tire pressure - again

[Effy]

I know, I know, this has been brought back more times than the living dead. My question is very simple. My tires on my 16k# coach are Goodyear g670s. I like them. The sticker inside says to run them at 83 psi. And I do. But the ride is rough. Smooth on smooth roads but hit a pothole or concrete road and the feedback will rattle your teeth. My coach is light and in talking with my dealer he says I can run as low as 75 psi to soften it up. Looking at Goodyear’s rating table, there is a marginal difference in weight at the wheel between 85 and 75 PSI. Talking 300 lbs. Now I have never weighed all 4 corners and doubt I ever will. I mean a very small change in weight at a corner is so small, it might be attributed to filling up with gas or emptying the tanks, to loading the refer or a cooler. Not to mention shifted weight. Heck even a person moving around. That’s a constant in RV’s. So my question, to soften the ride, can one safely reduce the psi 5-8 ? Now I will say the gap between my duals is about 1.5”. It would scare me a bit to lower this too much as I know I don’t want these to rub. I know I’ll get a ton of blasts about how unsafe all this is without weighing and breaking out an abacus. But I can tell you I will run different psi in my truck depending if I am hauling, going on a trip etc. Changing Psi 5-8 really does not seem to be a big deal based on road feel. I mean I have to imagine it changes that much on its own going from hot to cold climates, low to high elevations etc. Blast away.

[Daveinet]

Effy wrote:
I guess I have very little unsprung weight (unless that's backward). So my spring compression is minimal and rebound fast and hard. = harsh road feedback. I thought about spring compression kit but that thought is about as far as my meager knowledge of suspension systems will carry me. Airbags?

Unsprung weight is correct. The ratio of unsprung weight relative to total weight has an impact on the ride quality. It could be that your axles may be oversized/heavy compared to the weight you are carrying. Something else you mentioned compression vs rebound, Koni shocks have very low compression damping and very high rebound damping. That may be something of benefit to try soften the blow, but still control that axle movement. I'll be honest, I have mixed feelings about recommending Koni. While many here have been very pleased with Koni, you can not count on them for warranty support. Warranty is through the local dealer. I bought 1 set of shocks directly from Koni, and they are refusing to even consider warranty. The second set, I bought through Country Coach who is out of business. Koni effectively stated that if the dealer is out of business, then you loose your warranty.

[tropical36]

Effy wrote:
I know, I know, this has been brought back more times than the living dead. My question is very simple. My tires on my 16k# coach are Goodyear g670s. I like them. The sticker inside says to run them at 83 psi. And I do. But the ride is rough. Smooth on smooth roads but hit a pothole or concrete road and the feedback will rattle your teeth. My coach is light and in talking with my dealer he says I can run as low as 75 psi to soften it up. Looking at Goodyear’s rating table, there is a marginal difference in weight at the wheel between 85 and 75 PSI. Talking 300 lbs. Now I have never weighed all 4 corners and doubt I ever will. I mean a very small change in weight at a corner is so small, it might be attributed to filling up with gas or emptying the tanks, to loading the refer or a cooler. Not to mention shifted weight. Heck even a person moving around. That’s a constant in RV’s. So my question, to soften the ride, can one safely reduce the psi 5-8 ? Now I will say the gap between my duals is about 1.5”. It would scare me a bit to lower this too much as I know I don’t want these to rub. I know I’ll get a ton of blasts about how unsafe all this is without weighing and breaking out an abacus. But I can tell you I will run different psi in my truck depending if I am hauling, going on a trip etc. Changing Psi 5-8 really does not seem to be a big deal based on road feel. I mean I have to imagine it changes that much on its own going from hot to cold climates, low to high elevations etc. Blast away.

All this and you still haven't weighed your coach? No need to weigh all four corners, either, but do weigh each axle. Then use the chart and add 10-15psi for a cushion and to take care of all the variables when traveling all over. If that's more than you're running now, so be it and I wouldn't even think about taking a chance on blowing a tire, no matter how rough the ride might be. Might be looking into an alternative though, if it was all that bad.

[Dog_Trainer]

Effy wrote:

Dog Trainer wrote:
The Sticker On the vehicle should coincide with the tire on the vehicle as purchased. But that is a go by and does not take into consideration the weight difference corner to corner and overall. If you are not going to weigh the corners or the axle then the recommendation should be to inflate the tires to the maximum that is listed on the sidewall of the tire and not the coach. I would imagine that this is more than needed but it becomes the safety factor when not knowing the true weight. My suggestion would be to take your MH to a scale and if they do not offer corner weighing then get it weighed by pulling the front axle onto the scale ask them to get that weight and then pull the whole unit up and get an overall weight by subtracting the front from the overall it gives you a pretty fair starting point. Go to the tire website and find the pressure for the tire at the weight you are seeing then add 5lbs as a safety. I would rather see you with a little bit of a stiff ride as to see you take out the fender wells and area surrounding with a blow out.

