[JapanExpress]

What are the details I need to know when looking at fork compatibility? I have a new 19" Sawback 5xx and came across a deal on a Fox 32 F120 RL fork from an 09 Stumpjumper FSR Comp. Before I pull the trigger on it, what do I need to verify?

 

[falcodawgs]

you need to make sure that the steerer tube length on the fox is long enough for the head tube of your bike now and make sure that it has the same type of steerer tube (ex. 1 1/8" straight, tapered, 1 1/2").

 

[hdparrish]

Doesn't the replacement fork also have to have the same travel as the original?

 

[AndrwSwitch]

Needs to be close.

OP, if your bike came with an 80mm Dart, you may have to reduce the travel on the Fox. falcodawgs already hit on the steerer tube issues.

 

[jeffj]

Doesn't the replacement fork also have to have the same travel as the original?

It's a good idea to stay within the intended parameters for a few good reasons:

1) You might void the warranty on your frame if you use a fork that is outside of the frame maker's specs.

2) It could alter the handling of the bike in a negative way.

3) It might put more stress on the headtube junction than it was intended to take, which could result in a frame failure.

If I couldn't reduce the travel down to at least 100mm, I wouldn't do it. JMHO.

 

[Straz85]

You're putting on a fork that's worth more than the bike, doesn't make sense IMO. You could pick up a brand new 2010 Tora Solo Air for about $200. I just got one to replace the Dart 3 on my wife's bike. It weighs almost a full pound less and rides SO much better.

 

[JapanExpress]

Doesn't the replacement fork also have to have the same travel as the original?

The Dart 1 has 100mm travel, and the Fox has 120mm.

Also, the Fox has a 1 1/8" straight steerer tube with a little over 8" of tube left. I am still trying to find info on the Forge setup.

 

[Clones123]

You're putting on a fork that's worth more than the bike, doesn't make sense IMO.

I'm with Straz85 on this. Given how inexpensive a SR Suntour XCR LO fork is (under $100), I can't imagine putting a Fox fork on a Forge Sawback 5xx. No offense but even a modest hydraulic lock-out fork like the XCR is more in line with the rest of the Sawback's components while still being a HUGE step up from the craptastic Dart 1.

On the other hand, I can see buying the bike to you hope to one day have one piece at a time and a Fox fork is a nice step in that direction.

 

[JapanExpress]

Thanks for the input everyone, looks like I might need to hold off on this one. I wasn't planning on going that big but it came up at a good price so I wanted to see if it fit. I may be better off waiting.

 

[AndrwSwitch]

Looking at the Forge spec. reminds me of looking at a BD spec... It's actually got a nicer drivetrain than my significantly more expensive Hardrock came with, but those hubs are total garbage.

OP, I don't know how good a price you came across on that Fox. Used ones sell for around $300 on EBay, depending on the specific model. I'd say if you're being offered a better price than that and you can afford to spend the money right now, don't mess around with intermediate upgrades - just do it. Run whatever goofy spacer stack above the stem you have to in order not to cut the steer tube if it's too long, stick a tennis ball on top, whatever. But you don't get a comparable fork on a new bike until you spend at least $2000 on it. Of the various bits and pieces I've bolted to various bikes over time, I'd say upgrading my suspension fork has been one of the ones that improved the actual riding part the most. It's going to matter less, I think, since you're starting with a Dart and not an RST, but gaining stiffness and tunability and losing as much weight as this part swap will lose will be pretty noticeable.

Check the manual (available on Fox's site) and make sure you can spacer it down to 100mm. While I wouldn't be too worried about a 20mm travel increase blowing up your frame, it will mess with the handling. Whether that's good or bad is pretty subjective, but you should have the option to keep the bike handling as intended.

There was one other technical question you asked - how to measure the height of your current steer tube. It's actually pretty simple. Measure from the top of the fork crown to the top of the stem or top spacer, and subtract 3mm. If the length is very close to the amount of remaining steer tube on the Fox and you don't have extra spacers under your stem, you might want to actually remove the stem, so you can see the top of the steer tube, and tap the fork down a little, so you can see the headset baseplate and get a more accurate measurement.

If ultimately you decide not to do it, you might consider getting the correct spring kit for your Dart, if you find you never use your full travel or it bottoms out a lot. That's one advantage their forks have over some of the competitors that are showing up from other brands lately.

 

[rlouder]

I just measured the dart that came off a forge. The steer tube measures 7.7". This is from an older 80mm version, so measure yours to confirm. Measure from the top of the crown to the top of the stem, then subtract ~1/8".

You could make do with a little shorter, but I wouldn't recommend it. You would have to remove some of the spacers below the stem, which would lower your hand position.

A little longer like the fork with 8" would be ideal. You could leave it longer and put a headset spacer on top of your stem. Leaving it longer gives you more latitude in case you want to switch it to another frame or resell it.

I would stick with a 100mm, but I think you're doing the right thing by looking at better forks. Skip the suntours and toras.

 

[Eville140]

I have Reba race on my forge, it's at 120mm but I let it sag a little extra. Works great and took about 2 pounds off the bike. I weigh 225# and nothing has broke, picked it up used so the cost wasn't that bad.
If your getting a good buy, it'll be a great addition to the bike.

 

[jpeters]

I would get the fork and try it if its a good price. I have a BMC tf03 and it is a 120mm suspension stock but you can use from a 100 to a 140mm fork on it and to be honest I have a adjustable 100 to140mm fork and it feels fine on all settings 100 120 130 and 140. I don't understand all of the hype about changing the geometry of the bike my bike feels fine. What about all of the bikes that come stock with the Fox talas or the rs u turn? The fact is Fox is a superb fork and they have a great resale so if the price is good get it.

 

[jpeters]

Another thing the fox is like 1600 grams you will loose like 2 lbs of the front of your bike.

 

[rlouder]

Good lookin' setup, Eville.

Someone also tried a 120 or 130 in the big thread (luck finding it). Probably wouldn't have a problem with frame stress the way the forge is braced at the head tube. Some other bikes aren't like that.

I still wouldn't go with a long fork, though - simply because their is no advantage for me. I use a 80mm fork on the forge. Sometimes, I firm it up with the tpc so there is only 40-50mm of travel for smoother trails. Guess it depends where you're riding and personal preference.