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Old 11-11-2013, 09:39 PM   #1
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Join Date: Nov 2013
Location: Ft Worth
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Default Frame / Wheelbase - Used Cl 8's for Conversion

New to the forum, lots of good posts to study. Looking to build or buy CL 8 based rig within next 12 months.

Several posts note good builders such as Hawk Engineering that build a conversion based on buyer provided used Class 8 Truck/Chassis.

Question - how do you reconcile wheel base of existing truck proposed for conversion?

Does existing frame length represent limiting factor or do new builders replace/extend original OEM factory frame as well? Risks of doing so?

Many thanks,

N. Asplund
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Old 11-12-2013, 01:31 AM   #2
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Welcome to the forum. Most trucks will need to have the frame modified to match the wheel base of the coach being built. Many builders rely on frame shops to do the work for them, a few including IpHawk do it in house. Frames can be lengthened or shortened both before or after the axels. For smaller conversions one of the rear Axles can be removed.

Hawk engineering is a smaller shop and will build on pretty much any chassis. Showhauler is larger and sells through a dealer network and will also build on a used chassis. Both will also build a shell so you can finish the interior yourself if desired. I have also heard NRC builds a quality rig.

We toured a bunch of factories and all the builders are happy to show you around.

Dave
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Old 11-12-2013, 09:28 PM   #3
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Default RE: Frame/Wheelbase

Dave - thanks a million for your reply. I'm originally from the midwest and will be back for holidays. Good advice. I will look up these builders for a on-site visit.

Best,

Nate Asplund
Proud Graduate of Washington State University

(seeing you're based on the West Side).....
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Old 11-13-2013, 12:22 AM   #4
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Our oldest is currently working his way through a electrical engineering degree at WSU, now all five kids have grown up and moved out we can get serious about finalizing our plans for our conversion. Yet to be determined is if we will build all of it ourselves or have a builder at least build a shell. We have some very specific design ideas that we want in the coach and a particular model truck we want to convert that a lot of builders do not want to use. Michelle is not overly excited about the time and mess involved with a ground up build lol. Have to find time to get my napkin sketches turned into full cad drawings, then I can get a better idea of costs. I do wish there was some builders in the NW or at least on the west coast. Our factory tour road trip was the best thing we have done so far, after seeing how they all build, we came away with a list of which builders fit our needs. Now we have selected two builders and a possible third that we will solicit bids from when I have the plans done.
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Old 11-13-2013, 09:14 AM   #5
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Nate,

Frames are stretched by custom builders, (like in the water truck business) by bolting fish plates over the welds, adding steel plate to the exterior, or even double framing the whole truck behind the cab, (we did a stretch with a double frame from the cab back). You can also stop the frame behind the rear axle and drop it down for a garage or basement and end up with a longer coach than the frame rails will allow.

It is certainly less expensive to start with a frame that is long enough for your conversion.

Another factor is the type of rear suspension and gearing you want to end up with, (and the cost associated with a swap)

Some builders have very little overhang behind the rear axles. In those cases you will need a longer frame, AND a front axle rated fairly high. This is because most of the weight of your coach will be split between the front and rear, (between the axles)

Other builders have more overhang and are able to pull weight off of the front axle by placing holding tanks, etc behind the rear axle. Your truck will probably come with a front axle rated at 12-13k. If you have a long wheelbase with a small overhang you will be overweight on the front and have some cost associated with a front axle upgrade.

Your design preferences will also affect frame length and axle placement.

Other considerations are handling, maneuverability, wheelbase and ground clearance. A long wheelbase can cause ground clearance and turning radius problems. With a short wheelbase you need to think about dragging the rear end on the ground and the swing of the overhang, (I don't think you'd ever want to go less than 55% ratio wheelbase/length on a class 8, although some motorhomes are less).
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