"In this entry, I document the complete sewing processes of the Strada CS covers.

I chat threads, stitching techniques, and our choices to surpass Recaro's original specifications on the Sportster CS covers."
- Matt

The end starts here. 

My intention with the Strada series has been to share my experiences and knowledge I have l learned over the last 3 years. At its conclusion, my hope is you will be better equipped to understand and discern quality in the upholstery processes - and select your Bespoke Recaro's specifications with confidence. 

For many unfamiliar with upholstery work, they will most often be under the assumption it is mostly about sewing - yet as we begin entry number 7 in the Strada CS series, not a single thread has been sewn.

We will finally get to sewing in this entry - but to understand sewing, we first need to explore the world of threads. 

The world of threads. 

As a reminder, I speak to the choices we made to elevate the Strada cover and the specifications of my seats. 

For wider scope information and to explore options available, I have elaborated on threads in the material selection of the Bespoke Recaro seat program and created a page for it here. 

No matter your specifications, we use high quality threads from AMANN as used supplier by European OEMs.

Color.

The first step to selecting threads inevitably begins with color. A world of limitless choices present many opportunities to be tacky, selecting the right thread color to complement your covers requires mindful consideration. 

For the Strada CS, I sought to keep within a OEM Plus mindset. Unsurprisingly, I picked black - as Recaro did on the CS and BMW did on the original black leather seats. 

Size. 

We decided to divert from original by increasing the thread size. It's a subtle detail that will upscale the aesthetics of the cover.  

The original threads used by Recaro and BMW are size 135. We increased the thread diameter to size 210.

The numbers are trade lingo; they are used to match the thread with the correctly sized needle and sewing machine. The original 135 threads are usually paired with a needle size of 19 gauge. The Strada's 210 threads are paired with a needle size of 23 gauge. 

The auxiliary benefit to a larger thread is durability: our selection increases tensile strength from 20.64 lbs to 30.72 lbs. 

The Recaro is on the left. My Strada's thread selection is on the right. 

Style.

The original threads are made from polyester and use a continuous filament. We opted for a continuous braided filament. 

The thread is an assembly of multiple threads intertwined to create the braided aesthetics. It's an extremely subtle detail that further upscales the Strada covers. 

Settings to the craft.

With knowledge of threads established, we now needed to understand how a sewing machine operates.

In simplistic terms, sewing is achieved by piercing the materials with a needle upon which the primary thread is attached to. The primary thread goes around a bobbin, hooking upon a secondary thread to create the hook connecting the materials.

The process creates a single lockstitch - a stitch is defined by the thread between two holes.  For visual reference, watch this video. 

Every craft will have its secrets, beyond the myth - they are most often personal preferences of the artisan. The same applies to sewing techniques and the machines that are used. As such, I will glance over the sewing machine operations and the variables at play - it would otherwise require a complete upholstery class.

Of note,we use high quality German and Canadian industrial sewing machines, notably from PFAFF and TechSew.

We use needles from Groz-Beckert. They are coated with titanium nitride to harden the surfaces and improve durability. 

Needles come in various sizes and are matched to thread sizes. 

This is the bobbin for the secondary thread, hidden away under a sliding cover.

This is the spare secondary bobbin. It loads the thread in sync with the primary thread. 

The speed of the stitching action is controlled right here. The unit of measure is RPM. 

Below are walking feet - designed to provide alignment and pressure upon the material. 

They are bolted ahead of the needle and help move the material forward for the next step. 

Each will have their own features and are ultimately an upholsterer's personal choice.

The purpose of the large grey knob is to allow adjustment for material thickness. It raises the entire sewing machine off the table upon which it sits. We rarely use this for seat covers as most materials are similar in thickness. 

Stitch length.

The sewing machine enables control of the stitch's length - as a reminder, it is the distance between each hole. Using a knob on the machine itself, the distance is adjusted using round numbers ranging from 3 to 9.

Changes to the distance have an impact on aesthetics and strength. For the Strada design, we measured and mimic'ed Recaro's distance (no, it is not 5!). 

A turn of the wheel is highlighted by a flashing blue light - representing a single stitch made. 

Ready, set - sew!

With the basics laid down, it was time to finally begin sewing. We started with the lower sections' bolsters. On the Strada design, the design remains unchanged compared to a Sportster CS. 

The first step is to create the seam line by sewing sections together. This seam line connects and holds the sections together - yet it is unseen.

Sections are aligned per the templates previously created and the cuts made throughout the sections. They are used as visual references to align and precisely sew.

Throughout the sewing process, small cuts are made in the material to provide flexibility and stretchability for contouring the bolsters. 

Failure to do so will create bumps on the underside that translate to visible deformation on the top side. The section was test fitted on the foam to confirm the absence of imperfections. 

