What's the speed limit for a 26 straight truck in California ?

Double Yellow don't count on it. He/she might be pulling your leg.

 

Two axle trucks can do posted speed limit. Any car, truck with three or more axles and anything towing a trailer or combination vehicle is restricted to 55mph and right two lanes of the roadway...including bobtails. It used to be by trucks with GVW over 10,000...but now it is all based on # of axles (except for buses, which are exempt unless towing as mentioned above).

I have several class C straight trucks in CA. The only other restriction you have over a 4 wheeler is you have to stop at scales and have a log book. Legally you have to have a medical card, but if you have a non-commercial class C license and driving a class C truck under 26k GVW, they don't bother ya for that.