Rear axle position

Adam_Jones
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Adam_Jones
Edited Date/Time 8/25/2022 3:41pm
I always hear of riders/racers being partial to their sag being set, yet I never hear of anyone having a preference of where their rear tire is centered. Is this an actual setting or do I need to drink another one?
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Gravel
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Gravel 8/20/2022 7:57pm
8/20/2022 7:57pm Edited Date/Time 8/20/2022 7:59pm
I like the axle set in the back half of the slot on both my old KTM RFS 450 and my 2018 450xcf (with a 500excf engine). Better stability and the front end stays down on starts and hill climbs. Doesn’t turn in quite as nimble.

Different sprocket combos can have the same final drive ratio but put the wheel in a different place. I’m using 13/49 on my newer bike mostly for the way the axle is at the back of the slot.

It’s a trade off, like everything else!
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MKMX
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MKMX 8/20/2022 8:13pm
8/20/2022 8:13pm Edited Date/Time 8/21/2022 3:20pm
Bringing your rear wheel forward will make the bike more responsive meaning the front will want to come up more. Pushing your rear wheel out and increasing your wheel base will increase stability as mentioned above.

Works the same on a BMX bike, slam the rear wheel and manuals/wheelies are a breeze! Push it out and not so much.
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CPR
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CPR 8/20/2022 9:33pm
8/20/2022 9:33pm Edited Date/Time 8/20/2022 9:54pm
All depends on the characteristics of your bike, the balance it/ you need and what sort of riding you’re setting up for.
But basics are; forward for sharpness, back for stability.
suspensionguy
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suspensionguy 8/20/2022 9:38pm
8/20/2022 9:38pm
I run mine back but I’m a off-road guy, I like the added stability and leverage on the shock.
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SoCalMX70
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SoCalMX70 8/20/2022 10:00pm
8/20/2022 10:00pm
I have it nearly slammed to the rear on my '22 CRF450. Maybe 1-2mm off the very back. 14/53 sprocket combo with 118 links. Definitely a bit more stable.

Previously, I was running 13/50 (one up on the rear from stock) and it was almost all the way forward. Really didn't like that. Felt like I was riding a unicycle.

I have yet to hear/see anyone say they like their wheel more forward on any bike. Everyone always likes them back a bit more, or just dead center/stock.
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bvm111
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bvm111 8/20/2022 10:36pm
8/20/2022 10:36pm
i like mine almost always to the rear… just have always liked it better.
cwtoyota
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cwtoyota 8/21/2022 12:23am
8/21/2022 12:23am
OP, You are not wrong. As your chain wears "stretches" and you adjust your axle position, your bike will become longer and your weight bias moves toward the front wheel (all other things being equal).

Axle position can slightly change your sag too because the leverage on the swing-arm is changed by that small amount.

Have you ever put on a new chain and sprockets mid-season and felt like your bike turns a little better?

Keep in mind the factory level racers are going out on the track with a new chain, so their axle position is more consistent through a season than average dudes like us.

It changes traction (think about your starts).
It changes weight-bias and cornering.

Half-links are weaker than normal chain links and I avoid running them, but if you want to learn what all this feels like on your own bike, go buy a half link and use it to try your bike with the axle all the way forward vs all the way back on a new chain. Check your sag in each axle position. Consider playing with fork height too. It's easy to get lost, so buy a notebook and make a setup table of the combos you want to try.

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plowboy
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plowboy 8/21/2022 10:26am
8/21/2022 10:26am
Yep. For a really tight woods race I run the axle as far forward as possible. For the wide open places...all the way back. In conjunction with moving the forks up or down...it changes the bike completely.
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Yeti831
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Yeti831 8/23/2022 1:06pm
8/23/2022 1:06pm
‘21 Honda crf450r

I run mine pretty far back, about 1/2” from max with the forks about +2 in the clamps. Very stable and will still dive to an inside line if I want it to.
Mr. Afterbar
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Mr. Afterbar 8/23/2022 4:52pm
8/23/2022 4:52pm
I run mine further back for more stability. I’m 6’1” 210 lbs so my COG is a little higher than your average rider.
mxtech1
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mxtech1 8/23/2022 8:28pm
8/23/2022 8:28pm
When you realize that the swingarm is nothing but a lever arm with a wheel attached to Smile

Torque = Radius * Force * Sin(angle)

Radius is set by swingarm pivot center to rear axle center. Thus, moving the axle inboard or outboard changes the radius and impacts the torque being applied.
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Chris_Buehler 8/23/2022 8:42pm
8/23/2022 8:42pm
cwtoyota wrote:
OP, You are not wrong. As your chain wears "stretches" and you adjust your axle position, your bike will become longer and your weight bias moves...
OP, You are not wrong. As your chain wears "stretches" and you adjust your axle position, your bike will become longer and your weight bias moves toward the front wheel (all other things being equal).

Axle position can slightly change your sag too because the leverage on the swing-arm is changed by that small amount.

Have you ever put on a new chain and sprockets mid-season and felt like your bike turns a little better?

Keep in mind the factory level racers are going out on the track with a new chain, so their axle position is more consistent through a season than average dudes like us.

It changes traction (think about your starts).
It changes weight-bias and cornering.

Half-links are weaker than normal chain links and I avoid running them, but if you want to learn what all this feels like on your own bike, go buy a half link and use it to try your bike with the axle all the way forward vs all the way back on a new chain. Check your sag in each axle position. Consider playing with fork height too. It's easy to get lost, so buy a notebook and make a setup table of the combos you want to try.

Great post
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Shapi
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Shapi 8/25/2022 3:41pm
8/25/2022 3:41pm
mxtech1 wrote:
When you realize that the swingarm is nothing but a lever arm with a wheel attached to :) Torque = Radius * Force * Sin(angle) Radius...
When you realize that the swingarm is nothing but a lever arm with a wheel attached to Smile

Torque = Radius * Force * Sin(angle)

Radius is set by swingarm pivot center to rear axle center. Thus, moving the axle inboard or outboard changes the radius and impacts the torque being applied.
OK nerd. Just kidding. Can you expand on the torque aspect? I get the stability vs. turning ability, but how is torque positively or negatively impacted and finally when making an adjustment for turning/stability what are some other common adjustments i.e. forks, what is the rule of thumb there, or gearing, how does that change?
183Matt
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183Matt 8/26/2022 7:21am
8/26/2022 7:21am
Big S, I believe the torque is the lever torque, not the torque of the engine. Just like a longer handle on a breaker bar. The further the rear axle is in the swing arm, the more torque it applies to the movement.

I’ve always wondered how significant a change moving the rear axle has on the required spring rate for the rear shock, due to this lever effect. I know it impacts it, I just don’t have the knowledge on how to calculate it.
profeshenal125 8/26/2022 7:34am
8/26/2022 7:34am
I slid the axle all the way back in between motos for stability on my rm125. I got the holeshot and in the 1st turn a rt. It pushed the front end real bad and down I went in the sand. There is a huge difference in handling. Your sag is way off too.

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