The picture below shows the underside of the connected sections. As you can see, there are two stitches. The lower line is the seam stitch - or commonly called the assembly stitch. 

The upper line is the topstitch - it is what you see on top of the cover. It is not merely an aesthetic stitch, it is sewn through the connected sections and adds strength to the cover.

The French stitch. 

We continued with sewing the bolsters with its outer sections. They will be the first sections seen when opening the car, and are subject to the most wear along with the upper section's side bolsters. 

We diverted from the original Recaro stitching choices and chose to upscale the covers with French stitches. It is a dual topstitch technique, with stitches running in parallel to the seam line.

This technique is associated with premium upholsteries across exotic car manufacturers. Of note, it is what BMW M uses on most of their seats.

Even with matching color, threads create contrast with leather, Alcantara and fabric due to the different material. We felt having French stitching on both seams would have been excessive.

The French stitching process is more time intensive and requires an acute eye for symmetry. The end result is superb: the increased size and slightly offset stitch techniques add luxurious texture to the covers. 

Locking stitches. 

The original Recaro covers use specific stitching and underside material on the Bolster sections to lock the stitches.

By the front lower corners, the stitches are locked together using a stretch stitch technique. The machine settings are changed and the needles move backward into the previous holes, doubling up the thread and creating the locking stitch. 

Hiding sewing lines. 

Upon sewing the French stitches, additional fabric was put underneath to strengthen the assembly. The material connects the two top stitches, acting as foundation between both.  

The black fabric also acts as a cloak, ensuring the foam's bright white and yellow color is not seen when the cover is stretched. This technique is used across all outer bolster sections prone to stretching. 

The hidden stitch. 

With the lower bolsters completed, we moved our attention to the center section and M-Texture reproduction fabric. As with leather, alignment markers were cut after careful consideration for alignment of the M-Texture pattern. 

The lower section uses a hidden stitch: it is the assembly stitch alone that connects them.

This stitch type is used by Recaro and BMW on their seat covers. It is the go-to as exposed topstitching on center sections is problematic in the long term - threads can get caught onto clothing and damage can ensue. 

I've discussed M-Texture's alignment challenge at length in the entry "Style is eternal.". No matter the precautions previously taken, we validated the alignment on the seats once more - it checked out.

Afterwards, we proceeded with final assembly of the lower sections. The bolsters were stitched to the center sections using a hidden stitch. The rear Alcantara section was sewn during this process. 

Underside stitching.  

With the topside of the covers fully completed, we moved our attention to the underside. The next step was to stitch the various components that secure the cover to the shell and foam.

To begin with, we stitched the outer gasket - it is the rubber strip upon which clips are fitted to secure to the outer shell's channel. If gaskets and clips were damaged during removal of the cover, we replace them with brand new Recaro assembly components. 

The underside's center section of the cover is secured directly to the foam. Here, Recaro uses 2x mechanisms: velcro and clips. 

Velcro is used across seams perpendicular to the bolsters - whereas rubber strips are used in seams parallel to the bolsters. The later mechanism stretches the cover more firmly and is designed to sustain the loads from body weight shifting left to right. 

Both components are stitched directly excess underside material at each seams. Having the stitch properly located on the material is crucial to avoid bagging effects later on.  

The upper section's challenge. 

With the lower sections completed, we started sewing work on the upper sections. They are inherently more challenging than the lower covers: there are more sections, they are bigger and they will be more clearly seen.

The Strada design presents its own challenge: the added center section adds an extra alignment step . The difficulty is compounded with the M-Texture reproduction fabric. Tolerances to visual defects were far higher. 

No matter the precautions taken with alignment markers - we got it wrong. We had to cut and realign the middle M-texture section. On the 2nd attempt, we got it. 

With the M-Texture alignment confirmed, we proceed with stitching the inner side bolster section. As it traverses the entire cover from top to bottom - precise template work and alignment markers are of outmost importance.

Before proceeding with stitching the outer bolsters, it was easier to immediately stitch the underside velcros.

The outer bolsters. 

We followed up with sewing the outer sections together, matching the stitching styles of the lower sections. 

The outer stitch used the French dual topstitch and additional underside material, whereas the inner bolster stitch would use the Single topstitch.

These stitches are the most important to the aesthetics of the covers - they are also the most difficult. The shape and length of the bolsters require sustained concentration, dexterity and endurance to continuously hold, cut and align the material for precise sewing. 

The final trim. 

As with the lower sections, the assembly components were sewn on the underside of the covers, along with the outer gasket. Along the way, excess material was trimmed to ensure a precise fitment of the cover on its clips and velcro.  

Herein was the true final step: we positioned the original Recaro branded staple on the bolsters, in its original position.  

After writing this entry, my hands hurt - but not early as much as David's after sewing all covers.

Up next: the final assembly of the covers and the complete seats begin.

It was worth the pain.