Yes, you can put a longer bar on most chainsaws — but there are strict limits. The simple rule: you can usually go one size up (typically 2 inches longer) safely. Going 4 inches longer is the absolute maximum for domestic saws, and beyond that you risk overheating the engine, starving the chain of oil, and increasing kickback to dangerous levels.
Your chainsaw manufacturer always specifies a maximum bar length for a reason. Exceeding it isn’t just poor practice; it damages the saw and makes it unpredictable to use.
How Far Can You Safely Upsize Your Chainsaw Bar?
The general rule of thumb is straightforward: add 2 inches to your stock bar length, and you’ll almost certainly be fine. Add 4 inches, and you’re at the absolute limit for most domestic chainsaws. Beyond that, you’re into dangerous territory.
Here’s why: when you fit a longer bar, the engine has to work harder to spin a heavier chain with more drive links. The chain moves further before looping back to the engine, which means the oil pump has to deliver lubrication further down the bar. If the bar is too long, the oil simply doesn’t reach the tip, and the chain overheats and stretches.
At the same time, a longer bar increases leverage, which means kickback force increases dramatically. A saw that feels safe at 14 inches can become genuinely dangerous at 20 inches if it’s not designed for that length.
Maximum Bar Lengths by Saw Size
The safe maximum depends on your engine size. Professional 70cc+ saws are designed for long bars; a 35cc domestic saw is not.
| Engine Size | Stock Bar Length | Safe Maximum | Notes |
|---|---|---|---|
| Under 35cc | 12–14 inches | 16 inches | Battery saws often have fixed bars; upsizing not recommended |
| 35–45cc | 14–16 inches | 18 inches | Most domestic saws; one size up is safe |
| 45–55cc | 16–18 inches | 20 inches | Semi-professional range; consult manual for max |
| 55–70cc | 18–20 inches | 24 inches | Professional saws; manufacturer specs vary |
| 70cc+ | 20–24 inches | 36 inches+ | Milling and felling saws designed for long bars |
Always check your manual. The exact maximum bar length is printed in your chainsaw’s specification sheet. If it says 16 inches max, don’t fit 18 inches because someone on the internet said it might work.
What Changes When You Fit a Longer Bar?
When you upsize, several things happen inside the engine:
- Chain length increases. A longer bar needs more drive links. A Stihl chain that’s 72 links at 14 inches becomes 84 links at 16 inches. You must buy the correct chain length — you can’t stretch a short chain to fit.
- Oil consumption increases. The oil pump delivers the same amount of oil per engine revolution, but now it has to reach a longer distance. If the oil delivery isn’t sufficient, the chain overheats.
- Engine load increases. The motor has to spin a heavier chain with more inertia. On underpowered saws, this causes bogging — the engine loses RPM, the cut becomes slow and dangerous.
- Kickback risk increases. Longer bars create more leverage at the nose, which is where most kickback injuries originate. A tight knot or the chain catching wood will snap the bar up with greater force.
- Handling becomes more difficult. A saw that felt balanced at 14 inches will feel front-heavy at 18 inches, especially overhead. Fatigue sets in faster.
What About Fitting a Shorter Bar?
Yes, you can fit a shorter bar on most chainsaws, and it’s usually safe. You’ll need a shorter chain with fewer drive links, and the bar mount must be compatible — most chainsaws use standardised sprocket nose mounts, so any bar of the same pitch and gauge will fit.
The main disadvantage is that your cutting capacity shrinks. If you bought a 16-inch saw to fell small trees and now you fit a 10-inch bar, you’ve neutered the saw. The benefits are minimal — slightly less weight, easier handling, but no real power advantage.
One caution: if you fit a much shorter bar, the oil pump may deliver too much oil to the chain, causing excess smoke and oily discharge. This isn’t dangerous, just wasteful.
Battery Chainsaws — Can You Upsize the Bar?
Generally, no. Battery-powered chainsaws like those from Makita, DeWalt, and Milwaukee are engineered for a specific bar length. The motor, battery drain, and oil pump are calibrated for the stock configuration.
