Gears again

lopez · 08-26-2002, 05:47 PM

OK don't everyone scream at once. I have a 98 Cobra - tube headers, X-pipe, Star Clutch, pully's. Shows 281 at the wheels on the dyno. I have 3.27 gears. I want to go to 3.55 or 3.73. I drive highway a lot. Can anyone give me the difference (rpm) between the gear ratio's at 60 and 80 mph? I have stock Cobra wheels and 245/45 - 17 tires. I would really appreciate as I have to make a decision soon. I realize many people use 4.10's and higher but I really think for where i am and what I do 3.55 or 3.73 would be better. Much appreciate.

The Deuce · 08-26-2002, 05:53 PM

There is a tool on here that will give you that information in 4th gear. Since 5th is OD, there is no system that can give you that information. You should be able to calculate it based on your gearing info, and go that way.

My thoughts is there is twice as much 'new gear' in the 3.73's, so it wouldn't be worth the money to go with 3.55's.

Eric4Nitrous · 08-26-2002, 06:47 PM

3.73's rpm range at 60=around 1900 in 5th
3.73's rpm range at 80=around 2200 in 5th

3.55's rpm range at 60=1500 in 5th
3.55's rpm range at 80=2000 in 5th

I'd go with 3.73's

Titan · 08-26-2002, 08:56 PM

I don't have a cobra, but I do have a 98' w/ 3.73's. My 80mph rpm's are around 2600-2800.

98gt5sp · 08-29-2002, 07:15 PM

I personally think that going from 3.27 to 3.55 is a waste, and not worth the cost. I have 3.73 gears on my car, and I have a 35 mile commute on the freeway every day. 3.73 is not bad at all for highway driving, and this is what I would recommend.

fomocojo · 08-30-2002, 07:51 PM

Hi Lopez;
If you have a calculator handy this is the most accurate way I have found to do this .

For RPM's @ speed

Gear x 336 x speed (mph) divided by tire diameter x .68 ( overdrive)

Using this formula you can play with any speed or any gear ratio.Hope it helps you

Titan · 08-30-2002, 11:57 PM

There's no way...according to that, I run 3409 rpms @ 80 mph. That's way high...maybe low 3's...but not mids.

fomocojo · 09-01-2002, 01:27 PM

Hi again Lopez;
I think you've made a math error there. Let's try your 3.27 at 80 mph

3.27 x336 = 1098.72 x 80 mph=87897.6 divided by your 26' tire=3380.6769 x.68 (overdrive) = 2298.8602 rpm which is bang on what I run with my stock 3.27's

3.73 x336 =1253.28 x 80mph =100262.4divided by your 26' tire=3856.2461x .68=2622.2473 rpm

3.55 x 336 =1192.8 x 80 = 95424 divided by 26' = 3670.1538x.68 (overdrive) =2495.7045 rpm

After you play with it for awhile you get familiar with it.BTW it looks like 3.73 is the way to go.I 'm hoping to convert over the winter!

Titan · 09-01-2002, 04:58 PM

your tire diameter is 26 feet? Wow...even if that was inches, that's a big tire. I have a 17" rim and low profile tires, so that would make my total diameter just over 20"--not 26.

fomocojo · 09-01-2002, 07:46 PM

26 inches which is the stock diameter for 245/45 - 17 tires

08-26-2002, 05:47 PM	#1
lopez Registered Member Join Date: Aug 2002 Location: Clearwater, Fl Posts: 3	Gears again OK don't everyone scream at once. I have a 98 Cobra - tube headers, X-pipe, Star Clutch, pully's. Shows 281 at the wheels on the dyno. I have 3.27 gears. I want to go to 3.55 or 3.73. I drive highway a lot. Can anyone give me the difference (rpm) between the gear ratio's at 60 and 80 mph? I have stock Cobra wheels and 245/45 - 17 tires. I would really appreciate as I have to make a decision soon. I realize many people use 4.10's and higher but I really think for where i am and what I do 3.55 or 3.73 would be better. Much appreciate.

