Gordonm

It seems that the general thought on this is around a 10.1 ratio. Who came up with this number. I was paging through some car rags the other night and started looking at the trans ratio and rear ratios. There are quite a few new performance cars that have ratios well above the "magic" 10.1 ratio. Some as high as 13.1 ratio. Granted some are 6 speeds but I'm sure they are doing this for faster acceleration. Mine is quite steep at 12.1 ratio but I don't mid it at all. It will do 40 mph in 1st gear alone. Who came up with the "magic" 10.1 ratio rule. I looked at the new Vettes are they are a little over 10.1 range also.
Discuss

chris75stingray

how is the ratio found? do you multiply your first gear ratio by rear diff ratio?

TTT

Godfathers Ghost

Yes.

And 10-1 works good for us because our engines are nice and torquey (is that a word?) Most of the cars that are higher geared have higher reving, lower torque engines. Its all about balance.

Little Mouse

Would 1650 lb ft of torque with 1000 lb ft of torque at idle with
a 54.77 to one low gear work OK.

84rzv500r

I'll let you know this spring....

I have a 10.99 first (3.27x3.36) and 28 inch tall tires...

OD is 2.69 (0.80x3.36)....

and 4 more gears in between....

Godfathers Ghost

If we're talking about a Peterbuilt

gkull

I have two cars on each end of the spectrum. 67 Camero with 2.73 and closed rato 4 speed probably about 8-1 and needs that heavy fly wheel to get going.

The Vette with TKO 600 and 4,11 with a light flywheel 11.79 -1 first gear ratio

My vette first gear is about useless and on a lazy day I do a 1-2 in an intersection.

I probably see a rear gear and OD reduction in my future,

You want to make every gear count. I'd rather be able to go 55-60 in first gear at 7000 rpm and keep the next 4 gear so close that i have constant power.

Bob3700

I am curious about that 10 to 1 ratio number.

For an older C3, to get to or exceed that number with a manual trans, you have to have some pretty tall gears in the back. Like 4:10 or better. That is a lot of gear to pull around.

I will tell you that with a 2.5 low rear box and 4:10 final drive, if you have the HP, you got a tiger by the tail with a small block.

For a BB car, that is a awful lot of tire spinning ability! I would think that getting the car hooked up might be a challenge. Right now, I have 2.5 low with 3:73 final drive and haven't driven it yet. Think that it will be a spin the tires at will type of situation, a lot of feathering to launch from a dead stop, and a lot of revs on the highway. Should be fun though!

Wonder why the newer engines need so much low gear multiplication? Are they that low on torque? Are they strictly high rpm type engines? I am stuck in the 1970 time warp and have no knowledge of newer equipment.

RGDS

Bob

JPhil

I have asked this question of many people, and have come up with two main ideas for answers. Nobody seems to know for sure, but this is the general conjecture:
-"Back in the day", the cars which ran the best at the drag strips typically ran a tranny such as the M-20 with a 2.52 1st gear, combined with a rear end of 4.11 for a 10.35 overall 1st. It was a very good combo for the cars, tires & engines of the time.
-A ratio numerically smaller, like 2.52 1st with 3.55 diff for 8.96 overall, cannot deliver enough torque for a quick launch, and you will burn up the clutch due to the need to 'feather' it. A ratio numerically higher, like 2.52 1st with 4.56 diff for 11.49 overall is akin to a granny gear: you jump out of the hole but don't gain much initial speed and almost immediatly lose time with the shift to 2nd coming so quickly and at the slower speed.

John

63mako

4.56 rear end gear and M-22 Rockcrusher 2.20 first is 10.03 to 1. That 10 to 1 thing has been the rule of thumb in drag racing since the 60's. It is the ideal launch gear and what we always used to shoot for when I was racing. EDIT: Jphil beat me to it!

427Hotrod

I'm at 9.9775 in mine. That's a 3.07 rear gear and a 3.25 first. I have a 5 speed with underdriven 4th..so final overall in 4th is 4.083. Then I have 5th gear at 1 to 1 for cruising.

