Changing a Car Tyre

Dad noticed my car front tyres were different in size. Maybe one was flat or whatever? No, they were indeed of different size. Here’s there specs:

Front left Β : 155/80 R13

Front right: 155/70 R13

As you can see the aspect ratio of the tyres are different. Here’s a diagram below explaining the tyre and wheels terminologies:

By F l a n k e r, CC BY 3.0

Let’s calculate the circumference of the 2 tyres

$$ \text{tyre width}_{t1} = \frac{155mm}{1000} = 0.155m $$

$$ \text{rim diameter}_{t1} = 13\text{inch} \times 0.0254 = 0.3302 m$$

$$ \text{rim radius}_{t1} = \frac{0.3302m}{2} = 0.1651m $$

$$ \text{tyre height}_{t1} = \text{tyre width} \times \text{aspect ratio} = 0.155m \times 80\% = 0.124m$$

$$ \text{tire radius}_{t1} = \text{rim radius} + \text{tyre height} = 0.1651m + 0.124m = 0.2891 $$

$$ \text{tyre circumference} _{t1}= 2 \times \pi \times \text{tyre radius} = 2 \times \pi \times 0.2891 = 1.816m$$

Lemme try to write a function for getting the tyre diameter with variables w as tyre width, a as aspect ratio and r as rim diameter.

$$f(w,a,r) = 2 \times \pi \times (\frac{r \times 0.0254}{2} + \frac{w \times 80}{1000 \times 100})$$

Let’s calculate the diameter of the second tyre:

$$ \text{tyre circumference}_{t2} = f(155,70,13) = 1.719m $$

The difference in diameter is about $$0.097m \text{ or } 9.7cm $$

Does it matter if the 2 tyres are of different sizes?

Most cars in Mauritius are front-wheel-drive (FWD) cars. My VW Polo MK3 is too. Distinction is made between Front-wheel-drive rear-wheel-drive (RWD) cars by which wheels are connected to the engine; the drivetrain to be more precise.

In RWD cars:
– The front tyres handle the steering part.
– The rear tyres are responsible to acceleration the vehicle.
– Braking is divided among front and rear tyres.

In FWD cars, all the roles are performed by the front-tyres only except for braking which both rear and front do. I am not going to discuss FWD vs RWD in this blog post.

 

Ok, I was situation that my 2 powered tyres happened to be of different size. The 2 wheels are designed in such a way that they do not spin in strict synchrony with each other. The reason is simple, imagine you are going through a corner, your inner tyres will need to cover less distance than the outer tyre. Remember our circumference equation above? If the wheels were made to rotate at the same speed, the inner wheel would slip causing loss of stability. Car’s are fitted with a differential to allow wheels to spin at different speeds while be able to power them. The disadvantage of this is that most power goes to the wheel with the least friction. If one of your drive tyre is in the air, the other drive tyre will remain still and the tyre in air will spin leaving you puzzled why the car is not moving. To solve this problem, engineers invented the limited slip differential. Think I’m going into too much details. Back to topic:

If the 2 FWD tyres are different, it shall not cause tyres to slip due to presence of an Open Differential. But the smaller tyre would be the one accelerating your car since it requires less torque to get spinning. Thus, only 1 wheel is responsible for power delivery on a total of 4 wheels. That’s kinda unfair. It is also going to have much more wear than the others. This can cause the car to tend to either left or right as i was experiencing.

IMG_20151205_144253

Do make sure that the 2 tyres connected to the drivetrain are of the same size!

To upscale or downscale?
Ok, we got a bigger tyre and a smaller tyre. Do we replace the bigger one with a new smaller one or vice versa?

First advice, have a look at your owners manual. It will have best tyre size depending on your engine size.

Putting a bigger tyre than stock might give your car better looks and top speed but you lose in terms of acceleration and also fuel economy (rumour says).

Maintaining a car needs lots of time, money and research. Take care of your car as much as you can πŸ™‚

The Lunchbox (2013)

Wonderful movie. We grow old each day. We work. Work. We are interested in Gross Domestic Product (GPD) but nothing about Gross Family Happiness. We as humans do know what we want. But government make us think we need to pump their stats so as we become “rich”. At the end, we just worked. They enjoy everything.

