Which Tires Will Look Great On My Goat?
I "completed" the restoration of my '70 GTO Judge two years ago. I replaced the tires with BF Goodrich TA radials (P235/60R14) on the original restored wheels. The tires have always looked too small for the wheel openings, and I've never been satisfied with the look. In an effort to rectify the situation, I restored a set of 15-inch wheels, and I'm going to purchase a new set of rubber. I've looked through past issues of HPP to learn what tire sizes have been used by other hobbyists, but they vary too much to get a good sense of what works. I like the look of the wider tires on the rear but want to avoid rubbing or handling problems.
How do you measure a wheel to determine the width? I'm not certain if I have 7- or 8-inch wheels. Does having a different size tire on the front versus the rear affect the handling or overall performance of the car? What size tire is the maximum for the front and rear wheel openings? You commented on this in an earlier reader question regarding the front but not the rear. Since it takes a while to wear down an unsatisfactory set, I really want to get it right this time. John E. Gladden President and CEO, Delta Dental of Oklahoma -Via Internet
Melvin Benzaquen responds:
Let's address your questions in the order that you presented them.
The wheel is measured from the inside lip to inside lip. That is where the tire bead actually sits on the wheel. The stock rim width is 6 inches for your 14-inch wheels and 7 inches for your 15-inch wheel.
Having two different sizes of tires front to rear does affect handling, especially if there's a dramatic difference. A lot of the current sports cars have different size tires, but they are originally engineered for that setup. Drag racers almost always set up their cars with wider rear tires and very skinny front tires to reduce rolling resistance up front and maximize traction in the rear. Road racers usually have equal-size, wider-than-stock tires all the way around. We like to use a one-step difference when customers ask for the look you seem to want. That will be addressed in the next answer.
Your question of maximum sizes acceptable for front and rear is not easily answered. There are too many variables regarding how much tire one can stuff into a wheelwell. I will answer what tire size will properly utilize your Pontiac 14- or 15-inch wheels.
Aftermarket wheels are a whole different animal. The BF Goodrich 235/60R14 tires currently on your car have a height of 25.1 inches. They have a tread width of 7.6 inches and turn 820 revolutions every mile. In comparison, the stock G70-14 tires have a height of 26.3 inches and turn 780 revolutions every mile. That means your current tires are 1.2 inches shorter and turning 40 revolutions per mile faster. This throws off your speedometer and increases wear on your car components. The tire height difference is why you think the tire size looks too small.
Now, if you want to have the stock look and the stock height, go to a BF Goodrich Radial TA, size 225/70R14. The reason I mention BF Goodrich is to maintain consistency. Believe it or not, different tire manufacturers with the same tire size will have a different height and width. It's important to check all the differences in actual sizes before purchasing. The 225/70R14 BF Goodrich measures 26.5 inches in height and has 785 revolutions per mile. They will make your Judge appear more stock.
If you want a more aggressive look and stance, turn to your 15-inch wheels for a couple of reasons. First, the 1-inch-larger wheel gives a better look. Second, in order to maintain the same tire height as the tires used on the 14-inch rims, that inch has to be made up somewhere, and it will be done in sidewall height of the tire (distance from the rim to the tread). To do this, the aspect ratio is lowered. Aspect ratio is the relationship of sidewall height to tread width. A 70 series aspect ratio has a sidewall height that is 70 percent of tread width, a 60 series is 60 percent, and so on. A shorter sidewall and wider tread mean better handling and a slightly firmer ride.
And finally, another advantage of the 15-inch wheels is that there are a lot more tire sizes available than there are for 14 inchers. The rear tire size in a BF Goodrich that will fill the wheelwell like stock tires in height and provide a wider than stock tread is a 245/60R15. It's 26.6 inches tall so your speedo will still be accurate. You can use the same tire size for the front or go with a 235/60R15, which is shorter and more narrow than the 245s, for a staggered look. That tire is 26.1-inches tall, 7.6-inches wide, and turns 797 revolutions per mile.
I hope this answers your questions.
Slick Hydraulic Clutch For Second-Gen Stick Swaps?
I have an '81 T/A, and I'm converting from an automatic to a Borg-Warner Super T10 four-speed. I purchased stock pedals but nothing else yet. I want to go with a hydraulic-clutch setup instead of the factory manual-clutch linkage. Do you know of any aftermarket kits for replacing a factory linkage with a hydraulic system? Can any parts for other applications be used? Can you tell me what the fork throw might be or any other info that might help me in my search for info on this topic? Brian Dudley Via Internet
Converting from an automatic transmission to a manual is not overly difficult. The challenge of the entire swap is acquiring everything needed. But having a donor vehicle or another manual-trans Firebird accessible for viewing makes the job much easier.
My first suggestion is to invest in a '71-'79 Pontiac Service Manual. The transmission section contains complete repair procedures and exploded views for your Firebird. However, the '70, '76, and '79 manuals are supplements to the previous year and don't contain all the required information. The '75, '77, or '78 manual may have the most correct information for your particular car and is likely the cheapest too. The auction site eBay typically has a few of each available at any given time.
To perform the automatic-to-manual conversion, you need the transmission and shifter, bell-housing and clutch fork, and flywheel and clutch assembly. You also need an entire clutch-linkage assembly, including the block-mounted ball stud, frame mount, countershaft and pushrods, and return springs. And if you want a front-seat console, you need that too. You already have the pedal assembly and should be able to reuse your Turbo-350 crossmember and driveshaft.
Some of the small parts are still available from the mail-order restoration suppliers that advertise in HPP. However, anything not available from them will likely have to come from donor cars. The installation itself should be fairly straightforward, but you'll need to cut holes in the driveshaft tunnel and firewall for the shifter and clutch-pedal pushrod, respectively.
Popularity of the hydraulic-actuated clutch assembly has increased over the past few years, but it's unclear how much advantage it offers over a properly functioning mechanical linkage. It seems that its primary benefit is replacing the countershaft and clutch fork with a firewall-mounted master cylinder and a slave cylinder for the throwout bearing.
The system itself operates similarly to a hydraulic brake system. When the clutch pedal is depressed, the pushrod displaces fluid from the master cylinder into the slave cylinder, which applies pressure onto the pressure plate. Companies like Keisler Engineering, Mcleod, Mr. Gasket, and Wilwood may offer complete kits that fit your Firebird. Try searching those company Web sites or contact the technical support staff for current availability.