The only oil or grease that would get on a tone ring would be from the outer cv joint if the boot was ripped. Dirt isn't normally a problem because the sensor's magnetic field goes through that. Sometimes rust can build up on the tip of the sensor and that can interfere with its ability to generate a signal.
Larger tires will make the van go further with each revolution so the speedometer will read lower than your actual speed. On Chrysler products the "pinion factor" is set with a scanner to match tire size and axle gear ratio. I don't know if Fords are the same way. On older vehicles we changed the gear at the end of the speedometer cable to one with a different number of teeth.
You have to be more specific with "jittery". Do you mean how the engine is running? Shaking in the steering wheel? Where do you feel it and what do you feel?
Changing tire size affects a secondary alignment angle called "scrub radius". You won't notice that with tires that are just one size larger but when people start putting big mud tires on raised-up trucks, or when kids put low profile tires on lowered cars, scrub radius changes a lot and will adversely affect braking performance and handling. Scrub radius is not an adjustable angle. It is designed in as part of the steering and suspension geometry and helps all of the parts work together. Lawyers and insurance investigators love to find modifications that affect handling and braking. They will convince a jury that you were partly at fault for the crash when the other guy ran the red light because you were less able to avoid it, and they will be right. That's why in my classes at a community college, we never allowed anyone to modify the ride height or any part of their vehicles that affected the way it was designed.
Wednesday, February 6th, 2013 AT 6:04 AM