Doehring's (1955) German original is easier to read than the translation. 
The translation is pretty good, especially of the technical terms. 
It appears that he has compared his results with those of Klein and 
Sommerfeld, but he does not state it explicitly. He only says: Die bekannten 
linearisierten Bewegungsgleichungen ... Perhaps the thesis can 
shed some further light on this issue. 

I have just a few remarks: he uses wheels of equal radius, so his equations 
are a little less general than ours. In Eq. (20) and (21) on page 54, (page 
10 of the translation), the kinematic relations are not correct: r_2 and r_1 
should be multiplied by \cos\sigma, not divided by it. In the examples, it 
appears that D. has used the right formula, although not for the Vespa, for 
which both formulas give values that differ from from those of the table. 
It is possible that there is an error in the caster angle. 
In Eq. (35), the right-hand side should not be there, or be divided by the 
exponential function. 

JPM, Nottingham, 31 Oct. 2005.