mark kibort

you got it.... its been my world for years... after all, how many folks do you know are running a 30 year old stripped down, street car bolted up to be a race car with all original parts, bushings, etc, sans a bigger displacement engine as the only real mod. Working it out with what you have is a great education in racing to the limits and it transfers to other cars as well, almost instantly.

I hear you and that seems to be the flavor of most of the posts. however, to others "preference" going shorter in all gears, gives you some issues with noise on the highway in 6th and changing those lower gears has gains that are suspect from a performance perspective. what i mean, is that if you lower the gears, yes, you will or could be shifting more to get into 3rd or 4th, but you still need to go way above public road speed limits .. 80, 75, 70mph or whatever in 2nd is still pretty fast for the side streets! my only point and i have no beef with matt or anyone, is just providing the RAW information about gearing and its effect on RAW performance. (at the limit) . gearing rarely changes that for all speed ranges.. meaning.. its always trade offs. gears dont make HP as long as they are all close enough to allow you to drive in the max Hp range which is 6k to 7700rpm

actually, it would be pretty much what you have for good reason. its a wide range of gears close enough to stay in max hp range for all gears... .sans , the shift from 1st to 2nd, but there is good reason for that.... there is so much more power with the GT4 than base 981, that there are grip issues during track uses where you would be in 1st , which never happens on the track (its a 12.7:1 ratio) and 2nd is taller by a good margin for a speed vs engine speed range that matches its useful range. meaning... 1st gets you out of the pits (our rolling in stop and go traffic) and 2nd is the gear you drive in , with a slight reduction of power from 45 to 55mph, which is ok, since most turns as you accelerate from 45 to 55mph in 2nd, cant put any more power to the ground, especally with street tires. AND, this is the same spacing all the porsche race cars use!!!! big drop from 1st to 2nd and the rest very close.

this could be a perception that isnt backed up with any real facts, but feelings are real. dont have the answers, but im sure its easy to figure out with side to side comparisons. i drive the same exact gearing in my street performance car. 400hp, same gears, and a little heavier. because i race, i see no deficit, infact, i like the lower 1st for traffic.. and the big jump to 2nd as the power curve i have is close to the GT4 as well. the only lack of power you will ever see is from 45 to 55mph, the rest of the gears at any speed , is in the meat of the HP curve which by definition maximizes acceleration everywhere. there can be very little to be improved upon at any speed above 55mph, or below 45mph.

and that has been my message from day one.. but because street driving is usually always different( unless all you do is drive the same route to work every day), a gear box that is best for all is not possible. on the track, different gearboxes can change the optimization .. best example confirmed by Joe. (thanks joe for that video as well), sonoma was perfect, laguna had some deficiencies i mentioned.

mark kibort

Joe!! so refreshing to hear someone that has been on the track and, drive to the track, chime in. Great video and love all the data here! really enjoyed it and in fact lots to learn, even by me who races there probaly more than anyone. so, i appreciate your laps. let me address your question about turn 5 . yes, 2nd is optimal.. you moniter the the throttle well and its required because that is a steep climb up to turn 6.... you need the power to max the acceleration. its a tough one... in races ,my gear ratios are slightly different , enough and my hp curve is broader, which allows me to use 3rd, but when in a battle, i sometimes drop down. for a very quick punch out. the faster i go, and with better tires, its not required for me and im running 1:36s on my better days on DOTs.

as i mentioned, i had another version of my car with shorter gears 2.2 vs 2.75 rear end.... it was more fun on the street, as i like more shifting at the lower gears speed too. It was also optimal for another track, Thunderhill too... but i would never spend the money due to the fact that for sears and laguna, i was near optimal. But to some of the posters here.. i get the lower speed shifting preference.. but lets not confuse that with raw performance as illl address Matts's comments below regarding that.

Matt, good analysis of speeds but you are confusing RPM in gear vs speed, with gains. you need to look at the thrust force graphs. example.. just becuase you can redline at 145mph doesnt mean you are not at max acceleraioon forces at 125. if you are in the max HP range, thats the best you can do if you have more HP at 145, then you are right, but in actuallity, there is a big dip at the end of the HP curve you are not taking into consideration. but the bottomline is this..............if you are in the RPM of 6000rp to 7500rpm at anywhere on the track, that is maximizing the force to the wheels. its just basic physics here. acceleraiton = power/(mass x velocity) this means acceleration is proportional to power!!!! (at any same speed)

so, its not a fact that you can change gears and improve times. there are too many other factors. look at my car... 370rwhp and 3000lbs running on old used DOTs running 1:36s ... 30 year old technololgy.... its more about maximizing what you have at the track...... ive run a similar car with the shorter gearing... as another pro did as well. no change in time. NONE... this is often proven time and time again by consistant drivers, unless there is a HUGE problem with the gear ratios or narrow HP curve (which the GT4 doesnt have. ) as a track guy already said, it was perfect for sears and not so much for Laguna, and i agree with you regarding laguna. but you cant have it all. 3rd is NOT crap.... its perfect for sears and lime rock and not perfect for laguna, but not bad either.

