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 Most makers do not publish it, so I assume 15 mm and add 6 mm to the band, which on its own is enough to hold an answer at "probably" rather than "fits".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 A40 The Fixer
All-road · 6 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 A40 The Fixer · All-road · 6 sizes
- Geometry
- serk.cc, fetched 29 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.| Size | Stack (mm) | Reach (mm) | Head angle (deg) | Seat angle (deg) | Head tube (mm) | Chainstay (mm) | Wheelbase (mm) | Standover (mm) |
|---|---|---|---|---|---|---|---|---|
| XS | 519 | 366 | 71 | 75 | 90 | 420 | 981 | 710 |
| S | 548 | 374 | 71.5 | 74.5 | 121 | 420 | 995 | 755 |
| M | 567 | 382 | 71.5 | 74 | 141 | 420 | 1009 | 733 |
| L | 590 | 390 | 71.5 | 73.5 | 168 | 420 | 1026 | 796 |
| XL | 613 | 398 | 71.5 | 73.5 | 192 | 420 | 1042 | 819 |
| XXL | 638 | 406 | 71.5 | 73 | 218 | 420 | 1058 | 843 |
The table runs on to the right: 6 more columns after Reach. Scroll it sideways to read them.
The L 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-only frame: the frameset is sold in two fork / routing variants (store attribute "Cable Routing / Fork"): "Full Internal Routing for Integrated Bars" or "Semi Internal Routing" (product page also says "Integrated or external cabling").
Cockpit and seatpost, in the maker's words · 326 words
NOT an integrated-only frame: the frameset is sold in two fork / routing variants (store attribute "Cable Routing / Fork"): "Full Internal Routing for Integrated Bars" or "Semi Internal Routing" (product page also says "Integrated or external cabling"). Fork: Serk carbon "all-road plus", 12x100 mm, 435 g with 300 mm steerer, internal or external cable routing version; frameset "Includes Serk Headset Integrated, seatpost clamp, thru-axles, expander, rear seat stay bridge mudguard mounting accessory". Headset top cover height is published as a geometry row: "Additional top headset stack" +28.5 mm with the internal-routing headset, +10.1 mm with the external-routing headset (same for every size) - add it to the stack figure to get stack at the top of the headset. Headset bearing standard for the A40 is not stated (owners manual: A30/A21/A10 use ZS44 upper / EC44 lower, A30M integrated uses EC44/EC44, 44 mm straight head tube, fork tapered 28.6 to 39.8 mm - stated for those models, not explicitly for the A40). Spacer stack maximum NOT published; top cap bolt max 3 Nm (owners manual). Frameset handlebar/stem add-ons: Deda Super Box stem + Deda RS2 bar (+RMB 1000), THE ONE PRO carbon integrated bar/stem (+RMB 1500), EXS Aerover carbon integrated bar/stem (+RMB 2500). Complete builds: 105 Di2 = DEDA Zero2 DCR handlebar + DEDA Superbox V2 stem (two-piece); Ultegra Di2 = THEONE Pro Integrated; Force AXS E1 = EXS Aerover carbon integrated. Stem length and bar width per frame size are NOT published anywhere on the site, so stock_stem_length / stock_bar_width are null. Seatpost: Serk Carbon seatpost, 27.2 mm round; setback/offset NOT published; seatpost clamp included with frameset. Saddle on builds: Prologo Scratch M5. Frame weights (maker): XS 1500 g, S 1600 g, M 1640 g, L 1680 g, XL 1750 g, XXL 1830 g. Complete bike: 105 Di2 size S 8.48 kg; Force XPLR E1 1x13 size S with 37c tyres 8.25 kg. System weight limit 115 kg rider + bike (owners manual, all models).
