Every sport is going to have a different range. In part, because your fitness is not the same and in part, because they are - well - different.

Figure once you have been biking a while, expect your zones to be about 10 lower than the running zones.

Now, if you cannot get UP to the zones then that usually means you are not strong enough (muscle wise) but your cardio is great. This would make total sense if you are a long time runner (so cardio covered) but new biker. So work on strength training on the bike. Hill drills, for example. Basically, go up the hill, fast as you can. Repeat



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You don't need to be so scientific about it, from what I can infer, maybe you lack the leg strength to ride the bike hard enough on the flats, no worries just shift into a lighter gear and spin up the pedals faster, count them for 30 seconds and try to get 90-110 per minute and see what that does to your heartrate. Riding hill repeats like Ron mentioned or pushing a harder gear into the wind are both good ways to build some strength. Look at pictures of world class cyclists and runners and you will note a difference in leg structure from the demans of their respective sports. Riding a bike a couple days a week will not harm your running, in fact stronger legs are good for all.