1998 Toyota Revo Tires Upgrade

Tiny
RESTYTORRES
  • MEMBER
  • 1998 TOYOTA REVO
  • 1.7L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 165,000 MILES
I wanna upgrade my tires from stock to 16" rims, question is what width and offset I need for the bigger rims to make it work? Further, what's the bolt pattern of the stock tires? Your assistance will be highly appreciated.

Resty Torres
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Sunday, February 16th, 2014 AT 2:08 PM

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Tiny
CARADIODOC
  • EXPERT
That is hardly an upgrade. You can do a search for salvage yards in any state, then select through their drop-down menus to look for original wheels. You'll get another list of all the original wheel dimensions that were available for your model and year. The door sticker will list the original wheel size your truck came with.

Be aware that anything you do to change the wheel offset, or the tire's outer circumference could make you party to a lawsuit. The guys who sell aftermarket wheels won't tell you that and risk losing a sale. When you alter either of those things, or especially if you alter the ride height, among other things you change a non-adjustable alignment angle called "scrub radius". That was carefully designed in and has a big affect on braking, handling, and steering control.

To visualize scrub radius, look back from in front of the truck, and draw an imaginary line through the upper and lower steering pivots. Those are the upper and lower ball joints, or the upper strut mounts and lower ball joints. I don't know what a Toyota Revo is so I can't look up which suspension system it has. That line is designed to intersect the road surface exactly in the middle of the tire tread. The left half of that tread wants to "scrub" on the road surface and makes the tire want to pull to the left. The right half wants to pull to the right. Those two forces offset each other so the tire tends to go straight.

Most front-wheel-drive cars have a "split-diagonal" brake system so if one hydraulic system has a failure, there will still be one front brake working. That would tear the steering wheel out of your hands and be impossible to control, except the engineers modified scrub radius just a little to account for that. Now if just the left front brake is working, for example, that tire would pull real hard to the left during braking, and you'd need both hands to try to hold the steering wheel straight, but thanks to the modified scrub radius, the right 5/8 of the tire tread pulls harder to the right than the left 3/8 pulls to the left. Chrysler has that so perfected that you may not even know there's a brake failure. On all other cars all you'll see is a little twitch in the steering wheel, but the car will stop in a straight line. Altering scrub radius blows all that design work out of the water, and lawyers and insurance investigators know it. They will use that when trying to shift some of the blame for the crash from their client who ran the red light, onto you. They will convince a jury that you were partially at fault because you were less able to avoid the crash, and they will be right. That is my reason for giving you this reply.

The only way to know for sure that scrub radius hasn't changed with different wheels and tires is if all the important dimensions remain the same. It IS possible to change multiple dimensions and return to the original scrub radius, but we have no practical way to measure it. If you simply use a wheel with a larger diameter, and a tire with a corresponding smaller diameter, scrub radius won't change, as long as the wheel's offset and width are the same. You'll simply lose some ride quality. You can measure the old and new tires' diameter or circumference to see if they're the same, then measure between the inner edge of the tread between the two tires, on the ground, and the two outer edges. If those measurements are the same with the new wheels and tires, you likely will not have altered scrub radius enough to notice.

By the way, scrub radius also contributes to ride quality. When it is wrong, each half of the tire does not offset the other half's pull equally, but each tire still offsets the other tire. When one tire hits a bump in the road, the momentary increase in weight makes it more than offset the other tire. If the left tire hits that bump, it's going to tug the steering linkage to the left. You may interpret that as "increased road feel" at first, but on longer trips that becomes very tiring. I've had street-legal cars used for oval racing in the '70s and '80s, with wider wheels and tires, and believe me, after driving home 30 miles after the races, you're quite happy the ordeal is over with. Most of us put the proper wheels and tires back on for the rest of the week.

This gets further complicated when just one half of a tire's tread hits a bump, like a small rock. It happens very quickly but that part momentarily has more weight on it, and it tends to lift the other half of the tread up a little, reducing the weight on it. That exaggerates the effect of the bump. Wider tires and wheels with more offset make the effects of those road bumps more noticeable, and over time they add up to making the vehicle very tiring to drive. You may think you can't notice the "busy" steering wheel, but over time your arms will. All manufacturers have put so much research into ride quality and safety, that the poorest of car models ride and handle better than any car from the '60s. There's little chance you or I are going to improve on that.

I really hope you don't plan on altering ride height. If you do, I'll take as much time as necessary to explain why that reduces your braking, handling, steering response, and comfort.

When you talk with your tire and wheel salesman, explain that you want to maintain the original scrub radius and ride height. If they don't know what you're talking about, they're after your dollars, not your best interest. Find a different salesman or store.
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Sunday, February 16th, 2014 AT 6:30 PM

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