Tillett shells are thin single-skin composites with almost no padding, so the internal width is the seat width. Tillett publish it for every model, and the XL and W versions exist for a reason.
How Tillett size their seats
Tillett quote an external and an internal width for each shell. Because there is no foam to squash, your seated hip width has to fit inside the internal figure with 10 to 20 mm to spare. Every B-series shell has an XL, about 30 mm wider, and the W2i and W6 are the wide versions of the W1i and W5, made for drivers over 100 kg or over a 36 inch waist.
Several shells are offered with a rolled edge or a cut edge. The cut edge (B6-40, B7-40, B8-43) loses 30 to 40 mm of external width for narrow cars without changing the inside.
Brackets have to match the shellTillett brackets are angled to match the side of the seat: 8 degrees on the B2, 2 degrees on the B6, B7 and B8. A bracket at the wrong angle stresses the composite. Use a load-spreading spacer of at least 40 mm at every bolt.
Tillett dimensions
From Tillett’s dimension sheets, 2022 to 2025. Widths are the widest point.
Which Tillett fits you
The W-series shells are supplied single skin and need bespoke brackets, or the optional back frame on the W1i and W2i. The B6 comes bottom mount or side mount; the side mount version takes Tillett’s STB, VTB and Elise brackets.
Measure yourself first
Four numbers decide whether a seat fits. Take them in the clothes you drive in, and write them down before you compare models.
AWaistAround your natural waist, not your trouser size. Trouser sizes usually run an inch or two under the real figure, and the waist bands on our product pages use the real one.
BSeated hip widthSit on a hard chair with your feet flat and measure straight across the widest point of your hips with a rule or a straight edge, not a tape that follows the curve. This is the number that decides whether a fixed shell is tight.
CShouldersStraight across the back at the widest point. Fixed back seats hold you here, so a shell that is narrow at the shoulders is uncomfortable long before it is unsafe.
DHeight and torsoYour height, and if you are over 6 ft whether that is mostly leg or mostly body. A long body needs a taller shell with the head support set higher.
Before you order
- Check the car, not only the driver. Transmission tunnels, door cards and B pillars are what stop a wide shell going in. Our seat mounting and fixing points guide covers what to measure.
- Side mount and base mount shells are not interchangeable. Which one you need depends on the car and the subframe, so pick the brackets at the same time as the seat.
- If you run a HANS or plan to, filter on HANS friendly. The shoulder openings are cut to clear the collar.
- FIA seats carry an expiry date on the homologation label. Check what your championship accepts and how long the seat has left, particularly on discounted older stock.
Send us your measurementsWaist, seated hip width, height and the car. We have fitted a lot of Tillett seats and will tell you honestly if the one you have picked is going to be tight. Call 0115 989 3488 or email Sales@GSMPerformance.co.uk.
Waist bands are our product data, checked 6 September 2026. Widths, heights and weights are from Tillett’s dimension sheets dated 2022 to 2025; blanks are where the sheet gives no figure.