2002 Ford Expedition transmission

Tiny
CDUB0205
  • MEMBER
  • 2002 FORD EXPEDITION
  • 5.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
I was wondering if getting 24 inch rims will damage my transmission. A few guys at work said my transmission wouldnt handle them. It has a tow capacity of 8100lbs. Does it effect anything else on the car?
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Monday, January 27th, 2014 AT 3:57 PM

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Tiny
CARADIODOC
  • EXPERT
The transmission doesn't care what kind of wheels it's turning. Other than looking ridiculous, what you really need to worry about is changing the tire's outer circumference and wheel offset. Those things, along with suspension ride height affect a non-adjustable alignment angle called "scrub radius". If you look back from in front of the vehicle and draw an imaginary line through the upper and lower ball joints which are the steering pivots, that line was very carefully-designed to intersect the road surface in the middle of the tire tread. The half of the tire to the left of that point wants to scrub on the road and pull the steering system to the left. The other half of the tread wants to pull it to the right, and those two forces offset each other. When you do anything to alter scrub radius, especially when you alter ride height, that changes significantly. The tire will react to every little bump in the road instead of canceling them out. That makes for an extremely tiring vehicle to drive.

Scrub radius also has a big effect on handling in corners and braking. The brake hydraulic system is designed around a specific ride height, weight distribution, and weight transfer. When kids lower cars, they get the false illusion the car handles better and brakes in a shorter distance. In fact, less weight than normal transfers to the front under hard braking so the front brakes can lock up easier. A skidding tire has no traction or steering control so you can't press as hard as normal on the brake pedal. More weight stays on the rear wheels but those brakes don't get more stopping power.

You can be very sure lawyers and insurance investigators know all about scrub radius and will use it against you when they're trying to shift the blame from their client to you. That other guy may have run the red light but they will convince a jury that you were partly at fault for the crash because you were less able to avoid it, and they will be right.

I know that covers a lot more than you asked, but I'd rather you be informed before you start altering things. As a former suspension and alignment specialist, I make sure all of my cars, including a few '70s muscle cars, are exactly at the specified height, and nothing has been altered that could have me answering questions in front of a jury.
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Monday, January 27th, 2014 AT 4:47 PM

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