I am a runner past 34 years. I have cycled in the past but never serious. Well 3 years ago I got much more serious about cycling and cut back about 20% on running when in summer and cycling weather is good. I could with no training on a bike ride 30 miles no problem. The card was already their but average speed riding went up fast as I rode more. My running did not get faster but I could go longer without running any more and even less.

Honestly I ride because in love it no thought about cross training. I ride about 100 miles a week at least in season and run about 35. In the winter I run 45 and ride as weather allows. At this point if all I did was cycle I could ride faster and longer with more power. I I gave up cycling I could run a little faster but no much. I could lose endurance if I did run at least a longish 12-16 mile run every 2 weeks. Cycling allows legs a pounding break. I can run a fast 5 mile run then jump on the bike and ride 30-60 miles and get the benefits.

Finally riding the bike has just been a blast I wonder if I actually better on the bike than a runner. I have no way to know since at a 50 my running times have gotten slower. I was never fast but in my prime running years I ran 3 sub 3:10 marathons 3:06 the best. I ride solo but seem to ride ok. I don't race but my solo centuries I think I have done ok. I have rested or peak for a century like I would in a marrhon race. It would be cool to try this sometime with a group. I usually can do century in 5:30 hrs and have gone 5:15.