[gurudutt]

I have been wondering for a while, some numbers we find on the websites/car brochures don't make much sense. Fellow bhpian's, please share your thoughts on it.

To start with, i found ground clearance numbers of two cars quite surprising.

Figo claims around 168 mm of GC where as i have heard and also experienced thuds while crossing bumpy roads with 4-5 people on board.

Indica Vista claims round 165 mm of GC and i have rarely had problems negotiating bumpy roads without scrapping the underbody.

Mods, i have searched the forum for similar threads, didn't find any. Please take appropriate action if you sense duplication.

[Latheesh]

I think Figo wheelbase is higher than Vista (around 20 mm). That may be the culprit!

[amoghchaphalkar]

Refer this discussion : http://www.team-bhp.com/forum/techni...html#post50792

[Rehaan]

gurudutt,

Please refer to the link above. It will explain it in detail. (Also keep in mind the softness or suspension + load in the car affecting the GC as well).


I'm leaving this thread open incase you have any other numbers that don't make sense. However, for all GC discussion please use the thread linked to in amoghchaphalkar's post above.

cya
R

[Delta Wing]

I don't know if this is OT, but the numbers on pricetags of some cars come readily to mind (Honda Jazz?).

[rjstyles69]

Completely agree with what Rehaan say's, mostly has to do with the softness of the suspension. From what I know manufacturers display GC numbers for an empty car, no passengers or cargo. Beyond this if a car is fully loaded then yeah talk about softer suspension setups which is the main cause for the underbelly scrapping.

[Vishal.R]

Let me put this into another way,

some numbers "alone" don't make sense.

we have to understand relation between different numbers

sometimes it may be due to perception also,

one example is GC's relation with wheel base above

another example is BHP.

We already know about torque and peek torque @ rpm ( Ford TDCI / Vento / Old Verna CRDI) and their effect on driving.

[Rehaan]

Originally Posted by Vishal.R

another example is BHP.

We already know about torque and peek torque @ rpm ( Ford TDCI / Vento / Old Verna CRDI) and their effect on driving.

This is another good example!

BHP and in most cases torque are always mentioned at their peak value only.

However, two cars having the exact same power @ exact same RPM might have completely different power characteristics at a lower RPM. This would depend on several factors, engine displacement, # of valves, cam profiles, forced induction vs NA, etc.

The only way to compare on paper is to look at the full power curve, which manufacturers rarely provide.

Even if the power curves match exactly on paper, don't forget that power-to-weight ratio, as well as gearing can still make a difference to how powerful a car feels!


Lately, especially with the diesels, a lot of manufacturers have started mentioning peak torque across a band (eg. 500Nm @ 1700 - 2600 RPM). This also helps in showing the car's drivability across that rev range.

cya
R

[dhanushs]

Originally Posted by Rehaan

... The only way to compare on paper is to look at the full power curve ...

Exactly, the peak torque or power numbers alone does not make any sense. Its the area under the Torque or Power curve that counts.

Assuming all other factors to be same, an engine which makes 100bhp for only about 1000rpm should be much slower than an engine which makes 90bhp for say about 4000rpm. That's why manufacturers try hard to bring in torque early in the power band and allow it to stay flat across the range.

[libranof1987]

I'd created a thread some time back on how manufacturers come up with engine capacities. Eg. 998cc (Zen), 1494cc (City), 158cc (HH CBZ)

Really wonder how such figures are arrived at!

[figo_mba]

Originally Posted by libranof1987

I'd created a thread some time back on how manufacturers come up with engine capacities. Eg. 998cc (Zen), 1494cc (City), 158cc (HH CBZ)

Really wonder how such figures are arrived at!

Hi libranof1987
Its actually simple.
I hope you have seen the bore and stroke values for engines.
Now the bore is the diameter of the cylinder. And Stroke is the distance between the topmost distance that piston can traverse within the cylinder.

If you can imagine this volume, it would be a cylinder with half of bore as radius of base and stroke as height of cylinder.

