Rear end gearing change 86, options
07-05-2007, 02:51 PM
#46
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I think you went to the even more common debating technique. go to an extreme, like comparing a start in 2nd gear, to make a point.
jim, since we both agree that who ever puts downt he most amount of HP to the wheels wins, it doesnt take an Newton, to figure out that there are limits and trade offs with gearing. GEARING doesnt produce hp, it increases the effects of the hp available. since we dont use infinitely variable transmissions, where rpms would instantly go to max HP and stay there, we are left with matching the gear sets and the averages of applied hp over the different speed ranges.
that all said, if you dont look at the hp applied to the wheels over the entire run, you are missing the point. you talk of "feel" and that discounts your entire case and knowledge. you cant feel the acceleration differneces of the effecs of 5-10hp. howevever you sure can feel the difference that you are shifting a 2.75 racer at 45mph in 1st rather than 55mph in 1st with an S4 (assuming hp is near the same) ive raced both, ive driven both Ive owned both. So, you only know what is actually happening, when you put a G meter on the car or you do a timed drag. when you illimiate reaction time you are left with the gear spacing. the major varaible is traction.
the greatest example of this would be the 3.09. if you are experiencing wheel spin with a 400hp 2.2 S4, then putting a 3.09 may only make it worse, or give you a shift at 39mph that you wouldnt otherwise have. remember, the shift can take .1 to .2 seconds depending the skill level (ignoring a speed shift) . during a shift, would you agree that you have .1-.2 seconds of actual DECELLERATION?? Things like this need to be taken into account.
do yourself a favor. you have some real life experience here. go to any simulator. plug in the numbers of any car with any HP and see what comes out. the difference of a 2.75 gear box S4 vs a 2.2 S4 vs a S4 with just a 2.75 rear end ring and pinion change will all be pretty darn close. we have gone through this before and have seen the slight differences and trade offs.
I just noticed your comparison of the 225 50 tires vs the 295 35 tires. you notice a drastic differnce? i regulary change my tire diameter from 335x30 to 305x35 . thats near 3% and have never noticed an drastic change. the speedo still shows the same shift points, as they are tied to the tranmission, and are independent of the tires you use. you must be highly sensitive.
Ive raced the 2.75 rear end, and the 2.2 with all sorts of tire sizes. what matters most is the HP you have available. the rest is fine tuning. in fact, im turning better times now with the tallest tires, as it is matching up my redline speeds for many of the straights at laguna, sears and thunderhill.
Jim, its all trade offs. its not a matter of wrong or right here, its physics. you dont get somthing for nothing.
Mk
jim, since we both agree that who ever puts downt he most amount of HP to the wheels wins, it doesnt take an Newton, to figure out that there are limits and trade offs with gearing. GEARING doesnt produce hp, it increases the effects of the hp available. since we dont use infinitely variable transmissions, where rpms would instantly go to max HP and stay there, we are left with matching the gear sets and the averages of applied hp over the different speed ranges.
that all said, if you dont look at the hp applied to the wheels over the entire run, you are missing the point. you talk of "feel" and that discounts your entire case and knowledge. you cant feel the acceleration differneces of the effecs of 5-10hp. howevever you sure can feel the difference that you are shifting a 2.75 racer at 45mph in 1st rather than 55mph in 1st with an S4 (assuming hp is near the same) ive raced both, ive driven both Ive owned both. So, you only know what is actually happening, when you put a G meter on the car or you do a timed drag. when you illimiate reaction time you are left with the gear spacing. the major varaible is traction.
the greatest example of this would be the 3.09. if you are experiencing wheel spin with a 400hp 2.2 S4, then putting a 3.09 may only make it worse, or give you a shift at 39mph that you wouldnt otherwise have. remember, the shift can take .1 to .2 seconds depending the skill level (ignoring a speed shift) . during a shift, would you agree that you have .1-.2 seconds of actual DECELLERATION?? Things like this need to be taken into account.
do yourself a favor. you have some real life experience here. go to any simulator. plug in the numbers of any car with any HP and see what comes out. the difference of a 2.75 gear box S4 vs a 2.2 S4 vs a S4 with just a 2.75 rear end ring and pinion change will all be pretty darn close. we have gone through this before and have seen the slight differences and trade offs.
