Yes it makes a difference.
All coil springs have the potential to bow in one direction or ten. With Ford radius arm suspensions, you get to play with most of those options!
The longer the spring, the more likely to bow. It might also be a factor between linear rate and variable rate coils. With two or more winding rates, the tendency to bow might be reduced or enhanced. Never thought about it much, or tested that theory. But maybe others here have?
You can't tell a thing though, until the springs are at ride height first of all. That means letting the full weight of the suspension on them, assuming all the weight that's going to be on the vehicle is on the vehicle. Engine and such, which looks to be the case here.
Then you must make sure that the axle (or the spring mounting cups) are centered in the frame beneath the spring mounting towers. Any offset in either direction will let the coils bow out.
Next big factor is the mounting surface that the lower cups sit on. If the new arms take this into account exactly for a 3.5" lift, that reduces the bow effect. If they're set up more at a factory angle, or optimized for a lift that's different from a 3.5, then you can still have bow.
The longer the spring, the tighter the coils and the smaller the wire, and I think the more closely the coils are wound, the more likely they are to react to input by bowing out. Tall 4wd truck springs being the most prone to this. Short passenger car springs that are practically captured for much of their length might still bow, but you'll hardly ever notice it without looking very closely. Coil-over shocks retain the springs in a very straight aspect, so you don't normally get bow on those. They are usually linear rate as well, with variable rates handled by multiple separate springs instead of combining the features into a single coil spring. Exceptions being factory strut equipped vehicles with captured and often variable rate coils. Maybe they make them with the sometimes obvious beehive shape to reduce this? Also never thought about that, but might be "a thing' when it comes to designing springs and suspensions.
But those are mostly short anyway, with widely spaced coils, so perhaps not as much change to bow.
Add to that any change of angle of the cups or inconsistency in the towers, and these effects would certainly be enhanced.
All of this is at ride height. If you have perfectly aligned springs with no notable bowing, that is likely to change from moment to moment as the suspension cycles up and down during normal driving and flexing especially off road.
Next time you come across pictures of ramp contests, look at the coils of a fully flexed out suspension and you're very likely going to see extreme cases of bowed springs.
Paul
