What are the pros and cons of 18x8.5" tires VS 20x9" tires when it comes to handling, performance, speed and gas mileage? I'm considering getting new tires for my car, but don't want to lose performance by doing so.
Posts: 30
Joined: 4/30/2006 From: New Orleans, LA Status: offline
SB;
Unless you increase the overall diameter (effective rolling radius) of the rear wheel, you will not change the output gear ratio and will therefore not impact speed or gas mileage. Generally, a larger rim would theoretically be fitted with a lower aspect ratio tire which would minimize increases in diameter.
However, unless carefully planned you could increase the rolling radius somewhat which would render your speedomer out of calibration. A larger diameter tire will make you travel faster than the indicated speed.
As far as handling goes, the car handles very well with the original wheels (although I have retrofitted my SGT with 18x9.5 GT-500 wheels which has improved the handling somewhat without increasing the rim diameter).
A 20" wheel with a lower profile tire will generally ride rougher than a wheel with a larger sidewall, but will handle better around turns (at the expense of increased tire wear).
Much of this depends on what style of wheel you like and what you want to do with the car. I went with the GT-500 wheels (machined with gloss black openings) because I like the way they look, they have Ford part numbers on them, and they allow me to use wider tires without increasing the rim diameter or reducing the sidewall height. They also allow the fitment of upgraded brakes.
Note that when changing wheels you will need to add Tire Pressure Monitoring System (TPMS) sensors to the new wheels and train them to the car's computer. You can either purchase new ones or reuse the ones from your factory wheels. I chose to get new ones (ordered from Team Ford along with the mounting straps and the training tool) and keep the factory wheels in tact to use on my GT/CS convertible.
If I had an SGT Convertible instead of the coupe, I would not want to stress the body any more than the FRPP handling pack already does because I would not want the body to flex and cause the car to rattle in the future.
Hope that this info and opinion are helpful...
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(Hers): '08 GT/CS Vert - Vista Blue Automatic, Navigation, Ambient Lighting, Active Anti-Theft, Cloth Top
(His): '08 SGT Coupe #08SGT-0542- Vista Blue 5-Speed, GT-500/SVT Wheels - Machined w/ Gloss Black, Sirius
Posts: 30
Joined: 4/30/2006 From: New Orleans, LA Status: offline
...have you considered these as an option? They are about the same cost but I like the rotors better and they also have the rear kit to match... I have these front and rear kits but am waiting on the cooling kits w/ driving lights to arrive before I install them.
There is also an option for the Extreme kit which has the same rotors but better 6-piston calipers (at a higher price)
They are also about to release some additional 6-piston calipers priced in the middle of these 2 and will fit/use these same front rotors... Download the SPP catalog when you can to see what's out there...
...have you considered these as an option? They are about the same cost but I like the rotors better and they also have the rear kit to match... I have these front and rear kits but am waiting on the cooling kits w/ driving lights to arrive before I install them.
There is also an option for the Extreme kit which has the same rotors but better 6-piston calipers (at a higher price)
They are also about to release some additional 6-piston calipers priced in the middle of these 2 and will fit/use these same front rotors... Download the SPP catalog when you can to see what's out there...
I actually received an e-mail from Shelby that said the Shelby Type S1 18" Wheels with the 6" backspacing will fit the brakes I was interested in buying. But the brakes you have shown here are something to think about. I think either way I'm going to have to replace my wheels to allow more room for the calipers to fit.
ORIGINAL: SoulBurn18 Thank you for the tips. The reason why I was asking is because I wanted to upgrade my braking system to the 14" brakes that the GT500 has.
Hi SoulBurn18,
There is no advantage to the GT500 calipers and the rotors are not as good as the Baer 2-piece rotors. Call Hawaii Racing here in SoCal and order a set of Baer GT Plus 14" brakes and a set of matching rear Decelarotors for the same $1,300. I think they will even fit your stock polished 18" Bullitts because the Baer 2-piston calipers are actually 0.1" or so shallower than the stock caliper faces. The "Shelby" brakes are actually supplied by Baer, all they do is engrave Shelby's logo into the same GT Plus calipers instead of Baer's logo, the calipers and rotors are the same. The Baer GT Plus calipers are plenty good brakes, just ask anybody with a C6 Corvette because that's the same caliper. But Baer improved on them by adding lightweight 2-piece 14" rotors and stainless steel brake lines. Trust me they work just fine on the track.