as i mentioned, i would argue there is no "second" to be found in gearing, especially with a car with a broad HP curve and gears as close as the GT4.. if you can add up some HP /seconds gains, i would love to see them for laguna for example.. i do this all the time for clients... just look at the HP curves, vs RPM and see if there is any gains. HP at any speed equals the thrust curve by the way, PERFECTLY. the thrust curves willl say this clearly

you agree that 2nd is not really needed to be touched... then , if so, there is no real reason to change the rest. why? because alll gears keep the engine in the max HP range because of their closeness and specific to some tracks, it will hurt you , for example at Lime rock/sears, if you do change 3rd to be lower. this is easy to prove.

and Matt, taking nothing away from what you do with matching gearing for tracks for racers... thats an art form and fulll of trade offs.. certainly gains to be made when on the edge everwhere ... but for dual purpose cars like the GT4 as discussed here... not so much

you cant compare times.... 1:34s are guys on slicks.....that in itself could be the difference among many many others.

exactly!!! gearing has NEVER done this in any car... oh wait................i do have a story...........relivant to this discussion.... i raced for a guy that ran an enduro at laguna .. i got the car back from the pro who broke it, with ONLY 4th gear...... i was able to run a 1:47 in a car that would be able to run a 1:41 on the edge ... that was 5 seconds... but also only 1 gear... that is worth 4-5 seconds!

mark kibort

I just went through the lap again. great lap by the way.

Matt, there is not really any significant spots where there can be improvements do to gear changes. overall it would be subtle, and for reasons for higher RPM engine braking, like turn 6 approach, but generally, Joe is at 6000 to 7500rpm the entire lap when full throttle.

I broke i down this way:

into turn 11.. that would be the only thing that could be optimize, but not a lot of time there 2 seconds from 1:32.0 to 1:34.9 on the lap clock where you are down 50hp peak and about 25hp average. but 2nd is not in question here. we both agree its fine.

down the main straight, up to 125mph , even at 120mph, he is at 7000rpm.. clearly in the max HP range. remember if you are ever at max HP at any speed, that is the max you can accelerate.... if you can ever accelerate harder, in a lower gear, higher RPM that means you have to have more power.. AND YOU DONT!! this is a key point and usually very common to miss... even by top gear people. this is a great example.... say you are in the GTGears new 4th gear... running now 7500rpm at 125mph.... same HP, so why are you thinking you are accelerating harder?? Illl tell you why you are not... the HP is the same (lets say for argument sake) ... because the RPM of the engine is higher, the torque is proportioaly lower ( at constant HP, speed and torque are inversely proportional) . so the acceleration rate is identical.

going into turn 2 and 3 ,4, and 5 all the exits are at max HP levels 6000rpm to 7700 through the exits. turn 6 is a little light, but he exits at near 6000rpm

NOW where he can improve... there is 4 seconds at turn 9 (corkscrew) where he can be in 2nd.. he already is at full throttle at the apext of 9, but in 3rd gear. he is at 4500 he is losing near 50hp for 4seconds. that is the main loss per lap in time.

turn 10 looks good and then back to turn 11., where the only comment is that 2nd is a little talll. Hence my comment if i was going to optimize, the entire gear set could be brought down a hint.......... but, there are no seconds to be found.. only tenths.


HUGE gain. it took me 50hp to gain that 1second and then additional small mods to find the next .5 seconds. however, ironically, sometimes you can be 1 second slower on a weekend , driving exactly the same way, due to conditions. since i have so many race/qualifying days with the same car with NO changes for 15 years, its easy to see where the differences are.. usually, its the tires.

By the way.. love the laps... watched it a few times. my only comment would to be to go way up high to the right on the exit of the corkscrew and use 2nd. (carefully) its why the bmw squirted ahead there .. who was in the BMW? BRracing's Bmer??

