BFG AT 305/65/17 - Rear end "sway"..???

[nauidvr1]

Anybody that has had these size E-Rated tires, on a 3rd Gen truck, have you noticed a backend "seasway" or "waddle" - it's scary if you have to jerk the wheel to avoid hitting something in the road, then jerk it back to recover. I noticed it right away after the tires were installed today. I have new Bilstein 5100 shocks on the truck.



I had also noticed it a little bit with the TOYO Open Country AT's 285/70/17, but now, notice it a great deal more! I know the sidewall is a bit larger, but with an E-rated tire, I did not expect it. I had a load on today (3 yards of mulch) and that didn't calm it down either (yes tires were properly inflated for the load).



By my calculations (if I did this right): multiply width by . 70 or . 65 (70% or 65% of width = sidewall height).

Stock 265/70/17 has a sidewall height of 7. 23" (185. 5mm x . 039 = 7. 23)

Toyos 285/70/17 has a sidewall height of 7. 78" (199. 5mm x . 039 = 7. 78)

BFG's 305/65/17 has a sidewall height of 7. 71" (198. 25mm x . 039 = 7. 73)



These tires sidewalls are only 13mm (~1cm) higher than stock - so why the sway? On my other truck, that still has stock tires, the side wall looks much smaller when parked side by side (by 2 inches), compared to the new BFG's, than my calculations above - so I might be wrong on how to calculate sidewall height.



I guess that anytime you go bigger than stock size, your just going to have to install a rear stabilizer bar.



Any good suggestions on a rear stabilizer bar? Will that even help?



P. S. I am suprised that no one else has metioned this, as I simply can't be the only one who noticed this after going to two different size larger tires.

 

[silverram03]

Are they mounted on factory wheels? If so that has a lot to do with the sway you're referring to. They are simply to narrow for that wide of a tire. Minimum suggested rim width is 8. 5"



Greg

 

[juicedcummins]

Mine handles like it is on rails with the same tires, shocks and factory rims. More than one rider has aslo commented on this. The conditions vary from high speed m/t 800+ mile runs to loaded to over 23k gross cruisin @ 75-80 for the same runs.

My tires have over 30k on them and are wearing pefectly but I air them down to 40psi front 36psi rear when running m/t.



Check your front end with a fine tooth comb mine was just all replaced yet again.

 

[BigPapa]

I'm currently running the Toyo O. C. A/T's and they "sway" pretty bad. I think a lot of it has to do with the tread depth on the new tires. I noticed it before when I installed some Micheline LTX A/T's on the back. As the tires wore down it went away.



By the way, how'd your Toyo's do for you? Mine have only been on a couple of months.



Scott

 

[nauidvr1]

BigPapa,

The Toyo's only made it 14k miles and had 2/32 tread left - so for me, not so good. But I did work the heck out of them last summer with loads up to 26. 5k almost daily.

 

[nauidvr1]

Are they mounted on factory wheels? If so that has a lot to do with the sway you're referring to. They are simply to narrow for that wide of a tire. Minimum suggested rim width is 8. 5"



Greg

Yes they are mounted on factory Alum Alloy wheels - 8. 75 inch - I measured today while they were changing the tires.

 

[nauidvr1]

Mine handles like it is on rails with the same tires, shocks and factory rims.

Check your front end with a fine tooth comb mine was just all replaced yet again.

What do you mean by checking the front end? What to look for? And why was yours just replaced "again" ?

 

[TAbbott]

You aren't calculating the tire size correctly. The 265 or 285 refers to the section width of the carcass in millimeters. The 65 or 70 or 80 or whatever refers to a percentage of the section width and applies to the section height. On a 305/65 the nominal width is 305 mm and the height is 65% of that, or approx. 198mm. On a 265/70 the nominal sidewall height is 70% of 265 or 185. 5 mm.



I agree with Silverram03 when he says the stock wheels are too narrow for the tire for on highway use. They'd work really well at low pressures off road because you'd not only have lots of compliance in the tire but a large "belly" to protect the rim from rocks and such. On highway, not so good.



I think in order to get that tire/wheel combination as close to right as possible on highway, you'll need to raise the rear pressure slightly to try and stiffen the sidewall. If you can, you may also want to lower the steer axle pressures a corresponding amount to put a little more flex on that end. Don't go too low though, as our trucks are front end heavy and you don't want to generate to much heat from over flexing the tire.



From a tire pressure perspective, if you have a tight front and a loose rear you will experience the swaying moment you describe. If you can make them flex at the same rate, the entire vehicle will move together instead of just one end or the other. Too low pressures in the front will make the steering feel very unresponsive to steering inputs and the truck will tend to "push", which is just the opposite of the "loose" feeling you have now.

 

[nauidvr1]

TAbbott,

Thanks for your explaination. From what I am understanding, this is a function of wide tires on too narrow of a rim, and that a sway bar will not help the situation?



Why in the heck would "juciedcummins" above say his corners like its on rails?



P. S. If you look back at my calculations above I came up with the exact 198mm you did - then converted back to inches buy multipling by . 039

 

[juicedcummins]

Simply put because it does!

I have run oversized tires on most of my trucks for years and this is the best handling truck I have set up yet. Then again it is the hardest truck to keep the front end in even with the OEM rubber.

My occupation requires lots of off road travel through soft rough terrain and the wider tires are needed for floatation. (oilfield)



I am not much for calculations something either works or does not.

 

[juicedcummins]

What do you mean by checking the front end? What to look for? And why was yours just replaced "again" ?

Check wheel bearings,ball joints,stabiliser shock and steering box play. Your rig could be short of toe -in also.



My 99 2500 had a harder service life and all it need after 130k was one front wheel bearing and no ball joints. These american axels suck @ best!



Bring back the Dana's! WE just about never needed parts but when we did they were available almost about anywhere.

 

[nauidvr1]

I solved it!

To All,

I'm back to post the solution to my "issue" (hint - it was something juicedcummins said above, but not the front end).



The day I had the tires mounted, I was leaving and going directly to pick up 3 yards of mulch, so I asked them to take the tires to the full rated 65 psi for the load I was going to get.



I noticed the "sway" going down the road to pick up the mulch. After I loaded the truck and headed home, I also noticed the "sway". Two days later I unloaded the mulch and aired down the tires to 52psi Front, 43 psi Rear.



Now, "the thing corners like it is on RAILS". It was a simple air pressure adjustment - I was all worried for nothing. Now, if I really jerk the sterring wheel back and forth like an idiot I "can make" the truck sway, but it does not do it under normal driving conditions, nor during an emergency pothole/animal/kid on a bike swerve.



Does anyone feel the that these trucks should have a rear sway bar (I do not carry a camper, just bed loads and heavy trailer loads), cause while I got a litlle extra cash I could get the rear sway bar.



juicedcummins - thanks for all the helpfull replies. I'm not off road like you are, so I have not had front end trouble as of yet. What pressures front/rear do your run for on road use?

 

[BBoling]

Well, you can see from my sig that I DO carry a heavy camper, hence my mods. RE: your question about a sway bar, I bought the Hellwig, and for the $ is works great, made a big difference. Easy enuff install for a mostly-handy guy, too.

I agree with Juiced about the front ends of these 3G's, they wear out. I just had ball joints replaced at 30K. I'm sure the rest will be replaced under warranty, too b4 it's all over. 19. 5s are hell on front ends (cuz they are HEAVY). Happy Haulin'!

 

[Regcabguy]

I've got the 285-70-17 Toyo AT's on mine w/2000# popup on constantly. I'm running a Lorenz 2. 25 w/camper valving in the rear+ Carli airbags@33psi. I keep the Toyo's@60psi for added stability. I don't see how lowering your pressure gave you the stability you desired,but I can't argue with success.

 

[nauidvr1]

Just hauled a load of sod today and increaded the tire pressure of the rears up to 58 PSI (for the load). The rear end sway returned while the tires were inflated for the load.



This makes me a little uneasy while hauling. Hence, my question again - Would a rear sway bar help with any of this?

 

[MA2LA]

I wonder if it is that your balloning the tires at higher pressures is giving you the sway. other than that i have no clue. I installed a swaybar on mine and have been very happy with it.

 

[nauidvr1]

I am looking at purchasing a Hellwig #7658 Rear sway bar and also a set of Ladder bars. Still mulling it over though, as I am not sure that the sway bar is going to help with the issue I am having, I am afraid it is just the nature of the beast with this tire.