HTH!
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2005 Mineral Grey Mustang GT Coupe, Premium, M5, ICAP, IUP, Active Anti-theft, LoJack
Mods: Gave up trying to make it all fit, but ask if interested!
ORIGINAL: SoulBurn18 Thank you for the tips. The reason why I was asking is because I wanted to upgrade my braking system to the 14" brakes that the GT500 has.
Hi SoulBurn18,
There is no advantage to the GT500 calipers and the rotors are not as good as the Baer 2-piece rotors. Call Hawaii Racing here in SoCal and order a set of Baer GT Plus 14" brakes and a set of matching rear Decelarotors for the same $1,300. I think they will even fit your stock polished 18" Bullitts because the Baer 2-piston calipers are actually 0.1" or so shallower than the stock caliper faces. The "Shelby" brakes are actually supplied by Baer, all they do is engrave Shelby's logo into the same GT Plus calipers instead of Baer's logo, the calipers and rotors are the same. The Baer GT Plus calipers are plenty good brakes, just ask anybody with a C6 Corvette because that's the same caliper. But Baer improved on them by adding lightweight 2-piece 14" rotors and stainless steel brake lines. Trust me they work just fine on the track.
HTH!
F1FAN,
Thanks for the info, I actually checked Shelby's website and they offer the exact braking system you were talking about and the price is the same too. :) I may look into getting those instead. I'm really more interested in a better braking system, I don't really care if it's the GT500 system or not, just much better than what came with my Shelby.
Thanks for the info, I actually checked Shelby's website and they offer the exact braking system you were talking about and the price is the same too. :) I may look into getting those instead. I'm really more interested in a better braking system, I don't really care if it's the GT500 system or not, just much better than what came with my Shelby.
Hi SoulBurn18,
No the Hawaii Racing price was $1,000 for the front Baer GT Plus kit only, NOT $1,400 as on the Shelby site. The extra $300 was for improved rear rotors with matching machine work. If you can buy a Baer GT Plus with plain 2-piece undrilled rotors you don't need the Baer rear Decelarotors.
BTW, what is it you think is lacking in the stock brakes? Did you know that brakes don't actually stop the car, tires stop the car. All having bigger brakes can maybe do is improve brake pedal response and due to the larger mass and larger rotors hold off overheating a bit longer than the smaller size, lower mass rotors. So as you can see if we add cooling th stock brakes can perform just as well if not better than a much more expensive BBK. The limiting factor is not the stock brake system but it's ability to shed heat and the tire's grip as far as stopping distance are concerned.
At this price level you can upgrade your stock brakes with better parts. If you also add a good brake cooling system you can have brakes that work just as well as any BBK and last longer on the track with less fade than just installing that BBK which will just fade a little bit later than the stock brakes and take even longer to recover.
Consider this setup: EBC Yellow "R" or Ferodo DS2500 compound pads, high-friction street/race pads Goodridge stainless steel brake lines at all four corners Motul RBF600 or ATE 200 or Super Blue racing brake fluid V8-Power or Quantum Motorsports spindle mount brake ducts 10' of 3" of brake duct hose Quantum Motorsports lower grill ducts ducts or Agent 47 lower grill and front brake duct kit
The out of pocket cost is a bit lower and you will literally have brakes that are just as good as a big brake kit with none of the wheel fitment issues of larger calipers and 14" rotors. These new upgrade brakes will also be lighter and will not overheat as fast as a BBK and will recover much faster than the uncooled BBK alone.
HTH!
_____________________________
2005 Mineral Grey Mustang GT Coupe, Premium, M5, ICAP, IUP, Active Anti-theft, LoJack
Mods: Gave up trying to make it all fit, but ask if interested!
Interesting. Something to think about. There's nothing wrong with the stock brakes really. Was just looking for something with a little more grip since I'm going to be modifying the engine soon and thought the better brakes would help.
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