Inertia or Motor limited Acceleration
When you roll on throttle and there is no wheel slip possible then you have Inertia limited acceleration. This means that inertia in the driveline and the chassis are what is limiting acceleration. This also means you are probably running a spec motor and battery for examble 13.5/four cell. Since the battery and motor are specified you are left to tinker with chassis and drivetrain to improve performance. What to do. First make sure the car is no heavier than required. On a 50 ounce car an extra ounce slows you up by 2%. You will notice this the most when accelerating side to side with a car that is lighter than yours. No need to cheat in club racing just set your car to .2 or .3 ounces heavier than required with very short tires onboard of the lightest type that you will use. This is mostly easy to do these days as some ballast is required. Drill your ballast a little lighter.
Rotating inertia-Rotating inertia holds you back by a factor maybe 2 to 3 times more than the inertia of non rotating parts. The reason is the part needs to be accelerated in a straight line like all the rest of the car, but the rotating part also needs to be rotated which uses up extra energy. The faster the part needs to rotate (the pinion) and the larger the parts radius, the more the part slows you down. I have seen it posted that a lighter pinion will go unoticed. Maybe so. But if you take two or three little lightening steps then you will start to see changes on your lap time. In stock truck a light pinion could be "felt" just by watching the truck out of a corner and noting front end lift. It lifted more with a light pinion; you could see the truck accelerate just a little faster. In mod truck a heavy steel pinion was fine. In the former case we are inertia limited (on blue grooved clay). In the latter case we are traction limited because of tire slip.
World GT Car
What can we do here?. We can use a deep dished lightened Aluminum pinion indoors. The black model in the photo is from Robinson Racing. Some guys are using huge pinions (21.5 guys). It makes more difference to the car when you lighten a huge pinion. Outdoors you really need a steel pinion for durability if you want it to last more than one race day. The dished grey model is made in England by RP. This is the lightest steel pinion I have seen. I had to order this one and ship it oveseas. Lefthander-RC.com has some RP stuff now. Since the motor shaft is the fastest rotating part on the car it makes the most difference to lighten things attached to this shaft. Don't drill out the magnet. This won't help you and would not be spec.
On a pan car the second place to look is the rear axle. Note in the second pic that the inside diff flange that is pinned to this CRC axle has three lightening cuts. Sweet. The light weight diff-ring on the table is also installed and seems to fit and work fine. Ceramic diff balls are lighter than steel or carbide. This set of 12 Track Attack ball are from Left-haderRC.com.
The lightweight diff rings are from Track Attack (lefthanderRC.com) or I.R.S.
Note the red Nylock nut from Hyperdrive (Lefthander-RC.com). It is a thin model for some weight savings here. (Don't use a plastic diff nut or the diff setting is forever changing.)
Note the silver Associated diff cone. Nothing special here. I just forgot to order the CRC parts. The associated part is a lightweight cone but is a little oversize in diameter.
Robinson Racing and RP both make a lightweight 64 pitch white nylon spur gears that is narrowed to make it lighter. This black model from Kibrough is 48 pitch (my selection for outdoor use) and holds a full complement of 12 balls with only 69 teeth.
Wheel lug bolts.-I use 5/16 Aluminum screws. I use four per wheel to keep from warping the wheel in the crashes. The screw should be just flush with the end of the threads in the wheel. Excess length is not needed.
Left hand hubs- There are lightweight left hand hubs available from KSG. Mine became untrue with only a month of use. I have returned to the stock left side double clamp hub. Sometimes you just need the extra meat on a part for strength.
Left hand hub screws- These should be long and should be made of steel and should engage most of the aluminum threads in the hub. You have to tighten the crap out of these for good function. Alternately tightening one then the other until it is quite tight. Otherwise you will lose your wheel on the track. This is not peculiar to CRC but a property of the breed. I put on blue loctite the first time I tighten these two screws. This lubricates the screw and lets it tighten better and then sets up and holds it tight. The Loctite does not need to be reapplied every time.
Break-in those diff balls by holding one wheel and running the motor for 30 seconds. Now recheck the diff nut; grab left tire and spur with left hand; the right side tire should be hard to rotate. You are ready for weeks of use with little attention.
Now you have a world class lightweight axle assembly.
This CRC diff seems to have slightly tighter tolerances on the gear. It does not wobble much. I used to put in a thin 1/2 inch shim to take out some gear wobble, but this is not needed here. The shim actually killed the function so I removed it.
Man those are nice looking hubs! Just came in today.
Pics: click one more time after enlarging them for the sharpest view. Note Green rubber sealed bearing from BOCA for the longest wear. Grit entry combined with high load is mostly what kills this bearing.