23 replies to this topic

[Scuderia Pinguino]

I hope this doesn't sound naive but does anyone know a formula for calculating the effect of weight on lap times.

To give a specific example. I have a race car that weighs 600 kgs and the competition weighs 520kgs i.e 80 kgs overweight. My car laps a 2.62 circuit in 1 min 29.8 secs. I would like to try and work out what time improvement per lap would be per kilo reduced. If it helps, the engine develops a little over 300bhp.

Any help on this would be very much appreciated

Colin Pool

[karlth]

80kg is a huge difference.

Michelin publish in their race preview an estimate of how much of a difference 10kg of weight would make. It usually is around 0.3s per lap.

The accurate number in your case would depend on the track layout.

[Pong]

Also,

the weight is not the only criterion. You probably need to work out the Polar Moment of Inertia for the new and the old weight as well as the CoG. The polar moment of inertia will let you calculate difference in the energy needed to actually turn the car, while knowing the CoG could let you calculate the difference in tire loads. The resulting gain from these two might teoretically be used for increased speeds.

Sounds good?

[Double Apex]

Originally posted by karlth
80kg is a huge difference.

Michelin publish in their race preview an estimate of how much of a difference 10kg of weight would make. It usually is around 0.3s per lap.

The accurate number in your case would depend on the track layout.

In this case, the difference is probably even bigger as his car is seriously down on power compared to an F1 car with the weight being more or less the same.

[Dynojet]

Also,

the weight is not the only criterion. You probably need to work out the Polar Moment of Inertia for the new and the old weight as well as the CoG. The polar moment of inertia will let you calculate difference in the energy needed to actually turn the car, while knowing the CoG could let you calculate the difference in tire loads. The resulting gain from these two might teoretically be used for increased speeds.

Sounds good?

A SAE paper signed by Pat Symonds about minimum time manouvering simulation (Lap Time Simulation for Racing Car Design) concludes that polar moment of inertia has low influence in lap times, despite the importance to the car transient manouvering response and from the control viewpoint.

Thomas

[Schummy]

I think I remember an old thread about this somewhere in this forum. I don't remember the title of it so I'm sorry I cannot help to search it

[Scuderia Pinguino]

Thank you all for all this info. The more I think about it, the more factors come into play which makes the calculation more complicated. For instance circuit data must feature. i.e I guess that a circuit with a steep uphill section would have a more detrimental effect than a flat one. Tyre loading must also play a big part.

The circuit in my case is Brands GP which has more than its fair share of hills. Please keep the ideas coming

[Janzen]

Hi, What i thought was interesting was the fast laps posted after pit stops in the last race.
So it seems that the early advantage of new tires are a bigger advantage than a light car, but this might have been just this race and for sure every kg saved will help you.

[WPT]

Determine: 1)Hp vs RPM 2) overall gear ratios 3)drive tire rolling radius 4)drag Hp. Graph on one sheet of paper Hp vs MPH. Where the Hp curves intersect are the ideal shift points. Graph on the above Hp graph the drag Hp.

[WPT]

At any given speed the gear Hp minus the drag Hp is the Hp available to accelerate the car. For small speed interval determine the average acceleration (use F=ma, 1Hp=550 ft-lbs of work per second, Hp=FxSpeed). For the interval calculate the distance and time required to cover the interval. In this way a lap time can be determined. It is easy to account for wind and road grades by modifying the drag Hp curve. WPT

[karlth]

Originally posted by Scuderia Pinguino
Thank you all for all this info. The more I think about it, the more factors come into play which makes the calculation more complicated. For instance circuit data must feature. i.e I guess that a circuit with a steep uphill section would have a more detrimental effect than a flat one. Tyre loading must also play a big part.

The circuit in my case is Brands GP which has more than its fair share of hills. Please keep the ideas coming

You could try giving Bedford Autodrome a call and asking some of the engineers this question as I think the FPA cars have similar specs you mention.

[Scuderia Pinguino]

Thank you WPT, Since I failed my maths 'O' level many moons ago, this is going to take a bit of working out. Colin

[desmo]

http://www.atlasf1.c...&threadid=41544

The thread linked to above discussed this issue here. Benzing, looking at laptime data gives as a rule of thumb: 0.04sec/kg for low speed circuits, 0.03sec/kg for medium, and 0.02sec/kg for high speed for F1 cars.

[Double Apex]

Desmo, don't you think there's a big difference between a 900 Bhp F1-car and Colin's 300 Bhp car? Especially since the weight of both cars is pretty similar! I would expect a single kilo to be making a significantly bigger difference in Colin's case.

