Shortening BMW Boxer Forks
Why shorten forks: The original reason for shortening the forks of BMW 2-valve models was to improve handling. Classic BMW 2V Boxers are originally designed to be rather rear-heavy. This means that the feel for the front wheel and the handling are not really good; at higher speeds, the front end becomes light and the BMW starts to sway.
The first measure was to install new, length-adjustable shock absorbers. The original components were too soft from the factory, and the spring force had naturally decreased further over 30 years. In addition, these old shock absorbers did not have a well-functioning damping system. Replacing the shock absorbers was a significant improvement, but we at SE Concept Bike were not yet satisfied.
The second measure was to lower the front. Handling basically improved with every millimeter we lowered the forks. In the -50mm range, the feel for the front wheel was good and the handling precise. Riding comfort did not noticeably worsen.
What happens if I shorten it more? If the forks are shortened by more than 50 mm, no significant improvement in handling is achieved. However, comfort decreases with every millimeter. In extreme cases, if forks are shortened by 120mm, no residual spring travel remains. A Monolever has a total spring travel of 175mm. If you subtract the negative spring travel of approx. 40mm, 135mm remain. If you shorten the fork by 120mm, you have an effective spring travel of only 15mm.
Shortening forks, but how?
There are two ways to shorten BMW two-valve forks. I'll start here with the professional solution favored by SE Concept Bike:
The upper fork tubes (stanchion tubes) are shortened on a lathe by the amount the fork is to be lowered. The corresponding layout of the fork tubes from the cut-off area, i.e. threads or grooves, is transferred back to the shortened fork tubes, i.e. re-machined. Since the upper parts of the fork legs are now shorter, correspondingly shorter fork springs are also required. The advantage of this measure is that you basically only get the positive effects, as the suspension travel is largely maintained.
The second option is to reduce the spring travel of the original damping system (lower part of the original fork) with spacers. However, with this method, for every millimeter the fork is lowered, the spring travel is also reduced. Other fork springs are also required for this measure. For this reason, we favor lowering BMW forks by shortening the stanchion tubes in conjunction with new spring kits.
A very important note at this point: It is strongly advised against shortening the original fork springs. If you shorten a spring, the spring rate changes. Moreover, the original springs are progressive. Where do I cut the spring? At the top, in the soft area, or at the bottom, in the hard area? We have often ridden vehicles with shortened springs. The handling is poor, and on uneven roads, it is even dangerous.
How do I proceed if I want to lower my forks?
This depends on whether only the removed and cleaned stanchion tubes are delivered or, alternatively, the complete fork.
Upon delivery of individual stanchion tubes: We shorten the fork stanchion tubes, and for the assembly, which you then carry out yourself, you will also need a suitable spring kit.
Upon delivery of the complete fork: In this case, in addition to the "shorten fork stanchion tubes" and the suitable spring kit, you will also need a fork overhaul. In this case, you will receive a ready-to-install fork back.
Can the fork lowering on BMW two-valve models be registered?
A registration within the functionally tolerable range (50-80mm) can be carried out by individual inspection. We have not created a parts certificate for this, as the demand for it is simply too low. Especially since such a parts certificate is quite expensive and would therefore make the product more expensive.
Customers generally do not register the lowering. If the shortening is in the range of 50-80 mm, it is not really recognizable from the outside. To answer your question: If you want to do it correctly, the lowering / fork shortening must be registered. However, this is generally not how it is handled.
Why shorten forks: The original reason for shortening the forks of BMW 2-valve models was to improve handling. Classic BMW 2V Boxers are originally designed to be rather rear-heavy. This means that the feel for the front wheel and the handling are not really good; at higher speeds, the front end becomes light and the BMW starts to sway.
The first measure was to install new, length-adjustable shock absorbers. The original components were too soft from the factory, and the spring force had naturally decreased further over 30 years. In addition, these old shock absorbers did not have a well-functioning damping system. Replacing the shock absorbers was a significant improvement, but we at SE Concept Bike were not yet satisfied.
The second measure was to lower the front. Handling basically improved with every millimeter we lowered the forks. In the -50mm range, the feel for the front wheel was good and the handling precise. Riding comfort did not noticeably worsen.
What happens if I shorten it more? If the forks are shortened by more than 50 mm, no significant improvement in handling is achieved. However, comfort decreases with every millimeter. In extreme cases, if forks are shortened by 120mm, no residual spring travel remains. A Monolever has a total spring travel of 175mm. If you subtract the negative spring travel of approx. 40mm, 135mm remain. If you shorten the fork by 120mm, you have an effective spring travel of only 15mm.
Shortening forks, but how?
There are two ways to shorten BMW two-valve forks. I'll start here with the professional solution favored by SE Concept Bike:
The upper fork tubes (stanchion tubes) are shortened on a lathe by the amount the fork is to be lowered. The corresponding layout of the fork tubes from the cut-off area, i.e. threads or grooves, is transferred back to the shortened fork tubes, i.e. re-machined. Since the upper parts of the fork legs are now shorter, correspondingly shorter fork springs are also required. The advantage of this measure is that you basically only get the positive effects, as the suspension travel is largely maintained.
The second option is to reduce the spring travel of the original damping system (lower part of the original fork) with spacers. However, with this method, for every millimeter the fork is lowered, the spring travel is also reduced. Other fork springs are also required for this measure. For this reason, we favor lowering BMW forks by shortening the stanchion tubes in conjunction with new spring kits.
A very important note at this point: It is strongly advised against shortening the original fork springs. If you shorten a spring, the spring rate changes. Moreover, the original springs are progressive. Where do I cut the spring? At the top, in the soft area, or at the bottom, in the hard area? We have often ridden vehicles with shortened springs. The handling is poor, and on uneven roads, it is even dangerous.
How do I proceed if I want to lower my forks?
This depends on whether only the removed and cleaned stanchion tubes are delivered or, alternatively, the complete fork.
Upon delivery of individual stanchion tubes: We shorten the fork stanchion tubes, and for the assembly, which you then carry out yourself, you will also need a suitable spring kit.
Upon delivery of the complete fork: In this case, in addition to the "shorten fork stanchion tubes" and the suitable spring kit, you will also need a fork overhaul. In this case, you will receive a ready-to-install fork back.
Can the fork lowering on BMW two-valve models be registered?
A registration within the functionally tolerable range (50-80mm) can be carried out by individual inspection. We have not created a parts certificate for this, as the demand for it is simply too low. Especially since such a parts certificate is quite expensive and would therefore make the product more expensive.
Customers generally do not register the lowering. If the shortening is in the range of 50-80 mm, it is not really recognizable from the outside. To answer your question: If you want to do it correctly, the lowering / fork shortening must be registered. However, this is generally not how it is handled.