with 3:54's now What size tire for 3:73?

[Morepower]

I was wondering with 3:54 what size tire would give me the same effect of changing my rear gears to 3:73's. I have an automatic and was wondering how to calculate.

 

[Sky]

Not sure but a lot smaller.

 

[NVR FNSH]

The gear change is ~5% so you need to reduce the tire size by ~5%. Stock 265/75R16s are ~31. 9" tall so you would need to go to a 30" tall tire.



Truck's gonna look really funny with that size tire... ... .



Disclaimer: I think I'm correct but I don't gaurantee it. I've been wrong before but I was only mistaken..... I'm sure somebody will correct me.



Brian

 

[Mactruck]

Those little donut spare tires. :-laf



Seriously, I think you would need a 225/75r16 or a 225/70 r16. For the 225/75 r16, if you were going 65 on your old set (265's) it would increase your speed to about 70 mph. The diameter is about 29. 5. For 225/70's it would increase your speed to 72. Their diameter is 28. 5.



I used this program to figure some of it out. http://www.sgmotorsports.com/tiresize.htm

I guessed at the gear ratio.

 

[B KIRK]

Here's a link with RPM / Gear Ratios.





Brad

 

[Mactruck]

It looks like you need a 29. 5 inch tire.

Based on the bfgoodrich site here. (need adobe to view) you could use a 225/75r16 or a 245/70r16.

 

[BV]

gear ratio

Interesting - My 99 came stock with 3. 55's and 245-75r-16's so are you guys saying that the final drive is 3. 73?

 

[Mactruck]

Thats if you figure that the stock tires are 265's.

 

[RADdodge]

I have a spreadsheet you can use. The first column is for the original geartrain specs and the second is for what you think you might want to upgrade (or downgrade) to. It's set up for an Auto, but you could easily change it to the gearing of a 5 or 6 speed. It's fairly straightforward. It gives you the effective or resultant final gear ratio, comparative speeds at various rpm's etc. If you want to see a picture of it, click on my pictures link to the Reader's Rigs. If you want to try it, send me either an email or a private post and I'll send it to you. If you have questions about using it or suggestions on improving it - email me.

 

[Morepower]

The stock tires are 235/85/R16



Here is an interesting comment from rspinks

"Personally I'd be concerned about 14. 2 vs 14. 9 loaded radius. That's a 5% difference in front/rear wheel speeds in 4wd. Do you really want to be skidding your tires for 1/2 yard for every 10yards you travel in 4wd?



It's true that axle ratio's differ slightly front to rear sometimes, this is because they can't always get the exact same ratio of pinion teeth to ring gear teeth in different model axles. However 5% difference in tire diameter is almost like running 3. 55 in one end and 3. 73 in the other. "



This is what I was trying to do when I got the idea to adjust my gear ratio with different tires. Both tires are with . 1 inch in size but have a big difference in load radius.



" Toyo M55 Front tire with the following spec.

LT265/75/R16 (LI)123m, (SW)10-E, (1/32")18, (O. D. )31. 9", (SW)10. 8", (SLR)14. 2", (RV per KM)404, (Rim Width)7. 5", (Rim Range) 7. 00-8. 00"

Rear Tire.

LT235/85R16 (LI)119/116m, (SW)10-E, (1/32")18, (O. D. )32. 0", (SW)9. 3", (SLR)14. 9", (RV per KM)403, (Rim Width)6. 5", (Rim Range) 6. 00-7. 00"



Even the revolutions per KM were with in 1 rev. So how can a load radius be so critical when the actual revolutions per km are so close. Diameters are only different by . 1" It would seem to me that maybe Revolutions per KM are where I should be looking for the 5% difference instead of Diameters or load radius. Hummmm...

 

[Ted Constantine]

Morepower,



I may be mistaken but your last post was on the wrong thread. You intended it for your other thread on running two different size tires front and rear.



I am wondering why you feel the need to do this? Towing? Auto or stick?



Is this a 2500 or 3500?



Did you buy the truck new or used?



Ted