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  : 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.

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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 🙂

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.

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

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.

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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 😛

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 🙂

$ 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 😛

My Car: Volkswagen Polo Mk3 (6N)

I present to you my new “old” car. Here you go:

Exterior

The Front

IMG_20151205_144245

The back

Volkswagen Polo Mk3

The Rims

I must say it is one of the ugliest rims ever designed. No money to put alloy wheels for now :(.
IMG_20151205_144253

 

Interior

The Steering Wheel

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No Power Steering in this car. Such a pain to get out from home or to park it back. For my driving test, I learned to park using Power Steering and passed the test using Power Steering. Now I gotta learn how to park all over again and get laughed at for making lots of to and fro movements as compared to other drivers (including ladies ones) 🙁

But once the car is moving, the steering wheel is responsive and smooth like butter. No vibrations whatsoever. The height can also be adjusted which is a plus.

The Turn Signals

Since it’s a german car, It’s found on the left side of the steering wheel. Why can’t they put it on the right side? Cost issues? You are supposedly be selling “luxury” cars for premium a price but you can’t switch the signal levers for left-hand drive countries? I bet Japanese car do invert theirs.

I accidentally switched on my windshield wipers few times when I was supposed to put my full bean or signal my actions. But with habit it’ll be fine i guess.

IMG_20151205_121746

Manual Transmission

I wanted a manual transmission to really understand the car I was driving. To learn how to drive. To be economic. To have greater control. What could be better than that? It got a 5 speed gearbox.

Yesterday I went to PORLWI by Light festival and got stuck in a huge traffic jam through Caudan.

But I managed to survive it, park the car (took like 10 mins), walk around then return home happily 😀

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Side mirrors

The side mirrors position are controlled electrically. However it doesn’t fold in and out automatically.

IMG_20151205_122850

Light controls

Japanese cars usually have the controls on the turn signal levers. In this car, we have a rotary switch to activate the light beam. For full beam, just pull the turn signal lever.

 

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Accessories

 

IMG_20151205_121824

Radio

It got a Pioneer AM/FM radio, CD player installed. No fucking AUX port. Such a disappointment for me for not being able to play my own MP3. Can’t even read a CD-RW that I bought yesterday. Thinking of

  1. replacing the whole radio set with a new one with Bluetooth enabled
    • Rs 4500 – Rs 5000 locally
    • Rs 800 – 2000 from eBay after 2/5 weeks
  2. Buying an FM transmitter
    • Rs ~700 locally
    • Rs ~300 on eBay after 2/5 weeks

Any advice?

Other

Engine

It’s a 1043 cc. Just enough to get moving and not get speeding tickets 😉

Automobile layout

It’s a Front-Wheel Drive (FWD) car. Don’t expect to do “drifts” with this car.

Comfort

The driver’s and front passenger seats are very comfortable even on crappy roads. The shock absorbers seem to be doing their job perfectly. Didn’t have the opportunity to sit at the back while someone is driving. Sister says it’s not that bad.

It’s a relatively quiet ride too. The engine noise don’t infiltrate the cabin too much.

Pride of ownership

You’d always want to buy a car from someone who treats his car well. The car still had the owners manual in the glovebox which is an excellent sign of a responsible owner. The car was very clean in and out.

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Even the original Volkswagen key ring holder was still their as well as the second key.

Summary

Fully functional car. Almost everything is manual and unassisted. Can’t really complain for lack of AC,power steering, central lock, power windows for the price (Rs 70 – 80k) and age (MR 96).

Great car 😀

Think my next car will be a Volkswagen Polo MK4 (9N3) or later or a KIA Rio. But that’ll take a while 😛

Got the Driving License

Started the journey to start back in July 2011 by first Setting the Oral Test for Driving License.

Then passed the theoretical Oral exam like a boss. It’s just another exam afterall :3

July 2014, went for first practical test. Failed road test but managed somehow to pass the parallel and reverse parking.

October 2014, failed road test.

February 2015, failed road test again.

June 2015 finally managed to pass and got the driving permit 😀

My driving was still mediocre IMO. Car stalled on few occasions, car going slightly back on uphills while going off etc. The police officer said my driving was OK but most importantly, I didn’t breach any of Highway Codes i.e. I respected all white lines, yellow boxes, took signals from police officers, signaled my actions using flashers and hand.

The police officer was great. He was not just sitting mouth shut and just talk when something was wrong. He kept talking about stuffs from beginning till the end. He was friendly. That’s really helpful to relieve stress and give the best in that difficult situation.

Anyways, I end here. In total, I think I spent around Rs 15,000 – 22,000 in the process since 2014. Each driving session costs me Rs 350 at Port-Louis. Rs 250 to the instructor and Rs 100 to travel to Port-Louis via bus.

Want a Heavy Truck License now :3