Shock Travel

Front view · camera fixed to the frame 2.5 x 20 smooth body

0.0 in · ride height

Shock length shock stroke travel needs

30.5 incollapsed 50.5 inextended

Travel needs 22.9 in to 36.7 in: 13.9 in of stroke. 7.6 in shorter than the shock collapses.

Verdict

Make it fit: move the upper mount from 20.0 in to 30.8 in above the frame bottom. Nothing else changes.

Too long to install at this ride height The mounts are 26.8 in apart at ride height, but the shock is 30.5 in fully compressed. Raise the upper mount or lower the axle mount.
Where the upper mount has to go With these mount positions and 4.0 in up / 10.0 in down from ride height, this shock fits with the upper mount 27.7 in to 33.8 in above the frame bottom (20.7 in to 26.8 in above the top of the rail).
Upper mount sits 13.0 in above the frame That is shock hoop or through-the-hood territory on most trucks. Check hood, fender and engine clearance.

Travel: 4.0 in up · 10.0 in down
Stroke used: 13.9 in of 20.0 in
At ride height: 26.8 in · shorter than collapsed
Shock per inch of wheel: 0.99
Angle from vertical: 6° in droop · 9° in ride · 10° in bump

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Examples

Shock

30.50 in collapsed · 50.50 in extended · 20.00 in stroke. estimated No listing found. Estimated from the 16 and 18 in shocks: each adds about 10 in beyond its travel, and longer shocks add a little more.

Mounts

Upper mount above frame bottom in

Green: 27.7 in to 33.8 in keeps this shock inside its stroke.

Upper mount from centerline in

Lower mount above axle centerline in

Lower mount from centerline in

Travel and ride height

Up travel at the wheel in

Down travel at the wheel in

Ride height change in

Positive lifts the frame away from the axle.

Stops move with it: same up and down travel Stops stay put: lift trades up travel for down

Limit straps

Truck

Tire diameter in

Track width in

Frame bottom above axle at ride in

Frame rail from centerline in

Every shock at these mounts

Where the upper mount has to be for each shock to cover 4.0 in up and 10.0 in down. Click a row to try it.

Shock	Length	Upper mount above frame bottom	Above the rail	Here
2.5 x 8	16.00 to 24.00	Too short: travel needs 13.9 in of stroke		Problem
2.5 x 10	18.38 to 28.38	Too short: travel needs 13.9 in of stroke		Problem
2.5 x 12	20.65 to 32.65	Too short: travel needs 13.9 in of stroke		Problem
2.5 x 14 short body	21.75 to 35.75	18.9 to 19.0	11.9 to 12.0	Problem
2.5 x 14	23.25 to 37.25	20.4 to 20.5	13.4 to 13.5	Problem
2.5 x 16	26.00 to 42.00	23.2 to 25.3	16.2 to 18.3	Problem
2.5 x 18	28.00 to 46.00	25.2 to 29.3	18.2 to 22.3	Problem
2.5 x 20*	30.50 to 50.50	27.7 to 33.8	20.7 to 26.8	Problem

* Estimated length; no listing found.

This shock at other ride heights

Stops move with ride height, so the travel stays the same and the shock lengths shift.

Ride height	Up	Down	Spare at bump	Spare at droop	Compressed at ride
-3 in	4.0	10.0	-10.6	16.8	n/a	Problem
-2 in	4.0	10.0	-9.6	15.8	n/a	Problem
-1 in	4.0	10.0	-8.6	14.8	n/a	Problem
design	4.0	10.0	-7.6	13.8	n/a	Problem
+1 in	4.0	10.0	-6.7	12.8	n/a	Problem
+2 in	4.0	10.0	-5.7	11.8	n/a	Problem
+3 in	4.0	10.0	-4.7	10.8	n/a	Problem
+4 in	4.0	10.0	-3.7	9.8	99%	Problem

How this works

Front view, with the camera fixed to the frame, so the axle and the ground move. Lengths are in inches, eye to eye.
Up and down travel are measured at the wheel center from ride height. The drawn bump stops and straps are placed to give that travel in parallel bump and droop.
Flex puts one wheel at full bump and the other at full droop, through ride height. Real flex may stop sooner, at a tire, a link or a driveshaft.
A shock inboard of the wheel moves less than the wheel. Leaning it moves it less again, and the ratio changes through travel.
Bump stop compression, bushing deflection and fore-aft mount offset are not modeled. Leave margin at both ends.
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Shock lengths for 8 to 18 in come from reseller listings for the King 2.5 smooth body remote reservoir. The 20 in is an estimate. Check the maker's sheet before you build.