![]() |
Register or Log In To remove these advertisements. |
|
|
![]() |
|
Thread Tools | Display Modes |
![]() |
#1 |
Registered User
![]() Join Date: Jan 2006
Location: Warrington, PA
Posts: 403
|
general question about gear ratios
I've bee reading alot and have learned alot frorm the board about gear ratios...I think. I am still confused a bit, but I think i am getting it. Is this explanation correct?
1. If the gear number is larger (for example. 3.73 vs 3.08) 3.73 is a larger number, but the diamater of the gear is smaller than the 3.08, so the 3.73 takes more revolutions to turn the axle one time which equals high rpms at highway speeds, but more torque off the line? ![]() Am I getting close or am i totally wrong.....Thanks .... Rick Last edited by rick0312; 10-25-2007 at 12:37 AM. |
![]() |
![]() |
![]() |
#2 |
Registered User
Join Date: Apr 2005
Location: Chula Vista, California
Posts: 495
|
Re: general question about gear ratios
You are basicly on the right track. Let,s compare 3.08 vs. 4.56 gears. On the 3.08's the driveshaft/engine will have to turn just a fraction over 3 times to to turn the rear wheels one revolution. On the 4.56's the driveshaft/engine will have to turn just over 4 1/2 times to do the same thing meaning it will get rolling from a dead stop much easier than with the 3.08's.
__________________
rwgregory 67 GMC 2500 ,2w/d wide box 305 V-6, 4-speed |
![]() |
![]() |
![]() |
#3 | |
Registered User
Join Date: Jul 2007
Location: Toronto, On
Posts: 65
|
Re: general question about gear ratios
Quote:
![]() |
|
![]() |
![]() |
![]() |
#4 |
Senior Member
Join Date: Feb 2004
Location: Ponca city now kingfisher Oklahoma
Posts: 1,221
|
Re: general question about gear ratios
compare it to a 10sp bike, remember 10th gear was a mother to get rolling but 1st gear was easy but topped out quick.
__________________
Even the nicest dodge-chrysler is only 2years away from being parked outside of Section 8 housing. |
![]() |
![]() |
![]() |
#5 |
Registered User
![]() Join Date: Jan 2006
Location: Warrington, PA
Posts: 403
|
Re: general question about gear ratios
bump
|
![]() |
![]() |
![]() |
#6 |
Registered User
![]() Join Date: Jan 2006
Location: Warrington, PA
Posts: 403
|
Re: general question about gear ratios
so in order to get the best of both worlds I kind of want a rearend that is in the middle say a 3.42?
|
![]() |
![]() |
![]() |
#7 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
|
Re: general question about gear ratios
Depends on what you have.
A "low" rear-end gear is typically a higher number, like 3.73, 4.10, etc. A "high" rear end gear is typically a lower number, like 3.08. If you have a 700R4 you'll want a 3.42 or 3.73 to get good highway mileage and still have some "pull" off the line. Some say a 3.08 with a 700R4 is too weak and will make the rpm's in OD too low, outside of the range a 350 likes. If you don't have an OD transmission, you'll want a set of 3.08 gears. You'll still get decent pull off the line, but will also get fairly good fuel economy. If you tow with this set-up, you may want to keep the 3.73. Essentially, a higher rear end is better for fuel economy but loses "off the line" performance (but if you go too high, fuel mileage will actually suffer.) A lower rear end will give you better performance off the line but will run higher rmps on the highway and get less fuel economy than higher gears. The trick is to pick something in the middle of what you want. From experience, a 3.73 is great with a 700R4 and I've heard a 3.08 is good choice for a non OD transmission.
__________________
Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! Last edited by 67ChevyRedneck; 10-25-2007 at 10:25 AM. |
![]() |
![]() |
![]() |
#8 |
Senior Member
![]() Join Date: Sep 2007
Location: Albuquerque NM
Posts: 7,848
|
Re: general question about gear ratios
did our truks ever come with a 3.08 rear end? I`woldnt mind running one of those. that would really help out in gas.
__________________
1967custom |
![]() |
![]() |
![]() |
#9 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
|
Re: general question about gear ratios
Yes, they did.
__________________
Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
![]() |
![]() |
![]() |
#10 | |
Registered User
Join Date: Mar 2005
Location: 10-Uh-See
Posts: 5,609
|
Re: general question about gear ratios
Quote:
OK, Rick. The actual diameter of the gear isn't bigger or smaller. It's the number of teeth on the ring gear according to the teeth on the pinion gear. For example, a GM 12 bolt truck rearend with a 3.73 rear gear will have these measurements: 8 3/4" dia. ring gear with 41 teeth, and the pinion gear has 11 teeth. You get your final drive ratio by dividng the ring gear teeth by the pinion teeth which would look like this: 41 / 11= 3.727 (3.73 rounded out). A 12 bolt truck with a 3.07 gear will have a different amount of teeth but the ring gear is still 8 3/4" in dia. A gear ratio will read like this: 3.73:1. This means the pinion gear turns 3.73 revolutions per 1 revolution of the ring gear. A 3.07:1 ratio means the pinion gear turns 3.07 revolutions per 1 revolution of the ring gear. The quicker the ring gear revolves in accordance to the pinion gear the quicker the vehicle can accelerate, but it takes more rpms the faster it turns. That's all I can type now before I actually confuse you or myself. I'll chime in later with more info.