I just noticed your comparison of the 225 50 tires vs the 295 35 tires. you notice a drastic differnce? i regulary change my tire diameter from 335x30 to 305x35 . thats near 3% and have never noticed an drastic change. the speedo still shows the same shift points, as they are tied to the tranmission, and are independent of the tires you use. you must be highly sensitive.
Ive raced the 2.75 rear end, and the 2.2 with all sorts of tire sizes. what matters most is the HP you have available. the rest is fine tuning. in fact, im turning better times now with the tallest tires, as it is matching up my redline speeds for many of the straights at laguna, sears and thunderhill.
Jim, its all trade offs. its not a matter of wrong or right here, its physics. you dont get somthing for nothing.
Mk
Originally Posted by Jim bailey - 928 International
Mark I think you have been studing this ..."Commonly employed debating technique
Lately I have found myself in e-mail discussions with Induhviduals who employ debating tactics that are very similar. I suspect they are learning these methods in some sort of top-secret Induhvidual training facility.
The Induhvidual debating technique involves four steps:
Exaggerate your opponent's statement into an absurd absolute.
Make an inappropriate analogy.
Change the topic to something easier to defend.
Claim victory. ...." you are still wrong about lower gears ! The old very brown I have tires which range from 225x50x15 up to 295x35x18 and the way the car feels changes drastically with the smaller diameter tires...As I said before try a drag racing start using second gear it will help you understand ...
the concept in the real world
Lately I have found myself in e-mail discussions with Induhviduals who employ debating tactics that are very similar. I suspect they are learning these methods in some sort of top-secret Induhvidual training facility.
The Induhvidual debating technique involves four steps:
Exaggerate your opponent's statement into an absurd absolute.
Make an inappropriate analogy.
Change the topic to something easier to defend.
Claim victory. ...."
you are still wrong about lower gears ! The old very brown I have tires which range from 225x50x15 up to 295x35x18 and the way the car feels changes drastically with the smaller diameter tires...As I said before try a drag racing start using second gear it will help you understand ...the concept in the real world
07-05-2007, 02:56 PM
#47
Rennlist Member
this is complete non-science show me the ETs on a drag simulator, like this one, and we can talk. the gains are very easy to calcuate by hand too.
i had a discussion with one of the new viper guys about this. same types of things were promised with the lower gearing. however, at the track, no gains were found. he didnt get the "50hp" gains that were promsed. although it was more fun to drive. some folks like driving around at slower speeds shifting more. remember we are not comparing 2nd gear to 2nd gear. its the speed range we are talking about acceleration = power/(mass x velocity) this means that acceleration is proportioal to power, and if kept constant (close gears) inversely proportional to speed.
before you respond. plug in some numbers and see what you come out with with this simulator:
http://www.nightrider.com/biketech/accel_sim.htm
Mk
i had a discussion with one of the new viper guys about this. same types of things were promised with the lower gearing. however, at the track, no gains were found. he didnt get the "50hp" gains that were promsed. although it was more fun to drive. some folks like driving around at slower speeds shifting more. remember we are not comparing 2nd gear to 2nd gear. its the speed range we are talking about acceleration = power/(mass x velocity) this means that acceleration is proportioal to power, and if kept constant (close gears) inversely proportional to speed.
before you respond. plug in some numbers and see what you come out with with this simulator:
http://www.nightrider.com/biketech/accel_sim.htm
Mk
Originally Posted by mtcarrera
I guess I don't know what is meant by a "lower power band", since power is supplied by the engine, not the transmission. If you mean lower gearing, then there is a fairly straightforward answer that will lower 1-4 by about 18 percent and leave fifth the same and not involve the ring and pinion. This is a MAJOR improvement for the earlier cars which provides acceleration improvements that equate to a 40-50 horsepower increase. If this is what your're after, post back and I'll post an explanation.
07-05-2007, 03:02 PM
#48
Rennlist Member
5th gear is 1:1 for all years
changing the ring and pinion shifts the entire gear set up or down. My only point here, is that there are trade offs. depends on speed range to be used, traction, and of course, HP available. as the hp changes, so do the speed ranges being uses, and subsequently, so will the gear ratios needed to optimize the HP being appied over that speed range.
mk
changing the ring and pinion shifts the entire gear set up or down. My only point here, is that there are trade offs. depends on speed range to be used, traction, and of course, HP available. as the hp changes, so do the speed ranges being uses, and subsequently, so will the gear ratios needed to optimize the HP being appied over that speed range.
mk
Originally Posted by mtcarrera
And, upon re-reading the original post, an 85-86 car woud indeed have to to a ring and pinion change to lower the overall transmission ratios. The very early cars, however, can change to a later "fifth gear" and get the advantages outlined above. Did it, LOVE it.
