How much power can a FWD car have?

[DanielSan]

McSam said:

eally? The limit of adhesion is somehow not a limitation of the car's performance? Of course it is.

There's only electrical power going to the rear wheels on the Nissan though. There's a good 800bhp going just to the front at least.

[rsox87]

DanielSan said:

McSam said:

eally? The limit of adhesion is somehow not a limitation of the car's performance? Of course it is.

There's only electrical power going to the rear wheels on the Nissan though. There's a good 800bhp going just to the front at least.

Not electrical power, the hybrid system on that car is purely mechanical. The only electric motors on it are the starter, wipers, demisters and water pump.

The petrol V6 is 550-600bhp, and is only connected to the front wheels. There's then about another 300-400bhp from the hybrid system connected to the front wheels, and in theory another 200-300 from the one connected to the rear wheels. However, the rear wheel system has been discarded for the moment, so the car is pure FWD. The rear wheels are only there to stop the back end from scraping on the floor.

[McSam]

I didn't know Nissan had been running without the rear motors, thanks, must pay more attention to the testing. I was disappointed not to see it come out to play at Silverstone - thought the ZEOD might have taught them to maximise their mileage in the run-up to Le Mans! In any case, we learn little about road car design from an unconventional and very aero-heavy race car which never need travel below 40mph and is intended to be 4WD when it does.

kiseca said:

theboss said:

Thankyou Rob, that is exactly what I meant. The words limit and limitation are not synonymous.

They're not synonymous? Now you've got my interest. Explain the difference between limit and limitation. I'm particularly interested in the bit where a limit does not present a limitation.

Boss, I'm not sure if you saw my post explaining on the previous page but you're over-simplifying matters and forgetting to compare between the two different drive layouts. It's not about power output, tyres or the grip offered by the road surface - assume all those are equal and compare the behaviour of two otherwise identical cars. The one which spins its wheels more readily in straight-line acceleration will have less desirable handling characteristics at its limit. That's before we get into the obvious subtext that overwhelming the front tyres mid-corner is a one-way ticket to terminal understeer, while overwhelming the rears is a useful and/or entertaining tool to help rotate the car.

Edited by McSam on Tuesday 28th April 12:08

[theboss]

McSam said:

hehe:

Boss, I'm not sure if you saw my post explaining on the previous page but you're over-simplifying matters and forgetting to compare between the two different drive layouts. It's not about power output, tyres or the grip offered by the road surface - assume all those are equal and compare the behaviour of two otherwise identical cars. The one which spins its wheels more readily in straight-line acceleration will have less desirable handling characteristics at its limit. That's before we get into the obvious subtext that overwhelming the front tyres mid-corner is a one-way ticket to terminal understeer, while overwhelming the rears is a useful and/or entertaining tool to help rotate the car.

Edited by McSam on Tuesday 28th April 12:08

I'm not over-simplifying matters at all. The original statement I disagreed with, was a simple one which didn't concern lack of adhesion in cornering, or any such implication for handling characteristics.

Cast your eyes back to this:

kiseca said:

aka_kerrly said:

PorkFan said:

The problem isn't really bhp but torque.

I'm inclined to agree but would add that throttle control is essential.

It does nark me off when people make statements like 200hp/250/300 is too much because you can spin the wheels. It's such rubbish that people blame the car for their own lack of self control.

FYI PorkFan , I've survived many laps in a 360hp K20 rotrexed EP3 with Kaaz diff and Yoko AD08s , rain or shine it puts down a staggering amount of power.

If you have to use partial throttle to avoid spinning the wheels, that's admitting that the car has more power than it can manage.

When the driver then spins the wheels, it means that the driver is failing to compensate for a limitation of the car. It doesn't mean that the car's limitation no longer exists.

This is what I disagreed with - the assertion that a driver regulating throttle input is compensating for a limitation of the car.

Take any car which, at a given speed on a good road surface, is incapable of spinning its driving wheels. Now increase its power until the wheels do spin unless throttle is not regulated. In what way is the second car more limited than the first?

