Been lurking around here for awhile.Newby question If I'm staying with 35's should I stay with 3.73 or get the 4.30?I won't be towing anything that heavy very often.I will be using it in sand and on dirt roads though.I will be ordering the V-10 w/automatic.Thanks for the info.I enjoy reading about your trucks,poolman

 

Tell you what...try this site. Put in your info and it will tell you RPM your pulling at a particular speed. [link:www.ring-pinion.com/calc-rpm.html|Randy's calculator]. Use .71 as your final drive ratio. That's the 4R100's OD ratio.

I say go with 4.30's. I would. But compare all the numbers. Stock tire size is around 31.5".

 

You might want to consider getting the "free" 3.73s and saving the $$ for a set of 4.56 ratio aftermarket gears.

 

stick with the 4.30 from ford. 4.56's will be to low for a set of 35 inch tires... your highway rpms will be WAY too high!

i run 4.56's and 38" tires.... my rpm's are about in the middle of what i would see with stock 31.5" tires and the ford 3.73 gear ratio and 4.30 gear ratio.

nomo.... is there a cost difference from ford to get the 4.30 gears? i thought the only cost option in the diff was the LSD.

 

Limited slip with 3.73 gears is $285.
The 4.30 gear (with LS) costs $335.

So you're right- most of the cost is the limited slip diff that you MUST purchase with the 4.30 gears.

I'm curious as to what RPMs you're turning. Can you post them at a few speeds? I ask because I've been seriously considering some 4.56s for my truck w/33" tires. Almost all of my "highway" miles are pulling the 5th-wheel and usually with OD off. So I'm thinking that I might be better off (mileage wise) in OD with lower gears. Unfortunately, my favorite gear shop only uses Precision Gear R&P and PG doesn't make a 4.30 yet.

 

i like the 430's with the v-10 and 373's with the 7.3. 430 seems plenty low, would not go any lower than that. the v-10 power band is alot lower than the 460 that we are used to.

parts man

 

Poolman, why not try out the free 4.10's. It just might be the middle ground your lookng for! I run a 99 5.4 5sd with 4.10's and 285 16's. Tacks a bit high on the open road even with the overdrive, but never lugs in gear. My 88 250 had 3.55 gears and a set of 33X12.50's killed the truck. Actually in my case hauling some weight everyday those lower gears have been a godsend with gas mileage too! Trimman

 

>Poolman, why not try out the free 4.10's. It just might be
>the middle ground your lookng for!

I don't think the V10 is available with 4.10's...

 

Thanks for all the help guys.

 

Hey poolman thanks for coming back! So many others don't! They start what turns out to be a really cool thread then just disappear. >poof< Let us know what you decide!

 

To me, the whole idea of larger tires and changing ratios is to get the performance back to stock or maybe a little more. Stock Superduty is rated to tow X amout of pounds with the 3.73's etc. If you determine that a 3.73 equipped truck fits your needs then you decide to swap to larger tires and want the same performance then a gear change to return the rpms back to stock specs is in order. Using Randys calculator, this is what I came up with.

Stock 3.73's with 31.5" tires at 65mph in OD is 1810 rpms.

If you swap to 35" tires, then to get close to the 1810 rpms you'd need to change to 4.30 gears which would put you at 1878 rpms. Close enough. (4.10's would get you 1791) The easy route here is to just buy a truck with the 4.30's. Keep in mind however that changing to the larger tires will lower your towing capacity to the 3.73 specs. If you wanted a little more performance, swapping to the 4.56's would but you at 1992 rpms.

Now lets say you have the 4.30's stock and want to keep your performance but want the 35" tires.

Stock 4.30's with 31.5" tires at 65mph in OD is 2087 rpms.

Acording to the calculator, 4.56 gears would give you 1992 rpms. Slighly less than the stock rpms. (You'd need 4.78 gears to get back to 2087 rpms)

NoMo,

If you'd like to pick up a little performance, and use the 33" tires, 4.30 gears would put you at 1992 rpms. That's more than the stock 3.73 and less than the 4.30's with stock 31.5" tires.

Whew! did I write all that??

 

>To me, the whole idea of larger tires and changing ratios is
>to get the performance back to stock or maybe a little more.
> Stock Superduty is rated to tow X amout of pounds with the
>3.73's etc. If you determine that a 3.73 equipped truck
>fits your needs then you decide to swap to larger tires and
>want the same performance then a gear change to return the
>rpms back to stock specs is in order

<Snip informative ratio comparisons>

Another idea I have been giving thought is to go with larger tires to lower RPMs at a given speed. I currently don't tow anything near the rating for these trucks so I can take a little bit of a hit there with little problem. My main concern is how to determine before hand how what the largest tire would be that would lower RPMs without completely ******* the truck.

Using the calculator: 65mph, 3.73 gear, .71 trans ratio, and 31.5 tire height; Gives 1836 RPMs.

Changing to 33 tire height gives 1753 RPMs and so on. My gut tells me that 35's without a gear swap would be too much, but I do not know about the 33's. Any thoughts?

Scott

 

I think I've talked myself out of the gear swap. I'm back to considering a Banks PowerPack. The 3.73 gears and more power at lower RPMs should be a bit of the "best of both worlds"... towing power & economy.

 

Go with the 4.30's.

 

correct gearing is the only way to get better power across teh board.... well, maybe a supercharger would improve things too....