Getting a bigger one . . .
I have an '05 Spec Stumpy FSR comp 100 with a Manatou Black Elite 100mm (yes it sucks) and I want to switch fork with more travel. I understand that my head tube angle and bb height will change. My current headtube angle is 70.5 and feels a little steep anyways, so I'm not to worried about that. Is a 140mm shock to extreem of a change, or can I go further? I'm looking at getting a Fox float rlc. My last concern is how this will effect my rear end, not my ass, but the suspension. Does raising the front cause any serious concerns for how the rear end suspension will function?
Yes 140mm is a bit much. The rule of thumb is 20mm + or - and you'll likely be okay. And remember it's not the additional travel but the change in actual axle to crown height that makes the difference. Not all forks are created equal. Just because a fork has 20mm more travel doesn't mean that the fork is only 20mm taller. It can be a bit more or a bit less. Example: Mantiou SX 80mm, swapped out for a 00 Marzocchi Z3 100mm. The Zocch had a beefier crown that was about 20mm deeper than the SX. 20mm of travel + 20mm of crown for a total gain of 40mm in actual fork length. So actually comparing the Axle to crown heights of two different forks is highly recommended. It gives you a better idea of what you are doing.
As for the rear suspension. You're raising the front of the bike, that shifts weight to the rear. With more weight on the rear wheel you'll likely have to increase you spring rate to maintain proper sag. Also the stock Fox Triad rear shock tended to settle into the mid stroke a bit when riding, this tendency will be exaggerated with the weight bias more to the rear. How much so will depend a lot on your weight of course.
I wouldn't go 140mm on a 100mm Stumpy. A 120 would be okay though. I know, I've got the exact same bike, and yes the stock Black Elite sucks. The two best forks I've had on the bike so far have been a Fox Float RLC at 100mm and a 100mm RS Reba. I prefer the Reba. The RLC was set up for 120mm of travel to begin with and it pretty much sucked in the handling department, to slow for my tastes.
Anyway, your call.
"I do whatever my Rice Cripsies tell me to!"
Sorry to but in but how does frame size enter the equation. Would someone with an XL frame be able to add in a bit more travel than someone with a Medium frame? Geometry is not my strong suit.
Frame size will not make a difference. When you add a longer fork, You start to stretch out the front end. 20mm axel to crown works out to be about 1 degree of head tube angle. It doesnt sound like a big difference, but it is. Add more then your frame is designed for and you can have a frame failure.
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