The one I've seen the most is 53%, but I have also seen some that say 50%. Then there are those who will say that the whole length to wheelbase ratio is a myth, but personally I choose to go by 53%. If you look at the second question under the FAQs at
Henderson's Line-Up, a pretty good authority in steering and suspension, you will see that while they don't give a specific ratio, they do talk about shorter wheelbases being a contributing factor to porpoising.
Dewey & Sharon
Southern Maryland suburbs of DC
2014 Tiffin Phaeton 40QBH