Tag Archives: bike

The mess of bike tire sizes

My road bike has 700x23C marked on its tires.  

Last week, I was curious and Googled 700x23C to see what it meant – of course, so I could figure out what my tire diameter and circumference is to put into the bike computer.  And thus I stumbled upon the mess that is bike tire size designations!

There seem to be various ways of designating tire width.   I think the Wikipedia article here summarises the ISO, Inch markings and French designation very clearly with a nice diagram:  http://en.wikipedia.org/wiki/ISO_5775

For my wheel (which is a very common racing wheel size), 700 x 23C is an old French desingation broken down as follows:


This used to refer to the overall inflated tire diameter.  However, I think it’s lost its meaning/accuracy over the ages, and 700 now means a rim diameter of 622mm (across the bead set).

The French system can also append a letter code here to designate the width of the tire.  The common “700” tire is actually 700C.  Much more info here courtesy of the extremely knowledgeable Sheldon Brown:  http://sheldonbrown.com/tire-sizing.html


The second number is meant to be the tire width.  Since bike tires are nearly circular when pumped up, one can estimate that the “height” of the tire is the same as the width – in my case, 23mm.


I think this last letter refers to the type of rim.   C means Crotchet-type, whereas SS means Straight-side and HB means Hooked-bead.

Putting it together

If I assume that my bike tire is circular when pumped up (so the “height” is the same as the “width”), the overall diameter of my bike tire is 622 + 23 + 23 = 668mm.  This makes a circumference of 2098.58mm.  This sort of matches the range in various bike computer manuals.

Of course, it’s probably easier and more accurate to just marki a spot on the floor and your wheel, make sure your tires are pumped up to the right PSI, sit on your bike and roll it a couple of revolutions, and then measure the distance to work out the circumference 🙂

Oh, one interesting blog I discovered on my travels today – the Lovely Bicycle – great photos, stories and articles on vintage bikes and cycling – http://lovelybike.blogspot.com/

More info

ISO Standard – http://en.wikipedia.org/wiki/ISO_5775
Tire Sizing – http://sheldonbrown.com/tire-sizing.html
Rim Sizing – http://sheldonbrown.com/rim-sizing.html

LiveStrong’s article on Bike Tire Sizes – http://www.livestrong.com/article/336406-explain-bike-tire-sizes/
Mysteries of Tire/Tyre Widths – http://www.tricktrack.org/forum/viewtopic.php?f=2&t=5566&start=0

Sigma 1909 HR STS Bike Computer Review

After a year of serious cycling, I have finally bought a bike computer.  So far, I’ve been getting by by using TrailGuru on the iPhone for post trip analysis, or asking my fellow riding friends during the ride, “How fast are we going?”.  Not very scientific or useful.  Sort of like driving a car without a speedo, or having a bank account without transaction history.

Yesterday, my eBay purchase of the Sigma 1909 HR STS arrived! 

This little computer does speed, cadence and heart rate – all wirelessly too!  I definitely wanted speed so I can maintain a good pace which is useful when cycling in a pack.   I heard that cadence was useful to make my cycling more efficient.  And heart rate should be useful to improve my fitness.

First Impressions

I was worried that the screen would be quite small, which would make it hard to look at when cycling.  But no, when I unboxed the Sigma, I was happy to see a large clear display!

The wireless sensors seem a bit big, but I’ve heard that they are smaller than the Cateye wireless ones, so I’m not complaining.

Packaging all looks professional, instructions were very clear, all good!

Nice things about the Sigma package is that you get O rings as well as zip ties – you can choose which way to secure the parts to your bike.  It also came with a sample tube of Buh Bump heart rate monitor electrode cream!


The Sigma website actually has videos showing you how to install the sensors on your bike.  You gotta see the video once – it’s useful, but moreso because it’s all done in cheezy simulated slomo.  The actor must’ve had a ball recording this.

Mounting was pretty simple thanks to the clear instructions.   I just had some problems with the magnet on the front wheel.  It seems if it was mounted the correct orientation, the magnet jutted too far out and kept hitting the sensor. I couldn’t move the sensor any further away from the spokes.   So I’ve temporarily mounted the magnet facing the other way on the spoke.   Not ideal but it’s still registering OK.

Very small gap between magnet and sensor

One nice feature about the sensor – it seems to make a small clicking sound everytime the magnet goes by.  Not sure if this is the magnet relay inside the sensor or an actual click from a speaker, but it makes it easier to tell whether the sensor is working or not.

The cadence sensor was quite easy to install and didn’t seem to get in the way of my shoe at all.

Sigma cadence sensor


At first I wasn’t sure how to turn the device on or off!  But it seems to be always in standby, turn on when it detects movement from the sensors, and goes back to standby automatically after some period of not being used.

Speed and cadence worked fine for me.  Actually, I noticed I ended up pushing myself more on my ride to work today because of the computer!  So it must be doing something right 🙂    And it was nice to see the cadence so that I could keep it around 80-90rpm.  

The speed and distance sort of matched up with TrailGuru on the iPhone.   Yeah I know, a pretty short commute to work and “slowish” because of traffic lights, intersections, etc 🙂

The thing that didn’t work for me though was the heart rate monitor.  I had it strapped on, and I did wet it before I started (and it was pretty wet when I finished), but it didn’t register anything!  No heart rate.  I’ll need to investigate another time – maybe it was in the wrong location on my chest, or maybe the shape of my chest is not conducive to strap on heart rate monitors.  Hmm..

