Category Archives: timers

Cornering – the key to faster lap times

pairbikesOver the winter I’ve been thinking about the changes I need to make to my riding in order to improve my lap times. After reviewing footage from my last few track days, I can see that the biggest lap time improvement would come from changing the way I ride the corner entry and exit.

A few months ago, I rode the Silverstone GP circuit with Matt who was on his Honda VFR400 race bike. Despite Matt’s racing experience, I figured that the Daytona’s 10-15 mph speed advantage down the straights would result in similar lap times. The reality was that Matt’s greater skill and experience allowed him to cancel out my speed advantage by utilizing his brakes and tyres more effectively than I could.

Anyone can ride fast down a straight because opening the throttle and holding it open are easy as a bike is most stable under acceleration. Real speed gains come from:

  • carrying more speed in the corner
  • how quickly you get on the throttle at the corner exit
  • how well you brake for the next corner

I’m going to use a video of our bikes coming onto the Wellington Straight at Silverstone’s GP circuit to try and explain the things that I need to improve in my own riding order to achieve the faster lap times that I am after.

The video is running at half speed to give you time to pick up on the different things that I want to note. I suggest opening the video in a new window (by clicking on the YouTube logo in the bottom right of the video) so that you can see the text and video side by side in two windows.

The rookie on the Daytona is the top left view while the racer on the VFR is the bottom right view.

You can pause the video at the time intervals shown below as I try and explain some of the differences in our riding styles.

Time Comment
00:08 Notice the corner apex speed difference. My Daytona is doing 75 mph vs Matt’s 79 mph
00:12 Notice how much sooner Matt gets his bike upright – this allows him to get on the throttle harder
00:14 It takes the Daytona 4 seconds to reach the VFR’s speed on the straight by which time the VFR has pulled out a lead
00:25 The Daytona’s maximum speed is 123 mph vs the VFR’s 113 mph. The Daytona now passes the VFR, arriving at the bridge 0.2s ahead of the VFR
00:27 The Daytona is now easing off the throttle. The VFR is still flat out
00:31 The Daytona is braking at 0.6g while the VFR is only just starting to brake (hard). The VFR pulls 0.8g when braking
00:36 The Daytona arrives at the left hand turn sign board (arrow on the right of the track) 0.2s ahead of the VFR
00:37 The VFR has now caught the Daytona again because the turn in points for the two bikes are approximately the same and the VFR takes a tighter line to the apex
00:39 Notice how the VFR is carrying more entry speed into the corner; 62 mph vs 57 mph
00:46 The VFR reaches the apex of the corner 0.2s ahead of the Daytona and is carrying an extra 2mph of speed at the same apex point

The two areas that the racer on the VFR makes significant gains are coming onto the Wellington straight at the start of the video, and his approach to the next corner at the end of the same straight. Let’s focus on the corner exit coming onto the Wellington Straight.

image4249

Once your braking is over going into a corner, you need to apply sufficient throttle to settle the (front) suspension – Keith Code calls this “maintenance” throttle. As you approach the apex of the corner you can start to apply more throttle as you pick the bike up. Matt is able to get on the gas earlier and harder coming onto the Wellington Straight which means that he passes the apex point at 79 mph compared to my 75 mph. It then takes me 4 seconds to catch him down the straight despite the Daytona’s higher top speed.

However, the area where I lose most time compared to Matt is in the braking zone on the approach to the next corner. Let’s break this section of the track down using the following diagram.

image3047

Racers say that you should either be on the gas or on the brakes. The biggest mistake that rookie riders (myself included) is to coast in the transition phase between accelerating and braking. I spend nearly 2 seconds coasting from accelerating to braking in the transition zone while Matt spends just 0.3 seconds in the transition zone.

The other aspect that is important to note is that Matt’s braking marker is later than mine, so while I spend two seconds decelerating from 123 mph to 95 mph, Matt is still travelling at 115 mph. This combination of a later braking point and harder braking minimises the time spent braking so that he catches and then passes me at the end of the straight.

