# Can I put a 140mm fork on a 120mm hardtail?



## VikingRuler338 (Sep 10, 2020)

Hey, I am looking into getting a 2021 Trek Roscoe 6. It comes with a 120mm SR Suntour fork, and I want to upgrade to a 130mm or preferablly a 140mm fork. How will this affect the riding and do you think its a good idea.

The link for the bike is here: https://www.trekbikes.com/us/en_US/...scoe/roscoe-6/p/33192/?colorCode=grey_reddark

Any help would be appreciated


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## mack_turtle (Jan 6, 2009)

wheelbase: longer
head tube angle: slacker
BB: higher, less drop

https://bikegeo.muha.cc/

I would check with Trek. they very likely tell you that over-forking their bike bike void the frame warranty. that doesn't mean you can't do it, but it would be unwise. I'd just look for a bike that was designed with a longer fork.


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## Tommy E (Oct 30, 2019)

I did the same on my daughter's bike. I did contact Trek first though and they told me that they would NOT warranty the bike with a 140mm but they would warranty it with a 130mm.


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## dirtbyte (Aug 23, 2011)

Yes


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## Tommy E (Oct 30, 2019)

I reread your post and you state that you are "looking into getting a 2021 Roscoe". For some reason I thought you already had one. If you want a 140mm forked bike then I would not recommend getting a Roscoe. Plenty of other bikes out there that are already equipped with what you want and that are specifically designed for that travel.


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## VikingRuler338 (Sep 10, 2020)

*Thanks for the help.*

Thank you all for the help, I am most likely going to be going with 130mm with a few volume spacers.


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## Harold (Dec 23, 2003)

VikingRuler338 said:


> Thank you all for the help, I am most likely going to be going with 130mm with a few volume spacers.


If you don't have the bike yet, why bother planning to change it before you even have the bike? Buy what you want right away.


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## rangeriderdave (Aug 29, 2008)

It's always cheaper to buy once ,if you don't have the money ,wait til you do.


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## Sir kayakalot (Jul 23, 2017)

Over-fork that mother and ride the fur off of it, smiling the whole time.


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## Sparticus (Dec 28, 1999)

Sir kayakalot said:


> Over-fork that mother and ride the fur off of it, smiling the whole time.


My thoughts exactly. It'll probably ride way better with the 140mm fork.
=sParty


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## laurenlex (Sep 13, 2006)

All of my bikes since about 2000 have been overforked by 20mm or so. I like the higher bottom bracket, i like the slacker head angle, I dislike the slacker seat angle (I slide the saddle forward).


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## eb1888 (Jan 27, 2012)

The Nukeproof Scout 290 Comp comes with a 130mm Marzocchi Z2 fork already. And Deore 12sp with a real 148 Boost hub- microspline.
2021 Scout: The New Batch | Nukeproof


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## justwan naride (Oct 13, 2008)

Overforking by 10mm is usually ok enough with most manufacturers so you don't lose warranty. It also doesn't compromise geo that much.

My ht comes stock with a 130mm fork and I recently upgraded to another that can be internally adjusted from 100-170. After giving it a go at 150mm (+20 compared to stock, had to use a flatbar to keep hand position in a reasonable height) I decided to lower it at 140mm and have kept it this way since. Even this way I have the stem slammed al the way down. 

With +10mm the handling is not that different, the extra amount of travel is noticeable and the ever so slight increase n bb height is actually welcome since it was only 300mm with the original fork. 

It really depends on what you want from the bike but more does not always equal better and even descending can become worse if you go too far (less weight on the front=less traction).


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## VikingRuler338 (Sep 10, 2020)

I am still looking for bikes, the Roscoe 6 seemed like a good option but my decision isn't final. Unfortunately, due to Covid-19, most bikes are sold out, I am now looking for bikes that already have longer travel, Nukeproof seems like a good decision.


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## VikingRuler338 (Sep 10, 2020)

Thanks, I'm looking into a 27.5 bike, but I'm going for the Nukeproof Scout 275.

Great idea, thank you.


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## Sickmak90 (May 27, 2012)

What would that do to the already super slack seat tube angle?


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## One Pivot (Nov 20, 2009)

So a 120mm fork puts a lever of about 800mm from the ground to the headtube. Going to a 180mm fork, which is significant and drastically overforking a bike, puts you at 860mm. A modest 7.5% increase in leverage... kind of nothing, and thats a ridiculous example of putting on an inappropriate fork. The numbers will vary depending on wheel size and what not, but the percentages will be close. 

I don't believe longer forks negatively compromise the head tube. What I do know for sure is that often when people put big forks on, its because they're trying to ride harder and go bigger. That's what breaks the bike. A 100mm xc frame can ride xc perfectly fine with a 160mm fork... its just that no one installs a big fork to take it easy. Going hard on mild mannered frames breaks them, but it'll break them with the factory length fork as well. 

Same goes for warranty. If you shear a head tube off, overwhelmingly you already voided your warranty by riding outside the designed purpose. Some brands are pretty relaxed and will warranty anything, but those are the ones who don't ask about a little extra fork length either.

So thats my headtube rant. I'd be more concerned about the bike riding like a chopper from the slack seat tube and high bottom bracket.


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## noapathy (Jun 24, 2008)

Just swap back to the old fork before contacting for warranty. You did not hear this from me.


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## Sickmak90 (May 27, 2012)

eb1888 said:


> The Nukeproof Scout 290 Comp comes with a 130mm Marzocchi Z2 fork already. And Deore 12sp with a real 148 Boost hub- microspline.
> 2021 Scout: The New Batch | Nukeproof


This is WAY better than the Roscoe.

Sent from my iPhone using Tapatalk


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## Sparticus (Dec 28, 1999)

noapathy said:


> Just swap back to the old fork before contacting for warranty.


...assuming your arms still work. 
=s


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## Harold (Dec 23, 2003)

One Pivot said:


> What I do know for sure is that often when people put big forks on, its because they're trying to ride harder and go bigger. That's what breaks the bike. A 100mm xc frame can ride xc perfectly fine with a 160mm fork... its just that no one installs a big fork to take it easy. Going hard on mild mannered frames breaks them, but it'll break them with the factory length fork as well.


Pretty much this. The biggest functional change to a bike is going to be the handling, which may or may not be improved. But overforking is an indication that the bike wasn't right for you to begin with. It's less the actual travel, and moreso the axle-crown length that creates the lever and changes handling. It actually is possible to add 10-20mm of travel while only increasing a-c by no more than a couple mm. Different brands/models will have different dimensions that way. You definitely don't want to exceed the design parameters of your frame (by riding **** it wasn't built to ride). That can be very expensive AND very painful all at the same time.

The point I've been making is more that if you don't have the bike yet, and are considering spending even more money to make modifications to the bike before you even spend the money, then just buy a bike that exists in your desired configuration already. It's more of a question of an efficiency of your money spent.

If it's a bike you already have and spent the money on long ago, then it's a little different. Most manufacturers have a range of suspension fork lengths that they'll support. +20mm is usually okay. +10mm is almost always okay. Some manufacturers specify based on the a-c dimension. Some can be extremely strict (I had a bike where the manufacturer specified a single a-c length that was based on a single fork model). And yet some manufacturers are fine with even more of a range in fork length.


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## Lady (May 8, 2018)

I have learned a really neat trick.
On Trek website, you get WAY more info if you use the comparison tool. The second you add the bike to comparison rack and hit compare, you will have table with more information than on the bike overview itself.
It gives the max fork size and max tire size as well. 
Most bikes that I looked for give +10/20 mm fork. 
Check what it says for Roscoe 6.


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