Things learned on a Thursday evening.....
This thing is going to be freaking wicked! Here is a sneak peak!
I couldn't stand it anymore! I had to mount up the big tires in the fenders I have already cut to see what it was going to look like after this weekends last fender modification.
One more....
I did also learn some things....
So I might have mounted up the rear tires first and taken it for a little spin to test out the gearing
I really wanted to know how bad things where going to be with the 3.55 gears, 5-speed manual, and the big ol' tires. It was an interesting experience! Besides looking like a complete physco with 39s on the back and 31s on the front it was a great learning tool. I did my standard quick drive down to the highway and up to the top of the nearest little pass. This little test circuit always tells me a lot about how the truck drives with new modifications. Its also a pretty good test of gearing.
-First to head down the road loosing elevation towards the highway. Its about 3 miles or so and you loose a good bit of elevation in the process. Its a good test of what gear to use going down the hill. Generally in the past I have always been between finding a happy gear. With the little tires I could run 4th down the hill and not speed away too much. That was better than when I had the 315s on the truck....3rd was too low and 4th was much too high. With the 39s I found that 3rd gear works pretty well at keeping the truck at the speed limit. The rpms are a little high but not too bad.
-Once you get to the bottom of the hill you have to stop and turn onto a 65mph highway. There is a merging lane so you don't have to romp to get up to 65 if you don't want. Its always a good takeoff test and a 0-65 test. In the past this always works the truck a bit. With the 315s I would have to take off in 1st to get rolling than row through 2-4 before shifting into 5th at about 60mph or so. With the little 31s on the truck I would start in 2nd and row through 2-5. The truck always feels a little rapped out with the 31s. Its not that happy at 65 in 5th....or so it seemed. Now with the 39s I have to start in 1st for sure. I think 2nd is too high and would slip the clutch badly. 1st is now a pretty useable gear with the 39s. With the 35s it was still a little too low for anything, if you started in it you where just doing it to get rolling...then hitting 2nd. With the 39s you can start in 1st and use it as a full gear. I will have to watch the GPS to see what my shifting speed are for sure. You can tell the big tires are there...but its not that bad. The biggest loss in power 0-65 with the big tires is around 40mph or so....on the low end of 4th gear I think. The 3-4 shift is a little broad and you feel that with the big tires. Once you get up into the 50-65 range in 4th with the 39s the truck is right in the middle of its powerband. It doesn't seem like its over revving in 4th pushing 63-65.
-After you do the 0-65 merge onto the highway ( which is uphill by the way! ) you come up to a nice little hill that is about a mile long. It gains a few hundred feet at least. Its a great hill to test what gear you would go up mild 65mph passes. The truck easily went up it in 4th gear I could still gain speed easily and even passed a semi on the road at 65 or so. In the past with the 31s the truck would be in 5th and have plenty of power but just didn't feel right to me. With the 315s I could pull it in 5th but had to be going 65+, if I got stuck behind someone and had to slow down I would have to grab 4th gear and then it was a little too big of a jump to upshift.
-Once I got to the top of the hill I flipped around and headed home. I did another 0-65. It felt pretty good....1st is much more useful of a gear. Still plenty of takeoff power. Now I was going up the big hill I just came up in 4th. One of the biggest problems with the 31s was that you generally had to give it a little pedal to go down this hill at 65. The truck would not coast down the hill by itself at 65 in 5th with your foot of the accelerator. With the 315s I could coast down the hill with minimal pedal at 65. It was so bad with the 31s that I would often kick it into neutral to go down hills like this. The truck would coast at 65-75 like this....so its a pretty big hill. Now with the 39s I was able to kick it into 5th going down the hill and the truck would coast right at 64-66 with no accelerator. That was a nice little bonus. It was always a pain to kick it into neutral and then back to 5th on the flat.
-Now it was on across the flats for a mile or two and down a slight hill to the turn to the house. 5th gear worked great for this. The truck just loafs along at 65 on the flats in 5th, there is even one small uphill that it just loafed right up. I was pretty impressed that the truck would push itself along in 5th with the 39s and 3.55s at such a low rpm. The truck only has to be turning 1400-1500rpm at those speeds.
-Once you turn back onto the road leading up to the house it drops to 35mph and climbs back up about 3 miles to the house. This has always been a little bit of a finicky drive. With both the 315s and 31s I was always fighting between 3rd and 4th, especially on this one hill. Now with the 39s I was able to run 3rd gear at 35mph the entire way up to the house without thinking about downshifting at all. The truck was in a nice little sweet spot.
So that is what I learned about the gearing on my little gheto test drive with only the big rear tires on the truck. I am still laughing at what I must have looked like
I mounted up the one from tire to see what the truck would look like and snap some pics for you guys as a teaser. I did notice one thing. I took another picture of the front fender with tire. While I think everything would clear on the truck.....I think I may section another 3" out of only the front of the fender opening. I think that this would line up the lines better with the rear fenders. I will be able to lessen the angle on the trailing edge of the front bumper i am building also. What do you guys think?
I think the point where the fender ends should be ahead of the leading edge of the tire. To get the tire to clear I am going to have to taper the bumper a lot where it wraps around. Since I am doing the other fender this weekend now is a good time to make this change. I will only have to re-section the other fender on one side. I can also do this on the truck if I remove the airbox.
Other things I learned....
Even with near 39" tall tires the truck will still fit in a standard garage door.
The rear end needs to be 1.5" wider on each side or I need to tub out the rear a bit.
The tailgate has the feel of a bar instead of a table. I might need a few travel stools
I need to skin the inside of the tailgate to make it a flat table.
The dogs are going to have to work to get in the back of the truck now!
I might need to build a step or ladder of sorts for the SO to get in the back. That is a bit of a climb now!
Cummins engines seem to like really weird gearing!
I can't wait to try some nice interstate to see how the truck feels at 75 in 5th......
I think 4th would still make a really good highway towing gear even with the 39s.
Oh....these tires make some noise! Not bad with the Cummins and the stright pipe but you can still hear them for sure!
