2004 Volkswagen Jetta Upgrading the tires

  • 2 POSTS
  • 2.0L
  • 4 CYL
  • FWD
  • 100,000 MILES

If anyone can guide me on this issue I'd be very thankful. The current tire size on my VW Jetta Wagon 2004 is 195/65R15, I'd like to add an inch to it in terms of ground clearance. Would it be OK if I go with 205/70R15 I've found there's ample space in the wheel dome area? Please let me know if I'd be running into any other technical issues?

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Tuesday, June 2nd, 2015 AT 5:47 AM

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The first thing to be aware of is if you have anti-lock brakes, the outer circumference of all four tires must be the same for that system to work properly.

The second thing is if ground clearance is a problem, the coil springs should be suspect. The people at any tire and alignment shop will have a small book that shows where to measure on your car and what those measurements should be. Sagged springs let the car sit low by altering the geometry of the suspension parts. Larger tires won't fix that geometry. There's a number of things to be concerned with there. First, the numbers on the alignment computer may show your car to be set perfectly, but those numbers only pertain to a car that's standing still. When driving on normal roads, the wheels are going up and down and the suspension parts will travel through the wrong arcs when the springs are weak. That will result in accelerated tire wear even though the alignment appears to be perfect.

The next concern is you're going to messing with a non-adjustable angle called "scrub radius". If you stand in front of the car and look back at the upper and lower steering pivots, the lower ball joint and the upper strut mount in your case, and draw an imaginary line through them, that line must intersect the tire tread at a very specific point where it meets the road surface. If you alter the diameter of the tire, the width of the tire, or the "offset", meaning how far the middle of the wheel is moved out, it will change scrub radius.

Scrub radius has been very carefully designed in to provide balanced braking when you lose half of the system and one front brake. Correct scrub radius makes the car stop easily in a straight line with only one working front brake. With altered scrub radius, the steering wheel can just about tear your hand off when you brake with one front brake not working.

Even with properly working brakes, scrub radius affects steering response, handling, braking stability, and comfort. Lawyers and insurance investigators know all about scrub radius and will use it to convince a jury that you were partly at fault for the crash when the other guy ran the red light. They will say you were less able to avoid it, and they will be right. This is why no conscientious mechanic will raise a customer's truck or lower their car. Doing so can make them party to a lawsuit.

Now that I've given you the warnings, look on the door sticker where they list the tire size. If there is an alternate size listed, the engineers have determined you will not adversely affect the handling or braking by switching to what may have been an optional size from the factory. In that case you can use the larger size, but only if all four are the same. You may need to have the dealer program the new size into your Engine Computer so it can calculate the correct road speed so the speedometer will read correctly.

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Tuesday, June 2nd, 2015 AT 10:08 PM

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