[condor]

Originally Posted by sumannandy

Innova has a ground clearance of 170 mms, same as Ritz, and less than beat(175mm), .. Does that mean that Ritz and Beat are as efficient (or better) than Innova in bad roads (Rohtang pass types) or there is more to this story?.

What is the wheel base ? GC is just one dimension to this. WB, track measurements will also affect things.

The old Sumo has only about 170mm of GC. Does it make it bad ?

[sgiitk]

What is the quote GC figure. The height of the lowest part of the car above the ground. In fwd cars this point is almost invariably the steering linkage between the wheels. This will ride up and down with the wheel and is thus irrelevant. As mentioned by condor other parameters,like wheel base, softness of the springs, etc. have a greater role.

[vharihar]

Recently I did some math modeling of ground clearance and wheelbase and came up with a figure of merit that one can consider when comparing vehicles, especially as regards to their underbody's likelyhood of scraping speed-breakers. I would like to publish it somewhere in India. Any idea what would be a good technical semi-technical place where I can publish it. Which magazine/journal?

Any suggestions?

[Crazy4Power]

How the Ground Clearance is measured & reported in SUV, whether it is measured in Laden or unladen condition ?

[scythian]

Originally Posted by vharihar

Recently I did some math modeling of ground clearance and wheelbase and came up with a figure of merit that one can consider when comparing vehicles, especially as regards to their underbody's likelyhood of scraping speed-breakers. I would like to publish it somewhere in India. Any idea what would be a good technical semi-technical place where I can publish it. Which magazine/journal?

Any suggestions?

Thanks for your work. Would you be willing to share the metric/figure of merit that you came up with. I am looking to buy a car and GC is definitely a factor. I will completely understand if you would like to publish it first. Unfortunately I am not aware of any potential journals where you would submit something like this.

[Waspune]

It's not only about the ground clearance. The suspension also plays an important part as far as scraping in concerned. For eg: Abarth Punto with 155 mm of GC might still maintain its GC even after having 4 people on board owing to stiffer suspension while Honda City's GC might fall by around 10 mm with 4 people onboard owing to softer suspension.

[vharihar]

Originally Posted by scythian

Thanks for your work. Would you be willing to share the metric/figure of merit that you came up with. I am looking to buy a car and GC is definitely a factor. I will completely understand if you would like to publish it first. Unfortunately I am not aware of any potential journals where you would submit something like this.

I finally found a place to publish it. See http://www.grin.com/en/e-book/358591...for-navigating

As others have said, suspension also plays a role but I have not modeled it in a first order analysis. In any case, if the speed bump is navigated fairly slowly, then the suspension's effect is minimal (as in a quasi-static analysis)

Regarding your query, I am stating below the Figure Of Merit equation (FOM). For details, you can refer to the paper. The FOM equation is:

L_FOM = w*(2 - g/h)

where :
- 'w' is the wheelbase
- 'g' is the ground clearance
- 'h' is the height of the speed-breaker

You likely won't know 'h' and it is anyway non-standard, so what you can do is to plot a graph of the above equation for a range of values of 'h', like say 100 mm to 250 mm, with 'h' being on the x-axis and L_FOM on the y-axis, similar to Figure 5 in my paper. Plot this for various models you are considering. The plot that is the lowest, is the best one (ie. it is least susceptible to scraping speed-breakers)

Thanks,
Venkat

[vharihar]

Originally Posted by vharihar

...As others have said, suspension also plays a role but I have not modeled it in a first order analysis. In any case, if the speed bump is navigated fairly slowly, then the suspension's effect is minimal (as in a quasi-static analysis)...

I could be mistaken there. I was assuming the others referred only to effect on suspension on the *bounce* at the start and end of the speed-breaker-navigation. As a colleague of mine pointed out, car manufacturers likely measure and state GC in *unloaded* conditions. When fully loaded, the car sinks lower as we've all seen. In which case, yes, suspension will play a role (to the extent as to "how much does it sink") even if car is navigated at a snail's pace on the speed breaker!

Net net, as I stated, the model doesn't consider suspension as a first order analysis.

If its just the *bounce* effect we're talking about, then that effect of the suspension can be neutralized by navigating the bump slowly enough.

[scythian]

Originally Posted by vharihar

L_FOM = w*(2 - g/h)

where :
- 'w' is the wheelbase
- 'g' is the ground clearance
- 'h' is the height of the speed-breaker

Thanks so much for sharing this. I will go through the paper later, but looking at your equation, I started wondering if it is only the height of the speed-breaker that should matter. Let's say we model the speed-breaker as having a triangular cross section. Then should only the height of the triangle matter (as in the equation), or should the length of the base also matter. If we consider that a car has a small wheel-base and it tries to navigate a fairly spread out speed-breaker, it can be argued that it is possible that the car never has to "clear" the full height of the speed-breaker, because when the front tires are descending, the rear ones start ascending.

This scenario may be a little contrived though, but just something that crossed my mind. Thanks again.

[vharihar]

Originally Posted by scythian

Thanks so much for sharing this. I will go through the paper later, but looking at your equation, I started wondering if it is only the height of the speed-breaker that should matter. Let's say we model the speed-breaker as having a triangular cross section. Then should only the height of the triangle matter (as in the equation), or should the length of the base also matter. If we consider that a car has a small wheel-base and it tries to navigate a fairly spread out speed-breaker, it can be argued that it is possible that the car never has to "clear" the full height of the speed-breaker, because when the front tires are descending, the rear ones start ascending.

This scenario may be a little contrived though, but just something that crossed my mind. Thanks again.

Thats precisely why the wheelbase matters (bcoz for short wheelbase, the rear wheels start climbing up before front wheels complete the full speed-bump, thereby reducing the chances of under-belly scraping). And thats what my paper models.

Of course, if the speed-bump is shorter than the wheel-base, then the above is a moot point, in which case, the GC 'g' and height of speed-bump 'h' alone matter and the wheel-base 'w' is irrelevant. This is likely to be the situation for premium cars that tend to have a looong wheelbase (Mercs, BMWs, etc).