How does your car take a turn smoothly - The Differential

SLK · 4th April 2006, 18:58

To further enrich the team-bhp knowledge base, I am sharing an article published on indiacar.com
The link http://indiacar.com/infobank/takingaturn.htm

I hope it is no copyright infringement as I had originally written this, to which the 3rd page was subsequently added and some changes made in presentation. (My name still appears in the credits)

The preamble to the article has not been copied and is available on the original link only.

Here goes
How does your car take a turn smoothly

The answer could be as simple as “… because I turn the Steering Wheel”.

So what happens when you turn the Steering wheel? If you are thinking that the front wheels then point in the direction you wanted them to - you are not wrong. But there is more to it than what meets the eye.

Most of us are aware that when a 4-Wheeler/Car takes a turn, to enable it go through it smoothly, its ‘outer’ wheels need to turn faster than the ‘inner’ ones and this is facilitated by the ubiquitous ‘Differential Gears’. These are visible in a Rear/4- wheel Drive Car as a round/bulbous housing between the Rear/Front drive wheels of a 2/4 Wheel Drive Car but not so on a Front Wheel Drive one – as they are then accommodated in the Main Gear Box itself next to the Engine.

So let’s start with the simple principle of Differential Gears. Look at the two adjoining/concentric circles. The inner one represents the path of the inner wheels and the outer one like wise - when a Car is on a turn. If one were to compare the ‘circumferences’ of these two circles, obviously the outer circle has a larger circumference. The difference between the Radii of the two Circles is the ‘Track’ width of a Car. Clearly, the inner wheel is ‘tracing’ the smaller circle, and hence has to travel less ‘distance’ compared to the outer wheel - which is tracing the outer/larger circle – BUT in the same time ! Now, if these two wheels were to move at same speed/Rpm, they will skid & screech but that is not what happens – thanks to the Differential Gears!

Therefore, in other words, the Differential Gears ensure that both the inner and outer wheels rotate at different rpm ‘as called for’ and yet get the power they need to maintain satisfactory ‘traction’ while going over a Curve.

So now we know why the inner wheel rotates at a lower rpm than the outer one.

Next question that arises is “what’s the difference between the Rpms’ of the two wheels and whether they ‘related’ to each other”. The answer is Yes - the rotational speeds of these two wheels are related to each other and are influenced by two factors - firstly the ‘Track’ width of the car and secondly, the ‘Turning Radius’ of the Car – depending on to what degree the Steering Wheel is turned.

Interestingly, such a ‘relationship’ is not difficult to calculate. For the sake of simplicity, let’s take the example of a Maruti 800. The vital stats here are – a) the turning radius - which we assume to be the minimum it’s capable of (4.4 meters) and ii) the front wheel ‘track’ of the car - which in its case is 1.2 meters.

Armed with above data, we can now start calculating as follows :

(1) The distance the inner wheel has to travel is the circumference on the inner circle
i.e = 2 x Pi x R meters.

Where Pi is ‘Pi’ & R is the turning radius of the inner circle or = 2 x 3.141 x 4.4 = 27.64 meters.

(2) Likewise, the distance outer wheel has to travel but keeping in mind that the turning radius here is higher i.e. the inner radius + the wheel track -

Or = 2 x 3.141 x (4.4+1.2) = 35.27 meters.

Since both these wheels complete their one full (or part circle for that matter) in same time, it’s obvious again that the outer wheel has to cover more distance in the same time.

Therefore, the ‘relation’ between the two wheels’ speeds is such that outer tyre travels/rotates (35.27/27.64) = 1.27 times faster than the inner one !

Let’s call this ratio as ‘K’.

The point to be noted here is that it’s not just the front but also the rear wheels have to travel at such different speeds.

Contd. ….3rd page on the original link (http://indiacar.com/infobank/takingaturn2.htm)

cowboy45 · 24th February 2009, 15:02

Hello,

Thanks for the information. Strange to see no comments on this article.

My car Zen Vxi 2004 (mpi) has clocked 53,000 kms today.

Service adviser at MASS told me to get axle oil changed. I think he was referring to differential oil.

Reading the above article now I understand where its used.

I did not get it changed.

My question is can I get differential oil from any auto lubes shop and get it done locally?
Just don't want to visit MASS again to save on time, fuel and extra Labor charges.

What is differential oil called in general?
Not sure if my local lube vendor would understand the term!

Raccoon · 24th February 2009, 17:13

You sure can get it done at any good garage. You'd have to raise the car on a ramp; and it seems they use some kind of "gun" to pump the oil in.

