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SGT Handling


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#1 OFFLINE   gtup1

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Posted 13 December 2012 - 07:30 AM

I installed a set of Shelby 20 inch rims and now my car feels really unstable at speeds. Normal cruise feels just fine but if I'm running it and hit 100+ it feels like its going to come of the road. As you all know with the factory 18's it felt stabile and inspired confidence. What could be wrong? I have not changed anything else in the suspension.
Any of you handling gurus have any ideas you can share?



#2 OFFLINE   ChicagoChris

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Posted 13 December 2012 - 08:18 AM

Aside from the obvious concerns of front end alighment or bushings, I would do a Rim Out test where the dealer verifys the rims are balanced.

#3 OFFLINE   shelbymotorsports

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Posted 13 December 2012 - 08:19 AM

While I would not call myself a handling guru, I will say that what you are describing is unusual. Many SGT owners have upgraded to 20" wheels. If you would provide more info, like wheel style & offset along with the size & brand of tires perhaps we could figure out whats going on.

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#4 OFFLINE   gtup1

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Posted 13 December 2012 - 10:39 AM

While I would not call myself a handling guru, I will say that what you are describing is unusual. Many SGT owners have upgraded to 20" wheels. If you would provide more info, like wheel style & offset along with the size & brand of tires perhaps we could figure out whats going on.

Steve

CS66 Rims with Sumitoma HTRZ's staggered fit 245 front 275 rear. Not sure of the back space or offset. I assume whatever is standard for Shelby wheels. They do fit the big brake kit, that's why I installed them to clear the rotors and calipers.
The car feels fine until I hit that triple digit mark. No wander, unless there's a really bad crown on the road. Feels very stabile at normal speeds. The only other thing I noticed but just assumed was normal when going from 18's to 20's is very quick turn in compared to stock.
Hope that info helps, I appreciate the input. I don't hit triple digits often but when and if I do I don't want to feel like I'm taking my life into my hands. Of course maybe I am but I try to do it on the track not on the street.

Thanks

#5 OFFLINE   gtup1

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Posted 13 December 2012 - 10:45 AM

Aside from the obvious concerns of front end alighment or bushings, I would do a Rim Out test where the dealer verifys the rims are balanced.

Thanks Chris, I haven't thought about balance because I have no vibration or wobble in the steering wheel. I may try that along with alignment. I did not realign when I went to the new wheels and you can tell when the wheel is turned Caster Camber plates would probably flatten out the tire contact patch. I didn't do anything because it seemed to drive fine under normal conditions. I don't hit triple digits often and the tires and rims have been on for probably 6 months before I ever hit those speeds to notice it.

#6 OFFLINE   Albino500

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Posted 13 December 2012 - 11:42 AM

Couple of things to check - Wheel balance and load force variation ( a good tire shop with a Hunter GSP9700 balancer should be able to handle that ) , Check the wheel for being "hubcentric" in other words - is the hole size on the wheel the same as the hub on the axle - if it is larger, then the wheel may not be centered to the axle centerline - you may have to use a hub adapter ring ( not a wheel spacer ) , there are assembly clips on the rotors make sure that these have been removed so the wheel is sitting flush to the rotor. Also , vibration felt through the steering wheel is usually from a front end issue , a vibration felt through the body ( floor/seat ) usually indicates an issue from the rear axle/wheels/driveline.
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#7 OFFLINE   07SGT

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Posted 13 December 2012 - 02:53 PM

Does the 20 inch wheel and tire with shorter side wall have any effect on handling and ride? There is less side wall to flex. Thoughts?

#8 OFFLINE   carnut12

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Posted 13 December 2012 - 04:03 PM

I have had 20's for years and no issues what so ever, I do not hit over 100 often, but have hit 130-140 with these and they were as smooth as can be.

Something is wrong, it is not because they are 20" wheels
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#9 OFFLINE   slygray1

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Posted 13 December 2012 - 04:04 PM

I think the main reason some of the folks go to 20" wheels is they like the looks of them. I can't imagine the handling would be better with less side. wall. I just installed a new set of Shelby Razors eand stuck with the 18"s. You don't see nascar running around on skinny sidewalls. Just my thoughts. There are probably others that will disagree.
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#10 OFFLINE   Albino500

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Posted 14 December 2012 - 07:13 PM

Does the 20 inch wheel and tire with shorter side wall have any effect on handling and ride? There is less side wall to flex. Thoughts?

