Axle ratio inpact

[Craig Freeman]

Hi

I am in the process of restoring a 1960. The rear end is not orignal so I trying to decide which ratio would be the best for me. Once I finish the body off restoration I plan on driving my car on weekend trips and such. I was planning on putting in a 3.70 posi in. But I am being told that ratio will not work well with cruising down the highway at 70 mph. And maybe a 3.11 or even a 3.08 would be better. My main concern is drive ability on weekend trips. Any help you can provid would be greatly appreicated. P.S. what is the correct color to paint the rear end? I have heard the same color as the chassis and have also heard it should be gloss black.

Thanks for any information you can provide.

Craig Freeman

[Jack H.]

Re: Axle ratio inpact

My uncle's '58 had 3.70 rear and he/we found no problem with it. Of course, you know you're making a tradeoff between torque (acceleration) and top end speed/fuel economy. Issue is what do you want?

The tall rear ends (4.11 and 4.56) are considered drag race or 'mountain' equipment. They'll slam you into your seat with a vengence, make you wind +3K RPM at freeway speeds and 'seek out' virtually every gas station you pass. BUT, you'll have a blast in the city pulling away from stop lights. My '65 BB has 4.56 rear and it's actually TOO TALL for the car's native torque with factory stock 7.75x15 bias tires.

At the other end of the spectrum, 3.08/3.36 were considered highway cruising or 'economy' rear ends. Don't get me wrong, you can still enjoy considerable 'punch' with these, but your tach will drop to the 2-2.5K RPM range on the freeway, there'll be less 'whine', and you can push 20 MPG if you're judicious on the accelerator. My '71 SB 350 has a 3.36 rear that was considered 'performance' (3.08 was the 'economy' selection) in the first year of CR drop and readying the Corvette for lead free fuel.

The intermediate selections, 3.55 and 3.70 are considered nice compromises between acceleration and economy. I don't think you're going to have a major problem here since you're not at the strip and probably do want to experience some G....

I'd say this. You already own the 3.70 ring/pinon, so why not build and drive it? Since we're talking straight axle (a 'two spring' car without 'rubber' axle), it's not a nightmare to change out the rear ratio down the road if you want to cut back. Most don't see much difference by changing one ratio bracket up/down, so if you later decide you want less torque and more top end/economy the direction would be 3.70 -> 3.36.

Bear in mind that juggling rear ratios involves speedo gear changes at the tranny to compensate and one of the constituent gears lives in the tranny tailpiece (read that pull and really tear into 'er unless you visit a speedo shop that will make you up and external gear reduction box).

[Jack H.]

Re: Axle ratio inpact

My uncle's '58 had 3.70 rear and he/we found no problem with it. Of course, you know you're making a tradeoff between torque (acceleration) and top end speed/fuel economy. Issue is what do you want?

The tall rear ends (4.11 and 4.56) are considered drag race or 'mountain' equipment. They'll slam you into your seat with a vengence, make you wind +3K RPM at freeway speeds and 'seek out' virtually every gas station you pass. BUT, you'll have a blast in the city pulling away from stop lights. My '65 BB has 4.56 rear and it's actually TOO TALL for the car's native torque with factory stock 7.75x15 bias tires.

At the other end of the spectrum, 3.08/3.36 were considered highway cruising or 'economy' rear ends. Don't get me wrong, you can still enjoy considerable 'punch' with these, but your tach will drop to the 2-2.5K RPM range on the freeway, there'll be less 'whine', and you can push 20 MPG if you're judicious on the accelerator. My '71 SB 350 has a 3.36 rear that was considered 'performance' (3.08 was the 'economy' selection) in the first year of CR drop and readying the Corvette for lead free fuel.

The intermediate selections, 3.55 and 3.70 are considered nice compromises between acceleration and economy. I don't think you're going to have a major problem here since you're not at the strip and probably do want to experience some G....

I'd say this. You already own the 3.70 ring/pinon, so why not build and drive it? Since we're talking straight axle (a 'two spring' car without 'rubber' axle), it's not a nightmare to change out the rear ratio down the road if you want to cut back. Most don't see much difference by changing one ratio bracket up/down, so if you later decide you want less torque and more top end/economy the direction would be 3.70 -> 3.36.

Bear in mind that juggling rear ratios involves speedo gear changes at the tranny to compensate and one of the constituent gears lives in the tranny tailpiece (read that pull and really tear into 'er unless you visit a speedo shop that will make you up and external gear reduction box).

[Jimmy G.]

Re: Axle ratio inpact

I have 1960 270 H.P. wide ratio T-10 that I am driving from NC to Oregon and back to attend the NCRS Convention. I also drove this car to Collinsville last year on the road tour. Based on my experience I would recommend the following. If you have a solid lifter engine I would recommend 3.55, 3.70. A 3.36 with this combination is marginal in my opinion and very hard on clutches. If you have a hydraulic lifer engine and a close ratio 4 speed then a 3.36 is ok, with a wide ratio a 3.08 may be possible. With a powerglide same thing 3.08 is ok. Others may not agree, but this my opinion. I personally am looking for a 3.55 for my car, but it is hard to find a posi in good shape and reasonably priced. P.S., a 4.11 does superb around town as long as you have a gas credit card with a high limit. 4.56 - forget it - show / race only.