Anyways, back to the movie, some striking dialogues:

“We forget things if we have no one to tell themΒ to”

“The wrong train sometimes brings you to the right destination”

And yeah. In the movie, a woman complains to a guy about a delivery service. The guy says there is no fault in our system. A guy from Harvard came to audit it. Now I know from where the Mauritian mentality of importing foreign experts come from. LOL πŸ˜›

Browsing you Home directory on OS X (MacBook Air)

On most Linux desktop environment, it’s easy to browse your $HOME directory. On the MacBook Air running OS X, the link to the home directory is not listed on “Finder” on the left column.

Screen Shot 2016-02-19 at 9.05.16 PM

To add it, do the following
– Open the terminal
– Type the following

$ open ../

– Finder should now be showing all Home directories
– Drag and drop the Icon to the left sidebar

Screen Shot 2016-02-19 at 9.12.07 PM

-Enjoy! πŸ™‚

My Raspberry Pi Car Audio System with Bluetooth

After much trial and error, managed to get bluetooth AD2P profile on my Raspberry Pi which I then connected to my car auxiliary (aux) input. I followed the tutorial found here.

image

On the Raspberry Pi, I make the bluetooth in “Discoverable” mode and launch a bluez-simple-agent to make the initial connection.

$Β sudo hciconfig hci0 piscan

$bluez-simple-agent

Screen Shot 2016-02-01 at 3.47.38 PM

On my phone, just after having launched bluez-simple-agent, I can scan and connect.

image

 

And once connected, I need to link the bluetooth source to the Raspberry Pi audio output

pactl load-module module-loopback source=bluez_source.XX_XX_XX_XX_XX_XX sink=alsa_output.0.analog-stereo

I can play any songs on my phone and it plays on the car speakers πŸ˜›

Problem

After 10 – 20 secs, the sound would stop playing. Looking into /var/log/syslog, i found this

Feb 1 06:39:48 raspberrypi bluetoothd[2208]: Endpoint unregistered: sender=:1.36 path=/MediaEndpoint/HFPAG
Feb 1 06:39:48 raspberrypi bluetoothd[2208]: Endpoint unregistered: sender=:1.36 path=/MediaEndpoint/HFPHS
Feb 1 06:39:48 raspberrypi bluetoothd[2208]: Endpoint unregistered: sender=:1.36 path=/MediaEndpoint/A2DPSource
Feb 1 06:39:48 raspberrypi bluetoothd[2208]: Endpoint unregistered: sender=:1.36 path=/MediaEndpoint/A2DPSink

I don’t know yet why it happens but if i run this command just after pactl load module, it works fine πŸ™‚

$ pactl subscribe

The sound quality

Not that awesome. A direct AUX connection sounds much better. I can hear quite some background noise. Is it due to the raspberry sound card, the bluetooth adapter or just some configuration? I don’t know. Anyways, I got a working prototype for now.

Future plans

  • Add support for phone calls
  • Clean enclosure for the Raspberry Pi and cables.
  • Bypass the car radio and use an amplifier to connect to car speakers directly.
  • Use WiFi instead of Bluetooth
  • Maybe add a touch screen too πŸ˜›

Freedom and Chains

Free from physical chains. We are celebrating today, the 1st of February.

Government can at any point in time, put someone in jail for having different opinions, definition of “freedom”.

Source: zinfos974.com
Source: zinfos974.com

We are bound by chains. Written by lawyers. All laws being equal. Some more equal than others allowing “Human Rights” to be suspended.

Common ‘literate’ people can’t even read 1 single paragraph of the “Law” or “Acts” or dunno what the fuck they’re called. Yet, we are governed by it. Punished by it. Rewarded by it. Allowed to live by it.

Freedom is education. Not brainwashing.

Hack whatever you get. Learn, research. “Society” will of course not approve that. What happened to Galileo Galilei?

Be a Galileo Galilei!