How far back..

[Markymark]

When cycling through the park (around 1.5 miles) and on relatively quiet tarmac park road doing c20mph, how close is acceptable to ride behind someone - is around 2-3 bike lengths ok?

 

[akb]

However close you and they feel comfortable. For example, I dont like being drafted, freaks me right out. So I would ask you to overtake or back off.
If I was the follower on the Hybrid commuter with V-Brakes, I would leave a much larger gap then I would on the MTB with Hydraulic disc brakes. I have much more confidence in the Disc brakes!

 

[billy1561]

If you're doing 20mph then you should consider the road instead of the park. It would be ok for a 3 inch gap with your ride buddies otherwise give it a good few bike lengths.

 

[Ozzrahog]

When cycling through the park (around 1.5 miles) and on relatively quiet tarmac park road doing c20mph, how close is acceptable to ride behind someone - is around 2-3 bike lengths ok?

Depends on the view

 

[Markymark]

If you're doing 20mph then you should consider the road instead of the park. It would be ok for a 3 inch gap with your ride buddies otherwise give it a good few bike lengths.

Its victoria park (east London) and the road in it is a proper road wide enough for two cars to easily pass.