All of our weekly Tech Tips can be found here in one place.
When choosing which bearings to run in your hubs, remember that circle track and road race cars generate high lateral “g-loads” or side loads, which load the bearings from the side, in addition to the radial load from the vehicles weight. Angular contact or ball bearings work great in radial load applications, but do not perform well in side load applications, due to the limited contact area to distribute the load. Tapered roller bearings have slightly more drag in radial load only situations, yet significantly less drag in side load applications. For drag race applications, angular contacts are good. For circle track and road race applications, tapered rollers are the better choice.
All machined parts have peaks and valleys across the surface of the part. This is important when machined surfaces come in contact with one another in applications such as gears and bearings. These peaks and valleys create friction, temperature, and drag. Bearing surfaces are typically ground, giving the part a smoother finish for less drag. All surfaces with metal to metal contact will benefit from a smoother finish from processes such as our own DRP Premium or Super finishing. This process uses chemicals in a vibratory mill to cut down the peaks and smooth the surface. These parts often have a mirror finish due to the increased surface area and polishing effect. This type of surface finishing will reduce drag and temperature in hubs, rear ends, transmissions and engines.
When trouble shooting your brake system, remember to check volume as well as pressure. Large master cylinders can fill small calipers faster than small master cylinders can fill large calipers. This can lead to rear brake engagement before front brake engagement, causing a “loose corner entry” problem that’s hard to diagnose. Your caliper pressure gauges will read correctly at full pressure, covering up the problem early in the brake cycle. Watch your gauges and see which calipers engage first.
Bump Steer is dynamic toe change through suspension travel. Bump steer is caused primarily by the tie rod angle changing through travel, effectively shortening or lengthening the tie rod sleeve. When the chassis enters a corner, the springs are compressed and the chassis drops and rolls, moving the inner tie rod end and changing the tie rod angle. Simultaneously, the outer tie rod end height moves as the caster changes. Bump steer is also affected by camber change. The upper and lower spindle pivots (ball joints) move in or out as the upper and lower control arm angles change, which can induce steer as well. Bump steer affects each front wheel individually and is typically minimized as it is steering input that the driver cannot control.
Wheel bearings use a thin film of grease or oil to separate the bearing roller from the race. The ideal thickness of this film is dependent on the load and RPM of the bearing. When selecting a lubricant, choose one that is designed for high RPM applications as well as high load. A lubricant with too high of viscosity can add drag and temperature rather than reduce it.
2” Bearing 5x5 hubs are common in the late model circle track world. These hubs which use the 368A bearing on the inner and outer are offered in aluminum and steel. Many teams have difficulty keeping the aluminum hubs tight when they get up to temperature. To “fix” the problem, teams torque the spindle nuts excessively, which creates additional drag and temperature. The proper fix is to install a hub bearing spacer, preloaded to .003”, in aluminum 2” 5x5 hubs. This will let the hub roll more freely without the temperature build up or excessive end play.
When measuring your racecar dynamically (pulling the chassis down), it is critical to pull the rear down as well as the front. Sway bar bind, coil bind, bump stop load, caster and valance/splitter height are all affected by rear travel. As the rear of the chassis compresses it pivots off the front spindle centerline. Meaning, all chassis points in front of the spindle centerline lift and all points behind the spindle centerline drop.
Oil or grease? Wheel bearings use a thin film of grease or oil to separate the bearing roller from the race. Oil filled hubs have become more popular as teams found it hard to keep grease in angular contact (ball) style bearings. The oil also helps to cool the increased temperature in these bearings. Grease however, when used properly, has less drag than oil with less maintenance and less potential for failure.
Setting hub tension by “hand feel” may “feel” okay. However, testing shows that hub bearings without bearing spacers will always have preload or end play. When the hub nut is tightened to remove the end play, preload is present. When the nut is backed off to remove the preload, end play is present. Bearing spacers allow the exact bearing spacing to be set and the spindle nut completely tightened, eliminating any bearing movement.
When measuring Rear End Housing location, there are four primary measurements to make. First, the left and right axle tube should be measured for toe and camber. Next, the pinion angle should be set. Thirdly, set the lateral location (rear end location left to right). And, finally, set the static rear steer, commonly referred to as “square”, “forward” or “back” and typically referenced off the right rear. Skipping any of these steps can cause serious handling issues.
