Windows – To Roll Them Down Or Not

Windows – To Roll Them Down Or Not

People have often asked me, if I keep my windows rolled down or not, and why I roll them down.

There is a general tendency to reach for the AC as soon as you start the car, which I have strongly debated against.

This is my view point after doing some practical research on my car, stretched over a distance of 12 kms ( office to home ) and a drive time of 30 to 45 mins with top speed of 45kmph ( city traffic ) in temperatures of about 30+ ° C

I have done this drive over a period of 20 days and clocked each reading, both ways, in multiple settings, i.e. with the AC on, and with windows rolled down, at the same time period of the journey from Home – to – Work and Back Home.

The Gyan behind the debate and then the tabulated results

Just to Quote, there was this study done by the Society of Automobile Engineers ( SAE) which found that driving with the AC on and windows rolled up, actually only reduced the fuel consumption by 10% while driving with your windows down, decreased the fuel efficiency by almost 20%.

Hard to know how did they calculate and benchmark the fuel efficiency in the first place

That’s why I did my own benchmarking on my Hyundai i20, standard 1400cc Diesel engine.

As a general inference from the data I collected, I found that driving consistently over speeds of 60 to 70Kmph, then it’s advisable to roll up the windows and turn on the AC.

Reason, the engine is already powered up, and is capable of running the AC unit, without having to produce additional power just for the AC compressor. Add to this, at higher speeds, the drag (wind resistance) would be higher if the windows were rolled down, since the wind would enter the vehicle rather than flowing outwards. Besides at higher speeds  the higher drag could destabilize the vehicle compromising safety.

2^nd scenario, if you are cruising in the city, like the testing I did, then it would be advisable to roll down the windows and let in some air. At these low speeds, the engine develops lesser power, which isn’t enough to run the compressor. If the AC is turned on, then there is an additional load on the engine directly resulting in additional fuel consumption. At these lower speeds, the drag coefficient isn’t high enough to alter the stability and fuel efficiency of the vehicle

While you guys would still argue about the best option, the trick is to optimize both situations and alternate between them.

Condition	Week	Day	Kms	Drive Time	Avg Speed	Fuel Consumed	Inference
AC is ON, Windows are Rolled UP	1	1	24	0:45:00	32	14	Turned on the Ac as soon as I started the Car, till I entered the office parking and same while returning
		2	24	0:52:00	27.69
		3	24	0:31:00	46.45
		4	24	1:05:00	22.15
		5	24	1:10:00	20.57
Ac = OFF Windows = Rolled Down	2	6	24	0:51:00	28.24	17.5	Never turned on the Ac throughout the drive
		7	24	0:40:00	36
		8	24	0:50:00	28.8
		9	24	0:48:00	30
		10	24	1:02:00	23.23
Onward: AC = OFF Return: AC = ON	3	11	24	0:45:00	32	16.5	Slightly better than the below figures since the onward drive is slightly uphill, and most a third of the return journey was cruising downhill
		12	24	0:55:00	26.18
		13	24	0:50:00	28.8
		14	24	0:52:00	27.69
		15	24	0:44:00	32.73
Onward: AC = ON Return: AC = OFF	4	16	24	1:03:00	22.86	15	Very Close to the   mileage with AC on, because the Ac was turned on immediately on turning on the Vehicle and the road was uphill as well.

Know Your Tyre - Basic Safety

Understanding your Tyre and Basic Safety

In the interest of the Discussion I was having with a colleague about tyres and the pressure that needs to be maintained.

I thought I might as well pen down my learning and pass it to the guys who would like to know the same.

Article dedicated to my Hyundai i20

  

Introduction

Past studies have shown that simple tasks like maintaining proper tyre pressure, driving within the load limits, basic tyre inspection for cuts and cracks or irregularities are some of the most important things you can do which will certainly go a long way in avoiding a tyre failure and resultant accidents.

These activities carried out regularly, along with other activities will go a long way in

1.       Improving the handling

2.       Avoid Breakdowns and Accidents

3.       Improve Fuel Efficiency

4.       Increase the life of your Tyres

Tyre Information You Must Know

1.       Temperature Resistance

2.       Traction

3.       Thread Wear

4.       Max Load Capacity

5.       Speed Symbol

6.       Manufacturing Date

How to Read Your Tyre

Tyre Markings – Know Your Tyre

Temperature Resistance

These letters indicates a tyre's resistance to heat.

