what is the effect of using a bigger rolling radius on a tyre, e.g from 185/65 R14 to 205/50 R16?

Answer 1

Any move to a bigger-than-stock rolling radius will cause your speedometer to read low, and your odometer to read fewer miles than you have actually traveled. It will also make your car sluggish off the line, as it has the same exact effect as installing taller gears or an overdrive. If you correct the speedometer, you may notice a slight increase in fuel economy, but only if you spend a lot of time in high gear. You may notice a decrease in fuel economy if you spend a lot of time in stop and go traffic. You also may find that you have tire/fender clearance issues as the tires will be taller than stock. Replacing the tire/wheel package currently on your car with the new tire/wheel package that you are suggesting without correcting your speedometer will generate a speedometer and odometer error of -2.5 percent, meaning that for a given indicated speed, you are traveling 2.5 percent slower, and for a given odometer reading, you will have traveled 2.5 percent fewer miles than indicated. This tire will also be an increase over the height of the original tire by about .5 inches, as well as a width increase of about an inch. I doubt that you will have tire/fender clearance issues with this minor of a tire size increase, but because they are wider you need to make sure when you get them installed that there are no suspension/tire clearance issues when you turn the wheels full left and right lock, especially if the new wheels have a different offset than stock. Offset is the distance from the back side of the rim to the mounting surface where the wheel rests on the hub. If the offset is too great, the tires may rub the suspension parts, if it is too small, your car can be hard to steer at low speed, it may handle strange, and the tires may hit the fenders when the suspension compresses. Lots of things to consider when you alter a stock set of wheels and tires, eh? Here's a good web site to help you.

http://pw1.netcom.com/~sgalaba/tiresize.htm

Answer 2

The main complaint is the speedometer readings are off by a few miles per hour or a whole lot.

The other thing is that you will acutally have less traction on wet roads and icy and snowy roads. You spread out the weight over a wider area and this means good traction on dry pavement but terrible traction on wet and snow covered pavement.

Good Luck!

Answer 3

to add to me again's great answer, you also increase to rotational mass of the wheel. This puts more stress on the braking system, sometimes beyond what it was designed to do. This may or may not be the case with your vehicle, I see the most problems with people who put 20"+ rims on there cars. the most common problems are increased brake pad wear, warped rotors/ ground rotors and hung up calipers.

Answer 4

your speedo will be off, it will say you are going slower than you really are! think about it a bigger radius covers more distance in one rotation than a smaller radius. so one rotation of a small tire may cover two feet one rotation of a bigger tire will cover three feet but the car still thinks it has only traveled the two feet

Answer 5

Larger radius means larger circumference. Ideally, that would mean increased gas mileage, but, unless approved by the manufacturer, it may well not be a good idea.