mark kibort

0-60 for most of the speed GT cars are in the 3.5 second range. im probably in the 4-4.5 range. even 450hp 3300lb vets are running 4.0 seconds on street tires these days. Ill watch the video of the start and time my first gear to second shift. point is, most of the time is seen in the later gears after the initial launch. (just watched one of my starts. looks like about 2 seconds depending on the wheel spin. Ill check out Andersons)

MK

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blau928

So,

Ve haf many of zees interestink arkuments on acceleration... I vonder if many of zees people realize zat zee funktion of acceleration in zee car ees a combination of amny parameters other zan gearink..

A zimple von vould be engine torque's ability to overcome total drag correlated to zee mass of zee car as a funktion of tire grip.

Vee kann calculate zees in precise inkrements usink our quantum computer...

Vann more zink... zee skill of zee driver vill make much difference as vell..

yes, very confusink indeed...!

pappy92651

Is this what you wanted to know?

1) A stock automatic S4 with 2.20:1 gears will do 0 to 60 MPH in 6.6 seconds. 2) A stock automatic S4 with 2.54:1 gears will do 0 to 60 MPH in 6.3 seconds. 3) Same as 2 but with a torque converter having a 2150 RPM brake stall speed will do 0 to 60 MPH in 5.4 seconds. Everything else is stock!

mark kibort

All things being equal. grip, talent, engine HP , shape of that hp curve, etc etc, gearing will effect acceleration only to a level that it allows the engine to work at as close to its max hp as possible.

How efficienly is the HP applied to the rear wheels will determine how fast a car can accelerate over a given distance. since gearing doesnt generate hp, and acceleration is a function of HP, this efficiency factor and infuence is much smaller than most give it credit for. I have this discussion with some BMW racers all the time swearing by their 4.45 ,4:10 vs 3.83 ratio changes. I tell them it really depends on the track and the top speeds you will hit on the straights. often, when i would race a few of them, i would hear them off the slow turns go through the gears and end up in gears too tall for the "meat" of the straight . this is where smarts can win over brawn, and i would slowly pull ahead with equal or less HP to weight. the bmws that had the correct ratios for this track, i didnt see this happen

so, when somone asks does gearing make a car accelerate faster, you HAVE to answer, "it depends".

If you look at all the things ive done on my race car and the narrow range ive run in timewise at home tracks like laguna, it really tosses out the concern of "gearing" as a major factor. Ive run, 2.22, 2.75s, 200hp all the way to 335hp, and tires ranging from 255 to 335, with diameters from 24" all the way to 25.75" and equal as many compounds, there are more factors to acceleraton than this list has time to discuss. the goal is to pick a gear box, matched with your cars HP that gives you redline just before you have to put on the brakes for any corner in all gears if possible, keeping the engine as close to Max HP as much of the time you can apply full throttle as possible.

thats the undisputed "net-net" of it all


mk

GlenL

Yes. 2.54 will give faster acceleration than 2.2 from a standing start.

At speed (>70mph) it becomes a non-factor as you can select the forward gear that keeps engine rpms up. As there's no gear lower than 1st, a higher final drive ratio will provide higher acceleartion.

Don't forget, you want to maximize force on the drive wheels' contact patches. This is done by maximizing torque on the drive shaft. The transmission will step down rotational velocity and thus step up torque. To maximize acceleration you want to select the gear that allows the engine to provide maximal power into the transmission.

mark kibort

he wanted to know acceleration. below could be correct for 0-60, but what about 0-75??

barring the effects of your stall converter, you would see some changing of the guards here!

Mk

blau928

Herr Kibort,

zee quantum computer printout agrees vith your point.. Und added zee skill of zee driver as vell...

mark kibort

not really. if your auto or manual shifts at near 60mph, then a taller rear end would be in a lower gear having more of the torque you speak of, until redline is reached. and start the trade off again, for every gear. It especially gets more interesting after some of the variables are removed like Launch and traction. is pretty easy physics after 2nd gear.

go through the ratios, match them to torque speed curves, and see the trade offs yourself all the way to the target top speed.
this is why you can just use ave Hp over the operational range. Hp does some of the caclulations for you .
area under the curve used!!!!!!
trade offs!!!! one car can have an advantage until a shift, then it will be at a 15-20% disadvantage. question is, for how long!? Then, a shift and the cycle starts again.
not that complicated, but kind of counter intuitive.


mk

pappy92651

Sorry, thats all the stock S4 data that we can provide today . Next...

