Upgrade my 2012 Transmission or Gears For 65mph performance?

[sono]

I'm looking to improve my optimal rpm range at 65mph. I have 3:55's right now and I feel like 2nd gear is to short and 3rd gear is to tall when you get on it.

I could go up or down in gear or I was looking at the 2013 transmission.

It appears to have a different gear ratio that might optimize 1st and second gear on sub-13 gt500's.

I currently have 20" rims with 315/35/20 tires if that helps. Any input would be appreciated, thanks.

 

[Catmonkey]

The big difference between '07-'12 is first gear. 2.97:1 vs. 2.66:1. The difference in second gear is 1.78:1 vs. 1.82:1. Second is a minute change and '13-'14 ratio is lower. No difference in 3rd or 4th. My beef with the 2012 transmission in my car is first gear. I'm running 3.73 in my car with the same size tire. I would change the ring and pinion first if your issue is with second and third gear. However, it may have an effect on what you currently think of first gear.

 

[Snoopy49]

 

[Catmonkey]

View attachment 49457

The problem with the above calculations is that is uses the unloaded, inflated tire diameter. Using the tire revolutions per mile data, the above mph are inflated by 3.3%

 

[Snoopy49]

The formula uses the tires circumference.

 

[sono]

I'm with you Catmonkey. I hate 1st as well, but I really hate having no first and being caught between power bands at 65. You get the worst on both ends. I say 65 mph because on the rare case I need to prove a point my gearing is a problem. So I figure better to go 4:10 or the other way to 3:15's.

Is their a way to update our transmission to the 13' ratio in first and second. That seems like the best of both worlds. You may actually get to use 1st, dropping to 2nd at 65mph is not a redline.

 

[Catmonkey]

Snoopy, it doesn't matter if it's using the circumference of the stated tire diameter. The reason using the inflated tire diameter is flawed is because the unloaded radius will travel further than the loaded radius given a full tire rotation. My Michelin's have tire revolution per mile of 726. In other words, given real world conditions with the full weight of a car on the tire, the tire will rotate 726 times over the course of a mile. One mile in inches is 63,360". The circumference of the unloaded tire diameter of 28.7" is 90.16". That means the tire revolutions per mile would be 702 (63,360/90.16), which doesn't agree to Michelin's published data.

To get accurate results in these online calculators, it would be better to back into the circumference by the dividing 63,360 by the published revs per mile. In the case of the Michelin 315/35-20: 63,360/726=87.27. Divide 87.27 by pi and you get 27.78. Put that number into the online calculator and you'll get more accurate results.

 

[Catmonkey]

I'm with you Catmonkey. I hate 1st as well, but I really hate having no first and being caught between power bands at 65. You get the worst on both ends. I say 65 mph because on the rare case I need to prove a point my gearing is a problem. So I figure better to go 4:10 or the other way to 3:15's.

Is their a way to update our transmission to the 13' ratio in first and second. That seems like the best of both worlds. You may actually get to use 1st, dropping to 2nd at 65mph is not a redline.

You could send the transmission to Rockland Standard Gear and they can put it together with a bunch of different ratios of your choosing. I found a 2013 that I'm going to be installing in my car. The problem with going to a '13-'14 transmission in the earlier cars is the later transmission has CV joints on both ends. The spline count on the main shaft is different so the mounting flange is very different and not interchangable. But if you pick up the later driveshaft, it will bolt right in with the later transmission. Take a look at Tob's thread on retrofitting the late model carbon fiber driveshaft in the earlier cars and you'll get a better understanding of the driveshaft issue.

 

[Sirraf]

Why 65 mph?

If you are talking about roll racing or something slow down or speed up to get in your powerband. Not worth spending tons of cash to make 65 mph your hot zone.

 

[NightRide]

That's weird I'm at about 4k rpm in 3rd at 65 but on stock 19s, it's a pretty sweet spot for me. Maybe try a different tire size.

 

[CD07GT500]

Why 65 mph?

If you are talking about roll racing or something slow down or speed up to get in your powerband. Not worth spending tons of cash to make 65 mph your hot zone.

Yea why 65? If you just wanted a quick 65-135 or so pull go with a 4.30 and put the car in 3rd. If you want to run 1/2 mile events 3.55s or maybe even 3.73s should work well for the power your car makes imo.

