Sure HB...bear with me here cuz this can get confusin quick
lets use your 4:88/5:13 example
First the 5:13 is the lower of the two gears
(if this is to basic please forgive me)
When you install larger tires you raise the overall gear ratio (higher). To compensate for a higher gear ratio you install a lower gear (ring & pinion...Front AND Rear).
So if your running 33" tires with a stock 4:56 gear and you change to 35" tires, you RAISE the gear ratio (I'm gonna guess around 4:10).
What this translates to in the real world is at say 60MPH you will have gone from, as an example, 2000 RPM to 1750. Now while this does'nt sound like much, it can make a huge difference for us mountain drivers, highway cruisers, or heavy load carriers. Combine that with a torque sensing transmission or air conditioning (HP sucker) and you have now possibly created a gear hunting pig. The anemic (sp) 5 cylinder likes to gear hunt anyway due to the H3 weight.
Someone alluded that the gear calculators are inaccurate...actually they are pretty dog gone close for determining RPM. The poster then began to talk about weight, load etc...the gear calculator estimates RPM...not horspower to weight ratios..something completely different.
I have found my best friend when determining the sweet spot for gearing is an accurate speedo and a tach. Start noting what the readings are of your tach and speedo. Also note how your tranny shifts (in an auto) or what gear you seek (if manual). In the case of an auto the final gear 4speed auto is a 1:1 ratio. In other words for every rotation of the crankshaft, the driveshaft, connected to the R&P turn the same revolution...one to one, so highway speeds are typically used as the gearing vs. rpm benchmark. Why I bring this up is that tranny gearing can be important in choosing a gear set. Where do you need to develop the maximum torque. Are you a trail rider or streeter. It has been my experience to error on the side of being to tall(higher gear) than to be to steep (low gear). To steep of a gear on the road equates to a high revving motor....conversely, its no fun to have to high a gear...a gutless wonder. If you want all out balls to wall performance then the lower gear will bring a motor "in" fast. In a manual tranny you will do whats known as sawing the gear shift if your too tall....think about it LOL
In an auto it will constantly be looking for the right gear.
I have actually installed larger tire s to bring down the RPM 400 or 500 rpms for high way driving! Screaming down the road at 65 at 3500RPM SUX!!
Another consideration is ring gear thickness and tooth number. In the H3 differentials it not as big of deal as say in a Dana 30. But the steeper you go on a gear set the weaker it becomes. The reason for this is that you reduce the "contact" area of the R&P. You also have to compensate on the ring gear thickness. This is only a real issue ih high torque, high HP, heavy tired, or small differentialed setups.
Does this explanation help you any!
Also remember that even though a tire says 35" ALWAYS check the REAL diameter. Most 35" are in the neighborhood of 34". What that means is that you need to be CERTAIN what numbers you plug in to any ratio calculator.
I cannot imagine even considering 37" tires for the H3 without a gear change.
The 37" SSR I am running on my TJ are almost 100# EACH!@*$)&@*($
Combine that added weight with a tall gear, an underpowered 5 cylinder and you have built a four wheel drive underpowered slug LOL
Let me know how else I can help
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