Detroit Lockers or “Ratchet” style differentials work opposite on corner entry verses corner exit. On corner entry, during deceleration, the right-side wheel unlocks while the left side wheel is loaded due to engine braking. On corner exit, during acceleration, the left side wheel will unlock to keep it “timed” with the larger right-side wheel. This unlocking of the left will occur going down the straight away as needed to keep the tires in time, based on their size differential. Check out this video from DRPUniversity on how to test a locker style differential.
Steering Ackerman is dynamic toe change through the steering motion. Or simply put, it’s when one wheel turns more than the other. Ackerman is separate from bump steer, although the two work together as you are cornering. Positive Ackerman is created when the inside wheel turns more than the outside wheel and net toe-out increases. Negative Ackerman is when the inside wheel turns less than the outside wheel and net toe-in increases. Ackerman is controlled by the steering arm length (from center of lower ball joint to center of tie rod end). The longer the arm, the slower the steer. If the left front steering arm is shorter than the right, it will turn faster (further) and increase toe out. If the left front arm is longer than the right, it will turn slower (less) and decrease toe out.
Measuring Axle Tubes is critical each time the chassis is set-up. Axle tubes bend easily, often without any contact. A bent axle tube can cause serious handling issues if not recognized. For example, if the right rear tube has unknown toe and the static rear steer is set, the left rear can have significant undesired steer. Unknown camber is equally dangerous. As the pinion angle changes, camber converts to toe, creating unknown rear steer dynamically. Be sure to watch out for those bent tubes!
When measuring Static Rear Steer, three things should be considered. First, the points to which static steer is referenced. Second, the front toe, relative to the rear end. And, thirdly, the dynamic rear steer caused by movement of the trailing arm chassis mounts.
How to Know What Components to Buy for Your Race Car
When choosing to purchase any component for your race car, there are 4 primary factors to base your decision on. #1 Performance. Is this the best component available for my application? Weight, Durability, MOI, Resistance all play into a products performance. #2 Fitment. Will this product fit my application without alteration? Will it work properly? #3 Cost. Is this product within my budget? Is the added performance worth the added cost? Is the loss of performance worth the savings? #4 Legality. Does this component fit within the rules of my track or sanctioning body?
All true racers should put performance first, but do it wisely so that you finish the race, pass tech, and have enough money to get back home!
For must hubs set the bearing spacers to .0005” (1/2 of one thousandth) end play with the bearings dry and no seal. Some hubs (Howe/Port City Style 5x5) require preload as they pick up end play when hot. (Mention hub end play gauges and link to product in store.)
Wheel location is measured in 5 basic axes. Toe, Camber, Caster, Lateral Wheel Location and Longitudinal Wheel Location. All of these wheel measurements are referenced to the chassis or to the ground plane. These axes have a starting location called static location, which is when the chassis is at static ride height. All of these locations change as the chassis moves dynamically.
We are going to be talking about one the most important (and least expensive!) pieces of equipment you will purchase for your race team. It costs right around $1.00 and you might already have one. This is a notebook. You can be fancy or simple, the main thing is you take thorough notes during every set-up. Record all measurements taken, changes that were made, components that were replaced. When at the track, record complete driver feedback after every practice session and after the race. Time is of the essence. Get this feedback as quickly as possible. Record all measurements taken, wheel weights on your scales, wheel weights on the track scales. Record lap times from each practice, how many laps were run and every change that is made to the car, no matter how small. Record the weather, temperature, humidity, track temperature, tire temperatures, and brake temperatures. It may not be a bad idea to record the drivers’ temperature as well. Is he/she happy, mad, zoned out? Record suspension travels, fuel level, air pressures, stagger, tire hardness and tire serial numbers.
The quality of the notes that we take will directly reflect in our rate of performance improvement week to week and year to year. You will only remember the things that are important to you. To see the whole picture, you need good notes to study and review the days following the race or test session. Good notes allow every track experience to be valuable, no matter what the outcome on the track.
Good slip plates are critical to consistent set-ups. When you jack up the car to make an adjustment or to put it on the scales, the suspension drops. When you let the car down, the tires catch and do not fully relax on their own. If the tires are not relaxed, your ride heights, wheel weights, and wheel positions will not be accurate. Rolling the car back and forth in the same 24” span will not fix it. You need good grease plates or PTFE slip plates.
How to straighten the rear.
If you measure your rear regularly, and you should, you will need to straighten it regularly as well. To straighten the rear without a dedicated fixture, use a torch and water. If you need to toe the tube in, heat the front side of the tube in a nickel sized spot until it gets red (Not melting red, just red hot). Now, cool the spot with water. You can do this with a tub and rag. When the tube heats, it expands (actually moving it in the wrong direction), but when it cools it shrinks further than it expands, toeing the tube in.
