Bike Repairs – new bottom bracket

English: WD-40
English: WD-40 (Photo credit: Wikipedia)

I used to repair and upgrade my old road bike regularly, taking it from a 12-speed to 21-speed in the process.  The only things I haven’t replaced on that old thing are the front rim and hub, brake callipers and the frame.

My newer bikes are a different prospect.  Firstly, my big old tools aren’t needed or just don’t fit.  My Cannondale Super V is weird anyway and my Trek Domane can be taken apart using only Allen keys.

The Cannondale has been clicking on the bottom of the pedal stroke for a while.  At the last service I was assured that the BB was fine, whereas the rear hub bearings were stuffed.  I wasn’t so sure.

Luckily, I only needed a new BB tool, Park Tool BBT-32 as my old crank puller would do the rest.  I also bought new Park Tool PPL-1 PolyLube from Bike Culture.

Crank bolts were removed with 8mm Allen key, then the cranks were pulled.  I used the BBT-32 on the non-drive side to remove the plastic cup.  Removing this side first releases pressure on the drive-side thread and will make removal a little easier.  The hardest part is keeping the splines of the tool engaged; clean the cups with a brush beforehand.  Even then, the tendency was for the tool to twist out.  The thread is quite stiff until the cup is all the way out.

The drive side wasn’t budging.  I sprayed WD-40 from the other side to penetrate the thread and a few minutes later the BB was free.  The threads are integrated into the body of the BB.

A few turns of the axle and the grinding was obvious.  It is not unusual to have some resistance when you turn the axle, but this was gritty and sticky and yucky.  And not a user-serviceable item, either.  While everything was off the bike I removed the chain-wheels and gave everything a good scrub in the parts washer.  The black cranks and chain-wheels polished up nice.

As luck would have it, Pushys Wheels were having a Boxing Day sale, so there was hope of getting a new BB.  I needed a 68mm (width of the frame at the bottom bracket) x 111mm (width of the axle) but had to settle for a 68 x 113.  The extra 2mm would require a change of chain-line at the front, which shouldn’t be too much to compensate for, I thought.

Fitting was straightforward, using plenty of lube on the threads and a very thin layer on the cranks tapers.  (Old timers might shudder at the idea if greasing the tapers before replacing the cranks, but a thin layer will help to seat the crank and won’t make the cranks round out.)  Once it was all back together, I rode around for a bit and re-tightened.

The front dérailleur needed adjustment.  The front mech has always been temperamental; last weekend it threw the chain off the small ring and the large ring on one ride.  I shifted the limit screws to some semblance of 2mm and put some tension in the cable adjusters.  I had enough to get into all front chainwheels, though the middle needs a little more thumb than usual.  I really wanted a ride by the afternoon, so fine adjustment could wait.

During the ride (more on that later), I adjusted the shifting a little, but it is still hit and miss.  Fortunately the rear shifts as sweetly as ever, so I could stick to a chain-wheel and grind one out.

Or rather, not grind.  The smooth action from the new BB was immediately obvious.  I often put a lot of expectation on any adjustment or new component to have benefits several orders of magnitude greater than their cost.  But I could tell that even steep and loose hills were easier to climb and the pedal action was much smoother.  Not bad for $40 (+$40 for tools and lube).

Bicycle repair can be liberating and cheap; not only saving on labour costs but also by extending the life of existing components and knowing when to replace before failure in an inconvenient location.  Proper tools are essential to avoid expensive injury to bike and self.  And a workstand helps (Pushy’s have a nice one reduced to $99.)  And it keeps your mechanic honest.


Calculating the ideal weight for cycling (UPDATED)

English: The graph shows the correlation betwe...
The graph shows the correlation between body mass index (BMI) and percent body fat (%BF) for men in NCHS’ NHANES III 1994 data. The body fat percent shown uses the method from Romero-Corral et al. to convert NHANES BIA to %BF (June 2008). “Accuracy of body mass index in diagnosing obesity in the adult general population”. International Journal of Obesity 32 (6) : 959–956. DOI:10.1038/ijo.2008.11. PMID 18283284. (Photo credit: Wikipedia)

[This is adapted from the article Let there be Light by Selene Yaeger published in the Autumn 2013 edition of Ride magazine.]

What’s an ideal weight?

That very much depends on what you are doing.  Carrying a few kilos is fine for recreational cyclists (in fact, a little fat is usually better than next to none); however, a lower weight will help you become competitive and climb like a tiny Columbian, allegedly.  Since every extra kilogram above my ideal weight will make me 20-25s slower for each kilometre of a climb [Hunter Allen], then I need to figure out my ideal weight.  And reach it.  Here are the 3 methods and 3 rationales to determine ideal weight:

  1. Losing a bit of weight;
  2. Getting lean and a little mean;
  3. Competing at a high level.

What about BMI?

Body Mass Index is a fairly blunt instrument and much older than you might think.  Here is a mathematician tearing into it.

SIR – The body-mass index that you (and the National Health Service) count on to assess obesity is a bizarre measure. We live in a three-dimensional world, yet the BMI is defined as weight divided by height squared. It was invented in the 1840s, before calculators, when a formula had to be very simple to be usable. As a consequence of this ill-founded definition, millions of short people think they are thinner than they are, and millions of tall people think they are fatter. 

