After doing some training rides on courses without bigger ups and downs where I didn't make significant elevation gains, a recent ride was in more rough terrain. Of course, the relief changes the average speed one can achieve and I was wondering, if there are some rules of thumb to estimate the influence of the relief.

From hiking I know there is [Naismith's rule](https://en.wikipedia.org/wiki/Naismith%27s_rule) which allows to calculate the time needed for a certain route based on distance and elevation. I am aware of the fact that with cycling the rule would be less general and require more calibration depending on

* mountain vs. road bike
* different surfaces
* greater difference between uphill and downhill speeds.

On outdoors.SX.com also someone presented a [slightly different approach](https://outdoors.stackexchange.com/a/5595/2410) that translates different parameters (elevation gain, trail conditions etc.) into distance travelled, which could be another useful approach here.

So my question is, is there some rule of thumb or a set of rules of thumb for cycling as well?