The BBR Tuning PRO SERIES Spring Idler Pully has been upgraded for better alignment and tension. With an additional idler pully wheel your engine chain tension will stay consistent while offering better alignment than your stock idler. As with all of our performance idler pullies, this idler will reduce stress on the chain and keep a consistent tension through any ride. Compatible with all 2-stroke 48cc/50cc/66cc/80cc engine kits as well as 4-stroke 50cc engine kits, the PRO SERIES idler will have you riding like a champ without a worry on your mind