Nick Trefethen 
Professor of numerical analysis
University of Oxford

The Economist 5 January 2013

Wii Fit using a BMI of 21 expects me to aim for 83.5kg.  Starting from 115kg on 1 January 2013 it didn’t look like that was physically possible.  When I was quite thin about 15 years ago I was 90kg!

Using the slightly more realistic BMI range of 18.5 to 25 from the Heart Foundation’s handy calculator, at 195cm tall that gives a range of 72 to 95kg.  More realistic, but a bit vague. See also New BMI Calculator (below)

There are alternatives to the BMI that are better at determining risk factors of obesity, including two that only need a tape measure.  Or I could use three that are a more accurate.

1. Ride more weight less

The first method assumes that you are riding recreationally, maybe you used to ride a lot or perhaps you are trying to lose some weight to gain performance.  This formula is more advanced than BMI, but not by a lot.

Step Men Women
1 Baseline 48kg for the first 152cm 45.5kg for the first 152cm
+ 1.06kg for each extra cm + 0.9kg for each extra cm


 kg  kg
2 Frame size  


>165cm <158 158-165 >165


14-16.5cm Small <14 <15.2 <15.9 Small
16.5-19cm Medium 14-14.6 15.2-15.9 15.9-16.5 Medium
>19cm Large >14.6 >15.9 >16.5 Large


3 Ideal weight Small Baseline -10% Small Baseline -10%
Medium Baseline Medium Baseline
Large Baseline +10% Large Baseline +10%
My Ideal Weight (for now) is…  kg  kg

Step 1 is a fairly simple calculation based on averages.

Step 2 takes into account your inherent body shape, good for 10% adjustment either way.  The adjustment for women is more complex by virtue of a bigger range of shapes.

Step 3 is to compare the calculated amount with your current weight.

Based on 195cm my baseline weight is 94kg.  My wrist is 19cm which is a large frame (just), so I can add 10% to take my ideal weight to 103kg.


I’m now 104-105kg (down from 115kg at the start of the year) so what does this mean?  I’m interpreting this as indicating the end of the first stage towards fitness in readiness for more intensity.

And if the weight calculated is less than your current weight, then you need to move to the next formula.

2. Body Fat Percentage

Let’s say that you are riding several times a week, training for an endurance event, you want to change your body composition for more power, or you current weight is below the ideal weight calculated above.

The healthy body fat range is 10 to 25% for men and 18 to 30% for women.  Too little fat can compromise your immune system, so less is not always more.

 1 Measure your Current body fat %
 2 Goal body fat % Male 10-25% / Female 18-30%
3 Current weight x Body Fat Percentage Mass of body fat in kg
4 Current weight – mass of body fat Lean body mass in kg
5 (1 – Goal body fat %) Proportion of lean body
Result Lean body mass ÷ proportion of lean body [step 5] Ideal weight

If I use 27% as current body fat (average of recent measurements by a Tanita BC-522 scale) and 20% as my goal and 105kg as my weight, I have about 28kg of fat, 77kg lean.  From that my calculated weight is about 96kg.


This weight looks like a next step.  Assuming that I reach 103kg (see above) shortly, then 96kg should come with increased training.  That goal seems achievable by not being that far away and would be expected after an increase in training that I was about to undertake anyway.

3. Competitive streak (not bacon)

This is one’s “fighting weight”.  If you are not going for the highest level of the sport, then this weight will be a step too far.  If you focussed only on dropping to this weight you may actually lose power in the process!  But let’s do the sums and see what happens.

The creator of the Cycling Bible series coach Joe Friel analysed top cyclists to see what weight they carried per centimetre of height and found this range:

  • Male – 375g to 430g per cm
  • Female – 340g to 394g per cm

This empirical measure can’t explain everything (Cadel Evans is as wide as both Schleck brothers side-by-side!) but with statistical methods and a big sample you get very close.

So at 195cm the male weight range is 73 – 84kg.  Sampling the Tour de France squads, all but one rider near 195cm fits in that range:

  • Michael Schär BMC – 196cm 74kg
  • Bjorn Thurau Europcar – 193cm 78kg
  • Laurent Mangel FDJ – 195cm 83kg
  • Johan Vansummeren Garmin-Sharp – 197cm 79kg
  • Olivier Kaisen Lotto-Belisol – 195cm 82kg
  • Mercel Sieberg Lotto-Belisol – 198cm 82kg
  • Stijn Vandenburgh Omega Pharma-Quickstep – 199cm 83kg
  • Jens Mouris Orica-Greenedge – 197cm 91kg (!)
  • Christian Knees Sky Procycling – 194cm 81kg
  • Mirko Selvaggi Vacansoleil-DCM 195cm 73kg

4. New BMI calculator

While its author warns that the new BMI is still just one number, and that he is just a mathematician, the new formula at least normalises for height.

  • Current formula: BMI = weight/height2
  • New formula: BMI = 1.3 * weight/height2.5

Based on the new BMI Calculator I return to the Healthy range at 102.1kg.


It has been interesting to break up weight loss into goals that align to purpose and intensity of an activity.  Telling me to drop to 83.5kg from my former weight of 115kg is just absurd, even if Wii Fit Board is cute when he says that with a smile.  But if I make that weight via 103kg and 96kg, then 84kg seems reasonable; as long as I accept that I will be riding in most of my spare time every week and I’d better start racing to make it worthwhile.  I could ramp up to that.  Or I could slack off and be satisfied with something in the low 90’s and thighs that could break macadamias.  Wouldn’t that be nice?