My poor race track skills come from years of road riding where you roll off the throttle and use engine braking before applying the brakes on the approach to a corner. This style of riding has no place on the race track! Gains are made by choosing a later braking marker and reducing the transition (or coasting time) between accelerating down the straight and braking for the corner.

image5600

The lower part of the diagram shows the rookie rider while the upper part shows the more experienced (and confident) rider. It shows what kind of riding style change is required to improve a lap time. Note that the turn in point and the turn in speed should remain similar no matter where your braking marker is.

The first significant improvement that I can make, without even changing my braking marker, is to reduce my transition time from 2 seconds to 1 second or less. This means using the brakes as soon as I come off the throttle instead of using engine braking before applying the (front) brakes. The brake lever should be squeezed smoothly to load the front before being squeezed harder to rapidly slow the bike down. All (or almost all) of your braking should be done while the bike is upright in order to avoid having the front end wash out on you.

So instead of transitioning like this:

Off throttle -> change down -> apply brakes

the correct procedure is this:

Off throttle -> apply brakes -> change down

During the braking phase the throttle is “blipped” for each gear downshift. Downshifting should be done in the braking zone and not the transition zone.

The second significant improvement that I can make is to brake later by choosing a later braking marker. Focusing on a faster transition (between acceleration and braking) should automatically move my braking marker closer to the corner anyway. The important thing to remember is moving your braking marker closer to your turn in point means that you have to brake harder to compensate for the less time that you now have in the braking zone. Matt was braking at 0.8g compared to my 0.6g; however if he had been slowing down from a higher speed then his braking deceleration would probably have been even greater than 0.8g that is shown in the video. This also illustrates just how little braking force I am using compared to Matt and it is another area where I can make more of an improvement.

On an intellectual level I understand what needs to be done to achieve a better lap time, however putting that knowledge into practice is much harder than it appears. What’s that saying about “not being able to teach an old dog new tricks”!

I’ve been told that the best way to make this kind of riding style change is to choose one or two corners only and focus on trying your changes gradually throughout the day rather than trying to do it for every corner and all in one go as this quickly becomes overwhelming.

I’ll report back on any improvement that I am able to make on this particular section of track next time I ride it.

Garmin GLO vs QStarz 818XT Part 2

RC-GLOIn my previous post on the Garmin GLO vs QStarz 818XT I looked at the two units from a physical perspective without having done a real world test. In this article I’m going to look at and analyse the data produced by RaceChrono using both devices riding on Silverstone’s GP circuit.

HeadstockProtectorFor the test, I installed both GPS receivers on the bike. The Garmin Glo was strapped to the rear of the bike on the tail piece while the QStarz 818XT was taped between the top yoke and the instrument console on the head stop lock bracket (circled in yellow).

The test was conducted for one session with a detailed analysis of the fastest lap from that session. These are the raw numbers produced by RaceChrono for lap 4 of the test session:

  QStarz 818XT Garmin Glo
Lap Time 3:02.12 3:02.02
Distance (m) 5846.835 5854.346
Data Points 911 1346
Sample Rate 5Hz 7.5Hz
Trace Colour Red Blue

Taking the raw numbers from RaceChrono and plotting them against a schematic for the track is quite illuminating. The diagram below shows the two traces obtained from the GPS devices. The red trace is the QStarz 818XT while the blue trace is from the Garmin Glo.

Vale-Club

The first thing to notice is how both traces cut the right handed corner between Vale and Club. Neither trace is correct as I’m pretty sure that I was close to the right hand side kerb but definitely not over it. This isn’t totally unexpected because the reported accuracy of these devices is down to around 0.5 – 2m depending on the quality of the satellite signal and fix.

The second thing to notice is that the Garmin Glo (blue plot) records my line through those two corners more accurately than the QStarz 818XT. If you look carefully, you’ll also notice that the red trace (from the QStarz 818XT) looks smoother than that from the Garmon Glo. You can see this better in the detailed view below.

