120mm Fork for Spark RC?

I purchased my first MTB back in March after years of triathlon and road. So, naturally I went with a straight up race machine, the Scott Spark RC 900 100mm F/R

I love the feel of the bike but as I have gained confidence I was thinking of moving towards more of a trail geometry.

Has anyone modified the RC with a 120 fork like the Fox Stepcast 34?

How would this change my geometry? How much will it slacken the hta and sta?

Will it dramatically change the feel of the bike?

Am I just better off selling this thing and moving towards a trail geometry?

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It’ll slacken the head angle by 1 degree to 67.5, which is the same as the non RC bike. In theory that makes it more stable downhill, but I can’t comment on the mismatched suspension and how it performs in balance.

As to whether you should swap it for a trail bike that’s for you to decide. Are you unhappy with it? Do you race? Would the cost differential be an issue? Couldn’t you buy a 120mm fork and keep both forks for race/trail which may be less money than the loss on the bike swap?

The problem I see with a longer fork on the Spark RC is that it also slackens the seat angle, which is already fairly slack - certainly compared to trail bikes. This could impact the climbing ability of the bike - especially on steep climbs where it may be difficult to keep the front wheel on the ground.

Will the seat tube angle also change about 1 degree?

I would say so, everything else being equal

Thanks so much. Makes sense. No racing in my future so maybe putting this beauty up soon

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I have a Spark RC which I run with a 120mm fox 34 sometimes. My experience is that I hardly notice the change in geometry after a few minutes.
I run the 120mm on rougher trails with chunkier tyres and it is a nice solid platform.

Some other things to consider:

  • Get a dropper post. Your arms and legs have way more travel than any fork if you have the room to move.
  • Try some different tyre combinations. A larger volume tyre with large knobs can make more difference than the 120mm fork.
  • Are you actually bottoming out your 100mm fork and have you played around with the settings?
  • You can also look at things like your handle bars and stem length.
  • Get a dropper post. Just in case you missed that the first time😉. You can bomb a hardtail down trails with the seat down low.

I’d love to add a long travel trail bike to my collection, but there’s no way I’d chose one over the Spark. My abilities bottom out long before the bike and I’d miss it’s speed.


Thanks all.
Rosco. Just the feedback I was looking for. I am definitely concerned about getting too slack with the sta but good to hear it was not all that noticeable.

I think you hit the nail on the head. I already switched to a trail tire, Vittoria agarro 2.35. Made a huge difference.
A dropper post is in the near future but I hav a feeling this will be a big learning curve.
I just started bottoming out my front suspension as I have gained confidence and tackling more technical stuff at speed. Not bottoming rear suspension though.
Was planning on experimenting with a shorter stem from a 90mm to 70mm to see if that makes the handling less twitchy.

So basically converting it into a trail or “down country” bike.

So I guess my question is to continue to modify or buy a true trail bike.

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I can’t comment on the effect on the Spark specifically, but I have experience doing this to my last two race bikes. I was on an Epic, and swapped to a 120 fork; No unbalanced feeling or anything like that. I did notice a little more confidence in higher speed sections from the slacker head angle. The STA was slacker, too, but that’s easily fixed by pushing the saddle forward a small amount on the rails (I thinkI moved mine 9-10mm). The biggest gain was from the increased travel. I ran similar preload pressure, the bike just took a bigger hit before getting squirrelly. Other than that, no difference.

I’m now on a Pivot Mach 4 SL, and it came stock with 120 fork. I love it. At this point, I don’t see a need for a 100 fork on any race bike unless racing on really tight trails. If you’re comparing similar models, there is little-to-no weight gain from 100 to 120, and you can run similar preload/sag (measured in mm sag rather than percentage of full stroke), and pedal performance will be unchanged.

As others have said, dropper post will go further to make any bike feel more capable than just adding 20mm fork travel.


That’s going to depend on the type of riding you want to do.
If you intend to hit big jumps and drops you’ll probably be better served by a longer travel bike. If you’re riding general single track with obstacles you’ll probably be faster on the Spark.
I think too many people get caught up on having a gnarly looking bike and forget that they aren’t actually a master of extreme.

On another note. One of the biggest differences between a 100mm and 120mm fork is the stiffness IMO. It’s as much about the 32mm vs 34mm stanchions.
I got my 120mm fork because I was riding on lots of sandstone. It wasn’t so much for the extra 20mm travel as it was for the extra strength.

PS. Get a dropper post!

Agreed. My unsolicited advice would be:

  1. Shorter stem (like 50mm, not 70mm)
  2. Dropper post
  3. Stop - ride that for a few months and see it it now feels more capable.

If not, break out the wallet! :stuck_out_tongue_winking_eye:

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I’ve been thinking about ditching the Fox 32 SC that came on my Spark RC 900 (team) for a 34 SC for some slightly different reasons.

I feel like my 32 is too harsh and not “active” enough on small bumps so I’ve played with the setup quite a bit. Currently running no spacers and have ran the pressure as low as 70psi. I’m 172lbs btw. I have never felt the shock bottom out so in theory I should drop the pressure more but it does sit quite low in sag which I don’t like. So it really has a lot less travel setup this way.

So my thinking is, if I have to do something similar with a 34 I could go pretty soft on the setup, still have plenty of travel while also “correcting” the geometry. Hoping the added stiffness of it helps make it more active as well.

Hope this makes sense…

I did the mod long ago and was well worth it, no big downsides mostly just upsides, for more info you can check out this thread

Now I really want 110-120mm on the rear but only nino has managed this on a spark rc, it would require a new shock and rocker link and possibly even a new triangle but I just don’t have them and dont want to waste maybe over $1000 to test it