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Tire Question

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Old 04-22-2008, 04:55 PM
  #1  
SoulBurn18
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Default Tire Question

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.

Thanks in advance for the help.
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Old 04-23-2008, 08:09 AM
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msouhlas
 
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Default RE: Tire Question

SB;

Unless you increase the overall diameter (effective rolling radius) of the rear wheel, you will not change theoutput 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 therolling radiussomewhat which wouldrender your speedomer out of calibration. A larger diametertire will make youtravel 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 wheelswhich hasimproved the handling somewhatwithout 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 onesfromyour 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 thisinfo and opinionare helpful...
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Old 04-23-2008, 08:25 AM
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SoulBurn18
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Default RE: Tire Question

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.
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Old 04-23-2008, 11:55 AM
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msouhlas
 
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Default RE: Tire Question

...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 arrivebefore 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-pistoncalipers priced in the middle of these 2and will fit/use these same front rotors... Download the SPP catalog when you can to see what's out there...

http://www.shelbyperformanceparts.co...C%20front.aspx

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Old 04-23-2008, 03:26 PM
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SoulBurn18
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Default RE: Tire Question

ORIGINAL: msouhlas

...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 arrivebefore 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-pistoncalipers priced in the middle of these 2and will fit/use these same front rotors... Download the SPP catalog when you can to see what's out there...

http://www.shelbyperformanceparts.co...C%20front.aspx

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.
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Old 04-23-2008, 08:32 PM
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F1Fan
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Default RE: Tire Question

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.CallHawaii Racing here in SoCal and order a set of Baer GT Plus 14" brakes and a set of matching rear Decelarotors for thesame $1,300. I think they will even fit your stock polished 18" Bullitts becausethe Baer 2-piston calipers are actually 0.1" or so shallower than the stock caliper faces. The "Shelby" brakes areactually supplied by Baer, all they do isengrave Shelby's logointo the same GT Plus calipersinstead of Baer's logo, the calipers and rotors are the same.The Baer GT Pluscalipers are plentygood brakes, just ask anybody with a C6Corvette because that'sthe same caliper.ButBaer improved on themby 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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Old 04-23-2008, 09:24 PM
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SoulBurn18
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Default RE: Tire Question

ORIGINAL: F1Fan

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.CallHawaii Racing here in SoCal and order a set of Baer GT Plus 14" brakes and a set of matching rear Decelarotors for thesame $1,300. I think they will even fit your stock polished 18" Bullitts becausethe Baer 2-piston calipers are actually 0.1" or so shallower than the stock caliper faces. The "Shelby" brakes areactually supplied by Baer, all they do isengrave Shelby's logointo the same GT Plus calipersinstead of Baer's logo, the calipers and rotors are the same.The Baer GT Pluscalipers are plentygood brakes, just ask anybody with a C6Corvette because that'sthe same caliper.ButBaer improved on themby 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.
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Old 04-23-2008, 10:04 PM
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Default RE: Tire Question

ORIGINAL: SoulBurn18
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.
Hi SoulBurn18,

No the Hawaii Racing price was $1,000 for the front BaerGT Plus kit only, NOT $1,400 as on the Shelby site. The extra $300 was for improved rear rotors withmatchingmachine work. If you can buya Baer GT Plus with plain 2-piece undrilledrotors you don't need theBaer rear Decelarotors.

BTW, what is it you think is lacking in the stock brakes?Didyouknow that brakes don't actually stop the car, tires stop the car. Allhaving bigger brakes canmaybe do is improve brake pedalresponse and due to the larger mass and larger rotors hold off overheating a bit longer thanthe smaller size, lower mass rotors. So as you can see if we add coolingth 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 andthe tire's gripas far as stopping distance are concerned.

At this price level you can upgrade your stock brakes withbetter parts. Ifyou alsoadd a good brake coolingsystem you canhave brakes that work just as well as any BBK and last longer on the trackwith less fadethanjust installingthatBBK which willjust fade a little bit later thanthestock brakesand take even longer to recover.

Consider this setup:
EBC Yellow"R" or Ferodo DS2500compound pads, high-friction street/race pads
Goodridge stainless steel brake lines at allfour corners
MotulRBF600 or ATE 200 or Super Blue racing brake fluid
V8-Power or Quantum Motorsports spindle mount brake ducts
10' of 3"of brake ducthose
Quantum Motorsports lower grillducts ductsor Agent 47 lower grill and frontbrake duct kit

The out of pocket cost is a bit lowerand you will literally have brakes that are just as good asa 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 fastas a BBK and will recover much faster than the uncooledBBK alone.

HTH!
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Old 04-23-2008, 10:15 PM
  #9  
SoulBurn18
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Default RE: Tire Question

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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