Date: Mon, 6 Mar 2000 19:19:18 -0500
Reply-To: Tom and Dana Cates <dcates1@HOME.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom and Dana Cates <dcates1@HOME.COM>
Subject: Re: Mercedes wheels (Offset)
Content-Type: multipart/alternative;
Bearing failure is an important consideration when determining wheel offset.
More important is the scrub radius. Pardon my terms but I only distantly remember this from my textbooks.
A line drawn through the center of the pivot point of the two ball joints intersects the road surface at a certain point. A vertical line drawn through the centerline of the wheel (bisected like a bagel) intersects the road at another point.
If these lines intersect at the road surface, the vehicle has zero scrub radius. If these lines do not intersect at the road surface, then the vehicle has either positive or negative scrub radius, depending on where they do intersect.
Changing the total offset from stock changes the scrub radius. Changing the tire diameter changes the scrub radius.
So what?
When you have a tire blow out at speed, stock scrub radius is your friend, and my friend too, if I am driving my vehicle anywhere in your vicinity. Stock scrub radius allows you to maintain maximum control of your vehicle in these kinds of situations where control is severely diminished.
VW Engineers know a lot more about these kind of things than I do.
Tom Cates
83 Westfalia "Hammurabi"
Michael J. Sullivan Wrote:
I agree with your logic! -- however, are you saying that Winkler, HA Projekt, and Projektzwo are offering wheels that don't meet TUV? I thought they were!! In fact, I was counting on their expertise.
While it does make sense that, IN THEORY, all Vanagon wheels would always carry the same offset regardless of width, even Volkswagen didn't follow this logic!! For example, they use ET30 for their own 6" wheel and ET35 for their own 5 1/2" rim. Now WHY would Volkswagen do this??? And WHY would Winkler, HA Projekt, and Projektzwo offer 7" rims with ET23 and 6.6" rims with ET27??? It makes one wonder...
I can only offer my own theory: That for the Vanagon, there was too much chance of interference to allow the tire to move INWARDS without undue the possiblity of problems with rubbing on the trailing arm and other suspension components -- particularly with extra-wide tires and/or chains. Obviously, VW engineers felt confident that moving the tire slightly OUTWARD as you increased the width of the rim was desireable, without any undue consequences to the engineering of the suspension components.
I prefer to be conservative and trust people who are offering legitimate, TUV-approved, equipment made specifically for our Vanagons. If it turns out that either Audi or Mercedes ever made a wheel that was "proper" then we should actively promote this as a viable solution. However, as has been noted elsewhere, MOST (if not all) Audi/Mercedes wheels are designed for vehicles whose suspension geometry is vastly different than the Vanagon. And this is particularly true of all recent Audi/Mercedes vehicles.
Cheers,
MJS
At 09:12 PM 3/6/00 +0100, Per Lindgren wrote:
>Michael,
>
>YOu say that your rims have an offset of 23 mms, right? If so, you are way off concerning safe offsets! I cant say I'm an engineer, cause I'm not. I do know that rims with an offset of more or less than 7,5 mms than stock are illegal to use here in Norway without TÜV approval, so that wont ever happen for me.
>
>You also say to put in spacers, but there's more to it. The spacers are made to make wheels with deeper offset fit with cars that have less offset. E.g.: the 1996-2000 Eurovan have an offset of 60 mms, the Vanagon have an offset of 38 mms. For these wheels, one must use a 20 mm spacer for them to fit, and be within clearances and specifications over stock. A rim with 23 mm offset can not be used
>with spacers, and is also not good for the bearings. And that's what it all boils down to: The bearings! The offset is set to fit the bearings on the car, too much or too little will damage the bearings, as they will put excessive pressure on one of the sides of the bearings. A Mercedes rim that is opened up 2 mms is much safer than risking loosing a wheel because of ruined bearings, IMHO!!
>
>PerL
>87 Syncro 112i (soon with Audi rims)
>
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