ValeTrace

The QStarz 818XT delivers a data point to RaceChrono every 1/5th of a second (hence 5Hz) without fail. The Garmin Glo is supposed to deliver a data point every 1/10th of a second (ie 10Hz) but fails to do so, often skipping one or more data points within each second – look for the gaps in the purple dots on the blue plot. Over the course of the 3 minute lap, the Glo delivered a data point every 0.133 of a second resulting in an average frequence of 7.5Hz – about 25% below the quoted 10Hz. As noted in my previous article, this could be a flaw in the Garmin or more likely the Bluetooth stack in the Android operating system used to run RaceChrono.

Comparing the two traces, it looks as though the QStarz 818XT (red) has come kind of filter or smoothing algorithm because of the smooth nature of its trace. The Garmin Glo’s trace (blue) shows some “jumping” between two consecutive data points; almost as if the bike jumped one bike width’s to the side. Rather than being a flaw, this indicates to me that the Glo doesn’t attempt to compensate, smooth and adjust fixes but just reports the fix as calculated.

TraceLuffield1Over the course of the lap, both devices report pretty similar traces, except for the trace recorded by the QStarz 818XT at Luffield. You can see this in the red trace that leaves the track completely for a while before finally rejoining the circuit. A more detailed view is show below.

TraceLuffield2

It’s pretty obvious that the QStarz 818XT was unable to accurately locate itself possibly due to a temporary loss of view to the overhead satellites. It takes the device almost 8 seconds to re-establish its position back on track. This could have occurred because the QStarz 818XT was mounted in a position on the front of the bike where my helmet (and upper torso) could have been shielding the device from a decent view of the satellites. I checked the laps before and after and this problem didn’t recur so it’s likely to have been a one off that lap. What’s interesting is that a seemingly large error like this has relatively impact on the overall lap time and both devices report lap times within 1/10th of a second of each other for that particular lap.

Lap QStarz 818XT Garmin Glo Difference
1 3:11.55 3:11.52 0.03 3/100ths
2 3:06.13 3:06.12 0.01 1/100th
3 3:05.64 3:05.64 0.00 Same
4 3:02.12 3:02.02 0.10 1/10th
5 3:03.94 3:04.00 0.06 6/100ths

With the exception of the excursion off track described above, both devices show fairly similar traces around the circuit. In terms of position reporting, the Garmin Glo looks to be more accurate than the QStarz 818XT but that could be because the QStarz 818XT was located less favourably than the Glo. If you’re looking to plot your lines around the track, the Glo would be a better unit to use than that QStarz 818XT. If however, you’re just interested in your lap times, then both devices do a great job reporting very similar lap times as you can see above.

In my next article, I will analyse the speeds reported by the two devices at different parts of the circuit.

Garmin GLO vs QStarz 818XT Part 1

After hearing reading a lot of positive feedback on the Garmin GLO, I decided to get one and compare it with my QStarz 818XT which has worked perfectly for me over the past year. My primary interest in the GLO is to see whether it can provide faster updates and more accurate positioning information.

Garmin GLO and QStarz-818XT

Garmin GLO and QStarz-818XT

The Garmin GLO and QStarz 818XT are bluetooth GPS receivers and can be used to provide a much more accurate GPS signal for race track timing compared to the built-in GPS found in most mobile phones. The GPS in a mobile phone won’t typically update its position more than once a second (1Hz) while these units can update at up to 10 times per second (10Hz). I use RaceChrono to record my lap times and if you are new to this, you can find out how RaceChrono works in this detailed post on using RaceChrono.

Both of these bluetooth GPS devices are similar in size although the Garmin is slightly slimmer and longer than the QStarz-818XT. The battery in both is good with each device giving a minimum of 12 hours on a single charge – enough for a full day on track. In fact the battery life of the QStarz is actually a lot better than the GLO, supposedly lasting up to 40 hours (although I haven’t actually proved that).

