RPM vs speed

Ted · April 20, 2018

Hi all,

In a flat road or highway for my car which is a 1.5 engine, rpm is between 1800- 2000 when going at 70kmph. When I go 100kmph it is at 2700-2900. Is it normal? My car is Carina AT 192 , 5A-FE engine and A245E gear box.

Thanks..

MV-5 · April 20, 2018

On 4/20/2018 at 7:58 AM, Ted said:

Hi all,

In a flat road or highway for my car which is a 1.5 engine, rpm is between 1800- 2000 when going at 70kmph. When I go 100kmph it is at 2700-2900. Is it normal? My car is Carina AT 192 , 5A-FE engine and A245E gear box.

Thanks..

Expand

That is perfect. 70kmph probably it is in the top gear . so there is no gear change at 100kmph in this specific case.

so (2000/70) x 100 = 2857

Twin Turbo · April 20, 2018

Good, your o/d is on,..ride to the sun set without fear!

matroska · April 20, 2018

On 4/20/2018 at 7:58 AM, Ted said:

Hi all,

In a flat road or highway for my car which is a 1.5 engine, rpm is between 1800- 2000 when going at 70kmph. When I go 100kmph it is at 2700-2900. Is it normal? My car is Carina AT 192 , 5A-FE engine and A245E gear box.

Thanks..

Expand

looks pretty much ok to me

Magnum · April 20, 2018

On 4/20/2018 at 8:36 AM, MV-5 said:

That is perfect. 70kmph probably it is in the top gear . so there is no gear change at 100kmph in this specific case.

so (2000/70) x 100 = 2857

Expand

whats this equation all about?

Visa · April 21, 2018

I have a AE 111 with 1600 cc carburetor engine ( 4AF ) which also do the same RPM vs SPEED as yours. I feel it is OK.

iRage · April 21, 2018

On 4/20/2018 at 11:06 PM, Magnum said:

whats this equation all about?

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If RPM at 70 is 2000RPM...RPM at 100 should be 2857 Following the same logic when the engine is at idle it should be 0 RPM ???

MV-5 · April 21, 2018

On 4/20/2018 at 11:06 PM, Magnum said:

whats this equation all about?

Expand

On 4/21/2018 at 5:51 AM, iRage said:

If RPM at 70 is 2000RPM...RPM at 100 should be 2857 Following the same logic when the engine is at idle it should be 0 RPM ???

Expand

it is very basic who knows how a conventional auto box or manual box works,

in the same gear , speed is proportional to RPM.

IRage , you are right , that is why engine stalls when you release the clutch in a manual car without balancing it.

when a gear is fully engaged if the car speed is 0, then RPM is 0.

i thought this need no explanation because it is so simple , i repeat ,for the SAME gear, speed is proportional to RPM when gear is fully engaged (no clutch slipping)

you all know gear ratios and how power transmit happens and relationship between RPM and gear ratio and the speed and relationship between torque and RPM and throttle position, right?

IRage, in this case , if this is a manual car if vehicle speed is reduced to 20kmph then RPM will drop down to 571, which you feel engine is going to stall and power is not enough to accelerate the vehicle because even at full throttle RPM 571 will not produce enough power, that why we shift down to second to get a good RPM and accelerate the vehicle.

i guess you both are kidding

Edited April 21, 2018 by MV-5
typo

Rohnd · April 21, 2018

On 4/20/2018 at 11:06 PM, Magnum said:

whats this equation all about?

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No common equation.Slightly vary when the road is wet and slippery. Also a function of Tyre thread,air pressure and formula(Aspect ratio) etc.

MV-5 · April 21, 2018

On 4/21/2018 at 2:54 PM, Rohnd said:

No common equation.Slightly vary when the road is wet and slippery. Also a function of Tyre thread,air pressure and formula(Aspect ratio) etc.

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No, theoretically there is an equation , if you know these parameters you can calculate the speed from RPM

The Stig · April 21, 2018

On 4/21/2018 at 2:54 PM, Rohnd said:
No common equation.Slightly vary when the road is wet and slippery. Also a function of Tyre thread,air pressure and formula(Aspect ratio) etc.

All these affect acceleration, not cruising speed assuming they are within reasonable margin. So mv5 is correct.
However the final OD gear ratio can change from model to model. Depending on that the two vehicles can have slightly different rpms at 100 kph.

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MV-5 · April 22, 2018

On 4/21/2018 at 5:51 AM, iRage said:

If RPM at 70 is 2000RPM...RPM at 100 should be 2857 Following the same logic when the engine is at idle it should be 0 RPM ???

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engine is idle means engine does not transfer power to wheels, engine is completely decoupled from drive mechanism. so no relationship can be built in between vehicle speed and engine RPM.

FYI, engine is idle doesn't means vehicle is stand still (shift gear to N when you travel, engine is idle but vehicle is traveling) and it is possible to keep a vehicle keep stand still with engine running but not idle (thats how manual gear car stay stand still at when you start to travel in a hill upwards)

Clark'sson · April 22, 2018

For the car to be stationary either the gear ratio or engine speed should be 0

When you engage the clutch the ratio is 0

If you keep the car stationary with the break and release the cluch either it moves according to gear ratio x rpm. Or it remains stationary while the engine stalls.

