ET vs Backspacing!

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crazyswede

crazyswede

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I have some trouble figuring out you americans and your inches:) Over here we never use the term backspacing since we measure the ET in millimeters. I figure the ET is 0 on my -72 valiant with Small BP but im not sure. Could anyone here confirm thats what it really is?

Reason im asking is because just like you guys have a hard time finding rims with SBP its close to impossible here if your not loaded with cash. Because of that i was looking to change to volvo BP using bolton spacers and since the old volvos use ET-25 i would guess i need a 25mm spacer to get the wheel back where its supposed to be.

Regards
Staffan
 
Hi Staffan,

backspacing is pretty easy, the measurement from the inner lip of the wheel to the mounting flange. If you compare a wheel with 4" Bsp and 2" Bsp, the track width is increased with 2" Bsp.

ET (Einpresstiefe in german) is always measured from the center of the wheel, positive ET means the track width is more narrow than if you use negative ET. The amount of ET is always measured from the center!

http://www.google.de/imgres?imgurl=...Vm6k5pkT4wL_kp0_KRsiVzM=&docid=amY4pvtT4kdK1M

Hope this helps. So i think if these Volvo Wheels use ET -25 and you have to use the adapter.....the track width will increase too much.

What kind of wheel are you searching? Wheel vintiques has got the oem steelies with 4" Bolt Pattern.

Michael
 
We Americans use the same measurement but we refer it as offset. Any wheel you are interested in should have a supplied offset accompanied with a Backspace measurement.

Most tend to only use or pay attention to the backspace number because it is easier for most to understand.

Below I will include a picture explaining the backspace measure as described by 360duster above ans also a chart listing offset vs backspace on a desired rim width.

hope that helps.
 

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71swing said:
We Americans use the same measurement but we refer it as offset. Any wheel you are interested in should have a supplied offset accompanied with a Backspace measurement.

Most tend to only use or pay attention to the backspace number because it is easier for most to understand.

Below I will include a picture explaining the backspace measure as described by 360duster above ans also a chart listing offset vs backspace on a desired rim width.

hope that helps.
Click to expand...

now there is some info. !!
 
Never heard of ET. Learned something new today!
 
Nice chart there 71swing and its very handy allthough it doesnt really answer my question unless anyone can tell me if my stock 5,5" rims got 3,25" backspacing because if so the stock offset would be 0 according to that chart. Only reason im asking is because i dont want to go out and pull a wheel off just to measure.


And to correct my first post. I got a bit confused myself so i mixed up the positive and negative offset. the wheel i want to use have ET25 or as it say in that chart +25 mm offset.
 
Ohhh....So that's what ET means...

And I thought he was trying to phone home. lol

71swing - that's a pretty nifty chart you have there. Thanks! By any chance do you have a higher resolution copy of that? That's pretty useful!

I sort of never understood why a 0 offset on an 8 inch width wheel would give a 4.5 inch backspacing. This offset reffers to the plane that sits up against the wheel hub/drum/rotor/whatever right?

If it's smack dab in the middle of the wheel, wouldn't it be 4 inches from the center line either way (fore and aft)?
 
When they refer to the width of the rim they are referring to the mid section of the rim not including the channel edge that holds the tire bead lock. The channel is usually a 1/2" more to the rim each side.

So a 8 " rim is really 9", 9" rim is really 10" and so on.

Back space is measured from the mounting flange to the very outside lip. That is why 0 offset gets you 4.5" bs on a 8" rim, because 4.5 x 2= 9"

hope that helps make sense.

crazyswede no way around it. Your just going to have to take a rim off and measure the backspace yourself to figure out your offset/ET
 
Positive offset moves the mounting flange out whatever mm the offset is. So 25mm moves the mounting flange out 1" roughly (25.4mm to 1"). In turn that adds roughly 1" to the backspace. Now you can overcome positive backspace with spacers to a point depending how far you what to push it on spacers. Negative offset only has one fix and that is to move the mounting point of the rim in like narrowing the axles housing.

I have some trouble figuring out you americans and your inches Over here we never use the term backspacing since we measure the ET in millimeters. I figure the ET is 0 on my -72 valiant with Small BP but im not sure. Could anyone here confirm thats what it really is?

Reason im asking is because just like you guys have a hard time finding rims with SBP its close to impossible here if your not loaded with cash. Because of that i was looking to change to volvo BP using bolton spacers and since the old volvos use ET-25 i would guess i need a 25mm spacer to get the wheel back where its supposed to be.
Click to expand...
Click to expand...

So yes if you figure your offest is zero but the rim you want to use has a +25mm then using a 25mm spacer will bring it back to zero offset. That only matters if you are using the same width of rims as before. 25mm is also a pretty thick spacer. more than I would be willing to ever use. You would be adding a 1 inch a material between you hub and flange. Adding a lot more stress to the stubs, that if they are even long enough to work. They do make the spacers that bolt to the hub separate than the rim mounts to it, but I dont think that is the route I would personally go.
 
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