100mm vs 120mm Budget FS MTB Pros/Cons

I know it’s been relatively covered in several what to buy threads … but I’m wondering what are the pros and cons of 100mm vs 120mm.

I see a lot of 120mm options available here in Aus but not a lot of 100mm options unless they’re more XC race spec which are generally well above my budget.

Looking for something for XCM events - generally up to 50km. I guess it’s comparing the Specialized Epic or maybe Scalpel to maybe a Scott Spark 960/970 in 120. I was also looking at the Marin Rift Zone3 - which seems very affordable on special at $2500AUD

My thoughts are that in the category it’s comparing 12-13kg vs 13-14kg - current bike is 12.5ish. One concern is that pushing 14kg is getting a bit porky for going uphill.

Will a 120mm bike be considerably faster and more comfortable than 100mm when things are headed down and how much slower will it be when things are headed up?

That’s going to be 100% dependant on your local terrain. What are the fast guys riding? In Minnesota the fastest guys are riding full rigid and in South Dakota the fastest guys are riding 120 front and rear full suspension . Just an example. It also comes down to personal preference and rider skill level.

Theres a lot to consider but 120mm is the go-to travel for longer marathon events. Check out the Epic Evo and Scalpel SE for longer travel versions

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I guess I should have clarified - I’m not really chasing a what bike should I buy answer.

But more just thoughts on general pros and cons of going with more travel vs less.

Fastest guys of course are on XC race bikes generally 100mm - but I’m just aiming for mid pack where there’s a mix of all sorts. The point I had was - Due to budget constraints would I get a better bike in 120mm (simply because there’s lots of options) versus stretching the budget for an XC bike with a big S on the front.

The 100mm bikes have steeper head tube angles.

The 100mm bikes also have slightly shorter reach but are designed to be used with longer stems.

You can split the difference by getting a 100mm bike one size larger, use a shorter stem, and install a 120mm or even 130mm fork.


A 120mm XC bike will most likely be heavier if you’re keeping price points constant. 120mm for an XCO/XCM is a relatively newer concept as 100mm f/r full sus is the common norm to replace the traditional hardtail. Overall bike components may be lower on the 120mm to offset price points, so I’d take a look at that when comparing as well. That being said, I wouldn’t choose a bike solely on 100mm vs 120mm, but rather the overall package, geometry and the terrain I’d be racing/riding. If your local XCO/XCM are on the gnarlier side then 120mm may be the better choice. However XCO/XCM races are won on the uphill so being faster downhill is likely not to change much.

With this being an Olympic year and the XCO course being pretty burly, not to mention XCO courses in general trending towards tougher trails, it wouldn’t surprise me to see more 2021 model year XC bikes with 120mm. In my case in MI and in the Midwest, 120mm is too much though.

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I’d depends on what you want to do with the bike. If looking to optimize for racing on less technical trails, go 100. If looking for more flexibility to ride gnarlier stuff, go with a modern geometry 120. With 120, you won’t lose much in terms of speed in XCM, and the bike will be more capable and open up more terrain you can ride and have fun on.

FWIW, I have a 130mm trail bike that I ride in Leadville, XCM, XC, my local trails (big climbs, fast somewhat tech descents), and Moab. Works pretty well for all of them.


Pros of 120: typically better DH geometry, plenty of options that will still offer good pedaling dynamics.

Cons of 120: typically heavier builds. Some platforms not as efficient as a pure XC race 100mm bike.

Pros of 100: XC geometry is finally good, taking notes from longer travel bikes, longer reach, slacker HA. Most 100 bikes are unapologetically efficient, great pedaling but that can some translate to harshness on rough sections.

Cons of 100: still lots of old school geo bikes out there with 70 degree HA, short reach. Typically harsher than any 120 bike. May not have the fun factor of a 120 bike.

My Blur is the best of both worlds. Santa Cruz doesn’t get much love here but that’s a great XC or XCM bike depending on the build. If I could have two bikes it would be my Blur and then a Horst link 140+ travel 29er.

Keep in mind with the Specialized that they rely heavily on the shocks compression in order to compensate for pedal bob inherent in the design. That’s a sweeping generalization and I’ll take it one more - single pivot or dual link bikes tend to pedal better, Horst link tends to be more active and provide a plush feel.

The 100mm bikes are made for a specific purpose…going fast. They have just enough travel to take the sting off the occasional big hit. Just enough travel to let the rider sit and pedal smoothly over non-buff surfaces that would otherwise have them hovering over the saddle, burning unnecessary watts. Just enough travel to minimize flatting and equipment breakage.

The 120mm plus bikes are actually more fun, easier on your body, allow you to play more in rougher terrain, etc. But the obvious trade off is a little less pedaling efficiency, and a little more weight.

Unless you’re regularly competing for podium spots, you’re almost certainly served better by a +120mm. If you are a competitor at that level, you should probably have 1 of each. The 120 would be a good training bike and race day backup.

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