Mods Subaru WRX

Mod: GR STI Front Knuckles on a GD WRX

A comparison of the bolt-in bearings.

This modification was mostly inspired by the 22B owners looking for a better bearing solution for their Subies. In 2008, Subaru switched to a bolt-in bearing for their front 5×100 hubs. To make this work for earlier models, an 8mm CV spacer is needed between the axle and the hub.

Since I plan on going with 5×114.3 eventually, I decided go with a set GR STi knuckles that I found for pretty cheap. GD STi parts are getting expensive so finding compatible parts is becoming more helpful.

GR STi Front Knuckles and Hubs

Comparing the GR STi knuckle to the GD WRX there are a few changes. The most obvious is the bolt-in bearing (the bolts were removed for another comparison) vs the press-in bearing. The strut mount is wider and taller on the GR STi and the tie rod arm seems shorter and a bit lower on the GR STi. Although that could be the difference between the space the bolt-in hub takes up now. And there is a big section of cast iron between the caliper mounts on the GR knuckle as well. I’m not sure what that added material is for (probably added strength) but it interfered with my Evo Brembos. I thought about cutting it off but I when with some reman STi Brembos instead.

If the tie rod arms are shorter then that should improve the steering rate. The closer the tie rods are to the pivot point (SAI) the quicker the knuckles should turn at the cost of heavier steering.

5×114.3 v 5×100 Bolt-In Bearings

One thing that surprised me what the physical difference between the bolt in 5×100 and 5×114.3 bearings. I guess I shouldn’t have been surprised but the 5×100 hubs look really small in comparison.

Unfortunately, the bolt pattern is slightly different so they aren’t interchangeable; at least not without some machining.

The shot below really shows the difference between the two hubs.

Subaru front suspension has remained relatively unchanged since at least the 1990s. It depends on what hub bolt pattern you have. So upgrading your front suspension is doable as long as your struts, brakes, and axles will work together.

For bolt-in 5×100 bearings, the front cv axles are the problem. The GD splines stop at around 8mm before the face of the cv joint.

As a result, the axle will not full seat on 5×100 bolt-in bearings.

The 5×100 bearing splines also start sooner…

Whereas the 5×114.3 bearings have more of a recess before the splines.

So to fix this issue, people have been making 8mm cv spacers to take up the gap.

Image Source: user “GF8 Sti” [link]

GR axles do not have that space between the splines and the cv joint face, and if have a transmission that doesn’t use axle stubs then GR axles might be an option. Conversely, if you have axle stubs, then you can either convert to 5×114.3; use 8mm spacers; pull the stubs out (requires splitting the transmission), or potentially making hybrid axles with either GD trans ends on GR axles or GR hub ends on GD axles.

This is one reason I made the CV axle table. Subaru’s are legos but finding the right pieces can sometimes be a nightmare when you need to make custom parts. Considering how inconsistent the shaft splines are, you have to take the axles apart to verify, I decided to run GR knuckles and keep my stock axles.

The install is straightforward. Although if you have ABS I’m not sure what needs to be done to keep it. I deleted my ABS some time ago.

Also, in case you are wondering, the GR STi knuckles are heavier: 14.5 lbs v 19.3 lbs.

The next update will probably be my new wheels.


2 comments on “Mod: GR STI Front Knuckles on a GD WRX

  1. Peter Spinale

    What’s the strut solution? GR struts I assume or coilovers?


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