Dumb question about twisting tires/ Susp.

[Joan617]

So for about the second time in our 1 1/2 yr stint into FT RV living, I had to execute a 70-80 degree jackknife to back in to an RV site. It went well, but when I did a GOAL to check my progress with Joan on the speakerphone on the other side of the rig, I noticed that the tires were grotesquely twisted and deformed in relation to one another.

We were on a road of grass and scattered gravel so I thought it would be pretty pliable. Is there a limit I should look for that might hurt the rims or twist the suspension, or is all this twisting calculating in to the design?

Thanks for any help

Angus

[Riich]

I've wondered the same! I'll wait for replies, good topic! Thanks.

[Jagiven]

Mine get a hard twist every time I back into my driveway.
You would think they would break.

[JFlightRisk]

By design, radial tires will show flex more than bias ply. That's the nature of them. But the sidewall construction on ST rated trailer tires is designed to take that strain, so your tires will be fine. It just looks bad.

The part that doesn't like it that much is the suspension.

[Flyrotor]

Just back in a little farther than your desired parking spot, then pull forward to where you want to park, it helps to straiten the suspension so you are not parked in that awkward position, i often do the same when I am fueling my truck, I don't like letting it sit in that position any longer than necessary.

[Marcm157]

Spring shackles take the brunt of that twist / tire scrub. There are a few current posts here about broken spring shackles and even one by a member who used a GoPro camera mounted under his rig while moving to actually see the flex.

[Screwby]

Originally Posted by Flyrotor

Just back in a little farther than your desired parking spot, then pull forward to where you want to park, it helps to straiten the suspension so you are not parked in that awkward position, i often do the same when I am fueling my truck, I don't like letting it sit in that position any longer than necessary.

This, it’s better on everything to relieve that twisted tension as soon as possible.

[CAG]

It is not a dumb question. You have mentioned one of the reasons that most reputable tire dealers tell you that three to four years is the max tires should remain on trailer. No differential means mega stress on the sidewalls. Add to that sitting unused most of the time on one spot on the tire, and sun damage. Especially here in the desert you have the makings of a blowout.

[Joan617]

Originally Posted by Flyrotor

Just back in a little farther than your desired parking spot, then pull forward to where you want to park, it helps to straiten the suspension so you are not parked in that awkward position, i often do the same when I am fueling my truck, I don't like letting it sit in that position any longer than necessary.

Yes, the spot we had was long enough that I found myself doing just that while adjusting the position in the spot for hook-ups, etc. I'll just know to concertedly do so in the future in order to relieve the strain (and to keep it from looking like a train wreck)



Thanks everybody.
Angus

[RGVal]

Hello CAG,
In your reply to Joan 617 you said "No differential mean mega stress on the side walls" Are there t/t with differentials? I am not being a smart a_s, and I am not mechanic, just do not understand.
Thank you in advance for your helping me out

[CAG]

Originally Posted by RGVal

Hello CAG,
In your reply to Joan 617 you said "No differential mean mega stress on the side walls" Are there t/t with differentials? I am not being a smart a_s, and I am not mechanic, just do not understand.
Thank you in advance for your helping me out

Probably but I never saw one. I’m not a mechanic either so I would recommend searching for “how a differential works”. There are several good articles and YouTube videos. The short explanation is it evens the pressure on the axle and tires by using gears to slow one wheel. Without that the tire drags and flexes more. I do recommend looking at the articles. It explains much better than me.

[Joan617]

Originally Posted by CAG

Probably but I never saw one. I’m not a mechanic either so I would recommend searching for “how a differential works”. There are several good articles and YouTube videos. The short explanation is it evens the pressure on the axle and tires by using gears to slow one wheel. Without that the tire drags and flexes more. I do recommend looking at the articles. It explains much better than me.

CAG, Thanks; you make some good points and I totally get it now. I forgot about the effect of no differential. I am now changing my tire pressure cold inflation from the 65 lbs recommended on the Goodyear Inflation chart (based on weighed load) back to the 80 psi on the sidewall. This will stiffen the sidewalls, allow for the 10%+ padding on the load allowances, reduce tire running temps and will likely improve mileage.
Angus

[CAG]

My personal opinion is that you have hit on the one fact that manufacturers inflation charts do not consider with their recommendations.

My wife was the first to point out to me the enormous flex the side walls get when I was making the 90 degree turn backing into my storage. She was standing next to the rig watching them. And those loud popping sounds you hear from the axels is not because they are happy about the turn.

[Joan617]

Originally Posted by CAG

My personal opinion is that you have hit on the one fact that manufacturers inflation charts do not consider with their recommendations.

