Short Gears or Ring & Pinion?
- Thread starter NSXnBRLA
- Start date
Hope this turns out okay...
Did some calculations of my own..
Give or take a few mph, these would be max speeds attained in each gear hitting 8000 RPM, if there was enough power to overcome the drag...
Assume the tire diameter is about 24.9 inches....
These numbers look credible...I think
Stock 5 w/4.235 w/4.55
47.51 45.57 42.41
84.48 81.03 75.42
118.61 113.77 105.89
150.87 144.71 134.69
189.23 181.50 168.93
Japanese w/4.235 w/4.55
5 Speed
47.51 45.57 42.41
74.74 71.69 66.72
104.21 99.95 93.03
141.23 135.46 126.09
189.23 181.50 168.93
Stock 6 w/4.235 w/4.55
47.51 45.57 42.41
74.44 71.39 66.45
102.02 97.86 91.08
130.26 124.94 116.29
160.32 153.77 143.13
202.63 194.35 180.90
[This message has been edited by Redeye (edited 22 November 2002).]
Did some calculations of my own..
Give or take a few mph, these would be max speeds attained in each gear hitting 8000 RPM, if there was enough power to overcome the drag...
Assume the tire diameter is about 24.9 inches....
These numbers look credible...I think
Stock 5 w/4.235 w/4.55
47.51 45.57 42.41
84.48 81.03 75.42
118.61 113.77 105.89
150.87 144.71 134.69
189.23 181.50 168.93
Japanese w/4.235 w/4.55
5 Speed
47.51 45.57 42.41
74.74 71.69 66.72
104.21 99.95 93.03
141.23 135.46 126.09
189.23 181.50 168.93
Stock 6 w/4.235 w/4.55
47.51 45.57 42.41
74.44 71.39 66.45
102.02 97.86 91.08
130.26 124.94 116.29
160.32 153.77 143.13
202.63 194.35 180.90
[This message has been edited by Redeye (edited 22 November 2002).]
A common “error” in such calculations is to rely on tire diameter alone. Several other factors can make for small or even not so small variance. Manufacturers typically include both diameter and Revolutions Per Mile in their specs. Revs/mile is slightly higher than simple math would suggest based on their diameter, presumably because the “flat” spot on the bottom reduces the effective diameter. Those ratings are both assuming a specific rim width, but if you stretch it onto a wider rim the diameter decreases. Likewise, if you squeeze a wider but lower profile tire on the same rim it may be rated at the same nominal diameter but will pucker up a bit and therefore increase actual diameter. And of course tire pressure and vehicle weight have an impact on the degree of flattening impact. Then when you start talking about high speeds you experience a degree of tire “growth”. That would tend to offset some of the flattening, but I’m not sure how much more than that given the short stiff sidewalls and rigid belt structure of tires today.
That depends on the manufacturer. Some manufacturers calculate the revolutions per mile for their specs based on the calculated diameter of the tire size, whereas others base it on the "rolling diameter" which takes into account the deflection of the tire at the contact patch.
Quote NSXTASY:
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Not as much difference as the gearing. That difference of 8 lb-ft is about 3 percent greater torque, giving 3 percent more torque at the wheels. The difference in the gear ratios is about 13 percent, giving 13 percent more torque at the wheels. That means that more than 80 percent of the improvement in acceleration (torque at the wheels) is due to the gearing change, rather than from greater force from the engine.
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I understand this better now. The short second is faster; mostly because of the ratios and not so much where the rpm is.. Thanks
Ken, I have heard that the car is slower with shorties after second. The ratio of third short gear is shorter than stock? Do you know why is this?
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Not as much difference as the gearing. That difference of 8 lb-ft is about 3 percent greater torque, giving 3 percent more torque at the wheels. The difference in the gear ratios is about 13 percent, giving 13 percent more torque at the wheels. That means that more than 80 percent of the improvement in acceleration (torque at the wheels) is due to the gearing change, rather than from greater force from the engine.
--------------------------------------------
I understand this better now. The short second is faster; mostly because of the ratios and not so much where the rpm is.. Thanks
Ken, I have heard that the car is slower with shorties after second. The ratio of third short gear is shorter than stock? Do you know why is this?
This is because the car will be faster with the shorter gearing within the same gear, but not necessarily at the same speed.
Look at the shift points (speeds in mph at redline, which is approximately the shift point for maximum acceleration):
Stock gears
1-2 45
2-3 81
3-4 114
4-5 144
Short gears
1-2 45
2-3 73
3-4 101
4-5 139
At speeds for which you accelerate in the same gear with either set of gears, you will be a little bit faster with the short gears:
45-73 mph (gear ratio 1.952 vs 1.727)
81-101 mph (gear ratio 1.400 vs 1.230)
114-139 mph (gear ratio 1.033 vs 0.967)
(The higher the number for the gear ratio, the shorter the gearing and the faster the acceleration.)
At these speeds, the short gears are faster by 13 percent, 14 percent, and 7 percent.
