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Preamble
Having surfed through the basics of a Car’s Steering System, the
need for Wheel Balancing/Alignment and problems that may still arise,
in this concluding part we shall glance through what else can be in store
for an average motorist………
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12)
Restoring the Steering Geometry after an Accident.
It’s
quite commonly experienced that a car involved in a bad front-end collision
doesn’t cruise straight even after claimed ‘perfect’
repairs, at astronomical costs sometimes. So I’ll take you through
a typical QnA session of this front as below :
(i) Initial Query
A few days back I had an accident. My Santro hit a pole and its front
left portion was damaged as it had a hit on the front left wheel also.
Complete Suspension Arm, Link Assy Front Stabilizer had to be replaced.
But I find now that when the steering is kept straight, with hands off
the car goes slightly to the left side. If the steering is tilted slightly
clockwise then the car moves straight.
I would like to know what could be the probable reason for this. Is it
because of wheel alignment or it has something to do with FR Chassis LH
dent that I was told has been fixed. I need your advice.
(ii) Initial Reply
To me it’s somewhat obvious that the Steering Geometry of your Car
is still upset and the main offenders could be :
1) Incorrect 'toe-in'/Wheel alignment.
2) The LH 'Wheel Base' being shorter than the RH one, by more than 5 mm
tolerance that's permissible. 'Wheel base' is the Centre-to-Centre distance
between the front and the rear wheels.
3) The LH 'Camber' setting not being within the specified range. FYI,
'Camber' is the inclination of the Wheel to the vertical and for a Car
like Santro, it's (+) 0.5 Degree to (+) 1.0 Degree. (+) means its lower
(road contact) end is inwards to the Car and correspondingly, the top
end is outwards. If it becomes zero or (-), the Car will pull to that
side even if (1) n (2) above are within limits.
Please let me know how it went with your Garage and whether your problem
has been solved.
(iii) Subsequent Response
Thank you
very much for your reply. I was anxious to know about it before visiting
the garage. It was due to incorrect 'toe -in' and is adjusted now.
(iv)
Final reply.
Although you say that the defect stands corrected via a toe-in reset,
I'll take it with a pinch of Salt - from what I have just learnt from
my own experience.
Here's what you can
do with the help of a friend, if so DIY inclined :
1) Park the Car on a level road.
2) Take at least 3-meter long measuring tape. Get your friend to hold
its beginning at the forward edge of the rear left wheel RIM, along its
horizontal center line.
3) You take the other end and measure accurately the distance between
(2) and the rear similar edge of the front left wheel rim.
4) Repeat the exercise on the other (RH) side of the Car.
5) The difference
between the two readings should not be more than 5 mm. If it is so, confront
your Garage for unsatisfactory repairs, which will show-up sooner than
later in accelerated FL Tyre wear.
6) There is another and simpler way of ascertaining the same thing, provided
you can find a level stretch of reasonably traffic free road. Accelerate
the car to about 50 kmph and shift to neutral and let it coast of its
own. Let go of the Steering Wheel for a while. If the Car was otherwise
cruising straight 'under power' starts to drift leftwards under such 'coasting',
your left side wheelbase is shorter than the right side, beyond permissible
tolerance.
13) Taking Care of your Wheels and on choosing Tyres
Query :
Which tyres would you recommend for my Maruti Esteem car? My driving is
mainly in the city with occasional trips to Pune & Panchgani.
Response :
Tyres play
a crucial role in the overall satisfactory performance of a car, including
fuel efficiency - assuming all other parameters are in their proper places.
For your kind of duty, I'd recommend that you stick to the OE Specs i.e.
"155/80-R13". Of the various brands available in the market,
I find 'Bridgestone' a good value for money, from their Ride Quality AND
'Tread Noise' points of view.
'JK Ultima' is also quite good.
