I recommend playing around with some online RPM calculators. You'll get a lot of different opinions on this subject. I have a T-5 3.35 1st (which is what you should have) with a 3.55 rear end. 1st is a little short but doable. OD is OK to cruise at 70 on flat surface. But I have to downshift at big hills or to pass. Rear tire diameter will make a difference too. I have 245/60/15 in the back.

 

If you want to get the best of all worlds, have first gear swapped for the T-5Z 2.95 ratio, then run 3.55 gears (if your engine makes a lot of low-end torque) or 3.80 (if your engine likes to rev).

If you are sticking with the 3.35 first gear, 3.25 or 3.55. And as G says, first gear will feel a little short with 3.55s.

My 2 cents
MrFreeze

 

☝What @G's 70 said. I have the exact same combo in my 67 with a 302, same tire size and all... I like it!

 

So I took out the gears I needed just my luck. LOL I have the complete pumpkin I took out, but the 4.21 has a Detroit Locker on it for 31 spline axles. I'll have to find somebody that can swap it around for me. My days are turning wrenches for over I'm on oxygen can't hardly walk to the car without running out of air.

 

Is it a 9" rear?

 

Yes

 

Agree with the above. Same set up with 25.9 in diameter tires. 1st is short but tolerable until I get around to swapping to a 2.95 1st. 2nd is wide enough to be quite usable. Often start off in 2nd. 5th gear I am turning 2200 rpm at 70 mph. Have gotten 27 mpg with a/c on a long flat trip along the coast. I am very happy with 3.55s. Cruise vacuum rarely dips below 15 inches; the sweet spot for mileage. Have run 15.1 @ 92 in 1/4 on a 100 deg day and never got 2nd gear in any of the runs due to equalizer bar binding. Then drove the 200 miles home with a/c on.

 

I have a 3.35/.68 T5 I'm using a 3.40TracLoc 8" 1st gear is a little short but no useless. I wouldn't go to a higher numerical rear gear. I have several sets of rims and tires but average tire diameter is 25"

 

I tried a 3.35 first gear T5 with 3.55 gears and did not like it. My tires are short at 24.5. I now have a T5z. Even with a .63 overdrive it cruises fine at 45 mph in 5th. (1,500 rpm). 70 mph is about 2,330 rpm at I can roll any hill on an interstate without problem. Even my C4 downshifted to pass.

 

Okay I got the to thinking I drove the 88 Mustang maybe 10 miles I love the torque it had. So this morning it dawned on me to check on the gear ratios the weight difference of the cars and the tire height. So I have rear wheels that are 16 in just like the 88 Mustang I plan on running a 225 60 15 tire on them. And the weight of both cars is basically the same within 100 200 pounds. So below or however this post it's a screenshot of the gear ratios used in the Mustang in 1988.

 

Confused 🤔 you have 16" wheels but plan on running 225/60/15. Maybe it was a typo? If you meant 225/60/16 that's kinda tall

 

I ran a set of 2.80s for a bit while repairing the pinion seal on the 3.55s and it really did lengthen 1st gear but didn't turn the car into a dog. It would still go sideways with the peg leg pumpkin. 5th was still usable due to the low-end torque of the 5.0. A really pleasant surprise was how much it increased the size of the gas tank. If gas prices get too bad the 2.80s will return. What did you need us for? Lol

 

I read some of the old threads related to my post. That being said. I am new here. And it suggests starting a new post.
I have a T-5 out of a 88 Mustang that I transplanted into my 65 Mustang along with the 302. When I first researched trying to find the right gear for the rear end I was told the 4.11 would be the best choice Now a few years later I am seeing that it isn't. So I have 2 ?
What gear would work best.
Anyone have the same set up that can give me some feedback to how they feel.

I guess I'd have to say that if I were to ever install a T5 it would be with a 2.95 first and .80 fifth gear. That said, if the only thing I was interested in was acceleration I'd go with a 3.55-3.73 rear gear and if I was interested in all around "cruising" I'd go with a 3.25-3.40. That's just me. Everybody is different.

 

Yes it was a typo they're only 26.6 inches tall

 

That's tall for these cars. A 225/60-15 is about as wide/tall as you can go. You really do not want to go any taller than about 25.6. That would mean a 225/55-16. BTW finding 16" wheels with proper width and backspacing to avoid suspension interference in the front is challenging.

 

Yes it's one inch taller. I have room for them and have 2 216 inch wheels for the rear and 2 15 inch wheels on the way for the front.

 

I have a T5 with 3.50 gears with 2.95 1st and think it works almost perfect. Tires are 215 60 15.

I would not want 3.55 with the 3.35 1st gear.

 

Where are you getting a T5z trans or kit to convert it?

Stock tires in the fox bodies were 225-60/15 or 225-55/16 (except SVO, 225-50/16). The standard rear was 2.73 with 3.08 or 3.27 being options. I believe the fox bodies were a little heavier than the classic cars, with the SN95 being even heavier. I put 180k on my 95 GT with 3.73 gears because it was perfect for drag racing with a mostly stock engine. It now has 3.55 in it.

What are the speed limits where you're at? Around my Dad it's max of 60 so I put 4.11 in his car. Speed limits are 70 by me so I have 3.55, also because I still frequently do trips with the cars.

 

Where are you getting a T5z trans or kit to convert it?

I just bought a T5z kit from MDL. New box plus fixins' about $4k. I'm not knowledgeable with these cars, nor am I patient to scrounge for deals. Includes tech support. It comes with 2.95 1st and 0.63 5th. It's quite a reach from 4th to 5th. I'm wondering if my 289 is gonna be tapping out, cryin' for mercy at 80mph or climbing hilly interstates. I saw after-the-fact that a 0.73 5th was an option. Well, my 3.0 rear is leaking so maybe throw in a 3.25 in the process. Hope for the best.

 

I'm not going to be doing anything to the transmission. A 225 60 16 is only one inch taller than a 225 60 15. I have two sets of wheels for the car. One set is going to be straight 15 inch. And the other sets going to be staggered 16 on the back and 15 on the front. There's only about a hundred maybe 200 lb difference in the two cars. So looking at the gears that the 88 Mustang was using the car ran perfect no reason it shouldn't work and my Mustang. I'm going to go with the 3.25 I believe.

 

That should be a decent ratio for a street car.

 

When picking an axle ratio you need to think about how it works with all gears not just one such as 5th. I've driven the 3.35 T5 with various axle ratios. My favorite was 3.27 with the 8.8 or 3.25 with 8 or 9 inch

I'll tell you something funny about the 3.35 T5 and 4.10.s. Besides 1st being about useless, 2-5 final drive ratios match almost exactly to a wide ratio Toploader 4 speed with 2.80 gears

 

I run a T5 with the 3.35 1st and a 3.70 rear gear with 26" tall tires. I love it. Neck snapping (or tire frying) off the line and under 2,500 at 75-80 mph.

 

3.55x3.25=11.53. Since 12 is the sweet spot for a fairly aggressive 1st gear without turning into a total granny gear, a 3.25 would be the highest I would choose....or maybe a 3.5 at the very most