At speeds for which you can stay in a lower gear with the stock gears than with the short gears, you will be faster - and significantly faster (because the difference in ratios is greater) - with the stock gears:
73-81 mph (gear ratio 1.400 vs 1.727)
101-114 mph (gear ratio 1.033 vs 1.230)
139-144 mph (gear ratio 0.771 vs 0.967)
At these speeds, the stock gears are faster by 19 percent, 16 percent, and 20 percent.
That's why all of the advantage of the short gears is at lower speeds and gears. To see this, let's look at the acceleration numbers up to 70 mph, when both gearsets have used up most of second gear, and then from there to 150 mph, when both gearsets are in fifth gear:
0-70 mph
Stock: 6.59 seconds
Short: 6.27 seconds
70-150 mph
Stock: 31.19 seconds
Short: 34.79 seconds
As you can see, once you're above 70 mph, the stock gears are significantly faster. That's why the stock gears are likely to be faster on the racetrack, whereas the short gears are faster in the "stoplight grand prix" in the city.
I understand this!
. Now, my biggest enemy in acceleration is drag. Another post!
Thanks
Thanks
The greatest advantage to the short gears is the elimination of that annoying dropoff when shifting to 2nd gear. It's a driveability issue more than anything else.
I would agree that for most people that the increase in timed performance is modest. If you drive your NSX around town, the more you stop and start, the more you're going to appreciate the short gears.
The ring and pinion change to the 4.235 also enhanced driveability, but in my opinion, less so than the short gears. With the 4.235 the car felt "lighter", "faster", and more perky in around town driving. This is of course, a subjective thing, as I didn't do any timed tests.
The 4.235 gears just made the car more fun to drive. The short gears, however, fixed something that was an annoying driveability problem.
To answer the original question that NSXnBRLA posed... If I only had the budget for one, I'd do the short gears only. Easy decision.
-Jim
------------------
1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
1976 Honda Accord 5 spd, 3 door Blue/Blue
1977 Honda Accord - Custom - Under Construction
1986 Chevy Suburban
http://homepage.mac.com/jimanders/PhotoAlbum1.html
I would agree that for most people that the increase in timed performance is modest. If you drive your NSX around town, the more you stop and start, the more you're going to appreciate the short gears.
The ring and pinion change to the 4.235 also enhanced driveability, but in my opinion, less so than the short gears. With the 4.235 the car felt "lighter", "faster", and more perky in around town driving. This is of course, a subjective thing, as I didn't do any timed tests.
The 4.235 gears just made the car more fun to drive. The short gears, however, fixed something that was an annoying driveability problem.
To answer the original question that NSXnBRLA posed... If I only had the budget for one, I'd do the short gears only. Easy decision.
-Jim
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1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
1976 Honda Accord 5 spd, 3 door Blue/Blue
1977 Honda Accord - Custom - Under Construction
1986 Chevy Suburban
http://homepage.mac.com/jimanders/PhotoAlbum1.html
Originally posted by Smoothaccel:
I understand this!. Now, my biggest enemy in acceleration is drag. Another post!
Thanks
True. Easy Options:
1. lower your car with dampners and/or springs; it will not only look better but the lower center of gravity will give it less drag and it will also go faster - don't ask mw how much more ....
2. use the new 2002 rear lower bumper and add the type R diffuser - killer looks, less brake dust, and I am sure it will go fatser ....... and this one, I am contemplating on doing ....
3. you can also put the stick on 2002 spoiler on top of the trunk lid but IMO that is ugly .... I don't mind giving up some mph for that ....
4. and if you want more ponies at low cost, to overpower the drag, go with a used header/exhaust combo if you have an earlier model ......
Now don't ask mw how much more mph .... I don't drive at those upper end speeds ...
Now that they have brought back the Type-R in Japan for 2002 with the 4.235 r/p you can order it for the 6 speed from Dali or your Acura dealer.
-matt
[This message has been edited by blurr (edited 23 November 2002).]
According to Acura, the stock U.S. market 2002 NSX, with its new body changes, has increased its top speed by 7 mph, to 175 mph, over the 2001 NSX.
Yes, and if you realize that those 7 mph gains aren't linearly distributed over the entire range (you won't see a 7/2 mph gain at 175/2 mph), you'll understand why efforts to decrease drag will be largely meaningless. Unless you plan to run your NSX at the Bonneville Salt Flats.
-Jim
------------------
1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
1976 Honda Accord 5 spd, 3 door Blue/Blue
1977 Honda Accord - Custom - Under Construction
1986 Chevy Suburban
http://homepage.mac.com/jimanders/PhotoAlbum1.html
[This message has been edited by Jimbo (edited 23 November 2002).]
-Jim
------------------
1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
1976 Honda Accord 5 spd, 3 door Blue/Blue
1977 Honda Accord - Custom - Under Construction
1986 Chevy Suburban
http://homepage.mac.com/jimanders/PhotoAlbum1.html
[This message has been edited by Jimbo (edited 23 November 2002).]
