Rear gear ratio question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

litebulblsc · 12-28-2023, 06:48 PM

I am considering a different gear ratio for my truck. Currently has 3.73:1. Playing with an online calculator, I could go down to 4.56:1 and still be able to get to 135 mph in 3rd. My fastest trap was about 118 mph, and I can only add so much more power with my current setup, that I do not see me hitting 135 mph in the quarter.

So is there a reason not to go with the lower gear ratio? It should make the truck faster, correct? The only down side I can think of is traction,but their are ways to overcome that.

**Getter-Done** · 12-29-2023, 12:10 AM

You could go with a 5:14.

The math is there.

**regan wilson** · 12-30-2023, 08:41 AM

A lot of things come into play on choosing the right gear. Tire size, transmission gear ratios, tq converter slip, max rpm etc.

litebulblsc · 12-31-2023, 07:38 AM

Quote:

Originally Posted by Getter-Done

You could go with a 5:14.

The math is there.

I am aiming to up my mph some. That would put me at "redline" at the stripe with the convertor locked

Quote:

Originally Posted by regan wilson

A lot of things come into play on choosing the right gear. Tire size, transmission gear ratios, tq converter slip, max rpm etc.

Tire is 29.5
Trans ratio would be 1:1
I have a lockup convertor, so slip could be zero
Max RPM is 7000

With those numbers it comes out to about 135 mph at 7000 rpm.

68racer · 01-08-2024, 05:24 PM

I calculated that changing from 3.7 to 4.1 would give me a tenth or two. It made no difference at all, although it became more consistent. These trucks hit aero problems at the top end.

**regan wilson** · 01-08-2024, 06:38 PM

I think 4.56 will work. Especially with the lockup converter.

Ziegelsteinfaust · 01-08-2024, 10:47 PM

I run 4.88's daily with a Detroit locker in a 32" tire. Or a 285/65R17.

To me the biggest hold back of the combo is the TH700R4. If I had the money's to do over. A 4L80e would of been a more optimal choice.

Even though my engine is just a highly tuned gen2 LT1 it is a absolute blast to drive. I do miss the way bigger cam I had before. If I replace the cam it will be with a smog legal performance cam to get a little more out of her, but keep my drivibility.

My gear ratio, and Detroit effectively stop me from burning out. So that would be good for the 1/8 mile.

The same gear ratio hurts my top end charges a bit because my engine is more torquey vs 4500 rpm plus performance.

So with out mentioning engine specs or build list, and tire size.

Even 4.11's or 4.33's maybe a better split the difference overall combo.

litebulblsc · 01-09-2024, 01:28 PM

I ordered the 4.56s and a detroit locker last week. Can't wait till the Spring to try them out.

litebulblsc · 07-16-2024, 07:49 PM

I can't get no tire traction. I can't get no tire traction. Cause I try and I try and I try and I try. I can't get no, I can't get no

That is the theme song of the truck now.

litebulblsc · 11-11-2025, 05:23 PM

Time to re-visit this...

**Getter-Done** · 11-11-2025, 09:37 PM

Flip for ya.

Name: gear ratio.jpg
Views: 257
Size: 31.2 KB

scottofksu · 11-12-2025, 01:34 PM

Quote:

Originally Posted by Getter-Done

Flip for ya.

Attachment 2435801

AND you hit 135 in the 1/4!

Keith Seymore · 11-12-2025, 03:48 PM

Quote:

Originally Posted by litebulblsc

Time to re-visit this...

That - uh - seems to have worked.

Good lookin' pass.

K

**regan wilson** · 11-12-2025, 06:26 PM

That's after the gear change? If so it looks like it was a step in the right direction.

litebulblsc · 11-12-2025, 07:26 PM

I forgot to mention, it was bouncing off the rev limiter the last 100 feet or so.

I think over the winter I will go up a ratio to 4.30s.

That was with a lot of changes, with more yet to come.

HO455 · 11-15-2025, 08:33 PM

Ýou may already know about this calculator. If not it may help you or just use it to the pass time while waiting at the doctor's office. It does have a nice function to insert converter slip into the calculations.

https://www.blocklayer.com/rpm-gear

litebulblsc · 02-05-2026, 10:46 AM

Well, I got a 4.30 and spool to try out. Wait for it to warm up a bit, and I will get it swapped in.

12-28-2023, 06:48 PM	#1
litebulblsc Registered User Join Date: Aug 2006 Location: LaSalle Mi Posts: 570	Rear gear ratio question I am considering a different gear ratio for my truck. Currently has 3.73:1. Playing with an online calculator, I could go down to 4.56:1 and still be able to get to 135 mph in 3rd. My fastest trap was about 118 mph, and I can only add so much more power with my current setup, that I do not see me hitting 135 mph in the quarter. So is there a reason not to go with the lower gear ratio? It should make the truck faster, correct? The only down side I can think of is traction,but their are ways to overcome that.

12-29-2023, 12:10 AM	#2
Getter-Done Senior Member Join Date: Dec 2009 Location: TN. Posts: 9,870	Re: Rear gear ratio question You could go with a 5:14. The math is there. __________________ ________________________________________________________________________________________ ____________________________________________ The early bird gets the worm, But the second mouse gets the cheese 85 Chevy K-20 63 Impala (my high school car) http://67-72chevytrucks.com/vboard/s...Crew Cab Build

12-30-2023, 08:41 AM	#3
regan wilson Registered User Join Date: Mar 2008 Location: tyler texas Posts: 1,582	Re: Rear gear ratio question A lot of things come into play on choosing the right gear. Tire size, transmission gear ratios, tq converter slip, max rpm etc. __________________ NHRA Super Street 469C It only runs 10.90 at 156 mph I was Dragtruck when Dragtruck wasn't Cool!

