I test rode a Specialized saddle in a 143 and it worked great, so I would guess you'd need the 140 in the Bontrager as well. I don't know how much padding a Jett has, but the InForm RL doesn't have much. The photo is deceiving as it looks all puffy in the back, but it's not at all. It's more padding than a Brooks, but less than a Terry Butterfly. Does that help?