GTgears

Mark,
I'm not confusing anything. You are making huge assumptions, as you usually do. Why don't you tell me, since you are so expert on this, what will the thrust force difference be on a 1.24 4th gear at 6800 rpm versus the stock 1.13 4th gear at 6200rpm?

Your 125mph to 145mph example is absolutely ridiculous. Show me an engine that makes max HP so low that you can have a 20mph range in gear and keep revving it. Furthermore, that fantasyland theoretical has NOTHING to do with the real engine and geabrox we are dealing. It's a useless comparison.

Though I love how you change your arguments to suit the circumstances. The other day you tell me I shouldn't cut it off at 7500rpm because there's no benefit on track to short shifting and that we should rap it out to the 7700rpm redline (as we should). But today you claim a yuge HP drop off at the end, which isn't true. There is a slight drop above 7500 rpm, where peak HP occurs, but the losses in that final 200rpm are inconsequential versus what one would lose if you shifted to 5th and gave up all that mechanical advantage.

GTgears

I'm just going to pull this one snippet because your response relies on the same basic false premise over and over again. You like to repeat that acceleration formula but you alway ignore one fact, gears are a force multiplier. The above example is terribly flawed. I don't care about 125mph. That's the max speed achieved at the END of the straight. I care about getting to that speed more quickly. So making your example of where he is in the powerband when he's done accelerating is just plain stupid.

This is a variation of my question in the last post. Let's say that we don't change 3rd gear. Leave 3rd gear stock, topping out right around 110mph, ok?

So we've got the stock 1.13 4th gear where we shift into it at 110mph at 6200RPM+/- OR we can start accelerating from 110mph in 4th gear 1.24 at 6800rpm. There is more horsepower to the ground in the second option. The car will accelerate more quickly.

I've seen you make this same argument over and over again and you never listen. It's why I block your posts. I only clicked in because I saw a couple quotes of you making the same BS claims and decided for the benefit of the readers I should reply. You never admit fault and always have to be right. It usually gets to the point that you get rude, abusive and get yourself put on time out over and over again. That's your deal. Whatever. Now that I've laid it out for others to think about I am once again blocking you.

mark kibort

Thanks for the reply Matt. Ill respond best i can below:
1. Regarding the thrust differece... if the HP is the same, and for reference ive provided a HP /torque curve vs RPM, then the thrust difference will be 0. But , since you gave us particulars, of 6200rpm vs 6800rpm, ill use those values on the published dyno for the GT4
as you can clearly see , HP at 6200rpm is 320 and at 6800rpm its 325hp. there is a 5hp difference, but rember that is peak hp and a peak thrust difference of about 1%.. . hardly enough to write home about

2. Regarding the range of max accelerative forces. again, looking at the stock HP curve, you can clearly see max hp range from 7700rpm to 6000rpm... this is a 20% drop of RPM.......and, ill do you one better. if you can get to 145mph in a gear, the RPM drop of 20% is actually closer to 30mph.. yes, 30mph. from 112mph you can go to 145mph , all in the max HP range. sure there are peaks and valleys, but you get the point.... it seems obvious that you might have missed something here, so help me understand the question if i got it wrong.

3. regarding HP drop at the end.. clearly , we are on the same page there.. i agree, alwasys tach the engine out to take advantage of the average HP gains. BUT, according to the published HP curve, there is a drop in HP.. its the same drop that was used in Bill's thrust curves. So, therefore, based on the stock GT4 curve, yes, a slight amount of short shifting is need (theoreticaly) But, due to shift time, that llittle short shift is probably not needed. i think you get my point there.

anyway..... its all about maximizing thrust to the wheels. so, take a look again... it may seem like you can make a lower 4th and have more torque, but if you are still in the max HP range, you have the same thrust forces. this is a key key point that is often overlooked.

mark kibort

I think everyone would agree, im being as polite as possible.. im not going to concede unless i hear of a logical explanation of why im wrong. Im trying to help here, its not pointed at you, so dont take it personally.

So far, you are giving me the same response ive heard from others, based on the lower gear, higher leverage theory application.
you are being a bit presumptuous thinking im ignoring anything here. im not. gear multiplication is as critical to the gear discussion as it is to the Hp vs torque discussion . sure, gear multiplication happens, but what is it multiplying........? yes, engine torque.... if you have constant HP, that means torque is falling at the same rate as engine RPM.. make sense?? this means, to get the same vehicle speed and increase the numerical ratio, you get a loss in engine torque of the same proportions.. there is a net net NO CHANGE in doing so. So, im not leaving anything out here. i think if you look closer, you will see im correct and change the story a bit. dont worry, many get this wrong..........a lot... i used this in my professional life for 20 years... its correct.

