The Amocat- 2005 Tacoma

[wdb]

Nice looking work!

Originally Posted by aardvarcus

Also it is amazing the difference in handling without the air dam, especially at highway speeds.

I'm curious about this. How was the handling different?

[aardvarcus]

The handling is different because of the large amounts of lift the truck creates when the air dam is not there. Because of how the front of the truck is, all the air that doesn’t get pushed over the bumper ends up compressing and being shoved under the truck. My air dam basically takes an approximately 8” by 68” section of that air that was going to go under the truck and moves most of it around the sides of the truck. It is especially noticeable on the rear axle, since there is not much weight there unloaded. Plus I have my air dam farther back than would be ideal for reducing front axle lift, according to Hucho’s graphs. The truck feels more planted in the turns with the air dam, which is really the only time you can “feel” the difference, though the truck is quieter with the air dam since it is deflecting large amounts of the air around the tires.

[aardvarcus]

So I got the step/slider/bellypan all mounted up. Started by drilling out the aluminum, then transferred the marks onto the slider frame. It was hard drilling all those large holes up into the steel slider frame, but I managed. Popped in all the Rivnuts, and then drilled out tapered holes in the aluminum, so the V headed bolts would sink up flush. I need to get two longer V bolts, since the end pieces are a little too thick, so temporarily I have some normal M8 bolts holding them in.

[aardvarcus]

So I mocked up my new full aero-shell rough foam core yesterday, the fit is pretty good, just need to start smoothing and shaping it. (Forgot the pictures, will add them to this post later.) After that test fit, I reinstalled my air dam and half shell, so I am back to having all my aeromods to date in place.

Also last week I pulled off my fairly worn Michelin LTX M/S2 LT235/85R16 Tires. I got a friend to help me grove and sipe my other tires, half worn Cooper Discoverer A/S LT255/85R16, to be a little more onroad friendly and installed them on my Tacoma. (You can see the results in my previous post.) The gearing is higher due to the larger diameter (11% over stock), but the more aggressive tread pattern is louder, which is the sound of aerodynamic drag.

I will use the next few weeks to test the MPG differences between the two tires. I will be using these tires primarily until I buy something to replace the other worn tires.


---Edit---
As promised, here are the pictures.

[aardvarcus]

After careful examination, I determined that my front air dam was not effectively channeling air around these larger front tires I am temporarily running. In fact, I am pretty sure it was channeling air right into the edges of the tire tread. My other “street” tires were about 31.7” in diameter and 6.6” wide, whereas these “all terrain” tires are about 33.2” in diameter and 7.2” in width. (Tread widths not section widths.)

To correct this, since I am unable to easily make the air dam wider, I changed how I was attaching the air dam and spaced it about 2” further forward. Since the air at this part of the vehicle is traveling at an angle, this kicks the air out around the tires roughly the same as if I had made the air dam wider. Per Hucho, moving the air dam closer to the nose should help with front lift anyway.

On my morning commute, I cracked the windows, and couldn’t hear the front tires anymore (over the sound of the rear tires that is) so it must be doing something.

Additionally, when I first swapped the tires I did not air them up to the same PSI as I had been running the other tires, so I also increased the PSI to what I had been running. It is fairly well established that higher PSI will result in better MPG, I am just trying to balance traction and wear into the equation as well.

Between those two things, my trip MPG was showing better than it had been, but I will wait for a full tank to surmise how much of an improvement I got.

[aardvarcus]

Filled up the truck after the Air Dam adjustment and tire PSI increase. This tank showed an approximate ½ to 1 MPG improvement over the prior four or so tanks. I am guessing a lot of that is due to the tire PSI increase. I got some lawn edging, and am going to make temporary “test” tire air deflectors and see if they offer any improvement. I would like to see how good I can get the MPG with these obviously not LRR tires on there, but I will most likely get another set of Michelin tires early in the year. I am hoping they will release their new Defender LTX M/S tire in a LT235/85R16 before I have to purchase, which is part of the reason for delaying replacing my worn out M/S2s.