Size and battery life isn’t the only difference between these two units – the technology used by them for determining their position is also different. The QStarz-818XT only uses the US GPS satellites in order to determine its position while the Garmin GLO uses both the US satellites and the Russian GLONASS system. This makes the GLO’s hybrid technology fairly unique in the market compared to most other makes and model of GPS unit, and it’s what gives the GLO an edge over the QStarz in terms of outright accuracy.

QStarz-818XT

This image is from RaceChrono showing the satellite information when connected to the QStarz-818XT. You’ll notice how the GPS unit has locked on to 7 satellites and is reporting its horizontal position accuracy as 1.1 – this is an excellent value indicating a high degree of precision.

The DOP values range from 1 to more than 20 where 1 is ideal, 1-2 is excellent, 2-5 good and values over 5 less increasingly less accurate . DOP stands for dilution of precision and you can get a detailed description of DOP values from Wikipedia.

Garmin GLO

Because the Garmin GLO is able to use both the US GPS and Russian GLOSNASS satellites for determining position, it has access to more satellites at any point in time which in theory allows it to determine its position more accurately. Under the satellite settings it reports its horizontal DOP as 0.7 which means greater accuracy than the 1.1 DOP value reported by the QStarz. This makes sense because the GLO is reporting a fix from 14 satellites compared to the QStarz’s 7 satellites.

To get these screenshots of RaceChrono, both GPS devices were placed side by side with each connected in turn to RaceChrono to grab the two screenshots. The two readings were therefore taken within a few minutes of each other and so should not really be affected by the fact that the satellites will have moved slightly during the test.

Startup times and operating speed

My feeling is that while the Garmin GLO gets its first fix a little faster than the QStarz-818XT there really isn’t that much in it, and since both devices lock on to satellites so quickly – you’re never stuck waiting for the first position fix. Both devices were also really easy to connect to RaceChrono running on my Android phone.

One major difference is the position output frequency of the devices. The QStarz is able to operate at 1Hz, 5Hz or 10Hz while the Glo only operates at 10Hz* – this means that it will send an updated position fix (over bluetooth) ten times a second or every 1/10th of a second.

While the QStarz-818XT is also able to operate at 10Hz, it will not output as accurate a signal as it will at 5Hz where the DGPS (differential GPS) capability can be enabled. In fact, the general consensus is that it is better to run the QStarz at 5Hz because although you only receive a new position fix five times a second each fix will be more accurate fix that the ones received at 10Hz. I’ve written another post that describes how to configure the QStarz-818XT to operate at 5Hz.

* When running RaceChrono with some Android 4.0+ devices using the Garmin GLO, the output frequency can switch from 10Hz to 5Hz and sometimes even down below 1Hz. This isn’t a problem with the GLO so much as a problem with the bluetooth stack in Android 4.0 and above. The device is sending too much data too fast for the OS to be able to process because some genius programmer decided to rate limit the receiving side of the Android bluetooth stack!

First impressions

My first impressions of the Garmin GLO are good. The unit is smaller than I through it would be, and it operates well with RaceChrono. It ships with a USB and a separate cigar charging lead which is good. The one thing I don’t like though is the On/Off switch which is too easy to knock. You could pack the unit away and find that the battery flat when you needed to use it because the On/Off switch got pressed by mistake in transit.

The QStarz-818XT is a solid performer. I’ve never had any problem with my unit. It locks on to satellites quickly and operates flawlessly at 5Hz with the DGPS enabled. I like the long battery life and the fact that the On/Off switch requires a more positive sliding action to switch it on or off which means that it’s unlikely to be switched on by mistake.

In my next post, I compare the operation of these two bluetooth GPS receivers on the race track.

Lap Timing with RaceChrono Part 2

In my Lap Timing Part 1 post, I gave an overview of some of the benefits and features of using a lap timer like RaceChrono. In this post, I’ll explain how to install the RaceChrono software and how it works.

If you already have an Android phone then skip the next section. Those of you who have just bought an Android phone in order to be able to use RaceChrono read on.

