I share a bike with my brother. I know it sounds weird, but it works out well. We are in different classes and, if we ask nicely, our local promoter will make sure that we are separated by at least one moto. The problem is that I weigh 15 pounds more than my younger brother and we can’t run the same race sag—and we don’t always have time to change it back and forth between motos. What can we do?
In the real world, when a racer is nice enough to let a friend ride his bike in a different class, it almost always comes with the caveat that, “You can’t change the sag, you have to race with my settings.” In most cases the borrower is so glad to be able to race, that he doesn’t care where the sag is set. However, since your brother and you share one bike it would be unrealistic for one of you to take a beating every week because you are heavy and he is light. The best solution is to forget about race sag (measured with the rider on the bike) and focus on the free sag (measured without the rider on the bike). If you can find a shock preload setting that keeps the free sag between 30mm and 40mm for both of you, there is a good chance of getting the suspension to work within reason. Yes, one of you might be at 30mm and the other at 40mm, but at least you have the correct shock spring.