What is "height stroke" on a tire? I am reading a tire review at 
http://www.bicyclerollingresistance.com/road-bike-reviews/schwalbe-lugano-2015
and it says 


  the Lugano had a gigantic height stroke. Most tires have this, but the Lugano was awful, you will probably notice it on the bike. This is a sign of low-quality control.


and


  quality control seems to be low as the Lugano used for this test came with a severe height stroke. To keep the price low, they probably just don't bin the bad tires.


What is it?   This tire is very low-scoring so I think it is bad.
It means height variation, and it is a non-idiomatic translation.

Edit: As pointed out in comments, the translation is from "Höhenschlag", where "höhe" means height and "schlag" translates to blow, slap or stroke. It means specifically bicycle tire or rim that is out of round vertically. Lateral out of round is Seitenschlag.

My original guess: There are many German words that translate into "stroke", and one of them is "Hub". It translates to stroke in the same sense as "stroke" in  four-stroke engine. Other possible translations are "travel [of piston etc.]" or "(vertical) lift", and it is used in phrase "Hub- und Senkbewegungen" meaning "up and down movements".

Even though the company behing Bicycle Rolling Resistance is located in Netherlands, the name Jarno Bierman sounds German (well, Jarno is Finnish name but there are people named after motorcyclist Jarno Saarinen all over Europe), and Dutch language is closely related.