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 Most makers do not publish it, so I assume 15 mm and add 6 mm to the band, which on its own is enough to hold an answer at "probably" rather than "fits".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 Madone SLR Gen 8
Aero road · carbon · 6 sizes
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This is the bike I ride
No account is needed to read the table. Report a wrong number · Correct this bike
- Bike
- Trek Madone SLR Gen 8 · Aero road · carbon · 6 sizes · integrated cockpit · seatpost offsets 0 mm
- Geometry
- api.trekbikes.com, fetched 28 Aug 2026, re-checked, no differences
- Cockpit
- Aero RSL Road integrated, -7, the maker's spec
- Solved with
- cover 6.5 mm (published), max spacers 40 mm (published), stem clamp centre 20 mm (assumed), so every verdict carries ±4 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 (47cm) | 507 | 370 | 71.6 | 73.8 | 100 | 410 | 971 | 704 |
| S (50cm) | 530 | 378 | 72.2 | 73.8 | 121 | 410 | 976 | 734 |
| M (52-54cm) | 546 | 384 | 72.9 | 73.6 | 136 | 410 | 981 | 762 |
| ML (56cm) | 562 | 389 | 73.5 | 73.4 | 150 | 410 | 980 | 790 |
| L (58cm) | 582 | 394 | 73.8 | 73.4 | 172 | 411 | 990 | 820 |
| XL (60-62cm) | 610 | 402 | 73.9 | 73.4 | 201 | 412 | 1007 | 863 |
The table runs on to the right: 6 more columns after Reach. Scroll it sideways to read them.
The ML (56cm) 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
What each size is solved on unless you choose another bar on the sheet.Trek Aero RSL Road integrated, -7Stockstem -7 · reach 80 · lengths 70-130
Stock stem and bar per sizeXS (47cm) 80 x 380, S (50cm) 90 x 400, M (52-54cm) 90 x 420, ML (56cm) 100 x 420, L (58cm) 100 x 420, XL (60-62cm) 110 x 440 (stem length x bar width, mm)
In the maker's words
Kept whole, as I read it off api.trekbikes.com.Stock (per size, from official spec feed https://api.trekbikes.com/occ/v2/us/products/49168/specifications, Madone SLR 8 AXS Gen 8): XS = 80 mm stem x 35 cm hoods / 38 cm drops; S = 90 x 37/40; M = 90 x 39/42; ML = 100 x 39/42; L = 100 x 39/42; XL = 110 x 41/44.
Cockpit and seatpost, in the maker's words · 279 words
Stock (per size, from official spec feed https://api.trekbikes.com/occ/v2/us/products/49168/specifications, Madone SLR 8 AXS Gen 8): XS = 80 mm stem x 35 cm hoods / 38 cm drops; S = 90 x 37/40; M = 90 x 39/42; ML = 100 x 39/42; L = 100 x 39/42; XL = 110 x 41/44. All are Trek Aero RSL Road integrated bar/stem, -7 degree stem, 80 mm bar reach, 124 mm drop, "Race Fit"; Trek names the bar by drop width (hoods are 3 cm narrower). Aftermarket Aero RSL barstem combos offered (Trek product W5316690 variant list, https://www.trekbikes.com/us/en_US/equipment/cycling-components/bike-stems-accessories/integrated-handlebar/stems/trek-aero-rsl-road-integrated-handlebar/stem/p/W5316690/ ): 38 cm (35 hoods) x 80/90/100/110/120; 40 cm (37 hoods) x 70/80/90/100/110/120/130; 42 cm (39 hoods) x 80/90/100/110/120/130; 44 cm (41 hoods) x 100/110/120; all -7 degree, 80 mm reach, 124 mm drop. Spacers: RCS Race 5 mm (W5316079) and 15 mm (W5316080); max 40 mm of spacers below the stem and max 40 mm above (Trek Madone Gen 8 service manual Rev12 Dec 2025, pages 9-10). Bearing top cover: standard W5316081 = 6.5 mm tall, low 5325626 = 2.5 mm tall (aftermarket only; the FAQ says the Gen 8 bar/stem top sits 4 mm higher than Gen 7 and the low cover compensates). Alternative cockpits per Trek Road Cockpit Compatibility Chart Rev 9 June 2026 (row "Madone SLR Gen 8 MY25"): Aero RSL barstem fully compatible; RCS stem (Trek's separate stem) needs parts W5317347 or 5326727 + 5296906 + 5296905, RCS Race stem offered in +7 deg x 60/70/80/90/100 and -7 deg x 60/70/80/90/100/110/120/130/140 (manual page 14); standard round stem needs parts 5328901 + 5253930 + 5253931; Aeolus RSL barstem needs the same +1 parts. RCS Race headset is electronic-shift only.
