Effect on lap times

[Bleu Omdurman]

Hey guys,

This post is directed at those that track their cars often and have made a couple of changes to the car, and noted the difference, if any.

As I posted in the "another physics question" thread, I am building a decision model to aid in picking the optimal modifcation set, given a certain budget. It uses Microsoft Solver. The objective function is to minimize lap time. In other words, modifications are decided upon based on their effect on laptime as a function of cost.

Three of my decision variables that effect laptime are:

1) Required lbs lost to drop 1 second of laptime.
2) Required HP gain to drop 1 second of laptime.
3) Required lbs of downforce to drop 1 second of laptime.

Clearly, what track you are minimizing laptime on, is important. That is why the three above are variables and not constants.

Here is a recommended format for your reply.

BWR S/C +53 hp, 1 second gain at Leguna Seca
CF Diffuser, -10lbs weight, +5lbs downforce, 8 tenths at Sebring

anything helps.

BTW, the numbers I am using now are 100 lbs/sec weight, 15hp/sec, 30lbs/sec downforce

(edit: up'd DF to 30 lbs.)

[apk919]

Originally Posted by Bleu Omdurman

Hey guys,

This post is directed at those that track their cars often and have made a couple of changes to the car, and noted the difference, if any.

As I posted in the "another physics question" thread, I am building a decision model to aid in picking the optimal modifcation set, given a certain budget. It uses Microsoft Solver. The objective function is to minimize lap time. In other words, modifications are decided upon based on their effect on laptime as a function of cost.

Three of my decision variables that effect laptime are:

1) Required lbs lost to drop 1 second of laptime.
2) Required HP gain to drop 1 second of laptime.
3) Required lbs of downforce to drop 1 second of laptime.

Clearly, what track you are minimizing laptime on, is important. That is why the three above are variables and not constants.

Here is a recommended format for your reply.

BWR S/C +53 hp, 1 second gain at Leguna Seca
CF Diffuser, -10lbs weight, +5lbs downforce, 8 tenths at Sebring

anything helps.

BTW, the numbers I am using now are 100 lbs/sec weight, 15hp/sec, 20lbs/sec downforce

Sounds like an interesting project; I've written software models for other fields, never for a car. Actually started in HS writing a mathematical model for the performance envelope of an F-14.

Which brings me to a question: are you adding in the effect of increased aero drag with the increased aero downforce? Also, are you taking into consideration that aero lift/drag has a square law relationship with speed?

[Bleu Omdurman]

While you are correct with those effects, I am not considering those directly, but accounting for them indirectly.

Specifically, I am asking for lbs of DF and how many seconds of gain. That would take into account the drag effect on top speed as speed is a function of time and distance. I get the distance from the track name, and the time from the poster. Hopefully,

[rwarden]

Originally Posted by Bleu Omdurman

Hey guys,

This post is directed at those that track their cars often and have made a couple of changes to the car, and noted the difference, if any.

As I posted in the "another physics question" thread, I am building a decision model to aid in picking the optimal modifcation set, given a certain budget. It uses Microsoft Solver. The objective function is to minimize lap time. In other words, modifications are decided upon based on their effect on laptime as a function of cost.

Three of my decision variables that effect laptime are:

1) Required lbs lost to drop 1 second of laptime.
2) Required HP gain to drop 1 second of laptime.
3) Required lbs of downforce to drop 1 second of laptime.

Clearly, what track you are minimizing laptime on, is important. That is why the three above are variables and not constants.

Here is a recommended format for your reply.

BWR S/C +53 hp, 1 second gain at Leguna Seca
CF Diffuser, -10lbs weight, +5lbs downforce, 8 tenths at Sebring

anything helps.

BTW, the numbers I am using now are 100 lbs/sec weight, 15hp/sec, 20lbs/sec downforce

One variable you've not listed is "driver experience" - perhaps intentionally, or not? If you consider youself an expert driver, and have little new to learn, great, this experiment makes sense, but if you are new to road course driving, your best bang for the buck in terms of reducing your laptime is driver training/experience.... just my $0.02...

R Warden

[John]

Another factor is the condition of the track. How "green" is it. What's the ambient temperature? On a track day with optimum weather, you'll often see track records get broken by almost 2 seconds in many "stock" classes.

[chrisp993]

Originally Posted by rwarden

One variable you've not listed is "driver experience" - perhaps intentionally, or not? If you consider youself an expert driver, and have little new to learn, great, this experiment makes sense, but if you are new to road course driving, your best bang for the buck in terms of reducing your laptime is driver training/experience.... just my $0.02...

R Warden

Unless any of the answers have the condition that the driver is a professional (as in good enough to get paid for his driving and opinion) then the answers are pretty meaningless in any scientific sense - the drivers own learning curve, conditions on the day and lack of consistency / clean data or even reliable data acquisition / laptiming would render the answer akin to butt-dyno stuff at best.

In any case, even with perfect driver etc. the answers to your questions would vary very widely from track to track and day to day e.g. a tight, twisty, slow track would have a very different answer to the lbs or hp per second answer than an oval with an infield. Ditto for a hot day, cold day, damp day etc.

