The internet is overflowing with placebo effects and exaggerated claims. Facts often get tangled up with feelings, blurring the truth. After spending some time driving with the Jass Performance seat lowering brackets, the honeymoon phase was over—it was time to put down the roses and pick up the tape measure.
At first, I suspected the brackets weren’t actually increasing legroom, but after more seat time, I began to wonder if they were making it worse. The increased seat rake made it difficult to tell at first—sitting lower in the seat pushes your knees and thighs up, creating the illusion that legroom is unchanged. Spoiler alert: it’s not. In reality, legroom wasn’t just unimproved; it was reduced.
I suspected this issue during installation—allow me to explain. Due to the shape of the brackets, moving the seat to its most rearward position limits its travel. This happens because the rails now dip below the seat mounting point rather than remaining level or above it.
This design constraint is why the Jass Performance instructions advise cutting off a portion of the inner seat rail. Removing that section allows the seat to move further back before the rail contacts the bracket, increasing total available travel.
Here’s a photo of the seat and rail in their most rearward position so you can see exactly what I’m talking about:
During installation, I was fairly aggressive in trimming the OEM inner seat rail to maximize seat travel. However, if you cut much more than recommended (which isn't advised), you'd start cutting into the captive bolt plate that secures the seat mounting bolt—a definite no-go.
So, how much seat travel do you actually lose with these brackets? To demonstrate, I slid the seat to its rearmost position (where it would provide the most legroom) and marked the front of the rail with a piece of bright green tape:
I then reinstalled the OEM seat rail brackets and moved the seat to its most rearward position. After photographing and measuring, the results speak for themselves:
As you can see, with the OEM brackets installed, the seat gains approximately 1.25 inches of additional rearward travel. However, I wasn’t sure if all of that travel was truly usable or if the seatback would hit the rear interior trim before reaching its full extension.
To test this, I reinstalled the Jass brackets, moved the seat to its rearmost position, marked a fixed reference point on the accelerator pedal, and measured the distance to the rearmost stitch line on the seat. To ensure accuracy, I had my wife take photos while I maintained consistent pressure on the tape measure. Here’s the measurement with the Jass Performance brackets installed:
I then reinstalled the OEM brackets and took the same measurement. Once again, the results speak for themselves:
Yep, with the OEM brackets reinstalled, I regained about 1.25 inches of seat travel. This was consistent with the seat travel measurements I had taken earlier with the seat out of the car.
While the brackets are well-made and do provide a substantial increase in headroom, I don’t find their claim of retaining full seat travel to be accurate. I can’t speak to right-hand-drive vehicles overseas, but for my USDM NC2, I lost over an inch of legroom with these brackets. Some of that was likely offset ergonomically by the lower seating position, but given my frame (more legs than torso), I ultimately decided to switch back to the OEM brackets. Finding More Headroom without Lowering Brackets? While going back to the OEM brackets did provide some relief for my right leg, I have to admit I did enjoy the extra headroom the Jass brackets offered. In a previous post, I modified the seat mounts to gain an additional 10mm of headroom. Since I was already working on the seat, I figured I’d dive further into seat-lowering mods that wouldn’t result in decreased legroom.
Next up was the infamous "Gordy M" mod, which is known for lowering the rear of the seat without making permanent modifications. The concept is pretty simple. There are four bolts that secure the seat rail to the lower seat pan, which I covered in my previous post (and used an angle grinder to remove the spacers/risers from). With a bit of maneuvering, you can actually position the rear seat mounts above the seat pan. Instead of bolting to the frame from below, the seat mounts attach from above, effectively lowering the rear of the seat pan and providing extra headroom. If you're having trouble picturing this, I snapped a couple of photos to help illustrate what that looks like. Normally the seat mounts would be below the rear of the seat pan:
Don’t mind the fact that mine have been cut up with an angle grinder—just minor details!
Both the front and rear seat mounts have a fair amount of rotation and maneuverability. As a result, you can actually position the seat pan below the rear mounts.
To accomplish this, you'll need a long bolt and something to use as a spacer to fill the gap between the seat mount position and the seat pan.
Keep in mind, this mod only lowers the rear of the seat pan by nearly two inches—not the entire seat. This doesn’t affect the seat back, which creates a nearly two-inch gap between the seat bottom and the seat back.
Did it provide a substantial amount of headroom? Absolutely! Was there any loss of legroom? None that I measured. Was it exactly what the doctor ordered? Not exactly.
