What changed to wheels or traction after KSP 1.4.5?

[ndiver]

Hello,

I realized today that an old rover design i used for a while totally lost its performance in KSP versions after the 1.4.5.
The design is basically a modified version of that with 8 wheels instead of 10 and with a 2.5m lab (~12 tons of weight):

Until 1.4.5, it was able to climb mountain slopes up to ~45° slopes (there was traction issues in the mountains on some slopes in the mountain range close to the KSC, but i went up to the mountain monolith with it), I used it on the Mün for long distance trip (including crossing the larger crater slopes and even finding a way across the canyon slopes).
In the 1.8.1 and 1.11 (stock), the same design is not even able to climb a 20° slope on Kerbin. My guess is that something changed in KSP on wheels, traction or friction  since the 1.4.5, my question is what?

What has changed by lovely rover in something useless?

 

Edited March 21, 2021 by ndiver

[rynther]

How gravity is handled has changed a bit, the way traction works not really sure, but many parts have had the specs changed, so that's the most likely culprit.