Compare two bikes: how do you sit on each?

Two frames cannot be compared on stack and reach alone — between the top of the head tube and your hand there are still spacers and a stem. This page works both bikes out all the way to the grip, with your body on them, and then says in millimetres what changes.

How you sit — drop, length and back angle, worked out for each bike separately.
What changes — as one drawing over the other, and as a number beside it.
What you would have to change — which stem, how much spacer, and what is still missing afterwards.

Put it together with an AI instead of copying out two geometry tables

Then paste it into ChatGPT, Claude or Gemini. The AI answers with a link to this page; the working out happens here. Check the figures against the manufacturer's page, an AI easily mixes up sizes and model years. You enter your body measurements yourself below.

Show the text

Build me a link for a bike comparison on Radhaltung. The page works out how I sit on two bikes; every input is in the address. Below I name two bikes and perhaps a few of my measurements.

ADDRESS — all on one line, without spaces
https://radhaltung.de/en/compare?name=<text>&art=<type>&stack=<mm>&reach=<mm>&sitzwinkel=<°>&vorbau=<mm>&vorbauwinkel=<°>&spacer=<count>&kurbel=<mm>&stuetze=<mm>&name2=<text>&art2=<type>&stack2=<mm>&reach2=<mm>&sitzwinkel2=<°>&vorbau2=<mm>&vorbauwinkel2=<°>&spacer2=<count>&kurbel2=<mm>&stuetze2=<mm>&schritt=<cm>&koerper=<cm>&arm=<cm>&sattel=<mm>
- Only if I say so explicitly, add after it: &schuh=<EU>&cleat=<mm>&pedal=<mm>&fuss=<°>
- Exactly these field names, lower case; the angle brackets only say what goes in and are not part of the link.
- Fields without a suffix belong to bike A (my bike, or the one named first), the same fields with a 2 at the end to bike B (the other one).
- Numbers with a decimal point and without a unit, minus as a plain hyphen (-6).
- Each field at most once. Leave out completely any field you are not sure about, together with its &.
- Text URL-encoded: space as +, & as %26, # as %23, + as %2B.
- The field names are German; keep them exactly as written here.

PER BIKE (bike A without suffix, bike B with 2)
- name / name2: what the bike should be called on the page: brand, model, the maker's size, at most 40 characters, e.g. Canyon+Endurace+CF+7+M.
- art / art2: exactly one of rennrad, endurance, gravel, trekking, mtb. rennrad: road bike, drop bar, road tyres. gravel: drop bar, wide tyres. trekking: flat bar (trekking and touring bike). mtb: mountain bike, hardtail or full-suspension, 29" with wide knobby tyres and a wide riser bar. The page has no model for other bikes (time-trial bike, cargo bike …) — say so instead of guessing a type.
- stack / stack2: frame stack, 300 to 800 mm.
- reach / reach2: frame reach, 250 to 600 mm.
- sitzwinkel / sitzwinkel2: seat angle, 68 to 80°. If missing, the page takes a typical angle for this kind of bike.
- vorbau / vorbau2: stem length, 30 to 160 mm. If missing, the page uses 95 mm (45 mm on a mountain bike).
- vorbauwinkel / vorbauwinkel2: stem angle with its sign, -30 to 30°. If missing, the page uses -6 (0 on a mountain bike).
- spacer / spacer2: the NUMBER of 5 mm rings under the stem, a whole number 0 to 8 — 10 mm is 2, 25 mm is 5. Not millimetres! If missing, the page uses 2 (10 mm).
- kurbel / kurbel2: crank length, 140 to 200 mm. If missing, the page picks one that suits the inseam.
- stuetze / stuetze2: seatpost setback (offset), 0 to 40 mm. For bike A only if I give it (otherwise the page uses 10 mm). Leave out stuetze2: then my saddle sits on bike B where it sits on bike A, which is exactly what the comparison should show.
- groesse / groesse2: do NOT use. These are the sizes of this page's example table, not the maker's. The maker's size belongs in the name.

ABOUT ME (once, without 2) — only what I state myself; never estimate, never derive from another figure
- schritt: inseam, 55 to 110 cm. Without it the page cannot compare and asks for it itself — do not estimate.
- koerper: body height, 140 to 215 cm. If missing, the page estimates it from the inseam.
- arm: arm length from the corner of the shoulder to the wrist, 45 to 85 cm.
- sattel: current saddle height, centre of the bottom bracket to the top of the saddle along the seat tube, 500 to 1000 mm.

