Long wheelbase vs short? - Mercedes-Benz Forum
 
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#1 (permalink) Old 03-01-2010, 09:45 AM
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Long wheelbase vs short?

I've been doing some thinking. What advantages/disadvantages does a long wheelbase offer? To give some idea why I'm asking I'm comparing U900s to U1100s.

As far as I know negatives with a long vehicle are the breakover angle is shallower and the turning circle is bigger. Are there any other down sides to it? As for positives they're often more comfortable on the road and you can fit more stuff on the back! Do they track better at speed on the road too? I assume that's why the LWB trucks were often fitted with high speed axles and the short ones not?

Would they be more stable on steep inclines? I heard some talk of the 900 lifting wheels when going down steep slopes on the weekend? Surely that's got to be a bad thing as it's well on its way to going right over? Would the long wheelbase be more stable because it has more weight behind the cab?

I've looked at the specs and the U1100 isn't actually that long. In fact I think it's only about 4" longer than my Defender. I could cope with that. It's about 2' longer than a U900 and 1' longer than a U1000 so there's not a lot in it!
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#2 (permalink) Old 03-01-2010, 10:50 AM
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Longer wheel bases are more stable at higher speeds. With a short wheel base truck like a U900, at high speeds you are more likely to be the victim of unpleasant and sometimes difficult to control bounces. Thus the short truck are generally limited to speeds in the high 40s for miles per hour.

I've had my Swiss 404 at speeds in the low 60s per hour, and even with the longer wheel base on the 404s, that speed was more than a little scary --much better to slow down a bit. It's variable, though. Some of the SBU trucks in the long wheel base are quite comfortable at those speeds.

Longer wheel bases also do help with steep uphill or downhill driving. Think of it as a triangle. Your wheels form two vertices of the triangle. The third is at an imaginary point in the air coming out at the plane of level from your uphill wheel. It lies at the point where the truck's center of balance will cause it to roll on over versus coming back down to or staying on the driving surface. Even if the angles are exactly the same, with a short wheel base truck there is less actual distance between that uphill vertex and the imaginary one that is your center of gravity. With a longer wheel base there is more room to bounce and move with the terrain without the balance of the truck either getting very loose or becoming completely out of control.

It's the same thing that happens if you stand with your feet together and have someone push you from the side. You get to the point where you feel like you are going to fall over much more readily than if you stand with your feet far apart and have someone push you.

It's all tradeoffs. As you say, the short wheel base trucks can manuever more tightly, and have a better breakover angle. And the reality is that regardless of wheel base, these trucks will do things that are just plain scary.

And you also have it right that even the long wheel base vehicles aren't necessarily all that big. My Swiss 404 looks big, but it's actually got about the same footprint at the Jeep Grand Wagoneer sitting beside it; it's smaller than my Suburban and most pickup trucks on the road in the US, and isn't even really a whole lot larger, footprint-wise, that the VW Beetle that used to sit next to it.

Now, the SBU series trucks are bigger, but even then, if you look at their width and footprint, and not height, most of them aren't any bigger than a lot of other trucks I see on the road every day around my home.

If you do plan on doing trail driving, though, one thing you need to think about are trees and that height factor. Sometimes that's more important than other footprint considerations. A really tall truck is going to be hitting its head on branches a lot more than someone in a shorter truck.
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#3 (permalink) Old 03-01-2010, 02:01 PM
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Thanks for the reply. It's pretty much backed up what I was thinking which is great! I don't do a lot of green laning but the height thing is worth considering for use in woodland. The 900/1100 looks to be considerably lower (it's a foot lower than a U1000 in fact) than the square cabs but still has the same ground clearance.

I remember the first time I drove a tractor for a local farmer to help him out. I was tanking it up a narrow lane at all of 25mph with a bucket full of feed, hit a big dip in the road and only just managed to hold it out of the ditch using both verges to get myself back on track. It scared the life out of me and I've driven (not just tractors) a lot more gently ever since. What's more, I had to go back for another bucket of feed! Life's too short to be silly, although I didn't really realise I was over doing it at the time.

Thinking back to that day I'm going to look more seriously at the LWB models. The U1300L I was looking at on the weekend wasn't that massive and I think that's the longest model made? It made some really tight turns that I wasn't sure it could and handled them extremely well. It's a shame it can't carry a 3 point otherwise I'd seriously consider one.
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#4 (permalink) Old 03-01-2010, 02:56 PM
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I'm sure I'll be corrected, but, I think a U1300 is 2850mm, a U1300L is 3250mm and a 1300L/37 is 3700mm.
On the SBUs the longest wheelbase available is generally 3700-3900mm, depending on the model.

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#5 (permalink) Old 03-01-2010, 03:12 PM
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