The gap created between the seat bottom and seat back significantly alters the lumbar support and overall feel of the seat. When I sat in the car, the seat felt awkward and unsupported. As a result, I decided this wasn’t the route I wanted to take.
As a long-time tall Miata owner, having owned several NA and NB models in the past, I turned to my old friend: the turkey carving knife. That’s right—it was time to revisit a popular mod on the NA and NB: the foamectomy.
I removed the seat pan from the seat foam but left the leather seat cover in place to avoid dealing with those maniacal hog rings and to ensure everything stayed tight when it was time to reinstall the seat.
I know from experience that when you start cutting seat foam, caution is your friend. In your search for more headroom, it’s easy to end up with an uncomfortable seat. So, I made a mild cut towards the rear of the seat to add a bit of extra headroom without feeling like I’m sitting on a piece of metal.
Pay no attention to the hideous marring of the seat foam. I’m not exactly a sculptor of beauty—just a caveman who enjoys playing with angle grinders and turkey knives.
The result? Between cutting off the seat mount risers and performing the mild foamectomy, I now have just over an inch of space between the top of my head and the soft top. Before I started, my hair was brushing against it. This didn’t provide as much headroom as the Jass brackets, but it also didn’t reduce my usable legroom. Overall, I’m happy with the amount of headroom I now have with the top up, and I have no plans to go searching for more.
But What About the Seat Rake?
When I installed the Jass brackets, they added quite a bit of seat rake, which helped with thigh support. The stock seats are fairly flat and leave something to be desired in that area. The Jass brackets might have been a bit extreme in terms of the rake I was looking for, but they were definitely a step (or slight overstep?) in the right direction.
Performing the foamectomy actually added a bit more rake and thigh support, but since I was determined to perfect the seating position for my body type, I had another idea in mind.
Since I was already messing around with the seat pan and seat mounting brackets, I figured the easiest way to gain seat rake without sacrificing legroom or headroom was to add a few washers between the front seat mounts and the seat pan. But instead of relying on guesswork, I grabbed my trusty angle finder gauge to get a baseline measurement of the seat rake:
I then added three washers between the front mount and the seat pan:
To gauge the results, I pulled out my angle finder again:
I gained just over a degree of rake without any loss of legroom. It’s not quite as aggressive as my previous measurements with the Jass brackets installed (over 24 degrees), but it’s a substantial improvement over stock (19 vs 21 degrees).
Subjectively, the seating position is now very comfortable, and the amount of thigh support is pretty much spot on.
At this point, I’ve pretty much exhausted all of the seat comfort modifications I can think of and believe I’m done tinkering. I might consider adding a couple of washers behind the upper throttle pedal mount to gain just a smidgen more legroom—but honestly, I don’t think it’s necessary. At that point, I’d just be tinkering... you know, for science.
After all the tweaks and mods, I’m finally happy with the seat position and comfort in my NC. While there’s always the temptation to keep tinkering and fine-tuning, I’m confident I’ve found the right balance of headroom, legroom, and support for my body type. The journey from stock to custom has been an interesting one, and while it might not be the easiest or most straightforward path, it’s certainly been worth the effort. Now, it’s time to enjoy the ride—and maybe, just maybe, leave the angle grinder and turkey carving knife on the shelf for a while.
UPDATE: I installed three washers behind the top mount of the throttle pedal, and... surprise! It was actually noticeable!
For science (and possibly to prove I’m not just messing around), I removed the throttle pedal again and taped three washers to the back of the top portion of the mount. The goal was to make the pedal act more like a lever, pushing itself slightly away from my foot. Was it strictly necessary? Probably not. But I grabbed a slightly longer M6 bolt just to be on the safe side—because why not?
To keep everything in place while I was reinstalling the pedal, I taped the washers together and then taped them to the top of the pedal. Call it a scientific experiment—or just an excuse to play with tape and washers.
It actually worked!
When I trimmed down the pedal mounts by a millimeter or two before, I didn't really notice much of a difference. But adding 3 washers? Now that I actually felt! I’ve gained just a bit more legroom for my right leg while driving—and it only took a few minutes to do. Absolutely worth it!
I can still heel-toe downshift without issue, but I do have to be a little more deliberate when pressing the throttle.
Easily one of the better space-adding mods I've done to the car. It’s not a huge change, but it definitely makes a noticeable difference. And hey, who knew washers could be the key to just a bit of extra comfort?