70 miles on road and 10 miles on a bit of rough road with sand covering it. So what do you set yourself up for?
Two ways- get a Rigid MTB and set the bike up with semislick tyres. These look like worn out slicks with Knobbles at the edge og the tread. This will cost you as the Bike will still have to be sensible quality but you may be lucky in getting one secondhand
The other alternative is to get a wider tyre fitted to your current road bike and possibly get a tyre with a bit of tread. Your LBS can advise on the maximum tyre width you can go to but any tyre over a 28 will be suitable. You may even be lucky enough to get a Cyclocross tyre that will fit the frame and forks and these will work on both road and sand. Whether you will with a couple of panniers is a different matter though. Riding in sand is hard.
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How long was I in the army? Five foot seven.
Spike Milligan