So, I went to Discount Tire and ordered my tires that I will have installed on the stock wheels for winter use. However, the size of the tires I picked were not in stock. Also, they didn't have any available TPMS sensors, so those are also on order. I'll have to go back Saturday to get everything installed.

Now my dilemma.

The stock tire size for my car is 235/50/18, however they do not make the Yokohama AVID TRZ tires in that size. Therefore, I thought I'd go with 225/50/18 instead. With this other tire size my speedo would be off 1.4% too fast, reading 60 MPH when I'm actually going 59.1 MPH. The sidewall would be 0.2 inches shorter, the diameter would be 0.4 inches smaller, and revs per miles would go from 740 to 751.

But since the 225/50/18 wasn't in stock he set me up with 225/55/18's. With these tires the difference from stock is as follows. My speedo would be off 1.8% too slow, reading 60 MPH when I'm actually going 61.1 MPH. The sidewall would be 0.3 inches taller, the diameter would be 0.4 inches larger, and revs per miles would go from 740 to 727.

What tire size should I go with, 225/50/18 or 225/55/18? The salesman mentioned that the smaller tire could put stress on the transmission and it's not a size that my car should use, but the larger tire is fine. Is this true?? I personally wouldn't think it would matter at all as long as the change isn't drastic. With both tires there's going to be a difference from stock, I'm just curious what you all would think about this. I need to call them today to make a change before they place the order.

Thanks all!

 

No help?

 

I hope a member that is better suited for tire sizes can give you some help, but to me the taller tire sounds like it might not be a great idea, I don't know about your clearance, but it might rub on the rear?

 

Thanks!

 

The reason I mention that is because if I were to take your stock tires and put them on my car, if the numbers are 235/50/18 it will rub in the rear, but a 235/45/18 won't. So maybe the 5 number difference would be bad for you also.

 

OK. You don't see, in any way, that this would affect my transmission do you? I didn't believe him, but I'm curious about what others here would think.

 

IDK I see people running low profile tires all the time, and I never heard of anything about the transmission being ruined because of it?

Is there a tire forum that you can quickly look that up on?

 

1. The Speedometer
   The speedometer in almost every vehicle runs off the speed of the transmission, not the actual tires. However, some old Volkswagens and other makes and models do have a speedometer cable that runs directly to the front wheels, but this is extremely uncommon. The gears that are rotating inside the transmission will spin at a known rate for every speed the vehicle travels at, and this is transferred to the speedometer via a magnetic current known as an "Eddy Current." The faster the gears spin, the more electromagnetic field is created and the further the needle goes up on the speedometer in the dashboard. Therefore, as long as the wheels and tires are stock sized, the speedometer will read accurately. Let's look at why changing tire size would affect the speedometer.
2. Altered Tire Size
   For those who have off-road vehicles and put larger tires on for better performance on the trail, the speedometer will be affected. Since there is more surface area and a larger circumference on the outside edge of the tire, the wheels will actually spin slower at any given speed than the stock setup would. Therefore, the speedometer in the vehicle will read less than the actual speed that is being traveled. Likewise, a smaller tire on a low-rider, for instance, will have to spin faster than a stock one to maintain the same speed, and therefore will cause the speedometer to read faster than the actual rate traveled. It is important to know this for local speed laws and safety in general. The faster the vehicle goes, the further off the speedometer will be. When the vehicle is sitting still, the speedometer will read zero with either set of tires on. However, once the vehicle begins rolling, the discrepancy grows.
3. Things to Know
   When the tire and wheel size are drastically changed on newer vehicles, the warranty may be affected adversely, or even completely voided. Changing the tire size affects the way the brakes work, it affects wear and tear on the drive train and engine, and it affects the way the vehicle handles in all road conditions. If going to bigger tires, the brakes will have more stress on them due to more rotating mass to slow. They may also cause the vehicle to handle and steer differently. If much smaller wheels are applied, the vehicle could sit dangerously low and have turning issues. If the vehicle has small rims and tires and experiences a blowout, the frame could actually scrape on the ground, causing a very dangerous situation. Check local ordinances before changing tire size to ensure that no laws are broken and safety is not compromised.

 

Interesting. I don't know what I want to do. If I go with the smaller ones I'll also save $50. Why can't they make these tires in my OEM size!? RAGE!

On Discount Tire's website they actually do have the 225/55/18 as an optional tire choice. Therefore, I guess that makes it so that that particular tire would be a better option. I hope they give me the online tire price though!

 

225/50/18 the 225 is the width of contact the tire gives the 50 is side wall hight and the 18 you will know this is the rim size if you allready have the 235/50/18 you will notice the other width sise will be smaller. also is prone to blow out if going around a corner or doing swerve to get away from a dog or some thing bigger. be care full about that. i had a blow out with my mustang avoiding a kid running out into the main road with 225/55/18 and it should have had 230/55/18 the width of the tire is crusial to the equivelent of the rim, lets say 18x9.5. the tire hight the middle number is negotiable to help the tire fit corectly. with all tire and rim jumps its always a good thing. to do a tune as in calibrating the trans tcm and computer and the speedo all at once telling them there is a bigger tire or performance gain added to the engine or the body like the tires. to avoid power train problems its always a good thing for the car to get tuned for the different sise of tire