Engine guard bars do their job only once. And that one time, they get scratched.
It is the paradox of the accessory most often bought by adventure motorcyclists: you install it to protect the bike, and then, when it is truly needed, it is the part that gets damaged. Which is perfectly fine—as long as it is the right part that gets damaged.
The part that wears out instead of the tube
The bumpers are two technical-plastic shells with rubber pads that clamp onto the bar’s most exposed point. In a stationary or low-speed fall, the bumper is what scrapes along the asphalt: the tube underneath remains intact.
The price difference says it all. A pair of bumpers costs 22,50 €; a new engine guard bar is in a completely different price range. It is not a cosmetic accessory, but a consumable deliberately placed there to break instead of something that costs twenty times as much.
There is also a second, less obvious effect: the rubber pad keeps the bike off the ground. The added thickness widens the contact point by a few millimeters and keeps the fairings and engine block away from the ground. In a slide, a few extra millimeters between plastic and asphalt are worth more than you might think.
Four bolts, not two
It is the construction detail that matters. The clamp distributes its grip across four points, so the bumper does not rotate around the tube when hit from the side—which is exactly the direction of impact in a lateral fall. A two-bolt clamp, under the same stress, turns and moves away from where it is needed.
The rest is just reassuringly small numbers: 108 g per piece, 216 g per pair, negligible weight, and positioned low and close to the bike’s axis to boot. No drilling: open them, position them, and close them again with an Allen key. Move them whenever you want, and the bar shows no trace of having had them fitted.
Where they go
At the bar’s most protruding point, the part that touches first if the bike goes down: normally, the vertical section at engine-block height.
The simplest way to identify it, without any theory: look at the bike resting on its side stand and see which part of the engine guard protrudes the most. That is it.
The manual recommends not fully tightening it straight away—first complete the positioning, then tighten it—and checking the tightness again after the first few miles.
The bar diameter determines everything else
This is where we get to the part that almost no one explains, and that is worth far more than the bumpers.
An engine guard is not just protection: it is the only open structural mounting point in the lower part of the motorcycle. Everything you want to mount there — protectors, bags, lights — depends on one number: the tube's outside diameter.
| Diameter | What it fits |
|---|---|
| 25 mm | Clamp-on bumpers, 6 L inflatable bags |
| 22-28 mm | Rigid crash bar bags with adjustable straps |
| 22 mm | It is the standard size for auxiliary-light clamps |
A 25 mm tube opens up more options than a 22 mm one, but it rules out auxiliary-light clamps designed for the standard size. That is why spacers and adapters exist: they reconcile two measurements that the market has never standardized.
How to measure it in one minute
- Using calipers, measure the tube's outside diameter at the point where you want to mount something.
- Without calipers: wrap a measuring tape around the tube and divide the circumference by 3.14. A 25 mm tube measures approximately 78.5 mm in circumference; a 22 mm tube measures approximately 69 mm.
- Check that the chosen section is clear and free of welds or obstructing brackets.
And here is a clarification that prevents half of all incorrect orders: the diameter does not depend on the motorcycle; it depends on the engine guard you have installed. Two identical BMW R 1250 GS motorcycles may have different tubes if they have bars from different brands. The measurement should be found on the engine guard's specifications, not the motorcycle's.
What you can mount on it besides bumpers
There is an empty space between the bars and the sides of the motorcycle that no pannier can make use of. It is the quickest-access storage there is: six liters per side, standing next to the motorcycle, without taking off your helmet. The rigid bags fit tubes from 22 to 28 mm, while the inflatable bags fit only round 25 mm tubes. The complete comparison, including water-resistance ratings, is in the soft luggage guide.
Auxiliary lights can also be mounted on the bars, which is the most protected position in the event of a fall — but how you secure them makes all the difference, because a clamp tightened around the tube relies on friction, and friction degrades with vibration. The complete discussion is here: where auxiliary lights are really mounted.
A recommendation that applies to anything you attach to a bar: check the distance from the exhaust and cylinder heads. The engine guard passes close to hot parts by design, and not everything you mount on it can withstand that.
The order in which it is best to proceed
- Measure the tube. Before buying anything, using calipers or a tape measure.
- Crash protectors, if the diameter is 25 mm. They are the smallest expense with the best ratio between cost and damage prevented.
- Bags, choosing the type based on the diameter and the level of protection you need.
- Auxiliary lights, with a mount that anchors to a hole rather than a collar.
See the crash protectors for 25 mm bars →
Frequently asked questions
What are the crash protectors on engine guard bars for?
They are the sacrificial part: in a fall, they scrape along the ground instead of the tube, which remains intact. The rubber bumper also adds a few millimeters between the fairings or engine block and the asphalt.
Why does the clamp need four screws?
Because it distributes the grip across four points instead of two: the crash protector does not rotate on the tube when it is struck from the side, which is the typical direction of impact in a sideways fall.
Where should the crash protectors be positioned on the bar?
At the most protruding point, normally the vertical section level with the engine block. Identify it by placing the motorcycle on its side stand and observing which part of the engine guard protrudes the most.
How do you measure the diameter of an engine guard bar?
Using calipers on the outside diameter, or by wrapping a tape measure around it and dividing the circumference by 3.14. A 25 mm tube has a circumference of approximately 78.5 mm, while a 22 mm tube has approximately 69 mm.
Does the bar diameter depend on the motorcycle model?
No, it depends on the engine guard installed. Two identical motorcycles may have tubes of different diameters if they use bars from different brands: the measurement must be found on the engine guard's specification sheet.
Do I need to drill the bar to install the crash protectors?
No. They open, are positioned on the tube, and close again by tightening the four screws with an Allen key. Installation is reversible, and they can be moved at any time.
Do the crash protectors fit bars of any diameter?
No, only on 25 mm tubes. The clamp is shaped for that diameter: on a thinner tube it would remain loose and rotate on the first impact; on a thicker one, it would not close.
If you don't know the diameter of your bars, send us the make and model of the engine guard: we'll check it before you order.
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