07-05-2007, 03:12 PM
#49
Rennlist Member
http://www.nightrider.com/biketech/accel_sim.htm
Here is a copy of a run i did with the simulator to talk to a friends desire to change his brand new viper from 3.07 gears to 3.56 gears.
If you can read it, its shows the trade offs at the bottom. the data was brought over from the other set of times to show the differnces and trade offs.
this is a classic example of what we are talking about.
in this case, if traction wasnt a problem. (meaning he had enough traction with the new gear box to take advantage of the lower 1st gear) then it was a slight gain in the 1/4mile . HOwever, if he was street racing and had certain speed ranges he wanted to accel at, then he was actually at some disadvantages . they are clear to see below.
1st chart is the stock 3.07 gear box and comparison data
2nd chart below is the modified change to the 3.57 rear end
MK
Here is a copy of a run i did with the simulator to talk to a friends desire to change his brand new viper from 3.07 gears to 3.56 gears.
If you can read it, its shows the trade offs at the bottom. the data was brought over from the other set of times to show the differnces and trade offs.
this is a classic example of what we are talking about.
in this case, if traction wasnt a problem. (meaning he had enough traction with the new gear box to take advantage of the lower 1st gear) then it was a slight gain in the 1/4mile . HOwever, if he was street racing and had certain speed ranges he wanted to accel at, then he was actually at some disadvantages . they are clear to see below.
1st chart is the stock 3.07 gear box and comparison data
2nd chart below is the modified change to the 3.57 rear end
MK
Last edited by mark kibort; 07-06-2007 at 03:36 AM.
07-05-2007, 03:20 PM
#50
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Mark you are still wrong ....the tires I mention one is a 24 inch diameter the other is 26.1 the revolutions per mile are 870 and 797 which is about a 10% difference in gearing and that makes a big difference. After all I only have 195 hp at the rear wheels
07-05-2007, 05:03 PM
#51
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Mark .."depends on speed range to be used" which by necessity in drag racing starts at ZERO and an exageration would have been suggesting that you try launching in 5 th gear ! How about you do that Viper simulation using a 2.20 final drive gear like a 928 ?? One person's non-science is anothers nonsence...
07-05-2007, 07:27 PM
#52
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there you go again, feeding the problem. WHO CARES what the final drive is, its the total ratio that maters. it just so happens that the comparison above is very similar to the 2.75 vs a 2.2 tranmission (notice i said, "transmission", not just rear end, as its a system)
the 2.2 vs a 2.72 rear end is about 16 % difference per gear. putting a 3.57 on a 3.07 transmission on a viper is 16% as well. however,i f we just put a 2.75 on my S4 2.2 gear box, its more like 25% (ie big difference)
there is apoint of diminishing return as well. It crosses that line well before you hit 3.09 on our cars and then as you hit 3.09, you get the gains of having one more gear to use for drag racing from 0mph, if you can take advantage of the 3.09 with increased traction.
The simulation uses the viper's gears that are very close to the 928 gears. remember i said before, all that really matters is the speed at redline that you hit. If that is equal and the HP curves are equal, that is all you need to look at for the same torque, through the gear boxes at ANY vehicle speed, including "0"mph.
you are the only person touting a "non science" here! say it after me, " final gear ratios are all that matter, not the rear end!" I know you know this, as you have written all about this before.
Now, as far as why your190hp 928 with 225s acts differently than it does with 295s............well, in 1st gear that could be an interial diff. 25lbs (x2) of wheel compared to a bigger diameter 55lb wheel and tire. from the Dyno diatribes, we know on a dyno, it is a rouding error, but in 1st gear it could have a big effect, probably more than the gearing effect due to the larger diameter. that effect goes down to less than 1hp based on the acceleration rates you would see in 4th gear. as a rule of thumb, if we are talking 50lbs of different wheel weights total, its like having near 100lbs in the car. that you may be able to feel. (in my book, 10hp or equivilant is tough to feel and the gearing effects in average g forces, would be even less than that)
an other interesting data point, is on the viper acceleration chart. look at the max G's accelerating for the first 30ft. that number maybe fixed based on the cars grip. if that doesnt change, all the gearing in the world doesnt change that until the tires more closely match the speed of the ground passing by!