[Jimmy G.]

Re: Axle ratio inpact

I have 1960 270 H.P. wide ratio T-10 that I am driving from NC to Oregon and back to attend the NCRS Convention. I also drove this car to Collinsville last year on the road tour. Based on my experience I would recommend the following. If you have a solid lifter engine I would recommend 3.55, 3.70. A 3.36 with this combination is marginal in my opinion and very hard on clutches. If you have a hydraulic lifer engine and a close ratio 4 speed then a 3.36 is ok, with a wide ratio a 3.08 may be possible. With a powerglide same thing 3.08 is ok. Others may not agree, but this my opinion. I personally am looking for a 3.55 for my car, but it is hard to find a posi in good shape and reasonably priced. P.S., a 4.11 does superb around town as long as you have a gas credit card with a high limit. 4.56 - forget it - show / race only.

[Bill W.]

Re: Axle ratio inpact

Mornin' Craig,

It would be nice to know if you had a three or four speed tranny and the ratio of it's first gear. But since you say highway driving as opposed to in town driving is your main concern, I will base my recommendation on that. A 3.36:1 or 3.55:1 will give good milage and still allow you the ability to start on a hill from time to time without slipping the clutch to much. I think 3.08:1 is worthless unless you have an automatic. Bill

[Bill W.]

Re: Axle ratio inpact

Mornin' Craig,

It would be nice to know if you had a three or four speed tranny and the ratio of it's first gear. But since you say highway driving as opposed to in town driving is your main concern, I will base my recommendation on that. A 3.36:1 or 3.55:1 will give good milage and still allow you the ability to start on a hill from time to time without slipping the clutch to much. I think 3.08:1 is worthless unless you have an automatic. Bill

[Bill Clupper]

Re: Axle ratio inpact

Craig, I had a 3.70 in my '62 fuel car with a closeratio 4-speed, and drove on a 500 mile round trip with no problem at 65-70 mph. I pulled it for maintenance & put in a 3.36 (two tooth adjustment on the driven gear for the speedo) and used the 3.36 for the road tour last year. The car is noticably more fun to drive with the 3.70! In a past life, 30 + years ago, I put 40,000 road miles on a '58 with 4.56, but I might not do that today. Use the 3.70 & don't look back.

Clup

[Bill Clupper]

Re: Axle ratio inpact

Craig, I had a 3.70 in my '62 fuel car with a closeratio 4-speed, and drove on a 500 mile round trip with no problem at 65-70 mph. I pulled it for maintenance & put in a 3.36 (two tooth adjustment on the driven gear for the speedo) and used the 3.36 for the road tour last year. The car is noticably more fun to drive with the 3.70! In a past life, 30 + years ago, I put 40,000 road miles on a '58 with 4.56, but I might not do that today. Use the 3.70 & don't look back.

Clup

[Joe L.]

Re: Axle ratio inpact

Craig-----

I totally agree with Bill Clupper. I consider that the 3.70:1 ratio should be, overall, an excellent ratio for your circumstances. With a relatively torque-limited engine like your original 283, I don't think that you'd be satisfied with low end performance if you used a higher (lower numerical)rear gear ratio. This problem would be particularly pronounced if you are using a close ratio manual trans.

[Joe L.]

Re: Axle ratio inpact

Craig-----

I totally agree with Bill Clupper. I consider that the 3.70:1 ratio should be, overall, an excellent ratio for your circumstances. With a relatively torque-limited engine like your original 283, I don't think that you'd be satisfied with low end performance if you used a higher (lower numerical)rear gear ratio. This problem would be particularly pronounced if you are using a close ratio manual trans.

[bob bridge]

Re: Axle ratio inpact

I have a 77 with an older M21 and a 3.70. I have considered the same things, but came up with leaving the 3.70. A 2.20 low would be a bear in town with any high gears and I think I would miss the 3.70's when I boot it. On the feeeway I feel sorry for the engine, so just keep the speed down a bit or better still, make your trip on a secondary road which will be more fun and the speed with be down and the 3.70 will mean not much shifting. Bob

[bob bridge]

Re: Axle ratio inpact

I have a 77 with an older M21 and a 3.70. I have considered the same things, but came up with leaving the 3.70. A 2.20 low would be a bear in town with any high gears and I think I would miss the 3.70's when I boot it. On the feeeway I feel sorry for the engine, so just keep the speed down a bit or better still, make your trip on a secondary road which will be more fun and the speed with be down and the 3.70 will mean not much shifting. Bob

[Jeff]

Re: Axle ratio inpact

From my perspective (61, 315/4.56), I would say that the optimum set-up for highway driving, assuming you have the 4 speed, is a 3.55 open rear if you stick with a stock height tire. You may possibly want to try 3.70s if you go to a taller tire, (which, BTW, I'd suggest because the straight axles are a night/day different car on radials vs rag tires.)

JP

[Jeff]

Re: Axle ratio inpact

From my perspective (61, 315/4.56), I would say that the optimum set-up for highway driving, assuming you have the 4 speed, is a 3.55 open rear if you stick with a stock height tire. You may possibly want to try 3.70s if you go to a taller tire, (which, BTW, I'd suggest because the straight axles are a night/day different car on radials vs rag tires.)

JP