Acceptable tire size?

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Initially I was looking at 245/45-18 tires (0.2% difference on the speedometer) on steel Dodge Charger wheels (18x7.5) for my Grand Marquis, but I'm exploring the possibility of going with wider tires. I came across these 20x8.0 Mercury Mountaineer wheels, which have an offset of 35mm: The offset on my car is ~6mm (depending on rim model) and I will need to use spacers if I go with these wheels, which isn't going to be a problem. I'm just wondering if these 20x8.0 wheels would be able to accommodate a tire size of 275/30-20. I'm basically looking for bigger wheels to go with my suspension upgrades: - Stiffer springs (130 lbs/in vs. 172 lbs/in rear/440 lbs/in vs. 744 lbs/in front) - Bilstein HD shock absorbers - Bigger front sway bar (28.5 mm vs. 31.75 mm) - Bigger rear sway bar (17 mm vs. 25.5 mm) - 6061 T-6 aluminum rear control arms - 6061 T-6 aluminum Watts linkage
 
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Just watch the weight and most importantly the total overall diameter. Add much weight and you'll really feel them if your suspension isn't up to it. Add much diameter and it will affect your gearing killing acceleration and economy.
 
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Every 275/30-20 that I know of is supposed to be used with a 9-10" rim. You could put them on, but they would mushroom a bit.
 
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Agreed with others. A 275/30/20 tire will require a rim width between 9" and 10". I'm not sure what sort of look you're going for, but 20" rims on this car would be pushing it, to the point of looking ridiculous, IMO. I'd stick to 18". It'll provide a better ride and your suspension will last longer.
 

Falcon_LS

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Thanks for all the input! thumbsup In that case, the way forward with a 20" will be at least a 20x9 wheel and I'd have to take a look at Mustang wheels for that. Still a bit half hearted about the 18s, but it appears that's the way forward. Maybe I can go with 255/45-18s.
Originally Posted By: Quattro Pete
I'm not sure what sort of look you're going for, but 20" rims on this car would be pushing it, to the point of looking ridiculous, IMO. I'd stick to 18". It'll provide a better ride and your suspension will last longer.
The 18" wheels are actually much cheaper, at roughly $100/wheel, and the tires are more "generously" priced compared to the 20s. I'm really trying to improve the car's overall handling, which is why I was looking at lower profile tires with a bigger wheel. I would say 20" is the limit for me with this particular car, because certain wheels can look decent in 20" size. I do agree though, especially with 22+ it can look really big. If I was going with the Mountaineer wheels, I would have had them powdercoated black. Similar to this, minus the chrome lip:
 
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Originally Posted By: Falcon_LS
I'm really trying to improve the car's overall handling, which is why I was looking at lower profile tires with a bigger wheel.
There are other ways to achieve this apart from getting rubber band tires. Some tires have very stiff sidewalls which in itself will tighten up the handling without having to resort to ultra low profile. Bridgestone S03/S04 comes to mind. I'm sure there are others...
 
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