[McSam]

The first car is limited by its engine power, and the second car is limited by the available grip. I won't say this makes the second car "more" limited, and I think we all agree on the type of limitation we prefer around here, but you seemed to be saying it's somehow not a limitation at all. It is, quite plainly.

I'm not saying it's a bad thing, certainly my cars have sufficient power to overwhelm their tyres and I wouldn't have it any other way. But it is a limitation, simple indisputable fact wrapped up in the definition of the word. It's a "new" limitation in the second car, if you like. It goes from being power-limited to grip-limited. To suggest that it's not limited at all is daft, it would have infinite performance.

I was trying to drag this back around to the subject matter, how much power is appropriate for a front-wheel-drive car, by explaining how the straight-line wheelspin issue can be used to highlight handling flaws.

[kiseca]

theboss said:

The two words have subtly different meanings and cannot be unused interchangeably - as you apparently understand yourself in posing the above question.

No I don't, that's why I asked. As far as I'm concerned they are two forms of the same word. You know better, here's a golden opportunity to teach.

theboss said:

I'm not going to argue or explain this point further.

I didn't expect you'd want to, quite frankly. As for "explaining it further", you haven't explained it at all.

theboss said:

I disagreed that the ability or propensity of a car to overcome its limits of traction should not be construed as a general limitation of the car - though of course this presents a literal limitation in its ability to accelerate in those circumstances. Maybe I have misinterpreted the point you were asserting here.

What?? Is it a limitation or is it not?

theboss said:

If a car is constantly overcoming traction limits then it could be argued that the limitation is of the tyres (fit better ones), the road surface (find a dryer/stickier one) or the driver (learn to regulate throttle input).

No, not a limitation of the driver. A limitation of the car that the driver is failing to compensate for. No driver would be able to deploy as much power to the road in that car at that moment as the one sitting there spinning the wheels is asking for. If we all tried to introduce that much power at that moment, we'd all spin the wheels. Regulating throttle input is compensating for a traction limit. Or limitation. Whatever you'd prefer.

theboss said:

It's only a limitation of the car if you consider it to be generally overpowered or underwheeled. But my point is that a 1.0 Micra could spin its wheels when leaving an Aldi carpark, and it cannot reasonably be argued that such a car is limited by virtue of being being overpowered or underwheeled.

It is limited. At that moment it has more power than it can use. Just in a 1.0 Micra it's a limit that's awfully easy to manage and rare to be encountered, therefore unlikely to become the topic for a thread such as this.

theboss said:

Personally I would be inclined to believe the opposite point - that the *inability* of a car to overcome limits of traction in any circumstances, is a limitation of the car. It's not fking powerful enough.

I agree. I don't think these two viewpoints are mutually exclusive. The car either has more power than grip, or it has more grip than power. Or in most cases, it has one or the other depending on conditions. Whatever the case, when it runs out of power or grip, you've reached the limit of how much power you can put on the road in that car at that time.

[kiseca]

theboss said:

This is what I disagreed with - the assertion that a driver regulating throttle input is compensating for a limitation of the car.

Take any car which, at a given speed on a good road surface, is incapable of spinning its driving wheels. Now increase its power until the wheels do spin unless throttle is not regulated. In what way is the second car more limited than the first?

I didn't say it was more limited, and I don't now. They both have limitations on acceleration and grip, but how you find that limit is different in each. The first car can't use all the traction it has. The second one can't use all the power it has. So you compensate for the first by dropping a big fat turbo in (or something). Once you've done that, now you're compensating for the second by limiting engine power by regulating the throttle.

EDIT: Actually, McSam said it a lot better than I did.

Edited by kiseca on Tuesday 28th April 13:00

[mwstewart]

Curently building a 500+bhp FWD hatch. A mechanical diff, 'Revo Knuckle' type uprights, and decent mapping (throttle vs boost) certainly help, but your right foot is the best traction control out there.

[RobM77]

McSam said:

RobM77 said:

McSam said:

theboss said:

The notion that the mere ability to spin its wheels is a limitation of the car, is ridiculous.