There is no question that the 16% gear change helped (slightly) the 1/4 times with the viper. im sure similar values would be seen on the 928 with a GTS vs S2 box, DEPENDING on the hp available. however, the net differences are not that great. AND, most importantly, now look at the speed range from 25mph to 110mph. that actually got worse for the higher numerical rear end (for the factors im talking about). Most of us, especially on the street, would care most of this kind of performance, than how fast we can scoot along from 0-30feet!
this is the point. rear ends dont buy hp. they buy better effectiveness of HP over certain speed ranges.
mk
mk
the 2.2 vs a 2.72 rear end is about 16 % difference per gear. putting a 3.57 on a 3.07 transmission on a viper is 16% as well. however,i f we just put a 2.75 on my S4 2.2 gear box, its more like 25% (ie big difference)
there is apoint of diminishing return as well. It crosses that line well before you hit 3.09 on our cars and then as you hit 3.09, you get the gains of having one more gear to use for drag racing from 0mph, if you can take advantage of the 3.09 with increased traction.
The simulation uses the viper's gears that are very close to the 928 gears. remember i said before, all that really matters is the speed at redline that you hit. If that is equal and the HP curves are equal, that is all you need to look at for the same torque, through the gear boxes at ANY vehicle speed, including "0"mph.
you are the only person touting a "non science" here! say it after me, " final gear ratios are all that matter, not the rear end!" I know you know this, as you have written all about this before.
Now, as far as why your190hp 928 with 225s acts differently than it does with 295s............well, in 1st gear that could be an interial diff. 25lbs (x2) of wheel compared to a bigger diameter 55lb wheel and tire. from the Dyno diatribes, we know on a dyno, it is a rouding error, but in 1st gear it could have a big effect, probably more than the gearing effect due to the larger diameter. that effect goes down to less than 1hp based on the acceleration rates you would see in 4th gear. as a rule of thumb, if we are talking 50lbs of different wheel weights total, its like having near 100lbs in the car. that you may be able to feel. (in my book, 10hp or equivilant is tough to feel and the gearing effects in average g forces, would be even less than that)
an other interesting data point, is on the viper acceleration chart. look at the max G's accelerating for the first 30ft. that number maybe fixed based on the cars grip. if that doesnt change, all the gearing in the world doesnt change that until the tires more closely match the speed of the ground passing by!
There is no question that the 16% gear change helped (slightly) the 1/4 times with the viper. im sure similar values would be seen on the 928 with a GTS vs S2 box, DEPENDING on the hp available. however, the net differences are not that great. AND, most importantly, now look at the speed range from 25mph to 110mph. that actually got worse for the higher numerical rear end (for the factors im talking about). Most of us, especially on the street, would care most of this kind of performance, than how fast we can scoot along from 0-30feet!
this is the point. rear ends dont buy hp. they buy better effectiveness of HP over certain speed ranges.
mk
mk
Originally Posted by Jim bailey - 928 International
Mark .."depends on speed range to be used" which by necessity in drag racing starts at ZERO and an exageration would have been suggesting that you try launching in 5 th gear ! How about you do that Viper simulation using a 2.20 final drive gear like a 928 ?? One person's non-science is anothers nonsence...
Last edited by mark kibort; 07-05-2007 at 07:47 PM.
07-05-2007, 07:36 PM
#53
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10% is 10% in fact, you probably would feel it less by you than if it was someone in a same weight car with more HP. 10% of 190hp is 19hp if you had 500hp, it would be 50hp. 18:9 hp to weight compared to 17:3:1 hp to weight , vs 7.2:1 at 500hp and 6.5:1 with the extra 50hp. probably would be easier to feel the later. (based on a 3600lbs car with driver)
anyway, 26.1 / 24" is near 8% roughly the difference of gear ratios of my old "S" version 928 with the 2.226:1 gear box vs my S4. i didnt notice any real difference. as you said, you may be more sensitive than the average bear though!
mk
anyway, 26.1 / 24" is near 8% roughly the difference of gear ratios of my old "S" version 928 with the 2.226:1 gear box vs my S4. i didnt notice any real difference. as you said, you may be more sensitive than the average bear though!
mk
Originally Posted by Jim bailey - 928 International
Mark you are still wrong ....the tires I mention one is a 24 inch diameter the other is 26.1 the revolutions per mile are 870 and 797 which is about a 10% difference in gearing and that makes a big difference. After all I only have 195 hp at the rear wheels
07-05-2007, 07:51 PM
#54
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You are still wrong ...try that 2nd gear start or plug that into the simulator. If you are rolling along at 70 mph in 5 th (driving to the track) and need to pass do you just floor it at 2,000 rpm or do you down shift ? Now make that pulling away from a stop at 25 mph 2,300 rpm when the Vette beside you hits the gas ? do you downshift ? OH right you are in FIRST GEAR ALREADY .