With the greatest respect, this isn't a serious exercise!

All that said, with the goal of at least being a bit helpful, have you checked out the (free) Bosch Lapsim also discussed here RaceSim Central

[Bleu Omdurman]

Originally Posted by rwarden

One variable you've not listed is "driver experience" - perhaps intentionally, or not? If you consider youself an expert driver, and have little new to learn, great, this experiment makes sense, but if you are new to road course driving, your best bang for the buck in terms of reducing your laptime is driver training/experience.... just my $0.02...

R Warden

Thanks. I am not new to the sport. However, this is a tool to decide what mods to do to the car not to the driver. I think I have a pretty decent plan going on the driver education bit. Many people here choose to mod their cars, I probably will someday too. When that time comes, I intend to make the optimal selection. What is an optimal selection? Well that depends on quite a large number of factors. I'm asking for help with three of those factors here.

I know it is hard to picture exactly what I am trying to do. So imagine this. You are about to spend (pick your budget) on your car. In general, you either want to improve how it looks, or how it performs. So lets say that you decide you what to focus on performance. Should you buy brakes? If so what kind. how do you know which brakes are best? Is it the 60-0 time? some other function? Maybe a function of how fast they stop the car, how long they last on the track until they fade, and cost? Ok, lets work that out for each brake kit on the market. do you need to make a couple of reasonable assumptions to avoid complicated calculations involving expensive test equipment? of course you do. Now at this point, most people just give up and say "it depends on too many variables". On the other hand, I say, actually, with a couple of simple assumptions you can get to about the 95% confidence level (so to speak) of the correct answer. Is that close enough for you to make a decision? Probably. It is close enought to put a person on the moon? Probably not.

So in short, this is not a simulator (it will not tell me how fast I will go around a track.) It is a decision tool. It will tell me which modification set will most improve the car, given certain constraints. So far the results have been interesting. Not amazing, but it saves some work and thought.

[Bleu Omdurman]

Originally Posted by chrisp993

Unless any of the answers have the condition that the driver is a professional (as in good enough to get paid for his driving and opinion) then the answers are pretty meaningless in any scientific sense - the drivers own learning curve, conditions on the day and lack of consistency / clean data or even reliable data acquisition / laptiming would render the answer akin to butt-dyno stuff at best.

In any case, even with perfect driver etc. the answers to your questions would vary very widely from track to track and day to day e.g. a tight, twisty, slow track would have a very different answer to the lbs or hp per second answer than an oval with an infield. Ditto for a hot day, cold day, damp day etc.

With the greatest respect, this isn't a serious exercise!

All that said, with the goal of at least being a bit helpful, have you checked out the (free) Bosch Lapsim also discussed here RaceSim Central

I can always count on someone to miss the point and not answer the question. Again, this is not a simulator, it is a decision tool. With the greatest respect, the is a serious exercise.



Again, please respond only if you have something useful to add. I.e you track your car and have made an adjustment to the car and noted a difference. All else being equal.

[chrisp993]

Bleu

My apologies - I didn't mean to be quite so negative. But I am serious that the biggest single difference one track event to the other, is likely to be the driver, so - I didn't miss the point - I do not believe you will get data that is meaningful for YOU.

I'd also be suspect of your model / assumptions: by way of example - in your OP you stated that 10lbs of downforce = 1 sec. Can I tell you what 10lbs of downforce equals. No .... but I can tell you that an Exige with 100lbs of downforce is not even close to being 5 seconds faster than an Elise, all else equal. I wish

If your goal is to decide an upgrade path .... that is relatively simple - and I would suggest should be based more around what is holding you back or frustrating you as a driver instead of laptimes, although there is some correlation between the two.

For my money, as you get more skilled, then you'll probably want to upgrade to Track Pads, then upgrade the Suspension, then run Hoosiers: in that order. Or maybe not - maybe you will be happy with stock suspension but the tracks you run or your technique are hard on brakes - YMMV. My point being YOUR Mileage May Vary. Someone else's experience may be very different. Summary - I think, once you have done a few track days, the upgrade will be pretty obvious to you and for only YOU. Advice is all good, but I think you will know what your "weakest link in the chain" is pretty quickly and without the advanced modelling. Of course ...... taking my own advice, YMMV

[Bleu Omdurman]

Originally Posted by chrisp993

Bleu

My apologies - I didn't mean to be quite so negative. But I am serious that the biggest single difference one track event to the other, is likely to be the driver, so - I didn't miss the point - I do not believe you will get data that is meaningful for YOU.

I'd also be suspect of your model / assumptions: by way of example - in your OP you stated that 10lbs of downforce = 1 sec. Can I tell you what 10lbs of downforce equals. No .... but I can tell you that an Exige with 100lbs of downforce is not even close to being 5 seconds faster than an Elise, all else equal. I wish

If your goal is to decide an upgrade path .... that is relatively simple - and I would suggest should be based more around what is holding you back or frustrating you as a driver instead of laptimes, although there is some correlation between the two.

