Tech tip: Spread in upper link arms!
The popular upper link arms option which is included in XRAY X4’25 & 26 cars allows for some interesting variables which some drivers may not be aware of, or have spent time with - upper arm spread. In this post I’ll guide you through what it is, and how you can use it to tune your car.
Most people (including myself) will use the same eccentric caster inserts with upper link arms as they would with the CFF upper arms. As an initial setting, and to make a fair test between CFF and upper link arms, this makes sense. Most of the time, it will give you a neutral and predictable handling. I don’t plan to confuse you, so whenever changing the spread in the upper arms, do it step by step, small steps at a time, to best understand what it does and how to apply it in a race situation.
The theory:
More spread: links further apart. The caster inserts are either reversed, or changed to a different dot, to bring them further apart. See example in pictures. Links further apart makes the upper suspension assembly stiffer.
Less spread: links closer to each other. The caster inserts are either reversed on one side, or brought closer together by using a bigger dot number. See example in pictures. Links closer together makes the upper suspension assembly softer.
More spread in both front and rear: makes the car feel stiffer, takes grip away, which makes the car flatter and often more predictable. Recommended mainly for higher grip situations.
Less spread in both front and rear: makes the car feel softer, increases grip, which makes the car roll a bit more, sometimes to the point where it’s less predictable. Recommended mainly for low- to medium grip situations.
More spread in front: the car will be initially more reactive, but will have less grip during mid corner and on corner exit. The front grip will generally feel reduced.
Less spread in front: the car will be initially less reactive, but will have more grip during mid corner and on corner exit. The front grip will generally feel increased.
More spread in rear: the car will feel more stable/supported, mainly on corner entry, and the car won’t feel as it’s rolling or diving as much. The rear grip will generally feel increased, and the car will feel more predictable.
Less spread in rear: the car will feel less stable/supported, mainly on corner entry, and the car will feel like it’s rolling or diving more. The rear grip will generally feel decreased, and the car will feel less predictable.
Use the above info to fine tune the handling for different conditions. My preference as of lately has been regular spread for the front upper links (kit setting) and more spread rear links, for a more stable car on corner entry, but with maintained mid corner to exit steering.
 
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