1L vs 3L on a hill.

[Crispin]

So this might seem like a dumb question….


I now drive the iQ to work which has a 1L engine producing pure raw power. The A41 is a series of hills with very few level sections on it and constant adjustment is needed to keep the speed the same more so than I remember when driving the 120 so today I drove the 120 in to compare.

The iQ loses about 10-20mph on an incline and the same incline in the 120 only costs around 5mph. Both occasions my accelerator is kept in the same position.

What confuses me is that both engines, when driving on a level road, would surely be producing the same amount of power (let’s ignore drag on the vehicles and rolling resistance should be quite similar?) They only require enough to maintain speed. Any excess would cause the speed to increase.

So why would the iQ drop so badly in speed while the 120 does not if the amount of power being produced does not change. The 120 would have to work much harder on an incline because of the weight so I would have expected it to drop more.

I assume (correct me if I am wrong) but torque would be the same – only enough is being developed to turn the wheels to maintain the speed. Any excess would cause the vehicle to increase in speed?


Having a 20odd mile of straight road with no traffic gives me time to ponder the down sides of iQ

 

[Graham]

Hi Crispin,

Perhaps a better way to look at it is this.
Which has more reserve power ?
I would say the LC has more power in reserve than the IQ.
So the IQ is using more of it's maximum available than the LC ?

As the IQ is running up the hills using say, 80% of its power, the LC is running up teh same hill using just 50% of it's power?

Maybe?

May be a load of bull ?

Gra

 

[Justin_Elliott]

So why would the iQ drop so badly in speed while the 120 does not

Inertia?

 

[Crispin]

It’s not got anything to do with reserve power if I did not change the throttle position. Sure, if I floored both then the LC would run away from the iQ as it has a shed load more.


Inertia on a small speed bump sure but the hill it makes most of a difference to is a few miles long.

 

[Andrew Prince]

Crispin, the short answer is torque

 

[Justin_Elliott]

Lets assume that:

Inertia + rolling resistance + aerodynamic losses etc... = Total Mechanical power lost.
The engines are putting out a constant amount of power (not equal but constant)

So for the car to remain at constant speed:
Power Output (after gearing) - Total Mechanical Power Lost = 0

So either your total power lost is reduced (due to inertia or lower rolling force) or your engine outputs (inc gearing) are better matched in the 120 than in the iQ.

But as your engine outputs (Torque) and gearing are totally different, not to mention car characteristics (size, weight etc..) its not clear what you're trying to work out....

 

[Gary Stockton]

Less sticky buns for you, m'boy!

I go with Andrew's solution!

 

[Rob]

Crispin, the short answer is torque

 

[Crispin]

So 3L engine still develops more torque than 1L engine when both cars are going the same speed? All else being equal.

Edit :
Just reread Justin's reply. Seems to suggest that.

I thought it would be "just enough to keep speed " which would make the two card similar.

Sent from my Desire HD using Tapatalk

 

[Marius De Kock]

Let's talk about it tomorrow.



I’ll give you some tips.

 

[Sam]

Confidence Crispin.

Don't underestimate the power of feeling good in an LC.

By my reckoning (and I've just done a lengthy calculation including symbols and squiggles), you get at least 60% more momentum sitting behind the wheel of an LC - purely out of added "feel good factor".

Fact........... probbly!

Oh - and torque

 

[Crispin]

Ha ha. It's awesomeness that propels me up the hill.

Sent from my Desire HD using Tapatalk

 

[Beau]

I have the same issue with my golf 1.9tdi.

When going up a long hill I would need to accelerate a lot more in order to maintain my speed, but with my Colorado a touch more and your fine!

I think its due to amount of torque there is.