On Apr. 18, Brent H. wrote:
>Here's what I've learned or been told about the 17x9 R/T wheels
>(mostly from all the helpful people on the DML):
>
>- backspacing is 6.5" (15x7's are 5.5", 15x8's are 6.0")
>- "frontspacing" therefore is 2.5" (9" total width)
>- same OFFSET as the 15x7 and 15x8 Dodge wheels, therefore
> a 17" tire with the same diameter and section width as the stock
> 15" tires should not rub because it would be located in the same
> place relative to the truck (note that the RIM LIP will stick out
> a bit more to the inside and to the outside, but the tire's sidewall
> should be in approx. the same location, just with less bulging)
I know the 15x7 backspacing is 5.5" (measured it myself). For this
reason, I am almost 100% sure the 15x8 backspacing is 5.0" (a 6.0"
backspacing would move the rim inward towards the truck ... cannot
do as it would hit the end of the A-arm). A 16" rim may clear
this A-arm but it would be close ... a 17" rim would definitely clear
it but there may be other obstructions as you turn lock to lock.
Backspacing, frontspacing and offset are inter-related. Whenever
you are using these concepts for measuring, you have to take into
consideration that ALL rims have a real width that is 1" more than the
advertised width (extra 1/2" on each side of the rim for the bead of
the tire to nest).
For example, the advertised width of the R/T rim is 9" but when
you start calculating backspacing/frontspacing/offset, the figure
you use for real rim width is 10". Using the above figure of 6.5" backspace,
the R/T rim has a front space of: 10 - 6.5 = 3.5"
and the offset is:
backspace - (1/2 x real rim width) = 6.5 - (1/2 x 10) = 6.5 - 5 = 1.5"
Once you have these figures, you use them, along with a specific tire
dimensions (cross-sectional width, overall diameter, tread width),
and see if you can clear suspension obstructions, have enough wheelwell
space and where the rim/tire combo sits in relation to the fender lip.
For me, personally, I use backspace to see if the rim will hit any of
the suspension/truck parts. I use backspace and frontspace to see
where the rim will be in relation to the fender lip. I use a tire
dimensions with the aforementioned to visualize if a tire mounted on the rim
would hit any obstructions ... the rear are easier; the front more difficult
because of the different positions when turning lock to lock.
Bob
Burlington, Ontario
'97 CC Sport, 5.2L, 3.55, auto., 4x2
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