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Technical FAQ: More on stack and reach

  • By Lennard Zinn
  • Published May. 8, 2012
  • Updated May. 9, 2012 at 12:46 PM EDT

Editor’s Note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

Dear Lennard,
I am curious about frame design and as you are a frame builder, I’m sure you can educate me. I have a “classic” Italian road bike, a Basso that I purchased in 1990. I purchased a new bike in 2004, a “made to measure” Merlin Cyrene. Both bike shops fitted the bikes to me at the time, and when I got the Merlin, the shop owner said he would make a few changes to “modernize” the new bike from 1990’s geometry. I have noticed all the changes are in the front end of the bike. The Basso has the traditional, threaded fork/headset of the era, with a lot of rake, the Merlin is threadless with a Look HSC straight(ish) fork.

I used your article as a reference to compare the two bikes (and to see if they are set up the same) and here are the numbers:
Basso: frame reach – 14.5” frame stack – 22.0” handlebar reach – 17.5” handlebar stack – 25.0”
Merlin: frame reach – 14.0” frame stack – 23.0” handlebar reach – 18.0” handlebar stack – 25.5”

The measurements of the rear of the bikes are the same, from the rear wheel to the center of the cranks, from the floor to the center of the cranks, and the seat height of both bikes is the same.

I hope you can clear things up for me as I am unclear why the above measurements are what they are.
James

Dear James,
The increase in frame stack I can explain as a function of going from a threaded to threadless system. You need more frame stack with a threadless headset to get the same handlebar height, since you do not have the quill of the stem sticking above the (threaded) headset anymore.

With the other things I’m guessing as to your shop owner’s motivations.

In order to decrease frame reach, he either decreased the seat angle, decreased the top tube length, or a combination of both. I don’t know why he would have done either.

The handlebar stack and reach are functions of frame stack and reach as well as headset spacer stack, stem angle, and stem length. That’s too many variables to guess what’s going on, and I have no idea why he would have wanted to raise you up and shorten you up on the bike. Maybe he thought you were getting older and stiffer and need to sit up more…
― Lennard

Dear Lennard,
Saddle height, and saddle setback behind the BB are two very important measurements to me. Saddle height is pretty easy to set, but to get setback the same on all of my bikes I put the front wheel against a wall and measure the distance to the center of the BB, then the back of the saddle, and subtract. The difference should be the same even though the actual measurements are usually different (i.e.: 131.5-99=32.5 and 124.5-92=32.5). I have used the Selle Italia Flite since the early ’90s, so the saddle is the same (this wouldn’t work as well on bikes with different saddles).
Justin

Dear Justin,
Judging by a lot of the mail I got about this, not everyone understood how to use the stack and reach procedure I described to find the saddle fore-aft position. I said, “You can use the same procedure to find the X-Y position of the saddle relative to the bottom bracket (pick a reference point on the saddle to measure to, like the tip of the nose).” I guess I needed to go into more detail.

You describe a perfectly sound way of doing exactly what I said, namely measuring the “reach” to a chosen point on the saddle. In this case, you set the front wheel against a wall rather than the rear wheel and make the “reach” measurement the same from the center of the bottom bracket to the rear of the saddle on both bikes, thus ensuring the same saddle setback.

Going a little deeper into the nuts and bolts of exactly what I do to speed up and simplify this process, rather than using a wall, I actually bungee-cord the rear tire into the vertical channel the rollers in my garage door ride in. Then the bike is held vertically fixed. I line up the front wheel with the plane of the frame and secure the handlebar from turning with a handlebar holder attached to the seatpost. Then I use a carpenter’s level to ensure that the bike is standing up straight.

I measure reach measurements from the inner back surface of the garage-door guide channel (the same surface the rear tire is sitting against). (To review, “reach” to any given point on the bike is the horizontal measurement from my garage-door channel to that point, less the horizontal measurement from the channel to the center of the bottom bracket.) I measure stack measurements up from the floor. (Likewise, “stack” to any given point on the bike is the vertical measurement from the floor to that point, less the vertical measurement from the floor to the center of the bottom bracket.)

To minimize the eyeballing required to avoid parallax problems of estimating the measurement when sighting down at the saddle and the tape measure, I usually remove the spare-tire bag from under the saddle and slide the tape measure under the saddle (above the seatpost clamp) to the garage-door channel (again, I have the rear wheel against the back of the channel). The sharper lower edge of the nose of the saddle sits right on the tape measure, which makes it very easy to view exactly which millimeter line it reaches. (This is a big improvement over having the tape above the saddle; if you’re sighting down on the saddle nose and the tape measure is above the saddle, the measurement can be off by a number of millimeters, if your eye is not exactly vertical above the tip of the saddle.) Measuring to the tail of the saddle is usually easy to do, but it is not completely straightforward on a split saddle. If you have different saddles on the two bikes, you may choose to measure to the point at which one sit bone contacts each saddle. Or you may average the distance from the wall (or channel) to the nose and from the wall to the tail.