07-05-2007, 10:16 PM
#55
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Originally Posted by Shane
Put a Euro '86 ring and pinion (2.72) in your US box, that will give you gears in 1-4 very close to what Scott has in his 3.09 equiped GTS, but gives you a taller 5th gear which would be the same as a GT (2.73).
PN for Euro 2.72 = 928.302.911.55
This is what the one of the previous owners of my second 5sp did to the car. I'm impressed with the way it runs!!
PN for Euro 2.72 = 928.302.911.55
This is what the one of the previous owners of my second 5sp did to the car. I'm impressed with the way it runs!!
07-05-2007, 11:43 PM
#56
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Did I start somrthing again ??? My 68 Vette with a stroker went from 340's to 373's big difference off the line but a little too high at 70 with a 4-speed. Seems like the motor is were to put the money.
07-06-2007, 01:56 AM
#57
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Someone locked in a rubber room in Zuffenhausen decided that different ratios for different horsepower ratings for different markets would be good. A person two doors down the hall decided that a five-speed manual would be better than a two-speed manual. Why would those idiots think those things? With a two-speed manual, you'd only have one shift to make between zero and top speed. You'd calculate the final drive times the layshaft ratio in top gear times the tire size in cubits, multiply by the square root of the tire pressure (in bar of course) so you could make sure that the car is making maximum horsepower somewhere near where the car reaches top speed.
Mark, those same idiots decided that my '89 S4 needed a slightly higher numerical final drive ratio for the US market. Is it quicker from a standing start to top speed compared with the same car built for 1988 model year? Yes. Is the top speed different between the two otherwise identical cars? No. Is it more responsive in almost any normal driving situation, even though your numbers suggest that the gains I see in rear wheel torque in any gear will be offset by the early reduction in available torque when the '89 car shifts up earlier? Yes. Were those the same idiots who decided that the GT needed an even higher ratio final drive? Could it have been to get more performance out of the car? Yes and Yes again.
I wonder why the did that...
Mark, those same idiots decided that my '89 S4 needed a slightly higher numerical final drive ratio for the US market. Is it quicker from a standing start to top speed compared with the same car built for 1988 model year? Yes. Is the top speed different between the two otherwise identical cars? No. Is it more responsive in almost any normal driving situation, even though your numbers suggest that the gains I see in rear wheel torque in any gear will be offset by the early reduction in available torque when the '89 car shifts up earlier? Yes. Were those the same idiots who decided that the GT needed an even higher ratio final drive? Could it have been to get more performance out of the car? Yes and Yes again.
I wonder why the did that...
07-06-2007, 02:52 AM
#58
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Again, still missing the point. Of course, you need to drop a gear. its all about maximizing hp to the rear wheels.
now to address your comment below. if you are already at max grip for the Gs of acceleration you are at, dropping down to a lower gear (say the 1st you speak of) would not buy you any acceleration. However, if you do have the grip, you do have an advantage. Now the real question is what you did to the other gears in the gear box when you dropped all of them. please think about this before you respond again . it seems you are missing the mark by your response " you are wrong" and then your suggestion that i should start out in 5th gear. remember we all agree, that close ratio gear boxes and a 1st gear that can be used for min slip and acceleration would be best, as well as trying to end up (for a quarter mile run) at near redline. if you dont end up at redline with a rear end gear change (which shifts all the gears up or down) you will have some serious sacrafices.
PLEASE do yourself and others a favor. read very carefully, my last few posts.
I am not wrong, you are not understanding the basic concepts. gearing doesnt creat hp, it only optimizes its application. if a 3.09 works, will a 4.09 work better, and when do you stop? when you limit the top end to the target or expected speed???? there are trade offs and REAL racers know this. (also folks that have taught this related subject matter professionally!)
