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Technical FAQ: Big bikes for big people

  • By Lennard Zinn
  • Published Apr. 8, 2008
  • Updated Nov. 17, 2009 at 3:05 PM EDT

Zinn’s big bike

Photo: Lennard Zinn

Dear Lennard,
I am 6-foot-6, weigh 200 pounds and have a 36-inch inseam. I currently ride a 61cm 2003 Tourmalet steel frame and was looking to upgrade to a livelier ride with an aluminum frame. I am trying to get the most out of a stock bike that costs under $1300.

I talked to the shop about putting on an Alpha Q fork and using the longest stock cranks arms I can find, relying on 180mm Rival Compact cranks, which are only 5mm longer than the 175mm Bontrager cranks the bike comes with. Even if I could afford to the correct crank length you recommend, I would need a custom frame with raised bottom bracket.

First, the shop told me the longer and beefier steerer tube of the Alpha Q fork won’t work (or at least won’t give me any more headset height, I know there are limits to the stack height, but I found the Cane Creek Solos can be stacked to 38.8mm not much but better than the 27mm stack I have now).

Now, the shop is telling me that longer cranks would be too hard to push. Does this make sense? They are only 5mm longer and would allow me to drop my seat height and move my seat forward. Or does this sound more like a shop has no expertise or real knowledge about fitting stock frames to tall riders?
-Ben

Dear Ben,
Neither comment makes sense, but both are typical of the lack of understanding in general in the bike industry and among shop employees about the issues facing tall (and short) cyclists.

Harder to push? If you want to pull a stuck nail out of a board, which will be harder on you – pulling it with a claw hammer or with a long crowbar with a nail claw on it?

From long experience with myself and with hundreds of customers over more than a quarter century, I know that you will find those 180s to be a revelation – it was for me back when I was on national team under Eddie B.’s tutelage. Eddie wanted me to use considerably longer cranks, but I could not find any at that time. Those even longer than 180mm will benefit you yet more.

Your legs are certainly long enough to get over that pedal on the 180mm cranks – your knee and hip angles will still be less acute than the majority of cyclists out there, since those cranks as a proportion of your leg length will be lower (around 19.7 percent, vs. 22 percent and far more on short riders on 170mm cranks) and the extension and contraction of your muscles will be relatively lower as well.

I’m your height and ride 207.5mm and would not go back – they are 21.6 percent of my inseam length. And as you know, I am constantly testing and reviewing cranks of all different lengths, so I constantly am re-checking my experience on 207.5mm, 205mm and 200mm (on both road bikes and mountain bikes) vs. the 175mm and 177.5mm cranks I usually am sent with groups for review.

According to True Temper, you can cut an Alpha Q Z-Pro fork steerer to 144mm longer than your head tube (I’ve included the 14mm for the bottom headset cup: 130 + 14 = 144). I then ran your question past Bert Hull at Alpha Q:

Dear Lennard,
Spacer stack height limit on the Z-pro is 130mm from frame to top of stem. With standard stems and headsets, that works out to about 90mm of spacers, which is quite a lot. There is no magic to this number, but we need to set a limit somewhere. The issue is not so much safety as it is stiffness. The steerer is not going to break because you put extra spacers above the upper bearing. As you know, the deflection of a cantilevered beam increases exponentially with distance. Adding spacers quickly adds up to a less stiff cockpit. We set recommendations on spacer stack height so that people who use our products will enjoy the performance we design them for.

Sometimes people ignore our guidelines to customize their ride, and if they can live with the compromise of performance in order to get their position more comfortable, then for them it is a situation they can live with.

As for the question about bearings not working with tall stack heights, I don’t see why there would be a problem with going higher. Perhaps that bike shop owner could enlighten us all with his logic on that one.

I could run a special test if you like.

I can set up a 100000 cycle CEN test on a handlebar mounted on a stem above a ton of spacers and see if the bearings give out before the test is complete. I will take a week or so to run it.
Bert Hull
Product Manager, Alpha Q Components

I would do those upgrades. You won’t regret it.
Lennard

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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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