Calling all Automotive Engineers

[Brian Root]

Why did Toyota design the 4runner body mounts this way? What impact does altering these have?

I have to imagine that if the extra material wasn't needed they wouldn't have designed them this way. I'm very interested to hear technical explanations to try and understand this from an engineering perspective.

 

[Lanlubber In Remembrance]

Why did Toyota design the 4runner body mounts this way? What impact does altering these have?

I have to imagine that if the extra material wasn't needed they wouldn't have designed them this way. I'm very interested to hear technical explanations to try and understand this from an engineering perspective.

What do you see wrong with the way the Toyota engineers designed it that way. Looks to me they were trying to mount the body on the frame as low as they could to hide the frame. You can raise it if you want but I dont see an advantage unless you want more tire clearance for bigger tires. It's a big job because only the body goes up.

 

[Brian Root]

Why did Toyota design the 4runner body mounts this way? What impact does altering these have?

I have to imagine that if the extra material wasn't needed they wouldn't have designed them this way. I'm very interested to hear technical explanations to try and understand this from an engineering perspective.

What do you see wrong with the way the Toyota engineers designed it that way. Looks to me they were trying to mount the body on the frame as low as they could to hide the frame. You can raise it if you want but I dont see an advantage unless you want more tire clearance for bigger tires. It's a big job because only the body goes up.

I don't see anything wrong with the way they designed it, structural engineers are pretty smart and don't typically do things that don't have a purpose. I'm trying to understand from a structural engineering point of view why it may have been designed the way that it is. Ultimately I'm trying to understand how cutting into it (a body mount chop) is going to affect their design and if it can truly be altered without diminished structural integrity. I find this kind of stuff interesting and like to understand it, just the geek in me.

 

[Lanlubber In Remembrance]

I don't see anything wrong with the way they designed it, structural engineers are pretty smart and don't typically do things that don't have a purpose. I'm trying to understand from a structural engineering point of view why it may have been designed the way that it is. Ultimately I'm trying to understand how cutting into it (a body mount chop) is going to affect their design and if it can truly be altered without diminished structural integrity. I find this kind of stuff interesting and like to understand it, just the geek in me.

Okay, to my knowledge the way a body is mounted to the frame is more of a preference than a structural issue. It probably had more to do with working with parts that already existed on previous models. They dont reinvent the wheel (frames) every time they change body styles. Instead they design body's to fit the frame as a matter of economics.

Hanging a body off the side of a frame is common practice among all manufactures. Like I have already said, it is a way to hide the ugly frame while lowering the body, thus lowering the center of gravity. Just be glad they are still built as a body on frame design rather than a unibody type design. And finally, yes you can alter the body mounting of any vehicle. My question to you would be why would you want to ? You could put a Chevy body on a Toyota frame with modifications to the body or the frame or both. It's no big deal for a car builder. Ask any NASCAR builder, they mix and match parts from different manufactures as a common practice.

 

[smritte]

If you look at other ladder framed vehicles, you notice that the frame width match's the engine width. Framed vehicles really weren't built with comfort or handling in mind. Supporting the body on top raises the weight center and you cant go too much wider with the body before you start creating body roll. The suspension is mounted to the frame, not body. This is where we deal with body roll.
If you look at real narrow frames like the old Jeeps you see they added side mounts to the frame that stuck out quite a bit but the body sits high. The older SUV's they brought the outer edge of the body down slightly to cover the top of the frame but that was all.

Looking at your picture, the body is supported lower. This will improve the body roll slightly and as @Lanlubber mentioned, hides the frame for ascetics. One can argue that moving the body down wont make a big difference. This is true but, its all the little things added together is where you see the change.

Structurally, your not going to change anything by trimming the mount. Just make sure you weld a cap over the hole and seal it well. If that was a point that flexed, it could be an issue. On my old TJ, the rear shocks were at the wrong angle (thanks Jeep). I had to move them outward at the top. That meant notching the frame and mounting the shock almost in the middle of the frame. The frame did its flexing about 14 inches in front of the shock so this wasn't a stress point.

An observation on my end based on a lifetime in this industry, just because a manufacture did something, doesn't mean its correct. Years ago I stopped asking "why did they design it like this", "it doesn't work". The nice thing about Toyota is, most of the engineering is correct. For this reason, I stopped building Jeeps and went back to Toyota.

 

[Brian Root]

If you look at other ladder framed vehicles, you notice that the frame width match's the engine width. Framed vehicles really weren't built with comfort or handling in mind. Supporting the body on top raises the weight center and you cant go too much wider with the body before you start creating body roll. The suspension is mounted to the frame, not body. This is where we deal with body roll.
If you look at real narrow frames like the old Jeeps you see they added side mounts to the frame that stuck out quite a bit but the body sits high. The older SUV's they brought the outer edge of the body down slightly to cover the top of the frame but that was all.

Looking at your picture, the body is supported lower. This will improve the body roll slightly and as @Lanlubber mentioned, hides the frame for ascetics. One can argue that moving the body down wont make a big difference. This is true but, its all the little things added together is where you see the change.

Structurally, your not going to change anything by trimming the mount. Just make sure you weld a cap over the hole and seal it well. If that was a point that flexed, it could be an issue. On my old TJ, the rear shocks were at the wrong angle (thanks Jeep). I had to move them outward at the top. That meant notching the frame and mounting the shock almost in the middle of the frame. The frame did its flexing about 14 inches in front of the shock so this wasn't a stress point.

An observation on my end based on a lifetime in this industry, just because a manufacture did something, doesn't mean its correct. Years ago I stopped asking "why did they design it like this", "it doesn't work". The nice thing about Toyota is, most of the engineering is correct. For this reason, I stopped building Jeeps and went back to Toyota.

Great info, thank you!