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September 20, 2006

Camber and Caster Explained

The terminology used for vehicle dynamics is lengthy and detailed. You can run across a term as simple as a one sentence definition easily committed to memory or it can be a long drawn out equation that you wish you had never crossed paths with. For today’s discussion the terms will be rather simple and will allow you to better understand what is going on in your car.

The first term I want to cover is camber. Camber is simply the tipping of the wheel to one side or another. Positive camber tips the top of the wheel outward and negative camber tips it inward. Imagine the front tire on your car was perfectly straight up and down with a vertical line going through your wheel perpendicular to the plane of the ground. Looking at the wheel head-on you would see the line is vertical - representing 0° camber. See diagram A.

dia a.jpg
Diagram A, Road and Track Dictionary; John Dinkel 2000

There are a number of ways to look at and analyze camber, but camber thrust is the most important effect. Camber thrust is the lateral force produced by a tire when changing the camber angle. For road courses positive camber has no purpose, but negative camber is good for several reasons most importantly even tire wear (and temperature) and maximum cornering forces. Camber thrust is an additive force to those already generated by a tire going through a turn. You remember slip angle, right? Maximizing camber (and slip angle) can be difficult, but when you get it right it pays off in grip. In diagram B, you can see a plot of lateral force versus camber angle. You can see that with increased negative camber the lateral force increases too, however too much camber can cause handling trade-offs that are not justified. These tradeoffs include darting, skittishness and loss of braking force. It’s always a balance to maximize the variables that dictate a cars overall handling.

dia b.jpg

Now I’ll discuss castor, what it is, and how it affects steering and handling. Castor is a little tougher to visualize so I included diagram C. Viewed from the side - castor angle is the angle between the steering axis (Kingpin axis) and the vertical. Positive castor angle is when the steer axis contacts the ground forward of the contact patch and negative for the opposite case. Cars use positive castor, but as you approach 0° the steering behavior changes.
The biggest effect of castor is in the steering response. Castor angle plays a major role in the quickness of steering and how well a car tracks a given line. Quicker steering allows for a better turn in to a corner, but the downside is a car has a tendency to dart around. I think we’ve all gone down a hill as kids on a tricycle only to input too much steering and boom - off you go. Conversely, going down hill at high speed on a Bigwheel was a piece a cake.

dia c.jpg
Diagram C form “Fundamentals of Vehicle Dynamics” Gillespie 1992; pg 284

The Kingpin axis offset is something else that one must look at and there are a couple interesting things related to it. The main reason it is done is for packing of components i.e. brakes, suspension and steering. The wheel is essentially pushed out to make room and the resulting rotation is not about the center of the tires contact patch in a vertical sense. It rotates about a point toward the inside of the contact patch which adds steering feedback from the front end and we all know feedback is good.

This pretty much covers the basics of camber and castor and will give you a better idea of what is going on down in the wheel well of your car.

Project Mazda6

We have a bit of catching up to do—many projects have gone through the overhead door of our workshop since we opened last year. This section of the VRBlog deals with the interesting projects we’re working on, have worked on or will work on.

To get things kicked off, I thought I’d start at the beginning with one of our first projects. This particular project also highlights the fact that any car can be improved with a few simple modifications.

Mazda 6 with Eibach Pro-kit 005a.jpg

The Mazda6 is a great sports sedan straight out of the box. With ample power, decent handling and aggressive good looks, this Mazda midsizer needs just a few tweaks to go from mild mannered to something special.

The first thing we did was open up the breathing by adding an Injen cold air intake. Injen produces some of the best turned out pieces on the market today and the CAI for the Mazda6 did not disappoint.


Now that more air is coming into the engine, we focused on the get it all back out. Again we went to our friends at Injen and purchased a great looking catback exhaust system. Not only do the new tailpipes look great, the car sounds so much better under hard acceleration.


The final thing we tackled was the suspension. We dumped the stock springs and replaced them with Eibachs all around. The ride and handling improved and so did the overall look of the car. Before and after pictures really show the amount of drop, which ended up being about 1.5 inches:

Mazda 6 with Eibach Pro-kit 002.jpg Mazda 6 with Eibach Pro-kit 006.jpg

Mazda 6 with Eibach Pro-kit 003.jpg Mazda 6 with Eibach Pro-kit 007.jpg

Between the opened up intake sound, throatier exhaust note and the aggressive new stance, the subtly tweaked Mazda now means business. Added horsepower through the entire rev range and increased mpg figures don't hurt either!

The Workshop

In a previous post I talked a little about the two owners, Eric and myself (Horst), so I figure this time I should fill you in on the shop. Yes we sell worldwide thanks to our online store, but our focus really is the workshop. It’s there were we get to mess around with cool cars, work with our customers one on one, and just plain get out from behind the desk and do some real wrenching.

