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 Most makers do not publish it, so I assume 10 mm and add 6 mm to the band beside every answer.
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 hands sit than your saddle. On a riser bar I count the bar's rise, so the drop is that much less than it is to the clamp.
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
Tantan GR042
Gravel · 4 sizes
The GR042 on tantancycling.com
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
- Tantan GR042 · Gravel · 4 sizes
- Geometry
- bikeinsights.com, fetched 22 Oct 2026
These numbers are second-hand, from Bike Insights. I have not checked them against the maker's own table. Bike Insights cites tantancycling.com. - Seat angle convention
- Calculated from Bike Insights' table
- Cockpit
- Generic stem and bar, assumed
- Solved with
- cover 10 mm (assumed), max spacers 40 mm (assumed), stem clamp centre 20 mm (assumed), so every verdict carries ±10 mm at the bar
- Sheet
- 22 October 2026 · 879 bikes, 79 makes, 4,979 sizes in the catalogue
Geometry, every size, from Bike Insights
The tinted row is the size drawn beside it. Press a size to draw it.The table runs on to the right: 6 more columns after Reach. Scroll it sideways to read them.
The 510 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.
Frame facts
not read off the maker's page yet: tantancycling.com- Tyre clearance
- not recorded yet
- Bottom bracket
- not recorded yet
- Axles and brakes
- not recorded yet
- UDH
- not recorded yet
- Seatpost
- not recorded yet
- Frame weight
- not recorded yet
Notes on the source
SECOND-HAND NUMBERS: copied from Bike Insights (https://bikeinsights.com/bikes/6006bd2118aecd0017dbc885-tantan-cycling-seraph-gr042?version=2021&build=base ), not read off the maker's own table. Source: aggregator (Bike Insights)
How I read Bike Insights' table
Bike Insights cites the maker's page: http://tantancycling.com/index.php?_m=mod_product&_a=view&p_id=933. The maker no longer publishes this table, so these numbers have not been checked against it; the seed stores this version as an aggregator source and caps its band (D17, D4 second amendment). Build: Base. Bike Insights files it as Road Bike / Mixed-terrain Road Bike / All-road/Gravel. Trail is left null: Bike Insights computes its own and the maker's is not on the page. Not checked against the maker's archived page: web.archive.org blocked this machine on 22 Oct 2026; a later pass should read the capture and upgrade this file to the maker's numbers. Tantan (Shenzhen TanTan Sports Equipment, also sold as SERAPH) still lists its frames on tantancycling.com, but on 22 Oct 2026 the site's chart images answered HTTP 302 to a third-party host (api03.miancp.com), which was not followed, so the maker's own chart could not be read; a later pass should read it and upgrade this file.