But, dont trust me.. show me an instance where this ISNT true and ill certainly listen .

now, re-read your question below (or comment) i also give as much due to the fact of being in the end of the speed range for a gear as it deserves. sure, its the AVERAGE HP over the range...AND if we start out at 6000rpm to 7700rpm and this is the max HP range. GT4 has a flat HP curve in that range) the thrust or rear wheel torue will be the same regardless of engine RPM for a given vehicle speed. for the reasons i mention above.


Now, instead of calling me "stupid" (and blocking me)lets talk about it.. I like the fact that you have given me a scenario. great one by the way... thanks! here is my feedback on it:

1. so you dont change 3rd gear.. it revs to 110mph. 7700rpm

2. you shift into 4th (original and have a 1.13:1 ratio or the option of the 1.24:1 ratio) Now, you make a dangerous assumption. just because the ratio is better, doesnt mean there is more torque. again, go back to the HP curve (and torque curve) whats the hp difference ?? 1% whats the torque difference? also 1%. WHY?? because , again, if the HP is the same the rear wheel forces HAS to be the same.. its what I've been preaching for 20 years here!

3. I almost forgot... now, the shift point is earlier as well 3rd to 4th for the example you used.... the trade offs are obvious. if you do the math, through a couple of shifts, the gains cancel. in other words, you shift earlier because you are in a gear with more mechanical advantage for a say 2000 rpm ... then you shift at an earlier point (same % earlier as the gear ratio difference) and go up in a gear for that difference of speed and spend time at a 30% mechanical disadvantage, then enter a gear with a 10% advantage (using 10% change of gears as you suggested). the net difference will usually be close to nothing. it has to... gears are only hp optimizer, not HP generators. if you are in the 6000RPM to 7500rpm range you are close to extracting 100% of the engine availity to accelerate the vehicle at any speed. its simple physics. i didint make the law, Newton did.

THE REASONING: the reason is that if the HP is the same, the torque has to be less for a higher RPM at the same proportions.. this is the answer you are looking for.

stout

C’mon now. Let’s stick to discussion points and answers to valid questions rather than attacking fellow Rennlisters and/or minimizing someone's profession while demonstrating very little knowledge about it.

Yes, part of my job includes road testing, which is an important way to evaluate, you know, road cars. A lap time or a spec sheet will never help convey what a Carrera GT or a CTR is like to drive, but 1,000 miles in the driver’s seat on road and track helps quite a bit. And if lap times or ultimate performance numbers are all that matters, we should all be driving something besides GT4s.

While my work is certainly fun at times—just as racing is—I wouldn’t reduce it to “playing.” There are different skill sets, and there is value in each of them. I’m not here to attack or discredit your racing experience or the basic tenets of the info you’ve shared. But I am asking how much GT4 seat time you’ve got on the road because I think it would really balance the “on limits/ultimate speed at certain tracks” perspective you are bringing. It is not an invalid perspective, unless it ignores or throws all other inputs away. The best thing you’ve noted is that gear sets are a compromise, which is of course true.

Agreed. But it doesn’t overshadow all else—and what works on track doesn’t always work on the street. I think we can probably agree that a lot of good road cars have been ruined for the road by track-oriented mods. Conversely, many of the things that make the GT4 great on the road compromise it for track work. I suspect we can both name mods that work well in both uses, and agree they’re usually rarer than those that compromise the car for one or the other use.

[QUOTE=mark kibort;13810940]

Not sure if you read my first posts, but I decided to start this thread after another 8,000 miles in GT4s since the early 2015 press launch in Portugal on road and track. For me, the additional miles have indicated the gearing is more annoying to live with than it was during the launch.

I’ve listened to Matt and others and tried different approaches to driving the car, but the fuel economy and too-tall 2nd and 3rd gears—one the street—along with the too-short 6th on the freeway are hard to ignore in what is otherwise such a brilliant Porsche. I’ve thought quite a bit about this, and listed my reasoning out carefully. None of it really disagrees with what you are getting at—for track use. I think I agree with your analysis of Joe’s drive, and also agree that the GT4 may be geared nicely as is for some tracks (which is good perspective).

Even so, I believe the 991-1S gear set would go better with the 991-1S engine in the GT4, and be well worth the tradeoff at some tracks. One of the 991-1S’s seven gears would have to be sacrificed in the conversion, but its 6th gear is a “flyover” gear here in the U.S.

