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I'm designing a four-wheel velomobile as a small city bike with good weather protection. The top speed in the city is about 25km/h (7m/s).

The total weight of the velomobile is 35-45kg, and I expect the rider with some luggage to be 65kg to 100kg. So the total weight is 100 to 150kg. The weight distribution is 40/60, where most of the weight is on the back wheels. The velomobile is to be front-drive, and it adds complexity in the design but should not affect the suspension.

The small bumps that make the person bouncing about and make them uncomfortable are 0,5cm to 3cm in the city. It should be a firm but smooth ride on cobble roads and across potholes.

How do I design and calculate the suspension to make it good? The suspension design is double wishbone. Yes, I could (and would like to) make adjustments when changing from a 65kg rider to a 100kg rider, but how do I calculate the proper settings?

suspension front

I've seen this answer - but I did not quite understand if that also works for very light loads: Car Suspension Force Equations

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  • $\begingroup$ First of all the subject is very interesting and you have given a lot of the relevant information. I am not an expert on tuning suspensions, however I feel that you should start by defining the specifications of a comfort ride (you mention the bump size but not what is acceptable for the rider). Additionally, since you are mentioning a double wishbone, you have a MDOF system, therefore the equations at the other question do not apply as they are presented there to your problem. In any case for an MDOF system you'd need to consider center of mass and mass monent of inertia for your velomobile. $\endgroup$
    – NMech ♦
    May 12, 2021 at 8:06
  • $\begingroup$ Nmech - good point. I looked at this: researchgate.net/publication/… but it looks like I need to test and test before I get the data to analyse. I'd like to understand this better from a theory and other persons experiences to get this right faster. $\endgroup$
    – Anders Carlius
    May 12, 2021 at 9:45

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How do I design and calculate the suspension to make it good?

This is quite an ask. This is frankly beyond the capability of a degreed Mechanical Engineer without some specialist training. Sure, I'd know where to start but I'd never take on such a thing by myself. You're talking about design of the linkages plus the appropriate spring and damper rates. So I guess you probably need to start with Statics, Dynamics, Machine Design, and Vibrations as starter courses (Vibrations has some serious math pre-requisites).

What I would do is go look at similar products and see how they do it. You'd probably have better luck with someone who fabs bikes for a living than an engineer, unless the engineer did this type of work already.

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  • $\begingroup$ ok, I will start looking at how the other have done it. Getting into the "standing on the shoulders of gigants" seems to be a good way forward. $\endgroup$
    – Anders Carlius
    May 15, 2021 at 8:26

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