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Old 06-22-2015, 06:55 PM   #1
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Advise on "offset" when selecting new wheels

In the process of replacing the current wheels on my Sportsmobile and hoping someone out there can confirm my deductions: . The OFFSET (If I understand this correctly): I'm told my current 17x8 wheels have a +2 Offsest, and am looking at a 17x9 with a declared -4 Offset.
Now, if I understand the process, this means that I would be pushing the wheels/Tires outward by 2 more than what they are currently sitting at... Can someone confirm if I have figured this correctly?
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Old 06-22-2015, 08:19 PM   #2
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Re: Advise on "offset" when selecting new wheels

I base wheel selection on backspacing instead of offset. More backspacing tucks the wheels in closer to the chassis. We try to use 4.5", its ideal.
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Old 06-22-2015, 08:49 PM   #3
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Re: Advise on "offset" when selecting new wheels

Im glad someone ask this question. I just ordered these

http://www.summitracing.com/parts/rl...8080/overview/




for my 94 coachmen rv. It says 3.625 back spacing. How do you think they will work out? I was trying to mimic this

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Old 06-23-2015, 08:04 AM   #4
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Re: Advise on "offset" when selecting new wheels

applications will be different so there is no right offset or backspace. especially when going for a certain look. just gotta bust out the plum-bob and do some measuring.



Some members have been posting useful info in this thread that might be of assistance too:

viewtopic.php?f=3&t=15619
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Old 06-23-2015, 09:10 AM   #5
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Re: Advise on "offset" when selecting new wheels

Stock E-Series wheels had a 0 offset - the wheel mounting surface is centered.

Your current 8 inch wide wheel has the mounting surface 2mm (5/64 just over a 1/4 inch) outboard of center. So basically you have 4 5/64 inches of wheel inboard (backspacing) and 3 59/64 inches outboard.

The new 9 inch wide wheel has the mounting surface 4mm (5/32 of an inch) inboard of center. So basically you have 4 20/64 inches of wheel inboard (backspacing) and 4 42/64 inches outboard.

The outside to outside width will be almost 2 inches wider because of the wider wheels and change in offset - I think it will be a good option.

Disclaimer - math done in my head while chewing gum so...


Quote:
Originally Posted by Twoxentrix
In the process of replacing the current wheels on my Sportsmobile and hoping someone out there can confirm my deductions: . The OFFSET (If I understand this correctly): I'm told my current 17x8 wheels have a +2 Offsest, and am looking at a 17x9 with a declared -4 Offset.
Now, if I understand the process, this means that I would be pushing the wheels/Tires outward by 2 more than what they are currently sitting at... Can someone confirm if I have figured this correctly?
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Old 06-23-2015, 09:45 AM   #6
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Re: Advise on "offset" when selecting new wheels

And remember that offset is the amount off the center. If you get wider rims than you had before, you have to account for that change as well.
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Old 06-23-2015, 05:58 PM   #7
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Re: Advise on "offset" when selecting new wheels

OK - Seems the calculations I have done pretty much hold value - without benefit of chewing gum This leads me to the next question: If I choose a wheel with an offset that increases the stance of the vehicle by about 2 to 3 inches, will that create any problems with the Front end handling >> such as steering drift, or can I assume this will be negligible? (I have a Dana 80 rear axle, and a Dana 70 Front if that makes any difference)
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Old 06-23-2015, 11:27 PM   #8
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Re: Advise on "offset" when selecting new wheels

Besides 2 to 3 inches looking a little cholo...? Steering will feel a little heavier but your axles are up to the task.

Personally, I like 8 inch wheels the best and close to stock back spacing.
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Old 06-24-2015, 06:16 AM   #9
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Re: Advise on "offset" when selecting new wheels

I think the key to the offset is the steering axis inclination and the scrub radius. Anyone know what these settings are stock?

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Old 06-24-2015, 06:30 AM   #10
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Re: Advise on "offset" when selecting new wheels

Quote:
Originally Posted by jydog
I think the key to the offset is the steering axis inclination and the scrub radius. Anyone know what these settings are stock?

Of course. I don't know stock scrub radius (steering axis inclination is not affected by wheel changes as it is built in to the axles assembly), but do know that stock wheels have 0 offset and staying as close to that as possible is the best for maintaining stock scrub radius - although it is not as important on our live axle suspensions and people get away with lots of scrub radius. Not my preference - I don't like the "look".
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