SOURCE: https://www.serk.cc/a40/ (WordPress page, published 2025-10-07, last modified 2026-08-28), HTML table under the GEOMETRY heading, six columns XS/S/M/L/XL/XXL, rows lettered A-J against the generic Serk diagram https://www.serk.cc/wp-content/uploads/2022/10/geo_2023_550.jpg (viewed, not stored). Source: html_table (brand site product page, GEOMETRY section; identical table repeated on the Owners Manual page, A40 tab)
How I read the maker's table
The Owners Manual page https://www.serk.cc/ownersmanual/ (A40 tab, "A40 | The Fixer - The New All-Road Bike") repeats the identical table. WooCommerce Store API (https://www.serk.cc/wp-json/wc/store/v1/products?search=a40) confirms product "A40 The Fixer", SKU 40M, sizes XS/S/M/L/XL/XXL, US$2499 frameset. STACK DATUM: the diagram draws STACK vertically from the BB centre to the TOP OF THE HEAD TUBE and REACH horizontally from the BB centre to the same point; the headset top cover is NOT included - the maker publishes it separately as "Additional top headset stack" (+28.5 mm internal-routing headset, +10.1 mm external-routing headset). Derived stack to the top of the headset cover, NOT published as such: internal 547.5/576.5/595.5/618.5/641.5/666.5, external 529.1/558.1/577.1/600.1/623.1/648.1. SEAT TUBE ANGLE: the maker's wording is just "Seat Tube Angle" (row D); the diagram measures D at the BB between the horizontal and the seat tube axis, and this is a straight-seat-tube titanium frame, so actual and effective coincide - left null because the maker uses neither word. HEAD TUBE ANGLE row E: 71 (XS) then 71.5 for S-XXL. TOP TUBE row B "Top Tube Length" is drawn horizontal in the diagram, so it is recorded as effective. SEAT TUBE row A "Seat Tube Length" is drawn BB centre to top of seat tube. TRAIL: the maker publishes trail for three tyre sizes; the trail field carries the 28C row (XS 67, S-XXL 63.9) because the stock builds ship 28 mm tyres and 28C is the size every other Serk model quotes; 35C row = 69.4 / 66.2 / 66.2 / 66.2 / 66.2 / 66.2; 40C row = 71.2 / 67.9 / 67.9 / 67.9 / 67.9 / 67.9. STANDOVER: also published for three tyre sizes; the standover field carries the 28C row; 35C row = 717 / 762 / 780 / 803 / 826 / 850; 40C row = 722 / 767 / 785 / 808 / 831 / 855. DATA QUALITY FLAG: size M standover 28C is published as 733 on both the product page and the owners manual, which is lower than size S (755); every other size's 28C figure is exactly the 35C figure minus 7 mm, so 733 is almost certainly a maker typo for 773 - the file keeps the published 733 verbatim, do not treat it as measured. FRONT CENTRE not published (null). SIZES are named XS-XXL only; no rider-height sizing guide is published on the maker's site as of 2026-08-29. MODEL YEAR: none stated; the page went live 2025-10-07 and the tyre clearance graphic is named tyre_size_2026_A40.gif, so treat as the 2026 model if a year is ever needed (left null). CATEGORY: the collection task labelled this bike endurance road; the maker calls it an "All-road titanium bike" with "a new endurance geometry" and says the 40 mm clearance puts it "into the 'all-road' category and capable as a gravel bike", so category is recorded as all-road per the source; 420 mm chainstays, 73-77 mm BB drop, 71-71.5 head angle, 47 mm offset, rack and full mudguard mounts. TYRES: geometry optimised for 30-32 mm; clearance 700c x 40 mm (measured 40 mm width) or 650b x 47 mm; stock builds 28 mm. FRAME: titanium 3Al/2.5V hydroformed tubeset (100 g lighter than the A30), carbon fork, T47 BB shell, flat mount, 12x100 / 12x142 thru axles, custom UDH dropout, 1x and 2x compatible from 8-speed mechanical onward plus Di2 / AXS, 3rd bottle mount. PRICES (maker, 2026-08-29): frameset from RMB 16,000 / US$2499; 105 Di2 RMB 29,000 / US$4375; Ultegra Di2 RMB 41,000 / US$6100; Force E1 2x12 or 1x13 XPLR RMB 45,700 / US$6790.