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Chain And Sprockets Guide

Changing your sprockets is the cheapest way to change how your WR feels. A few teeth either way can make the bike much happier on tight trails, or calmer at highway speed. This guide covers the stock setup, the most popular gearing changes, and what to watch out for when you swap parts.

The Stock Setup

WR250R final drive: 13 tooth front sprocket, 43 tooth rear sprocket A small front sprocket on the engine drives a large rear sprocket on the wheel through a 520 chain. The final drive ratio is the rear tooth count divided by the front, 43 divided by 13, or 3.31. Front · 13T countershaft Rear · 43T on the rear wheel 520 chain · 108 links Final drive ratio = 43 ÷ 13 = 3.31
The ratio is rear teeth divided by front teeth. A higher number means shorter gearing: quicker acceleration, lower top speed.
WR250RWR250X
Front sprocket13T13T
Rear sprocket43T42T
Final drive ratio3.313.23
Chain520, 108 links520, 108 links

The two bikes share the same front sprocket and chain. The X has one less tooth on the rear to suit its smaller-diameter supermoto tires.

Which Way Should You Go?

Gearing is always a trade. There’s only so much range in a six-speed gearbox, so you’re choosing where to spend it:

  • Shorter gearing (bigger rear sprocket, or smaller front) gives you more pull off the line and more control at walking pace in technical terrain. You give up some top speed, and the engine revs higher on the highway.
  • Taller gearing (smaller rear, or bigger front) lowers your highway RPM and raises your top speed, at the cost of acceleration and slow-speed control.

Most owners find the stock 13/43 a little too tall for dirt riding, which is why going shorter is the most common change by far.

Popular WR gearing options compared to the stock WR250R 13/43 Percentage change in final drive ratio versus stock. 14/43 is 7.1 percent taller. 13/42, the WR250X stock gearing, is 2.3 percent taller. 14/47 is 1.5 percent shorter, 13/45 is 4.7 percent shorter, 13/47 is 9.3 percent shorter, 13/48 is 11.6 percent shorter, 13/50 is 16.3 percent shorter and 13/51 is 18.6 percent shorter. ← Taller: top speed Shorter: more pull → 14/43 14/43: ratio 3.07, -7.1% vs WR250R stock −7.1% 13/42 (X stock) 13/42 (X stock): ratio 3.23, -2.3% vs WR250R stock −2.3% 13/43 (R stock) 13/43 (R stock): ratio 3.31 ratio 3.31 14/47 14/47: ratio 3.36, +1.5% vs WR250R stock +1.5% 13/45 13/45: ratio 3.46, +4.7% vs WR250R stock +4.7% 13/47 13/47: ratio 3.62, +9.3% vs WR250R stock +9.3% 13/48 13/48: ratio 3.69, +11.6% vs WR250R stock +11.6% 13/50 13/50: ratio 3.85, +16.3% vs WR250R stock +16.3% 13/51 13/51: ratio 3.92, +18.6% vs WR250R stock +18.6% −5%0+5%+10%+15%+20%
Change in final drive ratio compared to the stock WR250R (13/43).
Front / RearRatioBest For
14/433.07Mostly highway. The tallest practical option.
13/433.31Stock WR250R. A compromise that leans toward the road.
13/453.46A small step shorter. Good if you ride a lot of highway but want a bit more pull.
13/473.62The most popular dual-sport setup. Noticeably stronger in the dirt, still fine on back roads.
13/483.69Trail-focused, with highway use as a secondary concern.
13/50–513.85–3.92Tight, technical off-road riding. Expect a noticeably lower top speed.

If you’re not sure, 13/47 is where most owners land. One owner who tried it loved it in the dirt but found it limited on the highway and settled on 13/45 instead, which is a good illustration of the trade-off. Also remember that tire size changes the effective gearing too, so a taller or shorter rear tire will shift things slightly. See the tire guide for sizes.

Change The Rear, Not The Front

You can get the same ratio by changing either sprocket, but on the WR it’s better to leave the 13-tooth front alone and change the rear:

  • Avoid a 12-tooth front. It’s tempting because one tooth up front is a big change, but the smaller sprocket pulls the chain down at a sharper angle. Owners have had the chain wear through the swingarm’s rubber slider and into the swingarm itself.
  • A 14-tooth front works, but check clearance. It lifts the chain away from the swingarm, which is a plus. Some owners found it rubs the stock countershaft sprocket cover or a case saver, so check before you ride.

Chain Length

The stock 108-link chain fits the stock sprockets with room to adjust. A bigger rear sprocket wraps more chain, so you’ll often need a longer one:

  • 13/45: may just fit the stock 108-link chain, but you’ll be at the end of the axle adjustment range with no room for the chain to stretch.
  • 13/47 and up: plan on a longer chain. Owners running 13/47 typically use around 110–112 links.

The easiest approach is to buy a 520 chain with 120 links and cut it to fit your sprockets, with the rear axle near the front of its adjustment range. Use a rivet-type master link rather than a clip, and use the master link made for your chain brand.

Whenever you change the chain, change both sprockets at the same time. A new chain on worn sprockets (or the other way round) wears out quickly. Once it’s all installed, set the slack using the chain adjustment guide.

Your Speedometer Will Be Wrong

The WR’s speedometer takes its reading from the gearbox, not the wheel. That means any sprocket change throws off both the speedometer and the odometer by roughly the same percentage as the ratio change. With 13/47, for example, the speedometer reads about 9% fast, on top of any error the bike already had from the factory. One owner on 13/47 saw 120 km/h on the dash at a GPS-measured 100.

Check your real speed against a GPS app. If the error bothers you, an inline speedometer calibrator (such as a SpeedoHealer) can correct both the speedometer and the odometer.