[wheelguy]

Found this interesting and useful video which demonstrates about how to start a car when self-start fails due to various reasons like inadequate charge in the battery etc.

For the front wheel drive vehicles:

https://youtu.be/NeYHDJ5qi0Y

For the rear wheel drive vehicles:

https://youtu.be/q5Q41zMSxAc

[Kosfactor]

The TUV3OO`s engine starts, wheel spins and then the MLD engages - India`s first driverless car casualty.

Risky methods like this should be used only as a last resort, like no one is left on earth etc.

[amit_purohit20]

I have watched a couple of videos on You Tube by this guy and he puts on a sincere effort to give his best in his videos.

Coming back to the topic, this is not the first time I have come to know about this technique, we often find many such videos on You Tube from the western part of the world and I believe its a really good technique.

In the middle of nowhere where there is no help around we can try this technique offcourse by taking enough precautions like engaging the hand brake (for a fwd car), keeping stones in front of the other tyres etc. I probably also think that pushing a car to start especially a diesel vehicle takes at least two persons pushing the car at good amount of speed to crank the engine. Probably this idea would require less effort as you are winding a string around the wheel which can apply torque to the wheel for a longer duration and at good rotational speed.

One more tip I would like to provide here would be to try starting the car in 3rd or even 4th gear using this technique. This will ensure that we need to apply less effort.

@kosfactor I agree with you that if its a vehicle equipped with MLD it may lead to an accident. If you do not give accelerator input to the MLD equipped vehicle while using the string technique I doubt the MLD will engage. My observation from the videos showing MLD engagement is that it requires quite a bit of rpm input at the wheel to engage. (Probably we will have to start the car only in 1st gear here to keep wheel rpms low after the engine starts.) Just a thought, off-course someone will have to validate it practically!

[R2D2]

I find this method very risky (and rather silly) maybe doable for a small car. If that car goes off the jack as it starts you're going to have a run away.

Why not just get some help and push start it?! Better still buy a good set of jumper cables and keep it in the boot. Or if you have the budget get a portable jump starter by NOCO or other company.

[MegaWhat]

I'm not sure if this is a stupid query.
But what's stopping the other front wheel of the kwid (the one that's on the ground) from rotating once the engine is running? When the engine is running and the reverse gear is engaged, torque would be transmitted to both wheels wouldn't it?

[Reinhard]

Originally Posted by wheelguy

Found this interesting and useful video which demonstrates about how to start a car when self-start fails due to various reasons like inadequate charge in the battery etc.

Originally Posted by Kosfactor

The TUV3OO`s engine starts, wheel spins and then the MLD engages - India`s first driverless car casualty.

Similarly - that puny wheel jack under the Kwid falls on the tug, car jumps and we have a person run over by a tiny hatchback on a YouTube video! This is just insane. Someone needs to educate that bloke in the video about a word called "accidents". Urgently.

P.S. - Renault really has saved a lot of cost in the wheel jack! It looks like a toy. Talk of cost cutting at hidden places! Maruti are you watching this? Here's one place you have missed so far. My Alto's wheel jack is literally premium!

Originally Posted by Kosfactor

Risky methods like this should be used only as a last resort, like no one is left on earth etc.

Originally Posted by MegaWhat

I'm not sure if this is a stupid query.
But what's stopping the other front wheel of the kwid (the one that's on the ground) from rotating once the engine is running? When the engine is running and the reverse gear is engaged, torque would be transmitted to both wheels wouldn't it?

For that to happen, you'd need the differentials to be "locked" - like in an off road 4x4 vehicle that has lockable diffs. In an "Open" diff, the wheel on the other side keeps spinning with drive if one wheel is stuck. Under normal running conditions even 4x4 cars have wheels in open differentials. It is a necessity.

To make it simple - if the wheels are always locked on both sides - imagine how the car will take a turn. During a turn, the inside wheel must turn less rotations compared to the outside wheel. This needs "open" differentials.
P.S. - There is no such thing as a stupid query.

