It's what I do for a living. Better over engineer than under, right?


If you go for a better tire compound and tread design than stock, I think that would make up for all the shortcomings I pointed out.


Yeah, what he said. I thought you were getting new rims.

Besides, I don't think you've got a full inch to play with before you start throwing schmutz on the car.

On a NA Solstice a set of GoodYear F1 GS-D3's 245/45/R18 or one that has the same performance ratings as these GoodYears is all this car needs.
Now if you want to do something for show or you like the looks of a wider tire then go for it, but it is not going to make the car handle any better than with the above or something comparable.
It is going to be a while before I can put a set of GS-D3's on the GXP, it seems these tires are MIA, maybe next year I will have better luck, the GS2's are very good but I still do not think they are as good as the GS-D3's.

__________________
Aggressive GXP at $25,995.00 shipping of $600, Manual Transmission.
Options:
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MODS (RKSport/Magnaflow dual exit exhaust system, K&N filter, Ventureshield.
First 1000. Aggressive with everything, NO XM/OnStar. SOLD
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Founding member
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HERE, HERE! I like the look of the stock rims. I would buy a set of wider ones in a New York minute if someone would make them. There are generic versions of many other OEM wheels out there but I suppose the Solstice is just not high-volume enough to produce any.

Maikai GXP

You did a nice job a walking around my questions. Lets try it again, please answer the following:

1. What is your track experience, have you ever raced anything? I am just trying to find out your track experience level. Having an engineering license means little you could be a landscape architect. At this point I don't believe it means much, but, I also have a PE license.
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2. Please answer why all the following cars have much wider tires on the rear and they are all cars pulling over 1G in the skid pad:

viper, vette, porsche, Ferrari, lamborghini

These are basically road course cars (twisty's per your jargon), why the wide rear tires.
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3. Please explain what type of traction your car would have with a one inch wide tire, after all the unsprung weight (your belief) is such a advantage
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Another area where you seem a bit uninformed is the principles that apply too drag racing slicks, believe it or not they don't rely primarily on a fat a tire. The flex and distortion in the sidewall allows for a footprint that increases disproportionally from front to back. As an exampole the Outlaw 10.5 class refers to the tire, width (and thats not wide). The modern drag tire can provide unbelievable traction due this huge contact patch, I forgot you don't believe in that theory. The transfer of weight also comes into play, but with all the weight transfer in the world , without that contact patch the car is not going to run 9's and 10's.

One last observation You seem to think stiffer side walls are a negative, obviously you have never tracked a car that can pull plus 1G in a corner, if your sidewall is not stiff the movement will unsettle the car and you will loose control, the same condition exists in a slalom. That is why most track tires are at 37-38 psi plus (cold). I have a set of Kumho 710's that are so stiff that they could be driven (not far) without air and there is no apparent deflection. Even though they too wide and too stiff to have any traction (per your disertation) the car is pulling 1.1X G's thru the corners.

Once again, no flame intended, but, I have spent too much time setting up cars for performance to sit back when comments are offered that are so contrary to reality. I believe you mean well but, you are totally ignoring the compound and tread design and are applying the principles that exist with two perfect not deflecting surfaces. Probably the best tire selection man in the country is John Purner (CCW) , you should really get on the phone with John and get an education. John did the wheels for the Solstice/corvette conversion in Hot Rod magazine and they didn't put on smaller tires.

Let me ask you a question.

If you owned a front wheel drive car, would you ever, even for a second, consider putting bigger wheels or wider tires on the front?

__________________
Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam.

All the cars that were listed are very high power cars, the NA Solstice is only 143WHP and already has a 245/45/R18 tire, a wider tire in the back or front will not do anything for it.

__________________
Aggressive GXP at $25,995.00 shipping of $600, Manual Transmission.
Options:
Air, $960; Chrome Wheels, $545; PCQ, Premium Package (Leather), $525; Radio, 6-Disc with MP3, $495; Monsoon, $395; Premium Acoustic Headliner, $150; and Sport Metallic Pedals, $115; all totals $29,180.00.
No XM/OnStar and NO Spoiler.

MODS (RKSport/Magnaflow dual exit exhaust system, K&N filter, Ventureshield.
First 1000. Aggressive with everything, NO XM/OnStar. SOLD
~~~~~~~
NASSOA
Founding member
~~~~~~~

Little to no track experience. I have already indicated the value of experimentation by referring lil goat to LatinVenom for his opinion based on experience. I thought that made it pretty clear I was talking from the "sound engineering principles" side of things.