Ride quality is much harsher with a shorter sidewall and because it is shorter and does not flex as much you will not need as much negative camber to compensate for tire roll over ( other factors are involved with concerns pending the amount of grip )

I have had 20's for years and no issues what so ever, I do not hit over 100 often, but have hit 130-140 with these and they were as smooth as can be.

Something is wrong, it is not because they are 20" wheels

Agreed
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#11 OFFLINE   RACERX009

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Posted 21 December 2012 - 03:44 PM

Never had any problems with 20's at any speed as far as handling no issues on any of my past cars M3 20's handled like an animal

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#12 OFFLINE   RACERX009

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Posted 21 December 2012 - 03:48 PM

Ride quality is much harsher with a shorter sidewall and because it is shorter and does not flex as much you will not need as much negative camber to compensate for tire roll over ( other factors are involved with concerns pending the amount of grip )
Agreed


My ride quality on 20's is not harsh and thats with 255/35/20 front and 275/35/20 you do feel small bumps but highway its a nice ride

Proud borrower of my future wife 2014 Mustang gt Automatic Brenspeed tune and CAI 4.10 gears


#13 OFFLINE   JeffJ

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Posted 21 December 2012 - 04:21 PM

I've been 165 on my 20's. I would lean more to the tires then the wheel size as far as feel. Ride harshness on the street will certainly be increased with the 20's, but handling at 100 mph should not be effected. I do not have any experience with the Sumitoma's, but the construction of the tire can make a huge difference in high speed handling. I think there has been some good advise given above as far as making sure everything is in balance. These Mustangs are designed to be lug centric and I'm sure your wheels have divits in them for the lug holes and also coned lug bolts to make sure that the wheel is properly located. That is one thing to verify that I didn't see mentioned above, are the lugs properly torqued? I would imagine yes, but just did not see that mentioned. 20's have nothing to do with high speed handling. It's all in the tire and suspension design. Somebody above said that you don't see Nascar running skinny sidewalls, well in Cup, that is true, but the Nascar road racing cars (Grand-Am Rolex) do run skinny side walls with 20" rims and run over 170 mph. It's all in the tire construction.

P.S. on the street I run BFG GForce 20's., on the track, I run BFG R1's with 18" wheels. More because 18" race tires and wheels are way cheaper then 20" combinations.

Edited by JeffJ, 21 December 2012 - 04:25 PM.

JeffJ
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#14 OFFLINE   Jer

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Posted 21 December 2012 - 06:04 PM

on the track, I run BFG R1's with 18" wheels. More because 18" race tires and wheels are way cheaper then 20" combinations.


Even on his rental cars... cough, cough... right, Jeff? :hysterical:


Jer
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That's when it became OFFICIAL, in my opinion! A Shelby was born!
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UPDATE: In 2009, I drove cross-country with my wife from NY in the SGT and finally just MOVED here. I figured Vegas was lucky for me.
UPDATE: GT/SC upgrade completed at SAI on July 22, 2011.
UPDATE: Left Guitar Center and joined SA as Vice President, Shelby Performance Parts, August 2012-May 2014

#15 OFFLINE   JeffJ

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Posted 21 December 2012 - 06:22 PM

Even on his rental cars... cough, cough... right, Jeff? :hysterical:


Jer


I know nothing.... I wasn't there....... It wasn't me...... :shrug: :hysterical2:
JeffJ
2006 Shelby GTH-SC #102
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1993 F150 Lightning #711
1989 AutoKraft/Kenny Brown Short Wheel Base T-bird #001 with a 1969 Supercharged Boss 302 5 speed
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1965 Mustang Coupe 289 Auto
1990 7-Up LX 5.0 Convert - Auto (current basket case, building for my daughter's first car)
1969 Datsun 2000 Roadster 5.0 supercharged Ford V-8
1953 Ford Customline 4dr w/ 1998 4.6 Crown Vic Running gear
1973 Datsun 610 302 Ford V8 power, drift and road race car.
1951 Ford F6 Dump Truck powered by 1985 Ford roller 5.0, full tilt font, can haul 6 tons of rock and run a 18.0 quarter!
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#16 OFFLINE   Albino500

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Posted 21 December 2012 - 06:26 PM

JeffJ rent a car ? Really ? LOL . A shorter sidewall ( in reference to aspect ratio ) will enhance the feel of turn in but toe setting effect it more as far as corner entry . One thing to mention is that when changing tire/wheel combinations or sizes ( and use of wheel spacers ) that one has to be aware of the effect that it can create due to the change in scrub radius in which stability is subject to change .