[blackwasp]

Originally Posted by wheelguy

Found this interesting and useful video which demonstrates about how to start a car when self-start fails due to various reasons like inadequate charge in the battery etc.

This should be last ditch effort. Also keep the car in R. You can also try to jump start a car in R as less effort is needed.

I have not tried starting a car with this method, but have seen 3 wheeler cargo carriers in Rajasthan do this to start their vehicles. But I have jumpstarted a car in reverse thanks to a slope out of the parking. Kept the door open and push the car back auto-driver style.


Edit - just saw the RJ registration.. Why am I not surprised.

[MegaWhat]

Originally Posted by Reinhard

For that to happen, you'd need the differentials to be "locked" - like in an off road 4x4 vehicle that has lockable diffs. In an "Open" diff, the wheel on the other side keeps spinning with drive if one wheel is stuck. Under normal running conditions even 4x4 cars have wheels in open differentials. It is a necessity.

To make it simple - if the wheels are always locked on both sides - imagine how the car will take a turn. During a turn, the inside wheel must turn less rotations compared to the outside wheel. This needs "open" differentials.
P.S. - There is no such thing as a stupid query.

So if my car ends up with one front wheel suspended in a really deep pothole, there's no getting out of it and I'm bound to be towed or pushed out. I mistakenly imagined I could rely on the other wheel on the ground.

Thanks for clearing that up. Learnt something new today!

[Reinhard]

Originally Posted by MegaWhat

So if my car ends up with one front wheel suspended in a really deep pothole, there's no getting out of it and I'm bound to be towed or pushed out. I mistakenly imagined I could rely on the other wheel on the ground.
Thanks for clearing that up. Learnt something new today!

Well - Yes & No.
You see - the engine (and transmission) is supplying torque to both the wheels even when you see just one of the wheels spinning. Its just that - it is not enough to turn the wheel that is stuck.

So technically in the scenario you mentioned - If you modulate the gearing & your throttle inputs well - the wheel that has traction can still pull the car out, depending on how well you have managed to entrench it.

Even in the video above - the car isn't moving because at idle, the torque of that engine is not enough to turn the wheel touching the ground. Sit in it, rev it in gear & the car will lunge forward surely with just 1 wheel on ground too. I'm a bit surprised that the TUV in that video didn't lunge. A bit disappointed at the low near idle torque on that engine looking at this video!

[alpha1]

I have a question on this:
1) what allows the jacked up wheel to "freewheel"? (Ans: differential?)
2) if it is freewheeling then how is it able to crank the engine?

[Reinhard]

Originally Posted by alpha1

I have a question on this:
1) what allows the jacked up wheel to "freewheel"? (Ans: differential?)
2) if it is freewheeling then how is it able to crank the engine?

Do you have the question only when it is jacked-up? Because the behaviour is absolutely the same when the car is pushed to roll on road surface also. Just that both the wheels turn & crank the engine.

Why only one wheel spins - is the open differential indeed.

[amit_purohit20]

Originally Posted by blackwasp

You can also try to jump start a car in R as less effort is needed.

No its not the case less efforts are required to rotate the car wheels in as high gear as possible.

Consider this lets take the classic example of leverage of a spanner and nut which has to be tightened. You require less effort to tighten a nut due to the leverage the spanner length provides.

In case of first gear there are two gears in mesh, one is the smaller one called the "pinion" and the bigger gear is called simply the "gear". In case of 1st gear of a vehicle the pinion is the input gear which is attached to the engine side and the bigger gear is attached to the wheel side. That's how the reduction in speed takes place and also the torque multiplication takes place.
In this the torque is applied to the bigger gear ie. at a tooth which is at a larger distance from the rotational axis of the gear. This distance acts like a lever and thus you get the torque multiplication.



When you use the string technique you are doing the reverse that is trying to drive the engine through the car wheel and hence instead of a torque multiplication you get a torque decrease at the flywheel end. This means that you will have to apply more effort to start the vehicle.

