Plan to go from my stock 16x8 w/255x50x16 to: 17x9.5 and
245/45/17 (front), and 285/40/17 (Rear).

In order to purchase the right size wheels, what are the numbers
re: offset, backspacing, pattern,etc.
And do I need to buy "Rear Jounce bumper spacers"
SLP states they are required when moving from 16 to 17"ers.




95 Z28 LT1 Red w/black t-top. too many mods to list...Thanks.

 

Always a good idea to start with the "Wheels and Tires FAQ".... everything I have typed below is contained in the FAQ.

Many manufacturers do not recommend that you put a 245/45-17 on anything larger than a 9.0" wide wheel. Some will accept a 9.5" wide wheel, but its probably going to look a little "stretched" and not provide much in the way of protection from road rash.

For your wheels:

5 x 4.75" (120.65mm) bolt pattern

Offset in the range of 38mm (puts the tires at the very edge of the front fenders) to 56mm (puts the tire 3/4" deeper in the wheel well). There are pictures in the Wheel and Tire FAQ showing the various offsets. Read the post regarding "17x9.5" and 17x11 wheels on a 4th Gen".

Once you select the correct offset, the backspace will be correct.

(not in the FAQ) You do not need to alter the stock jounce bumpers when going to 17" wheels. Not sure why SLP keeps saying that. Many of us drive daily with 17" wheels, and have no problems related to the jounce bumpers.

 

Thanks for info. Understand most. Not mechanic, but musician.Offset
range 38 to 56mm . How to determine. Can wheels be ordered with correct
offset for 95 Z28 that is tire sizes given for a Z28 demand what offset
44/45 ? Also is 245/45-17 not a good size for front? Have to be able to
order wheels slap on tires and fit....Thanks...Theo

 

When you order your wheels, you need to specify the bolt pattern (5x4.75), the wheel diameter and width (17x9.5) and either the offset or the backspace. Offset and backspace are mathematically related, so you need to specify only one of them, not both.

To get your wheels to fit correctly, and avoid rubbing of the tires on the body, you need to get a wheel with an offset of 38mm to 56mm. Anything less than 38mm, and the tires will be outside the front fenders, and will rub on the fenders. Anything more than 56mm, and the wheel will be hitting the steering knuckle.

I would personally recommend that you get one of the following:

45mm offset = 7.0" backspace
49mm offset = 7.2" backspace
56mm offset = 7.5" backspace

While offset and backspace are mathematically related, you need to know the exact width of the flange on the wheel that holds the tire bead on the rim. That can be anywhere from 0.25" - 0.50". I used 0.50" for the above calculations, since that gives you the most conservative limits on the backspace.

245/45-17 is not a good tire for a 9.5" wide wheel, if the tire manufacturer does not recommend that it be used on any wheel wider than 9.0". As I noted, many manufacturers do not recommend anything wider than 9.0". Some do allow you to go to 9.5" wide for that size tire. You need to go somewhere like Tire Rack, and check the specs for the specific brand and model you want, because each manufacturer can be different, and you can find two different tire lines from the same manufacturer that are different.

Generally, when you want the "skinny front/wide rear" approach on the tires, you use a narrower rim in the front and a wider rim in the rear. Maybe a 17x8.0 in the front, 17x9.5" in the back. That allows you to put a 245/45-17 tire on the 8.0" wide wheel, and it will not looked "stretched'.... it will fit similar to the rear tire/wheel combo.

If you want to go 9.5" wide on the front and rear wheels, consider a 255/45-17 tire for the front. Those will fit better on the 9.5" wide wheel, and will also be a better match for the same outside diameter as the 285/40-17's you want to put on the rear.

I'll repost the picture you get in the FAQ when you click on the photo of the 17x9.5" wheels with 49mm offset (tires on all 4 wheels are 275/40-17):

 

Thanks so much for your time, very much appreciated.
Tirerack does not provide specs re: offset etc, you give details re:
your car and they match with a pic a set of tires with the wheels chosen.
discounttiresdirect, however, does give you a whole list of available offsets
etc. for wheels chosen. I guess when I order the wheels I need to ask
them which of the 3 offsets you gave- 45/49/56 would be recommended
given the Brand. BTW: Whls are "Smoothie 2 or Torque Thurst 2."
Thanks again...Theo