Ok i have researched some info for for you guys with fitment questions that are too lazy to research yourself. ;)

The bolt pattern on s10/sonoma/blazer/jimmy and sytys is
5 X 4.75 and 5 X 120.65 mm

a 5 x 120 wheel will bolt up fine as long as you have the small hubs (newer s series) since most of the 120 wheels are for bmws and are hubcentric.

the best backspacing and offset for 2wds
Originally posted by 98layinframe on s10forum

The best backspace is:

4" with a 7" wide rim

4.5" with a 8" wide rim

4.75" with a 8.5" wide rim

best offset for 2wd

7" --- 0 - 4mm

8" --- 5 - 10mm

8.5" --- 10 - 15mm

now these are just approximations, the wheels you chose can vary from these measurements a little and still work.
i wouldnt go more then 4.5 backspacing up front since you will probably have rubbing issues depending on tire sizes with anything bigger.

backspacing refers to the measurement taken from the mounting pad on the wheel to the outside (back) lip in inches

heres a chart to show you how to measure these two things thanks to summit

offset is measured in mm and is the distance the mounting pad is skewed from the wheels centerline.

for example, a +15mm offset wheel would mean that the mounting pad is moved 15mm from the wheels centerline towards the face
heres a pic (right) that describes how offset is measured.

dont be fooled by offsets though. the offset doesnt tell you anything if you dont know the width of the wheel.

backspacing can be different for two wheels even if their offfset is the same. if you have a 15x7 wheel, with a 0 offset you will have 4" of backspacing, yet on a 15X9 wheel with a 0 offset you will have 5" of backspacing

dont get confused thinking that since the wheel is 15x7 that its backspacing would be 3.5" with a zero offset since the mounting point is right in the middle.

ZZ4 describes why there is this discrepancy
Originally posted by ZZ4Blazer
A wheel width is measured from the inside, like where the tire bead would set. but, If you measure the overall width of the rims, it will measure 1" wider. This is because of the outer lip of the rim.

So, a rim thats 15x8", will measure 9" wide if you measure across it without the tire on.
this is why you have a 4" backspace on a 7inch wide wheel because backspacing measures to the outside of the lip, which is .5" more.

so an effective method of finding out backspace if you only know the offset and the width would be like this:
18X8 wheel, with a +15mm offset.
the wheel is actually 9" wide (see ZZ4 qoute above)
divide the width by two (9 / 2 = 4.5)
so your mounting center is at 4.5" (from the outside edge of wheel) but it has an offset of +15mm

1" equals 25.4mm and 1mm = .04"

15mm = .59inches so you add that to your 4.5 and you get a total of 5.09 inches of backspace:bigthumb:

on to tire sizes

245 is the width of the tire in mm

40 is the ratio of width to Height
if im not mistaken it is the measurement of
the side wall given in a percentage of width
example, 40 in this case means that the sidewall height is 40% of the width (245mm) making the sidewall 98mm tall
so the tire is 9.6457" wide and the sidewall is 3.8583" tall

the last number is obviously the wheel size

here is a link to a thread on s10forum where the author describes which tire sizes are the best to use on drops and bagged vehicles
tire size info for drops and bags

hopefully this thread helps people to understand measurements and how to find them and gives usufull info on tire sizes and the such

i will try to find all the stuff for the 4x4s to post up soon.
if im mistaken on anything feel free to correct me, also if you want to post more usefull stuff or info for the 4x4s please do so.