Power to weight vs power and weight
Discussion
An interesting case study into the differences in power & weight (and even if irrelevant, it's good fun to watch)
http://youtu.be/t3ppTh3TYtA
http://youtu.be/t3ppTh3TYtA
NJH said:
Woof it was obvious as soon as the 996 was introduced a few years back that it was the car to have. Then Hartech went and won the thing with a boxster turning all expectations on the head, same when the 968 was allowed into class 2, they might be much heavier than an S2 in the regs and in theory very little difference in straight line performance but everyone quickly felt that the two most powerful allowed cars (boxster 2.7 and 968) became the cars to have.
Something else is that these comparisons are very dependant on the circuit, I don't like driving my car so much on the GP circuit at Silverstone as it just feels utterly gutless along those straights, a much more powerful car like a 964 or 993 or 996 just romps off into the distance once in front. The gear ratios also don't work there as you keep hitting the top of 3rd in the bends whereas the more powerful cars have the longer gears which work better there (gears must be standard in regs same as for lots of production car based racing).
One thing is fairly certain though, the heavier cars always cost a lot more to run.
Having Tom Bradshaw definitely helped Hartech win that year for sure. It's very hard to try and match car for car and I know the PCGB come in for a lot of stick for not getting it right. I really like the CSCC modern & future classic format. Almost all comers style and gives some terrific racing. Something else is that these comparisons are very dependant on the circuit, I don't like driving my car so much on the GP circuit at Silverstone as it just feels utterly gutless along those straights, a much more powerful car like a 964 or 993 or 996 just romps off into the distance once in front. The gear ratios also don't work there as you keep hitting the top of 3rd in the bends whereas the more powerful cars have the longer gears which work better there (gears must be standard in regs same as for lots of production car based racing).
One thing is fairly certain though, the heavier cars always cost a lot more to run.
Anyway back to topic
matlockscot said:
An interesting case study into the differences in power & weight (and even if irrelevant, it's good fun to watch)
http://youtu.be/t3ppTh3TYtA
Enjoyed that, Yes, VERY much shows the power to weight differences http://youtu.be/t3ppTh3TYtA
I think the Lotus Cortina drivers spacial awareness needs a bit of work!
Ask Barry Hart (Hartech). When they started in the PCGB Championship I modified one of the cars in rFactor to produce similar max and corner apex speeds (and hence lap times) to that recorded on the data logger of a real car such that we could estimate the effects of doing different things. This was very time consuming but quite enlightening. Baz then found a software package for doing the same things that didn't involve someone or an AI driving around in a computer game. He has done stacks and stacks of analysis over the past few years much of which isn't public as its the stuff those guys do to improve their race performance but its this work he has done which led to the many posts over on the PCGB forum about the power, weight and performance comparisons of the various models in the Championship.
Back in the day, the Scottish Saloons was dominated by a 205 running an MI16, and 3 cossies.
Mostly, the 205 qualified first (but only just) at Knockhill. The problem it had was that unless it scampered off into the distance, once it got tangled with the Cossies it'd get overtaken no matter what over the top of the hill on the straight on the last lap - so come second over the finishing line.
For ultimate lap time, it seemed pretty even but with nimbleness ever so slightly ahead - but in racing reality, the higher power car was more capable of fighting for position - just like we see in F1 when the high drag, low top speed Red Bull often can't overtake the lower downforce, but faster down the straight Force Indias..
Mostly, the 205 qualified first (but only just) at Knockhill. The problem it had was that unless it scampered off into the distance, once it got tangled with the Cossies it'd get overtaken no matter what over the top of the hill on the straight on the last lap - so come second over the finishing line.
For ultimate lap time, it seemed pretty even but with nimbleness ever so slightly ahead - but in racing reality, the higher power car was more capable of fighting for position - just like we see in F1 when the high drag, low top speed Red Bull often can't overtake the lower downforce, but faster down the straight Force Indias..
NJH said:
Ask Barry Hart (Hartech). When they started in the PCGB Championship I modified one of the cars in rFactor to produce similar max and corner apex speeds (and hence lap times) to that recorded on the data logger of a real car such that we could estimate the effects of doing different things. This was very time consuming but quite enlightening. Baz then found a software package for doing the same things that didn't involve someone or an AI driving around in a computer game. He has done stacks and stacks of analysis over the past few years much of which isn't public as its the stuff those guys do to improve their race performance but its this work he has done which led to the many posts over on the PCGB forum about the power, weight and performance comparisons of the various models in the Championship.
I like Barry - got a lot of time for him. Just wonder if I could ply any info out of him ! Just as a general question. If a car weighed 1280kg (Porsche Boxster) I wonder if taking out 30kg would make the slightest difference ?
woof said:
Just as a general question. If a car weighed 1280kg (Porsche Boxster) I wonder if taking out 30kg would make the slightest difference ?
what you doing carrying 30kg around you don't need?I was running in the CSCC future classics around 6 or more years ago, I was consistently qualifying between 10th and 14th. I took 50kg out, mainly HVAC, pop up lights and passenger seat. I then became a consistent top 5.
it took a 1100kg car down to 1050kg and knocked off around 1 second a lap at Brands hatch indy.
I always view how much weight I can liberate from my car in fuel terms. 30kg would almost be equivalent to a full tank of fuel for me so it would definitely make a difference (same difference as lap times at the start to final lap with an empty tank) It would also make a difference depending on where you took the weight from. My car is definitely more tail happy with an empty tank so if im not careful it would make me slower! I also noticed a huge difference when I fitted lighter alloys, they couldnt have been more than 2kg a corner lighter but I could feel the difference in acceleration. All about reducing rotational mass and unsprung weight!
