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Okay.. here's some of the things I've learnt during my course of modding my car.. hopefully this will be a place to put together various forms of calculations in one place for reference to any new or current members of Honda ZTH forum. Some of this calculations will be applicable to other makes as well so hopefully this will be a definitive resource for all car models. Of course, I'm a human, so I tend to make mistakes, so hopefully forummers can help correct any mistakes that I make. It's also a chance to check for mistakes in anything I have learnt.
Forummers can also contribute any information they know.
Here's to more knowledgable, savvy, car modders in Malaysia. Cheers!
Now you know why we learnt all that stuff in Maths 101 back in secondary school.. ROFL! Can also consider all these stuff 'brain food' (^_^)
Remember that 'pi' value = 3.1416 is used to approximate calculations of circular areas and circumference, and there's likely to be a deviation of 1% or so if you measure manually, but it's still widely used.
also note the units of measurements.. I always get this wrong, so I rechecked some to make sure I got them right, but when you do apply this, remember the units of measurements since there's where you'll make mistakes. Most will be in converted from milimetre to centimetre.. just move that decimal point up by one, and you're good to go.
Calculating engine capacities
Engine capacity = no. of pistons * stroke in cm[(2/bore in cm)² * pi]
For B16A, Engine capacity = (4 * 7.74cm) [(2/8.1cm)² * 3.1416]
= (30.96)[(16.4025) * 3.1416]
= 30.96(51.530094)
= 1595.37171024 cubic centimetres.
Simple only, no?
Note : Chart for stroke and rod ratios for B series will be added later.
Calculating tire rollout (distance a tyre covers in one rotation)
This one will be relevant once I get around to calculating speeds with gear ratios, but that'll be another day. All measurements for tire will be in milimetre, until the last part where we just move the decimal for cm, or km, whichever you prefer.
Tires are spec'ced with 195/55R15.
195 = tire width
55 = aspect ratio (how thick are the sidewalls)
R15 = do I even need to explain this?
Section 1 (the main part)
Circumference of tire = pi * tire diameter
1.1 Sidewall thickness = (tire width * aspect ratio) / 100
So for the tire above,
Sidewall thickness = (195 * 55) / 100
= 195 * 55% (simplified)
= 107.25mm
1.2 Rim width in mm = rim inches * conversion rate
= 15" x 25.4
= 381 mm
Note: 25.4 is for converting inches to mm.. it's a good number to remember.
1.3 To get the tire diameter, add 1.1 and 1.2 up, remember that 1.1 is the height of ONE sidewall, so....
Tire diameter = (2 * sidewall thickness) + rim width
= (2 * 107.25mm) + 381mm
= 595.5 mm
So, put the 1.3 into the tire circumference = pi * tire diameter,
tire circumference = 3.1416 * 595mm
= 1870.8228 mm
1.4 Convert to km =
1870.8228 mm / 1000000 =
0.0018708228 km per rotation.
distance per tire revolution = 0.0018708228 km per rotation.
So one round your tire rotate or 'pusing', your car moves 0.0018708228 km. Haha!!! So FAST! Not!!! (o_O)
This formula will be useful once I finish the speed calculating formula below.
Calculating speeds vs. RPM with gear ratios and tire sizes
This is a fun way to learn clutchless shifting without causing damage to your gearbox with trial and error, provided your RPM meter is not too inaccurate. Draw a vertical line from your max rpm to get your RPM drop, once you constructed an RPM chart of your own.. for example mine at 8K rpm would result in a little over 60Kmh (61.71, if you can read the chart) and shifting to gear two would result in an RPM drop to a little over 5K rpm. (visualize how the vertical line would be)
Pump the clutch once (or not, depending on whether your gearbox allows you to, mine does it easily, since it's an worn out one) to release the gear, release, and push into second at 5K or so.. done right, you get immediate continous acceleration without that slight lag as the clutch grabs. Too late, and grruunkkk! sound would be the result.. :P
I'll get around to posting the excel/staroffice worksheet of mine once I get my website up and running. For now.. DIY yourself lah.. tech savvy people mah you all, since all in ZTH... :P
P.S. In my opinion, short shifters are invented so you can do clutchless shifting.. hehe. Must resist temptation to get one.. :P ---- Edit: Too late.. I already bought one.. (>o
Anyway, back to the topic.
The formula for calculating is:
speed your car depending on rpm =
distance per tire rotation * [(rpm * 60)/(gear ratio * final drive)]
*Note the "60" is to convert to rotations per hour, since the final result we want is kilometres per hour, not kilometres per minute.. (O_o)
Okay.. so collect the ratio of your g/box, and write them down.. in this case, I'll use my Y21 B16A g/box for illustration purposes.
1st: 3.307, 2nd: 2.105, 3rd: 1.458, 4th: 1.107, 5th: 0.848, Final Drive: 4.4
So, Let's just choose one gear for an example.. say.. the 5th gear, so we can find out the theoretical max speed achievable (if you have enough power, and a long enough stretch of clear open road like the Salt Flats in the US.. ROFL!)
1.1[/B] Using the formula above, you put in the numbers. In this case, we try to see how fast the car is travelling at 8K rpm at 5th gear.
Car speed depending on rpm (“Car speed” for short) =
distance per tire rotation * [(rpm * 60)/(gear ratio * final drive)]
Car speed = 0.0018708228km * [(8000 * 60)/(0.848 * 4.4)]
= 0.0018708228km * [(8000 * 60)/(0.848 * 4.4)]
= 0.0018708228km * [(480000)/( 3.7312)]
= 0.0018708228km * 128644.93996569468267581475128645
= 240.67188679245283018867924528302
The decimals don't really matter, so feel free to round them up.
So, at 5th gear, my civic can go up to 240.67km/h at 8K if my engine power and ECU allows it.
