It is critical to use a seatpost that exactly matches the inside diameter of your seat tube. A difference of even .1mm can cause the post to slip or bend. Therefore, you should contact the manufacturer of your frame to determine the required seatpost size. You can also measure your existing post with high-quality calipers, but even this technique is prone to error. Consider taking your bike to a local bike shop to be measured and fitted with an appropriate post. If you still don't see the answer to your question, please email us at customerservice@profile-design.com.