Motocross

Yamaha YZ125 2027

Motocross, 125cc 2T, EU/AU identical

Verified

Illustration: a Yamaha motocross bike, not this exact model.

From the owner’s manual: premix 30:1, p. 2-2; coolant 0.93 L, p. 2-2; front tire 80/100-21 51M, p. 2-5; rear tire 100/90-19 57M, p. 2-5. Checked 28 Sep 2026.

No CPSC recall found for the 2027 Yamaha YZ125, checked 2026-10-15. Recalls

Spec card PDF

Gearing

5 of 5 filled

Stock front sprocket: 13T; Verified, read off the manual page: Manual p. 2-3 · checked 2026-09-28 source [1]
Stock rear sprocket: 49T; Verified, read off the manual page: Manual p. 2-3 · checked 2026-09-28 source [1]
Chain pitch: 520; Verified, read off the manual page: Manual p. 2-7 · checked 2026-09-28 source [1]
Stock chain links: 112; Verified, read off the manual page: Manual p. 2-7 · checked 2026-09-28 source [1]
Stock final drive ratio: 3.769 : 1; Verified, read off the manual page: Manual p. 2-3 · checked 2026-09-28 source [1]

Wheels and tires

4 of 4 filled

Front rim: 21x1.6; Verified, read off the manual page: Manual p. 2-5 · checked 2026-09-28 source [1]
Rear rim: 19x1.85; Verified, read off the manual page: Manual p. 2-5 · checked 2026-09-28 source [1]
Front tire: 80/100-21 51M; Verified, read off the manual page: Manual p. 2-5 · checked 2026-09-28 source [1]
Rear tire: 100/90-19 57M; Verified, read off the manual page: Manual p. 2-5 · checked 2026-09-28 source [1]

Suspension

5 of 7 filled

Fork: Telescopic fork, coil spring; Verified, read off the manual page: Manual p. 2-5 · checked 2026-09-28 source [1]
Fork travel: 300 mm (11.8 in); Verified, read off the manual page: Manual p. 2-6 · checked 2026-09-28 source [1]
Shock travel: 315 mm (12.4 in); Verified, read off the manual page: Manual p. 2-6 · checked 2026-09-28 source [1]
Stock fork spring rate: 4.2 N/mm; Verified, read off the manual page: Manual p. 10-12 · checked 2026-09-28 source [1]
Stock shock spring rate: 48 N/mm; Verified, read off the manual page: Manual p. 10-13 · checked 2026-09-28 source [1]
Static sag, bike only: Not yet verified
Race sag, rider on: Not yet verified

Fluids and capacities

3 of 3 filled

Coolant capacity: 0.93 L (≈ 31.4 fl oz, converted by MotoXSports); Verified, read off the manual page: Manual p. 2-2 · checked 2026-09-28 source [1]
Premix ratio: 30:1; Verified, read off the manual page: Manual p. 2-2 · checked 2026-09-28 source [1]
Fuel capacity: 7.0 L (1.8 US gal); Verified, read off the manual page: Manual p. 2-2 · checked 2026-09-28 source [1]

Maintenance

3 of 3 filled

Tire pressure (off-road): 100 kPa (15 psi) front and rear; Verified, read off the manual page: Manual p. 2-5 · checked 2026-09-28 source [1]
Chain slack: 48-58 mm (1.89-2.28 in), on a maintenance stand; Verified, read off the manual page: Manual p. 2-7 · checked 2026-09-28 source [1]
Spark plug and gap: NGK BR9EVX, gap 0.6-0.7 mm; Verified, read off the manual page: Manual p. 2-2 · checked 2026-09-28 source [1]

Dimensions

3 of 3 filled

Seat height: 980 mm (38.6 in); Verified, read off the manual page: Manual p. 2-1 · checked 2026-09-28 source [1]
Wheelbase: 1445 mm (56.9 in); Verified, read off the manual page: Manual p. 2-1 · checked 2026-09-28 source [1]
Weight: 96 kg (212 lb); Verified, read off the manual page: Manual p. 2-1 · checked 2026-09-28 source [1]

Service specs

0 of 6 filled

Gearbox oil, fork oil, brake fluid, coolant type, fuel octane, idle speed: Not yet verified

Solid marks are owner's-manual pages; hollow marks are manufacturer web or spec-sheet figures still waiting on a manual page. Last reviewed 2026-09-28. Rows marked not yet verified are blank on purpose.

