92bonny

So I need some new tires and want to get new tires in the front only cause in 3-4 months I'll probably be getting new rims. So I still have the stock 225 60 goodyears all around. I want to put on 245 50's in the front for now. I went to the firestone dealer today and they told me that my car would not handle well with the 245 50 firehawks in front and the stock 225 60 goodyears out back. I then told him the new GXP's had 255's in the front and 225's out back. He was surprised Pontiac did that but said the offsets and suspension were, understandably, tuned for the tires. He told me to do more research then come back. So what do you think. Will my handling suffer from such a setup and am I better off with 235 in front. Thanks for the input. BTW my car is a 97 GTP with stock rims.

BNaylor

Yes, the 18" wheel on the GXP is definitely offset. My guess would be if the handling may be affected it will be because of running different brand tires on the front versus rear and the different tread design to include diameter. You might get whats called radial pull. As to 245 50s, they will fit on stock 16" wheels. My Nittos are 245/50R-16 and they work fine.




Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

__________________

'08 Pontiac Grand Prix GXP (Dark Slate Metallic) - LS4 5.3L V8
'08 Pontiac Grand Prix GXP (Liquid Silver Metallic) - LS4 5.3L V8
'02 Oldsmobile Alero GL2 - LA1 3400 V6
'99 Buick Regal LS - L36 Series II 3800 V6
'03 Honda CR250R MX - 2 Stroke 250cc
'97 Pontiac Grand Prix GTP - L67 Series II 3800 V6 Supercharged
Timeslip 08/12/06

AF Community Guidelines

ttintman

the 245/50 is wider and should help in cornering but it is also shorter and may affect overall gear ratio and transmission shift points. shorter tires increase gear ratio. car will seem to shift earlier and not run slower than miles per hour shown on speedometer,

BNaylor

The 245 tire width gives you much better overall traction too. To get rid of the gearing and speedo error you would need to run a 17" wheel size. A P225/60-16 (stock) is approximately 26.63 inches in tire diameter. A P245/50-17 is 26.65 in diameter which is very minor. When the speedo reads 65 mph the car is actually doing 65.05 mph whereas with a P245/50-16 there will be an error of 3 mph. When speedo reads 65 mph you will actually be doing around 62 mph. Plus fuel economy will be affected with this combination.






Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

__________________

'08 Pontiac Grand Prix GXP (Dark Slate Metallic) - LS4 5.3L V8
'08 Pontiac Grand Prix GXP (Liquid Silver Metallic) - LS4 5.3L V8
'02 Oldsmobile Alero GL2 - LA1 3400 V6
'99 Buick Regal LS - L36 Series II 3800 V6
'03 Honda CR250R MX - 2 Stroke 250cc
'97 Pontiac Grand Prix GTP - L67 Series II 3800 V6 Supercharged
Timeslip 08/12/06

AF Community Guidelines

datastream

Personal experience:

The rolling ratio provided by the stock-sized tires is critical in more than just the speedo deviation.

I went to 215/55-16 on my 97 GP-GT. The results were dismall. It felt as though the center-on place in the steering went MIA. It never drove straight, even after 3 alignments and replacement of every moving peice from the inner half-shafts, out. You weren't so much pointing it were to go with the steering wheel, as much as you were telling it where not to go - constant and irradic adjustments in input to the steering wheel - see-sawing.

Once the ratio was changed by the 215/55's, the road surface suddenly weilded much more directional control over the vehicle as well. WHere before, a 3lb forcce on the steering wheel would actually turn the wheel and change your direction, a force of 10lb's or more was necessary after the ratio changed. This made highway driving an exausting event, not to mention the higher the speed, the more irradic and unstable the car became.

Don't get me wrong, the look achieved by the 215/55' in conjunction with lowering springs and struts was super sharp. It looked totally factory, if Pontiac had made a slightly sportier model, and many people say its not lowerd because this size tire gave the same wheel-to-fender gap as a stock setup, so it looked stock height. Reality is its about 3 off the ground. It will drag coke cans lying on their side. And, so far its cost me a tranny pan, but thats another, fluid-smoke story.

There also seemed to be more binding in the drive train, more stresses on components. I say that because I have gone back to 225/60-16's while keeping the suspension peices installed, and much of the binding feels like it has gone, and much of the directional control has returned - and my speedo is accurate again In theory, just changing tires as I just described make no sense, but the results speak for themselves.

Just get a cheap set of used 225/60's and wait for your wheels. Just remember to keep the rolling ratio as close to factory as possible.

Speaking of wheels, have you checked out Borbet Type E? I heard they were being discontinued, but I have seen them availbe at tirerack and some other places. The are the closest to stock wheel you will find, and they add 'sleeping menace' to the look If your'e in to that kind of thing . . . .