It's 85% of kerb weight (or mass in service), not 85% of towing weight. This is advisory only and applies only to those new to towing.
This figure is now decades old and appears to have been selected arbitrarily in the first place. In my humble opinion, it's given far more credence than it really deserves. Taking a kerb weight of 1385kg for your Volvo (as stated earlier in this thread, I haven't checked it), 85% of this would be 1177kg. An increase to 1200kg would result in a ratio of 86.7%. I very much doubt you'd notice any difference.
------------- "Don't wait for the perfect moment. Take the moment and make it perfect."
That’s great thank you for all your help it is very gratefully received.
About the tow bar my car currently doesn’t have one on would you happen to know what a rough price to have one fitted with the electric hook up aswell??
Prices vary so much, fixed are cheapest, Detachable are top end.
I've bought about 5 towbars over the years and i usually pay about £400 for a detachable fitted with 13pin electrics. But i get quoted right up to £8/900 for the same bar, You need to shop around
I personally would only get a detachable, I have a towtrust on my current car & its miles easier to get on and off the car than the Witter i had last time