Professional Suspension Setup Tool for Motocross Racing
Calculate Your Spring Rates
Include full riding gear weight
Select skill level
Beginner (First year racing)
Intermediate (1-3 years experience)
Advanced (3+ years competitive)
Expert (Pro/Semi-Pro level)
Affects recommended spring stiffness
Select riding style
Casual/Practice
Motocross Racing
Supercross
Aggressive/Jumping
How you primarily use your KTM 85
Select track type
Hardpack
Intermediate/Mixed
Soft/Sandy
Rough/Choppy
Most common terrain you ride
Recommended Spring Rates
Front Spring Rate:–
Rear Spring Rate:–
Front Sag Target:–
Rear Sag Target:–
Setup Recommendations:
Understanding KTM 85 Suspension Setup
The KTM 85 SX is a high-performance youth motocross bike that requires precise suspension tuning for optimal performance. Spring rate selection is the foundation of proper suspension setup, directly affecting how the bike handles jumps, corners, and rough terrain.
What is Spring Rate?
Spring rate is measured in N/mm (Newtons per millimeter) or lbs/in (pounds per inch) and represents how much force is required to compress the spring one unit of distance. For the KTM 85, typical spring rates range from 3.6 to 4.4 N/mm for the front fork and 45 to 55 N/mm for the rear shock.
Factors Affecting Spring Rate Selection
Rider Weight: Heavier riders require stiffer springs to prevent bottoming and maintain proper sag. A 120 lb rider typically needs softer springs than a 150 lb rider.
Skill Level: Advanced riders generate more force through aggressive riding, requiring stiffer springs to handle harder landings and faster cornering speeds.
Riding Style: Motocross racing demands different spring rates than casual trail riding. Aggressive jumping requires stiffer springs to absorb high-impact landings.
Track Conditions: Hardpack tracks allow for slightly stiffer springs, while soft or sandy conditions benefit from slightly softer settings for better traction.
Proper Sag Measurement
Race sag (rider sag) should be measured with the rider in full gear on the bike in riding position. For the KTM 85:
Front Fork Sag: 65-75mm is ideal for most riders, with beginners toward the higher end and experts toward the lower end.
Rear Shock Sag: 95-105mm provides the best balance of comfort and performance, allowing the suspension to work through its full range.
Signs You Need Different Springs
If you experience any of these issues, your spring rates may be incorrect:
Bottoming out frequently on jumps or whoops
Bike feels harsh or deflects off small bumps
Cannot achieve proper sag settings with preload adjustment
Excessive front-end dive under braking
Poor traction in corners or over rough sections
Bike sits too high or too low at rest
Installation and Tuning Tips
Always change fork and shock oil when installing new springs. Use high-quality suspension fluid at the manufacturer-recommended weight (typically 5W for forks, 2.5W for shock). Start with recommended sag settings and make small adjustments (2-3mm) based on feel.
Pro Tip:
Keep a suspension log noting spring rates, sag measurements, clicker settings, and track conditions. This data helps identify patterns and optimize setup for different tracks and weather conditions.
KTM 85 Stock Spring Specifications
The 2024 KTM 85 SX comes with 4.0 N/mm front springs and 50 N/mm rear spring as standard. These are designed for an average rider weight of approximately 110-130 lbs with gear. Riders outside this range should strongly consider aftermarket springs.
Recommended Spring Brands
Quality aftermarket springs are available from manufacturers like Race Tech, Eibach, and Pro Circuit. These companies offer springs in 0.1-0.2 N/mm increments, allowing precise tuning for individual rider weight and style. Always purchase springs specifically designed for the KTM 85 SX model year.
