Tech Tip: Make Your RM-Z Handle Better For Free 12

A simple look at the numbers and we notice that Suzuki's recommended torque specs are pretty high...

 

By Chris Siebenhaar

It’s no surprise that the Suzuki RMZ-450 can use some help in the chassis department, not in terms of agility and turning, but rather comfort and compliance. In this test I wanted to see if there was anything that can be done with the chassis, sans buying optional brackets and hangers, but rather just play with how the frame is tied together via the engine and engine mounts. 

Over the years of peaking in and out of factory pits, one thing is an obvious constant, testing and change. Everything from major items like linkages, braced swingarms, to complete suspension packages, all the way down to seemingly obscure items like bolt material combinations (Ti vs. Steel) or the type of grease to use and where. Even teams like JGRMX appear to use a combination of Ti & Steel bolts on the engine brackets and hangers, as well as custom machined hangers to get the desired feel from the chassis. 

You can see the custom engine hanger and different front mount bolts.

On a recent post from SLC, mechanic Derick Dwyer went over Chase Sexton’s championship winning Honda CRF250. One thing he pointed out, was how the team spent a great deal of time coming up with specific torque specs for the bolts on the front end to get the exact flex and feel the riders liked. This sparked an idea of conversations past about endless testing of torques, materials, etc. and immediately I dug into the RMZ’s manual to find all the torque specs to the chassis. Then I did the same for the other Japanese 2020 450cc machines (see below) and noticed that they were all less, and in some cases, significantly less, than the Suzuki recommended specs. 

Front Suspension SUZUKI HONDA KAWASAKI YAMAHA
Axel Pinch Bolts 13.5 15 17 15
Front Axel Nut 26 65 59 83
Upper Triple Clamp Pinch Bolts 17 16 17 15
Lower Triple Clamp Pinch Bolts 17 15 17 15
Chassis
Engine - Lower 49 40 36 38
Engine - Front: Bracket to Frame 40.5 19 21 25
Engine - Front: Engine to Bracket 49 40 36 40
Engine - Upper: Bracket to Frame 26 24 21 26
Engine - Upper: Head to Bracket 40.5 40 36 33
Subframe - Top 26 N/A N/A N/A
Subframe - Lower 26  N/A  26 27

***All figures are foot-pounds of torque. 

Initially I went down by percentages, 5%, 10%, 15% and there was not much difference. At 20% less torque, the frame began settle a little. Instead of just going down less and less across the board, I went with Kawasaki’s 2020 KX450 engine/chassis torque specs (which on average are 20-25% less with some bolts being 50% less!). This was like Baby Bear's porridge, just right. The Suzuki, began to feel much more planted and comfortable in long ruts, and the constant feel of the front climbing out of the rut when the throttle was applied, went away. Additionally, corners that had ruts exiting a corner with acceleration chop through the rut, the bike tracked slightly better. There was less “bucking” from the rear end, especially when there was still lean angle accelerating out.

Overall, the area of improvement that was most noticeable was at the initial application or crack of the throttle. This can be felt best around flat turns where you enter the turn off throttle, get the bike settled, then open the throttle to start accelerating. At this moment the Suzuki torque settings cause the bike stand up, and immediately stops the bike from finishing the exit of the turn. Every lap I would have to let off the throttle, turn again, and accelerate. With the Kawasaki torque specs, the chassis had a much more planted feel when applying the throttle around these types of turns. The rear end settled and squatted through the exit significantly better than with a “softer” torque setting, and the chassis felt less antsy to react to throttle input. 

Now it’s no surprise that Suzuki would have exceedingly high torque specs. In 2015, both Suzuki and Kawasaki ran the Showa TAC (Triple Air Chamber) fork on their 450s. It consisted of an outer chamber and inner chamber (both designed to act like a fork spring) and a negative chamber (like a rebound spring). Suzuki chose not to run air pressure in the outer chamber for fear of failure, instead they ran A LOT of pressure in the inner chamber. This resulted in an extremely harsh feeling fork. Kawasaki on the other hand, ran air in both and had a much more compliant fork. Sounds familiar right? It seems to be that Suzuki went with “THIS NEEDS TO BE TIGHT!”, whereas Kawasaki went with “this feels right” when settling on chassis dynamics. 

Now, understandably, reducing torque specs is NOT recommended by the factory or in your service manual. So, this should be done at your own risk. However, for this reason is why I didn’t loosen bolts willy-nilly, but rather used another manufactures OEM spec that they recommend and trust. 

For additional comfort and peace of mind (which I did as well), take a sharpie when running the softer spec and mark each bolt, and check for movement after each moto.

I torqued the engine/chassis in the following steps…

  1. “Relax” the frame by loosening all engine & bracket bolts
  2. This is important in order to make sure the frame is in its natural state and there is no unnecessary tension or stress lingering. 
  3. Torque the lower engine bolt
  4. Torque front engine bracket to frame
  5. Torque front engine bracket to the engine
  6. Torque upper hanger to frame
  7. Torque upper hanger to the head/engine
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