Hence its advisable to use a higher gear to start the vehicle. 1st gear and reverse gear ratios are nearly the same (More often the reverse gear ratio is more shallow ie higher than the 1st gear) so that means if you try to start the vehicle in 1st gear or reverse you will have to apply more efforts to start the vehicle.

With that logic someone would want to start the car in fifth or sixth gear. This is also not recommended because there is a minimum rotational speed of the engine required to start itself. Higher the engine rotation speed better for starting, so we want engine rpms to be higher. One will get higher engine rpms in 1st, Reverse gears but that requires more torque to be applied at wheel.

So the right balance would be reached in either 3rd or 4th gear using this string technique.

In case of push start technique for starting a car:

Its obvious that the car will be easier to start in higher gears but still you will observe that the general practice is not to put the car in 4th or 5th gear.

The reason is quite simple that as soon as the engine will start the engine is going to drive the car wheels that means there would be too much load applied on the engine if the car is in higher gears and there is a high chance that the car will stall again!
Also the speed at which the car is pushed has to be higher if you use higher gears.

[amit_purohit20]

Originally Posted by Reinhard

So technically in the scenario you mentioned - If you modulate the gearing & your throttle inputs well - the wheel that has traction can still pull the car out, depending on how well you have managed to entrench it.

For open differential cars this is again based on how much torque can be applied on the freely spinning wheel. If the free spinning wheel even gets to touch the sides of a ditch there is a temporary traction build up which can help the other tyre to pull the vehicle out of the ditch.

Originally Posted by Reinhard

Even in the video above - the car isn't moving because at idle, the torque of that engine is not enough to turn the wheel touching the ground.

Its not because of the torque of the engine which is not enough to turn the wheel on the ground. Its because the torque required to turn a wheel which is in air is very very less and so the whole torque gets transferred to the free spinning wheel.

Originally Posted by Reinhard

Sit in it, rev it in gear & the car will lunge forward surely with just 1 wheel on ground too.

It all depends on how the throttle is modulated, if you give very gentle throttle and slowly ramp it up it might not lunge forward at all. Its the jerky (read sudden acceleration and deceleration) throttle modulation that throws off balance a vehicle when its on a jack.

Originally Posted by Reinhard

I'm a bit surprised that the TUV in that video didn't lunge. A bit disappointed at the low near idle torque on that engine looking at this video!

Your conclusion is not right infact TUV 300 is one of the vehicle having the best low end torques. Judging the low end torque of the engine at near idle based on "whether the vehicle lunges forward or not" is not the right way.

Torque is like pressure, it will not get developed unless it meets any resistance. As there is very less resistance to the free spinning wheel the engine will not produce higher values of torque!

Please note that I am not advocating this idea of starting the vehicle nor denying the chance of probable accidents.

[alpha1]

Originally Posted by Reinhard

Do you have the question only when it is jacked-up? Because the behaviour is absolutely the same when the car is pushed to roll on road surface also. Just that both the wheels turn & crank the engine.

Why only one wheel spins - is the open differential indeed.

I don't recall observing this hence my questions:
When one wheel is jacked up, and in gear, does it spin freely (like how the rear wheel of FWD cars does?

If it is indeed spinning freely then how can it transmit the torque to the engine?

In case of vehicle on ground and push started, both wheels touch the ground. In order to start pushing the vehicle has to have the clutch engaged, and once it picks momentum, you disengage the clutch. The torque from the wheels is transmitter to engine and cranks it to life.

[.anshuman]

Please don't try these stupid methods. Not only are they unsafe, they will require a lot of effort, which can be saved with much smarter and simpler methods. If you can keep a rope handy, I'd rather you keep a jump start cable.

Buy a Amazon basics jump start cable and keep it in your car all times, find another car, jump start the car with dead battery. If no other car/jump start cable is available, get to 2 guys to push the car, keep the car in 2nd gear, release clutch and there you go. We live in a densely populated country, its highly unlikely that you would be out of luck with help. Then we have battery company helpline.

If your battery is old, be vigilant about weak self starter sound, on noticing first signs get the battery checked.