3:55 gears on the street

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3.55 gear is perfect for 90% of street driven cars.My Polara ran 3.55's with 28" tires (275/60r15) for years.
Only reason to run 3.23 or lower (numerically) is for extended higher speed cruising.
 
Perseus said:
I only have the small Crager 14" rims, so would 225 75 14 work to keep the rpms down? LOL. I mean people are talking about 27" tires. Cripe! So for 3.55 gears, what would be the minimum size tire I could get away with without winding out?
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I am surprised how tall the tires are that people are using. Maybe I was ultra conservative, but, when I looked to fit new wheels/tires on my 68 Dart, I made a tire-shaped template and checked for clearance to the fenders, control arms, brakes, steering linkage, strut rod, and "frame rail" -- at various combinations of suspension travel (up to full jounce/rebound) and various steering angles (up to full lock). The biggest I could go on an 8 inch wide rim without anything rubbing was 225/35R18. This is about a 24 inch tire, which is the same diameter that the car originally came with when I got it (175/80R13).
 
sdh148 said:
I am surprised how tall the tires are that people are using. Maybe I was ultra conservative, but, when I looked to fit new wheels/tires on my 68 Dart, I made a tire-shaped template and checked for clearance to the fenders, control arms, brakes, steering linkage, strut rod, and "frame rail" -- at various combinations of suspension travel (up to full jounce/rebound) and various steering angles (up to full lock). The biggest I could go on an 8 inch wide rim without anything rubbing was 225/35R18. This is about a 24 inch tire, which is the same diameter that the car originally came with when I got it (175/80R13).
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I wish I had a 3.55 at least. My 255-60-15's are 27" and didn't do my 3.23 gear change much good. 70 Swinger with 15x7 with 4.25" backspace.
 
toolmanmike said:
I wish I had a 3.55 at least. My 255-60-15's are 27" and didn't do my 3.23 gear change much good.
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On my B body I have 3.55’s on a 245/60/15. I find this an excellent street driver combo. It revs a little high @ Hwy. speeds. No big deal I think. I tend to keep it a little slow on the Hwy. I’ve driven it for hours in a clip, no issues.
 
rumblefish360 said:
On my B body I have 3.55’s on a 245/60/15. I find this an excellent street driver combo. It revs a little high @ Hwy. speeds. No big deal I think. I tend to keep it a little slow on the Hwy. I’ve driven it for hours in a clip, no issues.
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Yep, I maybe drive 60 on the interstate going to car shows up to 4 hours away. I'm not in a hurry.
 
Exactly! 60/65, I’m good, no rush. I’ve done 70/75 and the secondary side tends to tip in. Not good for mileage. It takes a nose dive when the secondary side starts feeding the engine! LMAO!!!

At the time, I had a smog era ‘78-400 B engine in it. 60 mph and 18 mpg’s, yea! I’m good with that!
Go to 75 mph, mileage tanks!
 
LOL! On this island, 70/75 is the norm in any lane.
So, I truly get it. I know some states have that speed as a regular posting. On the Island, it’s 55.
 
sdh148 said:
I am surprised how tall the tires are that people are using. Maybe I was ultra conservative, but, when I looked to fit new wheels/tires on my 68 Dart, I made a tire-shaped template and checked for clearance to the fenders, control arms, brakes, steering linkage, strut rod, and "frame rail" -- at various combinations of suspension travel (up to full jounce/rebound) and various steering angles (up to full lock). The biggest I could go on an 8 inch wide rim without anything rubbing was 225/35R18. This is about a 24 inch tire, which is the same diameter that the car originally came with when I got it (175/80R13).
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25.5" tires will fit just fine. At stock ride height The 225/60-15 tires fit on my '69 Dart just fine, front and rear. Rear tire can easily be up to 28", but personally I like them all the same size. Either your car is severely lowered or you have the wrong size/offset wheels, if 24"s are all you can fit on it.
 
69_340_GTS said:
25.5" tires will fit just fine. At stock ride height The 225/60-15 tires fit on my '69 Dart just fine, front and rear. Rear tire can easily be up to 28", but personally I like them all the same size. Either your car is severely lowered or you have the wrong size/offset wheels, if 24"s are all you can fit on it.
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I did my tire template clearance checks w/o torsion bars installed, so I could easily achieve max suspension jounce/rebound. For the jounce condition, I slightly compressed the jounce bumper to simulate a worst case condition. During "normal" driving, you will probably never see this condition combined with full lock steering.

