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[FX-1204]

Hi all, I am having super moto wheels made for my FX. With this obviously will be new tire sizes that are bigger/heavier than what is stock on this bike.

Is there a way to re-calibrate or do something to the computer to input the new tire sizes? Does this even matter? I know people swapping FX and FXS parts regularly and I see no mention of this.



My second question is I am wanting to beef up the rear shock a bit. I have worked with Hyperco in the past with great results from their springs you can buy independently. I saw on another forum that the 2015-16 FX had a rear spring rate of 73-82NM. I was thinking of going with a 700 in.lb (79NM) rear spring from Hyperco.

Has anyone swapped out there rear shock spring? I do quite a bit of two up and loaded riding so would like a bit more stiffness.

Any info would be great!

I still have quite a few parts for sale off my FX as well if anyone is interested!

Cheers 

[TheRan]

The only thing it will affect software wise is the speed readout as that's determined by multiplying the RPM of the wheel or motor (not sure if it uses the ABS sensor like an ICE bike or not) by the circumference of the wheel. An FX tyre has a circumference of 80.3 inches and the FXS tyre is 77.7 inches, so the speedo will read slow by something like 3%. That means at 60mph you'll be reading 58mph so not really a massive difference, obviously it'll be even smaller at lower speeds and a bit larger at higher ones (2.6mph lower at the 85mph top speed). You will in turn gain a tiny bit of torque at the wheel.

The bigger difference is going to be the geometry change, the front wheel will 4.3 inches smaller in diameter resulting in the axle dropping by over 2 inches and steepening the head angle and shortening the trail. I'm not that knowledgeable when it comes to geometry but I believe this will make the bike less stable but turn easier, so could be good or bad. The FXS actually has a shorter travel fork than the FX although I'm not sure if it's overall length is shorter, if it is then handling will be somewhere in between an FX and FXS.

[Moto7575]

One way to do this would be to disassemble the app, identifiy where the coefficient to compute the speed stays and change it. Not easy but doable.
You might find people on the internet willing to do it for some money.

[Richard230]

That change in geometry could be a real safety issue if only the front wheel size is reduced.  With a smaller front wheel your bike may become unstable, especially when hitting a bump while cornering.  To address that issue you would need to reduce the size of both wheels, but that might not be possible and the reduction in ground and cornering clearance would cause problems.  Before getting too far into this project you should consult with a local motorcycle chassis expert and ask their opinion.  I am pretty sure that converting a motocross-style bike to a super-moto is something that has been many times before and information on how this can be accomplished properly is available either locally at a chassis or dirt-bike shop, and/or an internet search.

[Say10 15FX 16FXS]

The FX forks are a few inches longer than the DS/SR/FXS legs. One thing you can do is hike the legs up in the triple clamps. Switching to 17" wheels you'll also need a shorter kickstand.

https://electricmotorcycleforum.com/boards/index.php?topic=8641.msg72784#msg72784

https://electricmotorcycleforum.com/boards/index.php?topic=8716.msg74018#msg74018

[FX-1204]

Hey all, thanks for the info.

Both wheels will be changing to a 17" size, not just the front as that would be a bit odd... I have already the FXS side stand on order.

Part number for reference if anyone else needs it :26-08099

I am not too concerned with the speedo calibration. As someone mentioned it is around a 3% change which is pretty marginal. Either way, I am stoked for the setup and look forward to seeing it all come together!

I should be ordering that new Hypercoil rear spring soon. I need to pull the rear shock and double check some measurements too. Once that is done I'll report back with feedback if anyone is interested!

Cheers

[BrianTRice@gmail.com]

You don't need to disassemble the firmware to understand how speed is computed.

MBB command "set" has one variable worth changing for the speed and odometer: rwhcirc (rear wheel circumference in mm)
https://zeromanual.com/wiki/MBB_Console#Settings

Your rear wheel size is unlikely to differ, since the stock rear wheel is already a 17" diameter rim.

spfront and sprear are the front and rear sprocket tooth counts, for when you change the gear ratio.

The front wheel size matters a bit for the ABS sensor.

[FX-1204]

You don't need to disassemble the firmware to understand how speed is computed.

MBB command "set" has one variable worth changing for the speed and odometer: rwhcirc (rear wheel circumference in mm)
https://zeromanual.com/wiki/MBB_Console#Settings

Your rear wheel size is unlikely to differ, since the stock rear wheel is already a 17" diameter rim.

spfront and sprear are the front and rear sprocket tooth counts, for when you change the gear ratio.

The front wheel size matters a bit for the ABS sensor.

Sweet, thanks for the link to the Command settings, that looks like something I can handle

I have an FX, so the rear currently is an 18" rim but as others have mentioned should only be a marginal change.

[Fred]

Will the ABS be affected? With a new smaller front wheel and a rear that is pretty much unchanged, the ABS will sense that the front wheel is turning faster than the rear.

[FX-1204]

So I am still trying to find the correct spring rate spec for the rear shock on the 2020 FX. They equipped the bike with a 41mm Showa shock. I found on unofficial Zero someone posted the rear rate for the 15-16 but I don't know if this applies to the 19+ models...I contacted Zero asking if they may know the rate for the FX and their reply was "What model are you looking for?" 

soooo...

If any one has any info that'd be great!