Now, do you know what the vet and viper 1st gear ends up at as far as speed?
right in line with the 2.2 928S4 . Hmmm, i wonder why????
Here are the vet and viper 1st gear speeds at their redlines.
Vet 7000rpm
9.10 , 61
6.09, 91
4.45, 125
3.42, 162
2.53, 218mph
1.71, 322mph
Viper
8.17 59 6000rpm
5.46 88
3.99 121
3.07 157
2.27 225mph
1.54
now look at the S4 gears.
53mph 1st
80mph 2nd
115mph 3rd
154mph. 4th
Funny the gears at max rpm look pretty close to the same. in fact, the vet and the viper are taller, by a good amount. i wonder why that is? AND, both of these cars are 6 speeds too! And, they both have some big reductions as far as rear ends. However, in the end, all that matters is the speed at max rpm in each gear. As I've mentioned before, the hp at that MPH will determine the torque used for acceleration at the rear wheels (through the multiplicaton of the gear box)
Mk
now to address your comment below. if you are already at max grip for the Gs of acceleration you are at, dropping down to a lower gear (say the 1st you speak of) would not buy you any acceleration. However, if you do have the grip, you do have an advantage. Now the real question is what you did to the other gears in the gear box when you dropped all of them. please think about this before you respond again . it seems you are missing the mark by your response " you are wrong" and then your suggestion that i should start out in 5th gear. remember we all agree, that close ratio gear boxes and a 1st gear that can be used for min slip and acceleration would be best, as well as trying to end up (for a quarter mile run) at near redline. if you dont end up at redline with a rear end gear change (which shifts all the gears up or down) you will have some serious sacrafices.
PLEASE do yourself and others a favor. read very carefully, my last few posts.
I am not wrong, you are not understanding the basic concepts. gearing doesnt creat hp, it only optimizes its application. if a 3.09 works, will a 4.09 work better, and when do you stop? when you limit the top end to the target or expected speed???? there are trade offs and REAL racers know this. (also folks that have taught this related subject matter professionally!)
Now, do you know what the vet and viper 1st gear ends up at as far as speed?
right in line with the 2.2 928S4 . Hmmm, i wonder why????
Here are the vet and viper 1st gear speeds at their redlines.
Vet 7000rpm
9.10 , 61
6.09, 91
4.45, 125
3.42, 162
2.53, 218mph
1.71, 322mph
Viper
8.17 59 6000rpm
5.46 88
3.99 121
3.07 157
2.27 225mph
1.54
now look at the S4 gears.
53mph 1st
80mph 2nd
115mph 3rd
154mph. 4th
Funny the gears at max rpm look pretty close to the same. in fact, the vet and the viper are taller, by a good amount. i wonder why that is? AND, both of these cars are 6 speeds too! And, they both have some big reductions as far as rear ends. However, in the end, all that matters is the speed at max rpm in each gear. As I've mentioned before, the hp at that MPH will determine the torque used for acceleration at the rear wheels (through the multiplicaton of the gear box)
Mk
Originally Posted by Jim bailey - 928 International
You are still wrong ...try that 2nd gear start or plug that into the simulator. If you are rolling along at 70 mph in 5 th (driving to the track) and need to pass do you just floor it at 2,000 rpm or do you down shift ? Now make that pulling away from a stop at 25 mph 2,300 rpm when the Vette beside you hits the gas ? do you downshift ? OH right you are in FIRST GEAR ALREADY .
Last edited by mark kibort; 07-06-2007 at 04:23 AM.
07-06-2007, 02:57 AM
#59
Rennlist Member
Bob, dont confuse (as you did below) a run to max speed, (which is highly dependent on the final drive ratio, for which we all know a 2.2 is way too high to be useful for any kind of acceleration in the lower speed range. However it can be used to reach a higher speed (eventually) if there is hp available. the higher rear end, also had different gear sets that reduced the changes of the actual gear ratios, besides the final drive ratio. In the GT, all the gears have near the same spacing whereas in the S4, it has the same spacing up to 4th gear, and then a huge 50% drop for the fuel efficient 5th. we are NOT talking about this part of the gearing discussion, but what happens to the acceleration ranges of 0-120mph or so. so, leave 5th gear out of this (for now)
you should know better!!!