Setting up your Android phone
In order to use Android, you need to link the phone to a Google account (email address) otherwise you cannot access Google’s Play App store. If you don’t intend using the phone for anything other than lap timing, I’d advise you to create a new Google account using the phone rather than using an existing Google account (for privacy reasons). The account isn’t really that important – if you lose or forget the account details, just wipe the phone, create another Google account and re-install RaceChrono again.

Usually you will be prompted to create or link your Google account when you first switch on your phone but don’t worry if you aren’t because you will be when you launch the Google Play app from your list of apps (on the phone).

Installing RaceChrono
google_playAndroid phones come with many pre-installed apps, but RaceChrono won’t be one of them! There is normally an icon on the home screen that gives you access to all the apps installed on the phone. Find and launch the (Google) Play app – it is this app that gives you access to Google’s App store. Older phones may have Google Market pre-installed instead of Google Play – don’t worry because Google Market will also allow you to find and install RaceChrono.

In Google Play, hit the search icon and type “racechrono” (all one word without the quotes). The RaceChrono app should be returned as the first search result. Tap on it. On the next screen that describes the app in more details, hit the Install button. You should see the app downloading and installing after that – it shouldn’t take more than a minute or two to install but that will depend on the speed of your network connection.

Launching RaceChrono
racechrono_iconReturn to your home screen, hit the icon that gives you access to all your (installed) apps and find the RaceChrono app in the list. Then tap on it to launch it.

device-2013-01-19-115353When you first launch RaceChrono, you will be asked to set up a RaceChrono account. Enter an email address and make up a password just for this account. Don’t use any existing password!! Within about 5 minutes, you will receive an email from RaceChrono with an activation link. Click on the link in the email to confirm your RaceChrono account details – you can receive the email and activate the link from any computer – you don’t have to do this on the phone itself!

Now hit the Sign In button and enter your RaceChrono account details. Don’t bother trying to enter your details until you have activated your account – it just won’t work!

Adding your tracks
device-2013-01-19-120132In order for RaceChrono to be able to calculate your lap times, you will need to add your circuit to list of circuits on the phone. Hit the Tracks button and select the Library tab.

There are nearly 400 circuits from around the world, so there’s every likelihood that your track is listed. Where different circuit layouts for the same track exist, normally this will be listed as separate circuits too, so you should always be able to locate the track/circuit that you need.

device-2013-01-19-120941Find your track in the list, and tap on it. The track will then be displayed on a Google Map. Above the map, you will see a download icon (downward arrow above a horizontal line). Tap on this icon, and the circuit will be downloaded on to your phone.

The significance of downloading the circuit into your phone is that RaceChrono then has access to the locations of the start/finish line and the split locations. And it can make use of this information when you’re at the track without requiring any network connectivity.

If you’re not sure whether you will be able to get a network connection, then make sure you install the circuit before you head to the circuit!

Using the Timer
Return to the RaceChrono start screen and hit the big red Start button. The timer will now be started for a new session and you will see the screen change.

device-2013-01-19-122735Three three vertical numbers signify your best lap time (this session), your previous lap’s time, and the current lap’s time. Above the numbers is an indication of the number of satellites that have been fixed and below in red is the circuit that you are riding at.

Although you can tap on the lower red band to select your circuit manually, there is no need as RaceChrono will automatically assign the track from your listed of downloaded tracks. However having said that, it is important to make sure that RaceChrono has figured out which track you’re at otherwise you won’t get any meaningful lap times.

Once you’ve started the timer, place the phone in pocket in your leathers or safely attach the phone to your bike so that it won’t fall off on track.

Reviewing your lap times
When you return to the pits after your session, hit the Back button on your phone. RaceChrono will ask you whether you want to stop recording – hit Yes and you will be returned to the RaceChrono start screen.

device-2013-01-19-124342In order to review your last session, hit the Sessions button.

The sessions screen will list all your sessions with the latest at the start of the list.

The following details are recorded for each of the sessions:

  • the circuit name
  • the date and time that the session started
  • the total number of laps that session
  • your best lap time that session

device-2013-01-19-124933If you tap on the session, you will be able to see a more detailed summary including a lap time for a theoretical “optimal” lap.