Edited by Albino500, 21 December 2012 - 06:29 PM.

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#17 OFFLINE   Jer

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Posted 21 December 2012 - 07:41 PM

I know nothing.... I wasn't there....... It wasn't me...... :shrug: :hysterical2:


Yeah, the Terlingua sticker didn't fool anyone....LOL... but it was COOL.


Jer
2007 SGT/SC # 446 - White, 5spd, Whipple 550 HO with Shelby/C&R radiator and heat exchanger upgrade, Painted stripes (rockers and Le Mans), painted lower fascia (a tribute to Whitey), Shelby Deep Draw (2 3/8") Hood with custom GT350 mesh inserts, Shelby brake duct/driving light bezels with PIAA 510XT lights, Shelby custom underbody front brake duct inlets and fabricated brake cooling plates, Terlingua billet hood pin plates, Shelby tensioner support brace, Shelby race-fabricated valve covers, Dark Charcoal Gray Interior and dash (signed by Carroll), IUP, Active Anti-Theft, Pioneer AVIC-Z130BT with XM Radio, NAV, HD Radio, DVD video touchscreen, Bluetooth, rearview camera, etc... Infinity Reference speakers, Shelby Kicker door subwoofers, trunk sub, and 4.1 amp, Chrome 20X9 Shelby-logoed Razors (ET24) with Nitto 555s (255 front, 275 rear), Baer Extreme+ 6 piston brakes all around, A'te Super Blue brake fluid, Goodridge s/s brakelines, SLP Loudmouths, Aeroforce Terminator gauge, Shelby gauge pod, CS Supercharged faux gas cap logo, billet lower grille, updated 2008-style front grille mount, grille, Shelby billet hood pin kit and pony emblem, Shelby floormats and trunk mat, Shelby Harness Bar, CG-Lock seatbelts, Shelby GT engine cap set and period-correct "Shelby Automobiles" license plate frames, Moroso and Shelby tanks, brake fluid reservoir, and fusebox cover, shorty antenna, Shelby billet fuel fill door, 3/4 window louvers, Shelby upper control arm and mount and lower control arms, CHE K-member brace w/ torque limiters, sequential taillights, Shelby billet Watts link, Ford Racing 3.73:1 gearset, Shelby GT500KR diff cover, de-rusted and painted rear axle housing, Eaton True Trac limited-slip differential, Moser axles, Strange Engineering axle studs, Shelby GT500KR Axle Reservoir, full of Mobil 1 with Ford Racing filter. H3R HalGuard fire extinguisher with Shelby and Brey-Krause mounting, Shelby Helmet and Driving Jacket. Of course I have lots and lots of Shelby doodads, knicknacks, merch, apparel, bling, and bric-a-brac. Many Shelby certificates and Monroney sticker shiny and intact. Fender SGT guitar. Tolerant wife.

Shelby Vegas Bash 2011 and 2012 Show Winner.

Lift #15
Technicians: John Orr/Randall LaViolette
2/13/2007 9:26:32 AM: Dash Badge Installed
2/13/2007 9:26:34 AM: Shelby Letters Installed
2/13/2007 9:26:35 AM: Side badges installed both sides

That's when it became OFFICIAL, in my opinion! A Shelby was born!
CUTE COINCIDENCE: The NEXT DAY, I was in Vegas getting married. True story.

UPDATE: In 2009, I drove cross-country with my wife from NY in the SGT and finally just MOVED here. I figured Vegas was lucky for me.
UPDATE: GT/SC upgrade completed at SAI on July 22, 2011.
UPDATE: Left Guitar Center and joined SA as Vice President, Shelby Performance Parts, August 2012-May 2014




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