I don't think over inflation above what a chart reccomends is always good advice either. Too much pressure can cause problems too. It might mitigate a blowout, but it can reduce surface area of the tire and cause handling issues.

I gave you the answer in the first part of the post before going on to say follow the manufactures tire recommendation. As you stated earlier you have the chart so go ahead and use it. You can always go back at the manufacture that put the sticker on if you think it will help. Most posters here are trying to answer your question. The tire mfg state PSI cold numbers so don't worry about the change unless you have some very radical temp fluctuations.

[Effy]

Daveinet wrote:

Effy wrote:
Too much pressure can cause problems too. It might mitigate a blowout, but it can reduce surface area of the tire and cause handling issues.

If you look at the contact patch on an overinflated tire, it makes very little difference in the size compared to weight matched inflation. Because of the belts, the tire doesn't stretch much, so basically the contact patch only changes longitudinally. Under hard braking, you are putting a lot more weight on the front end, which is going to change your contact patch anyway, so optimum braking traction would require over inflation. Not sure when the last time you have slid your motorhome sideways in a corner, or done burnouts, but if I had to guess, traction within reason is not your highest priority. That is why everyone fills according to the tables and then adds some fudge factor, so they know they will be OK.

Some thoughts: What size tires are you running and do you have the option of going to a nylon belted tire, rather than steel? Nylon will be much more flexible and have a softer ride for the same air pressure. The tire is also lighter, which will help as well. About the only real advantage to steel belted tires is they have less tread squirm, which improves the wear, but they are more expensive, so it kind of comes out in the wash.

Once you settle on what inflation you are going to use, it may be time to start a second thread requesting what people have done to their F53s to improve the ride. Make sure you also ask what year, because the F53 has evolved over the years, and the newer chassis do not ride as stiff as the older ones did. If I had to guess, half your battle is the fact that you have a chassis that can handle a lot more weight than your coach. Your coach is going to be unique on that regard, so you will have to filter the responses that you get. The early 2000s and older have added air bags, which raises the height to a softer part of the spring travel. I'm guessing that probably would not help in your case. From everything I have read, and instinctively I would start with shocks. The next thing I would look into would be Sulastic shackles. They may not list anything for an F53, but sometime ago, I had contacted them, and they pretty much said they could make/adapt anything. They also fit your criteria of cheap.

thanks dave, good info. I do the occasional burnout and donuts in the local walMart, they like the smoke show - Kidding.

You are right in one regard, my coach weight. One of the uneducated reasons I landed on the ACE was that it was considerably lighter than any other in it's compeition range. Initially I thought this would be a benefit. Daydreaming of easier handling and higher MPG. WRONG!. turns out, as you mentioned, lighter is not better. Especialy on the F53. I guess I havevery little unsprung weight (unless that's backward). So my spring compression is minimal and rebound fast and hard. = harsh road feedback. I thought about spring compression kit but that thought is about as far as my meager knowledge of suspension systems will carry me. Airbags?

[Daveinet]

Effy wrote:
Too much pressure can cause problems too. It might mitigate a blowout, but it can reduce surface area of the tire and cause handling issues.

If you look at the contact patch on an overinflated tire, it makes very little difference in the size compared to weight matched inflation. Because of the belts, the tire doesn't stretch much, so basically the contact patch only changes longitudinally. Under hard braking, you are putting a lot more weight on the front end, which is going to change your contact patch anyway, so optimum braking traction would require over inflation. Not sure when the last time you have slid your motorhome sideways in a corner, or done burnouts, but if I had to guess, traction within reason is not your highest priority. That is why everyone fills according to the tables and then adds some fudge factor, so they know they will be OK.

Some thoughts: What size tires are you running and do you have the option of going to a nylon belted tire, rather than steel? Nylon will be much more flexible and have a softer ride for the same air pressure. The tire is also lighter, which will help as well. About the only real advantage to steel belted tires is they have less tread squirm, which improves the wear, but they are more expensive, so it kind of comes out in the wash.