But there is one issue - if you get it done at a non MASS garage, the gun will likely have some other oil in it... and that means the oil you use will get mixed to whatever extent.

MASS will 99.9% have the same oil, which they use to fill all Marutis. But here, you'll have to trust them on the fact that they are using genuine unadulterated oil.

You should be able to get the oil at a good oil shop or a petrol pump (if you want a PSU brand or Shell). Its a thick oil... 75W90 something... cant recall exactly. Please check your manual. Again, beware of adulterated oil.

In Esteems its supposed to last 20,000 km or 2 years. Zen should be similar/same.

I get mine done at a MASS. They say they use Servo (IOC) oil.

SirAlec · 25th February 2009, 23:35

Quote:

Originally Posted by cowboy45

Hello,

Thanks for the information. Strange to see no comments on this article.

My car Zen Vxi 2004 (mpi) has clocked 53,000 kms today.

Service adviser at MASS told me to get axle oil changed. I think he was referring to differential oil.

Reading the above article now I understand where its used.

I did not get it changed.

My question is can I get differential oil from any auto lubes shop and get it done locally?
Just don't want to visit MASS again to save on time, fuel and extra Labor charges.

What is differential oil called in general?
Not sure if my local lube vendor would understand the term!

Zen doesn't use differential. It uses transaxle drive shaft. and there is no such thing as differential oil. Its just gear oil which lubricates the gearbox.

to change gear oil in zen you don't need to raise the car. just open a lid and fill with a help of a cork or a cut-off Bisleri bottle.

SLK · 26th February 2009, 00:09

Quote:

Originally Posted by SirAlec

Zen doesn't use differential. It uses transaxle drive shaft. and there is no such thing as differential oil. Its just gear oil which lubricates the gearbox.

to change gear oil in zen you don't need to raise the car. just open a lid and fill with a help of a cork or a cut-off Bisleri bottle.

Yes, deferential is a functionality, just that its in-built in the gear-box for the front wheel drive cars (or cars where engine is on the same side as the driving wheels).

So, coming to the question, changing the gear oil is the way to oil the deferential mechanism.

Oiling the axles might just mean something to like opening the axle boots and oiling the stuff.

cowboy45 · 26th February 2009, 12:26

Quote:

Originally Posted by SirAlec

Zen doesn't use differential. It uses transaxle drive shaft. and there is no such thing as differential oil. Its just gear oil which lubricates the gearbox.

to change gear oil in zen you don't need to raise the car. just open a lid and fill with a help of a cork or a cut-off Bisleri bottle.

Hello Sir,

Thanks for your reply.

Can you please tell me looking at the picture below where is the Gear oil inlet plug located?

As per the owner' manual, I could not see anything similar under the hood!

Regards

SirAlec · 27th February 2009, 00:26

Quote:

Originally Posted by SLK

Oiling the axles might just mean something to like opening the axle boots and oiling the stuff.

As I said before, it comes with its own grease and not oil.

^^^^ Cowboy.

behind the radiator you will see a small cap on a big block of alumunium. no 1 in the figure.

amitk26 · 28th February 2009, 00:06

If the turning radius is decreased by adjusting steering idler nuts will there be any problem with differential gears specially for a RWD , I am asking from PoV of my Safari

Atlblkz06 · 28th February 2009, 12:58

The differentials typically just use 75W90 gear lube//oil. Get it done at any decent place.

About the MTF: Make you sure find the right type of fluid for your car. My Manual transmission actually Automatic transmission fluid for some reason! (Tremec TR6060)

The article seems to miss out another part of turning: Ackerman angle!

The principle of Ackerman Steering is the relationship between the front inside tire and front outside tire in a corner or curve. It is the term used to define the steering geometry where the inside tire needs to turn tighter than the outside tire. This allows both tires to roll around a common point in a corner or curve. This can greatly improve cornering ability and performance. When doing any rc suspension tuning it should be one more thing to consider.
Rudolf Ackerman discovered and defined this principle early in the 19th century. Since then Ackerman Steering has had a huge impact on many different vehicles.
Ackerman Steering is used on all sizes of vehicles from full size down to scale models, no matter if it is 2wd or 4wd.
Some refer to Ackerman as the degree of toe-in or toe-out a wheel or tire has. Ackerman does have a relationship with the amount of toe-in or toe-out on your rc vehicle.
But, Ackerman Steering deals with the angle of inside tire and outside tire in a corner or curve relative to the degree of toe-in or toe-out. Will that is about as clear as mud. Let see if we can clear it all up.

