Thinking about new tire size

[~MRVIBE2006~]

I know that the suggested size for a 17" wheel is 225/45. I did a little figuring with the tire calculator about another size (225/50). Would this be too big? The calculator says that it would only be exactly one inch bigger than suggested size. Is this a bad thing? Possible fitment problems? Was just wonderin'.

[manicdan]

if your rim is 7" deep then 225/50 is right, if its 6.5 then i think they suggest 205/55. compare our stock 16" with 205/60 to the 225/50 on 17s, its like .3% difference.

[Raven]

225/45/17 is the correct size. 225/50/17 is nearly 4% too big. The 50s may be cheaper but don't do it.The 45s are nearly a perfect match, the car will handle better and there will be almost no speedometer error.

[~MRVIBE2006~]

I understand that the 225/50 is a little bigger than the 225/45 (an inch but the tire calculator). But how do you figure the percentage difference? Is it by the circumference or the diameter difference? I thought the 50's might be a better ride.

[prathman]

Quote, originally posted by Sunny »225/45/17 is the correct size. 225/50/17 is nearly 4% too big. ...The 45s are nearly a perfect match, ...there will be almost no speedometer error.Seems unlikely. Both of our Vibes have about a 4% speedometer error (they read faster than actual) using the stock tires. Using replacement tires that are 4% larger than stock would therefore lead to a much smaller speedometer error than using replacement tires that are nominally compatible.To MrVibe2006:The percentage difference is the same whether based on diameter or circumference. I.e. you might have a 25" diameter stock size and therefore a 26" diameter replacement is 4% larger. The stock circumference would be 78.5" and the replacement would be 81.7" - also 4% larger.

[~MRVIBE2006~]

Ok, no offense, but now I'm lost. So using a tire that is almost 4% bigger than stock is GOOD because the stock size tires run 4% off anyway?

[prathman]

Quote, originally posted by ~MRVIBE2006~ »Ok, no offense, but now I'm lost. So using a tire that is almost 4% bigger than stock is GOOD because the stock size tires run 4% off anyway? I was only commenting on the speedometer accuracy issue. At least on our two Vibes using a tire with a diameter about an inch larger than stock would make the speedometers read more accurately than they do now. But there are other issues as well. Primary would be if there's any chance of the tire rubbing on the wheel well or any suspension parts. I'd think there's enough clearance, at least if the car isn't lowered, but I'd check a little more carefully first before getting bigger diameter tires. The bigger tires also change your effective overall gear ratio, so the engine would be running a little slower for a given speed and gear. That should be a slight plus for fuel economy and a minus for performance. A 4% change is pretty small (people who change the drive axle gears usually go for much larger changes), so I wouldn't expect the change to be very dramatic in either the pro or con direction. The larger tire sidewall would also be expected to have slightly worse handling (more sidewall flexing) but better comfort and ability to handle potholes and obstacles - the increased ground clearance is also good for this.

[~MRVIBE2006~]

So, you're saying that a 50 series tire would be ok to put on a 17" wheel knowing that I would be sacrificing handling (I don't do autocross), have more protection for potholes (especially here in central IN), and the possibility of the speedo off a couple of ticks? I guess the thing to do is to take a couple of measurements to see about clearance issues huh?

[Raven]

There's no problem with clearance even if the car is lowered. I have 205/60/16 snow tires which are also about 4% taller and Tein S-Tech lowering springs (2" drop) and drive on the roughest roads in North America here in Quebec. They don't come close to rubbing.