Friday, August 21, 2015

Wheels, Studs, Chrome and Backspace

Today's post is about wheels, rims and going larger-than-stock. There are so many opinions on this topic, that finding the gems of key information in the sea of religious wars is really hard. Case-in-point, there are literally thousands of threads each dating back years, covering hundreds of pages on TheSamba. Seriously, try a search for "tire" in the Samba search engine. Ridiculous. Trying to find actionable intel is virtually impossible, but, frustratingly, it is in there. There are some great sites, though, and Google can help. I'm putting everything I figure out here so I can find it again later.

I've mentioned Richard Atwell before. He's like the new Bob Hoover for bay window buses. I've never met him, but we've emailed over the years. His site ( has a section on tires, and it, like the rest of his site, is much more geared towards those who wish to keep their bus as stock as possible. There is a short section about going larger than stock, and the show-your-work math helped me build a spreadsheet to figure out what rims would work. If I can figure out how, I'll upload that spreadsheet so you can leverage it too. If I don't, this is a neat calculator I stumbled upon after I'd already created the spreadsheet.

Anyway, with the info from RAtwell in my head, I found a set of Mercedes 15" aluminum 5x112 rims with flaking chrome. Yucky looking but the $50 price was right for perfectly round, undamaged rims. I started my usual way: learn how to remove the chrome first, then see if it makes more sense to pay someone else to do it. Well, with muriatic acid, it is possible to remove the chrome at home. This is strongly discouraged. No matter how many sites say that it is easy and you can handle muriatic acid safely with the right gloves, etc, the resulting chemical (Cr-6) after the stripping is highly toxic. Think "your own personal super-fund site" or Erin Brockovich. There is a reason why chroming companies are disappearing across the US. The waste produced is some of the nastiest stuff around. In short: don't do this.

So, if I can't do it, I can pay someone else to do it, right? Yes. In Portland Oregon, August 2015 it will cost $100 per wheel for an environmentally responsible shop to do it and it will take up to 6 weeks to get them back. So, my $50 rims just became $450 rims. Hmm.. Maybe I can simply scuff them up a bunch with sandpaper and paint them?

That's what she said
With the reality of stripping the chrome still stinging, I thought I'd test fit these things while I thought about it. The memory of the failed jacks (see Santa Clara by way of Wheeler) still in my mind, I slid a 2-ton floor jack under the shock absorber mount and pulled the driver-side front wheel. The kinda grody 15" rim's holes aligned, but the rim couldn't slide home. This brought up my first new discovery: many MB rims, like the ones I got, have 12mm bolt holes, some have 14mm holes. VW buses need 14mm, so the stud is too thick for the hole. This can be resolved with a 9/16" or (better yet) 37/64" 19/32" drill bit, shaving that little bit of material out of the hole so the stud's fit.

Yes, Size Matters
I also noted that the thickness of the rim at the bolt-hole is much thicker than the old steelies. Yeah, that's obvious, but its about 20mm thick. The existing studs aren't long enough to stick out the other end with enough threading for the wheels to be safely held onto the hub by lug nuts. These studs aren't very expensive, and many people claim swapping out the studs isn't that hard.
used without an "ok"

For posterity, I derived these numbers from The bay-window bus studs are all press-in, after 1970:
Rear (drum brakes): 37mm long, 14mm thick
Front (disc brakes): 44mm long, 14mm thick

If I were to replace the studs with a set that would fit, I would need 57mm rears and 64mm fronts (stock plus 20mm) plus or minus. has studs available which are close, and after conferring with John, the 2.2" (55.9mm) should work on the rear and 2.5" (63.5mm) should work on the front. I know my history enough to know that it could take me a day per wheel (I'm slow. I make mistakes and I don't like doing too much at once). Once I run that math, I expect mounting these $50 rims to cost me thousands in my usual charge-myself-$50/hour planning. Before I take that plunge, I switched my focus to thinking about simply buying rims from Cip1 or jbugs.

Rub Rub Rub
nicked from JBugs
There are all kinds of really nice looking, shiny rims on the market. They so pretty. Unfortunately, the new rims out there are not designed for the rear fenders of the bay window bus. Those rear "flares" don't flare out very far, and most of the rubber above the top of the rim is covered by it. This limits the ET the bus could support.(from RAtwell's tire section: ET is German for Einpress Tiefe. and it's the measurement in mm from the rim center line to the mount where the brake drum or hub contacts).

The websites don't publish the ET of these new rims. They talk in terms of inches of backspace. Backspace is the distance from the inner lip of the rim to the wheel mounting face. Since we know the backspace and the ET for the stock wheel, we can figure out the ET, though. Ha! The stock rim has a backspace of 4.75 inches and an ET of 39mm. Most of the new ones have a backspace of 3.75 or 3.5 inches. These lower numbers push the wheel further out from the hub, lowering the ET. If you've ever tried to put tire chains on the stock rear tires, you know there simply isn't that much room. Once we add in the section width, pretty much any tire that isn't one of those extreme low profile (requires special tire-mounting equipment) tires won't fit. Still, let's do the math: 1 inch equals 25.4mm, so shifting the ET of 39mm down by an inch puts it around 14 (39-25=14). I ran another math model where it was closer to 20, but the point is the same: the new rims are designed for a Vanagon at best, but more likely a beetle or squareback. Some metal work, either to the rims or your rear flares, will be required to make them fit.

Hope Glimmers?
There's one last glimmer of hope for a relatively quick swap rim: the newer Passat rim. The newer Passat, and some Audi's, were shipped with a 15" steel wheel on the 5x112 base. Unfortunately, the center hole for these rims are closer to 1.5" than the required 2.5" needed to clear the grease caps and castle nut on the old bus. I happen to have a set of these 15" rims. Of course I do. You knew I would. I've read about expanding the center hole, but tire shops won't do it out of fear of getting sued. Gotta love the American system sometimes. Anyway, it is entirely possible to figure out the right line to cut and then cut it with a special drill bit, or a Dremel. Frankly, that sounds like a bad home-mechanic idea. The probability of making the rim unusable is pretty high. And, while the tire shops fear lawsuits, they fear someone getting hurt or killed because of one of their rims failing even more. That fear is contagious; now I fear that too. I suppose, if I knew a tire guy who could assure me that it could be done right, maybe my fear could be eased. Until then, that set of rims will sit, and eventually fall onto craigslist for someone to use for snow tires.

I'm back to the original grody-looking rims. I picked up a 9/16 drill bit last night, and tonight I'm going to have a go at one of the rims.

UPDATE (August 24th, 2015): 9/16 is too small. While it did shave some material away, 9/16" is 14.29 mm and the threads are bigger than .29 mm. I have since ordered a 37/64" (14.68 mm) and a 19/32" (15.08 mm) bits. I'll update once I've determined which one worked best, removing the least material.
test fit success

UPDATE (August 29th, 2015): 19/32" is right. 37/64" didn't make a large enough hole for the rim to fit. 19/32 made it fit without wrestling, and the rim isn't flopping about sitting on the studs. As you can see from the picture, the 15x6 MB rim should look pretty good, once that chrome is covered up. Next, I'll have to get after the studs, etc. I'll post about that separately, when I get to it.

Thanks for following along... if you did. There's many hours of research distilled down into about 1400 or so words.

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