Where to start... You ask about HT vs LT so I considered all the variables.
When ford builds the cargo van and sets a GVWR, axle, suspension, etc. this sets the limit for which mods should be based. Problem is the conversion companies didnt do this and ended up with vehicles almost at the GVWR before adding passengers, etc. This is common knowledge so let us move on to the next problem. Ford has changed van specs over the years so I'm going to use the 2004 platform and work my way forward. The 2004 E-150 is rated at 7000 GVWR ( 3600 front & 3800 rear axles ) The suspension vs axle rating doesnt matter because ford rated at these max specs. They selected a light duty truck tire 235/70R/16 rated at 1984 lb. @ 44 psi. X 2 = 3968 lb. I just weighed my van when loaded for a camping trip and with cargo racks on front / rear hitches. I was only going for the weekend so not fully loaded but pretty well loaded and full of fuel. The rear axle was 3760 or something, very close to the 3800. The front was 3000 without me in the van. But remember this included the leveraged weight of cargo racks on front hitch adding about 300+ lb. of leveraged weight most people wouldnt have and rear cargo rack adding 750 lb. of leverage weight to rear axle. Add my 200 lb. and we would have 3200 on front. If I packed more into the van with another person I doubt the front would exceed the 3600 but I could easily exceed the 3800 on rear if adding more. But for this topic we are going to say the max GVW was at 7000 ( 3200/3800 ) We are well under the tires 3968 lb. max up front but almost reaching the max on rear. Now let us reduce tire psi to 35 because that is what the conversion van co. sticker on door said it should be. Don't do that, but many convesion van owners follow this since the engineers all know better right. Even though ford specs show 41 psi front/rear. The conversion company idiots know better and said 35 psi. For this test our tires are at 44 psi. Now let us hit a dip/bump or add leveraged wind load forces. If the wind is blowing at 20 mph against the passenger side it will apply extra load force on the drivers side over loading that tires max weight and causing stability issues. The higher your vehicle, more forces will be applied but then add the extra weight up high along with the increased surface area for wind loads and you have even more leveraged forces. The rear axle controls body roll not the front so by adding E rated tires to the rear only, you added stability to handle these forces. As for the diff. size/rated tires, your tire dimensions are so close it is meaningless to discuss. 710 rev. per mile vs 718 is nothing. The Michelin tires I use would add 18 lb. to the vehicle going with E rated on rear only. Many people claim rotatiing weight is like adding about__ lb. to the vehicle per 1 lb. of additional rotating weight or requires more HP to turn the heavier wheels and bigger brakes to stop the added weight. But if you are not accelerating quickly the extra rotating weight is not as big a factor and since your not adding it to the front where most of your braking is applied, you get the best of both worlds. If the vehicle is loaded to 7000 lb. which is fords GVWR and they spec the van with 235/70R/16 to handle all that weight / forces being applied to the front when braking you cant say we are changing any of that because we have not exceeded fords specs, and only added more stability on rear. Why dont we go ahead and put 4 - E rated tires on ? because we cant afford to loose braking power up front and dont need another 20lb. to an already over loaded vehicle if not needed. If the front axle weights were closer to the max then maybe but they are not.
Read my other above post talking about ford changing axle and suspension weights to give a higher GVWR but never increased the braking power till 2007 and then again in 2010 there abouts. why would they design some of the crazy combo things they did ? 5000 lb. front axle rating with 3900 lb. suspension or something crazy like that. E350 GVWR with same brakes as lessor GVWR makes no sense. Also same E rated tires based on the ford specs I read. I know it is cheaper if they use the same tire on all these vehicles and you can always change to a higher rated tire if you need it but dont claim the engineers set the specs because they know better and you shouldnt change it. They based their design on the assumed avg. and if you go outside of that box it is on you. Conversion co. have exceeded that many times over the years which leaves it up to the consumer to sort problems out.
If you want to talk 2004 E250, you already have 4-E rated tires with a higher GVWR. Now if you maxed out the rear axle rating to the point of reaching the tires max rating you would have the same problem.
If you want to know how to make a E250/350 ride like a car you need to focus on full air ride suspension because reducing suspension/tires to offer a softer ride will always be give and take depending on how you load it. Ford has trucks with full air ride but once they hit 5 yr. of age people complain the system cost to much for repairs although you wont find a nicer ride. Comes back to the sky is the limit if money is no object. These big camper vans in E250 can be overloaded just like the E150 conversion vans are and the solution is F rated tires on rear unless your driving off road and need larger contact patch. If you add 2 more tires on rear to handle the extra weight, your adding 150-200 lb. of roatating weight just so you can keep the stock tire size vs going up to F rating. Also you have to stop that extra rotating weight and we are not talking about 20 lb. so you will notice it much more.
