How To: Set-Up A Grass Drag Sled
By Jeff Oberg
Perhaps the simplest form of snowmobile racing to get involved with is grass drags. There are many races across the Snowbelt every fall and most have classes suited specially for beginners and their stock sleds. Even though grass drag racing is pretty straightforward, it¹s necessary to make sure you and the sled are prepared.
Chances are you or someone you know owns a late-model sled like a Firecat, EDGE, REV or SRX just like the ones professional drivers raced a few years ago. Your trail sled¹s carburetors need to be re-jetted, the clutches need to be tuned and the suspensions must be set-up to get the most traction on dirt. Many of these set-up tips apply to impromptu, laketop drag races, too.
It¹s up to you make sure your sled is safe and legal for competition. Most circuits follow rules set by International Snowmobile Racing (ISR). Sled manufacturers¹ race shops and performance shops have access to ISR rule books, or contact the race circuit for class-specific regulations.
Suspension And Chassis Prep
Weight transfer is perhaps the most important part of setup for a grass drag sled because it helps the sled hook up and accelerate. An ideal setup allows the sled to transfer weight quickly at take off with the skis 1 to 2 inches off the ground and hold them there until the end of the run. If the skis touch the ground, the drag will slow the sled. Too much transfer would raise the front too far and not allow enough of the track to touch the ground for traction.
To check weight transfer, the driver should sit in ready position while a helper lifts on the front bumper. The front of the sled should lift fairly easy until the skis are up to 2 inches off the ground. At that point, the lift should require more effort. If this happens, it means the sled will transfer weight correctly, but stop the transfer with the skis hovering above the ground.
The correct transfer is set by lowering the front end and the back half of the rear suspension. The sled should be set as low as possible. The front can be lowered by installing soft springs, short shocks or by compressing the shocks with chains or straps. Shock spacers are the best way to lower a sled, but the shocks will have to be disassembled. Expect to pay a shop about $100 to install a set of spacers. Using straps to tie down the front end is cheap and easy, but it reduces suspension effectiveness.
The rear suspension can be lowered with a limiter strap and a shortened rear shock. Adjust the length of the front limiter straps and spring to tune the weight transfer. When this is set, the sled will pivot on the center shock and spring. Once the correct length of the center shock and front torque arm is achieved, make sure the spring is stiff to prevent compression and hold the skis off the ground during the run.
Your race sled¹s track will need the right traction products, too. The best studs and stud configuration will vary by racetrack conditions. For example, chisel point studs work very well for starts due to the big face of the stud that can grab more dirt for traction than a pointed trail stud. However, a chisel stud requires more power to pull it out of the dirt.
A 50/50 ratio of chisel studs and ice picks works well on racetracks with a clay starting line. Use as few studs as possible to reduce weight of the track but provide enough traction to eliminate slip. Most rules require the length of the studs cannot be more than one-half inch above the tallest lug.
Stock classes will usually run 87 octane fuel in a stock engine and most rules state that up to 10 percent
ethanol is acceptable. Fuel from a gas station may state that it contains 10 percent ethanol, but it might actually have more, which could result in disqualification. Have your fuel tested before the race. Some circuits supply fuel, so check with race officials.
To achieve good performance on race day, the fuel delivery needs to be adjusted by installing smaller (leaner) jets in the carburetors. Follow the sled manufacturer¹s jetting chart that compensates for altitude and temperature. Not all jetting charts are right on the mark, so make a few test runs to verify good performance.
Keep in mind that your sled needs to remain stock, so don¹t remove any air delivery components such as air box dividers or filters. Trail and stock classes do not allow engine modifications.
Reduce Rolling Resistance
Hyfax cause a lot of resistance in grass drag racing, so they should be removed and substituted with idler wheels where the track clips would contact the slide rails. Idlers with a rubber contact surface will cause more friction, whereas metal or hard plastic idlers provide less resistance.
Thin idler wheels have less contact area and reduce rolling resistance, too.
Low-resistance idler wheel bearings might speed up the machine, but this can be a costly upgrade. An economical tip is to remove the seal from one of the stock bearings and wash out the grease with a lubricating spray. Re-install the seal to prevent dirt and debris from contaminating the ball bearings. Be sure to clean and re-grease the bearings before you hit the trail again this winter. A track aligned perfectly will be most efficient and keep the sled rolling straight.
Clutching And Gearing
A dialed-in drive train is key to get rock-solid performance and start a trophy collection. The only way to find the best setup is through trial and error. A good starting point might come from performance shops, however these setups will usually need to be fine-tuned. Pick a clutch performance shop that has grass drag experience.
The top-end goal for gearing should be 85 to 90 mph for a 600cc sled and 90 to 95 mph for an 800 at the finish line of a 500-foot run. Sled manufacturers provide information about the gear ratio that will meet this goal. In most cases, the top gear will need to be reduced by four to six teeth, which means a shorter chain will need to be installed.
A clutch setup is more complex and will likely require the most test time.
For a starting point, a clutch performance shop can provide a clutch kit. At a bare minimum, the engagement needs to be raised a few hundred rpm from a trail riding clutch combination due to the increased traction on the starting line. This can be achieved by installing a stiffer primary spring.
Engagement that¹s too low will cause the engine to bog at the start.
Belt slip is more likely due to more traction at the ground. Lightly scour the clutch sheaves and belt with emery cloth between each run. Remove the dust with acetone or clean water, reinstall the belt and adjust the deflection. Clutch alignment should be set, too.