I would like to add 20 rims to my 07. Nothing to flashey (chrome) , but silver 20's to fill out the wheel well a bit without lowering. I have read that 20's will kill the performance. Question is why?, how much?. Thanks
The reason is that the wheels and tires will be taller then stock. That brings the effective ratio of your gear ratio down number wise. Now that also depends on the tire size and diameter And it will affect ride quality.
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07 REDFIRE GT 5 SPEED 3.55 gears
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20 inch rims are so much larger than stock therefor require more power to turn them. a simple fix would be higher ratio rear end gears. the rims wont hurt performance a whole lot, but there is a very slight difference in acceleration..but the higher gears will compensate great.
I love DD rims and i think that 18's are plenty large enough. 20's unless they are shelby razors, are just too big IMO. And the extra weight would become a PITA when rotating tires. My stock 17" bullitts are heavy as it is...
In addition, 20" rims usually use tires with a smaller aspect ratio. Because there is less sidewall to flex they are more likely to lose traction and spin. They also make your stock brakes look tiny.
18" rims are as big you want to go with the right rim you can still get a brembo big brake kit on if you are thinking of down that route.
I've been looking for wheels that will fit the big brakes kit. r those ur wheels in the photo? if they are what r they called? where did u get them from ?
thanks
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2007 GT Alloy Metal with Auto transmission.
JLT II CAI, Steeda UDPs , Steeda CMDP, Borla full exhaust (LT's + x-pipe + stingers) , Bamachips 95 octane Race/ Torque tune
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Yes they will affect performance and handling. 20's add considerable unsprung weight.
+1 It's the unsprung weight that hurts performance not the rim/tire size, you can get the exact same over all size as stock with 20's. You can also find lighter 20's than the stock 17's. I dont believe that your stock size tires will out perform my 20's Maybe in a straight line But I dont race straight. (Road racing).
They are freaking heavy for one. Try picking up a 20" rim with tire and a 17" rim with tire. It's like night and day. And the ride is very harsh.
If you are just cruising around town and can tolerate the ride, they are fine. They are worthless at the track and probably for any kind of racing. Mine will be coming off as soon as I get the cash.
Why would Ford offer 19 and 20 rims on the new 2010 mustang if they are so bad ? .I have not read of any differant gears for the larger rim option.
for the same reason they have gear options the gear options are for us that like performance the bigger rims are for people that need to look cool and aint worried about the performance end of it got to appeal to all the crouds
I am one of the few who made the jump to 20 inches within a week of buying the car. The difference in acceleration was very noticeable. However, I did not notice much of a difference in ride quality. There's a slight difference, but not really uncomfortable. As far as acceleration goes, I feel like I'm just now getting back to slightly-faster-than-stock with the addition of the JLT intake and 87 Performance tune. Both the 93 Torque and Race tunes are even better. I still have the stock 3:31 gears.
Its the weight of the larger wheels that slow the car down. Personally, I think looks outweigh the slight drop in performance. You have to look at your car everyday, but I doubt you'll be racing nearly as much.
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i too went for the 20"s and i tried to compensate with installing 4.10 gears. personally i love the look of the rims with the bodykit, i know its too flashy for most of you here but the looks are great!
i raced a friend with exact same mods except he had the stock 3.31 gears and stock rims and he was ahead of me by 2 cars length!!!
i would assume the 20s will take off .2-.3 at the track if not more!
Why does 20" rims affect the performance? 
(Mods in profile)
