Tech tips | Understanding fender rolling, downsizing tires, wheel spacers and what makes a race wheel

Staff
By Staff Writer
Aug 12, 2022 | wheels, Shop Work, Wheels & Tires | Posted in Shop Work , Tires & Wheels , News and Notes | From the Aug. 2022 issue | Never miss an article

Photography Credit: David S. Wallens

Questions about fender rolling, downsizing tires, wheel spacers or even what separates a racing wheel from a street wheel? Lucky for you, we have answers.

Quick Tips for Using a Fender Roller

Most metal cars have a fairly aggressive lip inside the fender opening that stiffens the panel and provides support to the arch. This lip can be a dangerous point of contact for tire sidewalls on a lowered car with wide tires. Rolling over that sharp edge is an easy way to get a potential hazard out of the way.

[Fitting the largest tires possible on our MR2 did require some massaging | Project Toyota MR2 Turbo[

Fender rollers are fairly affordable these days. Eastwood and others will sell you one for about a hundred bucks, but rental units are still available from a variety of vendors for around $40 per week plus shipping. But their ubiquity doesn’t mean you can’t still screw things up really badly and really fast. So here are a few tips when working with a fender roller:

  • Things can go very wrong in a hurry, so work in very small increments. When rolling fender lips, we’ll turn the main adjustment screw about a quarter turn for each “bite.” It’s much better to take too many small bites than too few large ones and risk creasing some sheet metal.
  • Not all fender openings are circular. In fact, hardly any are. But the fender roller–being anchored by the hub–will sweep in a circular arc. This means it could put more tension on a certain part of the fender than another during a sweep. So when you make that first contact and get ready to start rolling, be sure to check the tension through the entire range of motion before you lean into it.
  • Heat is your friend. Rolling the fender lip can sometimes crack the paint. Heating the lip with a heat gun softens the paint as well as the metal to lower risk of collateral damage. Too much heat can blister the paint, but raising the temperature of your work area can make your job easier and less risky.
  • Tension works both ways. Remember, while you’re pushing up on the fender lip, the fender is pushing down on your suspension. This articulation can aid in negotiating non-circular fenders–as we mentioned before–but understand that as your suspension droops to the point where it runs out of travel, the tension on the roller can change dramatically from one adjustment to another. 

Chonckers: Why Did We Downsize Our M3’s Tires?

The quest for the perfect tire setup doesn’t always involve going bigger. Sometimes you might want to go down a size.  While a lot of people track their BMW M3s on 18-inch tires–and that can be said for both E46- and E92-chassis cars–why did we move our 2004 BMW M3 to 17s? To lower operating costs. 

[Do we like chonky boi tires? | E46-chassis BMW M3 project]

Let’s compare some prices regarding the Falken Azenis RT615K+, a popular track day tire: The 265/35R18 size retails for $203 each, while the 255/40R17 goes for $166. 

Does moving from 18s to 17s reduce footprint? About 0.3 inch per corner, but remember, in this situation we’re talking about noncompetitive track events, and we’re still doing better than the stock setup of 225/45R18 fronts paired with 255/40R18 rears.

Could smaller wheels be the answer? In the case of our BMW M3, going down to 17-inch wheels allowed us to save about $150 per set of track tires. 

The final piece of the puzzle for fitting those 17-inch Falkens on our M3? Apex Race Parts offers 17x9.5-inch square setups specifically aimed at E46-chassis M3 track cars. A square setup allows tires to be easily rotated, with a 12mm spacer properly placing the rear wheels inside the fenders. 

We ordered Apex’s flow-formed ARC-8. These hubcentric wheels weigh less than 17 pounds each and feature knurled beads, lots of socket room and clearance for big-brake kits. They also pass the paper test with our BimmerWorld spacers. Each wheel retails for $319, and should you damage one, Apex will sell you a replacement for 50% off.

Are we giving up that much speed with this setup? For track days, we don’t really care. The car feels properly balanced, as all four corners work together properly. Plus, we’ll get to enjoy less expensive consumables. 

Bonus of this swap: The extra sidewall gives our M3 the now-fashionable chonky boi look.
–David S. Wallens

Spaced Out: How the Simple Paper Test Can Prevent a Major Failure When Running Wheel Spacers

Wheel spacers are very much part of our world. They’re even used on the factory-built BMW M4 GT4 race cars. But there’s no set standard. Many wheel spacers feature some kind of snout that mimics the one found on the hub, but there’s no intergalactic governing body that ensures Spacer A is compatible with Wheel Z. 

Why does this fit matter? If the spacer’s chamfer isn’t properly engaging the wheel’s center bore, then there’s a slight gap between the spacer and the wheel. The result: Can you say broken studs? (And we’ll let you figure out what happens next, but let’s be honest, it ain’t gonna be pretty.)

So how do you know if your spacers are properly seating against your wheels? The BimmerWorld crew recommends the paper test. To perform this test, the wheel and spacer should not be mounted to the car. 

  • Step 1: Simply place a piece of paper between the spacer/wheel interface. You can use notebook paper, copy paper or whatever’s handy. 
  • Step 2: Apply finger pressure to the spacer–just press down on the spacer 90 to 180 degrees away from wherever you inserted the paper. 
  • Step 3: While applying that pressure, give the piece of paper a tug. If it slips out, there’s a gap between the spacer and the wheel, meaning things aren’t properly seating. Go fix. 

 

What Makes a Race Wheel?

While there might not be an official motorsports stamp of approval, a few details do make certain wheels more suited for competition–details beyond simply being lightweight. Of course, these perks can add to the price tag. What’s that line about speed costing money? 

  • Spokes that don’t poke out are less likely to suffer damage in side-to-side incidents. 
  • Knurled beads help prevent tires from rotating on the rim during lateral, high-g maneuvers.
  • Ample clearance around the lugs allows room for impact sockets and also facilitates tire changes. 
  • Off-the-rack or custom-tailored? If the latter is needed, that will cost extra. 
  • Will the requirement to use centering rings slow down pit stops? 
  • Running big brakes? You’ll need ample clearance. And can that be achieved without increasing rim size? 
  • Will any sharp edges slow down the crew during tire swaps? 
  • Light weights are important, but what’s the load rating? And are the wheels strong enough to surf the curbs?
  • How well is the lip supported? Again, is it strong enough to survive on-track punishment?

This wheel here

Forgeline designed its GS1R for IMSA competition. Weight depends on size and offset, but figure about 18 pounds for a 19-inch size. No matter the size, though, this model carries a 2100-pound load rating–basically, one Miata. All are made to order, meaning custom offsets for any application. The 19-inch version starts at $1945 per wheel, with the 17s costing at least $1495 per wheel.

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Comments
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rsmith7
rsmith7 GRM+ Member
8/13/22 2:34 p.m.

Glad this was posted as I'm looking to get wheels for my GTI and don't need them flying off on the commute. 

David S. Wallens
David S. Wallens Editorial Director
8/17/22 12:01 p.m.

In reply to rsmith7 :

Thanks and hopefully it helps. 

And thank you, BimmerWorld, for teaching us about the paper test. 

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