Radius Arm Location/Length

[GahnRacing]

I feel like this could be a useful thread for people building their own radius arms

When I built my Ranger, I sort of just followed the “monkey see, monkey do” method. I feel like there must be a sweet spot for radius arm lengths. I had the notion that building your radius arms to the same as your driveline (TTB) would be the key, but looking back, does it really matter?

1.How long is too long, how short is too short?
2.What angle is best in relation to ride height?
3.Is driveshaft plunge really a major issue?

 

[Caidan97]

For a note on radius arms that are long..
If your radius arm pivot is past the kick on the frame more than a few inches then it starts to interfere with up travel and you will be forced to move then outside of the frame rails or lower the pivots.. yikes. I believe mine are 36” long if I remember correctly and it leaves about 1/4” gap between the radius arm and frame when the beam hits the frame. I have no problem with driveshaft plunge but tbh I never payed attention to it…

 

[dwphoto]

@mikeee805 Big radius arm guy

 

[Giant Geoff]

I like them to be in front of the tranny cross member. If they are too long, you don't get that caster increase. If there are too short, you get wheelbase change. Main thing is to add a lot more caster when you make some.

 

[gtrainor21]

I like them to be in front of the tranny cross member. If they are too long, you don't get that caster increase. If there are too short, you get wheelbase change. Main thing is to add a lot more caster when you make some.

I see that C10 lurking in there, how did that truck come out with beams set up on the stock frame? I've got a K5 I'm looking into beaming the front like that... but I've seen several people graft new frame horns on the front for beams since the stock ones cause issues with up travel? At least that's what I'm assuming since that's the Issue I'm running into with my other K5 that still has a solid axle up front.

 

[Giant Geoff]

I see that C10 lurking in there, how did that truck come out with beams set up on the stock frame? I've got a K5 I'm looking into beaming the front like that... but I've seen several people graft new frame horns on the front for beams since the stock ones cause issues with up travel? At least that's what I'm assuming since that's the Issue I'm running into with my other K5 that still has a solid axle up front.

The old Chevy frames are weak but the I-beams have way less stress upon the frame unlike an a arm that has localized pressure on each frame horn trying to twist in. Those frames are narrow and take up high to where you have a lot more travel and shock space unlike an F150 where the frame horns are low and wide.