Now volume = Pi x r x r x h = 3.14 x half of bore x half of bore x stroke

Do these calculations and you will know where the manufacturers get their funny values for engine displacement;

Hope it helps

[libranof1987]

Originally Posted by figo_mba

Hi libranof1987
Its actually simple.
I hope you have seen the bore and stroke values for engines.
Now the bore is the diameter of the cylinder. And Stroke is the distance between the topmost distance that piston can traverse within the cylinder.

If you can imagine this volume, it would be a cylinder with half of bore as radius of base and stroke as height of cylinder.

Now volume = Pi x r x r x h = 3.14 x half of bore x half of bore x stroke

Do these calculations and you will know where the manufacturers get their funny values for engine displacement;

Hope it helps

This is actually enlightening. Thanks!

Ok, so is it like this : When manufacturers design a car, they first determine the engine capacity. So they come up with a 1.5l engine requirement, then build a chasis model and then based on the engine and chasis, come up with the actual values of the bore and stroke; which leads to a 1497cc engine.

[figo_mba]

Originally Posted by libranof1987

This is actually enlightening. Thanks!

Ok, so is it like this : When manufacturers design a car, they first determine the engine capacity. So they come up with a 1.5l engine requirement, then build a chasis model and then based on the engine and chasis, come up with the actual values of the bore and stroke; which leads to a 1497cc engine.

In real life its not like that. It is a lot more complex than that. Sometimes keeping cost considerations and power requirements in mind the designers would say a rough displacement that would be required. I mean the character of the engine and thereby whether the engine needs to over square or under square etc etc (i am sure there is a section that deals with this in the technical thread) are all decided based on infinite number of considerations like cost, models in which it is going to be in, market, preferences in market, utility etc etc.

Engine development happens independently of the vehicle model sometimes. Eg: Fiat develops this 1.3MJD that is being plonked on many diesel car models in INdia. They are also developing the Multi Air engine independent of the car model ( We could call it basically engine research). Here the CC is restricted by the complex hydraulics involved in the engine design.

3 cylinder mpfi engine of 800 or alto and the 1061cc 4 cylinder of Old maruti wagon R have same bore and stroke. Meaning its like they have glued an extra cylinder to the 800cc engine and got a 1061 cc engine just check this out.. although it seems easy said like this the engine development for just adding another cylinder in itself is very complex.

So I hope you see the point. It is not as simple as I decided on bore and stroke and displacement and started constructing the engine.

I have read somewhere that the engine designing and development (not related to any vehicle model) cost around Rs100crores.
Then there is ECU development which is a totally different story altogether. All the characteristics of the engine needs to be mapped. Since most engine development activities happen in trial and error, programming and re programming are just every day job (not suggesting that they happen everyday or that it is simple; in fact very tough)

[GTO]

Nice thread. As Vishal posted, numbers alone make little sense. Example:

- The Civic's torque curve on paper isn't really that bad. However, thanks to the poor throttle response, I have yet to drive a car that's as bad to drive in traffic as the Civic. I'm just glad I got the exhaust changed and improved my low-end torque delivery. It was a ROYAL pain in stock form.

- They say Korean horses are generally weaker than Japanese / European ones. This is much the case with the petrol Accent, as an example. It simply isn't as fast as the power to weight ratio would suggest. Another example is the Punto 90 BHP. Hardly a difference from the 75 BHP variant.

- Kerb weight : Not necessary that the heavier the car, the safer it is (or even feels more solid).

- Wheelbase : The Linea is a prime example here. While the wheelbase ain't too bad, it's the most cramped from the segment. Poor interior packaging, really.

- Boot capacity : Larger doesn't necessarily mean better. The layout, and usable space, are equally important.

[oxyzen]

The most baseless number is KMPL. You may end up getting more FE in a car that claims less FE.

- These days engine calibration is done in such a way that ARAI certified fuel effeciency is maximum. The first thing they do is kill the throttle response. The next thing is to provide a taller 2nd & 3rd gear. Then they make the cars forcibly wear skinny tyres. And finally measure the FE with AC off.

- Now when it comes to real life driving, you see the car is just not performing. You give it more gas. You drive it in a gear less.
Moreover some of us obviously upsize their tyres. And practically everyone drives the car with AC on.

So does the Arai certified FE hold any value?