Technical Q&A with Lennard Zinn – My, my, time for Pi

By Lennard Zinn

Dear Lennard,
I am considering purchasing a compact chainring with my next bike.I am confused. Some literature suggests that the 50/34 tooth compact chainringwith a 11-23 cassette has a more expanded range than the conventional 53/39chainring with a 12-25 cassette. Is there a formula for determining the”high” and “low” range of gearing?
RobDear Rob,
There sure is!
Gear = (number of chainring teeth) X (tire diameter) & divide; (number of cog teeth)If you want the gear in inches, put in the tire diameter in inches.
To find out how far you get with each pedal stroke (gear rollout), multiply the gear by Pi (3.14159).To measure the diameter of your tire:Mark the spot on the rear rim that is at the bottom, and mark the floor adjacent to that spot.Roll forward one wheel revolution, and mark the floor again where the mark on the rim is again at the bottom. Measure the distance between the marks on the floor; this is the tire circumference at pressure with your weight on it.Divide this number by Pi — 3.14159 — to get the diameter.
Of course, you can always just look it up in a gear chart
Lennard

Dear George,
Without knowing where your tendonitis is located and just what kind of biomechanical alignment you have, I can’t give very specific advice but I can tell you that the wedges can be very useful if they are put in correctly. For most people (approx. 90 percent) the wedge would go in with the thick part toward the inside of the foot or toward the crank arm, asmost feet (again 90 percent) are designed so that the big toe/ball of footare aligned slightly higher from the ground than the little toe. This isvery useful in walking and running gait but a wasted movement and potentialinjury cause for many cyclists. The Specialized Body Geometry shoe is actuallydesigned with 1.5mm of medial sole build up called forefoot varus. Thedesign eliminates guesswork on where and how to put in the wedges.I suggest you try one wedge on the effected side, installed as I describedabove, putting the cleat back where is was and riding your trainer andsee how it feels. As the wedge is not made of aspirin, it doesn’t makethe tendonitis go away, only realigns the knee and foot, and if your injuryis because of that particular mal-alignment, then it should get betterover a short bit of time. If this fails, I would suggest you visit a doctor,physical therapist, athletic trainer, chiropractor or other medical professionalto help you with your injury.
Andrew Pruitt, Ed.D
Founder/Boulder Center for Sports Medicine

My groovy new seatpost
Dear Lennard,
I’m building a new Klein road bike for the upcoming season and havea question regarding a Specialized Pave seatpost I’ve purchased. The Kleintakes a 31.6mm seatpost. The Specialized is only available in 27.2mm. Ipurchased a shim reducer to allow the seatpost to fit in the frameset.How should I align the “grooves” from the frame and shim and collar? CurrentlyI’ve aligned the shim with the frameset cut and have the collar at 180degrees to the seat lug. No grease has been used per instructions and I’veonly tightened the collar clamp bolt enough to hold the post. I’ve yetto buy a torque wrench to properly tighten the bolt. Any help would begreat.
Peter

Dear Peter,
I would flip that shim slot to 180 degrees from the frame slot, too.You might want to put some grease between the shim and the frame, so itdoes not get frozen, but none between the post and the shim, as you havedone.

Choke up on the hex key, tighten the bolt as much as you can when holdingthe hex key close to the bend. Mark the post to make sure it is not slippingdown.
Lennard

How strong is my carbon fork?
Dear Lennard,
I am about to purchase a Fuji touring bicycle. My only concern is thecarbon fork, the rest of the bicycle looks like a wonderful package. WhileI am not a hard rider, and my present touring bike- Fuji America has beengreat for about 18+ years, I feel it is about time to upgrade. I am justworried about a carbon fork and the strength of a carbon fiber fork forfully loaded tours.
Thanks
Robert

Dear Robert,
It obviously depends on the particular fork and its construction, but,in general, the industry has found that carbon forks hold up better thanmetal ones, rather than the inverse.
Lennard

Staying warm
Last week’s posting on how to keep the private parts warm on cold ridestouched off a flood of mail. There are a lot of men interested in thissubject! I could by no means post all of them, but these four pretty muchcover the spectrum of the suggestions I received. Thanks to all of youfor your letters!
Lennard

Dear Lennard,
I just read a letter from Jay about the windproof shorts. I took apiece of Gore-Tex material from an old jacket I had torn in a previouscrash, I cut it out in an anatomical shape to fit the “sensitive” areain the front of my shorts. Even with my terrible hand sewing skills, itstayed in place pretty well. Here is a photo of the shorts with the “sewn-in”wind-blocking piece.

The test conditions: a balmy 32 degrees and slight breeze in centralNJ, perfect. I would usually wear tights in this weather, but, for thesake of the test, I wore just leg warmers and my new homemade windproofcrotch shorts.

I took the fixed gear out for 1.5 hours and it worked a treat. I hadno discomfort or chafing from the material and it kept the wind off quitewell. I also had no breathability issues with the material being there,it’s cold anyway and I never felt it was a hindrance. I could feel thecold more on my upper thighs and hips than on the front of my shorts. WhenI got home, I immediately tested the area, I could feel that the skin temperatureon my thighs was colder than in my crotch. I also had more redness wherethe Gore-Tex material was not placed. No doubt my “sensitive area” wascold but not like it is in regular shorts where you feel numbness and slightstinging sensations during these temperatures.

It was definitely cold all over but the material definitely worked,I don’t think I could have ridden for 1.5 hours without it and not havefelt some discomfort down there. So if you ask me, there is a market forthis type of short.
Brendan

Dear Lennard,
For the guy asking about shorts with a Windstopper front panel, thereis a much simpler solution. Take a sock and fold it in half, then put itin a strategic place. On not so cold days you can use a cycling sock, colderdays require an upgrade to cotton socks and on the coldest days you cango wool. This method works pretty well down to some pretty cold temps.I also know guys that just carry a spare pair of gloves there on cold days!
Matt

Dear Lennard,
I have a solution for Jay’s question on keeping his jewels warm duringcool winter rides. This winter I started wearing baggy mountain bike shortsover my bib shorts and leg warmers on training rides and estimate thatI have the toastiest testicles in the peloton. My favorite setup is touse the shell from a pair of Sugoi Gusto shorts, which are convenientlydesigned to detach from their liner. The lightweight shell has just enoughwind-blocking properties to keep the cold wind off, while their breathabilityand lack of bulk make them comfy and unnoticeable.
Worn with a jacket or vest, they look acceptably dapper, though I mustadmit I was recently chided by a member of the cycling fashionista on agroup ride. The fact that he was wearing a Mapei skin suit made his opinioneasy to dismiss….sort of like an elephant telling a hippo his ass isfat. Anyway, it works for me.
Don

Dear Lennard,
I’m probably not the only one to suggest this, but check out the cross-countryski clothing products. They have items that have wind-proof panels justin the front crotch area.
Marvin

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