My wife was the first to point out to me the enormous flex the side walls get when I was making the 90 degree turn backing into my storage. She was standing next to the rig watching them. And those loud popping sounds you hear from the axels is not because they are happy about the turn.

Yeah kind of like those nasty sports injury photos where the victim ends up with bones and limbs pointing the wrong way. Hard to un-see.

[Jmac54]

Originally Posted by CAG

It is not a dumb question. You have mentioned one of the reasons that most reputable tire dealers tell you that three to four years is the max tires should remain on trailer. No differential means mega stress on the sidewalls. Add to that sitting unused most of the time on one spot on the tire, and sun damage. Especially here in the desert you have the makings of a blowout.

"No differential???" I think I know what you're saying but your analogy is wrong. Yes in effect there is a differential because each wheel is independent of the other. The only time a differential comes into play is variable ratation speeds on a driven axle.
The problem is yaw or twisting around a verticle axis that happens most severely when backing up, but also on a sharp turn. Think of attaching a chain on the front left and another to the right rear of a vehicle and pulling in opposite directions. Without rotation of the tire to gradually absorb the side draft it will either slide or if on clean pavement the sidewall is going to flex first and eventually break loose or break the bead and deflate. Trailer tires are designed to handle a certain amount of this stress by having stronger sidewalls. However it is always prudent to avoid sharp angles when backing up. The strain is worse when heavily loaded or on clean pavement. If you are backing with the vehicle at 90 degrees to the trailer the stress is identical to my analogy above pulling in opposite directions.
Keep your angles gradual when backing and you should be fine.

[CAG]

Originally Posted by Jmac54

"No differential???" I think I know what you're saying but your analogy is wrong. Yes in effect there is a differential because each wheel is independent of the other. The only time a differential comes into play is variable ratation speeds on a driven axle.
The problem is yaw or twisting around a verticle axis that happens most severely when backing up, but also on a sharp turn. Think of attaching a chain on the front left and another to the right rear of a vehicle and pulling in opposite directions. Without rotation of the tire to gradually absorb the side draft it will either slide or if on clean pavement the sidewall is going to flex first and eventually break loose or break the bead and deflate. Trailer tires are designed to handle a certain amount of this stress by having stronger sidewalls. However it is always prudent to avoid sharp angles when backing up. The strain is worse when heavily loaded or on clean pavement. If you are backing with the vehicle at 90 degrees to the trailer the stress is identical to my analogy above pulling in opposite directions.
Keep your angles gradual when backing and you should be fine.

Some how I knew some expert would come along and critique this thread.

[sturgissteele]

Originally Posted by Jmac54

"No differential???" I think I know what you're saying but your analogy is wrong. Yes in effect there is a differential because each wheel is independent of the other. The only time a differential comes into play is variable ratation speeds on a driven axle.
The problem is yaw or twisting around a verticle axis that happens most severely when backing up, but also on a sharp turn. Think of attaching a chain on the front left and another to the right rear of a vehicle and pulling in opposite directions. Without rotation of the tire to gradually absorb the side draft it will either slide or if on clean pavement the sidewall is going to flex first and eventually break loose or break the bead and deflate. Trailer tires are designed to handle a certain amount of this stress by having stronger sidewalls. However it is always prudent to avoid sharp angles when backing up. The strain is worse when heavily loaded or on clean pavement. If you are backing with the vehicle at 90 degrees to the trailer the stress is identical to my analogy above pulling in opposite directions.
Keep your angles gradual when backing and you should be fine.

Welcome to the site from SW Michigan!

[Jmac54]

Originally Posted by sturgissteele

Welcome to the site from SW Michigan!

Thank you. I'm fairly new to RV'ing, but spent my previous career farming, which included various types of towed equipment and trucking.
I should have noted that it's a non-issue with a single axle trailer.

[t18skyguy]

On the cheaper trailers, the stress from that yaw will sometimes show up as a crack where the shackle is welded to the frame. It's a good idea to inspect that area now and then. There's been a number of reports in the RV forums of this issue, a few had photo's. One guy even had his welder with him and rewelded it on the spot. That's what I call being prepared.

[mgodsey]

Originally Posted by JFlightRisk

By design, radial tires will show flex more than bias ply. That's the nature of them. But the sidewall construction on ST rated trailer tires is designed to take that strain, so your tires will be fine. It just looks bad.

The part that doesn't like it that much is the suspension.

I hope this doesn’t hijack the OP’s thread but is this why ST is really the way to go? I read the debates all the time about LT vs ST. But I read a good article on TireRack about why ST is really the way to go and it was because of how the sidewalls are designed. I ended up sticking with ST. Just threw out my Raniers and put on Goodyear Endurance all around. Have a long-ish trip coming up.