Page 68 - Issue 49

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II
Tinman Kustoms

Ditching the straight Axle: Part 2 (IRS)

PHOTOS AND WORDS BY LUKE MERRILL (TINMAN 2 KUSTOMS)

WOOFTA! That’s a scary title. Fortunately this article is not on the IRS that might
give you the goosebumps: rather, it’s based around “Independent Rear Suspension”.
IRS is a somewhat modern form of suspension which was initially developed by
European engineers in the 1950’s. The design of an IRS is very similar to the design
of an IFS (my previous article), but with some important differences; the largest
being the addition of a drive axle (in rear wheel drive applications).

Keywords To be unique and offer the most (aka drifting, drag racing, etc.),
modern ride quality, I am installing & more confusing to setup & align.
Camber: The angle of the wheel/ bagging a 2017 Mustang IRS setup Function of IRS
tire in relation to perfectly vertical in the 1940 Chevy that I am building
(When looking at tread of the tires) for my Mom & entering into the 2018 The primary purpose of independent
SEMA Battle of the Builders. While suspension is to keep the wheels in
Caster: The angle of an imaginary
this one is going to be a high quality maximum contact with the ground
line between the balljoints, in
(painted) street rod build, I saw this at all times. The wheels essentially
relation to perfectly vertical (when
as a great opportunity to give ya’ll act independent of each other, so
looking at the face of the wheel)
a little rundown on how they work if you hit a pothole on one side, the
Toe: The relative parallel-ness and some of the benefi ts, as I have other side is not affected. This helps
between each tire on each side a feeling this will become a more keep one tire in maximum contact
of the vehicle (when looking common swap in the years to come. with the road at all times, which
overhead) leads to the best ride & handling.
Pros & Cons of IRS There is also less “unsprung”
Sagitta: Lateral movement
Pros: Appearance (can look very weight. Basically, this means there
(defl ection) of any component
unique), handling, adjustability, is less weight that isn’t dampened
traveling on a radius (i.e. link bars,
compactness, no change in pinion by the suspension, which leads to a
trailing arms, etc.)
angle because suspension travels more stable ride.
Subframe: A section of frame independently of axle housing. Although many of us “Rat-
that is removed from a uni-body Cons: More moving parts to Rodders” are resourceful and
Vehicle. In my case it’s a complete potentially repair, more “points of ingenuous: The factory designed
assembly including axle housing, weakness” or “points of fl ex” for IRS assemblies are tried & true.
axles, control arms, etc. high power and/or high load driving You may be able to engineer and/

68 RAT ROD MAGAZINE ISSUE FORTY-NINE

68x72tinman.indd 68 4/23/18 10:52 AM