How Tire size effect handling. (1 Viewer)

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Tlb

Joined
Jun 15, 2019
Threads
7
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32
Location
Ohio
My son just bought a 1977 fj40. It has B.F. Goodrich 33 x 12 inch tires. How do these tires handle on open road at 50 or so mph. We are both new to this type of vehicle so we are just in the very beginning learning stage. I want to make sure every thing is safe before we take it out on the road.
 
Depends on how well balanced the tires are and condition of vehicle suspension/ steering components. In general taller/wider tires will magnify any problems you have in these areas. One of you could stand in front of 40 and watch while other person turns steering wheel from side to side for the purpose of detecting play in steering. You could also jack up each front tire and wiggle on it in and out to see if there's any looseness. Good idea to play it safe and keep highway speeds low, especially if it starts to wander about.
 
I'll second the call for some photos. '77 FJ40's usually aren't cheap, even in crap condition. How old is your son?
 
Short wheel-base vehicles will feel more squirrely than others when you first drive one on the highway, they take some getting used to. But like @89GASHOG said, these inherent differences will be magnified greatly by any wear or deviation from stock-spec tires and steering. A good example is a spring lift - almost everyone installs one (along with taller/wider tires) on their 40, but if you don't correct the steering caster with shims or an axle cut-and-turn, then the steering is going to feel very twitchy and will catch every groove or rut in the pavement.

Even if all the steering specs are perfect after the modifications, wider tires are going to take more effort to turn, unless you have power steering installed. More so at slow speeds than on the highway.
 
^^^^^ This x10 ^^^^^

Welcome to Mud.
 
FWIW... I went down from 33x12.50 to 33x10.50 and it made a big difference!
I’m postponing PS upgrade for now ;)
 
Pictures would help a lot.

It's all about how good of shape everything is in. I had an FJ40 on 37x12.50 tires, SOA lift Chevy V8 and it drove pretty dang well down highway at 70. I've also had one on 31's and no lift that drove terrible.

As others have said, it's an old vehicle and even replacing everything it won't drive like any independent front suspension (IFS) or rig from the late 80's and up.
 
My son is 41 years old and is a first time dealing with and old vehicle. His is a 77 fj40 and has had all new front and rear springs, power steering, front end all rebuilt. I have a 1948 ford f1 pickup that had been completely done but it is not the same type of vehicle. So we are going to learn together what we can. This looks like a great forum to learn with a lot of people willing to help. I went thru the same thing with my truck on a ford truck forum. It was a big help.
Thanks everyone for all your replys.
 
I have never ran anything larger that 31's and usually keep 28 psi in the rear and 30psi front.
Pulling a loaded trailer I pump up to 40 psi all around.
Early on when I first got my 70 FJ40 I ran 35psi all around and it steered good but in a hard brake the rear end wanted to come around.
I finally settled on the 28/30 combo that seams to work.
Low air is going to give more flex in the sidewall and high air will stiffen the tire up but make it like you are driving on ice.
In my opinion the larger the tire the more prominent the problem.
 

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