[Double Apex]

His brakes are also likely to be a lot weaker than brakes on an F1-car...

[Halfwitt]

Colin,

eat a lot of pies (say 50kg worth) and see what difference it makes to lap times. If it is significant, then use the time it takes you to diet back to your normal weight to take the weight off the car.

[Schummy]

The weight-laptime effect has to be put in terms of percentage of laptime. So it not only takes in account the different lenght of laps but it partially takes in account the level of HP in the car.

I'm with Halfwitt, the old good experiment automatically gives you what happen when you modify the weight: put extra weight and then interpolate or extrapolate to guess the approximate "law" weight-laptime (in terms of percentage).

[Yelnats]

Originally posted by Scuderia Pinguino
I hope this doesn't sound naive but does anyone know a formula for calculating the effect of weight on lap times.

To give a specific example. I have a race car that weighs 600 kgs and the competition weighs 520kgs i.e 80 kgs overweight. My car laps a 2.62 circuit in 1 min 29.8 secs. I would like to try and work out what time improvement per lap would be per kilo reduced. If it helps, the engine develops a little over 300bhp.

Any help on this would be very much appreciated

Colin Pool

Since tracks can vary in configuration from Daytona to Monaco it would be impossible to develop a single formula to calculate the effects of weight on lap times. The best we can do is apply approximations developed from F1 lap times as fuel is consumed and this is tricky because tire degredation must be compensated for.

If you looked at the lap times in the Atlas race summaries and examined the before and after lap times of a few cars that were refueled without changing tires (almost certainly Michelins) I'm sure you could develop a pretty good approximation for us.

[WPT]

The method outlined by me above is ideal for programing on a digital computer. I would think there is software already available, perhaps in predicting 1/4 mile ETs and trap speeds. In the fifties Mercedes Benz did such calculations for their GP team. They used this info for selecting what ratios to install in the gear box, and the drivers could compare their lap times to the predicted. WPT

[Yelnats]

There is inexpensive software that any of us can purchase at the local shopping mall that will do an excellent job of calculating the effects of weight on lap times and that that is the racing sim/game software GP4 (Grand Prix 4).

Over the last decade some of the very good minds in the computer and racing world have dedicated their efforts into making GP4 as close to reality as possible. By modifying the weight of the sim racer with third party software a pretty accurate picture of the effects of weight on lap times can be found (especially with the computer driving). It will also spit out some excellent graphs of speed/distance showing shift points and rpms to save all that graphing and paperwork when attempting to do this manually.

[Scuderia Pinguino]

Since starting this thread, I have come across an old copy of Carroll Smiths' 'Tune to win'

Although written in 1978, it does go into this subject in depth but there any number of factors involved that require consideration e.g Linear acceleration, Rotational inertia, Centrifugal acceleration, Power to Weight ratio, CG, Mass centroid axis, Roll centre, Roll moment, Polar moment of Inertia, Static weight distribution, Dynamic load transfer, Aerodynamic load, Longitudinal load transfer etc etc etc.

Having struggled through this lot, I think I like the idea of GP F1 !!!

[Dynojet]

Hi

I finaly put my hands on the Pat Symonds paper called "Sensitivity to mass variations of the fastest possible lap of a formula one car".

The results show a increase between 0,036 and 0,037 s/kg/lap. It's a teorethical result, but valuated by the measurements.

[AndreasNystrom]

at a recent trackday I was on, (where we drove our roadcars), the fastest cars were lightwheight cars (Honda Civic 3d, Sierra), where the ones (which mainly was sportscars, and rallyesque Subarus and mitsus) with bigger engines, and way more wheight didnt corner as fast, nor could they leave the corner with as much speed as the lighter cars, and their brakes were no good after a few laps.

Lets say the honda could corner at 100km/h, and the bigger cars 80km/h, the honda could start accelerate earlier too out of the corner, which would make him maybe 25km/h faster out of the corner then the bigger cars, which the bigger cars, which are faster on the straights never could catch, since they already were approaching the next corner when they got a bit closee.


I would never tune my engine in my car, before i fit some better brakes, and lower the overall wheight of the car overall.
Just my hood for the engine wheights 8kg+ and get a carbonf. one would probably make it better, aswell as the wheightbalance could be a little little bit better.
Remove all glasswindows, with some lowwheight material, move battery to rear of car, etc etc.

Then install big-motha brakes, with some kind of cooling-duct, then i would go for the engine

even an old Lotus Europa showed big class at the track btw less then 700kg and 126hp+

[Ben]

http://www.ee.ic.ac....VSDmass_sen.pdf

Ben