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  #81  
Old 12-13-2017, 10:31 AM
gills gills is online now
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bump for experiences about GK knuckles for grip....

Was going to open up the wallet and purchase their grip knuckle, but like anything else, after further research I get more hesitant.

Their current "grip knuckle" uses OEM ackerman, which I believe is a compromise to "appeal to a wider customer base." Ackerman tuning is very tire specific, but I think it's somewhat safe to say that the tires we all use have very similar tire load sensitivities and could probably benefit from less Ackerman. Plus, I'm rarely steering more than a 1/4 turn to begin with out on track.

Like Def mentioned earlier in the thread, a less loaded tire (inside tire) requires less slip angle to achieve peak lateral force. In conjunction to running static toe out usually on the front (which most of us do), lots of Ackerman can drag the inside tire more at corner apex, heating it up more, wearing it more and decreasing grip potential.

The counter argument is that increased drag on the inside tire relative to the outside from pro-ackerman causes a torque on front axle in the direction of the turn, which seems like it can be beneficial.

The general consensus in the end is that for highly transitional events like Auto-X, pro-ackerman is desirable. Car running on tracks with larger radius turns and sweepers, less ackerman should be beneficial. F1 does actually use reverse Ackerman for many tracks apparently as well.

Since my car is track only, I'm very curious to the less ackerman approach.

As per GK, their current V3 knuckle is near zero Ackerman with very quick steering. They actually have two V4 revisions in the works; a standard and a pro-drift. The pro-drift is similar to V3 with steering but also has extra mechanical trail. The standard V4 will be same Ackerman to their V2 but with some extra brake caliper clearance.

Anyway, what has been everyone's experience with less Ackerman geometry at the track and GK knuckles as a whole?
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  #82  
Old 12-13-2017, 07:04 PM
Def Def is online now
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F1 cars ALWAYS use anti-ackerman from what I've seen on on-board shots. In Monaco at the hairpin it's very easy to visually see the anti-ackerman.

Me personally, consumables are too expensive to burn up for just a theoretical tiny improvement of creating a turning torque on the front axle. And I'd argue that WHENEVER a tire slips to a large degree, it provides less grip than a tire at a small/optimal slip angle. The high inner tire wear on track with stock ackerman of many cars gives evidence that the inner tire is slipping a lot. Therefore, the whole, "it'll provide more turning torque" is debunked thoroughly with just that simple observation.


So for me, less ackerman gave better tire wear, and it seemed like better front grip (although lots of things changed when changing the knuckles, so it's hard to narrow it down to just that).
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  #83  
Old 12-14-2017, 08:46 AM
gills gills is online now
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What version GK knuckle did you have again?

I'm in the same line of thought, which is why I was surprised that they market the GK knuckle with stock ackerman as the grip knuckle. But, I also understand they want to cover a broad base. One thing their grip knuckle has is a provision for ABS sensors, where their others do not.

However, most of us do run some toe-out combined with -3.5+ degrees of camber, so rolling down the straights isn't doing the inside of the tires any favors either.

Anyone ever map out OEM Ackerman over a steering angle range? I guess I'll do this when I check bump steer as well, but I have modified OEM knuckles that I didn't modify so who knows where it's at.

Anyone have experience with these: https://www.driftworks.com/driftwork...ter3-hubs.html

Settings for drift and grip, but it doesn't say what ackerman relative to stock.
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  #84  
Old 12-14-2017, 08:49 AM
Def Def is online now
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Aluminum modular knuckles with extreme arms.

The wear was always on the VERY inner edge of the "inside" wheel for the track direction that had the most wear. It wasn't from braking or going down straights, definitely a narrow strip that exactly matches what it looked like for a contact patch when cornering. My E36 M3 did the exact same thing. Going to the knuckles eliminated the wear completely. My roll center height was similar between the two knuckles (stock with FLCA and balljoints spaced down vs. GKTech and stock ball joints).
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  #85  
Old 12-14-2017, 09:09 AM
gills gills is online now
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Were there two versions of aluminum knuckles?

I'll have to take a closer look at my tires next time then. Tire temp spread for the track direction inside front (RF) at my home track has inside tire temps that are 20 degrees hotter than the center. The outside tire is a 10-20 degree spread from inside to outside (-4* camber). I don't want to pull camber out of the RF either because the most important turn on the track is a left hander that starts the longest WOT section of the track.

So is that Driftworks/Geomaster 3 knuckle something to run far, far away from? Looks interesting nonetheless.
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  #86  
Old 12-14-2017, 04:43 PM
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Only one version of Al upright, modular steering arms.
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  #87  
Old 12-23-2017, 10:21 AM
PoorMans180SX PoorMans180SX is offline
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Quote:
Originally Posted by gills View Post

So is that Driftworks/Geomaster 3 knuckle something to run far, far away from? Looks interesting nonetheless.
It definitely has less ackerman than stock, you can see that easily enough.
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