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Service Body Sizes and Cab-to-Axle: How to Order a Body That Fits
Service body size is determined by cab-to-axle, not wheelbase. Cab-to-axle is the distance from the back of the cab to the rear axle centerline. A 60-inch CA chassis takes a 9-foot body, an 84-inch CA takes an 11-foot body, and a 108-inch CA takes a 14-foot body.
Every service body order that goes sideways goes sideways for the same reason: somebody specced the truck from the wheelbase. Wheelbase is the number printed on the window sticker, the number the salesman quotes, and the wrong number to build a body from. The number that decides what fits is cab-to-axle, and on a chassis cab it is the only dimension that matters when you are ordering a body.
This guide gives you the cab-to-axle figures, the body lengths they pair with, and the three mistakes that turn a fleet order into a return freight bill. Read it before you order the chassis, not after. Once the truck is built, cab-to-axle is not something anybody can change for you.
Cab-to-axle on the most common dual-rear-wheel one-ton chassis — pairs with a 9-foot body
Source: industry chassis sizing charts
Share of the thousands of service bodies we build each year that arrive on a chassis that will not carry the ordered body
Source: OEM Truck Equipment build data, Okarche, OK
Maximum crane capacity on a Reading crane body, 9 to 14 feet, 60 to 120-inch CA
Source: Reading Truck product data
What cab-to-axle actually measures
Cab-to-axle, written CA, is the distance from the rearmost point of the cab to the centerline of the rear axle. Truck body manufacturers size every service body, dump body, and flatbed from this figure. On a tandem-axle chassis, CA is measured to the midpoint between the two rear axles.
Put a tape on the back wall of the cab. Run it straight back along the frame rail to the center of the rear axle. That distance, in inches, is your cab-to-axle. It is the amount of frame you actually have to mount a body on.
Wheelbase measures something different: front axle centerline to rear axle centerline. That figure includes everything under the cab, which is frame you cannot mount a body to. Two chassis with the same 60-inch CA can carry different wheelbases depending on whether they are a regular cab, extended cab, or crew cab. That is exactly why body manufacturers publish their catalogs in CA and not wheelbase — CA is the same number no matter what cab the customer ordered.
The body itself is longer than the CA figure. A 9-foot body on a 60-inch CA hangs past the axle centerline, and that overhang is deliberate: it balances the load and gives you room for a bumper, a receiver, and a step. Manufacturers have already done that math. Your job is to bring them a chassis with the CA their body was engineered for.
The cab-to-axle to body length chart
A 56-inch cab-to-axle takes an 8-foot body, 60-inch takes a 9-foot body, 84-inch takes an 11-foot body, 108-inch takes a 14-foot body, and 120-inch takes a 16-foot body. These pairings are industry standard across service bodies, flatbeds, and dump bodies.
This is the chart. Print it, tape it inside the cabinet door in your purchasing office, and check every chassis order against it before the PO goes out.
| Cab-to-axle | Body length | Wheel config | Example chassis |
|---|---|---|---|
| 56″ | 8 ft | Single rear wheel | Ford F-250 / F-350 SRW, Ram 2500 / 3500 SRW |
| 60″ | 8.5–9.5 ft (9 ft standard) | Dual rear wheel | Ford F-350 / F-450 DRW, Ram 3500 DRW, Chevrolet Silverado 3500HD |
| 84″ | 11–12 ft | Dual rear wheel | Ford F-450 / F-550, Ram 4500 / 5500, Silverado 4500HD / 5500HD |
| 102–108″ | 14 ft | Dual rear wheel | Ford F-550 / F-600, Ram 5500 |
| 120″+ | 16 ft and up | Dual rear wheel / cab forward | Class 6–7 chassis, cab-forward medium duty |
Sources: Quest Fabrication cab & chassis body sizing chart; industry CA-to-body-length reference tables. Body length ranges vary slightly by manufacturer — confirm the exact pairing with your body supplier before ordering.
Two things to notice. First, the jumps are not smooth — there is no 72-inch CA sitting between 60 and 84 that lets you split the difference with a 10-foot body. You pick a step on the ladder. Second, the step you pick determines the truck class, which determines the price, the licensing, and in some configurations whether your driver needs a CDL. Choosing an 84-inch CA when a 60-inch would do the work is one of the most expensive habits in fleet purchasing, and it usually happens because somebody wanted margin they never ended up using.