So for AUD $129 off eBay, the Sigma 1909 HR seems like quite a bargain.   Especially when a Cateye RD400DW double wireless without a heart rate monitor goes for the same price on eBay and the Polar CS400 and CS500 ones with heart rate monitor go from $349 to $399.

I’ll need to try different positions for the HRM strap and see if it makes any difference…   and try that sample Buh Bump cream!

More info here: http://www.sigmasport.com/en/produkte/bikecomputer/topline_2009_wireless/bc1909/

I survived the 60km HBF ride

Getting there

It was an early start – we had agreed to meet up at a friend’s house at 5.30am so we could drive in convoy down to Kwinana.   It was still dark and I forced myself to eat some Nutri Grain, part of an energy bar, have a banana and drink some energy drink before I left.   It’s not fun forcing yourself to eat when you’re half asleep, but I knew I needed the energy later on. 

On the drive down, I was thinking, “It’s taking ages to drive down here, you mean I have to cycle this plus go up to Joondalup?”.   The further it took to get to the starting point, the more anxious I got about how long 60kms really is. 

We eventually got to the Kwinana train station and there was a major buzz in the air.  I was starting to feel good about signing up for this.  Yes, I’m part of a whole bunch of other fit people!  Does that mean I’m fit?  Are there people in this group who will struggle like me to do the 60km? 

Gathered at the start line

We nudged our way to the start of the C group and waited patiently to give the earlier groups some distance.

The ride


And then suddenly the eight of us in our group were off!  And at an extremely fast pace!!  Too fast really… wayy too fast.   I started to get worried..  I was struggling to keep up now, how would I ever last the distance? 

After around 10kms, I decided, that’s enough, I’m peeling off and doing my own pace.   And luckily eventually so did some others in the group and so I rode with them for a while. 

Before I knew it, I was going over Mt Henry bridge and could see the city on the horizon.  Had I come this far already?  It’s basically half way!  And having cycled to/from Mt Henry bridge before, this was familiar territory.  The riders seemed to bunch up into the city and soon I was in the middle of a 100-strong peleton and it felt great!   We were moving as one big mass towards Mitchell Freeway. 

And I saw some familiar faces!  The team I was with had stopped at the Charles Street turn off to wait for us!  So we teamed up again and it was so much fun.   But I wasn’t starting to get knackered and so didn’t really put my time in at the front of the pack.  But this stretch from 35-45kms was most enjoyable, riding 38-40 km/h in a group. 

But problems struck at the 10km to go mark.   My right calf started getting a cramp.  Argh!!   What do I do?   Should I stop and stretch it out and wait until it’s better?  Or just bear the pain and keep going?  I shouted the rest of the boys that I have to drop off because of my cramp (and because I was soooo tired by now) and tried to stretch my calf and ride slower.  I drank the rest of my Gatorade, ate the rest of my energy bar and said to myself…  “10kms?  That’s my commute to work.  I can do this.”   My speed dropped down to about 25-30 km/h.

Speed over the 60km ride

Yes, so I thought, until I saw the hill.   Whoever designed the freeway decided to put a big hill leading up to Joondalup!  Well, OK, wasn’t the freeway designers fault…  but it was not welcome!   I really had to reach to the bottom of my energy barrel and push on..   after all, it’s too late to stop or turn around now! 

And then there it was – the finish line!   I did it!   Here we are gathered at the end of the ride – 

Finished 60kms!

Final time was around 1 hour 48 minutes, which is an average speed of around 33 km/h. 

To finish off the morning, I got to be part of the amazing squeezing in of bikes and riders onto the train back to Perth.  

Squeezing bikes onto the train

Road bike on the way!

I can’t believe it – I’ve now spent more on a bike than a digital SLR body!  How did this ever come about?   Why didn’t I just buy a D700 🙂

After a year or so of pushing my Diamondback Apex mountain bike around Perth and 6 weeks of rides increasing from 26kms to 40kms, I’ve decided to take the plunge and get a road bike.  A little zippy carbon one with a 105 groupset and entry Mavic Aksium wheels.  I’m sure that should be more than I need for the next few years!  (Don’t tell wifey that there’s even more expensive bikes and components to upgrade to later!)

So which one?

I really couldn’t decide.  All I know is that my budget was just over the $2k mark and I wanted to get the best “bang” for the buck, so after considering the Merida Road Race 905-COM, runout Cannondale 6 Carbon 5, Trek 2.3, Felt F75 and Giant TCR Alliance, I decided to go with the Malvern Star Oppy C5.   Yep, the brand name might be shunned by experienced rideres, but I couldn’t find a better deal – I really don’t know how Malvern Star are doing it besides just not making as much profit as other companies.

For anyone who’s reading this who is thinking of getting a road bike, just remember that there are accessories to add onto the cost – like clip pedals, shoes, pump, tube, drink holders, clothing, etc.  It all adds up!

Looking forward to my first big ride on the weekend!

By the way, if you’re interested in looking up prices to compare, the best place I’ve found so far is here:   http://www.bikeexchange.com.au/