Ackerman angle:

Source: What is Ackerman Steering and how it affects handling.

Rehaan · 10th August 2009, 20:34

Here is an absolutely GREAT video explaining the working of a differential.

(Start watching @1min50sec - thats where the good stuff begins)

Must Watch!

YouTube - How Differential Gear works (BEST Tutorial)

cya
R

athalaga · 11th August 2009, 10:57

Quote:

Originally Posted by Rehaan

Here is an absolutely GREAT video explaining the working of a differential.

(Start watching @1min50sec - thats where the good stuff begins)

Must Watch!

YouTube - How Differential Gear works (BEST Tutorial)

cya
R

excellent informational video was really amazed the first time I got this as a forward, was just hoping someone had the link. thanks Rehaan

anoopap · 18th September 2009, 10:00

But what about trains ?? their axle and wheels are a single solid iron piece. So how do they accommodate for changing circumference on a turn.

I looked up for answer. Found reply as

--

On a train, a right and a left wheel and the axle that connects them make up what is called a “truck.” A train truck is one solid chunk of iron. When one wheel of a train truck turns, its partner on the other side turns, too. One cannot turn without the other also turning. How, then, does a train truck go around a curve without one wheel slipping or skidding? Look closely at a train “truck” and you can see that each wheel, outside the rim or flange that keeps it on the track, is tapered or sloped. It is smaller in diameter at the outside edge than it is next to its inside rim. So when the train rounds a curve, it tends to “hug” the outside of the curve. The outside wheel of the truck rides where it is largest in diameter – next to its rim. The rim keeps the wheel from rolling off the track.

On the other side, which is the inside of the curve, the truck rides at its smallest diameter. So the inside wheel of the truck travels a shorter distance than the outside wheel. When the track straightens, the wheels will move right or left until both wheels travel the same distance with each rotation of the truck. But the truck may have to move left and right a little for the wheels to find that position that makes each of them move the same distance with each rotation of the truck. The squealing and screeching that you hear when a train goes by slowly is mostly the wheels trying to find that position on the track where the wheel on the left side travels the same distance as the wheel on the right side.

Do the wheels wear from seeking a position where left and right wheels travel differing distances? Yes! So from time to time a train truck must be returned to a special shop where the tapered part of each wheel is heated and pressed off, and a new “sleeve” with a restored taper is pressed onto the old wheel. Quite different from changing the rubber tire on a car!

Source: Science Fun: Differential

Now im clear.

Rehaan · 18th September 2009, 17:02

Man that is a superb peice of information anoopap.

Originally i thought it would just be allowed to slip, since trains dont really take such sharp turns, but this is such an elegant and simple solution!

Thanks,
R

FlatOut · 19th August 2013, 19:22

I came across this video elsewhere and was about to post on team-bhp but thought I'd do a quick search first - and here it already is. Best explanation of a differential I've ever seen.

Quote:

Originally Posted by Rehaan

Here is an absolutely GREAT video explaining the working of a differential.

(Start watching @1min50sec - thats where the good stuff begins)

Must Watch!

YouTube - How Differential Gear works (BEST Tutorial)

cya
R

mchanna · 19th August 2013, 19:54

What an amazing piece of information. Just wondering is it the same technique used for AWD?