How Reading and CM bodies map to cab-to-axle
The chart above is generic. Here is how it lands on the specific lines we build and install in Okarche, so you can go from a job description to a part number without guessing.
| Body line | Body length | Required CA | Material | Typical application |
|---|---|---|---|---|
| Reading Master Mechanic 100-series | 9 ft | 60″ | Steel | Mobile mechanic, field service, one-ton DRW |
| Reading Master Mechanic 200-series | 11 ft | 84″ | Steel | Heavier field service, larger tool and parts load |
| Reading crane bodies | 9–14 ft | 60–120″ | Steel | Crane service up to 12,000 lb capacity |
| Reading Classic II | Multiple lengths | Varies by length | Steel | General service body, Latch-Matic locking, optional aerial or crane |
| Reading SL | Multiple lengths | Varies by length | A60 galvannealed steel, E-coat + powder coat | Corrosion-exposed service, road salt and chemical environments |
| Reading Aluminum | Multiple lengths | Varies by length | Recycled aluminum | Payload-sensitive and weight-sensitive fleets |
| CM Truck Beds service bodies | Multiple lengths | Varies by length | Steel, powdercoat | Component-configured builds, faster availability |
Source: Reading Truck published product data as carried by OEM Truck Equipment. Confirm current-year specs with your OEM Truck Equipment rep before ordering.
The Master Mechanic series is the cleanest illustration of the whole principle. Reading did not build a 9-foot body and a 10-foot body and an 11-foot body and leave you to figure out the chassis. They built a 9-foot body for a 60-inch CA and an 11-foot body for an 84-inch CA. The chassis and the body are engineered as a pair. Order half the pair and you own an expensive problem.
SRW vs. DRW: why wheel count changes the body you can order
Single rear wheel chassis generally top out at an 8-foot service body on a 56-inch cab-to-axle. Dual rear wheel chassis start at a 9-foot body on 60-inch CA and go up from there. The difference is rear axle capacity and lateral stability, not available frame length.
A loaded service body is not a static weight sitting in the middle of the frame. It is several hundred pounds of steel plus a thousand pounds of tools, parts, and fluids, distributed across compartments that hang outboard of the frame rails. That load wants to roll the truck, and dual rear wheels are what resist it.
Single rear wheel chassis can carry service bodies, and plenty of them do — an 8-foot SRW body on an F-250 or a Ram 2500 is a legitimate, common, useful truck. The limit shows up when the compartments get loaded to capacity. Rear axle rating runs out before frame length does. If your crew is going to fill every compartment, spec the duals.
Most fleets buying dual rear wheel chassis do not need them. They need the payload rating on paper for the one week a year the truck gets loaded heavy, and they pay for duals, a wider track, worse fuel economy, and six tires instead of four for the other fifty-one weeks. If your compartments are half full at the end of every shift, you bought too much truck. Weigh a loaded unit before you spec the replacement fleet.
The three things that get ordered wrong
1. Wheelbase quoted instead of cab-to-axle
This is the big one. A purchasing agent asks the chassis dealer for the specs, gets a wheelbase figure, and passes it to the body supplier. The body supplier cannot size from wheelbase. If the number you were given is 176 inches, that is a wheelbase. If it is 60 or 84 or 108, that is cab-to-axle. Learn to tell them apart at a glance and you will avoid most of the trouble in this article.
2. No clearance allowance behind the cab
The body does not butt up against the cab. You need two to three inches between the back of the cab and the front of the body so the frame can flex without the two rubbing. Trucks work on uneven ground; frames twist. A body mounted tight to the cab will chew the paint off both surfaces inside a season, and on the units we see come back for repair, that rub line is where rust starts.
3. Ordering the chassis before the body is decided
This one is a process failure rather than a measurement failure, and it is the most expensive of the three. The chassis is the long-lead item, so buyers order it first to get in the queue, then pick a body later and discover the CA does not support what they wanted. Decide the body first, then order the chassis the body requires. The body determines the truck. Not the other way around.
“We build thousands of service bodies a year in Okarche, and about three percent of them arrive on a chassis that will not carry the body the customer ordered. Three percent sounds small until you run it against thousands of trucks.”
“Nearly every one traces back to the same thing: a wheelbase figure handed down the line as if it were cab-to-axle. When it happens, the customer picks between a body they did not want and a chassis they have already paid for. Neither is a good morning.”
How to measure and verify before you order
To verify cab-to-axle on a chassis you already own, measure from the rearmost point of the cab straight back along the frame rail to the center of the rear axle hub. Record the figure in inches. Confirm it against the body manufacturer’s published CA requirement before the order is placed.
On a truck already in your yard, this takes one person and two minutes:
- Park level. A slope will not change the horizontal distance much, but it will make the tape sag and cost you an inch.
- Find the rearmost point of the cab. The back wall of the cab itself, not the mirror, not a light bar, not an exhaust stack.
- Run the tape along the frame rail, not along the ground, and not diagonally.
- Stop at the center of the rear axle hub. On a dual-axle truck, stop halfway between the two axle centers.