 

[Snoopy49]

Snoopy, it doesn't matter if it's using the circumference of the stated tire diameter. The reason using the inflated tire diameter is flawed is because the unloaded radius will travel further than the loaded radius given a full tire rotation. My Michelin's have tire revolution per mile of 726. In other words, given real world conditions with the full weight of a car on the tire, the tire will rotate 726 times over the course of a mile. One mile in inches is 63,360". The circumference of the unloaded tire diameter of 28.7" is 90.16". That means the tire revolutions per mile would be 702 (63,360/90.16), which doesn't agree to Michelin's published data.

To get accurate results in these online calculators, it would be better to back into the circumference by the dividing 63,360 by the published revs per mile. In the case of the Michelin 315/35-20: 63,360/726=87.27. Divide 87.27 by pi and you get 27.78. Put that number into the online calculator and you'll get more accurate results.

I am using an Excel spreadsheet that I made up for another car. The problem doesn't lie with the spreadsheet, it lies with the diameter of the tires not being the same for all brands. The spread sheet determines the diameter using the size printed on the tire, in this case 325-35-20. The spread sheet has the ability to use the actual diameter of the tire if known.

Here is a copy of the spreadsheet I used. You will need Excel 97 or newer. I am open to anything that will make it more efficient.

View attachment Speed Charts.zip

 

[Speedboosted]

Yea why 65? If you just wanted a quick 65-135 or so pull go with a 4.30 and put the car in 3rd. If you want to run 1/2 mile events 3.55s or maybe even 3.73s should work well for the power your car makes imo.

Neither of those gears you mentioned are good for the half mile. 3.31's with that big rear tire is perfect for 1/2 mile. 3.73's would be good for a 65-ish hit, anything steeper and traction/usability becomes an issue

 

[Booky]

My 2012 with a 2.3 TVS upgrade and the OEM 3.73s will set you back in your seat when you drop it down into 3rd at 65 mph and slam the go pedal.:-D

 

[RedVenom48]

Ive always been puzzled why the 13-14 cars got taller gears. I mean all that power is WICKED, but you lose the multiplier with a taller gear. so 662 at teh crank means even less at the wheels with a 3.31 than if it had the old 3.55 or 3.73.

If for some reason I ever find a 13-14 in my stable, 3.73s are going in if I find the 3.31s are too... restrictive.

 

[Sirraf]

Ive always been puzzled why the 13-14 cars got taller gears. I mean all that power is WICKED, but you lose the multiplier with a taller gear. so 662 at teh crank means even less at the wheels with a 3.31 than if it had the old 3.55 or 3.73.

If for some reason I ever find a 13-14 in my stable, 3.73s are going in if I find the 3.31s are too... restrictive.

That gear allow the car to top 200 mph. With 662hp and 3.73s, you wouldn't know what traction was even on the interstate with street tires.

 

[Catmonkey]

I am using an Excel spreadsheet that I made up for another car. The problem doesn't lie with the spreadsheet, it lies with the diameter of the tires not being the same for all brands. The spread sheet determines the diameter using the size printed on the tire, in this case 325-35-20. The spread sheet has the ability to use the actual diameter of the tire if known.

Here is a copy of the spreadsheet I used. You will need Excel 97 or newer. I am open to anything that will make it more efficient.

View attachment 49506

Thanks, but I have my own excel spreadsheet I developed 25 years ago. I'm not getting through with my point. I would need video to explain it better and I'm not that talented.

 

[Catmonkey]

Ive always been puzzled why the 13-14 cars got taller gears. I mean all that power is WICKED, but you lose the multiplier with a taller gear.

It was all about the zero to 60 times and 200 mph top speed. That and the taller gearing probably added more of a safety factor on high horsepower car.

 

[Sinultros]

I think the 13-14 taller gears give them an advantage on races from a roll as well as 1/2 mile and full mile runs as well. I've seen a few races already having an 11-12 versus a 13-14, and the latter pulled away, despite making slightly less power than the modded 11-12.

 

[sono]

I Agree with you Sinultros. I think gearing in the 13-14 is a big advantage. The reason I want to address optimal power band at 65mph is because I just want to punch it once in a while without it being an official roll race. Most of these guys just drive you crazy and don't know proper etiquette. I avoid most, but sometimes I bite when they think double the money gets you a faster car.