275 60 15 with 3.55 gears

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Slantsix64

Slantsix64

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Hey guys i know i lost some gearing with my 275 60 15 tires i currently have 3.55 gears with that 28in tall tire, where would my actual ratio be at now? im thing around 3.23-30? would i need to run 3.91s or 3.73 to get back where i was? thanks again!
 
Divide your new tire size(28) by your old tire size (??) Take your answer and multiply it by your current gear ratio.

I will assume you had 26" tires before... so.....
28/26 x 3.55= 3.82
 
I've been in similar situations before. Any time I've made a change in tire diameter and wanted more gear I've usually found just getting back to what I had before left me thinking I should have just went to the next step. So if it's as in this example and a 28 inch from 26 inch tire made enough of a change to want the old gearing back, your probably geared to high to start with. If you aren't doing a lot of highway driving (or maybe even if you are and have a different mind-set than most others), grabbing a set of 3.91 gears is a step in the right direction,but you may find yourself wishing you moved up to a 4.10. Depends on intended use of the vehicle, though.
 
^^^Right On!^^^ One item that's overlooked when installing taller rear tires is the additional un-sprung weight. On top of effectively increasing the gear ratio, you've also given the engine more rotating mass to accelerate up to speed. The real reason why a little extra (sometimes a lot, as in the case of a lot of 4WD applications) gearing than what the basic RPM to highway speed calculations show.
 
abodyjoe said:
looks like using this calculator that was posted above Gearing Calculator | RPM and Tire Diameter to km/h - mph with Shift Tracer assuming you went from a 26" to 28" tire you'll need a 3.73 or 3.91 gear to put it close to where you were. one will give ya a hair less gear and the other will give ya a hair more gear.
Click to expand...

Like I said in post #3. Simple Math....

Mopar Sam said:
Divide your new tire size(28) by your old tire size (??) Take your answer and multiply it by your current gear ratio.

I will assume you had 26" tires before... so.....
28/26 x 3.55= 3.82
Click to expand...
 
those big rear tires destroy ride too.
Hit your buddy in the shoulder with a closed fist and then him with a
closed fist with a roll of quarters inside and see the difference.
Crazy what guys will do to get a look.
 

You can also go the other way to see what your swap made the 3.55s feel like.
26/28 x 3.55 = 3.30

To figure RPM change you do the same thing...
Say you were at 3000 rpm at 60 mph before the tire swap.
26/28 x3000 =2786 now.
These are just theoretical #s I made up to show how the math works.
 
RPMagoo said:
-- I believe that it is 26"/28" = .9285 X 3.55 = 3.296
Click to expand...

Yep, or rounded up like we always do gears is 3.30

I was just trying to point out that it is really simple to figure changes, even out in the shop with a piece of paper and a pencil.

I do not own a smart phone, and very seldom use a calculator.... Yes, I am an old fart... but I can still do math!

Now if I could just read my writing...
 
ir3333 said:
those big rear tires destroy ride too.
Hit your buddy in the shoulder with a closed fist and then him with a
closed fist with a roll of quarters inside and see the difference.
Crazy what guys will do to get a look.
Click to expand...
Actually rides pretty good in my 67 barracuda no rubs, grips pretty good off the line as well on the 15x8 rim
 
Looks like 3.91 it is! not much highway driving i never go over 60mph on freeway, street around town tyre fryre.

20200416_120612.jpg
 
Last edited:
Garrett Ellison said:
I've been in similar situations before. Any time I've made a change in tire diameter and wanted more gear I've usually found just getting back to what I had before left me thinking I should have just went to the next step. So if it's as in this example and a 28 inch from 26 inch tire made enough of a change to want the old gearing back, your probably geared to high to start with. If you aren't doing a lot of highway driving (or maybe even if you are and have a different mind-set than most others), grabbing a set of 3.91 gears is a step in the right direction,but you may find yourself wishing you moved up to a 4.10. Depends on intended use of the vehicle, though.
Click to expand...
Thanks Garrett! thats what ill do
 
ir3333 said:
yes...easy enough to swap out for a long highway trip....if you're a young guy!
Click to expand...
lol yeah not that young i am 29 but not going to be 29 forever! and yeah you are right those tires are a ***** to put on!!
 
So i took the car out on the freeway, shes turning 2500rpms at 65 mph this is with the 3.55 im guessing 3.91 would have me crusing at 2800 rpms at 65
 
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