FG buildup

[dhackney]

I checked on the www.michelintransport.com site about the 7.50R16 XZY.

Charlie,

I can't find anything on a 7.50R16 on the XZY model page:
http://www.michelintransport.com/ple...que=46&lang=EN

The only 7.50R16 I can find is an XS here:
http://www.michelintransport.com/ple...odeRubrique=47

Where did you find the 7.50R16XZY info?

[dhackney]

So what were the weights?

Heavy, but do-able.

The FG is such a small chassis to start with that you are pretty limited weight-wise. Once we knew the general range we'd end up in we put aftermarket springs & shocks on it to handle our anticipated load.

Both the springs and shocks made a very notable and discernable difference in ride and handling. The rear sway bar and the 50/50 shocks on the 3 point frame made a huge difference in handling as well. The whole rig drives so much better than when we tested it feels like an entirely different vehicle. The ride is still a cab over truck, but what used to be full on crash-to-the-stops bumps are now well damped and controlled. Tonight we will drink to the health of Deaver Spring and Bilstein.

When you combine that with the almost eerie quietness of the cab, it's a very, very comfortable driving experience period, much less in a cab over truck.

And how about that weather we've been having...

OK, I can see I haven't thrown you off the scent. If you are looking for specifics, see Darrin's disclaimer page on singles here:
http://www.ruf-inc.com/srt.htm. All the MFG quotes there are from Mitsubishi Fuso USA.

If you are still wondering, check out the heart of darkness here:
http://www.atla.org/
Note that they rebranded themselves for better PR.

If we come across you in South America, SE Asia, India or Africa I'd be glad to share them with you over a glass of wine.

Doug

[charlieaarons]

The info about the XZY is under "tyre characteristics", "technical tyre catalog".

Your CG height is not right. Eyeballing things I think it's under 60". Something is wrong with your calculation, I think.

Charlie

[dhackney]

Your CG height is not right. Eyeballing things I think it's under 60". Something is wrong with your calculation, I think.

I used the spreadsheet from the Jeep site. It is the only way I know to calculate the CG. If anyone is aware of another spreadsheet I'd love to run the numbers again. Especially if they came out with a lower CG.

[etbadger]

First: Awesome build. I can fully understand (and empathise) with all the delays. We were so gung-ho to get going on our travels that we ended up spending a month here, a month there just fixing and repairing while on the go. It would have been much better overall (time and facilities) to have it done right up front.

Second: That CG location looks way too high in the pictures. Unless you are carying a large slab of lead on the roof I cannot picture how the point would be so high.

The logic behind the CG calculations on the Jeep page are correct as best as I can figure from a quick glance, but I would suspect perhaps an implementation issue in the spreadsheet.

Would you be willing to dish out the raw numbers (weights, height of axle when on the tilt-bed, etc) for a few people to double check the numbers?

-e

[jgolden]

I'm dying to know what the final weight is!!!!

[dhackney]

Thanks to everyone who has contacted me regarding the CG / roll center, etc.

I did find an error in my inputs. Once I corrected that input the model lowered the CG to 72.28" / 183.59cm.

I located another model at:
http://www.kettlemorainemotorsports.com/cg.html

I ran the numbers through that model and it returned exactly the same values as the Jeep model.

Unless both models are identically flawed, I am assuming these to be valid for a static 3 point pivot frame, i.e. level load.

I am researching pivot tables that we can put the rig on and get an empirical measurement of the roll angles. I think that is probably the only way we'll ever know for sure where we are at with the 3 point pivot frame against the stops on either side.

I edited the previous "weigh-in" post to correct the values and calculated data points.

[dhackney]

Some further thoughts on the CG / roll angle test.

Tom has pointed out to me that if our rig was a solid block of mass, with no voids and of a completely consistent matter, the CG would be about 72”, or halfway up through the mass. This is just one more reason why I find if very hard to believe that our CG is 72” high.

If I make even slight alterations to the Jeep model that allow for even a small portion of the liquid rearward transfer or rearward suspension weight shift during the lift the CG drops to ~60” / 152.4cm and the roll angles increase to > 30 degrees.

My conclusion is that our CG is probably well below 72” / 182.88cm, probably closer to or well less than ~60” / 152.4cm.

I believe that in order for the Jeep model or others to be used accurately a much more rigorous approach must be taken to the test. I tried to be as accurate as I could with the front axle height measurement but I question the validity of the results of this model unless you take the additional steps of eliminating liquid transfer and the insertion of solid rods to eliminate suspension expansion/compression.

Due to the 3 point pivot frame, I believe our roll angles can only accurately be measured on a tilt table. I continue to seek that opportunity and will post the results if I can conduct that test.

I am currently unaware of any expedition vehicle with a 3 point pivot frame that has undergone a tilt table test, but would welcome those results if any are available.


My methodology for the lift was:
1. Locate and mark the horizontal centerline of front axle. This ensured I would always be using the loaded tire radius for the calculations. Since both tires are the same circumference, I didn’t have to worry about averaging those as you would on a race car set up for stagger.
2. When we lifted the front axle by driving it up on the tilt bed, I used the mark on the front axle and a laser level to obtain the lifted front axle centerline height of the loaded front tires.
3. I did not replace the shocks with solid bars to eliminate suspension height change, as this would have been impractical in my circumstances. I made no allowance for the compression of the rear suspension, the corresponding lift of the front suspension and the resulting weight transfer rearward.
4. I made no allowances for the shift of liquids in the tanks, specifically the fuel tanks, which are long and narrow. The estimated 185 lbs. of fuel in those tanks would have shifted towards the rear.
5. I only took one measurement and one weight at one height.


Test conditions:
• Fuel tanks: ~25 gallons. The tanks are saddle tanks located under the garage along the frame rails. Equal amounts in both tanks via a crossover. There are no baffles, so this weight would have all shifted back. That’s 180 lbs @7.2 lbs/gallon.
• Raw water: ~35 gallons. The tank is mounted between the frame rails aft of the garage. No baffles. That’s 291.5 lbs. but since the tank was ~75% full there would have been minimal shifting.
• Fresh water: 33 gallons. The tank is mounted under the dinette, left side of camper centerline, aft of the rear axle. Full load, 100% full. That’s 266.56 lbs.
• Gray water: 0
• Black water: 0
• Front axle centerline, static: 14.375” / 365.13mm
• Front axle centerline, raised for test: 42.875” / 1,089.03mm
• Amount front axle centerline raised for test: 28.5” / 723.9mm
• Front contact patch elevation raised for test: 28.5” / 723.9mm
• Front track: 71.75
• Rear track: 79
• Wheelbase: 154

On the front axle lift amount, I had previously contacted the author of the Jeep spreadsheet and asked if I needed to go higher than 24” since our FG was a longer wheelbase. He responded that any higher lift would not significantly improve the accuracy of the model.

Doug

[dhackney]

I'm dying to know what the final weight is!!!!

Surprisingly, the final weight and the cost are exactly the same: less than a Boeing 737.

[dhackney]

I adapted the Jeep Center of Gravity (CG) XL model so you can enter weight and weight shift to rear axle data and see the corresponding change in CG / Roll Center / Roll Angles / etc. to our FG data set.

The model demonstrates how relatively tiny amounts of weight shift make a very large difference in the CG.

The model is at:
http://www.hackneys.com/mitsu/docs/C...-hackneyFG.htm