what is your ideal gear ratios and why?

[ticopow]

Hey all,
Been looking around and found a question, as you read above I am wondering what everyone's favorite gear ratios are for both their differential and the transmission.
I have done a bit of research on the 2014 Mustang GT that I own, and I know what I would do if I swapped the tranny on that one (T56 Magnum XL with the 2.66 first gear and the .5 6th gear, I would also use the 4.10 for the differential), but from what I have read and calculated I don't really see a reason to get anything different when I do my roadster. That combo gets me a much stronger transmission, 700lbs of torque capable on my 3600lbs car, and those ratios keep my rpms around 2k rpm in 6th gear at 75mph. I understand that the 1000lbs or more of weight reduction means that the torque isn't as necessary in these cars, but I think buzzing around at 3krpm or more could get annoying in these cars.

Also why do most people choose a 5 speed over a 6 speed? Is this more to transmission options available versus gearing options available? I guess I plan on cruising in this car so 6th would be handy to keep the gas mileage up a little. No I don't care about gas mileage but if I can save money I will do what I can.

For differential options, I am thinking of going with the 2015 IRS, since it is very similar to what I own I know many of the options available. it seems like a lot of people are starting with the 3.55 because that's what is in the pumpkin when they get it. What are the common picks and reasoning behind those?

Thanks for all the help!

[walt mckenna]

Ideal ratios would depend on intended use and so I won't try to answer that one directly but will give you my experience so far.

I used an 04 Mach1 for a donor and it came with a 5 speed TR3650 which had a high numerical ratio in 1st gear to get that heavy car to launch well. That transmission started giving me trouble on my second track day and I didn't like that first gear ratio anyway, so I swapped it for a TKO600 with a 2:87 first gear and a .64 fifth gear for highway cruising. I only use third and fourth at the track because those two gears match well with the 3:55 rear and the 4.6 engine. The TKO fits the transmission tunnel well with plenty of room to work without modifications.

As I mentioned above, I use the 3:55 rear gear and I wouldn't change it because it provides a good compromise for cruising and track days. I have found that I could use a .82 fifth gear at the end of some long straights before the braking zone, but the engine has enough RPM capability to finish the straight, so that is a minor issue.

[RobReam]

I have 3:55 and like them.

[Mark Dougherty]

327/331 gear
for me the best all around

[ticopow]

Ideal ratios would depend on intended use and so I won't try to answer that one directly but will give you my experience so far.

I used an 04 Mach1 for a donor and it came with a 5 speed TR3650 which had a high numerical ratio in 1st gear to get that heavy car to launch well. That transmission started giving me trouble on my second track day and I didn't like that first gear ratio anyway, so I swapped it for a TKO600 with a 2:87 first gear and a .64 fifth gear for highway cruising. I only use third and fourth at the track because those two gears match well with the 3:55 rear and the 4.6 engine. The TKO fits the transmission tunnel well with plenty of room to work without modifications.

As I mentioned above, I use the 3:55 rear gear and I wouldn't change it because it provides a good compromise for cruising and track days. I have found that I could use a .82 fifth gear at the end of some long straights before the braking zone, but the engine has enough RPM capability to finish the straight, so that is a minor issue.

That's exactly the kind of answer I was hoping for.. I guess I could be a little more specific on what I would use the car for.

I want it to be a car I can get in and drive on any day. I would probably treat it just like my mustang. I have done both drag racing and autocross in it, both were a lot of fun actually. I did a lot more drag racing because it was cheaper and more often by far. My current mustang has the 3.31 gears and they are great because on the strip I cross about halfway through 4th gear at 112mph. with 3.55 I would be at the top of 4th and almost shifting to 5th and with 3.73 I would be into 5th gear when I crossed. With a car this light I would be into 5th gear with any of those, but 3.31 would keep me in 4th the longest.

With autocross and my car I stay in 2nd gear unless there are some way long straight parts, but I haven't seen those yet. I imagine that the speeds will be a bit faster with a lighter car so 3rd might happen if I had the same setup, but again that won't be all too affected by the rear end gear ratio.

Thanks for the replies everyone!

[Bob Cowan]

I'v tried a couple of different ratios: 4.10, 3.55, and 3.27. The 4.10 is nice around town, and on a short track. But for back road and highway cruising - and big tracks like HPR - it's just too short.

The 3.55 is a very good all around gear. Works well pretty much anywhere. >64 OD is usable down to about 55-60mph, so it works well on back roads and the highway.

The 3.27 does fine on the highway, and around town. BUT, in traffic - especially on the back roads - I find it too tall. Yesterday we drove back fro m Hartsel, CO, in heavy tourist traffic. Speed generally ranged from 55-70mph. I was doing a lot of shifting, looking for the sweet spot. I think I'll go back to 3.55. Or maybe try 3.73.

Most people use the 5 speed because it's readily available and fits well. You can use the 6 speed, but it's bigger, heavier, and longer. It requires IRS to get it to fit.

[CraigS]

The trans ratios you quoted for the 2014 you have now are very tall both 1st and 6th compared to what is more common in FFRs. So, yeah, I can see a 410 diff. But this I don't get.
"but I think buzzing around at 3krpm or more could get annoying in these cars."
Why would you be doing that? The ffr typical 5th is .64 and that, w/ a 331 diff, gives 70 mph at 2000-2200.
You can do the math but a .5 6th and 410 must be reasonably close.

