4SR Seam

At 4SR we've always put a heavy emphasis on safety, and we wanted to build something new, better, smarter. Even our first patent was about protecting the rider — specifically the knee and how knee protectors are mounted inside motorcycle trouser legs. Continuous development is often a demanding, complicated road, but "comfort and safety" have always come first in how we develop 4SR gear.

We regularly review the best protectors currently available in the segment and pick the most suitable, safest option for our products. We test leather to make sure we're genuinely offering our customers the best available. We listen closely to our racers and feed what we learn straight back into production. The result: first-class race suits with more than 18 protectors, leather that beat the strictest requirements of EN 13595-2:2002 Level 2 abrasion resistance testing by 60%, and a comfortable cut that delivers unmatched mobility even in extreme positions.

We've continuously refined the cut of our one-piece and two-piece suits for over 12 years, always working to bring customers an even better product. After years of that work, it was time to revisit one of the most fundamental parts of construction: the seams.

So what's a suit actually built from? Several dozen pieces of leather and other materials, stitched together following a precisely defined process. And because a chain is only as strong as its weakest link, the seams matter just as much as the quality of the leather, the kevlar stretch, and every other material and component.

There are several types of seams used in building protective motorcycle gear. A simple seam — completely inadequate from a safety standpoint — is just one line of stitching running through two layers of material, simply joining them together. A simple seam has no place on exposed areas or anywhere contact with the road is expected in a crash. When sliding on tarmac, the thread burns through, the whole simple-seam construction fails, and a hole opens up right where the seam was.
Most people have heard of double and triple seams. These are safety seams designed to stop the protective garment tearing open on impact. Triple seams are generally considered the safest, but they're demanding to produce, which is why they're not used as often in protective motorcycle gear. A triple seam's main advantage over a double seam is that it lies flat, making it more comfortable. It's often used on the back, elbows, crotch, or tailbone.

At For Street Racing, though, the number in our seam name stopped meaning "number of stitch lines" a long time ago — our double-seam construction is stitched 4 times over! From the outside you likely wouldn't notice anything — just like a standard double seam, only one line of stitching is visible. The other three are hidden inside.

Double seam, outer side


Double seam, inner side

4SR patented double seam, outer side


4SR patented double seam, inner side

In a crash and the slide that follows, only the single outer line of stitching gets ground away — the inner stitching never makes contact with the tarmac and keeps the leather held together. In a higher-speed crash, the slide can run long, and real-world surfaces are, as they always are, far from smooth. Potholes, stones, and other surface irregularities create sharp edges that can catch on folded leather and tear the stitching. With only one inner line of stitching, a hole would open immediately. So the second and third lines of stitching have to sit at exactly the right distance from each other, so no single edge can tear through two lines at once. That 200% backup at this critical point is what takes 4SR suit construction to another level.

You'll now find this double, 4-times-stitched safety seam in your own 4SR suit too — the new stitching process was rolled out last year.

The fact that we do our job properly at 4SR also shows in the racers we get to work with, including Karel Hanika, Oliver König, American Flat Track champion James Rispoli, Jack Kennedy, and Hannes Soomer. For five years running we've dressed Alastair Seeley, holder of the record for most North West 200 wins.