The optimal lap time for the session is calculated by taking the best split times for any of the laps in the session and combining them into one theoretical optimal lap.

Sometimes this time corresponds exactly to your best lap time, but sometimes your best lap time has a slower split than another lap which means that the optimal lap is theoretically faster.

Notice that Laps and Route panel on the window both have the legend, “Tap to analyze”. If you tap either panel, then more information will be displayed on the next screen.

The analysis screen for Route will show you your progress round the track for each lap. Its main usefulness is in allowing you to compare speeds, braking G etc at different sections of the track in different laps.

device-2013-01-19-142955The analysis screen for Laps is altogether more useful because it will give you the actual lap and split times for each of your laps that session.

The blue line (lap 4 here) denotes your quickest lap that session. Any green sectors (section 2 in lap 6) denote a sector where you rode faster than the same sector on your quickest lap – 0.21 seconds quicker in this example. The other sector times indicate how much slower you were in those sectors. The optimal lap is made up by taking the best sector times from all laps that session.

You can toggle between relative and absolute sector times, and split or sector times using the two triangles near the top right of the screen. Have a play with these to get a sense of what they tell you as the numbers on the screen change.

You might have noticed that lap 1 and lap 8 are “greyed out”. If you long press on a lap, a menu pops up with various options including one to make the lap as invalid. This is useful otherwise lap 1 would be shown as the quickest lap when it is in fact some kind of aberration. Lap 8 was caused by pulling into the pits and forgetting to switch off the lap timer for nearly 20 minutes!

Comparing laps
You can compare any two laps in a session by tapping on any lap from the list.

device-2013-01-19-145919In this example, I tapped lap 5 which is then displayed against your best lap (4 in this case). Lap 5 is the brighter line, while lap 4 is the slightly darker line – you can tell which is which by looking at the top of the screen as the two drop down triangles. Tapping either of these allows you to switch the two laps that you want to compare.

The graph here shows a higher entry speed into Druids with later braking – this in part would be one of the reasons for the faster lap time.

You can drag the lower graph left and right to replay the lap, and as you do so you can see your progress on the map above. You will also see the absolute numbers at the bottom of the screen change too – these can be useful to see the actual speed at a given point on the track.

device-2013-01-19-185643Speed is not the only variable that you can plot on the graph either. If you tap on the gear icon at the top right of the screen, you will bring up a menu that allows you to change the graph settings.

Tapping “GPS receiver channels” will produce a new menu for the lines you want plotted. Speed is selected by default, but you might want to see Longitudinal acceleration to gauge and compare your acceleration and braking forces.

The X-axis can be plotted by distance or time. If you select Distance, then ensure that the bottom setting “Scaled comparison X-axis” is set so that the two comparisons graphs coincide correctly.

It’s best to have a play with these settings after you’ve done your first track day because the numbers shown to you will make more sense than the example session which is preloaded into the app.

Lasting the day
Battery usage is a big concern on a track day where you might not have access to a phone charger. For that reason, I try and reduce the power usage on the phone as much as possible.

Before heading out on track, I enable Bluetooth (so the phone can communicate with my external Q818XT GPS) and also switch the phone into Airplane mode since I won’t need to take calls or receive emails out on track! I also switch off the phone’s inbuilt GPS because I’m using an external GPS.

When I get back from the session. I stop the timer, switch off Bluetooth and re-enable the phone’s network communications.

Conclusion
Once you start using RaceChrono, you’ll wonder how you ever managed without it. As a Track Day beginner, you’ll find it useful to see that you’re improving and where those improvements are coming from.

More expert riders will like the fact that they can quantify changes that they make to the bike including things like tyre or pressure choice, sprocket selection and/or suspension changes.

If you’re intending to use an external bluetooth GPS receiver with RaceChrono, then you’ll find this post on using the Q818XT external GPS useful – especially the information on device pairing.

QStarz Q818XT – 10Hz GPS receiver

The QStarz BT-Q818XT bluetooth GPS receiver is a 10Hz unit that is 100% compatible with RaceChrono. It also offers high poll rates, DGPS (differential GPS), AGPS (almanac GPS) and long battery life.