Buying parts

The stock sizes and specs this bike left the factory with, each with its source. Take them to any shop.

Retailer links below are affiliate links: we may earn a commission, at no cost to you, and it never changes the specs. Affiliate disclosure.

Chain: Chain pitch 520 Owner's manual p. 2-7Stock chain links 112 Owner's manual p. 2-7520 chains at MotoSport 520 master links at MotoSport
Sprockets: Stock front sprocket 13T Owner's manual p. 2-3Stock rear sprocket 49T Owner's manual p. 2-313T front sprockets at MotoSport 49T rear sprockets at MotoSport
Tires: Front tire 80/100-21 51M Owner's manual p. 2-5Rear tire 100/90-19 57M Owner's manual p. 2-5Front tires 80/100-21 at MotoSport Tubes 80/100-21 at MotoSport Rear tires 100/90-19 at MotoSport Tubes 100/90-19 at MotoSport
Coolant: Coolant capacity 930 ml (31.4 fl oz) Owner's manual p. 2-2Coolant at MotoSport
Suspension springs: Stock fork spring rate 4.2 N/mm Owner's manual p. 10-12Stock shock spring rate 48 N/mm Owner's manual p. 10-13Suspension at MotoSport

In stock at MotoSport

Prices from MotoSport’s catalog of Oct 26, 2026; check today’s price before you buy.

Front tire, stock size 80/100-21

Rear tire, stock size 100/90-19

Chain, stock pitch 520, stock length 112 links

Chains are sold by link count; this bike's stock chain is 520 pitch, 112 links.

Prices and stock from MotoSport's product catalog on Oct 26, 2026; they change, so check the price at MotoSport before you buy. Products are chosen by exact stock size, code or oil viscosity from the specs above, known brands first, then price. We have not tested them.

Use this bike

Tools for this bike

Compare with

All 27 comparisons for this bike

Other model years

All 4 model years, 2016 to 2027, side by side

Service schedule

63 rows from the owner's manual schedule, pp. 3-2 to 3-4, counted in races, at these intervals:

After break-in
Every race
Every third race
Every fifth race
As required

Check what's due or track it in My Bike. Buying one used? The hours check lists what the schedule calls for by its meter reading.

Gearing calculator

Gearing for this bike

Put your current gearing in Setup A and the setup you are considering in Setup B. Everything updates as you type.

Start from a bike's stock gearing

Pick a bike to fill both setups with its stock sprockets.

Front sprockets 8–16 teeth, rear 34–60. Values outside that range are brought back to the nearest limit.

Setup A — what you run now

Front teeth

Rear teeth

Setup B — what you are thinking about

Front teeth

Rear teeth

Final drive ratio

— — : 1

—

Pull at the wheel—

Top speed—

Ratio change—

A —

B —

Taller · more speed Shorter · more pull

—

Changing the rear sprocket changes the chain length too. The chain length calculator works it out from the chain you have now, with where the axle ends up.

Ratios are exact. The chain figure is an estimate of roughly one link per two teeth of change — confirm against your manual before ordering.

What's missing

22 of 30 fields read off a manual page.

Not yet verified (8): static sag, race sag, gearbox oil, fork oil, brake fluid, coolant type, fuel octane, idle speed.

See coverage for every bike

Sources

1
Yamaha 2027 YZ125 Owner's Service Manual, D68-2819U-52; owner-supplied copy from Yamaha's Owner's Manual Librarypp. 2-1, 2-2, 2-3, 2-5, 2-6, 2-7, 10-12, 10-13Manual page, verified. Covers stock front sprocket, stock rear sprocket, chain pitch, stock chain links, stock final drive ratio, front rim, rear rim, front tire, rear tire, fork, fork travel, shock travel, stock fork spring rate, stock shock spring rate, coolant capacity, fuel capacity, premix ratio, tire pressure (off-road), chain slack, spark plug and gap, seat height, wheelbase, weight; checked 2026-09-28.

Always confirm against the manual for your exact year before ordering parts or setting up suspension. Torque specs are deliberately not published here. How we verify a value.

Your manual prints something different? Report a value with the page it is on; every fix is listed in the corrections log.

My settings

Date / track
Sprockets run
Race sag / free sag
Fork air pressure or spring
Fork clickers (compression / rebound)
Shock clickers (low / high / rebound)
Tire pressures (front / rear)
Notes

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