Some dynamometer companies offer small diameter, low inertia rolls which they think can handle high HP accurately and are ideal for automotive tuning.

This just isn’t true and they can not cheat physics anymore than you or I. If they could they wouldn’t be making chassis dynamometers, they would be working for some top secret government laboratory. But don’t believe us or DYNOmite Dynamometers. Believe a company like GOOD YEAR or the EPA who require large diameter rolls with substantial inertia and/or A/C drives for all there testing.

Why do you need inertia for tuning on a chassis dyno?

Coast down or Decel tuning, better road load simulation, and more accurate test results.

Have you ever tuned a car, taken it for a ride and it pops/bangs when you let off the gas as it decelerates? Wouldn’t it be nice if you could tune this out right on the dyno?

If you were going to buy a dyno or use a dyno, specially one with an absorber, wouldn’t you want the most capability so that your only taking the car on the street to check your tune, not continue on with the tuning.

Low inertia chassis dyno’s or bolt-on chassis dyno’s decelerate much to fast for proper decel map tuning.

Why is roll diameter important on a chassis dyno?

Why do drag cars use largest diameter, widest tires verse small diameter skinnys? Traction!!!!! Traction!!!!! Traction!!!!!

This is why we purchased the 30” Diameter roll and why 95% of all chassis dynamometer manufacturers offer different size rolls which dictate there Hp capacity.

Excessive strap force is how companies who offer “High Hp small roll chassis dyno’s” get the power to the rolls. But they neglect to tell you the major sources of rear wheel horsepower losses are due to tire to roll slippage and sidewall deformation. Both waste energy as heat transfers into the tires, rolls, and surrounding air.