__________________
|
|
![]() |
![]() |
![]() |
#11 | |
Senior Member
Join Date: Aug 2002
Location: Valley Center KS
Posts: 3,525
|
Re: general question about gear ratios
Quote:
Of course you could run similar rpms with 4.11s and a T56 (50% OD in 6th) ![]() |
|
![]() |
![]() |
![]() |
#12 |
Registered User
![]() Join Date: Jan 2006
Location: Warrington, PA
Posts: 403
|
Re: general question about gear ratios
here's what i am gonna run
350/290hp SBC 3 speed transmission saginaw no groove 2.851st 1.68 2nd and 1.00 3rd Tires I currently have 31x10.5 R15LT's Might go a little smaller on the tire,but not by much. Any suggestions on a rear gear ratio that will get me decent power off the line and accepatable highway cruising....thanks |
![]() |
![]() |
![]() |
#13 |
Senior Member
Join Date: Feb 2004
Location: Ponca city now kingfisher Oklahoma
Posts: 1,221
|
Re: general question about gear ratios
3.42 or 3.55 with a 30x9.5 15's would be good.
__________________
Even the nicest dodge-chrysler is only 2years away from being parked outside of Section 8 housing. |
![]() |
![]() |
![]() |
#14 |
Registered User
Join Date: Sep 2006
Location: colorado springs colorado
Posts: 737
|
Re: general question about gear ratios
Don't forget in the equation is tire size.
Running a tall tire with a higher gear ratio(like 3.08s) will kill the bottom end torque,,,,but running a tall tire with a low gear ratio(3.73 or 4.11) will kill the highway milage. Personally I would be inclined to look at a 30" or 31" tire with 3.08 gear ratio for a good balance. If there were any towing or hauling involved I would look at the same size tire and a 3.73 gear ratio. Just my .02 though Frank
__________________
70 chevy lwb c10 454/th400 and a 9" rearend suicide doors, marker light fuel fill, 4" cowl , mini tub Last edited by sick69; 10-25-2007 at 10:54 PM. |
![]() |
![]() |
![]() |
#15 |
Registered User
Join Date: Mar 2005
Location: 10-Uh-See
Posts: 5,609
|
Re: general question about gear ratios
Rick, I would go with a 3.42 gear. If your truck was originally a 3spd truck it should have 3.73 gears in it now. You can buy a 3.42 R&P set that is machined to fit your 4-series carrier. If you don't plan to run a tire less than 30" tall, I wouldn't go with a 3.08 unless you just want better mileage.
The only thing that will hurt your performance now will be the 3spd tranny. It's not that it's a bad tranny, but it's the gap from 1st gear to 2nd. The engine has to work harder to catch up to the next gear. A 4spd would be better suited if you could find one and afford it. I'm not recommending a Muncie unless you just want one. A Saginaw 4spd would work great in your truck and they're easier to find the right length shifter for. The 3spd should be fine if you just want a dependable tranny and you want to play around a little here and there.
__________________
|
![]() |
![]() |
![]() |
#16 |
Registered User
![]() Join Date: Jan 2006
Location: Warrington, PA
Posts: 403
|
Re: general question about gear ratios
thanks guys.great info!
|
![]() |
![]() |
![]() |
#17 | |
I have a radical idea!
Join Date: Jan 2005
Location: Sweet Home Alabama!
Posts: 6,513
|
Re: general question about gear ratios
Quote:
+1
__________________
'67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club! |
|
![]() |
![]() |
![]() |
#18 |
Registered User
Join Date: Dec 2003
Location: here
Posts: 5,789
|
Re: general question about gear ratios
3:42 is the perfect all around ratio...
|
![]() |
![]() |
![]() |
#19 |
Registered User
Join Date: Mar 2004
Location: St. Louis, MO
Posts: 336
|
Re: general question about gear ratios
If you are going with a Saginaw 4 speed make sure you get one with the correct gear ratio for your set up. They are not all the same. They were made in 4 different gear ratios. You can tell the ratio by how many lines are on the input shaft. They have no lines, 1 line, 2 line or 3 line. I don't have the ratios handy but I have seen other posts on here that have the ratios. The transmission and rearend ratios need to be matched up to get the desired results.
Last edited by dave3156; 10-27-2007 at 08:49 AM. |
![]() |
![]() |
![]() |
Bookmarks |
Thread Tools | |
Display Modes | |
|
|