So I started a thread on the gearbox I am dreaming of, for the set of compromises that would appeal most to me. Those might not be what you want, or think are good. And that's okay.

Generally speaking, this REALLY resonates with me. Unless something is truly "off," or can make a real improvement for intended use. I think this is one of those cases.

THIS. This has been on my mind for a while. 987 Spyder worked beautifully, and I have been thinking about why the 981 Spyder didn't bug me the way it is geared, at least during a single day with the car on decent roads on the Big Island. Hard for me to say why, exactly. Is it grip levels? Brakes, or effective braking with more grip? Is it balance of performance within the car, altered by the GT4's "GT3" suspension and Michelins and bigger rear tires? I am not sure, but where the GT4 feels like it is crying out for short gears 2-4 to wake it up, the various 987s and 981s don't bug me.

mark kibort

I had NO intent of discounting anyone who judges these cars on the street, but when the feelings came in, or there was some advice giving without giving proper credit to the physics involved, i thought i would add a little color.

certainly there are two camps.. race-pure performance and street. street i break into two camps....... fuel economy-hyway noise/ and shifting fun-convienience. you asked how much time i had in a GT4.. a day at the track coaching, and also in a 991 turbo and 991S. loved all of them. but, my comments are not meant to sway any feelings the drivers have of the car, but sometimes we cant ignor the power of suggestion. how many times does your car run better after a car wash?

my point is there is confusion of what the gears actualy do for performance besides the obvoius, like how far the RPM drops from 1st to 2nd. (not in questio here, Matt already said) and the shortness of 6th vs the 991, do deal with the higher RPM when cruising on the hyway in 6th gear. (aslo matt said the gear was not going to change, its fine, stating, " it already can do 190mph at daytona which is plenty fast".)

So, what is my point?? The point is there sometimes DOESNT need to be trade offs . the GT4 is one of those cars with a powerplant that provides max HP from 6000rpm to 7700rpm.. this means that as long as you are in this range, you get the most amount of acceleration possible. Matt made a point showing that he might want to look at what im saying a little closer.. this way he can make the correct recomendations. he seems to think by going to shorter gears you pick up mechanical advantage and torque... he is half right. if the HP is constant, as it is with the GT4, there is nothign you can do from 6000rpm to 7700rpm to pick up any "torque" at the rear wheels. why, because HP dictates a cars capasity to accelerate at any speed!

if you have 6000rpm and 320hp, it will accelerate the same at that same vehicle speed, if you have 320hp at 7500rpm, even though the ratios are very different. that was my ONLY point. if you are in that range, there is no notelable performance improvment avaialable. its all about how much time you spend in the max HP range. think of it as ------HP-seconds. which is a unit measure of work. (not to get too technical with the math or physics). maximize the Hp-seconds and you maximiize acceleration over any speed range.

Now, going back to feelings.. yes, short geared cars seem like the gears are closer, but they are not.. (same spacing usually) and its cool and fun to shift more . actually, it can hurt performance when too short or tall of a gear doesnt allow for the max HP range to be realized but thats only when you are asking the most from the car.............Also, as far as fuel economy, its very debatable that the lower RPM of a super talll 6th (like the 7th of the 991S) would provide any more fuel economy. this has to do with the fuel burn characteristics at the lower RPM. sometimes it gets worse . sometimes there is a perfect RPM and load that provides the best gas mileage. the best advice there, is to just drive slower, as wind resistance is the biggest factor here., but i often wish for a taller gear in my street car for the same reasons. just less noise and it feels like the engine is working less hard... its more feelings , right?

So in the end, if you have all the information , you can make the decision right for you . shorter gears, talller 6th, better optimal performance on the track, etc. again, i have a car with almost idential gears to the GT4.. i think it has the best of both worlds, mainly because the engine shifts perfectly through the HP curve and has a slightly taller 6th than the GT4..... im at 80mph at 3000rpm... .i dont like it, because my race car overdrive 5th is at 2500rpm at 80 and is relaxing driving to the track. i think you hit the nail on the head regarding the desires and what is most important for each driver, on the street. and the track doesnt tell the story on the street. But, there are things that cross the lines easily, and ive found that if a car shifts well on the track, it shifts well on the street, but thats my opinon. You are very lucky to have a car the does both very well! my only purpose was to provide perspective in a small area of the discussion relating to bare bones pure performance concerns.
Mark

i did spend a LOT of time writing this response to matt who had given me questions and then didnt want to hear my reply... can you read this and let me know if it makes sense?
https://rennlist.com/forums/gt4/9648...l#post13812856

sharkster

The CS is basically a race car too on michelin slicks is it not?