Jim bailey - 928 International

Richard it gets more complicated with the stick shift car where you have wheels turning zero speed and rev the engine up to 5,000 rpm before you pop the clutch. Now you have stored energy to add to the equation and either the clutch has to slip ,the wheels accelerate instantly to the corresponding mph for that engine speed or the motor bog down to the speed of the wheels. All of which usually happens to a varying degree depending on the skills of the driver. A skilled drag racer often walks that fine line between too much tire smoke, destroying the clutch or getting the engine down out of the power band. The top fuel drag guys opt to slip the multiple clutches and destroy them each and every race ! On the street in an automatic if you can not overcome the traction of the tires at any time at any speed in first gear you can use the leverage afforded by lower gears ,more horsepower or both Road racing 50-150 mph close ratio gears with less rpm drop between gears is better and getting into 5th gear sooner is more efficient since power no longer has to jump to the lay shaft then jump back to the pinion shaft since 5th is direct drive.

blau928

Jim,

Zee quantum computer model calculates zee function of the slip etc. in zee computation of TOTAL DRAG... zees inkludes powertrain losses as vell as zee aerodynamik coefficients....

Zee funktion of tire grip ees computed as separate bekaus vee haf to akkount for zee dynamik modelink and zee road surface separately... Outside ambient veather konditions play a part of zee calculation...

ja vee are gettink closer to nirvana....!

Jim bailey - 928 International

IF YOU CAN NOT SPIN YOUR WHEELS when you push on the loud pedal you need to shift into a lower gear or build more horsepower. that is the bottom line! nirvana is having that much POWER.

blau928

Hi Jim,

I am understandink you very vell.. But from a scientific point of view, venn zee veels spin, zat is a vaste of zee power... Eeet does not kontribute to acceleration... zees ees zimple physiks...

I personally like zee much power as vell, but zees ees for zee fun meter, not for application of scientific optimal acceleration...!

Ketchmi

Hey Blau!

Either lay off whatever you are imbibing or share some with us! Maybe it will make your posts easier to read.

As far as drag gearing goes, it's all about average horsepower/torque for the duration of the run. The longer you can keep the engine wound up, the higher average horsepower you are creating. Proper drag gearing has you sitting at redline in top gear at the finish line regardless of how many gears, weight or traction. If you were geared tall enough to run 1st gear for the quarter reaching redline at the end, how slow would that be compared to someone with 5 gears reaching redline in every gear topping out in 5th at redline at the finish? Average horsepower underneath the curve, higher=quicker. If they built a centrifical clutch for automotive performance use like the new CVT's coming out, you could have the optimum transmission for drag racing with just your rear gear and tire height as variables.

BTW, they run snowmobiles on the 1/4 here with flat tracks and wheels. They run 9 and 10 second quarters all day long stable as a rock. They run faster, weigh more and have similar or less horsepower to most of the crotch rockets.........maybe due to never having to shift and always being at the proper rpm for maximum power production?

As far as road race gearing goes, it's different for every course and sometimes driver. There is no set formula as driver style varies almost as the courses do. Different horsepower and torque curves require different gearing for proper operation. You would want maximum speed on the straight geared for redline in high gear unless other corners effect driving style and which gears you would use for maximum acceleration out of said corners. If you would be over geared for launching out of the corners then your times will suffer more than if you didn't achieve your maximum top speed on the straight.

But we are only scratching the surface..............

Dave
Motorsport

blau928

Hi Dave,

I would be happy to share ny potion, but it may be addictive.. My point was that I agree that keeping the engine in the powerband will provide the optimal acceleration. However, on a more scientific note, the acceleration of any object depends on the mass, the force applied to it, and the drag on the object.. all physics..

Torque is the force, car is mass, tire slip, powertrain losses, Cx, and other things such as clutch slip etc. are drag.. The ability to control the amount of clutch slip etc. as used by dragsters is to regulate the amount of effective power transfer to the wheels (traction)..

Driver skill plays the part of the regulation or management of the effective applied torque to move the car in the quickest manner possible given the operating conditions...

This is a dynamic model, but spinning tires do not contribute to acceleration... If they did, F1 engineers would NEVER have gone to the trouble to develop active traction controls.. Drag racer use specific clutch packs for the same reason.. Control the traction, as the power is already enough to overpower the adhesion of the tires..

How's that for not smoking my pipe and writing...! Now, back to my pipe...!