Working out the effect of additional weight on lap times

[Carbon Dev Racing]

Good afternoon Gentlemen,

I have a question that I am having a problem working out accurately, below I have outlined the specifics of the race car parametres nessasary.

Class minimum weight is 525kg's with driver, helmet etc.
Driver A:
Weight compined is 527kg's and produces lap time of 1.08,55

Driver B:
Weight compined is 549kg's and produces lap time of 1.09,81

The engine is a small limited modification unit producing around 40KW's on the rear wheels and is around the same for each car.

The very simple way I thought of (but not sure whether it makes sence) is to use the 525Kg's as a base to work out the power or efficiency loss from the engine however this still doesnt help with projected lap times.

e.g. 549 - 525 = 24
525 / 24 = 21.875% heavier than the rule allow.

assuming a car could still produce the same 40kw on the wheels the Driver B would only have 78.125% of the 40kw...
for example 40kw / 100 x 78.125 = 31.25kw effective?

What are your thoughts on whether this is a fair calculation and please if you know the how to extrapulate potential lap time vs weight differences please could you explain it to me?

driver data above is accurate the drive B has been given a weight penalty for rule book infringement (not to sure what for) however the wieght will come off in three races from now - we just trying to work out our competitivness thereafter.

Thanks gents all the best.

[db__]

e.g. 549 - 525 = 24
525 / 24 = 21.875% heavier than the rule allow.

assuming a car could still produce the same 40kw on the wheels the Driver B would only have 78.125% of the 40kw...
for example 40kw / 100 x 78.125 = 31.25kw effective?

There are some far better mathematicians on this board than me but isn't the maths 24/525=4.57% over which is substantially different to 21.9%.

Thus following your logic: 40kw / 100 x 95.43 = 38.172kw

[rjsa]

First thing you should try is to add 22Kg ballast to the lighter driver and see if lap gains a full second.

[stez90]

It's not only straight acceleration (not power) loss, but also braking and lateral acceleration loss. So it's not so easy to project lap times.
Unless you are talking about dragsters.

The heavier one will accelerate less, brake earlier (bacause he has less negative acceleration) and more (he has to slow down to lower corner-entry speed than the other) and the go into the turn with slower entry and cornering speeds.

This is a simple way to think at it. In real racing there are other factors that may change the result (tire grip vs vertical load for example)..

[Carbon Dev Racing]

Thanks for the replies thus far,
Sorry about the poor math on my part it is closer to 4%...

Anyway, I know weight effects the cars abbility to:
- Accelerate
- Brake
- Hold corning load

The position of the additional weight would effect:??
- Yaw angle
- Pitch on braking
- Pitch mid corner

I read a paper a few years back where the author discusses Formula 1 fuel startagy and one of the big points was the effect of having extra fuel vs the disadvantage to the weight?
Will have a chat to an actuary mate of mine this evening regarding the parameters but would prefer to go in with an idea of how to work this out. I have been looking at photo's from the event inquestion seems like they are running the engine almost on its side in addition to some trick bits on the front beam - will attach in due course for discussion.

Regards,

[Lycoming]

First thing you should try is to add 22Kg ballast to the lighter driver and see if lap gains a full second.

This.

Also, it doesn't make sense to think in terms of "effective horsepower" because mass effects speed everywhere, but engine output only affects speed on straights. Depending on the nature of the courses you run, this may or may not be relatively insignificant compared to the effect of mass.

I'm not sure about yaw angle but in terms of % weight transfer under braking, mass won't cause a change if CoG position doesn't change (I think; the equation for this is in tune to win). However, total acceleration will be less due to load sensitivity. Will you have more actual weight transfer? not sure; but that will be what affects pitch on braking, assuming nothing else is changing.

If mid corner is steady state with 0 longitudinal acceleration, I suspect pitch wouldn't change.

Of course, a lot of the above is subject to how CoG position changes between drivers. Depending on your seating position, this may or may not be significant.

[Carbon Dev Racing]

Hi Guys,

A small update.
We run AIM telemetry and after reading the thoughts in this thread I figure well we keep track of our times and weights for each event as well as weather etc so should be fairly easy to pull a figure based on average sec vs Kg's above usual static race weight.

After looking through probably 70% of the data available the number that sticks out the most for our cars is .0932 per lap per extra Kg? It seems fairly accurate but that means although we won the first round we have a compititor who is roughly capable of going 2.2368 secs a lap quicker?

Most of the data used came from a test day where we ran 3 sets of balast based on the rule changes that we were expecting which was to increase the minimum mass which used to be 520kg's but grid speculation was that it would end up being changed to 530kg's. On our test day we had run our cars from 522kg's up in increments of 2.5Kg's.

Is this figure something you chaps would consider about right? (0.0932sec per lap / per kg)

[Jersey Tom]

Is this figure something you chaps would consider about right? (0.0932sec per lap / per kg)

Who knows. Maybe, maybe not. Honestly without having first hand experience in the series or this type of car, how can we even venture a guess?

If you have data and you come up with about a tenth per kg.. well.. then there ya go!

[turbof1]

I very much doubt the fuel load in function of the laptime is lineair. IMO, the more extra fuel you add, the bigger the marginal disadvantage will be in laptime.

[stez90]

Try to look at the correlation between % of ballast (or drivers difference) over the total car weight. I think it's better than just plain weight.
Extreme example:
Think to increase weight 1kg by 1kg.
If you have a 100kg car, +1kg ballast is 1% difference; if you have a 100kg car +100kg ballast already on, when you add another 1kg of ballast the difference between 100+100kg and 100+101kg configuration it's 0.5%, not 1%, so the extra 1kg is less influent on your performance than before.

[Greg Locock]

It might be a idea to grab hold of LapSim (free) and see if you can build a model that roughly represents your car, and then see what effect the weight difference makes on a similar circuit to yours. If you still listen tot he commentary on f1 then you will often hear them say that X kg is worth a second on that circuit.

[langwadt]

First thing you should try is to add 22Kg ballast to the lighter driver and see if lap gains a full second.

This.

Also, it doesn't make sense to think in terms of "effective horsepower" because mass effects speed everywhere, but engine output only affects speed on straights. Depending on the nature of the courses you run, this may or may not be relatively insignificant compared to the effect of mass.
-snip

eventually the drag down the straight means you have no power to accelerate, but until that as long as you can get the power to the ground more power and/or less mass means more acceleration if physics is to believed