Really? The limit of adhesion is somehow not a limitation of the car's performance? Of course it is.

It is in certain conditions at certain speeds, but I think what boss meant was that it wasn't really a significant or notable limitation of the car. For example, a FWD car that spins its wheels at full throttle under 30mph may deliver its power just fine above 30mph - the same in fact will be true of many RWD cars, it's just that they'll need more power to do it. For road driving, which I think applies to the majority of us, I think the choice of drivetrain is more down to handling than loss of traction at low speeds, which for me at least, is completely insignificant.

You have to be careful with this sort of thing, and not just consider whether or not the wheels spin in a straight line on a given road. The car's propensity to spin up in normal acceleration is a marker for how much of the available grip it has to use to deploy its power. This then moves into handling.

If we have two cars which are completely similar apart from which wheels they drive, and the FWD car spins its wheels more readily in straightline acceleration, that car will also be far more limited in attempting to put power down while cornering. A tyre generates a finite amount of grip and it can't give you maximum lateral force at the same time as maximum longitudinal force, so when you're using up some of its capability while cornering, you'd best hope you weren't going to need all of it to try and accelerate or it'll be overwhelmed when you do.

I agree that simply spinning up when you try heroics in first gear isn't a problem, but it is a measure of problems - real performance limitations - you'll run into in normal handling scenarios.

Very true, although power as a singular figure (i.e. 200bhp vs 130bhp) is only one part of the whole picture of a car's handling. If you imagine a typical corner, the initial phases of braking and turn-in are unaffected by power, the mid phase is unaffected, provided the car can reliably and consistently produce enough power to maintain speed and balance the car in the corner (although note that turbos and drive by wire throttles can cause problems here with power coming in and out at unwanted times, which is why I say 'power as a singular figure'), and it's not until you get to that final phase where the car puts its power down properly to leave the corner that what you describe above (traction and power) plays a part in handling.

As an example of this, compare the handling of a Caterham R300 and R500, or perhaps a BMW 318i and a 330i or 205 GTi 1.6 vs 1.9. I guess we come to the definition of 'handling' now, but on a race track power can only ever be a proportion of a car's handling when assessed (i.e. those latter phases of the corner I mention above) and on the public road, where most corners are taken close to or at the legal speed limit, power is usually completely irrelevant. For example, I take all the corners around where I live at the same speed in my 320d as I did in my 330i and that's almost always at the speed limit, so as far as I'm concerned, the handling I experience with the two cars is the same (give or take the subtle differences between 18 and 17 inch wheels), because I'm probably never deploying more than about 30-80bhp to the rear wheels (e.g. on a 50 limit road you may have corner entry @ 50mph, apex @ 45mph and exit @ 50mph), which is why I don't drive a performance road car anymore, as grip levels go up and speed limits come down, they cease to be worth it for me personally. If I lived somewhere full of hairpins and high speed limits, that would be different, but most of us don't.

[McSam]

I totally agree that the available traction only comes into the equation in the exit phase of the corner and doesn't much affect the rest, and that power output is largely irrelevant in normal driving on modern roads - but that would make the whole discussion irrelevant, so I opted to look at the limit handling case!

What you quite rightly point out is why things like 400+bhp Focus RSs can exist. Dynamically it's a horrendous proposition, but it's so rarely relevant in road use that it doesn't cause much of a problem.

[RobM77]

[theboss]

kiseca said:

I didn't say it was more limited, and I don't now. They both have limitations on acceleration and grip, but how you find that limit is different in each. The first car can't use all the traction it has. The second one can't use all the power it has. So you compensate for the first by dropping a big fat turbo in (or something). Once you've done that, now you're compensating for the second by limiting engine power by regulating the throttle.

EDIT: Actually, McSam said it a lot better than I did.

Edited by kiseca on Tuesday 28th April 13:00

I also agree with McSam's longer post on the previous page, despite the fact that he was (I think) disagreeing with me in the process

I think he conveyed his point well - better than I can on a pub lunch.

