A 130mm 29er fork probably as an a-c measurement (axle-to-crown) of 540mm. That's the fork at full extension. You can take the geometry of your bike and plug it in on this simple calculator to see what a shorter fork would do.

geometryCalc

What size is your frame? what year is the model?

Here's a very rough idea of what going from 130 to 120mm in travel would do to the bike on a medium frame. these are "unsagged" measurements, so keeping that consistent is a good idea. this change is pretty small, so I think 120 would be fine.

going to 100mm is probably too far, as it puts the bottom bracket—and therefore the pedals—really close to the ground.

are you upgrading to a nicer fork? removing 10mm from the travel seems like a poor use of money if that's all you're trying to do. if you want to ride something lighter with better damping, a shorter fork might be a good additional change.

Also, there's a good chance that the fork can be lowered by changing the air spring or adding some sort of spacer. How many miles are on that fork? if it's due for a service, swapping out parts while it's in the shop could shorten it. I'm not familiar with that fork, so you'll need to ask Giant or your local Giant dealer.

lastly, look into the Tandell rigid fork. under $200 for a super-light fork that will somewhat mimic the length of a sagged 120mm fork.

 

Wow!!! Thank you. It’s exactly the information I was looking for!

It is a ‘22 Giant Fathom size small. It has 600 miles at the moment. It is due for a lower leg service and I was quoted $130ish for parts and labor and that’s what got me thinking about options especially after hearing that some were having issues with this fork.

 

Perhaps you could consider performing your own service if that's within your mechanical comfort zone

 

That’s what I’ve decided to do. I don’t know if giant has their own fork oil/lubricants but I would imagine I could use Fox and other brands. Thank you!

 

120mm would be a fine change...probably barely noticeable if at all, either in geometry or suspension action.

100 would be reasonably significant but depending on the rest of the geometry and your riding, maybe not optimal. (that said, in Florida XC, a little lower and steeper likely isn't a terrible change either...)

More than travel, though, I'd look at adjusting/optimizing your suspension to ride in a more efficient, XC-like manner...looks like you have the Crest fork with one simple compression adjustment? You can look to play with how that works balancing air pressure and compression to get something that's supportive enough for efficiency but still takes the edge off (and/or just lock the sucker out when that's helpful...)

Honestly, going to the most conditions-appropriate set of tires with the right air pressure is going to make the biggest change in your bike's ride. If it's mile-munching XC you're seeking, a premium lightweight tubeless fast-roller is priority 1.

 

120mm would be a fine change...probably barely noticeable if at all, either in geometry or suspension action.

100 would be reasonably significant but depending on the rest of the geometry and your riding, maybe not optimal. (that said, in Florida XC, a little lower and steeper likely isn't a terrible change either...)

More than travel, though, I'd look at adjusting/optimizing your suspension to ride in a more efficient, XC-like manner...looks like you have the Crest fork with one simple compression adjustment? You can look to play with how that works balancing air pressure and compression to get something that's supportive enough for efficiency but still takes the edge off (and/or just lock the sucker out when that's helpful...)

Honestly, going to the most conditions-appropriate set of tires with the right air pressure is going to make the biggest change in your bike's ride. If it's mile-munching XC you're seeking, a premium lightweight tubeless fast-roller is priority 1.

Thank you! Will play around with dialing in the fork.
Yup, the aggressor and minion dhf are too heavy for what I’m wanting to do. With 600 miles on them, they still look great. I wonder how much I can sell them for.

 

Also, $130 is insane for a fork service. It's an easy job to do. You can probably open it up, clean it out physically, re-lubricate it, and call it a day. Get Slickoleum grease and the recommended fork lube oil (doesn't need to be damper oil; in fact I don't like using damper oil for lubrication-only roles...). I like having a syringe to measure out the oil and inject it through the foot bolt holes once you've reinstalled your cleaned/greased lowers.

 

thanks for the tips.

 

If your fork is the Giant Crest 34, they're meant to be serviced only by a Giant dealer. Not that they're harder to service, but you'll likely have issues accessing parts or service manuals. If you do replace the fork, you'll probably want to stick with the original size.

 

Thank you!

 

^^^^^
Yeah, I had forgotten about Giant's BS to stipulate a mandatory requirement to have Giant ONLY perform the service and the requirement to use ONLY Giant parts and fluids.

A really good reason to avoid Giant all together.

 

In my expereince, I notice the 10mm change more in the effects on geometry than on the suspension performance.

 

This is a great thread, and very timely for me.

just ordered a Ragley mmbop frame which is built for 150-160mm fork. I’m also not worried about having 160mm of travel as we don’t need that much in Florida in reality.

that geo calculator is awesome! I’m going to transfer my current 120mm fork to get it rolling and save up for a 140-150. If the axle to crown measurements equal for height, it would seem I could run a 29er fork and maintain the same geo…. Or am I nuts?

 

That geo calculator is awesome! From the fork they spec on the complete bike (axle to crown) I’m losing 10mm on my bb, which is a lot, and more than a degree in HT, again a lot.

But… still slacker than my current frame and only 5mm lower bb height. Should be ok until I get the money together for new wheel and fork.

again, that geo calculator is awesome!