Hi John
I have used Witter Towbar racks on several cars including the present one, Kia Sorento, and the previous one, Vauxhall Monterey, towing caravan and solo, for about 10 years. The racks have been fitted to Witter fixed towbars. The Vaux needed the bent type of Witter because of the rear-mounted spare wheel. Both these cars have a high towbar load capacity, sufficient for both the caravan noseweight and bike and rack weight combined. I have carried up to 4 adult size bikes on these racks, when the kids were younger and accompanied us, but now down to just mine and my wifes
I have used these racks all over Continental Europe and the UK without any problems, apart from once buckling a bike wheel (see below. Before I had these 4x4s I used a roof bar mounted rack but these are very difficult to use on such high cars and a big "lift" and not very accessible for bike loading/removal even on lower height cars.
I pad the "arms" of my racks with pipe insulation and attach the bikes with hooked elastic cords and bendy, foam covered, metal "cords" (from Aldi!) The latest Witter racks have improved "arms" for securing the bikes compared to my older type.
Advantages
(1) Easy access and loading of bikes, including quick removal to use bikes when arriving on site.
(2) Clearance height of the car is not raised.
(3) Probably less wind resistance than roof bike racks.
(4) Cycle rack socket is permanently fixed to car and rest of the rack can be quickly fitted/removed as required.
(5) Rack socket, which is bolted behind towball, has strong loop which can be used for securing bikes securely - I use D Locks.
(6) Less likely for bikes to damage car paintwork than roof or rear-hatch type racks.
Disadvantages
(1) Restricted turning circle as bikes can strike front of caravan or jockey wheel handle on very tight turns - this only applies to maneouvring onto site. If this is likely to be a problem I get my wife to watch and/or remove bikes before tight turns. I learnt this the hard way when I once forgot and buckled a bike wheel on the jockey wheel handle whilst reversing onto a tight pitch.
(2) Car's rear number plate and lights are obstructed by the bikes when solo and a lighting bar is necessary, also a striped warning square in Italy and some other Continental countries. I fit these even when towing and then just connect up the lights if I use the car solo with the bikes still on.
(3) Portugal does not allow the carrying of bikes on the back of the car.
(4) Rear car door is obstructed by rack and bikes. This is less of a problem on the Sorento as the rear window opens independently of the door and clears the rack and bikes when fitted.
(5) Bikes may overhang the car width, but not by much on 4x4s.
(6) Possible clearance problems on some types of hitch/stabiliser. I use a standard Alko hitch, none-stabliser type, with a Straightliner stabiliser.
(7) Longer towbar bolts are necessary to accomodate thickness of bike rack socket but these are widely available from car accessory shops.
(7) When the bikes are fitted it can obstruct hitching/unhitching the caravan. I hitch the 'van BEFORE loading the bikes and remove before unhitching and this is not a problem. (I did once have a problem when car broke down whilst towing on an Italian motorway and I had to remove the bikes before I could unhitch the 'van to be towed being the breakdown truck)
I hope this helps. Please post again if you have any further questions.
Regards
Tim