Skidpad Performance

Has anyone made any sense of these skidpad numbers ?!

Pontiac - .86 g's
Road and Track - .81 g's (200' radius)
Motor Trend - .80 g's (200' radius)
Car and Driver - .88 g's (300' radius)

600-700 foot slalom times for Road and Track and Motor Trend are similar at ~63.5 mph.

Car and Driver got the best skidpad numbers and listed tire inflation at 33 psi front / 39 psi rear. Is the GTO handling really sensitive to tire inflation ? Was C&D trying to overcome the built-in understeer with inflation offset? What does this imply for aftermarket tire and wheel selection ??

Quote: Originally Posted by dcbingaman... Has anyone made any sense of these skidpad numbers ?! Pontiac - .86 g's Road and Track - .81 g's (200' radius) Motor Trend - .80 g's (200' radius) Car and Driver - .88 g's (300' radius) 600-700 foot slalom times for Road and Track and Motor Trend are similar at ~63.5 mph. Car and Driver got the best skidpad numbers and listed tire inflation at 33 psi front / 39 psi rear. Is the GTO handling really sensitive to tire inflation ? Was C&D trying to overcome the built-in understeer with inflation offset? What does this imply for aftermarket tire and wheel selection ??

I have been autocrossing for over ten years now and can tell you that the handling of all cars (including the GTO) is sensitive to tire inflation.

I would venture to say that C&D was trying to overcome the designed-in understeer by increasing the tire pressure in the rear above the optimum pressure for optimum grip so that they could loosen up the rear end a bit and make the car more neutral. That is a very common technique.

IMHO those results imply nothing about aftermarket tire and wheel selection.

However, there is no doubt that the best way to improve handling on any car is to upgrade the tires. Our cars do not come with the best dry handling tires that are available and I will probably upgrade the tire type.

As far as tire size goes, that depends upon your goals. If handling in everyday driving and the type of conditions that you would find on an average autocross course, the tire size is probably just right.

You will have to ask others about the best tires for drag racing if you are interested in that.

Lastly, don't buy into the common misconception that you will necessarily improve the handling by increasing the diameter of the wheels. The reason is that if you do that, then you necessarily reduce the side wall of the tire, which is likely to make the tire less compliant and, therefore, less forgiving. Such a situation might be good for high speeds on a billiard table smooth racetrack, but is not helpful for normal pavement conditions and average driving conditions.

I hope this helps!

Jim

Quote: Originally Posted by JimHoward... Lastly, don't buy into the common misconception that you will necessarily improve the handling by increasing the diameter of the wheels. The reason is that if you do that, then you necessarily reduce the side wall of the tire, which is likely to make the tire less compliant and, therefore, less forgiving. Such a situation might be good for high speeds on a billiard table smooth racetrack, but is not helpful for normal pavement conditions and average driving conditions.

Thanks for bringing that up, Jim. There seems to be a lot of rim size mania going around lately. I would be very interested to know if anyone has worked up any numbers regarding unsprung weight and rim diameter. Last time I checked, aluminum weighed more than rubber. It would seem that the curves would cross at some point. Living in Cleveland, where the chuckholes can swallow a Subaru, an aspect much lower than 45 is asking for trouble.

Thanks guys - this is about what I suspected. I plan on running the Goat on the stock BFGoodrich g-Force T/A KDWS's until next Nov. and then switch to a set of Bridgestone Blizzak's for the winter, (cuts down on the number of times I have to beg the wife to use the QX-4 SUV - now there is a snow machine !!). Question I've got is what to put on for next summer. I'd like to leave the Blizzak's on a dedicated set of wheels, and put a new summer set of tires on either the stock wheels, or some new 17 or 18 in aftermarket wheels, to improve dry handling. The g-Force KD's are what a lot of road-racers are going to, but I dunno about wet performance with these. Tire Rack is supposed to get their Goat in June and publish some recommendations on their website this summer - they like the Bridgestone Potenza S-03 Pole Position's, but I would guess the BFGoodrich g-Force KDW's might be a good choice also, given GM's selection of the KDWS all-season tire. Of course this is all academic until my Goat shows up....one buzzed by the 'ole SHO on I-70 today going about Mach 1.5 !! Looked like fun-I've got to admit, the anticipation is killing me !!!

I remember reading that the cars are produced in Australia with 18 inch wheels and tires and that the suspension was set up for that wheel and tire combo. Pontiac left the suspension alone, but specced the 17 inch setup for US road hazard resistance. I live in the Greater Boston area, and man, I want to tell you we have potholes! I dodge them like a fiend when I can. I have seen many a ricer tuner running around on a donut and three wheels. For this reason, I'll stay 17 inch with the stock KDWS'es for a while and watch carefully.

Anyone trying to find out if the 'Holden by Design' optional wheels 18x8, 5x120 for the Monaro CV-8 might be doable? They already fit the car.

Someone else asked if the car was sensitive to tire pressure? In a word, yes. The Manual specs inflation at 30 psi all around, the door sticker says 35 psi all around. I asked Art Joseph Jr. (my Dealer) about the contrary numbers and he put a call in to Art Spong who said 30 psi for a comfortable ride and best tire wear. At 35, the ride gets a little 'tighter' and it seems to handle a little sharper, but in a 'punch it' situation, they go up in smoke a little easier without the T/C on. I ended up splitting the difference at 32 all around after a week at each pressure.