Thread: GMPP Handling Upgrade Kit question...

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  1. #1 GMPP Handling Upgrade Kit question... 
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    Hi,
    I'm thinking about upgrading my 98 GT's suspension with the GM Handling Upgrade Kit pk12456148 (ex. http://gmpartsdirect.com/results.cfm...ber=pk12456148 + replace all the rubber parts with polyurethane), and I would appreciate your input. I was wondering if this kit would work OK with different springs/struts and anything else that might be needed to eventually upgrade my rim size to 18". Right now I'm running stock 16" rims on a stock suspension, and while the ride is soft and nice for straight-line cruising, I'm really not liking all the body roll I'm getting going around simple easy turns. I'm not into autocross or extreme driving situations; I would just like a good deal more firmness and stability while keeping it soft enough that going over moderate sized bumps doesn't jar my teeth out. If I'm understanding it correctly, the GMPP handling upgrade should still work, even if I later change out the struts/springs/etc. I'm curious to find out if making the jump to an 18" rim size would change the suspension geometry enough to cancel out the handling improvements I might see with this kit. Any thoughts?

    (p.s. My car is nearing the 86,000 mile mark, and I know I'll have to replace the struts pretty soon. Just hoping look ahead and to do as much as possible in one shot. Tear it apart once; put it all back together once... and be done.)
    Black 1998 GT Coupe
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  2. #2 Re: GMPP Handling Upgrade Kit question... 
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    Nope your good man you can install the struts and springs no problem with the gmpp kit. Same as the 18" wheels.. changing the wheel size doesnt effect the sway bar or anything. Just make sure you get the proper size tire for the wheel so you dont change the speedometer reading.
    04 Top-swapped, 3.2 pulley, ZZP 1.9 rockers w/ #90 springs,Mild P&P heads, Pacesetter Headers, Sseilmnop 2" Phenolic Intercooler with stage 3 HE, ZZP billet fuel rails, 42.5lb injectors, 3" full exhaust, all poly mounts,other supporting mods.
    oh and weight addition mods: CTS-V brake upgrade, 14" GT500 rotors

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  3. #3 Re: GMPP Handling Upgrade Kit question... 
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    225/45/18 put the speedo dead on for me. Some say 245/45/18 works too. 18s will enhance the kit
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  4. #4 Re: GMPP Handling Upgrade Kit question... 
    GrandPrix Junkie machinegunsquid's Avatar
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    Sounds like a good plan getting the GMPP kit, new struts and springs, then going with bigger rims.

    I'm running 245/45-18s and the speedo is dead on.

    "**** bills. You can live in your car but you can't race your house" -dsmuts
    Want her to stop when she's not looking karate chop her in her crotch that should quiet her for a bit or at the very least put a smile on your face -REDCOMPG
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  5. #5 Re: GMPP Handling Upgrade Kit question... 
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    The wheel width wont change the speedo..as long as it 45 height your fine.

    And l67ss why you running 225's??? Thats stock size.. if your on 18's why not go 245
    04 Top-swapped, 3.2 pulley, ZZP 1.9 rockers w/ #90 springs,Mild P&P heads, Pacesetter Headers, Sseilmnop 2" Phenolic Intercooler with stage 3 HE, ZZP billet fuel rails, 42.5lb injectors, 3" full exhaust, all poly mounts,other supporting mods.
    oh and weight addition mods: CTS-V brake upgrade, 14" GT500 rotors

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  6. #6 Re: GMPP Handling Upgrade Kit question... 
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    Got a deal on them . Have 245s on rear. Prolly goin back to 235/40s tho.
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  7. #7 Re: GMPP Handling Upgrade Kit question... 
    GrandPrix Junkie machinegunsquid's Avatar
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    Quote Originally Posted by Alix0r View Post
    The wheel width wont change the speedo..as long as it 45 height your fine.
    You are partially correct in that wheel width wont change the speedo, but the "45 height your fine" is totally wrong. What you're saying is that a 225/45-18 tire will have the same size sidewall as a 245/45-18. That's completely wrong. The second number is the aspect ratio of the tires width in %. The 245/45 will have an 18mm height difference (9mm on each side of the sidewall) compared to the 225/45. So yes, it will change the speedo, just not by much at all (2.7%) This obviously becomes a much different beast when you start getting into much bigger tire sizes.

