Member III
One of the often-overlooked aspects of both ride confort and offroad capability is the anti-sway bar (ASB). People often generalize ASBs as only affecting offroad capability at maximum flex, and not affecting on-road comfort at all.
However, when only one side of the axle goes over a bump, the ASB will add a substantial amount of stiffness to the overall suspension's compliance. On my 2002 4Runner, the ASB actually more than doubled the effective spring rate in that corner. On my new 2019 F250 the front ASB (there is not one on the rear) adds about 35% more resistance to the effective spring rate on that corner.
So, even driving down the road, a pothole or even just a moderate bump on one side faces a suspension reaction force that is substantially greater than just the suspension's weight-bearing springs alone.
More specifically, say you have an everyday suspension setup where the spring's effective rate at the tire is 250lb/in--an extra 250lb of force to achieve every additional inch of compression. This same vehicle has an ASB on each axle that also has an effective 250lb/in spring rate at the tire. So, you go over a bump on one side, and compress the suspension 2". Without an ASB, that one side compresses, and the other side droops to compensate. With an ASB, on the other hand, the suspension is bound so that the bumped tire only rises 1" relative to the fra.e, and the same force that would have compressed it by the additional 1" actually lifts the opposite tire by 1". Of course, the tire doesnt actually lift off the ground--rather, the body moves to compensate. Not only does this actually result in the whole body moving more (because that transfer of force to the other tire occured through the frame / body), but the opposite tire has 250lb less downward force. If there is nornally 1250lbs of weight on the tire (in a 5000lb vehicle with perfect weight distribution), that is a momentary 20% reduction in traction for that axle if it doesnt have a fully-locked differential.
Ultimately, in the 4Runner, in my pursuit of a more compliant ride off road, I started by reducing the spring rates both front and rear by about 20% over my previous upgrades. I still wanted more so I decided to disconnect the front ASB just to test (the rear bar was already gone). Honestly, whatever improvement I saw with the new springs was doubled after removing the ASB. It flexed extremely well, and was so smooth even over very rough terrain that my baby would literally nap in his carseat while I was out wheeling aggressively enough to warrant an inclinometer. Moreover, it contributed to me making climbs that stumped several open/open Jeeps.
Having this experience in mind, I have had the ASB on my F250 disconnected since a couple days after I got it (after my first try on some very mild trails and forest roads). Of course, it still rides quite rough offroad compared to the 4Runner it replaced (until I get to my planned suspension and tire upgrades). But, before removing the ASB, the ride was about like what I'd expect in a Sherman Tank.
So, what about safety? Long story short, after a good bit of math, I determineed that my 3rd gen 4Runner was, at maximum, 3.7% more likely to roll over after disconnecting the ASBs.
On the F250, the front bar is a less substantial part of the suspension. For example, even without the bar, it has less body roll than my 4Runner did WITH the bar. Thus, the numbers make sense that this truck is only 1.44% more likely to rollover now, and will be 1.89% more likely to roll over after lifting it (with the lift height being partially offset by a wider track), if I keep the bar off. After seeing these numbers, I removed the bar today.
Obviously the formulae arent visible, but this is the spreadsheet I built to help me calculate it this time. I did it more for fun, as I did all my 4Runner's math on paper. But, this will make it easier to account for different variables (different wheel offsets, more or less lift, etc).
However, when only one side of the axle goes over a bump, the ASB will add a substantial amount of stiffness to the overall suspension's compliance. On my 2002 4Runner, the ASB actually more than doubled the effective spring rate in that corner. On my new 2019 F250 the front ASB (there is not one on the rear) adds about 35% more resistance to the effective spring rate on that corner.
So, even driving down the road, a pothole or even just a moderate bump on one side faces a suspension reaction force that is substantially greater than just the suspension's weight-bearing springs alone.
More specifically, say you have an everyday suspension setup where the spring's effective rate at the tire is 250lb/in--an extra 250lb of force to achieve every additional inch of compression. This same vehicle has an ASB on each axle that also has an effective 250lb/in spring rate at the tire. So, you go over a bump on one side, and compress the suspension 2". Without an ASB, that one side compresses, and the other side droops to compensate. With an ASB, on the other hand, the suspension is bound so that the bumped tire only rises 1" relative to the fra.e, and the same force that would have compressed it by the additional 1" actually lifts the opposite tire by 1". Of course, the tire doesnt actually lift off the ground--rather, the body moves to compensate. Not only does this actually result in the whole body moving more (because that transfer of force to the other tire occured through the frame / body), but the opposite tire has 250lb less downward force. If there is nornally 1250lbs of weight on the tire (in a 5000lb vehicle with perfect weight distribution), that is a momentary 20% reduction in traction for that axle if it doesnt have a fully-locked differential.
Ultimately, in the 4Runner, in my pursuit of a more compliant ride off road, I started by reducing the spring rates both front and rear by about 20% over my previous upgrades. I still wanted more so I decided to disconnect the front ASB just to test (the rear bar was already gone). Honestly, whatever improvement I saw with the new springs was doubled after removing the ASB. It flexed extremely well, and was so smooth even over very rough terrain that my baby would literally nap in his carseat while I was out wheeling aggressively enough to warrant an inclinometer. Moreover, it contributed to me making climbs that stumped several open/open Jeeps.
Having this experience in mind, I have had the ASB on my F250 disconnected since a couple days after I got it (after my first try on some very mild trails and forest roads). Of course, it still rides quite rough offroad compared to the 4Runner it replaced (until I get to my planned suspension and tire upgrades). But, before removing the ASB, the ride was about like what I'd expect in a Sherman Tank.
So, what about safety? Long story short, after a good bit of math, I determineed that my 3rd gen 4Runner was, at maximum, 3.7% more likely to roll over after disconnecting the ASBs.
On the F250, the front bar is a less substantial part of the suspension. For example, even without the bar, it has less body roll than my 4Runner did WITH the bar. Thus, the numbers make sense that this truck is only 1.44% more likely to rollover now, and will be 1.89% more likely to roll over after lifting it (with the lift height being partially offset by a wider track), if I keep the bar off. After seeing these numbers, I removed the bar today.
Obviously the formulae arent visible, but this is the spreadsheet I built to help me calculate it this time. I did it more for fun, as I did all my 4Runner's math on paper. But, this will make it easier to account for different variables (different wheel offsets, more or less lift, etc).
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