ONLY IF I SAY SO EXPLICITLY
- schuh: shoe size EU, 36 to 50.
- cleat: how far the cleat sits behind the ball of the foot, -10 to 20 mm (towards the heel is positive).
- pedal: pedal stack height, 5 to 25 mm.
- fuss: foot angle, -25 to 15° (negative: heel higher than the toes).

TRAPS WHEN COPYING
- Stack and reach from the column of exactly the size named, as frame measurements. Not the top tube length, not the head tube length, not "handlebar stack/reach" or "cockpit reach" including stem and spacers — the page works that out itself.
- If the seat angle is listed as "effective" and "actual", take the effective one.
- You do not need head angle, wheelbase, chainstays or top tube.
- Stem and cranks are in the spec list, often different per size — take the ones for the size named, not one figure for all.
- The stem angle is usually listed without a sign. Road and gravel stems are almost always mounted pointing down, so negative (6° → -6). Positive only for a stem explicitly mounted rising or flipped. On trekking bikes with a steep or adjustable stem only if angle and mounting are clear.
- Spacers without the headset top cap, the page already counts it. If the spec lists the spacers in mm, divide by 5 and round.
- Geometry changes between model years and frame versions, and women's models often have their own table. Inches times 25.4 give mm.
- Bike type only from the list above.

HONESTY BEFORE COMPLETENESS
1. Values only from the maker's geometry table and spec list for exactly this model, model year and size. If the maker no longer shows the model, a geometry collection (Geometry Geeks, 99 Spokes) will do.
2. For bike A, what I say about the parts on my bike comes before the stock spec.
3. Leave out whatever you are not sure about. Better a link with a field missing — the page then shows what is missing and I fill it in there — than an estimated value. Never invent stack or reach.
4. If you cannot open web pages and take a figure from memory, say so next to the source. Then I will check it.
5. If the model, model year or size is unclear, ask before building a link. That is the only answer without a link.
6. No fields that are not listed here.

OUTPUT — exactly like this, nothing else
<the one link>
Sources:
- Bike A: <address of the page the figures come from> (opened / from memory)
- Bike B: <likewise>
Left out: <fields you were not sure about, or "nothing">

My bikes:

Bike A — yours

Name — optional

Frame size

Stack (mm)

Reach (mm)

Seat tube angle (°)

Seatpost: setback (mm)

Stem (mm)

Angle (°)

Spacers (mm, without headset cap)

Crank (mm)

Type

Bike B — the other one

Name — optional

Frame size

Stack (mm)

Reach (mm)

Seat tube angle (°)

Seatpost: setback (mm)

Stem (mm)

Angle (°)

Spacers (mm, without headset cap)

Crank (mm)

Type

Add another bike

Bike C

Model from the catalogue

Frame size

Name — optional

Enter by hand

Stack (mm)

Reach (mm)

Seat tube angle (°)

Seatpost: setback (mm)

Stem (mm)

Angle (°)

Spacers (mm, without headset cap)

Crank (mm)

Type

Stem and spacers are not in the geometry table — they are on your bike. The stem length is usually stamped on its side, the spacers are the rings underneath it, 5 mm each. Leave a field empty and the page works like the calculator, with what a bike of this type comes with from the factory: on a road bike the stem that goes with your height, otherwise a standard stem, plus 10 mm of spacers.

Where do I find stack and reach?

On the maker's site under “Geometry”, one column per frame size, in millimetres. You can't read them off the bike itself.

What stack and reach are: Bike explained →

Bianchi BMC Bulls Cannondale Canyon Cube Focus Ghost Giant KTM Merida Rose Scott Simplon Specialized Stevens Trek

Older model? These collections often list past model years too: Geometry Geeks 99 Spokes

Your body

Height (cm)

Inseam (cm)

Arm length (cm) — optional

Saddle height as set (mm) — optional

Fine tuning — saddle, shoe, pedal

Shoe size (EU)

Cleat from the ball of the foot (mm)

Pedal stack height (mm)

Foot angle (°)

measure from a photo

The setback is set per bike: bike A decides where your saddle sits; if you leave it empty on bike B, the same post is in that bike and the saddle follows the seat angle of bike B. The comparison below shows which setback bike B would need for the saddle to sit as it does on bike A. Shoe, cleat, pedal and foot angle apply to both bikes.

The difference

Something is still missing for that:

Your frame's measurements — pick a size or enter stack and reach
The second bike's measurements — pick a size or enter stack and reach
Your inseam

Keep this comparison

As soon as something is entered above, this is where you will find a link that opens exactly this comparison again.