Here’s a cheat sheet: Toe in, heat the front side of the tube. Toe out, heat the back side of the tube. Negative camber, heat the top of the tube. Positive camber, heat the bottom of the tube.
Set-ups are performed in the shop, on a level ground plane. They are not performed at the track. This is not to say that we shouldn’t scale the car at the track or make any adjustments. Of course, we will. However, we don’t adjust suspension settings to match the un-level, rough asphalt at the track. All adjustments should be tested first in the shop to determine what offsetting adjustments may need to be made. This is very difficult to do at the track in an accurate or consistent way. Take your adjustments seriously!
Wheel bearings use a thin film of grease or oil to separate the bearing roller from the race. Any additional grease is just along for the ride, with no useful benefit. In fact, too much grease creates drag and additional bearing temperature. If you’ve ever had seals push out of freshly packed hubs, it’s due to the excessive temperature and pressure build up from over packing. A good rule of thumb for racing applications is to pack the bearing 50-66% full. If you injection pack your bearings, simply fill every other roller. This will provide more than enough lubricant, with less drag and less heat. Properly packed bearings can run longer between servicing than over packed bearings.
The ideal “end-play” for all hubs is zero. End-play creases drag due to increased toe and allows the bearings to run out of there proper seats. Pre-loaded bearings are not ideal either due to increased drag and temperature. Hub bearing spacers allow most hubs to be locked in with zero pre-load and zero end play, the ideal setting. Some hubs will require small amounts of preload due to thermal movement of the races. See our hub set-up chart for recommended settings.
Bump steer has been traditionally measured by moving the suspension, typically with a jack, on each front wheel. While better than not measuring at all, this method is not accurate. On the track, the wheel (outer tie rod end) does not move, it is always on the ground. The inner tie rod end (chassis) is what moves. As the shocks compress, the chassis moves down lowering the inner tie rod end. The outer tie rod end has some movement during travel due to caster change. As positive caster increases, the steering arm raises (and vice versa).
Your car should roll freely enough to be easily pushed (and steered) by one person. Hub Drag, Brake Drag, and Rear End Drag are the main culprits. Hubs should spin freely enough (with seal and grease) to spin dozens of revolutions with minimal force. Check out our YouTube video showing the difference in free hub spin our adjustable bearing spacers make.
Not all race teams have the budget to buy the best of everything. When it comes to low drag hub components, here’s what we’ve learned from years of laboratory and track testing. #1 Bearing Spacer. If your budget is tight, buy bearing spacers first. Bearing spacers make the biggest difference of anything you can do for your hubs. #2 Seals. Behind bearing preload, seals are the second biggest source of drag. #3 Lubrication. The right bearing grease, used properly, will make more difference than the best bearing. #4 Bearings are very important; however, testing proves bearings to be behind spacers, seals, and grease on the importance list. #5 Races. Bearing Cups, in lab testing, show the least improvement vs. the 4 previous components.
If your budget is tight, install bearing spacers on the RF first, then RR, LR, and LF. The RF takes the most load, leading to more RF drag than LF, pulling the car to the right.
Remember to always use slip plates on all four wheels during set-up. Standard scale roll-offs will not completely relax tire bind.
The proper tools and equipment for taking and verifying measurements on your car. Your equipment does not have to be the most expensive thing on the market. There are some basic tools that are handy to have when we need to verify a measurement. These tools include: (4) plumb bobs and string, (2) 72”-96” layout rulers, (1) large framing square, (1) small framing square, (2) matched, rigid tape measures, (1) roll kite or layout string, center punch, masking tape and digital level with calibration instructions. With these tools and enough time, we can measure almost any point on the chassis. In addition to these basic tools, invest in a good air pressure gauge and caster/camber gauge and take care of them. These measurements are too important to use cheap tools.
When measuring wheel position, use good wheel fixtures that eliminate tire and wheel run out. When these are not an option, measuring to the tire or wheel lip will work. However, each tire needs to be “high spotted” to remove the run-out. It does not matter if you have new tires or wheels. They have run-out too. To high spot the tire, jack the tire off the ground so that it will spin. Now measure from a fixed point over to the sidewall or wheel lip (whichever point you will use later). Rotate the tire and find the spot that has the shortest measurement. Mark this spot and place it at the top (12:00) and let the car back down. You need to do this on each tire.