Once you settle on what inflation you are going to use, it may be time to start a second thread requesting what people have done to their F53s to improve the ride. Make sure you also ask what year, because the F53 has evolved over the years, and the newer chassis do not ride as stiff as the older ones did. If I had to guess, half your battle is the fact that you have a chassis that can handle a lot more weight than your coach. Your coach is going to be unique on that regard, so you will have to filter the responses that you get. The early 2000s and older have added air bags, which raises the height to a softer part of the spring travel. I'm guessing that probably would not help in your case. From everything I have read, and instinctively I would start with shocks. The next thing I would look into would be Sulastic shackles. They may not list anything for an F53, but sometime ago, I had contacted them, and they pretty much said they could make/adapt anything. They also fit your criteria of cheap.

[Effy]

For sure I am overthinking it. I am an analyst by trade. Like I said, will weigh and get it as right as I can. Wish I could soften the ride, but it's an entry level coach on an F53. Only so much money I am going to throw at it. it is what it it. Is it ever what it isn't? :h

[wolfe10]

Correct-- weigh with fuel full, potable water full and whatever you normally drive with in gray and black. Same for people and stuff on board. Basically as you will be going down the road with heaviest normal weight.

The 5 PSI safety margin will not compensate if you start a rock collection or see a 50 degree temperature swing, but easily covers even large Walmart trips.

Don't over-think it, but don't just throw up your hands (like some have suggested) and not address it.

A little overinflated is much better than under inflated, so if you are going to err, err on the side of more PSI.

[mtrumpet]

Effy,
The symptoms of your harsh ride that you describe in your OP are unfortunately very typical of the F-53 chassis. Due to the heavy leaf spring suspension, you are only going to be able to do so much to try and soften the ride on the chassis. Obviously, sacrificing safety (i.e. too low of tires pressures) for what might only result in a slighty more comfortable ride should not be an option.

After you’re through getting your weight vs tire pressures resolved, you may consider a new set of high quality shocks. That will help with your ride. However, again, it’s only going to do so much. I know this all too well as my previous MH was on an F-53. I did everything that I could to try to improve the ride quality. Added front and rear track bars (to improve handling), new tires (weighed my axles and adjusted tire pressure accordingly) and installed new shocks all the way around. While these improvements did make a noticeable difference in ride and handling, in the end it was still a heavy duty leaf spring suspension.

Not trying to burst your bubble, just sharing my personal experience with a similar problem on the same platform.

I eventually solved the problem once and for all. I bought a DP! 😉

[Effy]

wolfe10 wrote:
Effy,

You are correct, but perhaps overthinking this.

Indeed, with change in temperature, tire pressure changes (very little change with change in elevation).

SO, here is my recommendation:

Best-- weigh individual wheel positions and use heavier wheel position on each axle to go to your tire manufacturer's inflation chart. If only axle weights, see *1.

The chart will tell you the MINIMUM PSI for your given weight. Add 5 PSI to that minimum for a small safety margin.

*1 If only axle weights, you must add a fudge factor for side to side imbalance (say 5 PSI) as well as the 5 PSI for a small safety margin (as long as this does not exceed the wheel or tire limits).

And, yes, if you experience a 60 degree temperature swing, you WILL have to adjust tire pressure!

Remember when the tire manufacturers say PSI cold, they mean before driving at current ambient temperature.

Understood and I TOTALLY agree with all of that. So knowing that (devil's advocate here) we all run our tires at 5-8 psi higher or lower than we start by proxy of conditions out of our control. And despite weighing it and getting a baseline, that changes EVERY time you take a trip. And who weighs their rig every time? I would bet dollars to Donuts that most on this forum could be off their weighed weight by a hundred to a few hundred pounds bewteen trips. And the difference on the chart for my tires between 75 and 85 psi is 340#. That's not much in the grand scheme of things. One person and a cooler. And that's my point. Unless you know each time, or weigh it dry and weigh every article you put on or in your coach, frankly it's a guess. I read to weigh it like you are going on a trip. Well my trips vary. A weekend might be light. A week diving might require a lot of gear. A bike race might involve a few riders and half a dozen bikes, stands, tools etc. I might take some of my son's friends on a weekender. SOOO many variables that change, and of course the ambient temp.

[wolfe10]

Effy,

You are correct, but perhaps overthinking this.

Indeed, with change in temperature, tire pressure changes (very little change with change in elevation).

SO, here is my recommendation:

Best-- weigh individual wheel positions and use heavier wheel position on each axle to go to your tire manufacturer's inflation chart. If only axle weights, see *1.

