Guide To Suspension Design For Going Fast In Comfort
The following are general rules of thumb that we have collected from working on all sorts of different vehicles. We recommend them as a starting point when thinking about your suspension. Professional builders, racers, and enthusiast are also great sources of information.
Allow Your Suspension Room to Move, But Don’t Over Do It
- 4” of up travel, and 4” of down travel are the minimum recommended for any type of off-roading
- 6” of up travel is a good minimum goal if you want to go fast
- As up travel increases from there, capability and comfort increase
- As suspension travel increases, handling decreases due to reduced spring rates and damping
- Design for the terrain you plan to encounter the most
- If possible, rear up travel should be 25% more than the front
- Rockcrawler vehicles may lean towards 1/3 of available travel as up travel
- Go fast vehicles should lean the other way with 2/3 of the travel as up travel, rock racers have proven this also works well in the rocks
Carefully Design Your Bottoming Control
- Air bumps provide great bottoming control, but can cause harshness and banging sounds if they’re contacted too frequently
- Give your air bumps at least 3” of clearance in the front and 4” in the rear.
- Air bump travel should be roughly 1/3 of your up travel or less.
- If you don’t have room for air bumps, foam urethane bumps stops are a great choice.
- Foam urethane isn’t tuneable like air bumps, but their progressive nature makes them more comfortable when frequently contacted near ride height. Foam urethane is also less durable.
Carefully Design Your Top Out Control
- Run limit straps, off-road shocks were not made to top out
- Some bypass shocks are exempt from this rule if designed to do so
Use Motion Ratios on Light Vehicles
- Motion ratios between 0.9 and .06 make shock tuning easier on lightweight vehicles
- Light weight vehicles should use a smaller (numerically) ratio
- Motion ratios reduce the impact of shock friction
- Mounting shocks at extreme angles are not a good way to achieve motion ratios
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