Stihl Trimmer Drive Shaft Systems: Flex Shaft Vs Solid Shaft

Flex shaft vs solid shaft drive systems: which is best, and what’s the difference?

The difference between a flex shaft and a solid shaft in trimmers refers to the design of the shaft that transfers power from the engine to the cutting head. Stihl homeowner trimmers, like the FS 45 and FS 55 have flex shafts, while professional trimmers and brush cutters have solid shafts.

A flex shaft, as the name suggests, is made of a flexible material (most often a wire cable) that allows the shaft to bend and flex. In contrast, a solid shaft is made from a rigid material (most often steel) that maintains its straightness.

Both types have their advantages and disadvantages, which might influence your choice based on your specific needs and preferences.

Stihl Drive Shaft Systems

Specifics on which Stihl models have flex shafts and which have solid change as Stihl releases new models or updates existing ones.

In general, Stihl often uses flex shafts for their homeowner or residential models, as these are designed to be lightweight and cost-effective for less frequent use. Their professional-grade models, designed for more rigorous, frequent use, often feature solid shafts for their added durability and efficient power transfer.

For the most accurate and up-to-date information, we recommend checking the Stihl website or contacting a Stihl dealer. They will be able to provide detailed specifications for each model, including whether it uses a flex shaft or a solid shaft. Here are the pros and cons of each.

Flex Shaft

Stihl trimmer models that have a flex shaft include the FS 38, FS 40, FS 50, FS 56, and FS 70, along with earlier versions of these weed eaters.

Flex Shaft Pros:

1. Lighter Weight: Flex shafts are generally lighter than solid shafts, which can make the trimmer easier to handle and maneuver, especially for extended periods.
2. Tolerant to Misalignment: Because of their flexibility, flex shafts can tolerate some degree of misalignment between the engine and the cutting head, which can be helpful in certain conditions.
3. Cost: Typically, flex shafts are less expensive to produce, which often results in a lower cost for the trimmer.
4. Easier to Service: Given their construction, flex shafts can be easier to replace if they get damaged. This can reduce downtime and expense if you experience a mechanical issue with your trimmer.

Flex Shaft Cons:

1. Durability: Flex shafts are usually less durable than solid shafts. Over time, repeated bending and flexing can cause wear and tear, which might lead to earlier failure.
2. Power Transfer: Because they can bend, flex shafts might not transfer power from the engine to the cutting head as efficiently as solid shafts.
3. Vibration: Flex shafts can often cause more vibration during operation than solid shafts. This might lead to more fatigue during extended use, and could potentially reduce the precision of your trimming.

Solid Shaft

Stihl trimmer models that have a solid shaft include the FS 90/91, FS 94, FS 111, FS 131, FS 240, FS 311, and earlier versions of these models.

Solid Shaft Pros:

1. Durability: Solid shafts are generally more durable than flex shafts, capable of withstanding heavy-duty use and rigorous conditions for longer periods.
2. Power Transfer: As they are rigid, solid shafts can transfer power more efficiently from the engine to the cutting head, often resulting in better performance, particularly in tougher cutting conditions.
3. Less Vibration: Due to their rigid nature, solid shafts generally cause less vibration than flex shafts. This can make the trimmer more comfortable to use, especially over longer periods, and might improve the precision of your work.
4. Greater Cutting Reach: Due to their rigidity, solid shafts often allow for a greater cutting reach, which can be advantageous when trimming tall hedges or hard-to-reach areas.
5. Compatibility with Attachments: Solid shaft trimmers are typically compatible with a wider range of attachments. This includes heavy-duty cutting blades, edging tools, and even brush-cutting attachments, enhancing the versatility of the tool.
6. Increased Value Over Time: Solid shaft trimmers, given their durability and robustness, often retain their value better over time compared to their flex shaft counterparts. This might be a significant factor to consider if you plan to sell or trade-in your trimmer in the future.

Solid Shaft Cons:

1. Weight: Solid shafts are typically heavier than flex shafts, which might make the trimmer more difficult to handle and maneuver, particularly for extended periods.
2. Cost: Due to their construction, solid shafts are usually more expensive to produce, potentially increasing the cost of the trimmer.
3. Less Forgiving to Misuse: Solid shafts, due to their rigid nature, are less forgiving to misuse or mishandling, like dropping or incorrect storage. This could lead to bending or damage to the shaft that may be more difficult or costly to repair.

While solid shafts are generally more durable and can handle more rigorous use, they might not tolerate certain types of misuse as well as flex shafts.

For example, the shaft could become bent if a solid shaft trimmer is accidentally dropped or stored improperly. Because it’s rigid, it might not be easy or even possible to straighten it back to its original form, potentially interfering with its operation.

Flex Shaft Vs Solid Shaft

Overall, the solid shaft trimmers and cutters are the better version—as you’d expect, given that’s what the professional models use.

Solid shafts are generally more robust and can endure more wear and tear than flex shafts, particularly for professional or heavy-duty use. The higher cost of solid shaft trimmers reflects this added durability and performance. They’re also more capable of handling heavier and more abrasive cutting attachments, making them more versatile for different types of tasks.

The choice between a flex shaft and a solid shaft will depend on your specific needs, such as your budget, the intensity of the trimming work you need to do, and how long you expect to use the trimmer at a time. Most Stihl users, ourselves included, would recommend the professional models over the consumer models, even for home use. That way, you have the option to do more in the future.

Let us know your thoughts in the comment section below, or find out what FS means on Stihl trimmers!