Carbonda fm936 Thoughts

[qwerty]

https://www.mbr.co.uk/reviews/full-suspension-bikes/vitus-rapide-fs-crx-review

[Mrbobbob]

Hi All,

I have a Vitus branded copy of the 936 (last year's model). It has a SID Luxe Shock with a maximum pressure rating of 325 PSI. At 188 cm and 83 kg (around 6'2 and 183 lb) on an XL frame I find that even at the maximum pressure for the shock of 325 PSI I have 30% sag. Whilst this is OK, I would be interested in experimenting with more like 25% sag or possibly adding a 120mm fork (instead of the stock 100 mm) which would shift weight back increasing load on the rear shock.

Is this normal? Are there other shocks that can cope with higher weights and larger riders on this frame design? Whilst I am no racing snake, I am at the shorter end for an XL and not that fat so suprised to run into this issue!

[ilyamaksimov]

Hi All,

I have a Vitus branded copy of the 936 (last year's model). It has a SID Luxe Shock with a maximum pressure rating of 325 PSI. At 188 cm and 83 kg (around 6'2 and 183 lb) on an XL frame I find that even at the maximum pressure for the shock of 325 PSI I have 30% sag. Whilst this is OK, I would be interested in experimenting with more like 25% sag or possibly adding a 120mm fork (instead of the stock 100 mm) which would shift weight back increasing load on the rear shock.

Is this normal? Are there other shocks that can cope with higher weights and larger riders on this frame design? Whilst I am no racing snake, I am at the shorter end for an XL and not that fat so suprised to run into this issue!

Is it possible that your pump is showing the wrong pressure? I am 78kg and frame L. Deluxe Nude and fox dps work at 25% sag at 200-220psi

[Swolie74]

Fox float X, and Manitou Mara both have higher pressure ratings (Float X- 350 and Manitou Mara 400). On my Mara I’m running around 225 for 20% sage at 265lbs

[Shinso]

Hi All,

I have a Vitus branded copy of the 936 (last year's model). It has a SID Luxe Shock with a maximum pressure rating of 325 PSI. At 188 cm and 83 kg (around 6'2 and 183 lb) on an XL frame I find that even at the maximum pressure for the shock of 325 PSI I have 30% sag. Whilst this is OK, I would be interested in experimenting with more like 25% sag or possibly adding a 120mm fork (instead of the stock 100 mm) which would shift weight back increasing load on the rear shock.

Is this normal? Are there other shocks that can cope with higher weights and larger riders on this frame design? Whilst I am no racing snake, I am at the shorter end for an XL and not that fat so suprised to run into this issue!

I have the very same issue on my 2021 Vitus Rapide FS with the SID Luxe shock.  I'm 65kg and can't put enough pressure into the unit within the maximum range to have less than 25% sag - I would like to run 20% ideally...

[Mrbobbob]

Thanks for the replies.

I checked the pressure with my other pump and got pretty much the same pressure. I have used the pumps on another bike and got pretty much bang on the manufacturer's predicted numbers so I don't think they are massively innacurate.

It is interesting that someone else with a SID Luxe has the same issue. It is a physically small shock so I wonder if it produces less force for the same pressure than the others that have been mentioned (smaller area for the pressure to act on?). I don't know if there is a way of finding out this information for different shocks?

[numberzero]

About shock pressure, do you easily go to max travel?
I run around 25% sag with 42,5 fox and i often end with using only 3/4 of the travel.

[casual_build]

I posted this a long time ago.

Reposting a comment I made earlier in the thread when asked about my shock setup, Please note with all my gear and water, I am closer to 80kg and my frame is a medium so  copying my settings is a bad idea. I put a picture of my gap below. Here is the comment from earlier:

I counted 10 clicks from full rebound toward softer, At just under 200psi. I bet the shock behaves differently on a larger frame.

For the newer people like me, when you pump up the rear shock make sure to equalize the chambers by compressing to 25% about 20 times. Then check the sag and PSI again. Also, this shock tune is: 2018, FLOAT DPS, P-S, A, 3pos, Trunnion Evol LV, Giant, Anthem 27.5 2, 165, 42.5, 0.8 Spacer, DCM, DRM, CML, YS 2272/YS 2272 Logo

That 0.8 spacer means bottoming out the rear shock is really tough. Thats why I go for such low rebound, with semi-high pressure. Of course, I dont really know what I am doing.

I also dont think the low BB is very noticeable. Not a big deal, has its advantages.

Still running the shock with a 0.8 spacer a progressive tune and just under 200 psi. It bottoms out on 3ft+ drops.

