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Cortex vs Koni gts

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Sbybossman

33
1
I own a 2013 SBY Boss since new and use it as daily driver and have recently experienced thumping from the front driver side going over bigger bumps. Thinking it could be something to do with the strut. That said I have always wanted to change up the struts to coilovers to slightly lower the car and improve the handling. Cortex xtreme grip street seem to be the way to go as I’ve read only good things in this forum. My questions are as follows,
- is the kit simple bolt on?
-does it require any other parts?
Also just realized Koni has new GTS system
-how does it compare to Cortex and what are the differences?

Cost is not an issue as I just want to make the best choice. Thanks, any input would help.
 
How many miles do you have on the car? You might disconnect the stabilizer bar end links and check them for wear. These are really cheap and easy to replace if they are worn out. If your mileage is high and you need struts replaced, it is a fairly straight forward job to replace them if you get struts with the springs already installed. Can be more of a challenge if you try to install the springs on the struts yourself. In fact, I recommend just taking them to a shop and have them assemble the springs and struts.
 
Paul McWhiskey said:
How many miles do you have on the car? You might disconnect the stabilizer bar end links and check them for wear. These are really cheap and easy to replace if they are worn out. If your mileage is high and you need struts replaced, it is a fairly straight forward job to replace them if you get struts with the springs already installed. Can be more of a challenge if you try to install the springs on the struts yourself. In fact, I recommend just taking them to a shop and have them assemble the springs and struts.
Click to expand...
Currently about 75000 kilometers or 46000 miles but currently in storage for the winter so will check this when I bring it out. Thanks.
 
Sbybossman said:
...I have always wanted to change up the struts to coilovers to slightly lower the car and improve the handling. Cortex xtreme grip street seem to be the way to go as I’ve read only good things in this forum. My questions are as follows,
- is the kit simple bolt on?
-does it require any other parts?
Click to expand...
I installed the CorteX xtreme grip street kit along with the torque arm on my 14 GT.

It was transformational.

The kit is complete, no other parts required.
Simple to bolt on? That's relative to your level of expertise. I did it on jackstands in about a week, a lot of that time was due to a steep learning curve. It could be done faster with experience.
 
"Cost no issue I want best choice" is a little confusing because it depends on use. I have Cortex/Koni coilovers on my 2011 and it works very well for a tweener street and track car. But I agree with the comments above - get the clunking fixed, figure out what exactly you don't like or are trying to improve, and then make decisions from there.
 
Another solid choice is an MCS system ( Motion Control Suspensions ). Have had them on various cars over the years and the improvements are dramatic with the 2 way or 3 way systems. Ran the dual system on my Boss 302S and my fabricator who is a huge Penske shock fan dyno'd the MCS ones and was blown away. My son runs a set on his EVO 9 and they are the standard use shock for NASA in American Iron ( if I remember correctly )
 
Last edited:
The thumping can be caused by many things and is less likely to be caused by a strut failure. If you do need to replace the struts, you should have an idea of what specifically you are trying to improve or change. Chances are you will be more satisfied with the outcome.

If you want mild lowering and stiffer rates, a set of matched lowering springs may be enough. While in there you can swap out worn components like strut mounts as needed.

FYI, see the classifieds, I am selling a set of Steeda Boss springs.
 
For just street driving, lowering springs (like those Steeda Boss springs for sale) and Koni yellows or Bilsteins are the easy button. Koni yellows give you rebound adjustment. Honestly, every additional thing you can adjust on the suspension is another chance to get the adjustment wrong. You can slightly slot the mounting holes on the strut ears to get a bit more camber and save money over camber plates - you don't need as much camber on the street. Put a paint marking at the strut-to-knuckle edge so you can check if the camber changes.

If you want a coilover option for the street, I'd recommend the Koni-based kits from either Cortex or Ground Control. Definitely talk to them before ordering about the road conditions where you are (potholes, frost heaves, etc.), your driving style and venues (street vs. autocross vs. track), and how you feel about the stiffness and balance of the stock spring package. Ground Control came up with custom rates for a Miata that were spot-on for what we needed.
 
Dave_W said:
For just street driving, lowering springs (like those Steeda Boss springs for sale) and Koni yellows or Bilsteins are the easy button. Koni yellows give you rebound adjustment. Honestly, every additional thing you can adjust on the suspension is another chance to get the adjustment wrong. You can slightly slot the mounting holes on the strut ears to get a bit more camber and save money over camber plates - you don't need as much camber on the street. Put a paint marking at the strut-to-knuckle edge so you can check if the camber changes.

If you want a coilover option for the street, I'd recommend the Koni-based kits from either Cortex or Ground Control. Definitely talk to them before ordering about the road conditions where you are (potholes, frost heaves, etc.), your driving style and venues (street vs. autocross vs. track), and how you feel about the stiffness and balance of the stock spring package. Ground Control came up with custom rates for a Miata that were spot-on for what we needed.
Click to expand...
 
Thank you everyone for comments and suggestions. I will sort out the clunking when I bring the Boss out in the spring and go from there.
 
Paul McWhiskey said:
How many miles do you have on the car? You might disconnect the stabilizer bar end links and check them for wear. These are really cheap and easy to replace if they are worn out. If your mileage is high and you need struts replaced, it is a fairly straight forward job to replace them if you get struts with the springs already installed. Can be more of a challenge if you try to install the springs on the struts yourself. In fact, I recommend just taking them to a shop and have them assemble the springs and struts.
Click to expand...
Hey Paul kinda digging up this old post buddy. I was looking to see of anyone has tried Koni GTS as well . I was planning on getting koni yellow s and steeda springs for a dual purpose but would love to know if I would get better handling and overall better suspension with the GTS system. I have 117k on a 2014 GT and it sounds like I should just my end Iinks too? Anything else that s probably worn out ? My shocks now make noise going over speed bumps
 
I am on FP Track Handling struts and shocks with BMR most everything else. Inspect every pivot point and replace everything that is rotted or loose. I have 74k on mine and all of the front is good. Had a bent front end link which I found when I installed the Steeda links.

When I did shocks, springs, and bars on the rear I found worn and rotted LCA bushings and replaced those with bearings. Good visual inspection and trying to flex everything joint to feel for looseness is very important.
 
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