The HT leveraged weight adds to the tire forces of an already over loaded tire once you factor in all the forces above curb weight. HD shocks to reduce sway and depending on how bad it is maybe sway bar. But tires using only 75% of the max rating vs 95% when van is fully loaded will do a lot to help the handling.
My brother has a GMC 2500 fully loaded crew cab 4 X4 with E rated tires and when they are inflated to 80 psi and the truck is empy, they are very rough on dirt roads. He rode in my van and said, this thing floats down these roads. Yep, I only have 30 psi in tires. If he reduced his to 60 psi it was not bad but still not as nice as mine with lower rated tires. You want a vehicle that can carry the house with you then it is going to have a very stiff ride if you want stability unless you spend a lot of money on air ride suspension.
Volvo makes a full air ride on air ride semi trk that can carry your house and it floats down the road. You dont feel anything and when cornering hard it attempts to level the cab so you have less lean. Other than full air, most semi trucks ride very rough and so will a heavy duty spring suspension van compared to air ride.
If you still feel this has not addressed your HT vs LT topic go back and read it again. It explains why your van sways and why a 250 could as well depending on how you load it. How many retired people bought one of those over sized camper vans built on 250/350 and complain about it being hard to drive. Once they filled the thing up and hit the max tire rating with this much higher top heavy camper van and applied wind load forces to the tires... but I pulled on the scale and I am under the max weight rating. Not after you apply 500 lb. of additional forces from bouncing over bumps/dips with side wind loads. Time for F rated tires but maybe you only need them on rear and you dont want to loose stopping power with your already over loaded vehicle.
Every watch a truck with boom lift that didnt put down the out riggers ? once that boom reaches out to the side of truck the leveraged weight puts so much force on tires that they look almost flat on one side. The wind is doing the same thing when trying to push your vehicle over because it applies additional forces.
Once you solve the tire issue, suspension, proper shocks etc. I dont think you will notice the HT flexing as much. Yes it makes sense that removing roof supports would cause additional flexing but what is flexing ? For it to effect driving, wouldnt it have to be transfered to suspension and tires. The extra weight up top moving around would be so your going to notice that either way but I think more flex is caused by suspension and tires.
You should check rim weight ratings and then if they are within specs on your van have Sam's put E rated tires on so you can eliminate that and determin how much HT sway is still there if you have already done suspension/shocks. Then within 30 days return them if you cant use on future van. Might save you from making a big expensive mistake on the next van if tires dont fix the HT sway you have now. I bet they will or I wouldnt be spending $450 to put them on rear axle of mine.
This will be my last post on this topic for awhile. Hope info helps...
Here is another twist to this discussion -- let's assume I put bags in my 250 (hypothetical van). I like to drive low -- I think that improves handling / rollover-- how do I lower the 250 without compromising much in payload?
Good discussion. I will note that the current E150 is really an 8-lug E250 that is only a few lbs short of the 250 in GVW. The car-like E150 is a memory and was gone in 2007, I believe.
Over the years, I had 2 Turtle Top vans (a '73 Ford E200 and an '86 GMC 2500, and although the tops were not *that* high, they were also not even attached to the van except via nylon straps. These were both unit body vans, and from my recollection, the old Ford was a handful to drive (but that was largely because the front end was really worn out badly) but the GMC, with some good 255/70 tires and real stiff truck shocks (Gabriel Red Ryders as I recall), was actually the best handling van I've had. They both had factory windows. These were nominally 3/4 ton vans, but in those days, the 3/4 ton vans were 5 lug vehicles. But they were much lighter than current vans--I believe the GMC was about 4600-4700 lbs.
I then had a low top '96 GMC Savana 1500 conversion which had a real nasty tendency to sway (really needed some big sway bars and more tire), compared to my current low top '02 E150 (a conversion but again with factory windows all around), which was really tight as a new van, but could use a new round of shocks at 89k miles. I prefer low tops also because I can drive them thru an automatic car wash, which here in salty Michigan is really a necessity... Tires have a lot to do with it, and with a high top van, even a 150, I'd think about load range C tires at minimum.
