Technical
PROCEDURE

TRAILER SUSPENSION SYSTEMS


SUBJECT: Recommended Ride Height Settings

LIT NO: L388 
DATE: October 2018
REVISION: I
The tables in this publication list the recommended
or “designed” ride heights for all current Hendrickson
trailer suspensions. The designed ride height helps
optimize suspension performance and helps maintain
load equalization among the axles.

For safety and precautionary statements, refer to
Hendrickson literature number T12007, available at
www.Hendrickson-intl.com/TrailerLit.
I. USING A HENDRICKSON RIDE HEIGHT GAUGE

NOTE: Ride height is just one of many factors that
influence load equalization. Even small
adjustments in ride height (within the specified
range) can impact the way the load is
distributed among the axles.
Operating an air suspension outside its specified ride
height range can reduce ride quality, damage cargo
and increase suspension wear. To take full advantage
of the benefits an air-ride suspension has to offer, each
suspension on the trailer should be operated at its
designed ride height.
Suspension mounting surface
(bottom of trailer or slider box)

A-23445
(Low-ride Suspensions)

A-23442
(Top-mount Suspensions)

Figure 2: Hendrickson ride height gauges

Follow instructions on the gauge (Figure 2) to measure
the distance between the axle and the mounting
surface of the suspension. A ride height gauge works
with both 5-inch and LDA™ Large-Diameter Axles. Just
make sure you are using the proper scale on the ride
height gauge. The tool can also be used as a GO/NOGO gauge.

Ride
Height

Axle
center
Figure 1: Ride height defined

A suspension’s designed ride height is defined as the
distance from the suspension mounting surface (the
bottom of the trailer frame or slider box) to the center of
the axle. See Figure 1.
There are two easy ways to determine a suspension’s
ride height:

NOTE: To order a Ride Height Gauge, contact the
Hendrickson customer service department at
866.RIDEAIR (743.3247) and specify:
A-23442 Ride Height Gauge for conventional topmount suspensions
A-23445 Ride Height Gauge for low-ride
suspensions.

Recommended Ride Height Settings 
II. USING A TAPE MEASURE

Any increase above the specified maximum ride height
can reduce the effectiveness of SURELOK to limit trailer
drop and/or walk. See Figure 4. Conversely, any ride
height set below the specified minimum ride height
value will prevent the SURELOK support arms from
properly engaging. See Figure 5.

1. Measure the distance from the top of the axle to
the mounting surface of the suspension (Figure 3).
2. Add half of the axle diameter to this measurement
to determine your suspension’s ride height.
For example: on 5-inch axles, add 2½ (2.5) inches
to the measured distance, and on LDA™ Large
Diameter Axle, add 27/8 (2.88) inches to the
measured distance.
3. Compare this measured ride height with the listing
in the appropriate table (see page 3 through
page 6).

Measure distance to
suspension mounting
surface and add half
the axle diameter.

NOTE: While we recommend that our suspensions
operate at their designed ride height, they
can be satisfactorily operated within the
range listed in the table applicable to your
suspension model or type.

Place end of tape
on top of axle

If the measured ride height does not fall within the
range listed in the table, the suspension’s ride height
must be adjusted. Refer to Hendrickson publication
L459 Checking Trailer Ride Height, for complete ride
height adjustment instructions.

Figure 3: Measuring ride height using tape measure

If your suspension model number is not listed in the
tables, contact the Hendrickson technical service
department in the United States and Canada at
866.RIDEAIR (743.3247) for ride height range
information.

DESIGNED RIDE HEIGHT AND SURELOK®

Figure 4: Ride height set too high

SURELOK® is a ride height locking device that uses
mechanical support arms to maintain the trailer’s
height for efficient trailer loading. When engaged, the
mechanical support arms help limit trailer “drop” and
“walk” during the loading/unloading process.

A. If ride height is set above the specified maximum
value (Figure 4), the trailer has the potential to
exhibit excessive “walk” and/or drop before the
SURELOK support arms can contact the beam and
maintain trailer height.