When to Replace Springs
Suspension springs fatigue over time and should be replaced every 100-150 hours of riding or when they no longer hold the specified free length. Worn springs will feel soft, cause inconsistent handling, and make proper sag adjustment impossible even with maximum preload.
function calculateSpringRates() {
var riderWeight = parseFloat(document.getElementById("riderWeight").value);
var skillLevel = document.getElementById("skillLevel").value;
var ridingStyle = document.getElementById("ridingStyle").value;
var trackType = document.getElementById("trackType").value;
if (isNaN(riderWeight) || riderWeight <= 0) {
alert("Please enter a valid rider weight");
return;
}
if (!skillLevel) {
alert("Please select a skill level");
return;
}
if (!ridingStyle) {
alert("Please select a riding style");
return;
}
if (!trackType) {
alert("Please select a track type");
return;
}
var baseFrontSpring = 3.6;
var baseRearSpring = 45.0;
var weightFactor = (riderWeight – 100) / 100;
baseFrontSpring += weightFactor * 0.5;
baseRearSpring += weightFactor * 6.0;
var skillMultiplier = 0;
if (skillLevel === "beginner") {
skillMultiplier = -0.1;
} else if (skillLevel === "intermediate") {
skillMultiplier = 0;
} else if (skillLevel === "advanced") {
skillMultiplier = 0.15;
} else if (skillLevel === "expert") {
skillMultiplier = 0.25;
}
baseFrontSpring += skillMultiplier;
baseRearSpring += skillMultiplier * 3.0;
var styleMultiplier = 0;
if (ridingStyle === "casual") {
styleMultiplier = -0.15;
} else if (ridingStyle === "mx") {
styleMultiplier = 0.05;
} else if (ridingStyle === "sx") {
styleMultiplier = 0.1;
} else if (ridingStyle === "aggressive") {
styleMultiplier = 0.2;
}
baseFrontSpring += styleMultiplier;
baseRearSpring += styleMultiplier * 2.5;
var trackMultiplier = 0;
if (trackType === "hardpack") {
trackMultiplier = 0.1;
} else if (trackType === "intermediate") {
trackMultiplier = 0;
} else if (trackType === "soft") {
trackMultiplier = -0.1;
} else if (trackType === "rough") {
trackMultiplier = -0.05;
}
baseFrontSpring += trackMultiplier;
baseRearSpring += trackMultiplier * 2.0;
if (baseFrontSpring 4.6) baseFrontSpring = 4.6;
if (baseRearSpring 58) baseRearSpring = 58;
var frontSagMin = 65;
var frontSagMax = 75;
var rearSagMin = 95;
var rearSagMax = 105;
if (skillLevel === "beginner") {
frontSagMin = 70;
frontSagMax = 75;
rearSagMin = 100;
rearSagMax = 105;
} else if (skillLevel === "expert") {
frontSagMin = 65;
frontSagMax = 70;
rearSagMin = 95;
rearSagMax = 100;
}
var recommendationText = "";
if (riderWeight 140) {
recommendationText = "Your rider weight requires stiffer springs. Make sure to achieve proper sag measurements – if you can't reach target sag even with minimum preload, you may need even stiffer springs.";
} else {
recommendationText = "Your weight is in the typical range for KTM 85 riders. These spring rates should provide excellent performance. Fine-tune using clicker adjustments for compression and rebound damping.";
}
if (ridingStyle === "aggressive") {
recommendationText += " Your aggressive riding style means you'll benefit from the stiffer spring rates calculated. Pay special attention to rebound damping to prevent packing on consecutive jumps.";
}
if (trackType === "rough") {
recommendationText += " For rough track conditions, consider adding 1-2 clicks of compression damping to prevent harsh bottoming while maintaining plushness over small chop.";
}
document.getElementById("frontSpring").textContent = baseFrontSpring.toFixed(1) + " N/mm";
document.getElementById("rearSpring").textContent = baseRearSpring.toFixed(1) + " N/mm";
document.getElementById("frontSag").textContent = frontSagMin + "-" + frontSagMax + " mm";
document.getElementById("rearSag").textContent = rearSagMin + "-" + rearSagMax + " mm";
document.getElementById("recommendationText").textContent = recommendationText;
var resultDiv = document.getElementById("result");
resultDiv.classList.add("show");
resultDiv.scrollIntoView({ behavior: "smooth", block: "nearest" });
}