Kart underwear is sized on your body, the same chest and waist measurements as a kart suit. The complication is that this category uses four different labelling systems, sometimes within the same brand.
The quickest routeSize it from your kart suit. The letters follow the same body ladder. If you are a Sparco M kart suit you are a Sparco M top and shorts. If you have not bought the suit yet, measure your chest and waist and use those.
Measure these
AChestAround the fullest part, under the armpits, tape horizontal.
BWaistAround your natural waist, level with the navel.
CShoe sizeOnly needed for socks. They go by foot, not by clothing size.
Charts
SparcoLetters follow their body ladder.▼
Sparco publish no separate underwear chart. These are the bands from their own body size chart, which is what their letters follow. The K-Carbon tops run XXS, XS-S, M-L and XL, so the middle two each cover two of these rows.
AlpinestarsXS to XL published, from their tech layer range.▼
Their own chart jumps from 98 cm to 102 cm between M and L, so a 98 to 102 cm chest falls in a gap. Ring us if that is you.
OMPSold in letters and pairs with no published measurements.▼
OMP put a size chart on every kart suit, boot and glove product page but not on their underwear. Rather than convert from another brand’s chart, size the KS range from your OMP kart suit size, or send us your chest and waist and we will confirm before it ships.
The KS Winter-R tops and long johns use unusually wide pairs, S/M, L/XL and XXL/XXXL, so each garment covers three suit sizes. If you are on a boundary there, take the larger.
Socks
OMP sell the KS sock in S, M and L against shoe size rather than clothing size.
OMP publish the shoe ranges for their racing socks and the KS kart sock follows the same ladder. Kart socks are thicker than everyday ones, so if you are buying boots at the same time try them together or allow for it.
Balaclavas
Every kart balaclava we stock is one size and stretches to fit, including the OMP KS and KS Summer, the Sparco Rookie and Softknit, and the Alpinestars Ride Tech V2. There is nothing to choose. If you wear glasses, an open face style is easier to get on without dragging the arms out of place.
What this layer is for
Everything in this category is marked Non-FIA, and that is normal. Kart underwear is a comfort, wicking and abrasion layer rather than fire kit, which is the opposite of car racing underwear. What it does do is stop the suit chafing over a long day, keep you warm in winter, and add padding at the ribs where the seat works on you.
The padded shorts are the ones people underestimate. They sit between you and the seat and they are the difference between finishing a wet club meeting comfortable and finishing it bruised.
Buying a kart suit at the same time?Measure in the underwear, or order it first. A suit sized over a t-shirt and then worn over a long sleeve top and long johns is the most common reason a suit that should have fitted does not.
Falling between paired sizes?Send us your chest and waist with the range you are looking at. The paired sizing here is wide, so it is worth a check. Call 0115 989 3488 or email Sales@GSMPerformance.co.uk.
Sparco bands from sparco-official.com. Alpinestars from the size guide on their Race V3 Top Tech Layer. Sock ladder from OMP’s published racing sock ranges. OMP publish no kart underwear measurements, which is why they are not tabulated. All checked 2 August 2026.
Is it time to replace your race suit? Let’s get you track-ready. 