NOTE: Refer to Hendrickson publications L816,
DOCK SOLUTIONS or T15001, TRAILER AIR
SUSPENSIONS CONCEPT AND FUNCTIONS for a
complete description of trailer drop and walk.
If a suspension is equipped with SURELOK, it should
be operated as close as possible to its designed
ride height. Suspension ride height is the primary
consideration for optimal SURELOK performance
(not the amount of clearance between the SURELOK
support arms and the suspension beam). When the
suspension is operated at its designed ride height, the
SURELOK support arms will have the proper clearance
from the suspension beams.

Figure 5: Ride height set too low

B. If ride height is set below the specified minimum
value (Figure 5), the SURELOK support arms (shown
in retracted position) cannot contact and properly
engage the beam.
2

L388 I

Recommended Ride Height Settings
INTRAAX® AAT 23K, AAT 25K & AAT 30K LARGE DIAMETER AXLE RIDE HEIGHT SETTINGS*
SUSPENSION
TRAVEL

STANDARD

HIGH CONTROL

LIMITED REBOUND

LIMITED JOUNCE

ZMD® STANDARD 1

ZMD® LIMITED REBOUND 1,2
1
2

DESIGNED
RIDE HEIGHT

MINIMUM
RIDE HEIGHT

MAXIMUM
RIDE HEIGHT

13.5"

13.25"

15.75"

14"

13.25"

15.75"

15"

14.25"

15.75"

16"

15.25"

17.75"

17"

16.25"

17.75"

18"

17.25"

19.75"

19"

18.25"

19.75"

13.5"

13.5"

16"

14"

13.5"

16"

15"

14.5"

16"

16"

15.5"

18.5"

17"

16.5"

18.5"

14"

13.25"

14.5"

16"

15.25"

16.5"

18"

17.25"

18.5"

14"

14"

15.75"

15"

15"

15.75"

16"

16"

17.75"

17"

17"

17.75"

14"

13.5"

14.5"

15"

14.5"

15.5"

16"

15.5"

16.5"

17"

16.5"

17.5"

14"

13.5"

14.5"

16"

15.5"

16.5"

Option available for AAT 23K models only.
Option available for RCA Raised Center Axle only.

INTRAAX® AANT 23K, AAZNT 23K, AAZNT 46K & AAZNT 69K RIDE HEIGHT SETTINGS*
SUSPENSION
TRAVEL

STANDARD

1
2

DESIGNED
RIDE HEIGHT

MINIMUM
RIDE HEIGHT

MAXIMUM
RIDE HEIGHT

12"

11.75"

13"

13.5"

13.25"

15.75"

14"

13.25"

15.75"

15"

14.25"

15.75"

16"

15.25"

17.75"

17"

16.25"

17.75"

18" 1

17.25"

19.75"

19"

18.25"

19.75"

Ride height not available on AANT 23K models.
Option available for AANT 23K models only.

* If any of these suspensions are equipped with SURELOK®, they should be operated as close as possible to the designed ride height. Refer
to the section titled DESIGNED RIDE HEIGHT AND SURELOK® on page 2 for details on how an improper ride height can reduce the
effectiveness of SURELOK to limit trailer drop and/or walk, or prevent the SURELOK support arms from properly engaging.
L388 I

3

Recommended Ride Height Settings 
INTRAAX® AANT 23K, AAZNT 23K, AAZNT 46K & AAZNT 69K RIDE HEIGHT SETTINGS*
SUSPENSION
TRAVEL

ZMD® STANDARD 2

HIGH CONTROL

LIMITED JOUNCE

LIMITED REBOUND
1
2

DESIGNED
RIDE HEIGHT

MINIMUM
RIDE HEIGHT

MAXIMUM
RIDE HEIGHT

14"

13.5"

14.5"

15"

14.5"

15.5"

16"

15.5"

16.5"

17"

16.5"

17.5"

13.5"

13.5"

16"

14"

13.5"

16"

15"

14.5"

16"

16"

15.5"

18.5"

17"

16.5"

18.5"

14"

13.25"

14.5"

16"

15.25"

16.5"

14"

13.25"

14.5"

16"

15.25"

16.5"

18"

17.25"

18.5"

DESIGNED
RIDE HEIGHT

MINIMUM
RIDE HEIGHT

MAXIMUM
RIDE HEIGHT

14"

13.75"

15.25"

Ride height not available on AANT 23K models.
Option available for AANT 23K models only.