Just Noticeable Difference

Every now and then I try to notice comfort and stiffness differences between bikes but I still can't. Saves me a lot of anxiety when picking bikes at least =) I only have to consider wind tunnel, paint, and price!
– Jack Mott[i]

Just Noticeable Difference

Jack, we’ve wondered the same thing and have looked into a relevant aspect of human perception: the Just Noticeable Difference (JND), especially as it applies to vibration transmission of different bicycles.

The concept of the Just Noticeable Difference comes from the field of psychophysics and is defined as the difference in a stimulus which is detectable as often as it is undetectable. In other words, a greater difference is reliably detectable, and a smaller difference is reliably undetectable. The just noticeable difference (JND) is at the edge of being reliably detected.

Some examples of just noticeable differences in familiar measures are the 4.8% change in loudness required for humans to detect a change in sound level and the 7.9% change in brightness of a light. These values will differ from one person to the next, and from one occasion to the next. However, they do represent generally accurate values.[ii]

Considering bicycles in this context becomes interesting because the difference in vibration transmission between different road bikes can be hard to notice sometimes. Some folks seem to notice everything, while others can’t seem to notice anything. And some riders notice differences that aren’t even there! So we decided to test peoples’ just noticeable difference.

 

Test procedure

 

600X200

Figure 1. The test procedure: (1) recording, (2) test rig, (3) human perception

To conduct this test, we:

(1)  Recorded the vibration from the road

(2)  Constructed a two-post vibration test rig in the lab

(3)  Asked human test riders to tell us which altered road signal has more vibration

 

Each test subject compared two simulated roads back to back. The only difference between the two simulated roads was the amplitude: 100% of the real road recording, 95%, 90% 85% or 80%, so that the differences tested were 0, +/- 5%, 10%, 15% or 20%. Each subject made a total of 100 of these comparisons, with random pairs of various percentage differences.

 

Results

No test riders could notice the smallest difference, 5%. Many riders could notice a difference of 10%. And most riders could notice a difference of 15% or more.

 

Takeaway

The bottom line is this: different bikes can transmit vibration differently, and sometimes some riders can just notice the difference. In your case Jack, either the bikes you’ve tried aren’t substantially different in how they transmit vibrations, or you’re one of the insensitive riders, or perhaps a combination. Either way, consider yourself lucky – among bikes you’ve compared, you don’t have to worry about comfort and stiffness differences. Instead, focus on things that make a difference to you: “wind tunnel, paint and price!”

Comments (4)
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  • Eerke

    Enyoyed the article. It is awesome to have an insight into how you see these things. I think there is a flaw in the one. And it's a quite common flaw. It my work we'd criticise this as a surrogate end-point. I can see how feel may be important for selling bikes in a shop, but what really matters is how fast you can ride and how much a rider enjoys going out for a spin. There may be an association, but there may not. For instance; if you had to choose between two bikes 1) feels smooth. Can put out x Watts on average and feel knackered at the end of a ride. 2) feels rough, but can put out 30 more Watts and at the end of the cycle feel all set for going for a run. Would you really pick 1? Also, if you can't 'feel' any difference between two bikes but the vibrations of one mean you can cycle faster and feel fresher; does it matter that you can't 'feel' the difference? I wouldn't be surprised if there were some vibrations that were knackering, whilst there were others t

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  • amino

    Damon, on vibration transmission what percentage relates to the kind of wheels/tires you install vs. the frame itself on JND?

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  • sausskross

    Oops, the comment system ignored that important sentence: I'm not talking about passive comfort and perception, Thank You!

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  • sausskross

    Great, I love to read it. The JND in steering a bike depends on 1. speed 2. acceleration 3. change of riding direction and 4. dynamic energies in rider movements. In a sprint with high speed, explosive acceleration and smallest changes of directions within a creatable balance by an athlete on two wheels your psychological release of powerflow has more variance to response in competetive situations with a "really cool head". That can be felt and even measured in frayed nerves at the same time, if someone is so brave to risk a collapse for another meter .. sCa >> Cheers, -sausskross

    > Cheers, -sausskross%0D%0AComment by: sausskross">Report this comment.
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