tire sidewall flex question - Toyota FJ Cruiser Forum
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post #1 of 6 (permalink) Unread 08-12-2019, 07:45 AM Thread Starter
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tire sidewall flex question

Getting ready to put 285 70 17 terra grapplers on and I know there has been a ton of proper air pressure questions, but I am in the mountains where we have nothing but curves which are a ball in our porsches with low profile performance tires and suspension that keeps it flat. However on the fj with stock 17 inch tires and stock suspension I am getting a good deal of body roll already and am installing Bilstein 5100's and the larger terra grapplers. I am assuming that with the larger tires and even more sidewall it will probably be no better and maybe even worse. Will more tire pressure take some of it out without wearing the middle of the tire tread out? I would be interested in anyones experience who has the same setup and what they did to minimize it. I know everything is a compromise, but just want to optomise it where I can. If I can figure out how much tire pressure I can run without adversely affecting the tire wear in the mountains, I can always readjust for long interstate drives and for offroad.
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post #2 of 6 (permalink) Unread 08-12-2019, 12:07 PM
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Re: tire sidewall flex question

Tire flex is probably the least of your problems. The stock rear springs are quite soft and are contributing far to the rolling than the tires. Also, those terra grapplers are probably going to be E rated which means the carcass is thicker and will more supportive at the same pressures than the stock P rated tires. If you really want to combat the body roll consider upgrading the rear sway bar and or springs.
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post #3 of 6 (permalink) Unread 08-12-2019, 12:30 PM Thread Starter
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Re: tire sidewall flex question

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PhoS previously said: View Post
Tire flex is probably the least of your problems. The stock rear springs are quite soft and are contributing far to the rolling than the tires. Also, those terra grapplers are probably going to be E rated which means the carcass is thicker and will more supportive at the same pressures than the stock P rated tires. If you really want to combat the body roll consider upgrading the rear sway bar and or springs.
Sounds like good advise. Do you have a specific brand of spring that would be appropriate?
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post #4 of 6 (permalink) Unread 08-12-2019, 01:12 PM
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Re: tire sidewall flex question

" ...mountains ... curves ... a ball in our Porsches ..."

Since you are installing Terra Grappler tires on your FJ, and you mentioned adjusting tire pressure for off-roading, it would appear that you have at least some concern about off-road performance.

The FJ is a big, heavy, tall, lumbering truck, not a lowered and stiffened 911. Anything you do to reduce body roll with the intent of "improving cornering" on the street will adversely affect articulation and usable suspension travel off-road.

Optimize your Porsche (what model is in your garage?) for street use, and optimize the FJ for the best performance off road, without too severely sacrificing basic, safe handling on the street.

Being able to adjust tire pressure when transitioning from street to off-road to street again is almost essential; a portable or on-board air compressor will be one of the most useful tools you can have if you are at all serious about off-roading.

I keep my "E" load range KO2's at 45 PSI on the street, and at 18-20 PSI off road. Decently crisp "handling" (for a tall truck) on the street, and great traction and pretty compliant ride off-road over washboard and rock.

Trying to do anything off-road at 45 PSI on E-range tires will quickly set you up for a new pair of kidneys.

Last edited by FJtest; 08-12-2019 at 01:14 PM.
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post #5 of 6 (permalink) Unread 08-13-2019, 10:02 AM
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Re: tire sidewall flex question

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bjfutrell previously said: View Post
Sounds like good advise. Do you have a specific brand of spring that would be appropriate?
For stock height? Probably OME, you're going to want to do the shocks as well of course. You would be better off going with a set of coil overs and matching rear springs/shocks. Buy once, cry once right? But i'm sure you're used to that if you're a Porsche guy.

I mostly agree with FJtest's post above. I have to say I don't really notice any less rear articulation since changing to a 7/8" sway bar. But I do more trail running in the woods than extreme rock crawling. You can have a decent road driving FJ and still be super capable off road. Most people are shocked at how my FJ can rip though corners. With the stock rear bar it would get squirrel and readily lift the front inside wheel but now it stays flat and hooked up. I'll list my suspension mods for reference.

Icon 2.5" ext. travel front and rear.
Icon 2" rear springs
Addco 7/8" Rear bar
Superpro/Prothane bushings all around
34" Toyo AT2 40PSI for street driving

I've posted this before, but here's the stock bar compared to the addco. This was one of my favorite upgrades bang for the buck.


Last edited by PhoS; 08-13-2019 at 10:05 AM.
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post #6 of 6 (permalink) Unread 08-13-2019, 05:46 PM
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Re: tire sidewall flex question

Addco 2301, they're cheap quality but ok, add lengthened sway bar end links if you lift
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