Well yes its all about weight acting at a distance.... but as I said earlier, a caravan puts 80-150kg directly onto the towing hitch.
You said you had:
2 bikes 13+kg each - 26kg
the bike rack - 17kg
(I'm ignoring the weight of the tow hitch as its the same with the caravan scenario, as is full tank of fuel and stuff/passengers in the back seats and boot full of stuff)
So you've got 43kg but if that is acting even half a metre away from the tow hitch vertical (and its not a simple calculation to work it out short of trying to balance the whole thing on scales like you do with a caravan nose weight check) that force increases quite a bit.
I'm sure some clever physics type could work it out or rather a rough calculation, but still would be surprised if it got to 80kg.
As we are just chatting - I think its the return force and how that
feels in the car due to hitting bump stops and not so much about a light or heavy weight.
A 100-150kg load on a tow bar will likely
feel less harsh on bump stops because the bumpstop when squashed will return at a slower rate than a lighter load for example 50kg. The damper won't control the return speed as the spring rate now is too high, but the change of direction from compression to rebound will be slower as the weight is very high 100 to 150kg and the bumstop struggles to fully stop and extend back up the weight. Using a light hammer vs heavy hammer when direction change is applied (kind of thing). All things being equal the return speed of a heavy object will be slower as the bump stop has to slow, stop, change direction and return a heavier load, this should
feel smoother or slower as it changes direction. Drop 1kg on a bump stop it will spring back up very quickly, drop a 15kg on a bump stop and it wil compress more and be slower to return to normal shape.
If you compress a bump stop the same amount, with the same springs and dampers, it will
feel more harsh with a faster return (light load) and low damper resistance. I think a heavier load will compress the bumpstop more (your caravan scenario) and return slower, but the return rate of a lighter load would
feel more harsh as its a more violent jolt/acceleration back up especially with the weak dampers on the Golf GTI GTD TCR (these are the same dampers from 1.0 Golf to TCR).
I may not have explained this clearly, but in my head it sounds correct.
Thanks Japes1275 for the tips, I don't think I have that much of an issue but interesting you had different experiences with different cars
