Optimum ground clearance of a Car? & how it is measured...

[Rehaan]

Ok,

Let me just get something straight here. When you look at a quoted ground clearance figure in a magazine or wherever it does NOT accurately indcate how likely it is that your car will bottom out on a speedbump.
For example, it is possible that a car with a GC150mm will not touch a speedbreaker that another car with GC170mm touches!

Why? - well, GC is measured between the lowest hanging point of the car to the ground. The lowest point usually tends to be the bottom of the differential (or the exhaust system.)
Now, keep in mind that the differential is directly between two drven wheels, which means hitting the differential on a speedbreaker is an almost impossible task.

So since that is eliminated, what are we left with as a point of reference for GC? Nothing.

Usually when a car hits on a breaker, it hits somewhere between the front and rear wheels. This is where measurements should be taken for "speedbreaker ground clearance" imo!!

Its illinformed to assume that a octavia is more likely to hit a breaker than an esteem (134mm vs 160mm), because all that is likely to mean is that an octavia's lowest point is 26mm lower than the esteem's lowest point.
Now since Rtech says he has not had major problems with the octi bottoming out, i cant help but to assume that it has just one really low (134mm) point, and the rest reasonably higher.

cya
R

ps - GTO, C-class is apparently 130mm, any problems? (although i think it is overall a lower car, hence would still be a bit of a problem)

[iceman91]

also the wheel base guys....that counts a lot. my baleno is higher then the sonata and i know a number of places where the baleno scrapes it underside and the sonata does not even touch.

[Rehaan]

Originally Posted by iceman91

also the wheel base guys....that counts a lot. my baleno is higher then the sonata and i know a number of places where the baleno scrapes it underside and the sonata does not even touch.

Hey Iceman,

The wheelbase is another factor indeed...especially in more of a "rural" setting. However, this example is kindof the opposite to the general logic that might be applied... (take SWB jeeps as an example)

Also, when you say your baleno is higher than the sonata....how are you judging that?

cya
R

[skamb]

So, if the car has longer wheel base AND the lowest GC is somewhere the middle of the body, then typically the car will have its wheels before and after the speed breakers and bound to scrap the middle part. Look at the diagram below. @ is wheels and ^ is speed breaker (I could not draw much better :-))

______________
_@____^____@_


On the other hand, if the lowest GC is on the axle side or very near to the wheels, there is no problem then.


But how to know where is the lowest GC of a car? . We can't expect that info from the sales staff

[Rtech]

Spot on with the explaination there rehaan. Going by figures alone will not give you an accurate representation of the "real world" GC.

But how to know where is the lowest GC of a car? . We can't expect that info from the sales staff

Just bend down and take a looksi under the car. The lowest hanging point would be the point at which the ground clearance is measured.

[navin]

SUVs are now coming with written warning about roll overs. ideally the CG of a car should be in the same plane as the axles. this is not realistically possible with the possible exception of the HumVee. Also wider cars have less roll. in fact Daimler benz got the A class to pass the Elk test by using wider tyres. as far as potholes and speed breakers go the entire suspension has to be considering holisitically. stiffness, independance, cross supports, shock absorbers, and height. From what i have learnt about speed breakers is that there is a LAW dictating the max height and width and H/W ratio and even location of a speed breaker but as is true with everything else there is poor execution of this law. Our traffic dept has great laws. they even have a law governing those large grills you see on tata sumos and toyota quallises. execution is the key.

[Rehaan]

Originally Posted by navin

From what i have learnt about speed breakers is that there is a LAW dictating the max height and width and H/W ratio and even location of a speed breaker

The TMC had then stated it would reassess and level all the speedbreakers as per Indian Road Congress standards, which is four inches in height and 3.5 metres in width.

