Stack and reach
How high and how far forward the top of the head tube is, from the bottom bracket. They are the two numbers that decide whether a frame can be set up like yours.
BB, or bottom bracket
The axle your cranks turn on, in the middle of the frame. Every number on this site is measured from it, because it is the one point that sits in the same place on every bike.
Headset cover
The little cap on top of the head tube, under your spacers. Most makers do not publish it, so I assume 15 mm and add 6 mm to the band, which on its own is enough to hold an answer at "probably" rather than "fits".
Stem clamp, and its centre
The collar on the steerer that your stem bolts to. I need the middle of it. Where a maker gives only the height, I assume halfway up and say so on the answer.
Steerer
The tube coming up out of the fork. The cover, the spacers and the stem all sit on it, and it is the thing a mechanic cuts to length.
Bar reach
How far forward the hoods sit from the middle of the bar. Two bars on the same stem can put your hands 20 mm apart, which is why I ask.
Setback
How far your saddle sits behind the bottom bracket.
Drop
How much lower your bar is than your saddle.
Rails, and the rail centre
The two rods under your saddle, and the middle of the straight part of them. That midpoint is the point I use, because it is the one you can find with a tape.
The band
How far out I could be, in millimetres, and why. It is a straight sum of everything I had to assume rather than a clever average, so it errs wide on purpose.
wb, stand, trail
Wheelbase, standover and trail: how long the bike is, how high the top tube is where you straddle it, and how steady the steering feels. I show them against your bike, and I leave them out when the maker does not publish them.
est.
Estimated: a number I worked out rather than read off the maker's table. Anything marked this way can move if the maker publishes the real one.
Close Escape closes it. The measuring guide has the pictures. Open the measuring guide
Serk A10 The Purist
Road · 5 sizes
Sign in and add the bike you ride, and this table will say what each size needs for your position.
Sign in
This is the bike I ride
No account is needed to read the table. Report a wrong number · Correct this bike
- Bike
- Serk A10 The Purist · Road · 5 sizes
- Geometry
- serk.cc, fetched 28 Aug 2026, re-checked, no differences
- Cockpit
- Generic stem and bar, assumed
- Solved with
- cover 15 mm (assumed), max spacers 40 mm (assumed), stem clamp centre 20 mm (assumed), so every verdict carries ±10 mm at the bar
- Sheet
- 6 September 2026 · 210 bikes, 43 makes, 1,262 sizes in the catalogue
Geometry, every size, from the maker's table
The tinted row is the size drawn beside it. Press a size to draw it.The table runs on to the right: 6 more columns after Reach. Scroll it sideways to read them.
The M drawn to scale from the table, with no build on it. Stack and reach run from the bottom bracket to the top of the head tube; every size is solved from those two. One square is 100 mm.
The maker's cockpit
No stock cockpit I can name, so every size is solved on a generic stem and bar unless you choose one on the sheet.Generic stem and barAssumedNo bar is listed for this frame.
In the maker's words
Kept whole, as I read it off serk.cc.NOT an integrated cockpit: the A10 uses a standard external stem and round bar with semi-integrated cable routing (maker: "Cables are hidden from the inlet ports near the head tube before exiting under the bottom bracket where they are exposed but hidden under the bike"; cable ports can be swapped for Di2 ports, and a port-free frame for wireless SRAM can be made on request).
Cockpit and seatpost, in the maker's words · 245 words
NOT an integrated cockpit: the A10 uses a standard external stem and round bar with semi-integrated cable routing (maker: "Cables are hidden from the inlet ports near the head tube before exiting under the bottom bracket where they are exposed but hidden under the bike"; cable ports can be swapped for Di2 ports, and a port-free frame for wireless SRAM can be made on request). Complete Ultegra build spec on the page lists "Handlebars : Fizik R5" and "Stem : Fizik R5" - no stem length, stem angle, bar width, bar reach or bar drop stated, and no per-size stem/bar table, so stock_stem_length and stock_bar_width are null. Frameset (RMB 14,200 / US$2200, in stock at time of collection) "Includes Serk Headset 40 Semi-integrated, seatpost clamp" and "Fork : Serk Carbon Road"; headset stack height, top cap height and maximum spacer stack are NOT published (maker only says you can "add in some spacers to achieve a more upright position"). Seatpost: "Seatpost : Serk Carbon 27.2mm" on the Ultegra build (round 27.2 mm post; offset/setback not published; frame takes any standard 27.2 mm post - maker stresses "Everything on our bike is standard size and commonly available"). Brakes: "Rim Brake / Quick Release" (rim-brake frame and fork, QR axles - not disc). Tyre clearance: "30mm measured tyres". BB: "T47 BB 68mm". Complete Ultegra build (RMB 23,500 / US$3599): R8000 rim-brake group 50/34 with 11-28, Shimano RS-11 wheels, Vittoria Rubino Pro 25c tyres, Prologo Scratch M5 saddle.
SOURCE: the maker's own product page https://www.serk.cc/a10/ (Serk Cycling, Beijing. Source: html_table
How I read the maker's table
also linked from https://www.serk.cc/titanium/ as "A10 - The Purist / Classic Rim Road Bike"). Geometry is a real HTML table (13 rows: Reach, Stack, then lettered rows A-J) with a labelled diagram https://www.serk.cc/wp-content/uploads/2019/07/geo.png (393x312 px, uploaded 2019-07). No aggregator was consulted. DIAGRAM CONVENTIONS (read from geo.png): Stack is the vertical distance from the horizontal line through the bottom bracket centre to the top of the head tube; Reach is the horizontal distance from the BB centre to the top of the head tube (standard stack/reach datum). A "Seat Tube Length" is dimensioned along the seat tube from the BB centre to the top of the seat tube (appears centre-to-top; not stated in words). B "Top Tube Length" is drawn as a HORIZONTAL dimension from the head tube top to the seat tube axis, so it is recorded as top_tube_effective (the maker does not use the word effective). C head tube length along the head tube. D "Seat Tube Angle" is drawn at the BB between the straight seat tube and the horizontal - i.e. E head tube angle, F BB drop, G chainstay, H wheelbase (axle to axle), I fork offset, J trail - all as labelled by the maker. NOT PUBLISHED: standover, front centre, fork length, frame weight, rider height guide (none on the A10 page or the titanium range page) - all null. SIZE NAMING: five sizes XS / S / M / L / XL; the seat tube lengths 470/490/510/530/550 mm are the closest thing to a numeric size. Table is undated; the page says "Our 2022 A10 now has clearance for larger tyres - 30mm measured", so model_year is set to 2022 (the current revision of the frame; the geometry diagram file dates from 2019 and may pre-date that revision - treat model_year as the revision year, not a proven geometry year). Page first published 2020-05-22, last modified 2025-10-22, live on 2026-08-28. Material: titanium 3Al/2.5V. Values are exactly as printed (trail to one decimal). Angles stored as numbers (degrees).