Re limits and limitations - there are multiple definitions and interpretations and I think we could argue until the cows come home, with neither of us being absolute outright 'winners'. That doesn't suit me, personally.

Google said:

a limiting rule or circumstance; a restriction.
"severe limitations on water use"

synonyms: restriction, curb, restraint, constraint, control, check, clampdown; More
hindrance, impediment, obstacle, obstruction, bar, barrier, block, deterrent, inhibition, damper, brake, reins

"there have been calls for a limitation on the number of newcomers"

antonyms: extension, increase

•a condition of limited ability; a defect or failing.
"she knew her limitations better than she knew her worth"

synonyms: imperfection, flaw, defect, failing, shortcoming, weak point, inability, incapability, deficiency, failure, incapacity, frailty, weakness; More
disability, foible, vice, disadvantage, drawback

"the critic must be aware of his own limitations"

antonyms: strength, strong point

•the action of limiting something.
"the limitation of local authorities' powers"

You can argue that one definition of 'limitation' is the state of reaching an inherent limit but there is a general implication, as above, of imposed limit or restriction. I wouldn't personally agree that it is a 'limitation' of a car that it is capable of reaching its limits of grip. As we both know, any car is subject to limits whether power or grip, there is no possibility of 'limitless' capabilities in either respect. A car that it not limited by power will be limited by grip, and vice versa. Saying that a limitation of a car is that it can overcome traction is rather like saying that a limitation of a car is that it can't take you to the moon and back. Literally true, I concede, but nonsense in the context of most PH conversations.

[McSam]

Not at all interested in the semantics, but I think Kiseca and I both misintepreted your statement that being grip-limited in straight-line acceleration isn't really a limitation of the car. I took that as you saying that front-wheel-drive was no worse, even if it meant more traction problems, because that's up to the driver/tyres to manage rather than being the car's fault. Now I think you were simply arguing that being able to break traction isn't a problem in and of itself, which of course I agree with.

[kiseca]

I thought this whole thread was about the traction limitations of FWD cars, actually. aka_kerrly said it's rubbish to blame the car when it's a driver's lack of control causing wheelspin, I said even if you can drive around it, a limit's still a limit. FWD cars typically have less traction than RWD ones. It's a widely accepted limitation of the layout. That remains true even if you do have a workaround (regulate the throttle more).

Some people like exploiting their car's traction limit, so don't see it as a problem, thus making the OP's thread impossible to answer (never mind that some FWD cars struggled with 150bhp while others now cope easily with 300) but it remains a limit none the less.

[Mr2Mike]

The answer is about 1100 bhp, in a Honda Civic.

[kiseca]

I stand corrected

[Wild Rumpus]

Mr2Mike said:

The answer is about 1100 bhp, in a Honda Civic.

Apparently this one is 1600bhp!
https://www.youtube.com/watch?v=WXBybxxTDk8

[GraemeP]

My old Renault had about 275bhp with trick diff and suspension, and that was very well suited / balanced, and didn't feel like too much power for the chassis.

My current hot Saab (9-3 aero, factory Hirsch upgrades) nearly put me in a hedge when I first overtook a line of slow traffic when it came on boost from me deploying WOT - the torque steer is not one of it's plus points.

I guess it just shows that in different configurations with different technology / application, it can be totally different - it also depends what your subjective view of too much, too little, or just right are (goldilocks).

I'd personally still rather have a narrow wheeled 140bhp Caterham with an LSD for driving fun. Possibly the same with FWD - perhaps a 106 rallye.

[Mr2Mike]

Wild Rumpus said:

Apparently this one is 1600bhp!
https://www.youtube.com/watch?v=WXBybxxTDk8

200mph in 8 seconds in a FWD hatchback, amazing

[kiseca]

CoolFool said:

Mr2Mike said:

200mph in 8 seconds in a FWD hatchback, amazing

Wow!!!!!! What a cool thing it would be to drive at 200mph in a Civic!

Ummmm..