Source

4 inches!! hahaha..wouldnt that be a dream!
cya
R

[man23ish]

Originally Posted by skamb

So, if the car has longer wheel base AND the lowest GC is somewhere the middle of the body, then typically the car will have its wheels before and after the speed breakers and bound to scrap the middle part. Look at the diagram below. @ is wheels and ^ is speed breaker (I could not draw much better :-))

______________
_@____^____@_

Skamb, I am getting impressed by you everyday all your topics and postings are thought provoking, you got the problem spot on. The wheel-base and ground clearance both come into play when dealing with speed breakers. My friends maruti 800 would glide over speed-breakers that my zen would scrape.

[speedsatya]

Originally Posted by dceite

whats the problem with raised ride heigt rtech??

i had to increase my ride ht in the rear by using rubber pads as my tire used to touch the body with 2 people on board.
as a result,i have to be more careful on turns as the car does tend to oversteer.

same with the corolla

[sanket12]

well i would say definately 170mm or more.... espically with the work going on on the highways....

[muni]

Rehaan has said it quite rightly that almost in most of the cases it is the differential which is the lowest point of the vehicle that hangs down..and GC alone may not be the only point!

we are discussing speed breakers arent we? one important point to consider is that the load in the vehicle( how many ppl ) and the speed at which you go over the speead breaker may cause the suspension to get activated and the body may dip a bit along with the tyres which may get compressed a bit..this may have something to do with the actual scraping..

Assuming a speed breaker is like this:
A) ^ i.e, 2.5 feet wide in cross section(profile view) and 1.5 feet heigh
b) 4 feet wide in cross section(profile view) and 1.5 feet high

The 4 wheeler which goes over the speed breaker is more prone to scrape its body if it is point A. 2.5 feet wide/1.5 feet high

[skamb]

Originally Posted by man23ish

Skamb, I am getting impressed by you everyday all your topics and postings are thought provoking, you got the problem spot on. The wheel-base and ground clearance both come into play when dealing with speed breakers. My friends maruti 800 would glide over speed-breakers that my zen would scrape.

Thanks man23ish, These are my car research queries and you guys are doing great in providing the inputs. Thanks to you all :-)

[man23ish]

Originally Posted by skamb

Thanks man23ish, These are my car research queries and you guys are doing great in providing the inputs. Thanks to you all :-)

Are you an automobile engineer doing some research for a PHD??

[Deeps]

Its strange how most people think that its the silencer that scrapes the bumps. But in reality, in mots cases, its the underbody that gets scraped.

[speedsatya]

Originally Posted by Rehaan

Ok,

Let me just get something straight here. When you look at a quoted ground clearance figure in a magazine or wherever it does NOT accurately indcate how likely it is that your car will bottom out on a speedbump.
For example, it is possible that a car with a GC150mm will not touch a speedbreaker that another car with GC170mm touches!

Why? - well, GC is measured between the lowest hanging point of the car to the ground. The lowest point usually tends to be the bottom of the differential (or the exhaust system.)
Now, keep in mind that the differential is directly between two drven wheels, which means hitting the differential on a speedbreaker is an almost impossible task.

So since that is eliminated, what are we left with as a point of reference for GC? Nothing.

Usually when a car hits on a breaker, it hits somewhere between the front and rear wheels. This is where measurements should be taken for "speedbreaker ground clearance" imo!!

Its illinformed to assume that a octavia is more likely to hit a breaker than an esteem (134mm vs 160mm), because all that is likely to mean is that an octavia's lowest point is 26mm lower than the esteem's lowest point.
Now since Rtech says he has not had major problems with the octi bottoming out, i cant help but to assume that it has just one really low (134mm) point, and the rest reasonably higher.

cya
R

ps - GTO, C-class is apparently 130mm, any problems? (although i think it is overall a lower car, hence would still be a bit of a problem)

,hey rehaan ,
that was terrific.ur explanation was spot-on.hehe i always used to wonder about these cars with 130mm Gc do not have problems ,while my zen with 165mm GC scraped everything that is raised along the road.