Part of the problem I am having is that at higher pressures the rear tires wear quicker than I would like in the center, mainly due to the lack of weight on the rear axle. This is especially aggravated by one particular spot I drive by often, which is a stop sign that you have to turn sharply at on a very steep hill. It is extremely difficult to make this turn without spinning the tires, and if it is wet I usually just put the truck in four wheel drive. There is no practical alternative route. I would guestimate this one spot took 10K miles off the life of my last tires.

My solution to both of these problems is to try and improve the weight distribution by shifting some of the existing weight on the truck to the back of the bed. Step one is getting some tool storage that can relocate some of my factory and added tools to the back edges of the bed. For step two (further down the line) I would like to relocate my battery from the front driver’s side corner to the front of the bed on the passenger side.

For tool storage, I presently have a tool chest bolted to the front of the Tacoma bed as well as some tools in the factory storage under the truck seat. I try to watch how much weight in tools I add, but I am constantly using the tools and several times I have needed and not had tools because I took them out to save weight. To store the tools, I bought two pelican cases (1520) and am going to mount them to the sides of the bed near the back, so that I can let down the tailgate and access the tools without climbing up in the truck bed which is very annoying to have to do constantly. The toobox I have now is annoying because it inhibits placing large items all the way forward. These pelican cases shouldn’t protrude significantly beyond the wheel wells, but they are taller than the wheel wells so 4’ wide sheets will have to sit on top of them. I figure this is an acceptable compromise, since I don’t carry 4’ sheets nearly as often as I carry lumber or other long items.

For those who haven’t figured it out, I have about ten different projects going on the Tacoma all at the same time, so my ADD always has an avenue to vent itself.

[freebeard]

I guess you know weight behind the rear axle will have more leverage than weight between the wheels.

Do you have an hitch receiver? Cut the end off a weight-lifting bar and stuff it in there. Then you have a quick-release mechanism and graduated weights for adjustment.

[aardvarcus]

Freebeard,

Rigging up some kind of weight rack wouldn’t be a bad idea for temporary use for icy/snowy conditions. When the forecast calls for snow and ice I usually start throwing cinder blocks or the like in the bed. I actually do have some steel weights hanging around…

For daily use though I would really prefer to have less weight than I have now, so dedicated weights are off the table. I am really just trying to readjust the “dual purpose” weights I already have and “need” to keep. Stuff like the jack, wrenches, sockets, come along, pulley, straps, shackles, air compressor, and a variety of other tools can all be relocated. I will put these side mounted toolboxes as far back in the bed as I can, definitely behind the axle.

I would (eventually) move the battery behind the axle too, but I don’t think I will have room without inhibiting the use of the truck bed so it will probably end up just in front of the rear axle. The battery is currently in front of the front axle (and thus taking weight off the rear axle), so relocating that 78lb weight backwards would really help.

Another thing is the Tacoma has a decent amount of uneven weight distribution side to side, with the battery, driver, and gas tank on the driver’s side. I will try to put more of the weight on the passenger side, such as the battery and the heavier tools.

I might have to get stiffer springs for the back after I do all this. I have the two leaf pack (2+overload) which are notoriously weak, but Toyota has a recall on my leaf springs so I am hoping early next year they will install a new three leaf (3+ overload) spring pack.

[freebeard]

How does the bar diameter compare to your receiver. Maybe all a 2nd-hand bar would need would be cutting it to length and drilling it for a linch-pin. The advantage is the location at the end of a lever arm. I like the range of adjustment 5 or 10 pounds or hundreds.

Moving weight to the middle allows the car to spin easier, heavy weight out at the bumpers tends to keep it on course and also ride nicer. I have two five-gallon cans under the hood and I keep the right one full to improve the left-right balance.

Beyond the springs (literally ) you have tire pressures and the contact patch. These can be biased to control the handling. Dune buggies are a good example of the extreme. Small hard tires on the light-weight front vs big low-pressure tires on the heavy rear end. Balance that!

[wdb]

Have you seen the swing-out toolboxes? They mount behind the fender well. Here's an example.

Tacoma Swing Case Toolbox