ET question

[diymirage]

i am looking to replace the rims on my plow truck and i am a little confused
(the stockers are long gone so i only got internet date to go on)


what i found is that stock wheels were 18X8 with an ET of 40

the wheels i want to get are 18X9 with a ET of -9

if the wheels were the same width, i would say this would push them out 49 mm, but with the difference in width, would that only be about 36 mm?

(i will try to see what exactly i have on there now, to complete the picture)

 

[Dana67Dart]

with an ET of 40

Is "ET" backspacing? Is that in mm?

Post some photos and part numbers of what you are looking at and have now.

Did some digging..

ET is german term for backspacing

"Offset is usually stamped or engraved into the wheel and is measured in millimetres of 'ET' [ET is the short form of the German word 'Einpresstiefe' which literally translates as 'insertion depth'] Positive Offset wheels have their mounting face toward the front face of the wheel"

So yes if you go from +40 to -9 you would be moving the centerline of the wheel 49mm outword. (About 2 inches)

 

[diymirage]

Is "ET" backspacing? Is that in mm?

Post some photos and part numbers of what you are looking at and have now

from what i understand, ET is the newfangled way of calculating backspacing, but with different parameters

ET is distance the back of the mounting flange is removed from the centerline of the wheel

i will pop out and snap some pic here in a minute of the old stuff

in the mean time, here is a website that shows what the comparison should look like with the stock wheels

Wheel size comparison calculator (wheelpcd.co.uk)

 

[Dana67Dart]

Keep in mind that moving the centerline of the wheel has an effect on the bearings. Might be negligible?

Do you have clearance on the outside of the wheel opening to accept the reduced backspacing?

 

[Dubob]

ET is the position of the wheel center in relation to outer ring of the rim. So a “0” ET puts the center of the rim right in the middle of the outer ring (the lug mounting area) A negative ET puts more of the rim and tire towards the outside of the vehicle a positive ET puts more of the rim and tire to the inside of the vehicle. So your ET of 40 puts the wheel to the inside of the vehicle. All things being the same the -9 would move the outer wheel towards the outside of the vehicle by 49 mm from where the current wheel is.

Wheel Offsets Explained - Konig Wheels

 

[diymirage]

this is the wheel i want to put on


Amazon.com: Pro Comp Alloys Series 69 Wheel with Polished Finish (18x9"/8x170mm) : Automotive


And here are some shots of what is on there now (pretty sure they are 20x10, but no idea what the ET is)

 

[Dana67Dart]

What truck are you putting these on?

 

[AJ/FormS]

There is, IMO, a very good reason companies went away from the old "offset" system . Offset tells you something ......... but it is by itself, a useless number, in that you have to also know the rim width to calculate where the rim will end up.
Whereas backspace tells you right off, no math required.

 

[diymirage]

What truck are you putting these on?

05 F350 superduty




a quick internet search leads me to believe the wheels on there now are "fuel Blitz" in 20X10
most of those seem to be ET-18
some ET-12

but IF that is the case, then the 18X9 -9 wheel will still fit within the "outline" of what is on there now, being just as for from the suspension, but sticking out less

(which i think is good, considering it is a plow truck and ideally, the tires dont stick out past the blade)

 

[Dana67Dart]

Any pick your parts near you?

Easy way to find cheap wheels?

 

[diymirage]

Any pick your parts near you?

Easy way to find cheap wheels?

a few, but id rather go with new



so..this is what im looking at
the first one is OEM , the second is what i am looking to buy

and this is the comparison with what i "believe" is on there, and what i want

so, if i am correct then the new wheels will be just as far out of the suspension, but because they are narrower, they will stick out less



so are we all in agreement this will work?

View attachment 1715805969

 

[diymirage]

here is the same picture, but only with the rims
(red is OEM blue is what i want)

and for comparison, red is what i think i have, and blue is what i want

 

[Dana67Dart]

Looks like you have coveted all your bases

 

[diymirage]

I went ahead and ordered the wheels and tires
I should be able to get things going in a week or so (depending on shipping)

For reference, here is a shot showing how far the wheels stick out now

 

[Dana67Dart]

that looked a lot more in your first photo.

 

[diymirage]

sure did, but i got the little wooden slat sitting pretty level on the tire, and there is no bend to it

who knows, the new setup might actually fit into the wheel wells

 

[diymirage]

got the rims in earlier this week
had a little bit of a hard time getting the tires in but the last two trickled in today, so tomorrow i will get it all mounted and hopefully on the truck

 

[diymirage]

Got the new wheels on

It turned out I was wrong on the specs of the old wheels, they were 20x9, ET0

All in all, I think I tucked them in a whole 1/4 of an inch more, but the thread pattern is probably a good inch narrower, which should help with snow...and I much prefer the looks