in 2008 I started my tour from Hvolsvollur heading north on the F210. Then we did continue heading north through Reykjadalir coming out on the F225 in Kringla, more or less.
This piece is very nice and with not so many cars. In Reykjadalir the road goes up, some parts are very very steep. For the worst pieces we had to push one bike in 2!!! then go down and do the same for the other bike. We were riding a MTB and used a BOB trailer. At that moment we were fully loaded with food for one week, so overall no less than 30 Kg of food and equipment. Water is not a problem, you can get it in the Eystri Ranga and later on the Markarfljot (you have to ford it but when the river is still little
) and in an other couple of places. Halfway on the road in Reykjadalir you get to the crossroad that goes to Hrafntinnusker. Landscapes in Reykjadalir are extraordinary! If the weather is good the view from the top (Pokaryggur?) is incredible. Then you go directly down to Kringla and the F225 junction here the road goes directly down, check your brakes before to start the descent! I would not recommend doing this part in the contrary direction! 
Overall I really liked that part, not so many people and beautifull landscapes.
If you need more info just ask.
If the pictures from Torsten are not enought try mine:
http://sites.google.com/site/icelandinbw/home
Ale
but you are right i never would do that with a BOB