While most decent GPS units use the SiRFstarIII chipset, the 818 uses the relatively unknown and new MKT II chipset.

My experience with the 818XT has all been positive. It acquires satellites very quickly, and I’ve not had any bluetooth issues with the connection to my Android phone. However, I was confused by a few of the features and settings when I first started using it, so hopefully this blog post will help answers some of the questions I originally had … as you might be having them too.

DGPS
There is a 3 position on-off switch on one side of the unit; those positions being Off, 1Hz and 10Hz. The differential (DGPS) capability is not enabled when operating at 10Hz, but is available when the switch is in the 1Hz (middle) position. However, 1Hz is not really fast enough for reliable lap timing, so what can be done?

Well, you can download the Windows drivers and the GPS View application (for Windows only) which will allow you to reconfigure the 1Hz switch setting to a frequency between 1 and 5Hz. You can find the downloads for the 818XT at QStarz Downloads page – select “GPS Receiver” as your product type and choose your exact model from the secondary (right hand) menu. There are also links to a quick quide and full user manual.

After installing the driver and application, connect your Q818XT to your computer and switch it on to the 1Hz setting. Open Settings->Control Panels and select the System control panel. Switch to the Hardware tab and look to see which LPT/COM port the 818 is listed as being connected to. Launch the GPS View application and set the appropriate COM port at the top of the window. You should then see the GPS messages scrolling in the top left panel of the window – if you don’t then you have probably selected the wrong COM port.

If you switch to the Setup tab, you can change the frequency for the middle (1Hz) switch position. Look for the section that says “Fix Update Rate” and hit the Query button. It should report 1Hz in the Data Bandwidth box to the right. Since we want 5Hz instead of 1Hz, all you need to do is change the rate in the pulldown menu from 1 to 5 and hit the Set button. That’s it, the 1Hz switch position will now operate the unit at 5Hz with full DGPS capabilities. It will remain at 5Hz until you pull the battery out of the unit or possibly until the battery runs completely flat.

Just remember to make sure you select the middle (1Hz) setting instead of the 10Hz switch position before you head out on track! In my opinion, a 5Hz refresh rate with DGPS is more valuable than a 10Hz rate without DGPS as the position reports will be both frequent enough and have a greater accuracy.

AGPS
The AGPS feature is less important for accuracy as it primarily affects how long the unit takes to get its first fix. It does this by updating its internal almanac which enables it to locate the appropriate satellites more quickly. You can use the Update button in the lower panel to download a new almanac automatically from the internet. The new almanac will last for 6 days, and you can update it as often as you like.

Bluetooth Pairing
Pairing this unit with your phone should be simple. Enable Bluetooth on your phone, switch on the Q818XT and it should show up in the list of available devices. The pairing code will be “0000” (four zeroes).

Make sure you change the “GPS receiver type” setting in RaceChrono to be “Bluetooth device” and select the QStarz 818XT as the external GPS device.

Unit Location
In order to give the unit decent line of sight with the satellites in the sky, I mount the unit on the tail of the bike. The 818XT has a rubberised bottom which is placed on the tail unit, and the whole thing is then taped to the tail.

I used a lot of tape; firstly to ensure that the receiver doesn’t fall off (?!) and secondly to try and form a waterproof barrier around the switch and the USB connector. Since the device lasts for 24-40 hours on a single charge you can switch it on before taping it to the bike, and then leave it on for the full track day.

Pre Track Day Preparation
I usually charge the unit for 2-3 hours before a track day. Using QStarz’s GPS View software, I also upload the latest almanac(which lasts for 6 days) and double-check that the 1Hz switch position is still re-mapped to 5Hz.

That’s really all you need to know about this receiver.

If you want background on using the QStarz 818XT then have a read of this post on how to set up and use a lap timer.

Update Summer 2014

You might be interested in reading a comparison between the QStarz 818XT and the Garmin Glo.

