Hello all,

So, I have some FJ springs to toss on the front of my runner pretty soon. I am also looking at going up in tire size. From what I have been able to gather, more caster will allow for bigger tires without a BMC. I don't mind clearancing the bumper and such, but would like to avoid cutting up supporting components. I plan to eventually go up a bit in height later anyways, so UCAs are inevitable. However, I was thinking about picking them up early to allow for the tire size. The biggest concern I have is that I am not sure if the JBA arms will provide enough caster to be an issue with the minimal lift of the FJ springs. Anyone have any experience/input with such a hair-brained idea?

For starters, the BMC doesn’t cut up anything g supportive to speak of. It just trims away a bit of steel that isn’t really needed. You can then replace it by welding in a new piece or just leave it open.

As for UCAs, JBA makes a great product. However, the UCAs they sell for non-lifting trucks is does not add any caster. In order to have additional caster you’ll need to install the UCAs designed for lifted trucks as well as lift your truck


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I'll admit, I haven't really looked into what the BMC entails, I just don't like to cut stuff if I don't have to. As for the UCAs, I know it would have to be the ones that have extra caster designed in. From my understanding, lifting the trucks causes a loss in caster at ride height. So, the arms have more built into them by default. In theory, that would just mean that I would have an excess of positive caster at a lower lift height, right? Would this be so much that I would end up with a front end that could not be aligned properly? From reading around, more positive caster increases straight-line stability and steering effort. I'm thinking about just running with the slightly too positive caster for a little while until my XREAS dies or I decide to lift it early.

Can’t speak to the effects of these arms on non lifted trucks, but in general I’ve always preferred to add extra caster to my performance cars because I prefer the more secure feeling at high speeds. Yes, it does increase steering effort, but I never minded that, and as said, always felt the trade off for added stability on the ighway to be well worth it. Not sure how much extra caster they add, but I’ve rarely seen a printout for one of these trucks where they have gotten more than 3 deg. I’ve always dialed in at least 5 for my performance cars.

So, I called JBA the other day. Their UCAs add 3* of caster over the stock arm geometry. This will apparently make the end result around 7* of caster at stock height. Marlin also said it would be fine to run them on a 1"-ish lift I have in the works with the FJ springs. So, I think I will pick them up to run at some point soon.

I don't see why the alignment tech couldn't add negative caster with the JBA arms to get you to 3 or 4 degrees.