For my money, as you get more skilled, then you'll probably want to upgrade to Track Pads, then upgrade the Suspension, then run Hoosiers: in that order. Or maybe not - maybe you will be happy with stock suspension but the tracks you run or your technique are hard on brakes - YMMV. My point being YOUR Mileage May Vary. Someone else's experience may be very different. Summary - I think, once you have done a few track days, the upgrade will be pretty obvious to you and for only YOU. Advice is all good, but I think you will know what your "weakest link in the chain" is pretty quickly and without the advanced modelling. Of course ...... taking my own advice, YMMV

While I am certainly always learning, I am also well past "a few track days". I had 3 track days last week alone. My skill level is progressing on a pace that I like. The part you are missing is that I am asking for data points, not recommendations. There is no simulation involved here. Please don't confuse a decision model with a simulation model. Totally different animals and goals. My goal here is not to find the most laptime drop per dollar. That would be impossible and driver dependent IMO. Forgive me for being terse, I am only trying to be clear and I am not sure I can be more clear than the OP.

And to show that I am a nice guy, here is a dancing banana for you...

[sndesign]

I think Loki "Alan" who has many track days on the same track
has gone from a stock Elise to shock upgrades to a wing and splitter and then a katana, he may be able to provide real data points.
He does not seem too active here so it may take a while for him to respond.

[xtn]

Badaraones, no weight change, no downforce change, 2 or 3 seconds at MSR-Cresson.

[Bleu Omdurman]

wait for it. Wait for it.

is there laughing yet?

Wait for it...

[JeffersonRaley]

Not sure what the laughing is for, Christian finally gave you a serious answer instead of criticisizing the exercise. I'll kind of do both. I can't give you laptime improvement estimates because, as you know, that will vary heavily from track to track. I can tell you what I recommend for changes in priority order for going faster.

* Toe link brace
* Toyo RA1s or R888s
* Light 15/16 wheels with RA1s or R888s
* Brake pads
* 4 or 5 point harness
* Camera system
* Lap timer
* Ohlins or Nitron suspension
* Replace other stuff (like brake rotors) as they wear out

Things that we all have, and that don't make a bit of difference to lap times:
* Rorty exhaust
* Wings and splitters
* SS brake lines

[UKphil]

I've been working on this for a while and should have some data soon.

I have so far got:

Driver rust removal (it's a while since I raced)
Instructor removal
Shim removal
AD07s to old R6s

All at the same track.

I should be running on Friday with Nitrons/corner weighting/alignment
Then next week with new R6s
Then - as soon as Charlie's mates pull their fingers out - I'll be SuperCharlied.

At some point I'll stick the roof on for a session.

I know the track pretty well and know that I'm a pretty consistent driver (typically running within half a second a lap each session).

So - watch this space.....

[Bleu Omdurman]

Originally Posted by JeffersonRaley

Not sure what the laughing is for, Christian finally gave you a serious answer instead of criticisizing the exercise. I'll kind of do both.

While I have no idea who Christian is, I am sure that xtn's post above mine warrants some laughter.

Thanks for your response though. You talk about safety gear which of course does not reduce lap times. I am after things that directly reduce lap times. The harness, HANS, suit, gloves, shoes, extinguisher, battery cut of, etc, are all beyond the scope. While I recognize safety gear is a necessary precondition to doing dangerous things, it is not the point of my solver to decide what safety gear provides the most safety for the dollar. That would be a different object function and one that would be based on user utility.

Thank you to everybody that has responded with data points. Most of them via PM, which is fine. Thank you!

For those interested in telling me this project is not a serious endeavor: If you don't have a data point to share, please go troll elsewhere. There are plenty of other threads you can pull off topic. Please let this one be.

[SteveLevin]

One comment. I would be willing to bet that going to a proper seat and a 6 point harness will be a significant improvement to your lap times.

Why? Because you will gain substantial finesse in all your pedal and hand inputs when you are no longer bracing yourself from being tossed around. Not to mention you'll "feel" what the car is doing MUCH better.

My belief is that 6 point and soft tires are the best bang for the buck by an order of magnitude that you can do for your car. Everything else will be very expensive and incremental. Horsepower is probably the biggest gain you can get and still drive the car on the streets (i.e., radical aero will make the car a trailer-only machine), but that just makes the straightaways shorter and the brakes work harder

Sorry for being slightly off kilter, but I really wanted to say that "safety" stuff has a lot of bonuses, especially when it comes to being planted in the car.

Steve

[rnr]

Originally Posted by Bleu Omdurman

While I have no idea who Christian is, I am sure that xtn's post above mine warrants some laughter.

xtn = Christian

What is so funny about his response? He gave you objective info that RA1s with no other changes are worth 2-3 seconds around MSR-Cresson.

[fishguy]

there is no set formula, this is why testing is done ON THE TRACK.

[fitfan]

Originally Posted by Bleu Omdurman

Thanks for your response though. You talk about safety gear which of course does not reduce lap times. I am after things that directly reduce lap times. The harness, HANS, suit, gloves, shoes, extinguisher, battery cut of, etc, are all beyond the scope.

everyone i know will tell you you harness / more bolstered seats will increase your lap times (as opposed to street 3-points and seats) - it makes perfect sense?!?! safety issues aside. not sure why you would discount them from a list of "things that make you faster on the track"