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Components affected by a wheelbase change

This was written as an answer to posts which ask, "why doesn't Chrysler just make a longer/shorter version of that vehicle?"

The following components are affected by a wheelbase increase (in this case, a pickup truck):

Frame group:

  • Lengthened left and right frame rails; upgraded material thickness if needed by by torsional and bending analysis
  • Additional frame crossmember if needed by torsional and bending analysis
  • Revision of location of cab mounts
  • Revision of body mounts

Suspension group-rear:

  • Revised spring rates
  • Revised shock damping rates
  • Upgraded axle if needed by vehicle dynamic analysis
  • Revised spring rate on anti-sway bar
  • Revised spring bushings
  • Revised anti-sway bar busings
  • Revised axle ratios (if changed axle)
  • Revised breakover angles on rear tire approach
  • Revised rear departure angle on rear tire departure
  • Revised tire rating selection for higher weight (if increasing wheelbase)

Brake group-rear:

1. Revised ABS calibration
2. Revised brake size
3. Revised emergency brake size
4. Revised emergency brake cable length and thickness-rear
5. Revised emergency brake cable length and thickness-front
6. Revised emergency brake equalizer

Fuel System group:

1. Revised fuel feed line-length
2. Revised fuel return line-length
3. Revised fuel pump suction and pressure values-if needed for revised length
4. Recertification of emissions due to pump change- if needed (FMVSS/EPA regulations)
5. Recertification of Rear Crash compliance due to pump change- if needed (FMVSS/EPA regulations)

Suspension group-Front:

1. Revised spring rates
2. Revised shock damping rates
3. Upgraded axle-4x4 if needed by vehicle dynamic analysis
4. Revised spring rate on anti-sway bar
5. Revised spring bushings
6. Revised anti-sway bar busings
7. Revised axle ratios (if changed axle)
8. Revised breakover angles on front tire departure
9. Revised front approach angle on front tire approach
10. Revised tire rating selection for higher GVW
11. Revised steering geometry to acommodate 10" increase. May require new knuckles due to decreased ackermann effect and increased tire wear

Brake group-front:

1. Revised ABS calibration
2. Revised brake size
3. Revised caliper hose length for revised steering geometry

Exhaust system group:

1. Revised intermediate pipe length
2. Revised pipe size if required due to increased backpressure (from increased length)
3. Revised silencer configuration and size if required due to other changes to exhaust system
4. Recertify MVSS and Australian Rule 95 "pass by noise" requirements

Driveline group:

1. Lengthen propshaft as needed and check critical speed and NVH characteristics
2. If a problem in item 1, convert to 2 piece propshaft with NVH damper integral with center bearing and slip shaft
3. If item 2 needed, configure revised frail rail crossmember details and location for center bearing support crossmember

Electrical group:

1. Lengthen main body harness to acommodate length change
2. Lengthen aux harnesses (trailer towing lights, electrical brakes, etc.) if required to acommodate length change

Body Group:

(Assumption here is that the increase in length is in the [truck] cab and cowl area, utilizing the existing tooling bed and bed underbody components)

1. Verify rear axle geometry tire "beehive" has acceptable clearance to body wheel house and underbody components
2. Verify front tire "beehive" has acceptable clearance to body wheel house and underbody components
3.Above in addition to normal body redesign processes

Vehicle testing:

1. Recertify frontal crash compliance
2. Recertify fuel system integrity compliance
3. Recertify emissions compliance
4. Recertify misc certifications for EU. Japan, Australia, etc....

As you can see, there is a bit more than "hack and whack" to make a wheelbase change. Money costs would be in the $250-300 million dollar range, in my opinion.

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