I don't know how the State of Ohio does it, but here in NY you need an engineering degree, years of experience and experience particular to mechanical issues. Then you take a grueling multi-hour pair of tests over a couple of days. Last time I looked, "Landscape Architect" wasn't an engineering degree. People that move big dirt are civil engineers. People that plant shrubs at your house are "Landscape Architects". I'd be less than honest with you if I didn't tell you this "Landscape Architect" comment casts some serious doubt in my mind about you. Any PE should know this.

On top of that... I haven't seen you risk any explainations for anything yet. You asked me for the sound engineering principles behind my opinions and I believe I gave them to you. It is now up to you to counterpoint.

Because they were designed for them. I thought that would be obvious. They have greater wheel torque than our Solstices and need to take advantage of what a fatter tire can offer. The car was designed with that in mind, so the handling losses were compensated for in the design of the suspension.

We are talking about a Factory Solstice on public roads in this thread.

"Twisties" is the local jargon on this forum.

Very little, but it would follow the contour of the road fantastically.

Unsprung weight is an issue for keeping the tire in contact with the road. The size of the contact patch, tire composition and tread design effect "traction".

I must say this is a seriously flawed question. As an engineer, you should have known well the compromise a designer would have to make due to the relationship between unsprung weight and wheel size.

WTF?! You must have me confused with someone else. I'm the guy that said fatter tires DO increase traction. I went on to say they reduce handling performance in "twisties".

WTF... AGAIN?!? Did I not state clearly enough in previous posts that I was discussing a Solstice on normal streets and roads? A professional track is way more uniform than any public roads. The uneven quality of a public road, coupled with higher unsprung weight and stiffer side walls would increase chatter in turns.

WTF... for the third time?!? Did I not underscore that tire compound and tread design were very important. Did I not suggest to lil goat that he speak with LatinVenom to discuss just that... LatinVenom's real world experience with tire compound and tread design?

The Solstice/Corvette conversion you're talking about probably had a lot more torque, right? Doh! It would need fatter tires to handle that torque.

Jack B, I suggest you actually read what people write before you comment back.

Now it's your turn. Please provide a counterpoint to any explainations I wrote. If you're a PE as you say, please use "sound engineering principles" in your counterpoint.

An engineer doesn't point to a Viper with fatter tires and assume all cars would be better off with fatter tires. An engineer knows the relationship between unsprung weight and surface following capabilities.... whether we're talking about a wheel on a road or a cam follower.

You are eager to tell me I'm all wet, yet I haven't read one single "sound engineering principle" from you yet, my "PE" friend.

OK. You guys are all over this thing, so what can I add?

Not much. No qualifications, not an engineer, not a racer, or even a “real” doctor.

Just a chiropractor with 9 years of college, some physics, 28 years in practice, thousands of additional hours of study and a lot of “butt” time on city streets.

From 92 to 2002 I drove two different Q45a’s. If you don’t know what the “a” stands for (most don’t), it was called “full-active-suspension”. It was really only half active, but worked wonderfully. I am looking for a 94 or 95 active now, but I digress.

There was a little book written by the owner of ADDCO. They produce anti-sway bars. The title was something like “Handling, what it is and how to get it”. Really nice little book. Does a great job of explaining the trade offs (there are no perfect anything, just trade offs to get as close as we can to what we individually want).

NOW. Wider tires DO NOT give a BIGGER patch, given the same car and tire pressure. They do supply a wider, shorter patch. Why is that important? Because of tread creep.

When one turns a corner the inertial of the vehicle tries to keep it going straight. That will deform the tire patch. The longer and narrower the patch the more it distorts in the inertial direction. As each bit of tire is picked up at the rear of the wheel another piece of tire is laid down in front. The wider and shorter the patch the less the effects of the inertia on distorting the tire in the inertial direction. In other words, a long narrow patch will push more in a turn than a wide short patch. The wider patch will take the vehicle in the direction you intend more precisely, assuming same tire compound, tire pressure, etc., etc, all things being equal, which of course they are not.

Back to the Q for a moment. It came with some very soft (wore out quickly, people complained – cause it was a luxury car) 215x65x15 on 6.5 rims. After the first set I went to 255x50x16 on 8” rims. No more patch on the ground, but a wider shorter patch with a stiffer side wall (remember some of the issues of unsprung weight were being addressed by the active suspension). Went through a lot of tires over the years. The difference in handling was amazing and the equal tire size made for the best handling with that car.