One point, would the more powerful car not always have more torque, which would always make a difference when it comes to acceleration once youre up and moving?
One point, would the more powerful car not always have more torque, which would always make a difference when it comes to acceleration once youre up and moving?
Edited by Trek930 on Friday 23 January 09:18
Trek930 said:
One point, would the more powerful car not always have more torque, which would always make a difference when it comes to acceleration once youre up and moving?
A more powerful car will make more torque at the wheels, but given that we are saying that the weights of the cars are in proportion to their power, that would be exactly offset by the weight.otolith said:
Trek930 said:
One point, would the more powerful car not always have more torque, which would always make a difference when it comes to acceleration once youre up and moving?
A more powerful car will make more torque at the wheels, but given that we are saying that the weights of the cars are in proportion to their power, that would be exactly offset by the weight.Regarding the original question, there are many variables to consider and as far as I am aware there isn't a simple 'yes or no' answer. There are factors to consider;
- Power/Torque curves : Absolute power to weight ratio doesn't tell the full story. This is the biggest flaw with your question in my opinion.
- Unsprung mass : A heavier car needs stronger (usually heavier) suspension. Unsprung mass included 1/3 of the mass of the suspension and it is undesirable to vehicle handling.
- Traction : A heavier car will actually produce more tractive force. So as you say, the differences between the two cars will depend on each circuit. The Nissan GTR is a good example of a car that was intentionally quite 'large' and yet still develops excellent cornering forces and acceleration and deceleration.
I will ask my lecturer in February for his views too. He'll be able to give a more concise, but detailed reply no doubt.
SpeedMattersNot said:
otolith said:
Trek930 said:
One point, would the more powerful car not always have more torque, which would always make a difference when it comes to acceleration once youre up and moving?
A more powerful car will make more torque at the wheels, but given that we are saying that the weights of the cars are in proportion to their power, that would be exactly offset by the weight.wildman0609 said:
woof said:
Just as a general question. If a car weighed 1280kg (Porsche Boxster) I wonder if taking out 30kg would make the slightest difference ?
what you doing carrying 30kg around you don't need?I was running in the CSCC future classics around 6 or more years ago, I was consistently qualifying between 10th and 14th. I took 50kg out, mainly HVAC, pop up lights and passenger seat. I then became a consistent top 5.
it took a 1100kg car down to 1050kg and knocked off around 1 second a lap at Brands hatch indy.
SpeedMattersNot said:
- Unsprung mass : A heavier car needs stronger (usually heavier) suspension. Unsprung mass included 1/3 of the mass of the suspension and it is undesirable to vehicle handling.
- Traction : A heavier car will actually produce more tractive force. So as you say, the differences between the two cars will depend on each circuit. The Nissan GTR is a good example of a car that was intentionally quite 'large' and yet still develops excellent cornering forces and acceleration and deceleration.
I will ask my lecturer in February for his views too. He'll be able to give a more concise, but detailed reply no doubt.
However, you'll find that the heavier cars actually tend to have much better sprung/unsprung weight ratio's, because there's fixed weights that can't be scaled in the system, or are stiffness related, and doubling the stiffness of something doesn't usually mean anywhere near a doubling of weight.- Traction : A heavier car will actually produce more tractive force. So as you say, the differences between the two cars will depend on each circuit. The Nissan GTR is a good example of a car that was intentionally quite 'large' and yet still develops excellent cornering forces and acceleration and deceleration.
I will ask my lecturer in February for his views too. He'll be able to give a more concise, but detailed reply no doubt.
As to the tractive force thing, this comes up with the GTR all the time - it's no good having more tractive force by virtue of weight, when all it means is you have more mass to accelerate, tyre adhesion being what it is, that's a loosing battle all the way.
Class B: GT300/1160kg
Class C: GT250/1100kg
Class D: GT200/1060kg
Class E: GT150/1010kg
Nippon Challenge classes.
I run my MR2 series spec car with 125 hoss in this series and it weighs in at 1065kg. It's the same weight as a GT200 and running 75 hoss less and is an equal match for many of the cars in that class. It does lose out on the straights and as we have control tyres, there is not so much advantage in the corners.
Sorry I have no maths but it's the same weight with less hosses so the size and layout must be a huge factor as well. Just saying.
Class C: GT250/1100kg
Class D: GT200/1060kg
Class E: GT150/1010kg
Nippon Challenge classes.
I run my MR2 series spec car with 125 hoss in this series and it weighs in at 1065kg. It's the same weight as a GT200 and running 75 hoss less and is an equal match for many of the cars in that class. It does lose out on the straights and as we have control tyres, there is not so much advantage in the corners.
Sorry I have no maths but it's the same weight with less hosses so the size and layout must be a huge factor as well. Just saying.
Classes in the BMW Kumho Championship have an engine size limit & power to weight cap. No max or minimum weights though.
I simply look at it more power will help you accelerate and get to a higher top speed.
Less weight will help you accelerate, brake & corner. Whilst being easier on tyres, fuel and brakes, and if starting with a road car as the base for a race car, removing weight is the cheapest mod :-)
I simply look at it more power will help you accelerate and get to a higher top speed.
Less weight will help you accelerate, brake & corner. Whilst being easier on tyres, fuel and brakes, and if starting with a road car as the base for a race car, removing weight is the cheapest mod :-)
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