Signal8 wrote:
I would suggest that even the seat height from your road bike will not necessarily translate over perfectly to your PR5 for two reasons:
1. Your 52 cm PR5 and your wife's 48 cm bike both have 165 mm crank lengths. Unless your road bikes both had 165 mm cranks (which is very unlikely), you are going to need to adjust the seat height on the PR5s. If the road bikes have cranks longer than 165 mm, you may be better off measuring the road bike's seat height from the center of the pedal spindle (while in the 6 o'clock position) up to the top of the seat; and then transferring that measurement to the PR5. By doing this, you allow for the variance in crank length between the road bike and PR5.
2. The ISM saddle that came on your PR5 is very different than what you probably have on your road bike. If you position the ISM the way it was designed to be ridden (with saddle rails level), then you'll notice there is a fairly significant downward slope from the back to the front of the saddle's top surface. If you measure to the highest point (at the rear), you get a much different number than if you measure to some point closer to the front of the saddle. It's kind of a crapshoot when it comes to choosing which specific point on the saddle top that you measure from. I prefer to measure to the saddle rails when transferring my seat height from one bike to the next...as long as I am using an ISM on both bikes.
In summary...unless the crank length and saddle style are the same between two bikes, saddle height (when measured from BB center to saddle top) may not translate perfectly. You can get the seat height pretty close doing it that way, but don't hesitate to adjust things up/down a bit get it better.
I can't claim to be an expert in any of this stuff. It's just that I took delivery of my 52 cm PR5 two weeks ago. So, I've spent quite a bit of time lately doing exactly what you are doing now. So far, I've swapped to longer stem, which involved re-cabling all but the front brake, and re-routing the shift cables so they exit out the back of the extensions instead of the middle. I've cut the excess steerer tube above the stem, which was unusual because it had a star nut and an aluminum sleeve inside the carbon steerer tube instead of a conventional expander plug.
If you run into any other issues and don't have anyone else to ask, don't hesitate to reach out.
Thanks for the insights, that helps a lot. I measured from the bottom bracket; my road bike had 170mm cranks, my wife's was 165mm (the same as the PRfive).
- John
"Have courage, and be kind."