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 Most makers do not publish it, so I assume 15 mm and add 6 mm to the band, which on its own is enough to hold an answer at "probably" rather than "fits".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
Trek Checkpoint SL / ALR Gen 2
Gravel · 6 sizes
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- Bike
- Trek Checkpoint SL / ALR Gen 2 · Gravel · 6 sizes
- Geometry
- api.trekbikes.com, 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) |
|---|---|---|---|---|---|---|---|---|
| 49 cm | 538 | 393 | 71.2 | 74.1 | 90 | 435 | 1025 | 735 |
| 52 cm | 553 | 399 | 71.6 | 73.7 | 105 | 435 | 1033 | 765 |
| 54 cm | 571 | 403 | 71.8 | 73.2 | 125 | 435 | 1041 | 789 |
| 56 cm | 592 | 407 | 72.2 | 72.8 | 145 | 435 | 1048 | 809 |
| 58 cm | 609 | 411 | 72.3 | 72.5 | 165 | 435 | 1058 | 829 |
| 61 cm | 639 | 417 | 72.6 | 72.1 | 195 | 435 | 1070 | 859 |
The table runs on to the right: 6 more columns after Reach. Scroll it sideways to read them.
The 56 cm 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.
Stock stem per size49 cm 700 mm, 52 cm 800 mm, 54 cm 800 mm, 56 cm 900 mm, 58 cm 900 mm, 61 cm 1000 mm. The maker publishes no bar width per size.
In the maker's words
Kept whole, as I read it off api.trekbikes.com.Complete bikes ship with Trek's two-piece stem and bar (RCS stem or Bontrager Elite / Pro bar, sizes per build, not per frame); the frameset carries no bar.
Cockpit and seatpost, in the maker's words · 60 words
Complete bikes ship with Trek's two-piece stem and bar (RCS stem or Bontrager Elite / Pro bar, sizes per build, not per frame); the frameset carries no bar. Spacer heights, top-cover height and maximum spacer stack are not in the sizing feed. stock_stem_length null unless the feed carries geometryLengthStem. The feed carries geometryLengthStem (stock stem 70/80/80/90/90/100 mm), stored as stock_stem_length.
OFFICIAL SOURCE: Trek OCC sizing feed for the Checkpoint ALR Gen 2 Frame Set (code 35668), geometry asset Geometry_Lines_2050x1500_Road_CheckpointSLR7, six numeric sizes 49-61 cm. Source: html table (official Trek OCC JSON that renders the "Sizing and fit" geometry table of the trekbikes.com product page
How I read the maker's table
the Checkpoint SL Frame Set (35076, Gen 2 carbon) feed lists sizes 49/52/54/58 with identical values, so this is the Gen 2 platform table (the 2019-2021 Checkpoint, before the Gen 3 of 2022). Size labels are printed "49 cm" with a space. Front centre not published (null). Model year not stated; null. UNITS: Trek publishes the table in centimetres to one decimal and angles in degrees; every length was multiplied by 10 to give millimetres, no rounding was needed. Column mapping from Trek's geometryDataHeaders: geometrySeattube -> seat_tube_length, geometryAngleSeattube -> seat_tube_angle, geometryLengthHeadtube -> head_tube_length, geometryAngleHead -> head_tube_angle, geometryEffToptube -> top_tube_effective, geometryBBDrop -> bb_drop, geometryLengthChainstay -> chainstay, geometryOffset -> fork_offset, geometryTrail -> trail, geometryWheelbase -> wheelbase, geometryStandover -> standover, geometryFrameReach -> reach, geometryFrameStack -> stack, geometryFrontCenter -> front_centre (where present). Stack and reach are Trek's frame stack/reach to the head tube top. The feed lists only the sizes of the chosen SKU, so the SKU with the fullest size run was used; where Trek publishes saddle-rail height ranges (short and tall seatposts) they are in the feed but not in the schema. Cross-checked SKUs: 35076 (Checkpoint SL Frame Set, Gen 2, sizes 49/52/54/58): identical rows.
Source: html table (official Trek OCC JSON that renders the "Sizing and fit" geometry table of the trekbikes.com product page, https://api.trekbikes.com/occ/v2/gb/products/35668/sizing, fetched live 2026-08-29, HTTP 200)