? Dunno - C-Channel Chassis Frame Design?

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Thu 22 Dec 2022 10:04
? Dunno - C-Channel Chassis Frame Design? - edlithgow

Sort-of-tempted by a (suspiciously)(relatively) cheap LR Series 3 (2500 quids) in an Edinburgh used car dealer, I did a bit of poking around on't nyet.

People enthusiastically refer to LR "sturdy box-section frames", but I've always considered "box-section" to be big hint of mortality, and a bit of poking around confirms that the frames rot out extensively from the inside. You can buy a new galvanised frame for Series III, but of course it aint cheap.

Which leads to the question: What relatively recent non-lorry vehicles, if any, use the relatively corrosion-proof C-channel frame?

only one I can think of would be the BL Sherpa chassis-cabs, as used in the BT workshop trucks, with a demountable back box. Sort of a mini-lorry. Not many of them left.

Anything else? I THINK early pickup versions of the Toyota Zace might be C-channel, i(ronic since you only find them in markets where corrosion isn't an issue) so maybe some other Toyotas (Hilux?) do?

Most off-roaders are probably going to sacrifice longevity for the strength of a box-section.

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Thu 22 Dec 2022 12:10
? Dunno - C-Channel Chassis Frame Design? - RT

C-channel frames are a lot less stiff than full box-sections (of the same size) so would need to be a lot bigger and thicker to achieve the same overall stiffness - not a problem for big HGVs but difficult to find the space on smaller vehicles.

As a youngster, I took a lot of interest in Ford specials using the chassis frames of pre-WW2 and immediately post-WW2 Fords - these were C-channel and all had to be boxed in to improve their stiffness before mounting a GRP sports car body on top.

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Thu 22 Dec 2022 14:31
? Dunno - C-Channel Chassis Frame Design? - edlithgow

C-channel frames are a lot less stiff than full box-sections (of the same size) so would need to be a lot bigger and thicker to achieve the same overall stiffness - not a problem for big HGVs but difficult to find the space on smaller vehicles.

As a youngster, I took a lot of interest in Ford specials using the chassis frames of pre-WW2 and immediately post-WW2 Fords - these were C-channel and all had to be boxed in to improve their stiffness before mounting a GRP sports car body on top.

Yeh’ that’s the story I’d heard, except I don’t really get the “space” thing. A c frame will presumably be heavier for the same strength, and a lot heavier for the same rigidity, (if achievable at all) but I don’t see it would take up much more space. OTOH, army Bedford 4-toners seemed to do ok off road, I think they were channel frames, and it was said, by people that might have known (not me. I never drove one when I was in the TA) that chassis flexing was a significant contributor to that ability. OTOOH. In the non-ideal context of reality, a substantially intact C-channel seems likely to be a lot stronger than a rotted out box section. Quick internet search only finds a couple of Sherpa van-based campers for sale, so probably not much chance of getting one of the wee lorries.
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Thu 22 Dec 2022 16:30
? Dunno - C-Channel Chassis Frame Design? - RT

A C-channel frame needs to be deeper/wider to get near the strength of a box-section frame - at least that's what my limited knowledge of stress analysis indicates.

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Thu 22 Dec 2022 22:13
? Dunno - C-Channel Chassis Frame Design? - edlithgow

Bit more poking around reveals its actually (or has been) a live debate in the USA, where trucks matter.

www.treadmagazine.com/features/open-c-versus-boxed/

Seems to equate box-sections with sophisticated hydroforming, which I'm pretty sure wasn't a thing for Series 1 Landrovers.

Think I read somewhere that one of the reasons they went for it was because it was simpler and cheaper to make than a C-channel, with the limited kit they had available.

They seem to imply that recent Toyota Tacoma's and Tundra's reverted to partial C due to enhanced corrosion resistance, which this guy

www.exploringoverland.com/overland-tech-travel/201...x

confirms, with a bit more detail.

But he doesn't seem to think that matters.

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Fri 23 Dec 2022 08:32
? Dunno - C-Channel Chassis Frame Design? - RT

In olden days, when the Series 1 was designed, box sections were usually created by welding in one side onto a simple pressed C-channel - in more modern times box sections are created by hydro-forming.

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Fri 23 Dec 2022 09:35
? Dunno - C-Channel Chassis Frame Design? - Andrew-T

In olden days, when the Series 1 was designed, box sections were usually created by welding in one side onto a simple pressed C-channel

To my untrained mind that sounds like a recipe for built-in corrosion initiation ?

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Fri 23 Dec 2022 11:33
? Dunno - C-Channel Chassis Frame Design? - edlithgow

In olden days, when the Series 1 was designed, box sections were usually created by welding in one side onto a simple pressed C-channel

To my untrained mind that sounds like a recipe for built-in corrosion initiation ?

Well, thats where we came in.

Box sections are a method for making vehicles with separate chassis suffer similar structural corrosion to that suffered by the moocoque unibody cars that most people drive.

Landrovers, Jeeps and Toyota pickups all do it, the last on a scale that has cost them A LOT of money in the past, because Toyota replaced frames at their cost, at least in the US.

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Sat 31 Dec 2022 12:38
? Dunno - C-Channel Chassis Frame Design? - edlithgow

Bit more poking around reveals its actually (or has been) a live debate in the USA, where trucks matter.

www.treadmagazine.com/features/open-c-versus-boxed/

Seems to equate box-sections with sophisticated hydroforming, which I'm pretty sure wasn't a thing for Series 1 Landrovers.

Think I read somewhere that one of the reasons they went for it was because it was simpler and cheaper to make than a C-channel, with the limited kit they had available.

They seem to imply that recent Toyota Tacoma's and Tundra's reverted to partial C due to enhanced corrosion resistance, which this guy

www.exploringoverland.com/overland-tech-travel/201...x

confirms, with a bit more detail.

But he doesn't seem to think that matters.

Based on a wrecked one I once found in a forest in the Scottish Highlands (wish I could remember where it was, probably worth money now) partly boxed (but mostly open) C-Channel is how the Willy's Jeep was done, so the above guy has proved, to his own satisfaction, that the Willy's Jeep is no good.

This will be a shock and a surprise to many people.

Edited by edlithgow on 31/12/2022 at 12:44

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Thu 22 Dec 2022 21:18
? Dunno - C-Channel Chassis Frame Design? - edlithgow

"so maybe some other Toyotas (Hilux?) do?"

Apparently not...though the second one may be "evolving" into C-channel...which I might call progress.

www.youtube.com/watch?v=VkKxIEPKUAQ

www.youtube.com/watch?v=OjFJhK-Qh1E

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