orthojoe

Original post

Not sure where 4 seconds is coming from? 36-34=2

As I said before, you can't compare different cars and different drivers.
If you are comparing the CS to a 987 3.8L with custom gearbox you need to consider:
1) different driver
2) different car
3) CS has PDK and different gearing than street GT4
4) 1:36 lap time for a GT4 CS is not a good benchmark, IMO. If Randy Pobst can do 1:37 on cup2 in a stock street GT4, a CS on slicks should be able to do 1:34

orthojoe

It is odd, isn't it? The only thing that makes sense to me is that it doesn't meet what our expectations were. We didn't expect those cars (987/981) to be particularly quick, but we expected more out of the GT4. The GT4 really feels like it doesn't make any torque. The 991GT3 feels like it has gobs of torque even down low. The odd thing is, the torque rating between the 2 cars are almost the same. On the street, the GT4 honestly doesn't feel much faster than my old 987 spyder. However, on track it is definitely hitting higher peak velocity on the straights, so there is no doubt it is making more power.

mark kibort

Yes it is.... i was thinking it was on DOTs.... it's not uncommon to pro drivers to run the same car two different weekends and have the times be 1-2 seconds off..... especially a different driver which i think that this was.


thats the "power" of power! yes, this happens offen... when the Honda S2000s came on the scene, everyone was afaid to rev to redline, as the car sounded like it was going to explode, but thats what you need to do to keep it in the power band. you obviosly got what i wrote down before, but its all about keeping in the max HP range . now matter what it feels like, if you are running more hp at any vehicle speed, you are accelerating faster... but, the sounds and sights can be different and skew perceptions, as you know

great points.......... mainly the two cars two drivers, two different sets of tires, two different days, im not too worried about the gear box changes as ive seen a top pro run a car with a 15% different gear box to the exact same times..... the response in the pits was.. "heck it felt faster" only to see it wasnt. " i was shifting a whole lot more".. was also said. it all boils down to keeping the car in the 6000rpm to 7700rpm range.... by doing this, you factor out gear box advantages for changes of ratios.

Mech33

Talking about gear ratios as force or torque multipliers generally results in intuitive conclusions that are incorrect. Sure, a transmission can gain up the torque, but it does so while gaining down the speed at the same time. The result is just different combinations of torque and angular velocity at constant *power* (ignoring losses).

I recommend keeping all analysis in the power vs. speed domain, because it is simple and intuitive.

But if you want to look at things in terms of wheel force, then now you have to take into account gear ratios (and final drive ratios, and wheel radii). But comparing two scenarios isn't too difficult:

(A) 6200 RPM, 1.13 gear ratio
- Per attached dyno chart, the GT4 engine puts at 270 ft*lbs at 6200 RPM.

(B) 6800 RPM, 1.24 gear ratio
- Per attached dyno chart, the GT4 engine puts at 250 ft*lbs at 6800 RPM.

The actual FORCE at the rear tire is easy to calculate:

Force = (engine torque) * (final drive ratio) * (gear ratio) / (tire radius)

So calculate the force in each scenario:

Force_A = (270 ft*lbs) * (final drive ratio) * (1.13) / (tire radius)
Force_B = (250 ft*lbs) * (final drive ratio) * (1.24) / (tire radius)

or

Force_A = (305 ft*lbs) * (final drive ratio) / (tire radius)
Force_B = (310 ft*lbs) * (final drive ratio) / (tire radius)

Comparing Force_B to Force_A, we see that Force_B/Force_A = 310/305 = 1.016.

So scenario A puts down 1.6% more force to the ground at *that exact speed instant* than scenario B.

But we didn't need all that analysis to show that... just compare the power curves at 6200 RPM and 6800 RPM:

6200 RPM: ~317 hp
6800 RPM: ~322 hp

Comparing that power: 322 / 317 = 1.016... or 1.6% higher. Much easier than worrying about all that gearing nonsense! :P

orthojoe

Thanks, Mark. I'll keep working on T5 using 2nd gear.

Thanks for the analysis! I've wondered about using 2nd for the corkscrew, especially since Pobst uses 2nd as well. I feel like the car is more stable entering 9 if I don't screw around with 2nd, but I'll try it.