Having a pretty good idea of where you are outside of Chicago and knowing how ridiculous traffic is there I think I'd just run with OD off. Not sure where your daily commute takes you and what speeds your traveling. If your rolling down the Skokie on a regular basis with all the stop lights, that would frustrate me not being able to accelerate from a stand still. Just the same, it seems like a high cost/low benefit venture unless your planning a tire upgrade in the future.

 

that is a HUGE gear for the tire size you are planning on running. stick with what you have it will be more then fine. go with 4.88 if you are ever planning on going 35s

 

Definitely not huge, about the same as 4.10s on the manual transmission. Probably not the best fit given highway speeds and traffic in that area but the end user hasn't really filled in enough blanks.

 

Most of my driving is at about 45 mph and not on the highway.

I guess I continue to be baffled by the chart. Right now, I'm in the yellow, 1900 at 70mph. Yellow is described as "sluggish" which I would completely agree with. Don't I want to move into the green "good daily driver"?

I don't mind spending the money if it is going to be an improvement in performance. I don't even mind losing a bit of mpg if it drives better.

 

agreed. I have 5.38's with my 35" KM2's which are really 33.75" tires and drives beautifully.

 

The chart is built out for 70mph, so at 45mph you need significantly less power. At the same time, given where you're driving you need to be able to accelerate. Driving the Edens or Skokie can definitely suck and I'd guess you can quickly become a hazard when you can't get up and move. Where most need to try and avoid kick downs to preserve economy, you're still going to rely on them to get moving.

That said, I'm not sure what your future plans are with tires but 5.13s would hold you trough 35s. Otherwise if you're just continue on with your existing tire size it's a coin flip between 4.88s and 5.13s.

 

I greatly appreciate the input. I think I'm going to run with 4.88s as I don't plan to ever run bigger than 33s.

Thanks to all for chiming in.

 

Where the chart may get confusing is what happens when you drop down to 3rd. You say that you currently spend a lot of time with OD Off, (like a dog unless you turn it off??) so just divide the rpm by .69 to get that number.

ex.
3.73, 32" tire, auto = 1892 @ 70 with OD On
divide by .69 = 2742 @ 70 with OD Off

So to match your current rpm's at 70 with od off?
5.38, 32", auto = 2729

4.88's with od on would put you at 2476 @ 70, or 266 rpm lower than you are right now with od off.



So you just need to decide what RPM (HP/Torque) range will be best for you for your location and performance needs.

 

This is a little off the usual path because of the traffic conditions. You pretty much need to drive like an idiot to get anywhere in the area, and you are going to be kicking down because of the lower speeds (45mph was mentioned). So it really becomes an issue of avoiding the double kick downs because you could probably cruise OK at 12-1500 rpm at that speed. Where the target ends up being is the general torque band of 23-2700 rpm but do so in 3rd gear at 45mph. 4.88s or 5.13s get him there and when actually at the mentioned cruise speeds he's rolling between 16-1700rpm @ 45mph.

 

Ah, gotcha, didn't see the speed. Just a reply to his comment that the chart was confusing and maybe a better way to put it into context.