- Round to the nearest standard step. If you land at 61 inches, you have a 60-inch CA chassis. If you land at 70, something is unusual — call before you order.
On a chassis you are about to order, you do not measure anything. You read the CA off the chassis order guide and you match it to the body spec. If the dealer cannot tell you the CA, they can tell you the exact model and configuration code, and we can look it up.
Pre-order chassis checklist
Run this before the chassis PO goes out. Every line is something that cannot be fixed after the truck is built.
- Body decided first — make, line, and length selected before the chassis is ordered
- CA figure confirmed in writing — from the chassis order guide, not a verbal wheelbase
- CA matches the body’s published requirement — checked against the manufacturer spec sheet, not assumed
- Wheel configuration matches the loaded weight — SRW or DRW decided from a real loaded weight, not a guess
- Rear axle rating verified against loaded compartment weight
- 2 to 3 inches of cab clearance accounted for in the layout
- Frame rating confirmed for any crane, compressor, or aerial device
- Cab configuration confirmed — regular, extended, or crew, since it changes wheelbase but not CA
- Delivery destination confirmed — chassis shipping to the upfitter, not to your yard
Frequently asked questions
What does cab-to-axle mean on a truck?
Cab-to-axle, abbreviated CA, is the distance from the back of the cab to the centerline of the rear axle. It is the measurement truck body manufacturers use to size service bodies, dump bodies, and flatbeds. On a tandem-axle chassis, CA is measured to the midpoint between the two rear axles.
What size service body fits a 60-inch cab-to-axle chassis?
A 60-inch CA chassis takes a service body in the 8.5 to 9.5 foot range, with a 9-foot body being the standard pairing. The Reading Master Mechanic 100-series is built as a 9-foot body on a 60-inch CA. Sixty-inch CA is the most common configuration on dual rear wheel one-ton chassis.
Can I put an 11-foot service body on a 60-inch cab-to-axle truck?
No. An 11-foot service body requires an 84-inch cab-to-axle chassis. Mounting an 11-foot body on a 60-inch CA leaves roughly two feet of unsupported rear overhang, shifts weight behind the rear axle, and unloads the front axle. The body will physically bolt down and the truck will still be wrong.
Is cab-to-axle the same as wheelbase?
No. Wheelbase is measured from the front axle centerline to the rear axle centerline. Cab-to-axle is measured from the back of the cab to the rear axle centerline. Two trucks with identical wheelbases can have different CA figures depending on cab configuration, which is why body length is always specified from CA.
What cab-to-axle do I need for a crane body?
Crane service bodies run from 9 to 14 feet and require 60 to 120 inches of cab-to-axle depending on body length and crane capacity. Reading crane bodies are rated up to 12,000 pounds. Crane applications also require a chassis frame rated for the mounted load, so the CA figure alone does not settle the spec.
Common questions about service body sizing
- How is CA abbreviated on a spec sheet?
- “CA” or “C/A” — always in inches, never in feet.
- Does cab configuration change cab-to-axle?
- No, cab configuration changes wheelbase; CA stays the same for a given chassis spec.
- What is CT and how is it different from CA?
- CT is cab-to-trunnion, used on dump and hoist applications, measured from the cab to the hoist pivot point rather than the axle.
- How much does a service body itself weigh?
- Varies by line and length — confirm the exact dry weight with your supplier, since it comes straight off your available payload.
- Can a service body be shortened to fit a smaller CA?
- Not practically — compartment layout, floor structure, and understructure are all engineered to the body length.
- Can the frame be extended to fit a longer body?
- Frame modification is possible on some chassis but requires engineering approval and is almost always more expensive than ordering the right chassis.
- Do I need a CDL to drive a service truck?
- It depends on gross vehicle weight rating and your state’s rules, not on body length — verify with your state before you spec above 26,000 lb GVWR.
- Does a longer body always mean more storage?
- Not proportionally — compartment count and depth matter more than raw length for most service applications.
- Can OEM Truck Equipment source the chassis too?
- Yes — OEM operates a chassis pool and holds a GM pool designation, so the chassis and the body can come from one order.
- How far in advance should I confirm CA?
- Before the chassis purchase order is issued — after that point the CA is fixed for the life of the truck.
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Send us the spec before you send the PO
OEM Truck Equipment has been building, painting, and installing work truck bodies in Okarche, Oklahoma since 1985, and shipping them nationwide. Send us the chassis you are looking at and the work the truck has to do — we will tell you whether the two match.
Sources
- Cab & Chassis Body Sizing Chart — Quest Fabrication
- Truck Cab to Axle Body Length Chart: Fitment Guide
- Reading Service Bodies — OEM Truck Equipment product data
- Ram 3500, 4500 & 5500 Chassis Cab Specifications — Stellantis media