01-08-2024, 05:24 PM	#5
68racer Yeah baby! Join Date: Feb 2001 Location: United Kingdom Posts: 436	Re: Rear gear ratio question I calculated that changing from 3.7 to 4.1 would give me a tenth or two. It made no difference at all, although it became more consistent. These trucks hit aero problems at the top end. __________________ 11.37 @116

01-08-2024, 06:38 PM	#6
regan wilson Registered User Join Date: Mar 2008 Location: tyler texas Posts: 1,582	Re: Rear gear ratio question I think 4.56 will work. Especially with the lockup converter. __________________ NHRA Super Street 469C It only runs 10.90 at 156 mph I was Dragtruck when Dragtruck wasn't Cool!

01-08-2024, 10:47 PM	#7
Ziegelsteinfaust Registered User Join Date: Dec 2012 Location: Temple City Posts: 3,838	Re: Rear gear ratio question I run 4.88's daily with a Detroit locker in a 32" tire. Or a 285/65R17. To me the biggest hold back of the combo is the TH700R4. If I had the money's to do over. A 4L80e would of been a more optimal choice. Even though my engine is just a highly tuned gen2 LT1 it is a absolute blast to drive. I do miss the way bigger cam I had before. If I replace the cam it will be with a smog legal performance cam to get a little more out of her, but keep my drivibility. My gear ratio, and Detroit effectively stop me from burning out. So that would be good for the 1/8 mile. The same gear ratio hurts my top end charges a bit because my engine is more torquey vs 4500 rpm plus performance. So with out mentioning engine specs or build list, and tire size. Even 4.11's or 4.33's maybe a better split the difference overall combo.

01-09-2024, 01:28 PM	#8
litebulblsc Registered User Join Date: Aug 2006 Location: LaSalle Mi Posts: 570	Re: Rear gear ratio question I ordered the 4.56s and a detroit locker last week. Can't wait till the Spring to try them out.

07-16-2024, 07:49 PM	#9
litebulblsc Registered User Join Date: Aug 2006 Location: LaSalle Mi Posts: 570	Re: Rear gear ratio question I can't get no tire traction. I can't get no tire traction. Cause I try and I try and I try and I try. I can't get no, I can't get no That is the theme song of the truck now.

11-11-2025, 05:23 PM	#10
litebulblsc Registered User Join Date: Aug 2006 Location: LaSalle Mi Posts: 570	Re: Rear gear ratio question Time to re-visit this... Attached Images __________________ 1972 Blazer- 1988 Fiero- 1976 Cobra II- 2004 Sierra "drag truck"- 1999 Corvette FRC- 2014 SS- 1965 Barracuda- 2019 Ducati Hypermotard-2003 Kawasaki Z1000- 2022 Silverado 2500- 1985 ATC350X- 1986 ATC250R

11-11-2025, 09:37 PM	#11
Getter-Done Senior Member Join Date: Dec 2009 Location: TN. Posts: 9,870	Re: Rear gear ratio question Flip for ya. __________________ ________________________________________________________________________________________ ____________________________________________ The early bird gets the worm, But the second mouse gets the cheese 85 Chevy K-20 63 Impala (my high school car) http://67-72chevytrucks.com/vboard/s...Crew Cab Build

11-12-2025, 06:26 PM	#14
regan wilson Registered User Join Date: Mar 2008 Location: tyler texas Posts: 1,582	Re: Rear gear ratio question That's after the gear change? If so it looks like it was a step in the right direction. __________________ NHRA Super Street 469C It only runs 10.90 at 156 mph I was Dragtruck when Dragtruck wasn't Cool!

11-12-2025, 07:26 PM	#15
litebulblsc Registered User Join Date: Aug 2006 Location: LaSalle Mi Posts: 570	Re: Rear gear ratio question I forgot to mention, it was bouncing off the rev limiter the last 100 feet or so. I think over the winter I will go up a ratio to 4.30s. That was with a lot of changes, with more yet to come. __________________ 1972 Blazer- 1988 Fiero- 1976 Cobra II- 2004 Sierra "drag truck"- 1999 Corvette FRC- 2014 SS- 1965 Barracuda- 2019 Ducati Hypermotard-2003 Kawasaki Z1000- 2022 Silverado 2500- 1985 ATC350X- 1986 ATC250R

11-15-2025, 08:33 PM	#16
HO455 Registered User Join Date: Feb 2016 Location: Portland Oregon Posts: 12,406	Re: Rear gear ratio question Ýou may already know about this calculator. If not it may help you or just use it to the pass time while waiting at the doctor's office. It does have a nice function to insert converter slip into the calculations. https://www.blocklayer.com/rpm-gear __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

02-05-2026, 10:46 AM	#17
litebulblsc Registered User Join Date: Aug 2006 Location: LaSalle Mi Posts: 570	Re: Rear gear ratio question Well, I got a 4.30 and spool to try out. Wait for it to warm up a bit, and I will get it swapped in. Attached Images __________________ 1972 Blazer- 1988 Fiero- 1976 Cobra II- 2004 Sierra "drag truck"- 1999 Corvette FRC- 2014 SS- 1965 Barracuda- 2019 Ducati Hypermotard-2003 Kawasaki Z1000- 2022 Silverado 2500- 1985 ATC350X- 1986 ATC250R



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