[ticopow]

The trans ratios you quoted for the 2014 you have now are very tall both 1st and 6th compared to what is more common in FFRs. So, yeah, I can see a 410 diff. But this I don't get.
"but I think buzzing around at 3krpm or more could get annoying in these cars."
Why would you be doing that? The ffr typical 5th is .64 and that, w/ a 331 diff, gives 70 mph at 2000-2200.
You can do the math but a .5 6th and 410 must be reasonably close.

That 5th gear in the mustang is .65 so that puts the cars at basically the same rpm at 70.
I guess from what I remember seeing I thought the 5th on the common transmissions were closer to .8, that makes 75mph closer to 2750rpm with 3.73 gears, with 3.55 its still 2650-2700, but with 4.1 you are over 3k.
A .5 6th with 4.10 gears is just under 2k rpm to get to 75, so yeah they are all pretty close.

After reading all this I don't see the point in getting a 6th gear unless I find an amazing deal on one or the motor comes with it, or if I swap my mustang tranny and have my mt82 just sitting around :).
Thanks for the clarification!

[edwardb]

After reading all this I don't see the point in getting a 6th gear unless I find an amazing deal on one or the motor comes with it, or if I swap my mustang tranny and have my mt82 just sitting around :). Thanks for the clarification!

Don't miss the point from Bob... That longer 6-speed transmission will only fit in an IRS rear suspension. If you're thinking solid axle, 5-speed is the only choice. Frankly, having installed a T-5 and then a much larger TKO600, I'm not sure I'd want to wrestle with anything any bigger. The TKO is a tight enough fit.

Regarding the diff ratio and your original question, I would be a little careful with direct comparisons to these cars and your much bigger and heavier Mustang. There's a reason 3.55 is the most popular gear for these. It's just about the best compromise. 1st through 4th work very well for nearly all town cruising, and 5th with the .6X (there are several) overdrive gives good highway cruising in the low to mid 2000's. Depending on the engine and how it's setup, many don't like to be lugged any lower than that. I use this online calculator, but nothing beats actual experience. http://www.tremec.com/calculadora.php

[ticopow]

Don't miss the point from Bob... That longer 6-speed transmission will only fit in an IRS rear suspension. If you're thinking solid axle, 5-speed is the only choice. Frankly, having installed a T-5 and then a much larger TKO600, I'm not sure I'd want to wrestle with anything any bigger. The TKO is a tight enough fit.

Regarding the diff ratio and your original question, I would be a little careful with direct comparisons to these cars and your much bigger and heavier Mustang. There's a reason 3.55 is the most popular gear for these. It's just about the best compromise. 1st through 4th work very well for nearly all town cruising, and 5th with the .6X (there are several) overdrive gives good highway cruising in the low to mid 2000's. Depending on the engine and how it's setup, many don't like to be lugged any lower than that. I use this online calculator, but nothing beats actual experience. http://www.tremec.com/calculadora.php

I am thinking of going IRS right now either way, but thank you for the reminder! I have been thinking of going with the TKO600 and a Coyote at the moment, but I'm not sure if I would get a crate motor or a used motor, or go another direction. Still very early in the planning process. :)

I have been using an excel file to figure out gear ratios for my current transmission and future possible options for my mustang. I am going to probably add the tko600 info as well at some point to figure out what gears I think would work best for that. I will be looking around here and the other forums for all the info I can find :)

I am wondering what the more common tire sizes are as well. I am planning on the 17" rims but I don't know what width or tire size, but I think I would prefer staggered tires for a roadster and of course the wider the better.

Thanks again for all the help and understanding!

[edwardb]

I am wondering what the more common tire sizes are as well. I am planning on the 17" rims but I don't know what width or tire size, but I think I would prefer staggered tires for a roadster and of course the wider the better.

If running the Factory Five 17 inch wheels (9 inch wide front, 10-1/2 inch wide rear) the most common size for the front is probably 255/40's. Some go slightly narrower, and some go wider. But 255's fit the rims very nicely and give reasonable clearance for the body and inner fender. For the rear, the most common and widest is 315/35's.

Wheel size is frequently discussed, as you may know. 15 inch is the classic size for a most authentic look. But definitely presents some challenges on available tires and brakes. All doable, but you'll work at it. 17 inch is probably now the most common. Still some limitations on tires, but there are several options. Plenty of brake options. 18 inch wheels were just released by Factory Five as another option. Some like them, some don't. Certainly a different looked compared to the originals.

[ticopow]

If running the Factory Five 17 inch wheels (9 inch wide front, 10-1/2 inch wide rear) the most common size for the front is probably 255/40's. Some go slightly narrower, and some go wider. But 255's fit the rims very nicely and give reasonable clearance for the body and inner fender. For the rear, the most common and widest is 315/35's.

Wheel size is frequently discussed, as you may know. 15 inch is the classic size for a most authentic look. But definitely presents some challenges on available tires and brakes. All doable, but you'll work at it. 17 inch is probably now the most common. Still some limitations on tires, but there are several options. Plenty of brake options. 18 inch wheels were just released by Factory Five as another option. Some like them, some don't. Certainly a different looked compared to the originals.

Thanks again! based on excel the differences in tire sizes make the roadsters run 70 instead of 75 with any of the transmissions and differential ratios we have talked about. makes sense with the roughly 2" smaller tires (same rpm means smaller tires).