We’re located just north of the city of Detroit in Sterling Heights (voted one of the top ten places to live in the United States but some national magazine if that counts for anything). We’re renting a unit in the back of a small industrial park. Here's a shot from the street:


Standing in front of the unit:


The unit is 3600 square feet which is larger than most small shops. Thanks to the space, we can work on several projects at once without being crammed.


Inside we have the full assortment of the usual tools including many specialized tools that are designed for specific jobs like taking the cam sprockets off an STI engine. We even have a $900 spring compressor designed specifically for Mercedes cars (everything for a Mercedes is expensive!).

We have a top notch air compressor to run all our air tools and two brand spanking new Rotary brand lifts to hoist the cars. At 10,000 pound capacity each, we can easily work on any car in full safety as well as most trucks. Frankly, if it weighs more than 10,000 pounds, we don’t want to touch it anyway.


So there's a quick tour of our workshop. If you're in the area, feel free to stop by and check us out.

VRPerformance LLC
43677 Utica Road
Sterling Heights, MI

September 19, 2006

Review: BMW 335i

I recently had the chance to flog the newest BMW coupe, the 335i, around Pocono Raceway and I came away extremely impressed. Not only is the 335i coupe a handsome car-- the best design exercise from the Bangle gang to date-- the engine is a true masterpiece.


The first things you notice when walking up to the car are the terrific proportions of the coupe silhouette and the wonderful BMW stance. BMW has always done a great job of hunkering the body down over the car's chassis, despite the compromises that need to be made for various arcane government regulations and standards. The gaps between the tire and the wheel well are as tight as you can get this side of the Fast and Furious crowd. The front overhang is artfully disguised by the chamfering of the corners and the character lines that run all the way to the bottom of the fascia. Yes, the overhang is relatively short, but it’s made to appear even more so thanks to these styling tweaks. The smooth flow up and over the greenhouse and into the trunk is much more elegant in the coupe, especially when compared to its blocky sedan counterpart. The longish rear overhang is perfectly in step with the overall design. Even the upward swooping side lines that BMW is slapping on every new model seems to work well here. Yes I would prefer fewer of these lines in the overall design, but given the new BMW design language parameters, it does work.

The IP is lifted straight from the now familiar sedan, though the rest of the interior has upgraded details that make it a much more sumptuous place to conduct business. The seats in the sport package equipped test car fit this bum quiet well offering enough support for spirited everyday driving. For track duty I would prefer a less slippery seat material or better side bolstering, but that may be an unreasonable request considering most people will not be tracking the car to and from work everyday.

Hit the start button (one of the more annoying automotive trends of late) and you are barely made aware of the potential of this masterful power plant. Just a whisper quiet idle tells you the machine is ready for your input. With 300 hp and 300 foot-pounds of torque, you will be happy with the result. The engine pulls smoothly, and without any discernable turbo lag from idle to redline with a linearity heretofore never felt in a turbo engined car. The accompanying sounds from the engine when it is under full load are spectacular—this is the first modern BMW that actually sounds good straight out of the box.

The handling around the combination oval and road course layout at Pocono Raceway, where we were testing, is solid. Understeer is its failsafe mode, but you can squeak out the tail if you try. Hit a corner just right and it’s neutral all the way around.

The 335i is by no means an M3, which despite being down on torque feels quicker in almost every circumstance thanks to its less compromised state of tune. The new coupe is however, fast, much more sporting than an Infiniti, Lexus, or Audi, and very easy to live with. You could call it an M3 in velvet gloves—power in abundance, capable handling, yet easy to live with.

September 02, 2006

Two Guys and a Garage

To kick things off I figure it might be a good idea for a quick introduction of the men behind not only the blogs you’ll be reading at this site, but also behind VRPerformance.

To kick things off I figure it might be a good idea for a quick introduction of the men behind not only the blogs you’ll be reading at this site, but also behind VRPerformance.

The “V” in VRPerformance is Eric, a graduate mechanical engineer and the technical force behind the shop. Fittingly, he’s also in charge of the “Tech Talk” category of the VRBlog. He spent his youth moving around the country, including a stint in Germany, but I think he considers himself a product of Iowa since his family’s roots are firmly planted in the Hawkeye state and it’s where he went to university.

Eric at Gingerman1.JPG

The “R” in VRPerformance is yours truly. My name is Horst and I’m the organizational member of the team. I’m also a graduate mechanical engineer but thanks to my prior business experience, I’m the one in charge of keeping the books straight. I’m a real automotive aficionado in the broadest sense and carry International Motorist Press Association credentials which grants me access to the latest scoops from the automotive world, and which I’ll talk about in the “General Automotive” category of the VRBlog.


The two of us met at a local BMW Car Club of America event years ago. Our mutual passion for working on and driving fast cars led to a good friendship and now a business partnership.

Please check back often to see what we’re working on at the shop in our third category titled “Projects”, or see what technical tips Eric has come up with, or the latest news and opinion in my blog. We hope to make this a forum useful for like minded car enthusiasts and certainly welcome your considered feedback.