I would think that reducing drag significantly helps not only top end, but also fuel consumption and acceleration at very very very high speeds, too.
Not that any of us drive at very very very high speeds, of course.
Not that any of us drive at very very very high speeds, of course.
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At this point, based on what I have read and learned, I seriously doubt it is a straight swap for a regular US 6-speed R&P. I think it will take some additional effort and cost to make it work.
Has anyone verified that it will work or actually done it yet? Until then I remain pretty skeptical that it's a straight swap.
Lud, by lowering the car wouldn't we have less frontal tire surface?
I would say 1" drop and 10" wide tire would give you 10 square inches less frontal area for each tire. 20 square inch frontal surface in total!
I would say 1" drop and 10" wide tire would give you 10 square inches less frontal area for each tire. 20 square inch frontal surface in total!
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gheba_nsx,
Yes, but you are asking a different question.
It is correct that changing the aerodynamics of the car, such as your example of reducing frontal area of the tires, will affect aerodynamic drag.
But that is aerodynoamics, not CG. The CG is NOT related to aero drag. If you are so inclined, you could signifigantly change the CG of a vehicle and it would have absolutely no effect on aero drag as long as you kept the exterior the same.
Yes, but you are asking a different question.
It is correct that changing the aerodynamics of the car, such as your example of reducing frontal area of the tires, will affect aerodynamic drag.
But that is aerodynoamics, not CG. The CG is NOT related to aero drag. If you are so inclined, you could signifigantly change the CG of a vehicle and it would have absolutely no effect on aero drag as long as you kept the exterior the same.
Say what? Talk to me in layman's terms ..... if there is less air going under the car because there is less air to go under the car when it is lowered [thus the reference or linkage to CG], lowered means there is less lift - everything else being the same, and you are telling me that doesn't affect the aero drag? Do we have some engineers in here before I check myself to an institution .....
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You are confusing/combining two unrelated facts into one:
Lowering the car affects the aerodynamics (though dropping an NSX 1" is probably a negligible difference in drag).
Lowering the car affects the CG.
But aerodynamics and CG are not related to each other. They are simply both affected by lowering.
You can easily adjust the aero drag on a car without affecting CG, and you can easily adjust the CG on a car without affecting aerodynamics.
In layman's terms, the center of gravity is the "average" location of weight of an object.
Layman's example: If I replace the heavy glass engine hatch with a lightweight Lexan hatch, I have changed the CG of the car because I have reduced the amount of weight up high. But this has NO affect on aerodynamics or drag.
Lowering the car affects the aerodynamics (though dropping an NSX 1" is probably a negligible difference in drag).
Lowering the car affects the CG.
But aerodynamics and CG are not related to each other. They are simply both affected by lowering.
You can easily adjust the aero drag on a car without affecting CG, and you can easily adjust the CG on a car without affecting aerodynamics.
In layman's terms, the center of gravity is the "average" location of weight of an object.
Layman's example: If I replace the heavy glass engine hatch with a lightweight Lexan hatch, I have changed the CG of the car because I have reduced the amount of weight up high. But this has NO affect on aerodynamics or drag.
Lud, you just said what I said in my first post!
Exactly! And I said:
"1. lower your car with dampners and/or springs; it will not only look better but the lower center of gravity will give it less drag and it will also go faster - don't ask mw how much more .... "
And I went a step further in next post so you don't pick one sentence out of context:
" ....... if there is less air going under the car because there is less air to go under the car when it is lowered [thus the reference or linkage to CG], ......."
I don't think I am confused, at least not yet. Both my posts noted that lowering the car will cause the CG to be lower. And a "lowered" car will have less drag .....
What, you are not busy today or did you not have coffee yet .... LOL!
Exactly! And I said:
"1. lower your car with dampners and/or springs; it will not only look better but the lower center of gravity will give it less drag and it will also go faster - don't ask mw how much more .... "
And I went a step further in next post so you don't pick one sentence out of context:
" ....... if there is less air going under the car because there is less air to go under the car when it is lowered [thus the reference or linkage to CG], ......."
I don't think I am confused, at least not yet. Both my posts noted that lowering the car will cause the CG to be lower. And a "lowered" car will have less drag .....
What, you are not busy today or did you not have coffee yet .... LOL!
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No, I may have said what you meant in your first post, but I did not say the same thing you said.
You said: "the lower center of gravity will give it less drag" which is not correct. This is not taken out of context in a way to change the meaning of the statement.
You probably did mean that lowering the car will affect drag, but you started that changing the CG changes the drag which is simply incorrect.
I'm sorry if you think I'm overly picky, but this is important stuff that a lot of people do not understand and I'm just trying to make sure no misconceptions are spread.
You said: "the lower center of gravity will give it less drag" which is not correct. This is not taken out of context in a way to change the meaning of the statement.
You probably did mean that lowering the car will affect drag, but you started that changing the CG changes the drag which is simply incorrect.
I'm sorry if you think I'm overly picky, but this is important stuff that a lot of people do not understand and I'm just trying to make sure no misconceptions are spread.
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