When keeping the engine running on a hill with the cluch partialy enguaged the clutch is slipping while the frictional power is sending the power to balance the gravitational power on the vehicle. In this situation too the effective gear ratio becomes zero which is why the car doesnt move. This dosent apply to cvts

Rohnd · April 22, 2018

On 4/21/2018 at 2:54 PM, Rohnd said:

No common equation.Slightly vary when the road is wet and slippery. Also a function of Tyre thread,air pressure and formula(Aspect ratio) etc.

Expand

Yes, The heading says 'RPM vs speed'

Ted's query was relative to his experience on a road test and he was asking accuracy of his figures probably at 1:1 gear ratio.

I hope he is within the range for most of the mid sized cars with 14" to 16" in tire sizes.He has also provided a RPM range for a particular speed.

What I meant were deviation factors for his figures.

MV-5 · April 22, 2018

On 4/22/2018 at 1:02 PM, Rohnd said:

Yes, The heading says 'RPM vs speed'

Ted's query was relative to his experience on a road test and he was asking accuracy of his figures probably at 1:1 gear ratio.

I hope he is within the range for most of the mid sized cars with 14" to 16" in tire sizes.He has also provided a RPM range for a particular speed.

What I meant were deviation factors for his figures.

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This gear box doesn't have any gear with 1:1 ratio ,

And AFAIK vehicle spedo meter doesnt know anything about tire size, it shows the speed based on axle revolutions and based on the preset constant which has been calculated for the stock tire size

@Ted

if your tire diameter is 24 inch (185/70x14)

based on given values and this gear ratios still your gear box in 3rd gear

if vehicle speed is 100 kmph

vehicle speed in inches per minute = (100x 39370)/60 = 65616

number of tire revolutions per minute = 65616/(3.14 * 24) = 870.7

convert to engine RPM through 3rd gear ratio and Final drive gear ration
= 870.7 x 1.296 x 2.655 = 2996 RPM

@iRage

please don't ask how on earth 3.14 came into this calculation.

Edited April 22, 2018 by MV-5
typo

Ted · April 22, 2018

On 4/22/2018 at 2:33 PM, MV-5 said:

This gear box doesn't have any gear with 1:1 ratio ,

And AFAIK vehicle spedo meter doesnt know anything about tire size, it shows the speed based on axle revolutions and based on the preset constant which has been calculated for the stock tire size

@Ted

if your tire diameter is 24 inch (185/70x14)

based on given values and this gear ratios still your gear box in 3rd gear

if vehicle speed is 100 kmph

vehicle speed in inches per minute = (100x 39370)/60 = 65616

number of tire revolutions per minute = 65616/(3.14 * 24) = 870.7

convert to engine RPM through 3rd gear ratio and Final drive gear ration
= 870.7 x 1.296 x 2.655 = 2996 RPM

Expand

Hi, Is the gear at 3rd position at 100kmph normal? If I calculated as if it should be in 4th gear it gives RPM of around 2000 at 100kmph, which has never been achived by my car yet..

Edited April 22, 2018 by Ted

MV-5 · April 22, 2018

On 4/22/2018 at 3:29 PM, Ted said:

Hi, Is the gear at 3rd position at 100kmph normal? If I calculated as if it should be in 4th gear it gives RPM of around 2000 at 100kmph, which has never been achived by my car yet..

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i believe that that is as designed (for 4 speed gearbox,it makes sense ). but you better to wait till some member/s who use the same vehicle (at least same gearbox) give their input . speed is not the only parameter to decide the gear. but for me this is normal. other members who use a car with this gearbox , please add your comments and please help Ted to clarify this.

again final drive axle ratio can be vary from car model to model , in fact it can not be considered as a fixed property for a gearbox model. but i don think that for you car model they have made FD ratio close to 4:1 which will produce this RPM at the top gear. but try to do some search and find out (FD ratios close 3 is somewhat common with this gearbox)

Edited April 22, 2018 by MV-5
typo

Ted · April 22, 2018

On 4/22/2018 at 4:12 PM, MV-5 said:

i believe that that is as designed (for 4 speed gearbox,it makes sense ). but you better to wait till some member/s who use the same vehicle (at least same gearbox) give their input . speed is not the only parameter to decide the gear. but for me this is normal. other members who use a car with this gearbox , please add your comments and please help Ted to clarify this.

Expand

Hi,

Thanks for the valuable input.. infact in my datasheet there is a method of checking the gear position using voltmeter ( since my car is OBD I port). Next time I will check this and let you know which gear engaged exactly at 100kmphs. Please see the attached pic below on how to check it.

The Stig · April 23, 2018

On 4/22/2018 at 3:29 PM, Ted said:
Hi, Is the gear at 3rd position at 100kmph normal? If I calculated as if it should be in 4th gear it gives RPM of around 2000 at 100kmph, which has never been achived by my car yet..

It should be in overdrive at that speed if you are smooth with the accelerator (4th gear)
Gear selection is base on 2 reading, vehicle speed and throttle position.
If you are flooring it then the car will go into 3 or 2 and give better torque but if you are just cruising then it should be in OD.
While going around 60 turn off OD and see if you notice a gear changed (ideally it should shift from 4 to 3). If you don't notice anything then your OD is not engaging properly.

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