If you currently have a stock front wheel size (less than 21" in diameter), and you plan to go with a 21" or 23" front wheel in the future. You will need to purchase the AXEO21 or AXEO23 depending on the wheel size you intend to run. If you purchase an AXEO21 or AXEO23 and are still running your stock front wheel, you will need to still install the AXEO21 or AXEO23 kit WITH the travel limiters.
The AXEO21 or AXEO23 kits are a shorter cartridge than the stock length. By installing either of these kits without the travel limiters, your overall fork tube length would be 1" to 1.25" shorter than stock. This shorter length would result in the front fender contacting the lower triple tree or fairing when the suspension is compressed, and the bike sitting excessively low in the front. The travel limiters in these kits, add the necessary length back to the overall cartridge length to match the stock fork tube length, while at the same time limiting travel to accommodate a larger diameter front wheel.