Category: Repairs

How To Choose The Perfect Stem

The wild west. A small and dusty town. A bar.  A derivative walks into the bar. All the functions scatter. In a dark corner, a lone function dares to stand his ground. The derivative walks up to the lone function and asks, “Who the hell do you think you are?” Without skipping a beat, the function, with eyes barely visible from under the brim of  his hat, replies “I’m ex.” The derivative gives a small, knowing grin and says, “Today is not your lucky day, I’m d/dy.” – Original source unknown

So it’s been a while  since whipping out the high school math books. I mean who needs that kind of grief in the real world?

Well, ladies and gents, for the first time ever, I’m going to show you a practical use for your trigonometry classes.

But fear not, I’ll be holding your hand through this, you just need to plug in the numbers.

Why This Is Useful

The best option for choosing a stem is to have yourself measured on your bike and get a stem that matches the angle and length of the one used for measurement. There is no guessing here, and it’s all worked out well.

But what if your bike is not quite right, or if you didn’t have it fitted, or after some time the “correct” fit just doesn’t quite cut it?

Amongst other things, the stem will need to be adjusted.

Simple?

No.

Doable?

Yes.

Because of the angles, every adjustment of the stem affects not only the height, but the distance from the top of the saddle to the handlebars.

How My Dilemma Helps You

I am 6’1″ (185mm) and my build gives me legs that are quite long, but not long arms. I’m like a Tyrannosaurus on wheels.

Ideally I’d be riding a custom built frame that’s just right for me, but I don’t have deep pockets for that kinda stuff, so standard consumer bikes is the only option. Fitting my body on a standard, production bike takes a bit of work, thought and adjustment.

My current mountain bike setup puts the handlebars about 79cm in front of the saddle (measured from where my sitting bones would rest). This is a position I have had on my bikes for over 10 years already, but after riding a small, folding bike that is only 72cm from seat to handlebar, and finding it quite comfortable, I need to make some adjustments to my bigger bike. The vertical difference between saddle and handlebar currently puts the handlebar 2cm below the saddle.

There is one other sure giveaway of being too stretched out. When riding for over three hours I often place the middle of my fingers on the handlebars, rather than the palm. This position eases strain in my back and just feels right.

Target: move handlebars 4cm closer to seat, and raise them by up to 2cm.

Ready?

Let’s go.

Preparation

First, some abbreviations:

  • hl = horizontal length, the length of your stem measured directly forward, parallel to level ground (we’ll calculate this number)
  • vh = vertical height, the height of your stem as measured directly upwards (we’ll calculate this number)
  • sa = stem angle, the angle marked on the stem
  • sl = stem length, the length marked on the stem
  • hta = head tube angle, the angle of your head tube (we’ll measure this)

To measure the head tube angle:

  • Take angle from manufacturers specifications (I did)

or

  • Stand bike securely (lean against something, tie rubber bands around brake levers and handlebars to stop sliding)
  • Find something long and straight (broom, etc)
  • Drop line straight down the head tube to the floor
  • Measure the head tube angle as shown in the diagram, between the floor and that line (you’ll need a protractor for this)

To measure the stem length:

  • Check specifications (often written on the underside of the stem)

or

  • Measure from the center of the head tube to the center of the handlebar.

The Math Part

You’ll need the online scientific calculator (or a real one) for these.

Calculate horizontal length and vertical height.

bignum = 90 – head tube angle + stem angle

horizontal length = cos(bignum) x stem length

vertical height = sin(bignum) x stem length

Original Stem Figures

My current figures are…

  • stem angle = 25
  • stem length = 120mm
  • head tube angle = 72

so…

bignum = 90 – 72 + 25 = 43

horizontal length = cos(43) x 120 = 87mm

vertical height = sin(43) x 120 = 81mm

Find A New Stem

Now you just need to plug in the numbers of a new stem to find the one that is closest to your requirements.

To get 4cm extra height is quite a rise, so I’ll try out a 45 degree stem first. These are available in a range of lengths, this angle is probably right, but the length will make a big difference.

120mm stem with 45 degree rise:

bignum = 90 – 72 + 45 = 63

horizontal length = cos(63) x 120 = 54mm

vertical height = sin(63) x 120 = 106mm

So I’ve moved back 33mm, but moved up by 25mm.

I was hoping to move further back and don’t need that much more height.

Next…

100mm stem with 45 degree rise:

bignum = 90 – 72 + 45 = 63

horizontal length = cos(63) x 100 = 45mm

vertical height = sin(63) x 100 = 89mm

Overall, for my bike, they work out as shown in the table below.

Stem Horizontal Length Vertical Height
120mm, 25 degree 87mm 81mm
120mm, 45 degree 54mm 106mm
100mm, 45 degree 45mm 89mm

Conclusion

Taking the time to get the right stem is worth it. However, this isn’t really needed any more and there are plenty of shops with adjustable stems in their stock. It’s much easier to use one of those to determine the right length, etc.

