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I am not going to sit here and tell you that you need to be as meticulous as we are at times here at Keefer Inc. Testing but if you like to tinker and make adjustments here are some key swingarm pivot to center of rear axle lengths. I have tried a lot of different gearing ratios as well as some lengths for this 2023-2025 Yamaha YZ450F chassis. These are the lengths as well as some gearing ratios that may help you.
Note: Obviously chain tension affects some of these numbers but these are the “ballpark” areas you need to be in to feel chassis benefits of each. Each length has an advantage and a disadvantage as we will note below. Special thanks to Mark at REP Suspension for giving us some starting measurements to try out.
Gearing: 13/49 Chain Links: 114 Ratio: 3.769 Length 585.4 Range Allowance: 585.4-586.8
This is the stock gearing of the Yamaha YZ450F and the length of this is usually what I stick to around Southern California tracks. Going to a 13/48 gearing although better for chassis feel on straight line (13/48 length is 589.8) isn’t great for third gear recovery or lugging the bike in corners. This measurement is best for all around straight line and cornering feel with sag at 105mm and fork height at 3mm.
Gearing: 13/50 Chain Links: 114 Ratio: 3.846 Length 581.1 Range Allowance: 581.1-582.6
Going up a tooth is commonplace with vet riders so I had to try and get a length/setting that didn’t add to the twitchiness of this machine. As your chain stretches (when it’s new) this setting becomes a little better on lean in and area 2 of corners. Since it’s shorter than the stock gearing lengths going to a flush fork setting and a sag of 106mm helps this gearing spec.
Gearing: 14/52 Chain Links: 116 Ratio: 3.714 Length 584.7 Range Allowance: 584.7-586.0
The two biggest benefits of this gearing is smoother roll on power which to me is needed on this bike and acceleration traction. Even though this gearing makes the length shorter I still feel like I get more rear wheel traction on hard pack tracks. I don’t notice more traction on softer soil but harder pack tracks this gearing helps acceleration comfort and traction. Running fork height at 2mm and a sag at 105mm is best with this length and gearing.