I eventually went to 255x45x17 on 8.5 front and 285x40x17 on 9.5 rear. This set up was never as good. Two problems. The weight/mass (yes I realize these are not synonymous terms) in the front of the vehicle tended to cause it to “push” or "plow" in high speed turns and the shorter patch in the rear compared to the longer patch in the front made this trait worse.

Therefore, for that car equal tire sizes front and rear was a much better combination. Many others with the same vehicle have come to the same conclusion.

Bach to our Solsties. IMHO the best step is to put an OEM sized tire of softer compound on the OEM wheels. The F1 gs-2 on the GXP are a 300 tread wear index. Now, there is no industry wide exact standard for tread ware or even tire cross section. That is why a 255 from one brand will clear on a particular car’s suspension and the same size tire on the same wheel from another brand will rub. But as a generalization, lower tread were index (like 180) will equate to shorter stops, higher g-force in corners, better turn in and faster wear.

To the question of 275’s and 19”. It is not the wheel diameter that is the problem, it is the width. Our OEM’s are 8” a 255 is about as wide as we can go on that width. Check out some of the high performance tires on Tire Rack. Go to the specs section and look at the wheel width range that is acceptable for a specific section width of tire and also look at the size wheel they measured their tire on to get the specs.

So, to boil it down, in my opinion the most cost effective thing to do for street handling on our cars is put on a softer compound tire.

Now, if you are talking about cosmetics, that is an entirely different discussion. Beauty IS in the eye of the beholder.

__________________
Sly GXP, ebony cloth, auto, air, 6 disc and monsoon, chromes. Bruce Weiland

Bruce
good points well taken, but do you agree that on a track all braking and acceleration should be done in a straight line, therefore the contact patch does matter. I run 3,25 and 3.35 Kumhos on my track car and it pulls way over a G when braking and that is not going to happen (on my car anyhow) with a small contact patch. Remember, braking and accelerating is where you win on a road course. You were right this is getting old quick.

Latin Venom:
I don't think we know what the GXP needs in the way of tires. Because the torque curve is so steep these cars may need more tire when accelerating out of the corners. They may tend to oversteer in the comp mode. Most of the faster vettes turn off the traction control so I am assuming our cars will run best in that mode. I agree with both you and Maikai if we are talking the base Sol, I just took a stance because the comments were general in nature and they do not apply to all cars. I can tell you this I will know for sure, come spring.

Maikai:
I think we have exhausted the the extremes of the topic. I think our differences reside in the fact that I am focusing on higher power cars in a track only scenario. I do agree with some of your point for a street car with low or moderate power.

Jack, I don't pretend to be and expert. I have only had one day in a high performance driving school. However, I do agree about braking, however one might choose to accerate earlier out of a corner. I read a review of GXP vs Boxster S. They mentioned the Boxster was more "precise" and could go into the corner hotter. However the GXP was faster around the track because it could come out of the corners faster.

Contact patch SHAPE really matters for cornering. In gerneral one can only increase the contact patch size by decreasing inflation. I will reiterate. If the tire had a four inch wide two inch loong contact patch, given the same inflation with the same vehicle and the correct rim width, a two inch wide contact patch would be 4 inches long.

The longer patch would plow more in the turns. However, under hard acceleration the longer patch might not break traction as easily.

__________________
Sly GXP, ebony cloth, auto, air, 6 disc and monsoon, chromes. Bruce Weiland

Jack B:
I have the GXP and with the GS2's it does not handle as well on corners as my NA Solstice with the GS-D3's, it does oversteer, but I am pretty sure is because of the GS2's, they seem to have less grip, but I will not know the answer until I can get the GS-D3's on my car.

__________________
Aggressive GXP at $25,995.00 shipping of $600, Manual Transmission.
Options:
Air, $960; Chrome Wheels, $545; PCQ, Premium Package (Leather), $525; Radio, 6-Disc with MP3, $495; Monsoon, $395; Premium Acoustic Headliner, $150; and Sport Metallic Pedals, $115; all totals $29,180.00.
No XM/OnStar and NO Spoiler.

MODS (RKSport/Magnaflow dual exit exhaust system, K&N filter, Ventureshield.
First 1000. Aggressive with everything, NO XM/OnStar. SOLD
~~~~~~~
NASSOA
Founding member
~~~~~~~