Your concern is vallid. We did a partial compensation by also upgrading the batteries in front to two 6v Trojen golf cart batteries. The added weight up front helps balance the weight in the back. About perfect for 2 adult bikes. When we haul 4, we add a few extra gallons of water in the fresh water tanks which is up front on our trailer.
2013 Cruiser RV / FunFinder 189FDS
2017 Ram Bighorn 1500 EcoDiesel