Tire Size to Effective Gear Ratio

[Caldwell]

Hey fella's,

* Need my drag strip guys help lol.

I am by not means a racer, other then the fact that I just like to drop the hammer on the truck from light to light. I recently failed PA inspection because I have a tear in the inner side wall of my front driver tire, that I was not aware of. So now im just gonna by some new tires cause I hate the oem good years anyway...

There are some pretty good deals on 305/50/20 tires out there. I know these tires are only 1'' shorter in height, but are 1.2" wider. Currently I have 3.55 gears, and im curious to know if my effective gear ratio would increase closer to a 3.73 gear with a shorter tire ?. Would I notice an increase in acceleration slightly, or would the added width of the tire negate those potential changes ?. Would a 275/55/20 see better results, as far as acceleration ?. I also know that tire weight can play a factor in this as well.

In an effort to keep rotating mass down, I'm leaning towards ( YOKOHAMA Parada Spec X ) tires as they only weigh ( 45 lbs ) per tire. That compared to 43lbs of the oem good years. the 2lbs difference doesn't bother me, as I would prefer the wider contact patch of the 305 tire over a 275. my rims are **** Cepek DC2's with a ( -13mm ) offset so I have plenty of room in the wheel wells.

 

[rustydagger]

I dropped from stock 20's with 33.6" tires to 17's with 31's. The acceleration feel definately improved. But thats all i know about it. There are calculators on the web to figure effective ratio's.

Sent from my NEC-NE-201A1A using Tapatalk

 

[hemihustlin]

Im on 305/40/22 and they are 31.5 inches high. But the rim/tire combo is a bit heavyer than stock. How much i dont know, didnt weigh them.
Love the feeling in the corners but the downside is you feel every single little crack in the road (we have alot here lol) cause there is alot less rubber to absorb the bumps.
As for the ratio, dont know, like stated there are lots of calculators on the net.

 

[Caldwell]

I found a gear ratio formula to help select the appropriate gear. I currently have OEM 33's and 3.55 Gears...

( 33 x 3.55 ) = 117.15 / 33 = 3.55 ratio.

( 32.2 x 3.55 ) = 114.31 / 33 = 3.46 ratio.

so now do I take the difference between the two, and add the difference ???

3.55 - 3.46 = .09

3.55 + .09 = 3.64 gearing ?

Im sure that im not gonna even feel that much of a difference. Assuming this is the correct math.

 

[BoldAdventure]

Im sure that im not gonna even feel that much of a difference.

You're not. It's an exercise in futility. You would see better results shedding weight from your vehicle than trying to use smaller tires.

 

[hemihustlin]

It might not be much in the way of gear ratio increase but getting lighter rims and tires is always a good thing. Less unsprung weight the better!

 

[Cynix]

I'm running 275/55r20 nitto nt420s tires on my truck and I don't really remember noticing a difference really

 

[nolimits76]

33" Diameter Original
32.2" Diameter New Size
3.55 Gear Existing

Yields a 3.64 gear after the tire conversion.

Wallace Racing - Gear/Speed Calculator

And here is a spreadsheet I picked up on a Challenger site. It takes into account different wheel and tire sizes + weights to show you expected net gains/decreases of HP & TQ of your wheel & tire choices.

http://www.filedropper.com/wheelgains3

 

[TylerB]

I found a gear ratio formula to help select the appropriate gear. I currently have OEM 33's and 3.55 Gears...

( 33 x 3.55 ) = 117.15 / 33 = 3.55 ratio.

( 32.2 x 3.55 ) = 114.31 / 33 = 3.46 ratio.

so now do I take the difference between the two, and add the difference ???

3.55 - 3.46 = .09

3.55 + .09 = 3.64 gearing ?

Im sure that im not gonna even feel that much of a difference. Assuming this is the correct math.

That math is pretty close. That little of difference in height will be negated by the additional weight from the width.
Wanna feel difference? Go with a 275/45/20(29.75"), even then your effective ratio will be closer only be like 3.92, but look at that rotational mass you'll shed as well...

 

[Caldwell]

I knew the difference was not going to be outstanding, but I was curious none the less. Can anyone tell me the OEM 20x9 Chrome Clad Wheel Weight ???

I know my **** Cepeks weigh in at 31.6 lbs each, and the 275/60/20 GY's weigh in at 43 lbs. From what I have found on tirerack.com, my rims are pretty light. I only have 2 other rims that weigh slightly less then the DC-2's.

74.6 lbs per corner @ the moment... If I can maintain under the factory wheel / tire weight that would be sweet.

Im not looking to become a drag racer, or lower my truck. I just want a wider contact patch on the street, plus I like the look. I would love to lift it, and go off road, but this truck is a pavement queen sadly unless it snows, or I head up to the pocono mountains in PA. Im about to start a new job that pays alitte bit better, and requires a longer daily commute to and from. So im really tossing around the idea of getting the ( 305/50's, Diablo Intune, Ported TB, JBA Shorties, True Dual mid pipes w/ X-pipe ). Basically what I would call a mild " street truck " if you will.

