I'm looking for help on gear ratios. Tires are 29"s tall, I might go with 31" I would like to put a 4.30 3rd member in it. I want to know what the ratio would be with that combo. If there is a formula could someone tell me what it is. I did a search and came up on the short end, so any help would be great. I would like to stay in the 4.11 area. I have a 700 R4 to help a little on the road. Thanks, Jim
I tried google and got some bs that's why I am looking to see if there is a formula that someone here knows. Thanks, Jim
The gear ratio with 29 inch tires and 4.30s is 4.30. Now if you install a 26 inch tire your gear ratio will change to 4.30. Only the ring and pinion determine the gear ratio. Not the tires. If you have an RPM target at some set speed then do the math.
The gear ratio is whatever it is.... if you put a 4.30 rear end in it, it is 4.30 revolutions of the drive shaft to one revolution of the wheel. If you are asking what the difference in rpms for a 4.11 with 29" tires and a 4.30 with 31" tires, here you go: 29" tall tires w/ 4.11 gears will run 2858 rpm at the drive shaft 31" tall tires w. 4.30 gears will run 2798 rpm at the drive shaft Is that what you are looking for?
details, details...... 60mph since the question seemed kind of vague, I thought I'd give a vague answer....
I have 31" tires on my coupe with 3:50 gears and a 700r4. I like it with this combo. At 70 mph the rpm is 1900 with the converter locked up. My car is a 33 coupe, highboy with a ZZ4 and a 750 Holley. On the open road, it will deliver a little better than 20 mpg.
Smart ***!!! Thanks for the help, I've been on google "my friend" for awhile. Jumping from 4x4 sight to 4x4 sight I think I fianlly found what I was looking for and it is the same as you guys got I think. Thanks for the help, I know I was a little vague in the question but you will have that sometimes with me.... I found something that goes like this rpm=speed x gear x 336 / Tire Diameter. What I found out is I'm gonna eat a lot of gas if I head out on the Highway. I don't see that 700R helping that much. Again thanks for the help guys!!! Jim
I think that he wants to keep the engine RPM the same as it was with a 4.11:1 rear gear and 29" tall tires, with 31" tall tires. For that, you'd need a 4.39:1 gear, which does not exist, but a 4:30:1 would be pretty close. 65 MPH with 4.30:1 rear gears, a 0.70:1 overdrive, and 31" tires is 2025 RPM (engine). 65 MPH with 4.30:1 rear gears, a 0.70:1 overdrive, and 29" tires is 2270 RPM (engine). 65 MPH with 4.11:1 rear gears, a 0.70:1 overdrive, and 31" tires is 2030 RPM (engine). 65 MPH with 4.11:1 rear gears, a 0.70:1 overdrive, and 29" tires is 2170 RPM (engine). All pretty close. Hope this helps.
Wow that's awsome. Mine has a 3.25 in it now and just ain't gonna be what I want with the meats on the back. You know when someone tells you to spin em and........ You know how it is. But I do love gas milage also...
Keisler has a neat tool on their website called a Speed ****yzer. You choose an RPM and tire size, and it shows you the vehicle speed for your rear end, in third and fourth gear. It is similar to the other calculator someone posted a link to early in the thread, but Keisler's tool shows the 4L60E, which has the same ratios as your 700R4. http://www.keislerauto.com/speed_****yzers.php?sa=mopar_auto Ignore the "mopar" in the address, this is the right one. They don't list the 4.30, but they show a 4.10 and a 4.56, you can split the difference.
This sounds so familiar! I asked this question a while back and just could not make anyone understand what I wanted. No RPM factors, and no "tires does not change gear ratio"... it does. Finally I found this and it answers my question perfectly. http://www.4lo.com/calc/geartire.htm
Rod and custom had a article not to long ago that had a formula ; speed x gear ratio x some number I cant rememer divided by tire size = rpm . Was looking at it last week .
Right - after all that, you still say no "tires does not change gear ratio"... it does. Really sorry to break this to you so abruptly: a GEAR RATIO is ... (wait for it) the RATIO between 2 GEARS. There are no tires involved.