Funny enough, the low BB drives me crazy now and pushed to building my FM1002 (which I am loving, but isn't as good for big climbs).

[adroitrider]

Thanks for the replies.

I checked the pressure with my other pump and got pretty much the same pressure. I have used the pumps on another bike and got pretty much bang on the manufacturer's predicted numbers so I don't think they are massively innacurate.

It is interesting that someone else with a SID Luxe has the same issue. It is a physically small shock so I wonder if it produces less force for the same pressure than the others that have been mentioned (smaller area for the pressure to act on?). I don't know if there is a way of finding out this information for different shocks?

I have the same issue but described differently. The SidLuxe Ultimate I have is a M M tune. I want to try a High compression tune.

It’s not a hard service. I posted the links in an earlier thread. Parts were sold out in the Spring but are $18 if you can find them.

[acedeuce802]

https://geared.bike/jack-rabbit

Found another US based company selling the FM936.  At least it's half the cost as the Boltcutter Groove Pony

[Fugezo]

Interessting that they specify it with 120mm rear travel and a 165 x 45 mm shock. I thought only 165 x 42,5 mm would fit into the frame.

[Swolie74]

https://geared.bike/jack-rabbit

Found another US based company selling the FM936.  At least it's half the cost as the Boltcutter Groove Pony

That’s basically the same price as buying from Carbonda

[Mrbobbob]

Regarding the sag issues on the SID Luxe. There are a lot of assumptions on my part; I am trying to figure this issue out so please correct me if I have anything wrong! The big uncertainty for me is how to understand the impact of the negative spring.

I have taken measurements on a few shocks that I have access to in order to try and compare the area of the piston. I figure this should be proportional to the force the shock produces at a given pressure - but I might be mistaken. I have measured from the outer diameter of the piston seal minus the diameter of the central shaft. For the uncompressed shock, this should mean that to produce the same force as a SID Luxe at its maximum pressure of 330 PSI, a fox DPS would need 290 PSI (max 350) and a RockShox Super Deluxe 230 PSI.

To me this suggests that the SIDLuxe is probably just a bit weedy for the suspension design of the FM936 and taller/heavier riders. It suggests that a fox DPS should be suitable; it should produce ~20% more force at max pressure. I need to work out the impact on equivalent sag at max pressure (taking my current 30-35% for the SID Luxe as a starting point). However, I will probably get a RS Deluxe Nude; I think these are the same basic air can as the deluxe so should have more margin than the DPS and are also one of the cheaper shocks that I have found in 165x40 mm that is remote compatible.

[adroitrider]

I did the leverage ratio calculation of 115mm of suspension divided by 42.5mm of shock stroke. This gives a ratio of 2.75. A value of 2.75 puts it in the high compression ratio category for most shocks.

The part is $18 but everyone is sold out. Sram has released the DIY documents.
https://www.probikesupply.com/products/rockshox-rear-shock-tune-assembly-compression-tune-configurations-sid-luxe-a1

https://www.sram.com/globalassets/document-hierarchy/tuning-manuals/rockshox-rear-shock-piston-tuning-guide.pdf

Don’t spend more than $18 to update the tune of your SidLuxe.

Has anyone done this?

I will be doing this service over the winter.

[adroitrider]

Regarding the sag issues on the SID Luxe. There are a lot of assumptions on my part; I am trying to figure this issue out so please correct me if I have anything wrong! The big uncertainty for me is how to understand the impact of the negative spring.

I have taken measurements on a few shocks that I have access to in order to try and compare the area of the piston. I figure this should be proportional to the force the shock produces at a given pressure - but I might be mistaken. I have measured from the outer diameter of the piston seal minus the diameter of the central shaft. For the uncompressed shock, this should mean that to produce the same force as a SID Luxe at its maximum pressure of 330 PSI, a fox DPS would need 290 PSI (max 350) and a RockShox Super Deluxe 230 PSI.

To me this suggests that the SIDLuxe is probably just a bit weedy for the suspension design of the FM936 and taller/heavier riders. It suggests that a fox DPS should be suitable; it should produce ~20% more force at max pressure. I need to work out the impact on equivalent sag at max pressure (taking my current 30-35% for the SID Luxe as a starting point). However, I will probably get a RS Deluxe Nude; I think these are the same basic air can as the deluxe so should have more margin than the DPS and are also one of the cheaper shocks that I have found in 165x40 mm that is remote compatible.

Se my post above. If you are running the 40mm stroke the equation could be 115/40 or 100/40.

This frame needs a High Compression tune.