Squirrel is right
If you can work out the speed you can travel, you will be able to join a group that suits your pace.

If you can't get a cycling comp to pop on your bike, simply record the time travelled, and travel over a distance you have perhaps measure in a car or that you know the distance for.

When you get home do this equation...

DISTANCE divided by TIME multiplied by 60 = SPEED

for example...
A little 10km course I did over the weekend would look like this...

10km / 22.02minutes x 60 =29.97 km per hour