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 Most makers do not publish it, so I assume 15 mm and add 6 mm to the band, which on its own is enough to hold an answer at "probably" rather than "fits".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
Specialized Tarmac SL8
Road · carbon · 7 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
- Specialized Tarmac SL8 · Road · carbon · 7 sizes · integrated cockpit · seatpost offsets 15 mm
- Geometry
- specialized.com, fetched 28 Aug 2026, re-checked, no differences
- Cockpit
- Roval Rapide one-piece -6 (400 mm bar), the maker's spec
- Solved with
- cover 7 mm (published), max spacers 35 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) |
|---|---|---|---|---|---|---|---|---|
| 44 | 501 | 366 | 70.5 | 75.5 | 99 | 410 | 970 | 723 |
| 49 | 514 | 375 | 71.75 | 75.5 | 109 | 410 | 973 | 735 |
| 52 | 527 | 380 | 72.5 | 74 | 120 | 410 | 975 | 746 |
| 54 | 544 | 384 | 73 | 74 | 137 | 410 | 978 | 768 |
| 56 | 565 | 395 | 73.5 | 73.5 | 157 | 410 | 991 | 786 |
| 58 | 591 | 402 | 73.5 | 73.5 | 184 | 410 | 1006 | 808 |
| 61 | 612 | 408 | 74 | 73 | 204 | 410 | 1013 | 834 |
The table runs on to the right: 6 more columns after Reach. Scroll it sideways to read them.
The 54 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.Specialized Roval Rapide one-piece -6 (400 mm bar)Stockstem -6 · reach 75 · lengths 75-135
Stock stem and bar per size44 75 x 380, 49 75 x 380, 52 90 x 400, 54 100 x 420, 56 100 x 420, 58 110 x 440, 61 110 x 440 (stem length x bar width, mm)
In the maker's words
Kept whole, as I read it off specialized.com.S-Works builds: Roval Rapide Cockpit one-piece bar/stem, -6 degree stem, bar reach 75mm, drop 127mm, hood width c-c 380/400/420/440 (drops 390/410/430/450, 4 degree flare), steerer clamp height 40mm.
Cockpit and seatpost, in the maker's words · 262 words
S-Works builds: Roval Rapide Cockpit one-piece bar/stem, -6 degree stem, bar reach 75mm, drop 127mm, hood width c-c 380/400/420/440 (drops 390/410/430/450, 4 degree flare), steerer clamp height 40mm. Size selector on the official product page (https://www.specialized.com/us/en/roval-rapide-cockpit/p/218323) lists 26 stem x bar combinations: 360mm bar: 75, 90, 100, 110, 120, 135mm stems; 380mm bar: 75, 90, 100, 110, 115, 120, 135mm; 400mm bar: 75, 90, 100, 110, 120, 135mm; 420mm bar: 90, 100, 110, 120, 135mm; 440mm bar: 110, 125mm. (Spec text on the same page says stem length "75mm-135mm (Dependent on bar width)" and lists hood widths 380-440 only, so the 360mm variants in the size selector may be newer or region-specific - uncertain.) Pro/Expert/Comp builds: separate "Tarmac integrated stem, 6-degree" (SL7-style alloy stem on a 1-1/8in steerer, any 31.8mm bar; hoses route under the stem) with a two-piece bar. Stock S-Works stem x bar per size: 44: 75x380, 49: 75x380, 52: 90x400, 54: 100x420, 56: 100x420, 58: 110x440, 61: 110x440. Stock 2026 Expert (SRAM Force AXS, https://www.specialized.com/us/en/tarmac-sl8-expert-sram-force-axs-/p/4293510) per size: 44: 70x360, 49: 80x380, 52: 90x400, 54: 100x420, 56: 100x420, 58: 110x440, 61: 110x440. Spacers: official spacer kit pages (https://www.specialized.com/us/en/tarmac-sl8-headset-spacer--transition-kit-for-rapide-cockpit/p/4242711 and https://www.specialized.com/us/en/tarmac-sl8-headset-kit-for-rapide-cockpit-spacers--tarmac-sl7-stem/p/4279373) state the maximum spacer/transition stack is 1 x lower transition cover (6.6mm) + 3 x 10mm + 1 x 5mm + 1 x upper transition spacer (height of upper transition spacer not stated); a one-piece slammed transition cover is 7.8mm; with the SL7 stem the steerer may protrude at most 5mm above the stem (open stem cover), and the SL7-stem kit is not compatible with SL7 stems shorter than 90mm.
OFFICIAL SOURCE READ OK. Source: html table
How I read the maker's table
The identical geometry table appears on three official pages: S-Works Tarmac SL8 Shimano Dura-Ace Di2 /p/216953 (page JSON modelYear: 2024), S-Works Tarmac SL8 Frameset /p/216956 (modelYear 2024) and Tarmac SL8 Expert SRAM Force AXS /p/4293510 (modelYear 2026), so the frame geometry is unchanged across 2024-2026 model years; Escape Collective (https://escapecollective.com/specialized-tarmac-sl8-a-hands-on-build-and-reveal/) states the SL8 geometry and 32mm tyre clearance are identical to the SL7. Units: all mm and degrees exactly as published, no conversion. Specialized publishes TWO stack/reach pairs: "Frame Stack / Frame Reach" (used for the stack/reach fields below) and "Stack to Stem / Reach to Stem": 44: 509/363, 49: 522/372, 52: 535/377, 54: 552/381, 56: 573/393, 58: 599/400, 61: 620/406. Stack-to-Stem is exactly 8mm above Frame Stack on every size and Reach-to-Stem is 2-3mm less than Frame Reach; Specialized does not define the datum on the page. Escape Collective says the to-stem figures account for "the lowest possible headset cover heights"; the slammed one-piece transition cover is listed as 7.8mm on the spacer-kit page, which is consistent with the 8mm delta (my inference - uncertain). Other published rows not in the schema: BB height 266 (44/49/52) and 268 (54-61); fork length full 370 all sizes; crank length 165/165/170/172.5/172.5/175/175; saddle width 155/155/155/143/143/143/143; seatpost length 300/300/300/380/380/380/380 (S-Works Tarmac SL8 carbon post, 15mm offset per frameset spec). The support.specialized.com fit page returned 403/"Missing Authentication Token" and was not read. Headset cap/max spacer height: see cockpit_options; the exact mm of the upper transition spacer is unknown. Escape Collective (secondary) reports the bike ships with 35mm of spacers under the stem plus 5mm above and that "you can ride with up to a 5mm spacer above the stem". Stock stem length / bar width per size below are from the S-Works Dura-Ace Di2 page (Roval Rapide Cockpit); the 2026 Expert build differs on sizes 44 (70mm x 360mm) and 49 (80mm x 380mm). The degree symbol in the HTML rendered as a replacement character in my console; the numeric values were read cleanly.