It all comes down to a cheap plastic disc called an "Optical Encoder." The plastic part is unable to withstand the forces going on, sometimes causing it to crack, shatter, etc. It seems to be one of the most common issues for Logitech G25's and G27's. Before anyone disassembles their wheel, I would recommend checking their warranty information. If your warranty is still intact, make use of it. If it is not, carefully open your wheel up to inspect the issue. If indeed the Optical Encoder is cracked, you may be able to glue it back together. If it is past, you can order a new one from cmlaserservice.com, just be sure to see which encoder disc you have. This site make much stronger brass disc, which are a lot stronger than the cheap plastic ones. The only problem is that the site is from Thailand, so it may take some time to receive the part, especially if you live in North/South America.