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Discussion Starter #1
Have 07 GXP
Front tires are 245/40R 18 93H
Back tires 275/40ZR 18 99W
Can this cause problems like car starting to shake at about 70 mph?
Can this cause any trouble.
And why is this good?
Bought with these tires.
And these tires cost so much.
See rims in pic American Racing Rims also on car when bought.
What are pros and cons of tires and sizes?
 

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I personally see no advantage in those tires, but the sizes won't cause vibration.

I suggest having them balanced.
 

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Have them "Force Balanced". Don't just balance them. This puts a pressure against the tire and if there is any odd lumps/buldges like a belt, it will balance it much better. And also they are wider tires, which force balancing works much better on.... Downside is that it costs like $90 to have that done....
 

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The tires and wheels won't cause shaking, but it's possible they have a wheel spacer or adapter out of alignment, which would cause shaking.

Also your ABS, stability control, and traction control aren't going to work to their fullest potential since the rear tires are taller then the fronts, and thus are spinning slower, making the car think it's losing traction.
 

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The tires and wheels won't cause shaking, but it's possible they have a wheel spacer or adapter out of alignment, which would cause shaking.

Also your ABS, stability control, and traction control aren't going to work to their fullest potential since the rear tires are taller then the fronts, and thus are spinning slower, making the car think it's losing traction.
I have to completely disagree.
I know that when I threw a balance weight once there was some definite high-speed shaking going on and that it went away after re-balancing.
What exactly would you say that an out-of-balance tire does cause?

Don't the rear tires spin faster when the car loses traction? Although I'm not saying that a mismatch won't cause some issues.
245/45 fronts would match the rears exactly.
 

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In Vincent's example, the 245 and the 275 refer to the width of the tire. The 40 refers to the ratio of height to width. (The part of the tire from the edge of the wheel to the top of the tire. Our standard is 45.) He probably meant to type ZR for both tires - and the 18 is the size of the wheel.

The "H" rates the tire to 130 mph - and the "W" rates the tire to 168 mph.

In his configuration, the rear tires are wider than the front and "stand" the same height - have an aspect ration of 40, which would be 5mm shorter than our 45s - and fit on 18 inch wheels. The full height of the tires & wheels would be a frog hair smaller than our standard 245/45/18s possibly lowering the car a smidgen.
 

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Discussion Starter #10
Have them "Force Balanced". Don't just balance them. This puts a pressure against the tire and if there is any odd lumps/buldges like a belt, it will balance it much better. And also they are wider tires, which force balancing works much better on.... Downside is that it costs like $90 to have that done....
Ty you sounds like good advice. Since they are wider I think I will try this. That's not a hefty price for something that sounds like it will work. And had 2 new tires put on so no it needs to be done.
 

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One other item to check.... There are 3 bolts that hold your hubs on. They are on the inside and are notorious for coming loose. Check those and make sure that you have all 3 at each wheel and that they are all tightened down to 85ft/lbs. Here is a link that has images that shows what I am talking about:

https://www.solsticeforum.com/forum/f11/reminder-about-hub-bolts-145185/

This might help someone else too....
 

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John - I'm assuming the wheel/tire combo already checks out on the balancer. Sorry I didn't re-write what was already discussed previously as to not confuse you.

Bama - you are completely wrong. A 275/40-18 is a full inch taller then a 245/40-18. As you clearly say yourself, 40 is a ratio, not a height. 40% of 275 is not the same as 40% of 245. The 275/40 is the same height as stock. The 245/40 is 25mm shorter then stock.
 

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John - I'm assuming the wheel/tire combo already checks out on the balancer. Sorry I didn't re-write what was already discussed previously as to not confuse you.........
Why would you assume that they had already been balanced? unless that was discussed in another thread there is no place in this one than Vincent mentioned having them done.

What confused me was the flat statement that "The tires and wheels won't cause shaking.." because we all know that they can.
 
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