Nashbar Parabolic Rollers Parabolic shape of the roller drums makes it easier to stay in the center of the rollers Sealed bearings guarantee a smooth, efficient pedaling action that more closely simulates riding on the road than other rollers do Lightweight design folds up easily for storage and transport Fits wheelbases from 37" to 43"&lt;br&gt;&lt;a href="/images/nashbar/web/PDFs/BN-PR11_Nashbar_Parbolic_Rollers_Instruction_Manual.pdf" target="_blank"&gt;Click for Instruction Manual&lt;/a&gt;