Besides, whatever be their make, you must also ensure the following :
i) That they are atleast "T" Rated - given 120 kmph+ sustained
cruising speeds now afforded by most 'Express Ways'.
ii) ALL the 5-wheels must be in good 'Dynamic Balance' all the time. It's
a fallacy that the Rear/Spare ones need not be balanced.
iii) Besides above, immediately after fitting a new Set, you must get
a "4-Wheel Alignment" done at a reliable place, preferably having
the 'Infrared' type of Computerised M/C - as opposed to the now obsolete
'String' Type. In normal course of usage, it's worthwhile to get the same
redone every 10,000 km to get max pleasure/life out of one's Tyres.
iv) Last but not the least, you should have your own good quality and
easy to read 'Dial Type' Tyre Pressure Gauge (available at most Tyre/Accessories
Shops) and never rely on the wayside ones. The TP's given on the Driver
Side/'B' Pillar Sticker are "When Cold". This means BEFORE you
start Rolling. Since the latter is somewhat impractical, here's what you
can do to overcome this :
a) Buy yourself a good foot pump or better still a Battery operated one,
freely available at above shops for ~ Rs: 700/-, and do the exercise at
home atleast once a fortnight before you roll off. These can be carried
in the Car all the time, as you never know when you may need them.
b) If not interested in (a), then inflate your tyres to "+10%"
of the recommended pressure if checking at a Wayside Facility BUT use
your own Gauge, after having rolled a few kms to get there. This will
more or less ensure that they are 'down' to the correct levels when cold,
the next morning.
c) You should check/correct
your tyre pressures once a week.
I hope the foregoing will be of interest and use to you and your friends
for all times to come.
14)
Speed vs 'mileage'
Let’s take a
real life example -
Getting 21 kpl @ 60-70 kph and 18+ @ > 100 kph out of an Mpfi Zen is
as good as it can be.
The variation experienced is quite normal, for it's a well known fact
that wind resistance goes up with speed in a complex manner - starting
with square of it and going upto the power of 4 - depending on its magnitude.
In other words, say at a cruising speed of 50 kph, 40% of the engine power
may go towards over coming the rolling resistance and the remaining 60%
to overcome the wind resistance. Assume it's 5 and 7.5 = 12.5 Bhp.
Further, assuming that the rolling resistance remains more or less constant
beyond 50 kph, at 100 kph the engine will have to produce 5 + (7.5 x 4)
= 35 Bhp. So as far as the engine is concerned, for 2x the speed, it has
to produce 3x the power.
Therefore, in terms of 'Specific Fuel Consumption' defined as 'grams per
Bhp per hr' - that's how the engine sees it - its FC stands to go up by
3x but then, at 2x the speed, it also has to run for half the time to
cover the same distance - or effectively the FC stands to go up by 1.5x
to cover the same distance. In other words, if it was doing say 25 kpl
@ 50 kph, at 100 kph it stands to do ~ 17 kpl.
And mind you, the 'SFC' that we just talked about above also varies with
the absolute Bhp demanded from it - coz an ICE's 'fuel efficiency' drops
above and below its peak torque rpm.
Further, since an ICE's max rpm AND Bhp is limited, 59 Bhp in this case,
it follows that at 100 kph, it's got only 59 - 35 = 24 Bhp left to propel
it any faster and going by the above relationship, this will get used
up by another 40 kph or so - leading to its top speed 'capability' of
~ 140 kph.
To sum-up, to get the best 'FE' (as opposed to absolute Fuel Consumption/kpl)
out of your Car, cruise as close to its peak torque rpm as practicable.
15)
Some more recommended Links –
http://www.indiacar.com/infobank/old_vs_new.htm
http://www.indiacar.com/infobank/discbrakes_abs.htm
http://www.indiacar.com/infobank/artofdriving.htm
http://www.indiacar.com/infobank/takingaturn.htm
http://www.indiacar.com/infobank/mileage.htm
http://www.indiacar.com/infobank/carservice.htm
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