Why Use diff drop kits and upper control arms on your Ute?
Diff drop kits and upper control arms serve very different purposes but together enable you to run much more capable suspension on utes and wagons with Mcpherson strut style suspension like the Toyota Hulux built from 2005-2019 and on
Diff drop kits are probably easier to understand as they only have a single purpose in life. That is to drop the front diff below factory height. This is done to reduce front CV angles to prevent binding, broken CV’s and damaged CV boots which tend to splatter grease all over the underside of your vehicle. Diff drops allow you to run longer travel shocks and higher lifts than what can be achieved when the Front Diff is in its standard location.
Upper control arms, on the other hand, are a bit harder to get your head around because they are essentially a wheel alignment product that restores camber and caster that is thrown way out of whack when doing a high lift utilising long-travel suspension.
Manufacturers have a wheel alignment specification for a reason, tyre wear, return to centre steering, tracking, high-speed stability, it’s a geometry thing. Well designed Upper Control arms as a bolt-in the system will have 5 key points that make them worth the investment.
- Will give you 4 degrees of caster correction,
- Give more clearance with larger tyre diameters.
- Shock and strut clearance to allow more wheel travel up and down.
- Angled ball joint cup to work with the extra travel and restore camber.
Let's have a look at caster first. By increasing caster on your ute, as well as improving on-road performance, you actually move the wheel further forward and away from the body mount situated at the rear of the wheel well and therefore make room for larger tyres. The diagram below will help understand what caster is.
Camber is also significantly affected by higher lifts. As you lift the suspension, the bottom of the tyre rotates inwards resulting in increased positive camber. This reduces the contact patch on the road which in turn results in excessive tyre wear and poor road handling.
So by angling the top ball joint realigns steering geometry for both camber and caster. As long as an aftermarket upper control arm gets caster back within factory specs, there is sufficient adjustment to get a perfect wheel alignment for Camber.
Caster, on the other hand, does not have much adjustment available. Some upper control arms have an adjustable ball joint, and the reputable brands usually do a reasonable job, some of these ball joints are expensive (up to around $150 or more) and seem to have a short service life. Also, the top nut that secures the balljoint has no locking mechanism to secure it and they frequently come loose.
Not only is this a bit risky, but you also lose your wheel alignment so you are up for the added cost to fix that! So on balance, we favour fixed ball joint upper control arms provided they have been well designed to cope with the changed suspension geometry that comes with a suspension lift. So a good set of UCA's is important when you are chasing the last millimetre of lift you can squeeze out of your suspension kits setup on your ute.
I recall the first time I drove my Toyots Hilux after fitting upper control arms, I immediately noticed much firmer steering feel that also made the steering feel much more precise. I put this down to the larger contact patch on the road. I’ve been enjoying the benefits of improved handling and better tyre wear ever since.
Just one final note on Upper control arms. Look for ones with a ball joint with a sealed rubber boot. Don’t be tempted to by a set with exposed uniball style top ball joints. These are totally unsuited to Australian conditions and have proven over the years to be expensive to maintain high maintenance part. If you aren’t involved in the desert racing scene where these ball joints are considered a consumable part, don’t be tempted to fit them to your Hilux.