The chart will tell you the MINIMUM PSI for your given weight. Add 5 PSI to that minimum for a small safety margin.

*1 If only axle weights, you must add a fudge factor for side to side imbalance (say 5 PSI) as well as the 5 PSI for a small safety margin (as long as this does not exceed the wheel or tire limits).

And, yes, if you experience a 60 degree temperature swing, you WILL have to adjust tire pressure!

Remember when the tire manufacturers say PSI cold, they mean before driving at current ambient temperature.

[Effy]

I plan on weighing this week. There are a few areas around that will do this. get my weights, and look it up on the grid. Thank you all for your input. (including you Dennis 🙂 )But I will add this, Tire pressure changes constantly and is subjected to temperature and altitude. So an example is something I saw on a post a while ago and started a bit of this line of thinking. If I am in Fla on the day I leave to come home, and it's 80 degrees. I check psi (something I rarely do on a trip honestly) and it's at my prescribed psi based on weight. Actually the weight I think it is because things have changed since I left home. I might buy things, I might reduce weight (drinking more beer than I planned and thus emptying my cooler, we might have less food etc). A LOT of things can change my weight and often this could be a few hundred pounds. Anyway I leave Fla and it's set at PSI but I am guessing at my weight quite frankly. So are all of you. Unless you weigh it EVERY time you get behind the wheel. So I head home and at home it's 20 degrees. There is a very good chance now I am under psi by as much as 10. The inverse could be true. I might leave an area that's 20 degrees an when I get to my destination it's 80 and now based on the tire heating up ambient temp etc, I am over by 10 psi and riding on balloons. My point is, despite weighing it and getting spot on, at the end of the day you are only ever going to be close. It might be right when you start cold, but all bets are off after that. It can go down or up based on ambient temp,road surface, altitude, heck even wind pushing the coach and heating up one side more than another. What's the tolerable range? And all of this is out of your control. Playing devil's advocate here but this is real life scenarios and nothing you can control unless you check, weigh and reset at every stop on a trip. Just sayin.

[Effy]

Dog Trainer wrote:
The Sticker On the vehicle should coincide with the tire on the vehicle as purchased. But that is a go by and does not take into consideration the weight difference corner to corner and overall. If you are not going to weigh the corners or the axle then the recommendation should be to inflate the tires to the maximum that is listed on the sidewall of the tire and not the coach. I would imagine that this is more than needed but it becomes the safety factor when not knowing the true weight. My suggestion would be to take your MH to a scale and if they do not offer corner weighing then get it weighed by pulling the front axle onto the scale ask them to get that weight and then pull the whole unit up and get an overall weight by subtracting the front from the overall it gives you a pretty fair starting point. Go to the tire website and find the pressure for the tire at the weight you are seeing then add 5lbs as a safety. I would rather see you with a little bit of a stiff ride as to see you take out the fender wells and area surrounding with a blow out.

I don't think over inflation above what a chart reccomends is always good advice either. Too much pressure can cause problems too. It might mitigate a blowout, but it can reduce surface area of the tire and cause handling issues.

[Dog_Trainer]

The Sticker On the vehicle should coincide with the tire on the vehicle as purchased. But that is a go by and does not take into consideration the weight difference corner to corner and overall. If you are not going to weigh the corners or the axle then the recommendation should be to inflate the tires to the maximum that is listed on the sidewall of the tire and not the coach. I would imagine that this is more than needed but it becomes the safety factor when not knowing the true weight. My suggestion would be to take your MH to a scale and if they do not offer corner weighing then get it weighed by pulling the front axle onto the scale ask them to get that weight and then pull the whole unit up and get an overall weight by subtracting the front from the overall it gives you a pretty fair starting point. Go to the tire website and find the pressure for the tire at the weight you are seeing then add 5lbs as a safety. I would rather see you with a little bit of a stiff ride as to see you take out the fender wells and area surrounding with a blow out.

[psw757]

I agree, you need at a minimum to get the axle weights from a cat scale. There is one in Havre De Grace MD that I am aware of at truck stop. ( see your from Md)

We just got a new coach last month and it was wandering a bit and a little rough. Was running at max psi from dealer 120psi. Had coach weighed fully loaded and was several thousand under max weight for each axle and was safely able to lower the front from 120 to 90 and the rear from 120 to 95 and this is still with at least a 5 psi buffer.

Made a huge difference in ride. If 83 is your max and you have a light coach, I'm sure you could probably come down more than 5 psi. However I wouldn't do it until I had the supporting evidence from the scale.

Good luck!