urbexHHR

Ok, so I just bought a set of 17s for my HHR, and I currently have the factory 16s. So, dumb question...but will this throw off my speedometer? If so, does anyone know which way it will go? Like, will it say I'm going faster than I am or slower?

SmootHHR

if you buy tires that have less sidewall then the speedo will stay the same. Just need to make sure that the overall diameter is the same as stock 16's.

djr1973

Hey Eric, when I first bought my car and they put the 16" wheels off of my other HHR, I asked about it and the service manager at the dealership where I got my car from told me it would only make it off by 1/2 mph, but I cant remember if it was faster or slower.

urbexHHR

Well that's what my dad said, be he wasn't 100% sure....

Yeah, I figured it wouldn't be off by much though. I was hoping that if it is, it speeds it up a little...because according to my GPS it's 1mph off. It says I'm going 60 when I'm really going 59.

solman98

Going from a 16" to a 17" is easy, just use the 215/50R17. Same height (or extremely close) to the 215/55R16.

Want to compare others:

http://www.1010tires.com/TireSizeCal...?action=submit

urbexHHR

Cool! Thanks for that link...

So, could I use 215/45R17? I know it's a little different, but it adjusts the speedo about 2mph so that would possibly fix mine from being slightly off.... Otherwise if I use the 215/50R17 that would add another 1/2 mph off more to mine...

djr1973

I know when I was gonna put 17's on my car I was looking at 225 or a 235 for the width, but not sure about the hieghth. If you goto discounttire.com you can look up for the stock tires for the 17's and there is a link that shows plus size tires and there is also a calculator that figures the difference between the two different size tires, and also will tell you how much your speedo will be off.

solman98

You could, but if your concerned about accuracy, I would stick with the 215/50. It's only .4 MPH too slow off verses 1.7 MPH too fast with the 215/45.

Slow means you will get that extra .4 miles not added to each 60 miles you drive.....

urbexHHR

But really it'd be 1.4mph too slow since I'm 1 off now.... Otherwise it'd be .7 too fast....

I do have some time to think though...looks like a set of tires will run anywhere from $500-$600 easily... Quite a bit when I don't need them now anyways.

mongo

Rule of thumb:

Larger diameter means you will be going faster than indicated speed, smaller diameter means slower than indicated speed.

Here's why-

If you multiply the diameter of the tire (not just the rim size, the actual 'height' of the tire) times pi (3.1416 is close enough) you will get the circumference, or how far the car travels on each rotation of the wheel.

Lets assume a 27" tall tire.

27" x 3.1416 = 84.8232" (how far you've moved in one revolution)

Go up one inch in diameter to a 28" tall tire.

28" x 3.1416 = 87.9648"

You travel a bit over 3" further per revolution.

When you are building a 4x4, this calculation is important since tire sizes often increase a foot or more, so you need to re-gear to get your low end torque back.

For example, going from a stock 215/75-15 to a 31x10.50-15 required me to go from a stock 4.10:1 axle ratio to a minimum of 4.56:1. I went to 4.88:1 as I wanted more pulling power out of my little 4 banger Jeep.