TESTING | Bhaack

Test 1 was performed by pedaling over a short test track that simulates firm pedaling up a slope and also over a bump. This test is configured to evaluate the pedaling performance of each system under pedaling load including over bumps, while also ensuring consistent and repeatable testing.

Test 1 consists of starting from a standstill on roughly even ground, then pedaling up an incline with a bump midway of about 35 mm height and finally coasting at the end as the incline flattening out. The start had a small ledge (~10mm) which was initially used for practical reasons (to start at the same location consistently), but as shown by the results, this feature itself highlights some performance advantages of the prototype system.

The following graphs show the shock movement results of the Prototype compared to 3 other contemporary systems during test 1. These results highlight how the system generates less suspension movement during pedaling and also that it remains active over bumps and actually absorbs bumps far better.

Note that Brand A, Brand B, Brand C are all high performance bicycles at or near the top of the range from well known bicycle companies. Further information will not be disclosed publicly.

Specifically, what this test shows is that the provision of high anti squat forces by other systems (Brand A & B) generates unwanted suspension rise during pedaling over bumps. (Note that Brand A and B are very different systems despite the similar results.)

Brand C was found to perform distinctly differently to Brand A and B. Upon evaluation it was found that Brand C has significantly lower anti squat performance around the sag point. As a result Brand C almost matches the Z-Link system over the bumps by not generating unwanted suspension rise. However, the clear negative outcome of this systems performance is then the significant system squat during pedaling.

Only a system like that of the prototype can provide high anti squat where it is needed and low anti squat when anti squat is not needed.

Note that a short summary of the testing process is provided below.

Test 2 was performed by pedaling over the same test track as Test 1 except that the test was started at the bump midway through Test 1 so that the bump acts as a ledge. This test is configured to simulate pedaling up a hill which includes climbing up over a root or ledge at slow speed. (This situation might be typical of a steep pinch or switch back near a tree where erosion has exposed the tree root).

As it is very difficult to replicate dynamics when getting over a root or ledge at slow speed, the test run was configured by starting from a standstill with the rear wheel up against a ledge of about 35 mm. After clearing the ledge it was necessary to apply firm pedaling to climb the proceeding incline.

The results indicate similar outcomes to Test 1. These are provided in the below graphs.

Brand A and B exhibit significant unneeded suspension rise when clearing the initial ledge. This is extremely unhelpful as it indicates the rear suspension is extending significantly at the bump - the complete opposite of absorbing it. What is not shown in the graphs is the difficulty the rider faces to force the rear wheel over the ledge through significantly increased pedaling effort.

Brand A and B also show higher levels of suspension oscillation compared to the prototype system once the ledge is cleared as the rider applies pedaling force to build a little speed.

Similar to Test 1, Brand C, with its low anti squat performs quite well when it comes to clearing the ledge. However, the lack of anti-squat is exposed as pedaling force is applied after the ledge. Initially the suspension compresses significantly as the low anti squat lets the chain force pulls the system down (using up around an extra 3rd of the systems travel below the sag point). Thereafter, when pedaling to build speed, the system oscillates more significantly than the Z-Link system, and that oscillation occurs in a sagged position due to the low anti squat the system provides around and below the sag point.

In comparison to these result, the prototype provides far superior performance. The protottyp system has minimal suspension rise at the starting ledge. It clears the ledge easily, does not compress unnecessarily after the ledge, has minimal suspension oscillation and travels near the sag point during firm pedaling.

Testing Process Summary

The following provides a very brief explanation of the testing process:

Bike Set Up

Each bike tested uses a unique suspension system in their own right.
To ensure pedal strokes occurred at the same position on the track, each bikes wheel diameter was assessed and gearing selected (and or gearing changed) to ensure gearing was within ~3%.
As it is was built some time ago the prototype bike was fitted with 26” tires with a diameter of 664 mm (something of a disadvantage).
All other bikes were fitted with 27.5” tires of diameters between 696 mm and 708 mm.
Tire pressures were generally matched with come consideration of tire construction and wall stiffness.
All bikes tested (to date) have between 150 mm and 160 mm of rear wheel travel.

Shock Set Up

All bikes were fitted with their own off the shelf air spring shocks.
It would be nice to swap shocks between each bike for testing to eliminate this difference. However, each bike comes with a different leverage ratio and/or shock size. Therefore this approach was not reasonable or possible. Instead, the OEM shocks were left on each bike.
Sag was typically set between 26% and 30% of shock travel with some consideration of the appropriateness of sag setting for each bike and shock combination.
Rebound adjusters were set to provide similar rebound speeds. When it was felt the rebound setting should be between clicks on other branded bikes, the setting was biased towards a slower rebound.
The shock switch was left open for the testing except for Brand C which did not have a switch and came with an unknown internal setting.

The Human Element

All testing has its limitations. Dynamic testing of bicycle suspension is particularly challenging due to human interaction – it’s hard to repeat exactly the same pedal strokes in terms of effort and speed.
To achieve a reasonable level of repeat-ability a tightly controlled test track have been used. Test 1 and 2 were performed on hard non wearing surfaces. Test run results were evaluated for consistency in speed and significant pedal stroke abnormalities. Also the results shown are not averaged but reflect a typical run which is consistent with other runs (e.g. not an outlier).
Where possible test runs were performed via sitting down pedaling to minimize variations in rider movement. Tests 1 and 2 were performed sitting down.
Gearing was selected to provide firm and slow pedaling effort. This facilitated slow leg movements during pedaling so that mass movement effects were consistent and also minimized.
Testing results for Test 1 were configured to be horizontally aligned by a key feature through the track (such as a bump) and vertical aligned at the sag point by completing the run without pedal strokes across the last meter or so of the track.
Testing results for Test 2 were configured to be aligned to be horizontally aligned at the initial ledge and vertically aligned at the sag point by completing the run without pedal strokes across the last meter or so of the track.

Data Collection

Data was sampled at a rate of 30 Hz. This sample rate is fast enough to catch most movements but will have missed some peaks during the more rapid stages of shock movement.

PERFORMANCE BENEFITS PROVEN BY TESTING

TEST 1 - Firm Pedaling up an Incline with Bump Midway (and Small Ledge at the Start)

TEST 2 - Stall Test Followed by an Incline

Testing Process Summary

The following provides a very brief explanation of the testing process: