Fox vs King: 2.0 Coilover Comparison - Evaluating Durability & Performance

*TRD*

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When it comes to 2.0 coilovers I have found that most people don't know the whole story about the differences between Fox and King. In order to better understand the differences, I dyno tested a Fox Remote Reservoir Coilover and a King Remote Reservoir Coilover. The article analyzes their performance as it relates to real world off-road driving. Next, I took the shocks apart to look at the piston, seals, oil, and piston rod in order to evaluate how they compare for short term and long term durability.

Fox vs King 2.0 Coilover Comparison

The article focuses on the most relevant information but I am happy to dive into the weeds and discuss any aspect you guys are interested in. For example, maybe someone wants to know why King disks are gold, and what that means for the performance/durability of the shock.

I have been tuning and engineering shocks since 2001. Before starting AccuTune Off-Road I was the chief engineer at an aftermarket shock manufacturer where I invented patented technology used in their premium products.
 

Dirty Harry

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Thanks for sharing Ryan, there was a lot of great information in there. I must confess though that it did feel heavily biased towards Fox, I was surprised to see that you carry both brands at AccuTune after reading the comparison. I was thinking "this dude is a Fox dealer". Like when you praise Fox for running higher nitrogen pressure for "improved resistance to cavitation" but then say if you increase the pressure in the King shocks "higher pressures increase friction and seal wear".

Clearly you put a lot of time and effort into this and know way more about shocks than I ever will, but the way the information was presented made me a bit skeptical. Personally I think that if you just presented the information and let people draw their own conclusions (like you did regarding friction with a statement followed by the graph) it would come across less like you are trying to push Fox shocks.
 

*TRD*

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Thank you for the feedback. Higher pressure leads to higher friction but the amount of increase depends on the specifics of the seals. Fox has less friction at higher pressure.

All of the information presented is from tests or each companies marketing materials, so there isn't a bias. I am working on adding the shaft hardness and possible shaft salt spray results in order to bring more data to that part of the article.
 

Goatpoker

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So, from your data can you say that the flow characteristics of each piston are not statistically different?


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*TRD*

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So, from your data can you say that the flow characteristics of each piston are not statistically different?
I would just say that based on the testing I have done, one piston does not appear to be better than the other, but dyno's are speed limited so some of the compression data has to come from the butt dyno or visual observation.
 

Sreidmx

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Very comprehensive article, man you dove In That pretty deep. I appreciate those graphs. Good job!
 

cllake

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Would be interesting to see a race series King vs out of the box Fox.

Too me the article is definitely unbiased - you are a dealer for both and would make a decent amount more $$ by pushing King products with all the upgrades. Thanks for the write up!
 

De Minimis

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Great write up! As I'm selling all my Fox shocks and replacing them with Fox, is does my heart good to see where my extra hard-earned is going (I did consider King for a bit as I'm having to start over with a new build, but glad I stayed the course).
 

wheezy

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Would like to see a race series king addes to the comparison.


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SPROCKET

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Wow! thanks, its nice to read something that wasnt thrown together and has hard facts to backup whats being said!! keep up the good work
 

Kritter

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To add :

Seals...Fox standard is buna/nitrile parker blend material. Viton is optional per website and every fox I have worked on. The only fox that come with a viton H wiper(their seal) is 1" and then the big dog 1.25" which uses a deep Z viton seal. OEM Raptor uses a HNBR seal and back up plus H wiper and has been touted as one of the best seal packs ever tested by a parker engineer....or so I hear. But .625, .875, and 1.125 dont offer a viton "seal"

Also good to notate that while viton is low friction and great with high temp, it lacks durability that urethane in the king prerunner seal package excels at. Both great sealing packages.

see note about viton(orings) optional here
2.0 Factory Series Coil-Over Remote Coil-over Shock | FOX Offroad

Shafts

Where on each shaft was the hardness tested? My guess is the tenon or at center of one of the ends which would be core hardness which is why the SS shaft wins as the tensile is much higher than the others. The induction harness of the king that goes .050" deep min would be 50HRC min and the chrome is 62-72 HRC for .0005" The results are a bit misleading.

Otherwise great article...if you do servicing or seal kit sales and move volume...give shockseals.com a shout.
 

*TRD*

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Interesting note on the Viton O-Rings, that's different than other marketing material I've read. I will look this afternoon when I revalve some 2.0 Coilovers and update the information. Thanks for pointing that out!

HNBR is arguably the best dynamic u-cup material available. A high quality HNBR will outperform cheap Viton on every test. I've also used XNBR and tons of different (premium) viton blends in custom u-cup designs.

Cheap Viton (every brown or red Viton I have ever used) has terrible wear characteristics, but that's just because they're cheap. High quality Viton can have good durability and low temp sealing characteristics.

Urethane is known for extreme durability (wear & abrasion) but poor friction performance, squeaking, and poor high temperature performance. For these reasons I'd only use Urethane as a wiper, and never a main seal (except cheap shocks which don't get hot ... air shocks/bumps).

Harness was tested on the full diameter away from the ends. The HRc test is the most real world test for evaluating resistance to flying debris due to the tests exact recreation of the events (pressing indenter into metal and measuring permanent deformation). I agree that the hardness results are surprising, but I had them tested again with the same results. The results also correspond to published data on the base material and their heat treatments. In addition I have damaged King piston rods by clamping them in a vise, I have never damaged a Fox or Sway-A-Way piston rod doing the same thing so it all corresponds to the results being accurate.

Here is some supporting information I posted on another forum:

I finally got a chance to send out some Fox, King and Sway-A-Way piston rods for hardness testing and updated the 2.0 coilover comparison article. The leading cause of shock failure is damaged piston rods. The harder a piston rod is, the less likely it is to be damaged by flying rock debris.

Rockwell Hardness is measured by pressing a round indenter into the material at a preset force. The resulting permanent deformation of the material determines the rockwell hardness.

Here are the results from hardness testing performed by a third party:
Fox: 45 HRc
Sway-A-Way: 32 HRc
King: 23 HRc

I thought the results for Sway-A-Way and King seemed low at first, but then I compared them to piston rod material specs.

Fox Material Specs:
17-4 H900
Material Specification Hardness = 44 HRc
Speedy Metals Information for 17-4 PH Condition A

Sway-A-Way Material Specs:
Nitro Steel
Hard to find a core HRc value
I was expecting this to beat Fox, but it didn't.
Nitro Steel is actually the same base material as King (1045/1050)
But it is Nitrocarburized instead of chrome plated
Nitro coating penetrates into the material and is thicker than chrome
I believe the additional coating thickness makes Sway-A-Way shafts harder than King

King Material Specs:
1045/1050 High Carbon Steel, 100 ksi min
Material Specification Hardness = 235 HB (21.7 HRc)
http://www.pmtsco.com/1045-50-high-strength-ihcp.php (see AISI 1045/50 HS**)
Hardness Conversion Chart
 
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