About as technical and engineering oriented as you can get. Excellent for understanding the theory behind design. Enjoy!
I haven't paid much attention to using to to try and design off-road suspension, but a great place to start is the Miliken text book. It has a good introduction to suspension dynamics and design even though it is a little dated. Still very usable though.
Also most of the backyard mechanics building their own have no clue what they are doing. You can certainly teach yourself and design something pretty good. Once you get the design down then your next step is figuring out ride and roll rates of the vehicle so you can figure springs and sway bars.
> On the other hand, do you know any book about the physics of racing cars? I found one but is very basic in my opinion.
Have you read good ol' Miliken?
https://www.amazon.com/Vehicle-Dynamics-Douglas-Milliken-William/dp/1560915269/
Further up somebody posted this: Race Car Vehicle Dynamics https://www.amazon.com/dp/1560915269/ref=cm_sw_r_cp_api_glt_fabc_WSY04ACDAEFVXB62QYJC