 

[nolimits76]

I knew the difference was not going to be outstanding, but I was curious none the less. Can anyone tell me the OEM 20x9 Chrome Clad Wheel Weight ???

I know my **** Cepeks weigh in at 31.6 lbs each, and the 275/60/20 GY's weigh in at 43 lbs. From what I have found on tirerack.com, my rims are pretty light. I only have 2 other rims that weigh slightly less then the DC-2's.

74.6 lbs per corner @ the moment... If I can maintain under the factory wheel / tire weight that would be sweet.

What year is your truck? Here are the 2014 specs. I only see (2) 20" wheels, both 20x8's. Cast @ 39.2# and forged @ 36.69#. I'm guess the forged is what came on my Sport. I would think the cast is what they use on chrome clads, but that's a pure guess.

http://www.rambodybuilder.com/2014/docs/intro/twlnwv.pdf

 

[nolimits76]

FYI, if you substitute out the "2014" in the link above with the correct year you have, it will pull that years specs for you.

For instance, a 2012....

http://www.rambodybuilder.com/2012/docs/intro/twlnwv.pdf

 

[Caldwell]

based off of those links i think its safe to say the 20x9 chrome clads a cast aluminum so 39lbs per rim.

if thats that case then I have already shaved 7lbs per corner, which I know isnt a whole lot, but none the less thats 28lbs of rotating mass that has been dropped from the drive line. WIN lol.

again not trying to be a serious racer, but this is cool info to learn !. shame I dont have 3.92's lol

thanks for the help gentlemen !

 

[smiley]

I have said it before and I'll say it again. Gears are one of the most noticeable mods you can do. It is amazing how much better it makes the truck. I run 34.7 inch 285/65R20 tires and 4.56 gears and I can still feel a big difference if I go back to stock or even 275/65R20 I would feel it even more. Throw on some factory 17 inch rims and tires it would be roast city. If you are going to run close to factory tires I would do 4.10 gears or less so RPMs don't get to out of whack.


$miley

 

[gunner1374]

I am very happy with the looks and performance of my Kumho Xsta 305 50 20 sport tires. They grip the road and corner waaaaay better than the ****** stock GY, and look better too IMO. Drawbacks...a little heavier, and they do grab every crack in the road as stated previously. I may change back down to a narrower front for less drag and weight, but the grip and effective gear change made truck run much better and quicker by not spinning the wheels through gears 1 & 2 lol.

 

[Graygoose]

Adding a question while staying on topic, if one was to go from factory 275/60/20 to a 285/50/20 thats almost 2" shorter. Does the Ram speedo need recalibrated?
I may try to stay up to a 305/50/20, which is only 1" difference, but they may not fit on an 8" rim for now.

 

[smiley]

Adding a question while staying on topic, if one was to go from factory 275/60/20 to a 285/50/20 thats almost 2" shorter. Does the Ram speedo need recalibrated?
I may try to stay up to a 305/50/20, which is only 1" difference, but they may not fit on an 8" rim for now.

Yeah any time you change diameter it will mess with speedo accuracy.


$miley

 

[nolimits76]

There's a reason why serious racers buy high dollar aluminum light weight wheels, and it isn't because they have money to burn, lol. Reducing your mass weight helps make you go faster. Even small gains can yield decent results.

In regards to tire sizes changing your speedometer -- yes! The real question is how much. The bigger the change (bigger or smaller) then the bigger the difference in the speedo.

Some info for you:

Wallace Racing-Home of Pontiac Powered Firebirds,Trans Ams,and Dragsters

Speedo Gear Calculator - Wallace Racing

 

[gunner1374]

Also, if planning on getting a Diablo Trinity, you can adjust for tire size. I'm sure that other tuners do this as well. A good all around size, easy to find and cheaper on the budget, is a 275 55 20. Stock tire size on 3rd gen Rams with 20s and nearly all Chevys with 20s. If going with a 305 50 20, I would possibly recommend a Hankook Ventus. I had them on my Rumble Bee in a 22" tire and, compared to the Kumho Xsta on my truck now, they are, if I remember correctly, right at 10lbs less weight per tire for the same size. They also worked very well on my Bee. Just a thought. I would have gotten a set for my Express, but I couldn't pass on the set I have...$260 for a set of 4 with 8-9/32nds of tread left. May take front off and go with a 245/60/20 or similar for less weight and drag and keep fronts for a back up pair on the rear? Maybe even look for a nice set of 17s that I wouldn't mind trading for my 20s. Tire spin kills speed though. It's a fine line between going faster and just spinning your wheels, haha

 

[Graygoose]

Yeah any time you change diameter it will mess with speedo accuracy.


$miley

Thanks!