Sorry panic, your wrong. Lets say you are running a set of 27 inch tall tires with a set of 4:11s. Then one day you decide to step up to a set of 30 inch tall cheaters! Hmm seems the car just dosen't launch they way it used to... Couldn't be the gear ratio has changed due to the tire change .... Nah.... You have just changed the ratio to 3:70s!!! Tires DO change the gear ratio! And so you have to consider tire size as part of the gear ratio.
You are both right. Tire diameter change does not change gear ratio, it changes the relative effective gear ratio.
Changing tire diameter has much the same effect as changing gear ratio. How ever as panic points even the words "Gear Ratio" should tip you off that the phrase relates to Gears. Not tires. If you go around asking what will my Gear Ratio change to when I put on 33 inch tires you sound misinformed. And we don't want that.
JIM...a 430 gear is more then you wan't for the street. but a 411 would be perfect for street driving...POP.
Exactly how many teeth are added, and to which gear, when you change tires? You're asking about MPH vs. engine speed, and that's a completely different question. Your turn: say I'm wrong again.
Say you have 10 teeth on your pinion gear. And you have 41 teeth on your ring gear. The ratio of ring gear to pinion gear is 4.1 to 1. You have 4.10s. No amount of tire changing will make that ratio different. Not for you. Not for anybody. If this seems wrong to you, I give up. Your beyond help.
Guys, I love a pedantic rant as much as the next guy, but I am not sure that anyone is on the other side of this argument. I don't think that anyone is saying that the tires pull out the ring and pinion in the night, and set up a new ratio, and are ready to go by morning. Changing tire size does change the "effective ratio" in relationship to the same gear set, with another tire size. As in a 4:10 on a 27" tire is like 3.57 with if you switch the 27" tires to 31" ones. No dial indicator required, just the maths. Actual ratio, effective ratio, it is all just semantics.
Ok, your wrong again. I am not saying anything about MPH vs. engine speed. Gimpy has it exactly right. I'm saying that if you don't figure in the size of the tire, your not getting the true gear ratio. Because tire size is part of the formula. The proof is the puddin'. Take whatever car your driving and bolt on a set of tires a couples inches taller or shorter and tell me different.
Intuition- 31 seems like a tall tire, you'll want a whole bunch of gear (like 4.30), and with an OD ******, the downside of short gears is mitigated Scientifics- Sure you can run a bunch of numbers, but can you really know until you try it on your setup? Final gearing (between ******, rear, tire size) changes how the torque hits the ground, and how it feels depends on how much torque you are feeding into it - what motor do you have, and have you driven it with other gears and tire setups?.... as a rule of thumb, for manual transmissions, final first gear should be between 10 & 11:1 (1st gear ratio multiplied by rear end ratio), but as noted above - the tire size changes that (reason you keep running into 4x4 sites), and flywheel weight will change driveability depending on final ratio. It gets muddy with an automatic since it has torque converter, and will behave differently depending on what TC you have in your 700R4. I'd say stick with intuition.... BUT, I *think* the gearing relationship to diameter of tire is linear, so a 4.30 rear end on a 31" tire would be similar to a theoretical 4.03 rear end on a 29" tire - i've been known to be wrong.
Tire size DOES NOT change gear ratio, it changes the RPM at any given speed. Different size tires change the RPM in high gear in a ratio of the old tire cir***ference to the new tire cir***frence. Taller tire, less RPM in high gear, shorter tire more RPM (at a determined speed). Gear ratios are usually refered to as the numerical ratio of the rearend gear and are a function of the number of teeth on the pinion in relation to the number of teeth on the ring gear. That never changes unless you change the ring and pinion. Frank
Fab32 is right on the money. Gear ratio is just that a mechanical relationship between the driven and the drive gear and if doesn't change with a tire change only if you physically change the gears can it change.... HOWEVER the ratio of the number of turns required to make one revolution of a certain sized tire does change depending on tire size with the resultant effect on the performance of the vehicle involved. You feel the effect of changing of tire size and it effects performance BUT it does NOT change the mechanical gear ratio.
do a search on cl***ic trucks mag tech art every couple years they do a story on this exact sub tire heigh x rpm and known gears will give you the formula sorry idont know exact tom
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