Now, you are also wrong about the lower geared car being more responsive in any driving situation. dead wrong. Just look no farther than the chart above that shows an identical viper, accelerating from 25mph to 110mph being faster with the stock gears 3.07 vs the higher numerical ration rear end of 3.57. why are there trade offs along the way? Certainly, to Jim's point, assuming traction control and effectiveness, the launch is better and yeilds a better 1/4 mile time with a standing start , BUT, if the race is from 25mph onward, the stock gears will yeild more acceleration. (overall) There are also areas where that is not true, but they would be speed RANGES! gears need to be looked at for a particular application. specifically, speed ranges. read the chart, look at the 25mph to 110mph times and tell me why the stock gear box worked better??? yes, you got it, trade offs.
MK
you should know better!!!
Now, you are also wrong about the lower geared car being more responsive in any driving situation. dead wrong. Just look no farther than the chart above that shows an identical viper, accelerating from 25mph to 110mph being faster with the stock gears 3.07 vs the higher numerical ration rear end of 3.57. why are there trade offs along the way? Certainly, to Jim's point, assuming traction control and effectiveness, the launch is better and yeilds a better 1/4 mile time with a standing start , BUT, if the race is from 25mph onward, the stock gears will yeild more acceleration. (overall) There are also areas where that is not true, but they would be speed RANGES! gears need to be looked at for a particular application. specifically, speed ranges. read the chart, look at the 25mph to 110mph times and tell me why the stock gear box worked better??? yes, you got it, trade offs.
MK
Originally Posted by dr bob
Mark, those same idiots decided that my '89 S4 needed a slightly higher numerical final drive ratio for the US market. Is it quicker from a standing start to top speed compared with the same car built for 1988 model year? Yes. Is the top speed different between the two otherwise identical cars? No. Is it more responsive in almost any normal driving situation, even though your numbers suggest that the gains I see in rear wheel torque in any gear will be offset by the early reduction in available torque when the '89 car shifts up earlier? Yes. Were those the same idiots who decided that the GT needed an even higher ratio final drive? Could it have been to get more performance out of the car? Yes and Yes again.
I wonder why the did that...
I wonder why the did that...
Last edited by mark kibort; 07-06-2007 at 04:18 AM.
07-06-2007, 03:09 AM
#60
Rennlist Member
looks like there are some errors on the sheet. i would love to think i hit the rev limiter at Road america in 4th and was going 170mph, but that simply was not the case. who did this spread sheet?
4th gear on a S4 is 3.2:1. the other gears look off too:
Select Transmission-> 83-86 Euro/ROW
Select Ring and Pinion-> 85-88 US
Layshaft Ratio 1.4545
Ring and Pinion Ratio 2.2
Gearbox Ratio Final Drive Ratio
1st Gear 3.7645 8.2820
2nd Gear 2.5122 5.5269
3rd Gear 1.7901 3.9381
4th Gear 1.3541 2.9791
5th Gear 1 2.2
Enter Tire Diameter (inches)-> 26 6.806778333
Enter Engine Speed (rpm)-> 6600
Tire Speed (rpm) Tire Speed (mph) Tire Speed (kph)
1st Gear 796.91 61.64 98.62536297
2nd Gear 1194.17 92.37 147.7895811
3rd Gear 1675.93 129.63 207.4121755
4th Gear 2215.43 171.36 274.1806278
5th Gear 3000.00 232.05 371.2788182
4th gear on a S4 is 3.2:1. the other gears look off too:
Select Transmission-> 83-86 Euro/ROW
Select Ring and Pinion-> 85-88 US
Layshaft Ratio 1.4545
Ring and Pinion Ratio 2.2
Gearbox Ratio Final Drive Ratio
1st Gear 3.7645 8.2820
2nd Gear 2.5122 5.5269
3rd Gear 1.7901 3.9381
4th Gear 1.3541 2.9791
5th Gear 1 2.2
Enter Tire Diameter (inches)-> 26 6.806778333
Enter Engine Speed (rpm)-> 6600
Tire Speed (rpm) Tire Speed (mph) Tire Speed (kph)
1st Gear 796.91 61.64 98.62536297
2nd Gear 1194.17 92.37 147.7895811
3rd Gear 1675.93 129.63 207.4121755
4th Gear 2215.43 171.36 274.1806278
5th Gear 3000.00 232.05 371.2788182
Originally Posted by FlyingDog
Fun with gears and Excel:http://members.rennlist.com/flyingdo...calculator.xls
Last edited by mark kibort; 07-06-2007 at 03:25 AM.