Is there a 'minimum' weight?

[Buen]

I was just thinking. How the car world is obsessed with light weight, is there a minimum weight for a car to be usefull?

What I mean is, if we immagine that we lived in a world where it was possible to make a 25kg supercar with 1000hp, would that be benefitial, or would it be better of, weighting, say 200kg?

Is that weight needed for it to handle, have grip and perform well? Or is the weight of the driver alone enought?

[TVR IS KING]

Lack of weight can always be alleviated with trick aerodynamics, that convert speed into downforce. The benefit of this is that, when doing slower corners, the car benefits from being lightweight, but at faster speeds it hunkers down.
Of course, acceleration at low speeds would be a problem. But I suppose it balances out to a degree. There's less downforce from weight, so less grip, but less grip is required as there's less weight to move. If you consider it that way, maybe there isn't a minimum weight.

[pimento]

The answer is no, except when it's yes. Or yes, except when it's no. There's pros, cons, arguements and realism but it comes down to how theoretical you want to be and what the circumstances are. At low speeds weight can help mechanical grip.. but at high speeds aero grip is more important. Blah blah blah.

[RacingManiac]

at somepoint environmental effect will be a concern, cross wind, low traction surface...anything that prevents you from applying downforce to actually grip the tire to the pavement.

[charged]

I have yet to see someone put extra weight in a race car, the lighter the better. Low speed mechanical grip wont be a problem, it can be over come but softer compound tyres due to the lack of weight and aero will help in highspeed corners

[whiteballz]

IIRC some company or UNI did a study and found around 250Kw per 500Kg.. Something like that.

[wwgkd]

I have yet to see someone put extra weight in a race car, the lighter the better. Low speed mechanical grip wont be a problem, it can be over come but softer compound tyres due to the lack of weight and aero will help in highspeed corners

This. I keep hearing how light weight cars don't have grip, then there's the Caterham 7 sticking to the road like a virgin on a supermodel. Granted 1000bhp in a 25kg car would have massive power to weight, but you would have the same problem controlling that as in a "normal" weight car with 50,000bhp.

[Matra et Alpine]

Agreed, charged, but these cars are ALREADY sitting with substantial weight.

As the initial thread asks .. with nothing else is there a MINIMUM and the answer is yes, determined by the tyres. More specifically the contact patch for the tyre. It determines a minimum for the mechanical grip necessary to permit enough traction to provide enough motive power.

So, as you drive the weight down, what you do is ALSO drive the wheel/tyre design to provide the most effective contact patch shape/size for the traction. Thus, why when you get to the minimum for human motive power you get to a bike sized tyre/wheel.

So, as already alluded to. Answer the other questions and we can decide whether to answer you yes or no

First one is how are you powering it and what purpose does the vehicle have ? To transport, one or more people ? What about safety ( coz again that is ANOTHER factor determining form factor ).

Isn't it a bummer when you think it's a simple question and hope to get a simple answer

EDIT. 25 years ago, Ford RS200 was the champ, 1000kg, AWD

[charged]

True Matra there would be a point were no traction for acceleration,braking, cornering come in to play.

Look at the fastest accelerating car in the world the Top Fuel Dragster they make over 8000hp and weigh about 1000kg, they overcome their ridiculously high p/w ratio by a combination of extremely soft tyres, clever use of clutches, flex in the chassis and once they pass the 60ft marker massive down force from the rear wing. If someone said my car has a power to weight ratio of 8hp/kg you would be thinking how can it possibly get all that HP to the ground without the tyres going up in smoke but with the design parameters mentioned above it achieves this feat.

[csl177]

Isn't it a bummer when you think it's a simple question and hope to get a simple answer

It can be simple: about 800kg & 400HP with 8" wheels and 50/50 weight distribution is the perfect weight/power ratio for a thoroughly entertaining but streetable car, regardless of configuration. Anything lighter and more powerful would be impractical and unusable for the average enthusiast.

The basic laws of physics are our friend. Defy them at your personal risk and social embarassment.

[charged]

It can be simple: about 800kg & 400HP with 8" wheels and 50/50 weight distribution is the perfect weight/power ratio for a thoroughly entertaining but streetable car, regardless of configuration. Anything lighter and more powerful would be impractical and unusable for the average enthusiast.

The basic laws of physics are our friend. Defy them at your personal risk and social embarassment.

That is a very quick street car and I'm not sure a average enthusiast wouldn't get in trouble with it, my nephews race cars virtually are identical to that except run a 53/47 weight distribution on 8 in rims with 225/50/15/ tyres and they are definitely not easy to drive

Your figures


RWD - 400bhp & 800kg
Power to Weight: 508 bhp/ton
0-60: 3.3
0-100: 7.4
60-100: 4.1
1/4 Mile ET: 11.40
1/4 Mile Terminal: 124
Dragstrip 1/4 Mile ET: 11.20
Dragstrip 1/4 Mile Terminal: 127

[Matra et Alpine]

posibly concur, csl, BUT that's not the question.

Your car WOUDL be entertaining and streetable - kind of.
You just described the first version of the RS200

Lots of cars are lighter and ARE practical and usuable.
eg Sylva Striker, 600kg, used as a daily driver including an occasional "commute" from Edinburgh to Doubreay and also in hillclimbs, trackdays AND rallies - me co-driver
It was a pussycat to drive.

[Alastor]

at somepoint environmental effect will be a concern, cross wind, low traction surface...anything that prevents you from applying downforce to actually grip the tire to the pavement.

I agree, generally speaking lighter = more grip, but it seems like the lower limit would be when external forces start to dominate the tire forces.

[Matra et Alpine]

typo Alastor ? lighter is LESS grip. Given all other things equal.
Drop the weight and the tyre contact patch shrinks.

[pimento]

More weight = more grip but more intertia. Gotsta find the sweet spot, see.