Sam,
Strava user is Peter . that’s Peter space dot
(at least that’s what it looks like)
If you can find some of my rides you’ll see there is a lot of climb / mile, there are some superb trails and downhills but they come with the uphills. Stroud is at the middle of five valleys (think of a star pattern) some of the tops are common land with good bombholes and flowing downhills. Have a look at Michinhampton Common, Selsley Common and Rodborough Common.
20 miles for me would be a three hour ride.
Martin’s advice is sound, he knows the local terrain well.
If you are looking for a 20 mile ish loop.
From Noah’s in Chalford Valley up Hyde Hill towards Michinhampton.
Turn Right across the common heading towards Box and Nailsworth.
Pass the Halfway Café on your left and onto the “W”.
Look on a map and you will see the W is named because if has switchbacks. At the left hand bend look for the trail off to the right.
“Aaaaaaaaaa” on Strava.
When you pop out on the road again keep hard right down “the ladder” also on Strava. This will be rocky, slippy and can be challenging, but that rather depends on your skill – that’s my perspective.
From Nailsworth find the road to Shortwood and head uphill towards Lower Lutheridge Farm (bridleway), Upper Lutheridge Farm and into Nympsfield.
From Nympsfield head NW toward Stanley Woods, if you look on an OS map there is a Gliding Club shown. Head into the woods near there and stay on the same contour level past Penn Hill, popping out on Selsley Common. Across the common however you fancy keeping the Severn plain to your left. At the NE end of the common you join the B4066.
Cross the B4066 onto Water Lane and follow this to Woodchester, it will be wet and slippy. (There is a spring half way down that was the water supply for the village).
You’ll find thi strailon my Strava feed.
Down through Woodchestr to the A46, turn right then left after Dennis Brown’s woodyard up Culver Hill, take the first left up steep tarmac hill until you see the entrance to a woods on your left.
OS map shows this as St Chloe and Hounscroft but I’ve no idea what the wood is actually called. This is a beech wood and at the moment the leaves are down, wet and hiding the plentiful supply of roots, which will be very slippy.
Keep on the same contour level following rooty single track until you come out on Bear Hill.
At Bear Hill left then almost immediately right onto small lane, OS map shows this heading North past Rooksmoor and Kingscourt.
Follow lane for about a mile until you see Rodborough Fort on the hill above you on the right.
Below the Fort double back to the right uphill off road over Rodborough Common.
Keep heading South across the common towards The Bear Hotel, cross the road towards Winstones Ice Craem Factory. (ask someone if you can’t see it).
There are two downhills from Winstones back into the Chalford Valley, the rocky one that Martin (qwerty) mentions above to the right of the factory or a smooth one to the left across the patch of common where the seats are.
Either option brings you out on a lane and then find the trail that goes over the railway line and down towards the canal into Chalford valley and back to Noahs. 19 miles in total.
Best of luck with that !
You did ask.