    *check this out if you'd like to see a neat little side by side with a graphic*
    http://www.tacomaworld.com/forum/tir...5r18-245-45r18

    "**** bills. You can live in your car but you can't race your house" -dsmuts
    Want her to stop when she's not looking karate chop her in her crotch that should quiet her for a bit or at the very least put a smile on your face -REDCOMPG
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  8. #8 Re: GMPP Handling Upgrade Kit question... 
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    Hmm good to know... so then based off that you would have to run a 225/50/18 in order to not change the speedo really
    04 Top-swapped, 3.2 pulley, ZZP 1.9 rockers w/ #90 springs,Mild P&P heads, Pacesetter Headers, Sseilmnop 2" Phenolic Intercooler with stage 3 HE, ZZP billet fuel rails, 42.5lb injectors, 3" full exhaust, all poly mounts,other supporting mods.
    oh and weight addition mods: CTS-V brake upgrade, 14" GT500 rotors

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  9. #9 Re: GMPP Handling Upgrade Kit question... 
    GrandPrix Junkie machinegunsquid's Avatar
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    Actually a 245/45-18 is the closest to stock size (only a .2% difference over stock)
    a 225/50-18 would make it .9% off, and you don't get the added traction of the wider tire.

    (this is based off of a stock 225/60-16 tire)

    "**** bills. You can live in your car but you can't race your house" -dsmuts
    Want her to stop when she's not looking karate chop her in her crotch that should quiet her for a bit or at the very least put a smile on your face -REDCOMPG
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  10. #10 Re: GMPP Handling Upgrade Kit question... 
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    With a 225/45 my digital speedo is only about a 1/4 mile off from my gps
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  11. #11 Re: GMPP Handling Upgrade Kit question... 
    GrandPrix Junkie machinegunsquid's Avatar
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    Sounds about right, cause at 65mph it should be off by about 1.5mph or so.

    "**** bills. You can live in your car but you can't race your house" -dsmuts
    Want her to stop when she's not looking karate chop her in her crotch that should quiet her for a bit or at the very least put a smile on your face -REDCOMPG
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  12. #12 Re: GMPP Handling Upgrade Kit question... 
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    i DO have a 9c3 cluster, theyre supposed to be more accurate
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  13. #13 Re: GMPP Handling Upgrade Kit question... 
    GrandPrix Junkie machinegunsquid's Avatar
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    ahhhh

    "**** bills. You can live in your car but you can't race your house" -dsmuts
    Want her to stop when she's not looking karate chop her in her crotch that should quiet her for a bit or at the very least put a smile on your face -REDCOMPG
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  14. #14 Re: GMPP Handling Upgrade Kit question... 
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    Thanks for telling me what I wanted to hear.
    Anyone have a better source for this GMPP kit than gmpartsdirect? Their parts prices are reasonable enough, but their shipping costs typically make me look elsewhere.
    Black 1998 GT Coupe
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  15. #15 Re: GMPP Handling Upgrade Kit question... 
    GTP Level Member nik12937's Avatar
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    You should upgrade your trailing arms too while you're going for the sways and such. The Dorman ones work nicely and are very inexpensive.

    Try looking on ebay or Amazon for them, I actually got my Dorman front sway bar off Amazon. Same thickness as the GMPP, except it's solid. Nice if you live in the rust belt.
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  16. #16 Re: GMPP Handling Upgrade Kit question... 
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    A lot of 2000-05 impala/montes had the sway bar. Police impalas had gmpp springs if you wanna check jys
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  17. #17 Re: GMPP Handling Upgrade Kit question... 
    GXP Level Member Grimsin's Avatar
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    the police package springs also raise the car one inch

    3.8l N/A POWA! :4'' HAI\L67 HVTB\HV3\ER Rockers\WP underdrive pulley\Headers\cat delete\91 octane overkill incar tune.3.69 gears, Trans go shift kit.
    My Car:http://www.grandprixforums.net/threa...2005-Impala-LS
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  18. #18 Re: GMPP Handling Upgrade Kit question... 
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    ^still at the usual $10 a spring jy rate, not bad
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  19. #19 Re: GMPP Handling Upgrade Kit question... 
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    Not really wanting to go the junkyard route this time around. Wanting to keep the ride for a while and don't mind ponying up the cash for new... as long as it's a good deal.
    Black 1998 GT Coupe
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  20. #20 Re: GMPP Handling Upgrade Kit question... 
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    Springs and sways dont really wear out....
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