If you are in the market for a very expensive stem, I’d recommend just buying an adjustable one (not that expensive), and then spend a little less on the full stem when you’ve determined the right size and length.

The Broken Seatpost

I take a long time to learn my lesson.

There are plenty of documented times when bike maintenance should have been done, but didn’t get done, resulting in a not-so-good ride. There are other times when I’ve done some slightly crazier offroad riding and broken parts, which is to be expected, and that is all in good fun.

But this time the blame falls squarely on crappy bike parts.

The Start

I was heading off on a ride early in the morning, I started at 4:15, which was a little later than planned, but that’s par for the course.

The destination was the 600m peak of the hill between Shrding and Pinglin on the 106A. To get there I had to head off towards Nangang, pass by Academia Sinica Road then head on.

Now, the most obvious way to Shrding is by going over the 109, but I wanted to try something new. With Google street view on hand I planned a decent looking route over a smaller road that would achieve the same elevation, but add some variety to my ride.

A Little Lost

The main turnoff to the road up the hill was where the Google car had decided to go the other way, so I was on my own to figure out which roads went where.

I made it through the first intersection unscathed, keeping to the left and avoiding a detour to a deadend in the middle of nowhere. But my luck would change.

Later I was faced with a similar choice.

The road to the right didn’t seem to have any more lights while the road that dropped sharply to the left was well lit. So I took the path down.

Grab a Fistful

Something I love about roads in Taiwan is that there is no maximum grade. If that’s where the road has to go, then that’s where it has to go.

Back in South Africa there were some steep hills, but they were all limited in how much they would challenge my breaks when needed.

So on the way down this “little” road down I ended up braking so hard that I had to carefully alternate front and rear brakes to give them time to recover from the glazing over that occurs during heavy, continuous braking.

And…

It was the wrong turn…

just a dead end…

should’ve taken the other turn, so I had to slog back up after trying to check my location on the map (BTW a map on your phone is only really useful if you have a GPS to pinpoint your location, duh, I don’t have a GPS).

So up I went, kept following the road, the lights returned and then I started heading down.

The Bang

Riding in the dark requires and abnormal amount of trust in the state of the road you are riding on.

Very few bike lights will light up enough road to allow for evasive maneuvers when travelling at 30kmph+

So I was following the road as usual, keeping to the parts of the road I could see, or at the very least not riding off the edge of the road.

When I spotted a construction team I had to change tact and move left into a darker area….

Whack…

Slide…

Quick recover…

Although my front wheel made a big move to the right I did manage to stabilize and continue.

But something wasn’t right. The saddle felt strange. I put it down to the seat being shifted slightly during the little incident that just occurred. I continued, and finished a wonderful ride to the top of the big hill.

Holiday Time!

So I headed back to the office and went off to the Taipei main station for a slightly early holiday (on a Thursday, a got the day wrong in the video).

Disassembling my bike outside the bus terminal and shock and horror I see my seatpost is bent, no quick realignment of the saddle needed, but a full replacement of the seatpost. And this is the third one I’ve had that’s bent, just none of the others have bent so far.

The insanity is that until more recently Giant have insisted on installing 27.2mm seatposts with a big old shim, whereas the inner diameter of the seat tube is actually made for a 30.9mm seatpot without a shim. Dumb, dumb, dumb, raise the skinny one to a height suitable for me, put my fat ass on the saddle and the poor seatpost doesn’t have a chance.

Well, all should be good and well in seatpost land from now on.

Here’s hoping.

How to Repair Shimano Cycling Shoes

My Shimano cycling shoes have taken quite a beating over the years. A month or so ago the hard, plastic sole started breaking from the leather uppers.

I was a little disheartened, but decided that the simplest fix would probably be the best. I had some electrical tape wrapped around my shoes for a few days to stop further separation.

Here’s the steps I took:

  1. Buy shoe glue. The type I bought simply had a picture of a shoe on it, so I just bought it. This glue was KS Brand and labelled as “Chloroprene“.
  2. Open up the areas to be glued as much as possible. I don’t recommend opening parts that are still firmly glued.
  3. Dust off the surfaces. Wipe with a paper towel, or in my case I just used my finger to wipe off dust and dirt.
  4. Apply glue to both surfaces (keep them apart for now) then allow to dry for 10-15 minutes.
  5. Carefully align surfaces then press together firmly for a minute or two.
  6. Leave for a few hours to fully dry. Use heavy objects to continue to apply pressure to those spots that need it.

I went on a 100km ride the morning after fixing these, so a long cure time is not really necessary. So far they are holding out, there are no obvious signs of further separation.

You’ve just saved yourself a bundle of cash and extended the life of your beloved shoes.

Next step: go ride your bike. Cheers.