I use 28" slicks at the track and have just about 700 ft lbs of TQ...and I actually am planning on adding a little more gear to trans to help out. First gear goes to just under 60 mph at the track..I grab 3rd just before the 1/8th mile mark and 4th just before the 1/4 mile. I cross the line at a little over 141 mph.

I want to keep 4th gear pretty similar but I want to get into 4th a LOT sooner. New gearing will have me in the 10.40ish range in 1st.


JIM

big_G

I've heard and been using the "10" figure since the early '70's. It may come to the fact that with the transmissions available at that time, a 2.20 or 2.52 first gear with a 4.56 rear gear gets you through the traps at about 6,000 rpm's in 4th. gear.

Glensgages

My Z28 currently is 11.3, but I've run a 12.54:1 effective First Gear ratio, too.

Gordonm

Most of the cars I was reading about were not just high rpm motors. Probably in the mid range of torque for new cars. Somewhere in the 300 350 ft/lb torque range. The 10 number came during the60s and 70s when that was all that was available. The drag guys were putting in 4.11 4.56 and even 4.88 gears to get the motor into the torque band as soon as possible. Why not go to the 12.1 range and get the motor in sooner. It seems that the manufacters are going this route with 6,7 and 8 speed trannys to keep the motor in its torque band. Sticks will require more shifting but the autos will do it with seamless power. I guess a lot depends on what motor you have. Jim with butt loads of torque can get away with his in the 10 range. A rice rocket will require deep gears and lots of gears to keep up.

big_G

This link has a calculator for gear ratios. The Z06 has about 10X factor.
http://www.xse.com/leres/bin/gearrat...diameter=25.21

Gordonm

I also see a lot of the C5 and C6 guys putting in steeper rear gears. Obviously for better acceleration.

big_G

I agree...the guys that are changing the rear gears usually rev. higher rpm than stock, and are also running a taller tire.

Hadez

I can tell you that the reason the new cars are having 6~8 speed auto tranny is to keep the car within its optimal torque band (as you said) but the reason behind this is lower mpg at both 60mph or 80mph. They gov't is changing the way they calculate highway mpg, currently it is a theorectical estimate with no real world testing assuming a steady state 60mph cruise, no ac, minimal passenger load, etc. For the auto makers...it makes a huge difference in their target figures to meet the gov't minimum fleet mpg average quotas and therefore these new trannys along with the new testing for real world mpg figures with AC on and standard passenger load will have significant impact for automakers.

jpatrick636

It has been my experience that for a street driven V8 with good performance, the 10-1 gearing is a pleasure to drive. Anything with more gear can become annoying in the long run and anything with less gear gives up too much performance. It's a good place to start for a street combination. That's why a lot of people say a 3.7 something gear is a good street compromise. With a lot of transmissions having a 2.5 to 2.8 first gear, a 3.73 puts it right in the 10-1 range.
Back in the 60's (omg that was 40 years ago) everything was "light to light". Everything was all over by second gear. If you had to make the 2nd 3rd shift, the gear advantage had to be substantial to make up for the extra shift, especially if you were up against a strong automatic.
Anyway, with up to 350 ft lbs, I might start at 11 or 12 to 1. With 350 to 500 I would start with 10-1. I would consider 9 or less with something well north of 500 ft lbs depending on traction.
This is pure seat of the pants science for a street car on street tires when looking for a compromise between performance and driveability. It also has something to do with personal preference. If you like to shift alot, go above 10-1. There is a performance advantage if you have the traction, but with stock size street tires on a C3, you probably will not.
The original question was "who came up with this?" I think it was born from experience on the street back in the 60's and has stood the test of time.
That being said, my car is north of 600 ft lbs, right at 10-1 in first and fun to drive. And yes, traction can be an issue with 295 street tires.

RHD '68 L89

I am using a Tremec TR3550 with 3.27 first and 3.7 rear gears which comes out as 12.1. First is a real granny gear with a BB's torque and I am considering a change to 3.08 (10.1) to make first more useable. It has the added advantage of lowering the RPMs at cruise as well. This is a street driven car with track (club day) use once a year.