|New Bike Set-Up||IF Guy|
Sep 30, 2002 8:28 AM
|I recently purchased a new bike and I want to get the exact set-up that I have on my old steed. What concerns me is that there is a slight geometry difference between bikes. The old bike has a 74.5 seat tube angle and my new ride has a 73.5 seat angle. For the most part all the other measurements are the same like top tube length (56 cm), etc. I have been told that the most important measurement for me to duplicate is the distance between the nose of the saddle is as compared to the center of the bottom bracket. Because the seat angle is 1 degree less on the new bike that'll probably mean I'll have to slide my saddle forward a bit to get the same measurement. Will that effectively shorten my top tube? What other measurements are important for me to replicate. Will I be able to use the same tilt on my saddle or will the different seat angle force me to change that? Thanks for the help. I can't wait to go ride.|
|re: New Bike Set-Up||Spoke Wrench|
Sep 30, 2002 10:23 AM
|1. To replicate the relationship between the saddle and the bottom bracket, you will have to slide your seat forward a bit. Have a helper hold a plumb bob from the nose of your seat and measure its distance to the BB spindle.
2. I have a little level for adjusting seat tilt, but I usually just eyeball it. Most seats aren't flat across the top and what's level depends on where you set the level.
3. Picking out the right stem is a calculated guess. Since the seat is forward and the top tube is the same, you may want a slightly longer (10-15mm) stem. The angle and design of the stem will affect the height of your handlebars.
|re: New Bike Set-Up||tao|
Sep 30, 2002 11:28 AM
|1) An alternative to the plumb line is to measure along the seat tube from the center of the bottom bracket to the top of the saddle. Say your height is 75cm, you'll need to move the seat forward 1.3cm.
sin(1) * 75 = 1.3
2) The one degree difference in saddle tilt should be pretty easy to obtain, I use a longer level (cheap at hardware store) so that I can set it along the back and tip of the saddle with overhang at each end. So even after the saddle's broken in you'll still get the same measurement and you don't have to worry about level placement.
3) A stem 1.5cm longer would be just about perfect considering the bars would be about .25cm higher (at -10), you'd retain the same knee position and reach, albeit at a slightly different angle. You could also go 1cm longer but then I'd recommend lowering the stem about .50 - .75cm to obtain the same reach, assuming of course you're not at your flexibility limit already. Fine tune with hood placement.
|effective top tube length...||C-40|
Sep 30, 2002 2:28 PM
|The one degree change in seat tube angle will require the saddle to be moved forward by about 1.2cm (1/2 inch).
This movement will shorten you effective top tube length by the same amount. Since the top tube length is the same, a stem that's 1-1.5cm longer will be required.
Also keep in mind that measurements to the tip of the saddle are only valid with the same model of saddle. If you change to a different model, even with the same length, differences in the width of the saddle may place your butt in a different place. Maintaining the same KOP position is what's important.
The seatpost has a wide range of angle adjustment. If you swap the post and saddle from the old bike to the new one, it's obviously got to be tilted down one degree to compensate for the change in STA.
Oct 4, 2002 12:20 PM
|Don't be so exact. Get it close and go for several easy rides. Bring allen wrenches along and tinker with it. Find a comfortable position over a few rides and then check the old bike. See how close you are. Ask other riders how you look on the bike.
Your position on the bike shouldn't be locked in. It evolves over the years. I remember a quote by Bob Roll who said he finally got his position dialed in a few years after he retired from racing.
When in doubt, use a longer stem and mount the brake hoods higher on the bars. Your reach to the hoods will be comfortable. When you get in the drops you will naturally reach more and your back should flatten and posture and aerodynamics improve. I lowered my saddle the other day because it's cold and we're into tights now. ramble ramble.