However, when simulating larger diameter tires, I actually had a clearance issue with the suspension at a more normal height and with the tire turned only slightly. The outer "corner" of the tire would get very close to or touch the bottom corner of the front fender. I think this issue is more prevalent with lower profile tires. Tires with a higher profile/sidewall often have outer tread widths that are less than that of the same nominal width tire with a lower profile. In other words, a 225/60-15 tire may have a tread width that is smaller than a 225/35-18 tire, even though they are both 225 width. The skinnier outer tread width creates a less "square" tire profile and can increase clearance to the various components. Of course, there is also variation between tire brands/designs.

FYI, my 18x8 wheels have the same offset as the 1975 Dart 14" steelies that were originally part of the car from which I removed the front suspension/brakes to install on my '68.
https://www.summitracing.com/parts/RPM-TTR16-886550

I spent many hours analyzing and measuring before I bought my new wheels and tires, and this seemed to be the best package I could get that was guaranteed to fit under all conditions.
 
sdh148 said:
FYI, my 18x8 wheels have the same offset as the 1975 Dart 14" steelies that were originally part of the car from which I removed the front suspension/brakes to install on my '68.
Click to expand...
pics of the car?
 
sdh148 said:
I did my tire template clearance checks w/o torsion bars installed, so I could easily achieve max suspension jounce/rebound. For the jounce condition, I slightly compressed the jounce bumper to simulate a worst case condition. During "normal" driving, you will probably never see this condition combined with full lock steering.

However, when simulating larger diameter tires, I actually had a clearance issue with the suspension at a more normal height and with the tire turned only slightly. The outer "corner" of the tire would get very close to or touch the bottom corner of the front fender. I think this issue is more prevalent with lower profile tires. Tires with a higher profile/sidewall often have outer tread widths that are less than that of the same nominal width tire with a lower profile. In other words, a 225/60-15 tire may have a tread width that is smaller than a 225/35-18 tire, even though they are both 225 width. The skinnier outer tread width creates a less "square" tire profile and can increase clearance to the various components. Of course, there is also variation between tire brands/designs.

FYI, my 18x8 wheels have the same offset as the 1975 Dart 14" steelies that were originally part of the car from which I removed the front suspension/brakes to install on my '68.
https://www.summitracing.com/parts/RPM-TTR16-886550

I spent many hours analyzing and measuring before I bought my new wheels and tires, and this seemed to be the best package I could get that was guaranteed to fit under all conditions.
Click to expand...
O.K., but the stock tires on a '69 Dart GTS were E70-14, which according to Coker Tire are 25.7" diameter x 8" section width. D70-14 were found on a Dart Swinger and they're 25.4" dia x 7.9" section. This size or a modern equivalent will fit.
 
kursplat said:
pics of the car?
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Sorry it's so messy, but this is all I can do at the moment. The rear is supported on jackstands under the body and axle, so the amount of weight on the front of the car could be a little different than normal.
20200708_212640.jpg
 
My uncle use to run 4.10 and swap to 3.23 anytime we went up to the cottage and swap back when got home. That's my plan since I could go my whole life without getting on the highway.
 
to each his own. my old M body I had 3.55's a lock up 3 speed and 27" tires (255/50R70) HATED it because it was revving >3k at 70mph....terrible mileage and very fatiguing....worked great with a 42RH and a .69:1 OD, though....

on an A body, where you're likely to have 26" tall tires, I think the deepest gear I'd go for without an OD is a 2.94. my duster has an A833OD, 323's, and 215/70 rear tires (26" tall) and it will keep up with traffic on the freeway without being too stressful
 
Can't speak much about the rear end or gear choice but on the "360/904" idea id say dump the 904 in the ravine and put a 727 in there.
 
I've actually had better reliability with 904's than with 727's.

As for 3.55 gears- I had no problem with 3.55 behind a 383 and L 60 15 tires.

The folks I ran around with that ran 3.91's always complained if we had to go anywhere at freeway speeds.
Not me.
 
I was running 26 inch tall 235/60 15s and 3.23 gears on my 67 Barracuda. Now have 28 inch tall 275/60s and 3.55 gears. Overall effect is very close to the same. (3.55 divided by 3.23 times 26 equals 28.5)
 
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