4th April 2006, 18:58	#1
SLK Senior - BHPian Join Date: Feb 2004 Location: Nomad Posts: 1,798 Thanked: 1,417 Times	How does your car take a turn smoothly - The Differential To further enrich the team-bhp knowledge base, I am sharing an article published on indiacar.com The link http://indiacar.com/infobank/takingaturn.htm I hope it is no copyright infringement as I had originally written this, to which the 3rd page was subsequently added and some changes made in presentation. (My name still appears in the credits) The preamble to the article has not been copied and is available on the original link only. Here goes How does your car take a turn smoothly The answer could be as simple as “… because I turn the Steering Wheel”. So what happens when you turn the Steering wheel? If you are thinking that the front wheels then point in the direction you wanted them to - you are not wrong. But there is more to it than what meets the eye. Most of us are aware that when a 4-Wheeler/Car takes a turn, to enable it go through it smoothly, its ‘outer’ wheels need to turn faster than the ‘inner’ ones and this is facilitated by the ubiquitous ‘Differential Gears’. These are visible in a Rear/4- wheel Drive Car as a round/bulbous housing between the Rear/Front drive wheels of a 2/4 Wheel Drive Car but not so on a Front Wheel Drive one – as they are then accommodated in the Main Gear Box itself next to the Engine. So let’s start with the simple principle of Differential Gears. Look at the two adjoining/concentric circles. The inner one represents the path of the inner wheels and the outer one like wise - when a Car is on a turn. If one were to compare the ‘circumferences’ of these two circles, obviously the outer circle has a larger circumference. The difference between the Radii of the two Circles is the ‘Track’ width of a Car. Clearly, the inner wheel is ‘tracing’ the smaller circle, and hence has to travel less ‘distance’ compared to the outer wheel - which is tracing the outer/larger circle – BUT in the same time ! Now, if these two wheels were to move at same speed/Rpm, they will skid & screech but that is not what happens – thanks to the Differential Gears! Therefore, in other words, the Differential Gears ensure that both the inner and outer wheels rotate at different rpm ‘as called for’ and yet get the power they need to maintain satisfactory ‘traction’ while going over a Curve. So now we know why the inner wheel rotates at a lower rpm than the outer one. Next question that arises is “what’s the difference between the Rpms’ of the two wheels and whether they ‘related’ to each other”. The answer is Yes - the rotational speeds of these two wheels are related to each other and are influenced by two factors - firstly the ‘Track’ width of the car and secondly, the ‘Turning Radius’ of the Car – depending on to what degree the Steering Wheel is turned. Interestingly, such a ‘relationship’ is not difficult to calculate. For the sake of simplicity, let’s take the example of a Maruti 800. The vital stats here are – a) the turning radius - which we assume to be the minimum it’s capable of (4.4 meters) and ii) the front wheel ‘track’ of the car - which in its case is 1.2 meters. Armed with above data, we can now start calculating as follows : (1) The distance the inner wheel has to travel is the circumference on the inner circle i.e = 2 x Pi x R meters. Where Pi is ‘Pi’ & R is the turning radius of the inner circle or = 2 x 3.141 x 4.4 = 27.64 meters. (2) Likewise, the distance outer wheel has to travel but keeping in mind that the turning radius here is higher i.e. the inner radius + the wheel track - Or = 2 x 3.141 x (4.4+1.2) = 35.27 meters. Since both these wheels complete their one full (or part circle for that matter) in same time, it’s obvious again that the outer wheel has to cover more distance in the same time. Therefore, the ‘relation’ between the two wheels’ speeds is such that outer tyre travels/rotates (35.27/27.64) = 1.27 times faster than the inner one ! Let’s call this ratio as ‘K’. The point to be noted here is that it’s not just the front but also the rear wheels have to travel at such different speeds. Contd. ….3rd page on the original link (http://indiacar.com/infobank/takingaturn2.htm) Last edited by SLK : 4th April 2006 at 19:01.
	(1) Thanks

24th February 2009, 15:02	#2
cowboy45 BHPian Join Date: Apr 2006 Location: NOIDA Posts: 77 Thanked: 35 Times	Hello, Thanks for the information. Strange to see no comments on this article. My car Zen Vxi 2004 (mpi) has clocked 53,000 kms today. Service adviser at MASS told me to get axle oil changed. I think he was referring to differential oil. Reading the above article now I understand where its used. I did not get it changed. My question is can I get differential oil from any auto lubes shop and get it done locally? Just don't want to visit MASS again to save on time, fuel and extra Labor charges. What is differential oil called in general? Not sure if my local lube vendor would understand the term!
	() Thanks

24th February 2009, 17:13	#3
Raccoon Senior - BHPian Join Date: Jan 2008 Location: Poona Posts: 1,851 Thanked: 116 Times	You sure can get it done at any good garage. You'd have to raise the car on a ramp; and it seems they use some kind of "gun" to pump the oil in. But there is one issue - if you get it done at a non MASS garage, the gun will likely have some other oil in it... and that means the oil you use will get mixed to whatever extent. MASS will 99.9% have the same oil, which they use to fill all Marutis. But here, you'll have to trust them on the fact that they are using genuine unadulterated oil. You should be able to get the oil at a good oil shop or a petrol pump (if you want a PSU brand or Shell). Its a thick oil... 75W90 something... cant recall exactly. Please check your manual. Again, beware of adulterated oil. In Esteems its supposed to last 20,000 km or 2 years. Zen should be similar/same. I get mine done at a MASS. They say they use Servo (IOC) oil. Last edited by Raccoon : 24th February 2009 at 17:18.
	() Thanks

