Depending on the grease you use, it will just simply be a matter of how often you have to grease them. If the manual does not call out a specific grease, then you should be okay staying with the same NLGI consistency rating. For example, if it just states No. 2 grease, theoretically any No. 2 grease should work, albeit there are some No. 2s that are better than others. I personally use Mobilgrease XHP 222 on anything with a zerk fitting. Fortunately my spindles are maintenance free, but if they weren't, I would use this as well. Besides, if you are looking at this like synthetic motor oil where you can distance the time between lubrication, you will likely find no good answer to your problem as other factors such as moisture, dirt and operating temperatures will change your lubrication frequency no matter how much you put in there.