You might physically be able to fit a longer bar if the sprocket nose mount is compatible, but the battery will drain twice as fast, the motor will bog, and you’ll get very little cutting performance. The manufacturer’s max bar length (usually printed on the motor housing) is a hard limit for battery saws.
Safety Risks of Oversizing Your Chainsaw Bar
Fitting a bar that’s too long introduces several serious hazards:
- Chain starvation and overheating. If the oil doesn’t reach the tip, the chain heats up, stretches rapidly, and can snap. A broken chain under tension can whip back at your face or legs.
- Bogging and loss of control. The engine can’t maintain RPM, the chain moves sluggishly, and you lose cutting power at a critical moment. In felling work, this is dangerous.
- Increased kickback force. The longer the bar, the more leverage a stuck chain has to flip the saw back towards you. Kickback injuries are the most common chainsaw injury, and they’re severe.
- Premature engine wear. Running an oversized bar puts sustained stress on the crank, piston, and bearings. You’ll need to replace the saw sooner.
- Vibration and fatigue. A longer bar resonates at a different frequency. Holding the saw steady becomes tiring, and vibration damage accumulates in your hands and wrists.
How to Fit a Longer Bar Safely
If your manual says you can safely go to 18 inches and your saw currently has a 14-inch bar, here’s the correct process:
- Check your manual for the maximum approved bar length.
- Buy a replacement bar that’s approved for your saw’s sprocket nose type (usually marked on the box — e.g. “Stihl .325 pitch .050 gauge”).
- Buy a replacement chain in the correct length. Count the drive links on your old chain and add the number of links needed for the extra 4 inches — usually 12–18 links.
- Stop the engine and let it cool.
- Remove the clutch cover and loosen the bar mounting bolts.
- Slide off the old bar and chain.
- Fit the new bar and chain, ensuring the chain is centred on the bar.
- Tension the chain so it lifts away from the bottom of the bar by about 3mm, then snaps back when released.
- Check for proper oil flow by running the engine briefly and looking for oil mist on a piece of cardboard held under the nose.
Frequently Asked Questions
Can I fit a 16-inch bar on a 12-inch chainsaw?
Only if your manual explicitly allows it and your engine is at least 35cc. A 4-inch jump is at the upper limit for most domestic saws. Check the specification sheet first — if it says 14-inch max, don’t exceed it.
Will a longer bar make my chainsaw cut faster?
No. A longer bar allows you to cut thicker wood in one pass, but it doesn’t increase cutting speed. In fact, an oversized bar usually slows cutting because the engine bogs.
What’s the most common bar upgrade?
One size up — from 14 to 16 inches for a 40cc saw, or from 16 to 18 inches for a 50cc saw. This is usually within the manufacturer’s limits and noticeable for general work.
If I fit a longer bar, do I need a new spark plug?
No. The spark plug doesn’t change. However, the increased engine load may require you to adjust the fuel-to-air ratio slightly, especially on older carburettor-based saws. Consult your manual if the saw feels sluggish.
Can I buy a bar and chain kit from a different brand?
Yes, provided they match the pitch and gauge. An Oregon bar will fit a Stihl saw if both are .325 pitch .050 gauge. However, Stihl bars are specifically engineered for Stihl’s oil pump flow, so OEM parts are always the safest choice.
What happens if I accidentally fit a bar that’s too long?
The saw will struggle to cut. The chain may not get adequate oil and will overheat. You’ll notice poor cutting performance and excessive smoke. Stop immediately, remove the bar, and fit the correct size.
Is a longer bar worth the cost?
If your manual supports the upgrade and you regularly cut wood thicker than your current bar can handle, yes. A 14-to-16-inch upgrade costs £40–60 for bar and chain and doubles your cutting capacity for larger logs. Beyond that, you’re paying for diminishing returns.
Ready to Upgrade Your Bar?
Start by checking your chainsaw manual for the maximum approved bar length. Once you know you’re within limits, browse replacement bars on Amazon UK.
For more on finding the right chain length and pitch, see our complete chainsaw chain compatibility guide.