From highest to lowest, a tyre's resistance to heat is graded as "A", "B", or "C".

Symbol	Area
A	Hot Area
B	Normal Area
B	Cold Area

Traction

This letter indicates a tyre's ability to stop on wet pavement.

A higher graded tyre should allow you to stop your car on wet roads in a shorter distance than a tyre with a lower grade.

Traction is graded from highest to lowest as "AA","A", "B", and "C".

Traction Indicator

Max Load Capacity and Tyre Speed Symbol

Number indicates the maximum load that can be carried by the tyre. 

Symbol indicates the maximum Speed at which a tyre is designed to be driven for extended periods of time.

Code	km/h	Code	km/h	Code	km/h	Code	km/h
A1	5	B	50	L	120	U	200
A2	10	C	60	M	130	H	210
A3	15	D	65	N	140	V	240
A4	20	E	70	P	150	Z	over 240
A5	25	F	80	Q	160	W	270
A6	30	G	90	R	170	(W)	over 270
A7	35	J	100	S	180	Y	300
A8	40	K	110	T	190	(Y)	over 300

Speed Indicator Chart

Code	Weight -Kgs	Code	Weight -Kgs	Code	Weight -Kgs	Code	Weight -Kgs	Code	Weight -Kgs
60	250	74	375	88	560	102	850	116	1,250
61	257	75	387	89	580	103	875	117	1,285
62	265	76	400	90	600	104	900	118	1,320
63	272	77	412	91	615	105	925	119	1,360
64	280	78	425	92	630	106	950	120	1,400
65	290	79	437	93	650	107	975	121	1,450
66	300	80	450	94	670	108	1,000	122	1,500
67	307	81	462	95	690	109	1,030	123	1,550
68	315	82	475	96	710	110	1,060	124	1,600
69	325	83	487	97	730	111	1,090	125	1,650
70	335	84	500	98	750	112	1,120
71	345	85	515	99	775	113	1,150
72	355	86	530	100	800	114	1,180
73	365	87	545	101	825	115	1,215

Load Carrying Capacity Indicator

Manufacturing Date

Tyres carry a DOT number on the sidewall that gives a production date.  

Since the year 2000 the numbers consist of 4 digits instead of 3. 

The first two digits indicate the calendar week of production and the next two the year of production.

Eg: 2413 – the tyre was manufactured in the 24^th week of 2013.

For tyres manufactured in the 1990's there is a little triangle ∆ after the DOT code. Eg: 4 2 8 ∆  - the tyre was manufactured in the 42^nd week of 1998.

Steps To Maintain A Proper Tyre Condition

Ensure Proper Tyre Pressure. Just looking at the tyre’s wouldn’t suffice, your eyes might deceive you.

Rely on a proper Gauge to check tyre pressure.

Tip: Ensure you check the air pressure every time you fill fuel. Any slight pull to either side, is an indicator of tyres not being at their optimum pressure.

Tyre Rotation

Tyre rotation or rotating tyres is the practice of moving automobile wheels and tyres from one position on the car, to another, to ensure even tyre wear.
Tyre wear is uneven for any number of reasons. Even tyre wear is desirable to maintain consistent performance in the vehicle and to extend the overall life of a set of tyres.

Tyre Rotation Pattern

Some of the Reasons for Tyre Wear

By design, the weight on the front and rear axles differs which causes uneven wear
With the majority of cars being front-engine cars,

·         The front axle typically bears more of the weight.

·         Front wheel drive vehicles also have the differential in front, adding to the weight, with a typical weight distribution of no better than 60:40

·         This means, all else being equal, the front tyres wear out at almost twice the rate of the rear wheels, especially when factoring the additional stress that braking puts on the front tyres

Thus, tyre rotation needs to occur more frequently for front-wheel drive vehicles.
For rear wheel drive vehicles, the weight distribution between front and back approaches 50:50.

Tyre Wear

Always check for Tyre Wear and Thread Depth. You can easily do a visual check which is also called the 1 Rupee Coin Test
Illustrated below in the diagram.
Insert the coin between the threads, and if the Rupaih in hindi is hidden, you are good to go, else if its visible, its Time to Change the Tyre.
Never go in for Re-Threaded Tyres

Summary

3 Golden Rules

1.       Inflate

a.       Check your tyre pressure Regularly

2.       Rotate

a.       Rotate the tyres every 8000kms

3.       Inspect

a.       Routinely look for signs of Damage and Thread Wear