Wednesday, May 4, 2011

Improving offroad capabilites. Starting point... Flex!

As we saw when I was stretching the 4Runner out to see where the new tires hit, my truck exhibits very low levels of flexibility in it current configuration.

With open differentials, keeping both the left and right tires on the ground makes an enormous difference to how far you can make it offroad. Open differentails provide power to the tire with the LEAST amount of traction (e.g., the one in the air spins, the one on the ground does nothing)

To the right is my truck, fully stock except with larger tires, fully flexed out.

The red box shows the truck is relatively level, but down in front a couple inches. The blue line shows what the height difference from the bottom of the front tire to the bottom of the rear tire. If the truck were fully level, that means it only has about 14-16" (the wheel is 16" in diameter) difference from front stuff to rear droop. I didn't bother with the other pics and doing the math, this was depressing enough. LOL

Left to right flex in the front was definitely nothing to write home about either. It's a few inchest at most.
The rear did a lot better.


Compare the pictures above to my Blazer at its pinnacle, from a suspension perspective, with 32" tires. Huge flex. It's not even fully stretched out yet and can do better. The top of the rear tire would be almost even with the bottom of the front tire at full flex. That's around a 32" differential. Much better than what the 4runner is seeing now.  This is one reason solid axles are a frequent conversion option for IFS trucks.

Here's my Blazer on 36s in a similar situation to the one the 4Runner is pictured in at the begining of this post. Same suspension setup as the Blazer pic above, just bigger tires. The sway bar is connected. Any further up the rock and the right front tire started to come off the ground. This is how good it was in street trim. :-D

Obviously we can't leave the 4Runner like it is! Off to Google to learn more about what this truck can really do! Here's a great thread showing various YotaTech IFS trucks' capabilities when it comes to flex. Some are stock, some are modified

To improve offroad articulation, disconnecting the sway bar is the first change to make, and can yield substantial results. has a good overview of the parts we're talking about.
Sway bars work by keeping both tires relatively level, from side to side. As one side gets compressed in a corner, the sway bar pulls up on the other side. There's an awful lot more to engineering a good handling car than that but, in rough terms, is how a sway bar works.

While my passenger tire in the pic above is stuffed in the fender, it's not quite as far as it can go. And it's pulling the driver's side tire up via the sway bar. And the driver's side tire is pulling the passenger tire down. Great in a corner, not great offroad when crossing uneven terrain.

With the swaybar disconnected, my driver's front will droop lower, and the passenger front will stuff up even more (which, I'm sure, means more tire clearancing activities as we take this step).

A surprising number of folks recommend removing a swaybar entirely. That's really not recommended and I would hate to be in an accident and have that come up as a possible reason. I need a vehicle to handle well on pavement at all times. My car is a BMW M3 and it is just flat out phenomonal on curvy roads. While I don't expect similar performance from an SUV, it is important that it is above all else safe for any of my family members to drive. Predictability is a critical component of "safe".

So... the swaybar stays. And, given its current road-handling manners, the truck probably will get a beefier front and a rear sway bar added at some point since current handling still leaves a bit to be desired.

Next - what options do we have?

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