Lap Timing Part 1

One of the most useful tools to measure your progress on track is a lap timer.

A lap timer enables you to “see” how changes in your riding style, race line, tyre choice, gearing or suspension setup affect your lap times.

Normally these devices cost from a few to many hundred of pounds (or dollars) depending on which make you buy and the features that it offers.

How would you feel if I told you that you could potentially have all this lap timing capability for free?

Pretty excited, I’d imagine…

With the advent of smart phones, this is a reality because a small group of Finnish software developers created a lap timer called RaceChrono for mobile phones. It runs on Symbian (Nokia), Windows (Mobile) and Android devices. Sadly, there isn’t a version of RaceChrono that runs on iPhones so those users might want to consider getting a “cheap” Android phone to use instead.

If you have one of these phones that can run RaceChrono app then you can get a fully featured lap timer… for free. Yes.. you read that right! All you need do is to ensure is that your phone incorporates a GPS receiver or has bluetooth capability built-in to allow it to connect to an external bluetooth GPS receiver. Without some form of GPS, RaceChrono cannot work.

How it works
RaceChrono has details of over 400 tracks around the world including different track layouts for the same circuit. The track at Brands Hatch for example has two layouts; the Indy circuit or the full GP circuit.

Each track has a start/finish line recorded as well as the location of either one or two additional split time markers.

As you ride around the track, RaceChrono will use the GPS receiver to determine where you are on track (up to 10 times a second). In this way, RaceChrono is able to determine when you pass the start/finish line or any of the other split timing markers. As you do this repeatedly during your track session, RaceChrono will mark off each lap and calculate your lap and split times automatically.

In order to use RaceChrono for your track day, just choose your circuit (and track layout) from the list. If the track doesn’t exist in the list then you always have the option of adding your own track and defining the start/finish line and any additional split timing markers that you want or need.

Just before you start your session, switch the app on to record, slip the phone into your pocket or attach it securely to your bike, and you’re good to go. There is no need for any external track side timing equipment for the app to work – just clear line of sight to the satellites in the sky.

Accuracy
In fact RaceChrono works so well, that anecdotal evidence suggests that it is accurate to within a few hundreths of a second compared to the times reported by official track side timing equipment.

But, that accuracy comes at a (small) cost…

The internal GPS units built into most phones, while often very accurate, cannot sustain a high poll rate. This means that they often cannot report a position fix more frequently than once a second. When you’re travelling at 100mph (160kmh) that equates to a distance between two fixes of around 48 yards (44 metres). A GPS unit that can operate at 10Hz (polled 10 times a second) will get a fix every 4 metres when travelling at 100mph. The faster the GPS can be polled, the more accurate your lap times will be.

A further issue affecting accuracy is that the phone internal GPS receivers normally don’t have a differential capability (DGPS) built into them. If they did, it would allow them to compensate for the selective inaccuracy that the US military build into the GPS network.

You can overcome both this issues by using RaceChrono in conjunction with an external Bluetooth GPS receiver. Two popular ones are the Garmin GLO and the QStarz 818 series – these typically cost between £50-90 (US$90-150) depending on the unit.

In the case of the QStarz 818XT (which I have), the DGPS capability is disabled at 10Hz, but can be enabled by running the unit at 5Hz instead. 5Hz means a position fix every 1/5 of a second and is perfectly good enough for accurate lap times, especially since the position accuracy is enhanced by the DGPS capability being enabled.

Although you might be wondering whether to bother with the hassle and cost of an external receiver, it is worth noting that in addition to providing inherently better accuracy, you can also mount these units so that they will have a better view of the sky compared to a phone in your pocket. Popular mounting points include on/under the tail or under the fairing bubble. All you need is some gaffer/duct tape to stick the unit in place.

Relying on the internal GPS of a phone stuffed into your pocket when your body is shielding much of the sky could lead to poorer quality position fixes at certain points on the track and as a result less accurate lap and split times.

Now that we’ve covered the preliminaries, I’ll explain how the app works in more detail in Part 2 of this article.