28th February 2009, 00:06	#8
amitk26 Senior - BHPian Join Date: Jul 2008 Location: Bangalore Posts: 2,089 Thanked: 716 Times	If the turning radius is decreased by adjusting steering idler nuts will there be any problem with differential gears specially for a RWD , I am asking from PoV of my Safari Last edited by amitk26 : 28th February 2009 at 00:07.
	() Thanks

28th February 2009, 12:58	#9
Atlblkz06 BHPian Join Date: Jan 2009 Location: Atlanta Posts: 164 Thanked: 25 Times	The differentials typically just use 75W90 gear lube//oil. Get it done at any decent place. About the MTF: Make you sure find the right type of fluid for your car. My Manual transmission actually Automatic transmission fluid for some reason! (Tremec TR6060) The article seems to miss out another part of turning: Ackerman angle! The principle of Ackerman Steering is the relationship between the front inside tire and front outside tire in a corner or curve. It is the term used to define the steering geometry where the inside tire needs to turn tighter than the outside tire. This allows both tires to roll around a common point in a corner or curve. This can greatly improve cornering ability and performance. When doing any rc suspension tuning it should be one more thing to consider. Rudolf Ackerman discovered and defined this principle early in the 19th century. Since then Ackerman Steering has had a huge impact on many different vehicles. Ackerman Steering is used on all sizes of vehicles from full size down to scale models, no matter if it is 2wd or 4wd. Some refer to Ackerman as the degree of toe-in or toe-out a wheel or tire has. Ackerman does have a relationship with the amount of toe-in or toe-out on your rc vehicle. But, Ackerman Steering deals with the angle of inside tire and outside tire in a corner or curve relative to the degree of toe-in or toe-out. Will that is about as clear as mud. Let see if we can clear it all up. Ackerman angle: Source: What is Ackerman Steering and how it affects handling. Last edited by Atlblkz06 : 28th February 2009 at 13:04.
	(1) Thanks

18th September 2009, 10:00	#12
anoopap BHPian Join Date: Feb 2009 Location: Trivandrum Posts: 56 Thanked: 22 Times	What about train differentials ?? But what about trains ?? their axle and wheels are a single solid iron piece. So how do they accommodate for changing circumference on a turn. I looked up for answer. Found reply as -- On a train, a right and a left wheel and the axle that connects them make up what is called a “truck.” A train truck is one solid chunk of iron. When one wheel of a train truck turns, its partner on the other side turns, too. One cannot turn without the other also turning. How, then, does a train truck go around a curve without one wheel slipping or skidding? Look closely at a train “truck” and you can see that each wheel, outside the rim or flange that keeps it on the track, is tapered or sloped. It is smaller in diameter at the outside edge than it is next to its inside rim. So when the train rounds a curve, it tends to “hug” the outside of the curve. The outside wheel of the truck rides where it is largest in diameter – next to its rim. The rim keeps the wheel from rolling off the track. On the other side, which is the inside of the curve, the truck rides at its smallest diameter. So the inside wheel of the truck travels a shorter distance than the outside wheel. When the track straightens, the wheels will move right or left until both wheels travel the same distance with each rotation of the truck. But the truck may have to move left and right a little for the wheels to find that position that makes each of them move the same distance with each rotation of the truck. The squealing and screeching that you hear when a train goes by slowly is mostly the wheels trying to find that position on the track where the wheel on the left side travels the same distance as the wheel on the right side. Do the wheels wear from seeking a position where left and right wheels travel differing distances? Yes! So from time to time a train truck must be returned to a special shop where the tapered part of each wheel is heated and pressed off, and a new “sleeve” with a restored taper is pressed onto the old wheel. Quite different from changing the rubber tire on a car! Source: Science Fun: Differential Now im clear.
	(8) Thanks

18th September 2009, 17:02	#13
Rehaan Team-BHP Support Join Date: Feb 2004 Location: Bombay Posts: 24,196 Thanked: 36,071 Times	Man that is a superb peice of information anoopap. Originally i thought it would just be allowed to slip, since trains dont really take such sharp turns, but this is such an elegant and simple solution! Thanks, R
	() Thanks

19th August 2013, 19:54	#15
mchanna BHPian Join Date: Dec 2006 Location: pune Posts: 78 Thanked: 53 Times	Re: How does your car take a turn smoothly - The Differential What an amazing piece of information. Just wondering is it the same technique used for AWD?
	() Thanks