How to guide to replacing a saddle or seat post

[MTBMaven]

The fit of my road bike is very important for me. Being off by 5mm - 10mm can be the difference between finishing a century and not. For me my saddle height and saddle fore and aft positions are vital. Due to my sensitivities, I have to get a professional fitting when I get a new bike. When/if I need a new saddle or post, or otherwise need to move my saddle or post, I need a methodology to make sure everything gets put back in the correct location so I don't waste $200. The following is my technique for ensuring things work when I am done.

Tools Needed:
Tape measure - preferably with metric measurements
Allen keys
String
Weight with hole
Grease / Lithium Lube (unless using carbon parts)
Tape

Step 1 - Measure Saddle Height:
Measure from middle of bottom bracket to top of saddle rail where it meets the post clamp.

Most guides will have you measure from the top of the saddle. Unless you have a level, I find it hard know exactly where the top of the saddle is located.

I use the gap on my Ultegra crank to find the middle of the BB.

Step 2 - Measure Saddle Fore and Aft:
Use string to measure where the tip of the saddle is located above the top tube.

Attach weight to string with a knot. Hang string in front of the tip of the saddle so that it hangs freely. Use tape to mark where string intersects the top tube. Make sure the string is not swinging and is hanging freely.

Step 3 - Replace/Install Saddle and/or Post:
Replace/install saddle and/or post. Apply a light amount of grease or lithium lube if using metal parts, DO NOT use grease or lube if using carbon parts. Use saddle height and fore and aft measurements to make sure everything is installed in the proper position.

[handlebarstar]

5mm? seriuosly...

Saddle height and position is important but 5mm isn't going to affect anything. Ever.

[MTBMaven]

Originally Posted by handlebarstar

5mm? seriuosly...

Saddle height and position is important but 5mm isn't going to affect anything. Ever.

My previous road bike had a saddle height of 75.5CM. After the first fitting on my new bike my saddle was at 76.2CM. After that fitting I did a 100 mile and 140 mile ride and experienced pain in the lower front knee on my legs. I went back and got refitted. He realized the saddle was a bit to high moved the saddle down to 75.4CM. This obviously required the saddle fore and aft to be adjusted as well. I have since had no problems.

On my previous bike he moved my saddle height a tad but moved my saddle fore or aft a few millimeters and solved all my problems. Before the fitting I would get debilitating over use pain in my upper Achilles around 70 miles of 5 plus hours on the bike. Once things were resolved I was able to finish 200 miles of riding without any pain.

So in my experience being off my 5mm-10mm with road cycling can cause pretty significant pain after cycling in the same position for 5 plus hours. When mountain biking you are moving around on the bike a lot, standing, stopping, etc. On a road bike you are pretty much in the same position hour after hour with minimal stops. My injuries were basically over use strains.

[dstepper]

Not a roadie, put some days all things being equal my legs feel heavy and my back cramps up on a same ride the day before was not a problem. I wish that my body was consistent that a few mm would make a difference.

Mr. Freak you got a few days on me, is it because I am old?

Dean

[2wheel_lee]

Very good information!

I don't put on nearly as many road miles as many others here, but as the OP said, 5 mm can be the difference between finishing a century in OK condition or in pain (a century is just a warm up for Pain Freak, so after a century, he is just ready to ride). Understandably, it's hard to understand until you start doing longer rides. A 50 mile road ride is easy for even a beginner. However, at 75 miles, you're starting to feel anything that may be uncomfortable. At 100, anything that's not "just right" is usually painfully obvious. Additionally, some people are very tuned in to how their body fits the bike, and so subtle changes are very noticeable. These kind of things are far more noticeable on a road bike than it is on a mountain bike (for me, anyway).

Using the tip of the seat as a reference does have some shortcomings - perhaps pun intended. Although it's a good starting point, where you actually sit on a seat relative to the tip may vary slighlty from seat to seat. But, you have to start somewhere, so starting at the tip of the seat is as good as you can really get.

The next step after installing the seat as described by the OP is to use the string and plumb bob to identify where your knee bone is relative to the pedal axle. Ideally, you'd measure it before you remove the old seat, then you'd set your new seat with the fore/aft adjustment so that the plumb bob lines up in the same spot. That will more accurately determine the seat's fore/aft positioning.

Then I fine tune the angle of the seat to where it's comfortable. And since changing the angle of the seat can affect where you sit on it, I'll again check the fore/aft positioning with the plumb bob just to make sure I didn't change my position on the seat. If I did, then I'll make adjustments as needed. Although I may make it sound fairly time consuming, I can usually set up my seat in less than 10 minutes.

[davidB]

Lee, not too long ago you told me how to/where to put the seat in relation to the cranks and stuff. It was pretty easy from what I remember, but now I forgot it. I noticed that today while racing, first my seat was too low, then it kept feeling like i was sitting too far forward on it.

[2wheel_lee]

Bike fitters often have different fitment philosophies, and despite what they say, it isn't entirely science. You'll note that the final statement after every fitment is to ride the bike, and make adjustments from there.

So having said that, the answer to your question is that I usually set the fore/aft positioning so that the bone that protrudes just below your knee cap is directly above the pedal axle when it is at 3:00 (straight forward). Some fitters will say that the knee cap should be 10 mm in front of the axle, which I think is almost the same, but I think the knee bone method is easier to measure. It is something you can do by yourself, but it is a bit tricky. If you can, sit on the bike in normal riding position, and have an assistant use the plumb bob.

On average, I'd say that, on average, most people have their seat too far rearward. Rarely do I see people with their seat too far forward. Although that comment is nearly meaningless, it can be interesting to notice that of other riders.

Seat height is a bit more difficult. There are many theories and calculation methods for determining this, but most of them still conclude with the knee having somewhere between a 25 and 35 degree bend. However 35 degrees is quite a bend. For aggressive XC type riding, I tend to run my xc bike in the low 30s, but my road bike is in the high 20s. Really, I think this is personal preference.

Remember, though, when you change your seat height, you change the seat's fore/aft positioning. So if you raised your seat, you effectively moved it rearward.

A quick and dirty method that some roadies use is to ride with your heel on the pedal, making sure that it's flat. If you're not familiar with how your body feels when your hips are rocking (from a seat that is too high), it can be helpful to have someone ride behind you to watch.

[HUGH]

Originally Posted by handlebarstar

5mm? seriuosly...

Saddle height and position is important but 5mm isn't going to affect anything. Ever.

5mm is HUGE!! Seriuosly....

HUGH

[MTBMaven]

Lee, You present several VERY good points. I will have to revise my OP accordingly. It must be noted that in my case I was just replacing the seatpost; therefore, the length of the saddle did not change. If I was changing the saddle or saddle and post then another methodology should have been employed.