OFFICIAL SOURCE: Trek publishes the Madone SLR Gen 8 geometry in the "Sizing and fit" tab of every Madone SLR Gen 8 product page. Source: html table (official JSON that renders the geometry table on the trekbikes.com product page; fetched live 2026-08-28
How I read the maker's table
the page is a Vue app and the numbers come from the OCC endpoint https://api.trekbikes.com/occ/v2/us/products/{code}/sizing (siteUid "us", found in trekbikes.com JS bundle chunk-common: fetchProductSizingData -> `/products/${code}/sizing`). The www.trekbikes.com/occ/... host returns 404; api.trekbikes.com returns 200. UNITS: Trek publishes the table in centimetres with one decimal (e.g. stack "50.7") and degrees; I multiplied cm 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. SIZE LABELS: Trek's Gen 8 uses letter sizes; the product size chart maps them to the old numeric sizes: XS (47cm), S (50cm), M (52-54cm), ML (56cm), L (58cm), XL (60-62cm). Rider height bands from the same feed: XS 143-158 cm, S 158-162, M 162-173, ML 173-179, L 179-188, XL 188-199. Trek's geometry line drawing (asset MY25_Madone_SLR_Geometry_Lines, letter B) shows the angle taken along the seat tube / seatpost axis. Fork offset column is Trek's "Offset" (rake). EXTRA published columns not in the schema: saddle rail height min/max with the short seatpost (XS 549-612 mm, S 585-648, M 621-684, ML 657-720, L 693-756, XL 754-817) and with the tall seatpost (XS 592-654, S 628-690, M 664-726, ML 700-762, L 736-798, XL 797-859), all converted from cm. Stock seatpost: 0 mm offset; short post on XS, S, M, XL and long post on ML, L per the SLR 8 AXS spec feed (the FAQ at https://www.trekbikes.com/us/en_US/FAQ/madone-gen8/ says all sizes ship with the short post, which conflicts with the spec feed for ML/L - flagging as uncertain). Wheel size 700c all sizes. Fork steerer: 210 mm tapered carbon (28.6 mm upper / 38.8 mm lower OD per service manual page 30). Max tyre 32 mm measured. INTEGRATED COCKPIT: yes, Trek Aero RSL Road integrated bar/stem (electronic shifting only; not compatible with mechanical or clip-on extensions per FAQ). Spacer limits and top-cover heights are from the official Madone SL/SLR Gen 8 service manual (TK_MadoneSL-SLR_Gen8_MY25_ServiceManual_EN-US_Rev12_Dec2025.pdf, linked from the product page technical tab): "Do not exceed 40 mm of headset spacers above or below the stem"; standard bearing top cover 6.5 mm, low cover 2.5 mm (dimension callouts in the RCS Race headset exploded view, page 9). Headset "top cap" height beyond that is not published. Trek's FAQ states the Gen 8 "Road Race" geometry is very similar to the previous H1.5 fit and that eight sizes were consolidated to six. Stock stem length and bar width fields below are from the Madone SLR 8 AXS Gen 8 spec (other SLR Gen 8 builds were not checked and could differ). stock_bar_width is the nominal drop width Trek uses to name the bar; hood (control) width is 30 mm narrower on every size.
Source: html table (official JSON that renders the geometry table on the trekbikes.com product page; fetched live 2026-08-28, HTTP 200)