But as I said, there are no more new 1/2 ton Ford vans; the current E150 is in name only. I suspect that the 5-lug E150's were just getting too heavy as passenger and conversion vans, and were either causing warranty problems or dangerous handling situations (and lawsuit potential) when overloaded.
Passenger conversions use 150s about 90% of time, as far as I understand. Premium models (like those ones from Eclipse, Explorer, etc), use the 250 -- first they have upgraded (i.e. heavier or more) finish components, plus they provide more "headroom" for payload. Eclipse and Explorer use the 150 platform as well, for their "lesser" models.
Nothing is a perfect solution - some pros and cons for each -- 150 or 250.
In terms of sway (which this thread was started for), my high-top 150 became very stable, after upgrades in suspension and tires.
Like Stkshooter indicated at one point -- the hightops have a larger envelope, thus are subjected to stronger wind-forces /drafts. These forces eventually path into the chassis suspension.
However, this is only part of the story -- these forces also hit the cabin, and I have to think that a scalped hightop is less rigid than an OEM lowtop. Cross-bracing that I installed into the hightop (to install the skylight), had a nice side-effect -- it lessened the shaking under strong winds.
One factor which I don't think we have talked a lot about is chassis height -- I would like to hear people's comments on this issue. My personal experience was that lowering the van (lower profile tires) also improved handling.
I would also think that skirts (again a small detail) do help as well. There are vans that a- have no skirts, b- those with concealed (Explorer's or Eclipse Signature's) or c- Cinderella skirts, like the older ones. Sure, some people think that concealed skirts look better than Cinderella's skirt, but the latter one might be more advantageous to handling.
I mean, every improvement helps. Some more than the others...
350 based hi-tops tend to be as stable as their profile can be.
Funny that for non-commercial apps, few buyers demand it or are willing to pay the premium for it.
Lowering the van do improve performance (CG lower), but if you go for 250 / 350, you are going to be higher by default.
I went for oversized tires at the expense of a bit more height, but they are wider, and hurt a bit in mileage, but gain lots in lateral stability --- except in snow / ice, where there is less ground pressure.
Maybe I am a minority here -- but I do like the idea of using heavier tires in the rear, and even HD shocks in the rear and Touring shocks in the front.
Since I am shopping for my next van -- I am wrestling with choosing a 150 or 250, low top or high-top. I don't like 250s ride height, and I don't like that it may require $$$$ to dumb down the suspension for passenger comfort. I don't mind improving the 150 (I have done it before) but I don't like that I have a very low "ceiling" with payload, at least legally speaking. I will be rolling at or slightly over the GVWR.
Add here that 250s are much harder to find, are more expensive to buy and run.
I do not want to sound negative, but I am looking for a regular (not long) wheelbase. I am also looking for conversion vans -- panoramic windows.
I get new listings for any Ford Conversions instantly, and actually noticed that although rare, 250s are more frequent than 350s. 350s that I have seen are long wheelbase and/or short (i.e. Ford) windows.
Ahhhh you want one used from the market.... you are right.
Have you considered getting a 350 and doing the conversion yourself or getting a local outfit to do it for you?
DIY Option: it is more work than I really want to do. I will be doing upgrades to the conversion anyways, so I am afraid it is more than I can chew, plus I want to use it, not just work for it for 1-2 years.
Outsource Option: I am not sure if there is a $ benefit over the option of just buying one van already converted, and adding my upgrades / mods.
I am budgeting about $ 6000 in acquisition costs. I am budgeting $ 2k in repairs/maintenance, and another $ 3-4k in DIY improvements / mods, regardless of which van I get.
I don't mind getting a 8-10 year old van and improving it. I would actually prefer this. At least I know that many components will be new and good for another 5-10 years. I want the van to be usable right-off-the-batt, and do the work as I go along.
Consider a fairly old Sportmobile conversion, they are normally built on 350 chassis.
I appreciate bouncing ideas off -- maybe I am not listening very well -- what is the advantage of a 350 over a 250 for my case?
250 is sufficient for me payload-wise, while I would have the same ride-quality issues with a 350 as with a 250, no?
At the moment -- there is only one or two 250s in the area, no 350s and about ten 150s that meet my search criteria. My problem with 250s is the very limited pool of selection. I already saw one or two, hated the colors. I could paint it, but that is another $2k or $ 3k for a decent/minimal job.
The reason I am looking for a regular wheel-base (not long) is since I live in NYC, I want to keep the footprint as short as possible -- easier parking. Of course I would like more room, but the regular wheelbase is just about right.