08-26-2002, 05:53 PM	#2
The Deuce Registered Member Join Date: Apr 2002 Location: Atlanta, GA Posts: 2,325	There is a tool on here that will give you that information in 4th gear. Since 5th is OD, there is no system that can give you that information. You should be able to calculate it based on your gearing info, and go that way. My thoughts is there is twice as much 'new gear' in the 3.73's, so it wouldn't be worth the money to go with 3.55's. __________________ 1997 Mustang GT "The Freak" - 13.80 @ 101.70, 2.07 60' 1995 Honda VFR750 - not much @ really fast (actual data pending.) 1964.5 Mustang 289 Rice Haters Club Member #13

08-26-2002, 06:47 PM	#3
Eric4Nitrous Registered Member Join Date: Jan 2002 Location: Va Posts: 1,122	3.73's rpm range at 60=around 1900 in 5th 3.73's rpm range at 80=around 2200 in 5th 3.55's rpm range at 60=1500 in 5th 3.55's rpm range at 80=2000 in 5th I'd go with 3.73's __________________ 68 Camaro Gene Fulton 632ci Two stages of Jug 8.41 164mph Rockingham 1-26-03

08-26-2002, 08:56 PM	#4
Titan Registered Member Join Date: Jul 2002 Location: Atlanta Posts: 296	I don't have a cobra, but I do have a 98' w/ 3.73's. My 80mph rpm's are around 2600-2800. __________________ Current Sophomore -- Mechanical Engineering Black on Black 98' GT 5-Speed Mods = Stuff

08-29-2002, 07:15 PM	#5
98gt5sp Registered Member Join Date: Feb 2002 Location: Washington Posts: 40	I personally think that going from 3.27 to 3.55 is a waste, and not worth the cost. I have 3.73 gears on my car, and I have a 35 mile commute on the freeway every day. 3.73 is not bad at all for highway driving, and this is what I would recommend. __________________ 1998 Silver Mustang GT 5sp My Mods My Web Page Rice Hater's Club - Member # 78

08-30-2002, 07:51 PM	#6
fomocojo Registered Member Join Date: Jan 2002 Location: toronto,ontario,canada Posts: 7	Hi Lopez; If you have a calculator handy this is the most accurate way I have found to do this . For RPM's @ speed Gear x 336 x speed (mph) divided by tire diameter x .68 ( overdrive) Using this formula you can play with any speed or any gear ratio.Hope it helps you

08-30-2002, 11:57 PM	#7
Titan Registered Member Join Date: Jul 2002 Location: Atlanta Posts: 296	There's no way...according to that, I run 3409 rpms @ 80 mph. That's way high...maybe low 3's...but not mids. __________________ Current Sophomore -- Mechanical Engineering Black on Black 98' GT 5-Speed Mods = Stuff

09-01-2002, 01:27 PM	#8
fomocojo Registered Member Join Date: Jan 2002 Location: toronto,ontario,canada Posts: 7	Hi again Lopez; I think you've made a math error there. Let's try your 3.27 at 80 mph 3.27 x336 = 1098.72 x 80 mph=87897.6 divided by your 26' tire=3380.6769 x.68 (overdrive) = 2298.8602 rpm which is bang on what I run with my stock 3.27's 3.73 x336 =1253.28 x 80mph =100262.4divided by your 26' tire=3856.2461x .68=2622.2473 rpm 3.55 x 336 =1192.8 x 80 = 95424 divided by 26' = 3670.1538x.68 (overdrive) =2495.7045 rpm After you play with it for awhile you get familiar with it.BTW it looks like 3.73 is the way to go.I 'm hoping to convert over the winter!

09-01-2002, 04:58 PM	#9
Titan Registered Member Join Date: Jul 2002 Location: Atlanta Posts: 296	your tire diameter is 26 feet? Wow...even if that was inches, that's a big tire. I have a 17" rim and low profile tires, so that would make my total diameter just over 20"--not 26. __________________ Current Sophomore -- Mechanical Engineering Black on Black 98' GT 5-Speed Mods = Stuff

09-01-2002, 07:46 PM	#10
fomocojo Registered Member Join Date: Jan 2002 Location: toronto,ontario,canada Posts: 7	26 inches which is the stock diameter for 245/45 - 17 tires

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