 4,940 lb's
RR to LF difference = 5,060 lb's

I understand how to rearrange for side-to-side differences but I would not have a clue regarding cross differences.

Dr4Film ----- Richard

[PushedAround]

Actually the math goes like this:

LF + RR = 6500+11560 = 18,060

RF + LR = 6700+11640 = 18,340

280 lb difference or less than 1% on the cross weight. Pretty darn good in my book. Most cars should be that close, percentage-wise.

If there were a big difference, like in my coach where it is over 1000 lbs I would/will correct the problem by checking my ride heights and lowering the heavy corner that is too high until I get the cross weight difference below 300 lbs or 1% for my coach.

For a reference, on the race cars that I have set up, I usually go for 20 lbs or less.

[Ray,IN]

On the other hand, read what Goodyear says about RV tire pressure. Running the absolute minimum air pressure to obtain a soft ride has consequences.

[Musikboy]

Originally Posted by Sleepy

My final suggestions is, absolutely have a tire-pressure monitoring system. My has alarmed twice in 7 years and saved me from a slow-leak pressure loss...wouldn't be without it. Good luck!

1. Thanks for the advice. Do you have all six tires on your TPMS?
2. Did you need to use a signal booster to pick up the rear tires?
3. Do you also have your toad on the TPMS?

Still trying to figure all this out myself. When at rest stops I feel each tire for heat, I check to see they are all the same temperature, I sometimes check pressure with a pressure gauge but not too often because I don't want to let air out.

[Dr4Film]

Musikboy,

Get yourself a good calibrated digital tire pressure gauge. I use THIS one.

Then do some reading and research on this forum as TPMS systems have been hashed around hundreds if not thousands of times. Use the "SEARCH" drop-down arrow button on the blue heading at the top.

I started out with a Doran TPMS. After three years of problems and frustration including a shredded trailer tire I dumped it on eBay. I now own the Tire SafeGuard with a signal booster as my trailer tires are pushed back far enough that I wanted to make sure I had an excellent signal. However when I have used it with the car in tow I don't need to have the signal booster running.

I like the Tire SafeGuard TPMS so much that I am purchasing another unit for my 2004 Victory Arlen Ness Edition Motorcycle.

Dr4Film ----- Richard

[Dr4Film]

Originally Posted by PushedAround

Actually the math goes like this:

LF + RR = 6500+11560 = 18,060

RF + LR = 6700+11640 = 18,340

280 lb difference or less than 1% on the cross weight. Pretty darn good in my book. Most cars should be that close, percentage-wise.

If there were a big difference, like in my coach where it is over 1000 lbs I would/will correct the problem by checking my ride heights and lowering the heavy corner that is too high until I get the cross weight difference below 300 lbs or 1% for my coach.

For a reference, on the race cars that I have set up, I usually go for 20 lbs or less.

Larry,

Thanks for the explanation!

I now see where you are coming from and understand the calculation.

Nice to know that my coach is within reasonable specs (less than 1% difference) since it is absolutely full with no more room for anything.

Dr4Film ----- Richard

[RickO]

Add me to the list of believers in the importance of matching PSI to actual weight. Long story short, my maiden voyage in my brand new 40DP made me fear I had made a horrible mistake because (with tires inflated to sidewall psi) every little expansion joint or bump rattled everything inside our nearly empty coach. Figured it out pretty quickly with the help of this forum though.

Originally Posted by Musikboy

1. Thanks for the advice. Do you have all six tires on your TPMS?
2. Did you need to use a signal booster to pick up the rear tires?
3. Do you also have your toad on the TPMS?

Still trying to figure all this out myself. When at rest stops I feel each tire for heat, I check to see they are all the same temperature, I sometimes check pressure with a pressure gauge but not too often because I don't want to let air out.

In our case we had all six coach and four toad tires on our Doran 360 TPMS. It required a signal booster to be consistently effective. IMO having the toad monitored is important because you really wouldn't know you had a problem until it might be too late to avoid fire and other such mayhem.

Originally Posted by Dr4Film

Musikboy,


I started out with a Doran TPMS. After three years of problems and frustration including a shredded trailer tire I dumped it on eBay.
Dr4Film ----- Richard

Similar experience with the Doran 360. They were nice people to work with and did seem to want to stand behind their product... but from what I've read from other forum members, it's an inferior product.

Rick

[jadatis]

Originally Posted by PushedAround

Richard, what I mean by cross weights is the difference between the left front plus the right rear vs the right front plus the left rear. Cross weights are more important than having specific ride heights. If you have a diagonal imbalance , it is just like having a chair with one short leg, and like the chair, your coach will teter-toter.

I have 40 years of race car suspension "engineering" and modification experience and from what I am seeing, these beasts are no different, just heavier. The side to side imbalance may be less noticeable on a big old truck chassis than in a stiffly sprung Porsche, but the effects are still the same. In my experience, you should get a median ride height for the front and back, and then adjust a specific corner up or down to get the cross weights right and the ride height close.

That crossed weight difference R/L ( as I understand you mean) is pretty common for RV but also multi axle 5th wheelers or TT.
In Holland where I live , there is a company "car support" who places different strenght of springs R/L to cover that . Read they also do springs for Armoured cars around the world.

Once had contact with an American on Samba forum who first put pressure in tires to give them all the same deflection and from the pressure differences the weight differences could be determined. also crossed weight differences.
Something like LF 45 , RF 40, LR55, RR 50 psi.

then after that he leveled the car , rear by putting something between it and front from the inside automatically, probably put edge of wheelsheeld at same hight Right and left.
Then he noticed that the tires had different deflection again ( measured it from middle wheel to ground) .

My explanation for that was that the leveling brougt back the torsion forces in the frame back to about zero , wich compensated the weight diffences a little. So by leveling the real weight diffences came up.
for the needed tire pressure that is important.

If you can level the RV R/L , going from the advice to give R/L on axle the same pressure and use pressure for highest weight on wheel, after leveling you need higher tire pressure.

[jadatis]

Originally Posted by PushedAround

Actually the math goes like this:

LF + RR = 6500+11560 = 18,060

RF + LR = 6700+11640 = 18,340

280 lb difference or less than 1% on the cross weight. Pretty darn good in my book. Most cars should be that close, percentage-wise.

If there were a big difference, like in my coach where it is over 1000 lbs I would/will correct the problem by checking my ride heights and lowering the heavy corner that is too high until I get the cross weight difference below 300 lbs or 1% for my coach.

For a reference, on the race cars that I have set up, I usually go for 20 lbs or less.

Forgot to read page 2 and reading back saw you already gave the answer.
What you write wich I bolded , is doing the other way around to get more even weight on the sides.
By lowering the heavy side, you bring more torsion in the frame, wich compensates more the weight differences , so more the same weight on R and left wheel.

Mayby thats a reason for having the same pressure Right and Left, then also the heavyest side deflects more wich has the same effect as lowering the heavy side . If that way makes the balance of the vehicle better is the question, but you already experienced in the racing that riding gets better then.

But then again, does the riding gets better because of the more even pressure on wheels or the more the same deflection of the tires.
Il bet on the second.

Also by shifting some weight the crossed weights can be lowered.
Then mostly put weights from behind rear axle to between the wheels.