I am trying to calculate maximum force various braking systems can apply and for that I need the ergonomic data as to how much force fingers can apply.
If your question is about the maximum hand grip can applied to brake so that the braking system will not be broken apart, then it is as another answer.
However it has little value on designing a braking system.
How I interpret the question is: how much force is typically applied to the brake lever to stop the bike.
There are many designing considerations and I only list a few main one:
- Maximum force on to lever that a person feels comfortable at gripping for a long duration (for me it's about 5-7 kg or 50-70N)
- Modulation how well the spread between the the force at which the bike starts to decelerate, and the Maximum force. This depends on the braking technology, the pad/rim surface/rotor. But in general, disc brake is superior because of the (more) linearity in braking.
- Linearity: how linear the stopping power versus the force applied by brakes? This is interesting and thus somehow explains why road bike is equipped with caliper, hybrid with cantilever, and mountain bike with disc brake. Linearity improves as we go from caliper-cantilever-disc. The discrepancy is large when higher stopping power is required. But at smaller (required) stopping power, a caliper is not that much different front disc brake for a given braking range.
- Maximum stopping power This is safety feature, but it should not be easy to flip the bike with too little gripping onto the brake lever. This has to take into account the bicycle geometry, and that is why road bike is normally equipped with caliper brake. Even some (supposed-to-be) road bike has disc brake, the rotor/leverage/cylinder was designed so that it has much less stopping power than a mountain bike disc brake.
Well, it depends on type of brake and how fast you would like to stop the bike, at what speed, and at what momentum.
If you just want a number to work with (for your home work?), I can give you. A normal cable brake on flat handle bar would need about 40-50 N (3-4 kg) for hard stop, about 20-40N (1-2 kg) for normal deceleration.
Same stopping power with drop handlebar and caliper brake would need about 1.5 to 2 times as much (comparing Figure 1 and 2), depends on hand position (leverage). Typically hands at hood position requires more force for same stopping power in comparison to hands at drop position.
Same stopping power with hydraulic disc brake needs about 0.5-0.7 fold. This depends on the rotor size/pattern and type of ceramic and thus it is hard to quantify. But the general still holds, if you are designing a disc brake that has an enormous stopping power for normal stopping, you actually degrades the modulation ability of said brake.
Figure 1a. Normal barking force on drop position of drop handlebar
Figure 1b. Braking force required to lever on emergency stop on drop position of drop handlebar
Figure 2a Braking force required onto lever in cantilever brake for normal stop
Figure 2b Braking force required onto lever in cantilever brake for hard stop
I suggest your analysis is flawed
Finger strength to cable pull has a lot of variability:
- internal leverage in the brake lever mechanism
- where on the lever the force is applied
- on the brake mechanism itself you have different leverages
Most mountain brakes are used with two fingers and many levers are not even long enough for 4 fingers
On a drop bar are you on the hoods or in the drops
If you want some good numbers then you need to put a weight on the brake cable
And most brakes can skid a tire. Once you skid the tire (rear) or go out font (front) the max does not come into play.
What are you trying to accomplish here?
I did a search with Google for "male grip force" and got quite few hits that look reasonable, one, the International Encyclopedia of Ergonomics and Human Factors, Second Edition, has an article on Hand Grip and Pinch Strength – perhaps that will help you get started.
Adding the term "bicycle" to the search finds an interesting looking article called , but you have to register for an account to read it and they seem to only be open to providing accounts to researchers.
If you are working on a bike related project it might be useful to use actual handlebars and brakes to collect your own data. I suspect that typical riding grips on brakes are not typical of what is published, but it would not be hard to rig a brake cable to a spring scale to measure force.