Thread: GMPP Handling Upgrade Kit question...

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.)

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.

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.

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

Originally Posted by Alix0r

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

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

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)

Sounds about right, cause at 65mph it should be off by about 1.5mph or so.

ahhhh

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.

the police package springs also raise the car one inch

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.