Rear steer is the most important, under measured suspension change on the racecar. Rear steer is extremely sensitive. If you’ve ever driven a forklift or other equipment with rear-wheel steering, you know that a little steering input makes a big change in the vehicle direction. Rear steer is 10 times more sensitive than bump steer, yet teams rarely measure it, while spending hours trying to get bump within .010”. To measure rear steer, measure the rear end location at static ride height and then drop the chassis to max travel and measure again. This is rear steer. Rear steer is adjusted by changing the angles of the trailing arms.
Asphalt late models get lots of travel these days (or they start out low) and for good reason. Traveling the chassis lowers the center of gravity and increases downforce. This travel also makes it easy for the chassis to hit the track. This is not good. Anytime any portion of the chassis hits the track, load is lost from the tire and put in the track. This goes for front valences, cross members, sway bar arms, etc. Less tire load means less grip.
Contrary to popular belief, on asphalt late models there is no wheel travel. The wheels (tires) are always on the ground. The chassis is what travels. If you have wheel travel, you have a major grip problem as the tire is coming off of the track! This is important to remember as you measure and study the suspension. The tires, spindles, rear end housing, etc. don’t move, the chassis does.
Ackermann is another often misunderstood measurement. Ackermann is dynamic toe change through steer. So when you turn the steering wheel and one tire steers more than the other, that’s Ackermann. Ackermann should be measured in inches, just like normal toe. And, it should be measured within the normal range of steer (5 degrees or less).
Build or buy a set of ride height blocks. These are simple pieces of wood, steel or aluminum that the chassis can rest on with the shocks and springs removed. They need to be the same height as your static frame heights. Have a second set that are the heights of your chassis at maximum travel on the track. This will allow you to take consistent suspension location measurements and investigate suspension movements while not under load.
Before you take any wheel weights or wheel location measurements, the steering should be centered and locked. If you don’t keep your steering in a fixed location, your measurements will not be consistent. When the wheels turn, your toe changes, caster changes, camber changes, ride height changes in addition to wheel weights and percentages. When you use good slip plates the steering will often move on its own. On steering box cars, the box should first be indexed (set screw at 12:00) and then the steering “X’d”. Measure from the pitman arm center at the steering box to the center link center at the idler arm. Now measure from the idler arm center to the center link center at the pitman arm. These measurements should be the same. We adjust this by shimming the steering box and/or idler arm at the frame.
Once the steering is centered, lock the shaft to prevent movement. We know a company that builds a neat tool for this, but a couple of vise grips on the shaft will work as well.
On rack and pinion cars, the rack should be centered and then locked. We use collar locks on the power cylinder shaft when available. This locks the rack solid and is quick and easy.
In another Tech Tip we talked about bump steer, how to measure it, and things that might affect it. Another factor that affects bump steer is tread width change. As the chassis drops and rolls, the control arms are shortened (typically) and the tread width is narrowed. As this happens the tie rod pushes out on the steering arm, steering the wheel. Additionally, the upper and lower control arm mounting points are angled during suspension travel, due to chassis roll. This is not simulated when jacking a wheel up and down. So, to accurately measure bump steer, the chassis needs to be moved through both pitch and roll, leaving the tire on the ground. Bump steer should also be measured at the tire diameter to give you a true toe number.
Today we are going to be discussing wheel alignment methods and accuracy. When DRP studied wheel alignment methods years ago, we found that the most inaccuracies come from aligning the string to the frame rail. Tape measures pushed up against an object are not highly accurate. Couple that with the tape measure not being level and “eyeballing” where the string crosses and you have lots of opportunities for error. DRP fixed the problem by building “frame squares”. These are rulers that clamp onto the frame rail and stick out under the body to align your string to. The rulers stay in place so you can verify your string location quickly. This is a huge time saver as well. Whether you build a set or buy a set, you need frame squares to save time and increase accuracy.
One of the most important measurements we can take at the track is accurate shock travel. This tells us when the suspension is moving, allowing dynamic measurements to be taken. Shock travels also tell us if we’re gaining or losing grip. The more grip we have the more the suspension travels (with the same spring). We need these travels for at least 3 corners. LF, RF, and RR are the best. Rear travel is essential, as it has substantial effects on nose height, caster, camber, bump, rear steer, bump stop load, etc. If your max travels are heavily influenced by a major bump in the track, use a camera to get more accurate data. It is recommended to always use separate travel indicators and not rely on hard to reach shaft bumpers.