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Monday, October 08, 2012

Automobile Technical Terms - Demystified

Today we all drive high ends cars, fancy super bikes, follow Formula 1, MotoGP and admire the Need for Speed. But do we really understand when the comparison charts are drawn between these Mean Machines. Do we really understand when the analysts actually talk about technical aspects of the vehicles? Or for that matter when you enter a showroom the executive gives you a Bumper to Bumper detailed presentation of the Car or a Bike of your interest.

Well here we go and try & understand what these all jargons are.

  • Bore/Stroke – Pick up any product brochure and the first thing which you will see under          Engine Column is Bore/Stroke. In layman’s language Bore is the diameter of the cylinder in    which Piston moves. Stroke is the maximum distance which piston moves from top to bottom.

Bore-Stroke Diagram

  • Engine HP – Horse Power (HP) is one of the units of measurement of Power. In pure terms 1H.P. = 746 Watts
  • Engine Torque – Torque is the tendency of the force to rotate an object about an axis. It’s the measure of turning force on an object e.g. a flywheel.

Torque Diagram

  • Gear Ratios – In layman’s language Gear Ratio is the ratio of (No. of Teeth on Driven Gear)/ (No. of teeth on Driver Gear). Higher the gear ratio, higher is the torque transmitted. To add to it, Torque & Speed are inversely proportional to each other. Any geared vehicle is classified as (5+1) or (6+1) where “5” & “6” symbolizes the No. of forward gears and “1” represents the reverse gear.

Gear Ratio Diagram

  • Final Drive Ratio (FDR) – It’s the ratio of the No. of Teeth on Crown Wheel to No. of Teeth on the Pinion.

After getting an insight to the Engine HP, Torque & Ratios one of the most important parameter for deciding the vehicle performance is the Torque on Wheels. Until and unless an efficient and powerful engine is coupled with a gear box with optimum gear ratios & Final Drive the performance of the vehicle can never be of the desired levels for which it has been designed.

Torque on Wheels further gives us a comparative idea of the pulling power & ability of two vehicles to over come different gradient levels. Nomenclature of this ability of the vehicle to cover come gradients is “Grade-ability” of the vehicle.

To understand it well “Torque on Wheels” is calculated as per the below formula:-

Engine Torque X Gear Ratio X Final Drive Ratio

To elaborate, below is the table giving the calculation of Torque on Wheels.

Prima 4028 - Prime Mover
Engine Torque
Gear Count
Gear Ratios
Final Drive Ratio
Torque On Wheels(Nm) - For both the Hubs Combined
970 Nm
Crawler Gear
970 Nm
1st Gear
970 Nm
2nd Gear
970 Nm
3rd Gear
970 Nm
4th Gear
970 Nm
5th Gear
970 Nm
6th Gear
970 Nm
7th Gear
970 Nm
8th Gear(Over Drive)
970 Nm
Reverse Gear
  *Approx 8% loss in TOW to be considered for practical conditions.

As you see the Torque decrease which each changing gear and getting to its least value in the Over Drive Gear. As mentioned above Torque is inversely proportional to Speed of the vehicle. Highest Torque is available in First gear or for that matter in Crawler Gear if vehicle is fitted with it – depending upon application of the vehicle. First gear transmits Max. Torque to the vehicle as opposed to Over Drive which gives the vehicle its Max. Speed.

In Over Drive Gear the gear ratio is less than “1”. This symbolizes that the No. of teeth on Driven Gear are lesser than the No. of teeth on the Gear driving.

Higher torque on wheels gives way to a new terminology - Grade-ability of the vehicle.

Gradeability in %

Gradeability Diagram

Well this is it as of now. Watch out this space for more insight into our Automobiles.


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