To get an exact measurement from the wall (or channel) to the center of the bottom bracket, I do it on the left side and rotate the crank until two corners of the hex-shaped wrench hole in the crank bolt are directly above each other (so you get the same measurement to the top corner as to the bottom corner). That ensures that you have found the center of the bottom bracket, but it doesn’t work with Shimano Hollowgram cranks, as there is no axial crank bolt. You’ll have to estimate with those, but it’s still better to do it on the left side, since the drive-side crank face is often completely smooth over the end of the bottom bracket spindle. To get an exact bottom-bracket height (vertical measurement from the floor to the center of the bottom bracket), I also do it on the left side and rotate the crank until two corners of the hex-shaped wrench hole in the crank bolt are lined up horizontally (so you get the same measurement to the right corner as to the left corner of the bolt’s hex hole).
― Lennard

Dear Lennard,
I recently read your article on the VeloNews website regarding matching the setup of one bike to another. Your article makes sense, but leaves out the position of the saddle. I’m not sure you want to hear from yet another reader who is putting his two cents in on the topic, so I will apologize ahead of time if you don’t, but here is the system I have used for years.

Here is my routine for matching the set-up of a new bike to my existing bikes. It first matches the height and set back of the saddle relative to the bottom bracket then matches the reach and drop from the saddle to the handlebar. After propping my bike up against the wall as you describe I utilize a tape measure, a plumb bob, a spirit level and an adjustable t-square as follows:

1)  From past experience I know that the nose of my saddle is 7cm behind the center of the bottom bracket and the seat height is 72cm from the center of the BB to the nose of the saddle. I use a piece of electrical tape to make a mark on the non-drive side chain stay 7cm back. Using a plumb bob and tape measure I can then duplicate the position of the saddle relative to the bottom bracket, both in terms of saddle height and setback. The first photo shows the red marking tape and plumb bob set up on my faithful old Look 481.

2)  Now that I have adjusted my saddle so that it is in the proper position relative to the bottom bracket, I next measure the distance from the tip of the saddle to the center of the handlebars. I choose a stem with a length that will set the reach from the tip of the saddle to the center of the handlebar at the appropriate distance. In my case the distance is 58cm.

3)  Finally, I set the “drop” from the tip of the saddle to the height of the bars using an adjustable t-square and a spirit level. I know that my bars belong 9.5cm below the tip of the saddle. I adjust the t-square to 9.5cm and place it on top of the bars with one end of the level on the t-square and the other end on the tip of the saddle. I add or remove spacers on the steerer tube to raise and lower the stem and handlebars. When the level is “level” the bars are at the correct height.

When I am actually setting up a new bike I stand both bikes next to each other and go back-and-forth between them fine tuning the fit of the new bike to exactly match the old one. This system totally bypasses the top tube length, the bottom bracket height, the seat tube angle, the type of clamping system on the seat post, the stem angle and everything else. It starts with the one non-adjustable piece of the puzzle, the bottom bracket, and allows me to replicate the position of all three places where the rider touches the bike (pedals, seat and bars) relative to that fixed point.
Joe

Dear Joe,
Actually, I did mention the saddle position (see above answer).

Yours is a very good method, and I used to use this exact method for years. I even did it alongside my workbench, which looks a lot like the one in your photos. I had a long bike hook screwed into one of the drawers; I would slide the drawer out and rubber-band the hook to the seatpost to hold the bike securely for taking the measurements. And I would use a handlebar holder  attached between the seatpost and handlebar to keep the front wheel lined up with the bike.

I stopped using it because I got tired of leaning the bike over to get the plumb bob to hang freely alongside the chainstay, and then waiting for it to stop swinging. I would tape the plumb bob string to the nose of the saddle, but still, to hold the bike steady enough while leaning to get the exact plumb bob measurement I found tiresome.

It is hard to beat the carpenter’s level measurement down to the bar for speed, but it doesn’t work if the bar diameters are different on the two bikes. For instance, I just set up two identical cyclocross bikes, but one had a Deda 35 (35mm diameter) handlebar, and the other had a 31.8mm diameter handlebar, and all of the measurements originally came from a bike with a 26.0mm handlebar diameter. Rather than getting the tops of the bars the same, I wanted the center of the bar the same on each bike relative to the bottom bracket and saddle. This is much more easily done measuring up from the floor to where the tape measure is tangent to the bar, which shows you exactly the center of the bar.

I also find it much easier to record the dimensions of the bike in stack and reach than describing various measurements from one component to another. In other words, if I know the stack and reach of the center of the handlebar and the stack and reach of either the tail or the nose of the saddle, along with the angle of the saddle in degrees, then I can set up another bike just like it from just those five numbers. This is key for somebody traveling and renting a bike for their European riding adventure!
― Lennard

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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