Plonk in the formulas the try it with different gears and rpm and check out the results with this graph.
Have fun!
Status: Static compression calculation removed pending construction of diagram illustrating the components involved.
Forummers can also contribute any information they know.
Here's to more knowledgable, savvy, car modders in Malaysia. Cheers!
Now you know why we learnt all that stuff in Maths 101 back in secondary school.. ROFL! Can also consider all these stuff 'brain food' (^_^)
Remember that 'pi' value = 3.1416 is used to approximate calculations of circular areas and circumference, and there's likely to be a deviation of 1% or so if you measure manually, but it's still widely used.
also note the units of measurements.. I always get this wrong, so I rechecked some to make sure I got them right, but when you do apply this, remember the units of measurements since there's where you'll make mistakes. Most will be in converted from milimetre to centimetre.. just move that decimal point up by one, and you're good to go.
Calculating engine capacities
Engine capacity = no. of pistons * stroke in cm[(2/bore in cm)² * pi]
For B16A, Engine capacity = (4 * 7.74cm) [(2/8.1cm)² * 3.1416]
= (30.96)[(16.4025) * 3.1416]
= 30.96(51.530094)
= 1595.37171024 cubic centimetres.
Simple only, no?
Note : Chart for stroke and rod ratios for B series will be added later.
Calculating tire rollout (distance a tyre covers in one rotation)
This one will be relevant once I get around to calculating speeds with gear ratios, but that'll be another day. All measurements for tire will be in milimetre, until the last part where we just move the decimal for cm, or km, whichever you prefer.
Tires are spec'ced with 195/55R15.
195 = tire width
55 = aspect ratio (how thick are the sidewalls)
R15 = do I even need to explain this?
Section 1 (the main part)
Circumference of tire = pi * tire diameter
1.1 Sidewall thickness = (tire width * aspect ratio) / 100
So for the tire above,
Sidewall thickness = (195 * 55) / 100
= 195 * 55% (simplified)
= 107.25mm
1.2 Rim width in mm = rim inches * conversion rate
= 15" x 25.4
= 381 mm
Note: 25.4 is for converting inches to mm.. it's a good number to remember.
1.3 To get the tire diameter, add 1.1 and 1.2 up, remember that 1.1 is the height of ONE sidewall, so....
Tire diameter = (2 * sidewall thickness) + rim width
= (2 * 107.25mm) + 381mm
= 595.5 mm
So, put the 1.3 into the tire circumference = pi * tire diameter,
tire circumference = 3.1416 * 595mm
= 1870.8228 mm
1.4 Convert to km =
1870.8228 mm / 1000000 =
0.0018708228 km per rotation.
distance per tire revolution = 0.0018708228 km per rotation.
So one round your tire rotate or 'pusing', your car moves 0.0018708228 km. Haha!!! So FAST! Not!!! (o_O)
This formula will be useful once I finish the speed calculating formula below.
Calculating speeds vs. RPM with gear ratios and tire sizes
This is a fun way to learn clutchless shifting without causing damage to your gearbox with trial and error, provided your RPM meter is not too inaccurate. Draw a vertical line from your max rpm to get your RPM drop, once you constructed an RPM chart of your own.. for example mine at 8K rpm would result in a little over 60Kmh (61.71, if you can read the chart) and shifting to gear two would result in an RPM drop to a little over 5K rpm. (visualize how the vertical line would be)
Pump the clutch once (or not, depending on whether your gearbox allows you to, mine does it easily, since it's an worn out one) to release the gear, release, and push into second at 5K or so.. done right, you get immediate continous acceleration without that slight lag as the clutch grabs. Too late, and grruunkkk! sound would be the result.. :P
I'll get around to posting the excel/staroffice worksheet of mine once I get my website up and running. For now.. DIY yourself lah.. tech savvy people mah you all, since all in ZTH... :P
P.S. In my opinion, short shifters are invented so you can do clutchless shifting.. hehe. Must resist temptation to get one.. :P ---- Edit: Too late.. I already bought one.. (>o
Anyway, back to the topic.
The formula for calculating is:
speed your car depending on rpm =
distance per tire rotation * [(rpm * 60)/(gear ratio * final drive)]
*Note the "60" is to convert to rotations per hour, since the final result we want is kilometres per hour, not kilometres per minute.. (O_o)
Okay.. so collect the ratio of your g/box, and write them down.. in this case, I'll use my Y21 B16A g/box for illustration purposes.
1st: 3.307, 2nd: 2.105, 3rd: 1.458, 4th: 1.107, 5th: 0.848, Final Drive: 4.4
So, Let's just choose one gear for an example.. say.. the 5th gear, so we can find out the theoretical max speed achievable (if you have enough power, and a long enough stretch of clear open road like the Salt Flats in the US.. ROFL!)
1.1[/B] Using the formula above, you put in the numbers. In this case, we try to see how fast the car is travelling at 8K rpm at 5th gear.
Car speed depending on rpm (“Car speed” for short) =
distance per tire rotation * [(rpm * 60)/(gear ratio * final drive)]
Car speed = 0.0018708228km * [(8000 * 60)/(0.848 * 4.4)]
= 0.0018708228km * [(8000 * 60)/(0.848 * 4.4)]
= 0.0018708228km * [(480000)/( 3.7312)]
= 0.0018708228km * 128644.93996569468267581475128645
= 240.67188679245283018867924528302
The decimals don't really matter, so feel free to round them up.
So, at 5th gear, my civic can go up to 240.67km/h at 8K if my engine power and ECU allows it.
Plonk in the formulas the try it with different gears and rpm and check out the results with this graph.
Have fun!
Status: Static compression calculation removed pending construction of diagram illustrating the components involved.
Last edited:
