Why do the supsension work better at low RPM?

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8/6/2018 6:14 AM

I hear this all the time but I've never understood why?

The chain and wheel would spin the same amount going the same speed. Does it have to do with how it breaks traction or reacts with no load (for example between bumps).

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8/6/2018 6:38 AM

I have some ideas, like engine response less touchy, muted tq response due to less rpm and taller gearing, less inertia, less wheelspin.

But that's an awesome question and hope someone more able to describe this chimes in.

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8/6/2018 6:48 AM

chain torque and how much the rear of the bike squats. Changes both how much travel you have and the dampening characteristics and how stiff the rear is.

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CR250 07
KTM 200 2016 EXC (XCW)
Husqvarna TE150 2019
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YCF 125 Bigy 2018

8/6/2018 6:54 AM

This is a great question. I believe it has more to do with momentum vs torque. IE if you’re carrying speed in a higher gear and lower rpm the bike is squatting less in the rear and the shock has full ROM balancing the bike. The action of the shock effects the action of the fork.

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8/6/2018 6:59 AM

I think it is more noticeable on hardpack, mostly due to wheel spin.

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Tomac and/or Anderson for 2020.....

8/6/2018 11:12 AM

Lowlander wrote:

chain torque and how much the rear of the bike squats. Changes both how much travel you have and the dampening characteristics and how stiff the rear is.

But how can the tourque of the chain be different?

Both riders are going the same speed, one with a low gear/high RPM, one with high gear/low RPM, nothing outside the engine changes, the chain travels at the same speed since the rear tire travels at the same speed.

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8/6/2018 11:17 AM

yz133rider wrote:

I have some ideas, like engine response less touchy, muted tq response due to less rpm and taller gearing, less inertia, less wheelspin.

But that's an awesome question and hope someone more able to describe this chimes in.

Some of that I can see being true for sure and is basically the factors I can see, I just wonder if it's more to it than that since it's been a "big" talking point the last couple of years (Barcia for example)?

smile

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8/6/2018 11:57 AM
Edited Date/Time: 8/6/2018 12:01 PM

Engine RPM effects 3 things really; Gyro effect (inertia), Suspension, Traction

Gyroscopic effect: A slower spinning motor has less of a gyro effect, meaning the bike will feel more nimble.

Suspension effect: Lower RPM allows the suspension to compress easier, allowing the suspension to effectively work better. Every power pulse of the motor causes the rear suspension to stand up/extend, and by running the motor at a lower RPM you are lessening that effect. This happens because of physics.

Traction: Lower RPM means more traction because there are less power pulses per revolution of the rear tire. Each time the piston is in the power stroke, it micro jults the rear tire and "upsets" it. Lower RPM is also less prone to traction runaway since there are longer gaps between the power pulses. These are one of the reasons why two strokes offer less traction than 4 strokes, in general. A 2 stroke pulses twice as often as a 4 stroke at the same engine speed, and it's even more pronounced since you run the rpm's so high on a 2 stroke.

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8/6/2018 12:12 PM

Higher gear/lower RPMs means less chain torque allowing the rear shock to move around more freely vs someone like Alex ray who may be going the same speed but in much higher RPMs with much more chain torque (chain is stiffer, making the rear shock stiffer)

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8/6/2018 12:21 PM
Edited Date/Time: 8/6/2018 12:23 PM

Lowlander wrote:

chain torque and how much the rear of the bike squats. Changes both how much travel you have and the dampening characteristics and how stiff the rear is.

Mike_Frisk wrote:

But how can the tourque of the chain be different?

Both riders are going the same speed, one with a low gear/high RPM, one with high gear/low RPM, nothing outside the engine changes, the chain travels at the same speed since the rear tire travels at the same speed.

I dont know the numbers and cant find them on a 2 minute google search...but the lower gears the higher the torque is multiplied - mechainical advantage. 1st gear accelerates Harder than 2nd and much harder than 5th due to this. So yes there is a difference in tq applied to the rear tire and the chain in a lower gear compared to a higher gear. Max Engine tq is the same regardless but when sent thru the trans the gesr ratios can multiply or even lessen the actual tq as in the case of overdrive gears.

Hope this makes sense. I really want some technical wizard to come in here and school all of us lol

Also in ur example low gear high rpm is making more power and sending more power to the rear, lower rpm is less power and more controlled less wheelspin less power pulses, less touch, less engine breaking when making throttle adjustments, less jerky.

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