MTB Coil Spring Rate Calculator
Use this to estimate a rear shock coil spring rate based on your weight, bike setup, and target sag. This gives a strong starting point for trail, enduro, and park bikes.
How this MTB spring rate calculator works
A coil spring on a mountain bike shock is rated in lb/in (pounds per inch). That number tells you how much force is required to compress the spring by one inch. Choosing the right spring rate affects your sag, traction, support in corners, and bottom-out resistance.
This calculator estimates a good starting point by combining:
- Your total system weight (rider + bike)
- How much of that load sits on the rear wheel (rear weight bias)
- Your bike’s leverage ratio (rear travel divided by shock stroke)
- Your target sag percentage
- Your preferred support feel
Like any setup tool, it is a baseline. You should still test on trail and adjust spring rate and damping to match your terrain and riding style.
Input guide: what each field means
Rider weight (with gear)
Include everything you actually ride with: shoes, helmet, pack, water, tools, and armor. A setup based on bodyweight only often ends up too soft.
Bike weight
Full ready-to-ride weight is best (pedals, bottle cage, inserts, etc.). This keeps calculations realistic.
Rear weight bias
Most modern trail and enduro bikes sit around 58% to 65% rear bias when seated or neutral standing. If unsure, 62% is a reasonable default.
Rear travel and shock stroke
These define your effective leverage ratio. Example: 150 mm rear travel and 60 mm stroke = 2.5 leverage ratio.
Target sag
Typical starting points for coil shocks:
- 25-28% for a firmer, poppy feel
- 28-32% for balanced trail/enduro use
- 32-35% for maximum comfort and grip
Quick setup ranges by riding style
| Riding Style | Suggested Sag | Support Multiplier | General Feel |
|---|---|---|---|
| XC / downcountry | 22-28% | 1.05-1.15 | Efficient, high support |
| Trail | 27-31% | 1.00-1.08 | Balanced comfort + control |
| Enduro | 28-33% | 1.00-1.10 | Grip and stability on rough terrain |
| Bike park / freeride | 25-30% | 1.08-1.15 | More ramp resistance and support |
How to dial in your spring after calculating
1) Set preload correctly
On most MTB coil shocks, use minimal preload just to remove spring play, then add about 1-2 full turns. Too much preload can mask an incorrect spring rate and hurt sensitivity.
2) Verify sag on the bike
Put on full gear, stand in a neutral riding position, bounce lightly, and let the suspension settle. Compare measured sag with your target value.
3) Adjust one variable at a time
- If sag is too deep even with low preload, move up to the next stiffer spring.
- If sag is too little with minimal preload, move down one spring rate.
- Use compression damping for dynamic support, not to fix major sag errors.
4) Test on repeatable trail segments
Use the same descent or loop so changes are easy to compare. Focus on corner support, braking traction, and bottom-out frequency.
Common mistakes when choosing spring rate
- Ignoring gear weight: This can shift your ideal spring by an entire rate step.
- Using too much preload: Better to change spring rate than crank preload.
- Confusing harshness with too stiff a spring: High-speed compression and rebound can also cause harsh feel.
- Not accounting for linkage progression: Very linear bikes may need firmer spring or hydraulic bottom-out support.
- Copying someone else’s settings exactly: Rider position and terrain matter as much as rider weight.
Coil spring rate vs air shock pressure
Air shocks and coil shocks can hit similar sag numbers, but they feel different on trail. Coils are often smoother off the top with more consistent damping through long descents. Air shocks usually offer easier progressivity tuning with volume spacers and wider on-the-fly adjustability.
If you’re moving from air to coil, don’t just chase your previous pressure number mentally. Start with measured sag and trail behavior. This calculator is designed for that transition.
FAQ
Is this calculator accurate for every bike?
It is accurate as a starting estimate. Real-world factors like shock tune, stiction, riding posture, and leverage curve progression will still influence the final choice.
What if I’m between two spring rates?
If you ride fast, jump often, or frequently hit bigger impacts, choose the stiffer option. If you prioritize traction and comfort on rough terrain, choose the softer option.
Can I use this for eMTB?
Yes. Just enter accurate system weights and start with a slightly supportive multiplier if you prefer extra chassis support under motor-assisted acceleration.
Final thoughts
A properly chosen spring rate makes your bike calmer, grippier, and more predictable. Start with the number from this MTB spring rate calculator, verify sag on trail, and then fine-tune with small, deliberate changes. Once spring rate is correct, rebound and compression adjustments become much easier and more meaningful.