Fork Geometry on Retrobike
- Thread starter Sithlord
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You'd be altering the geometry in a number of ways. Wheelbase and bottom bracket height would both increase, head and seat tube angles slacken off and the effective chainstay length would change.
Your climbing will be more impacted by fitness and technique, ie weight distribution and gear selection than changing your forks to a 20mm longer model, and the longer travel in your forks may actually help you get over some of those roots/rocks that have stopped you dead halfway up that technical climb in the past.
Something else to consider is how much sag you're going to run, and also the axle/crown length of the 80mm and 100mm forks. Just because there is 20mm difference in the travel, doesn't mean that they are 20mm longer.
To say that these changes 'compromise' steering is not strictly true as it depends how you want your bike to handle. I would say that a bike that was more stable at speed and less of a handful on the downhill bits was a positive thing, but it gets steep around here
Your climbing will be more impacted by fitness and technique, ie weight distribution and gear selection than changing your forks to a 20mm longer model, and the longer travel in your forks may actually help you get over some of those roots/rocks that have stopped you dead halfway up that technical climb in the past.
Something else to consider is how much sag you're going to run, and also the axle/crown length of the 80mm and 100mm forks. Just because there is 20mm difference in the travel, doesn't mean that they are 20mm longer.
To say that these changes 'compromise' steering is not strictly true as it depends how you want your bike to handle. I would say that a bike that was more stable at speed and less of a handful on the downhill bits was a positive thing, but it gets steep around here
For effects on the handling you need to take into account the actual change of axle to crown height and the rake of the fork. The actual difference may be more or less than the 20mm travel and fork rake is also important for steering feel.
If memory serves me right you'll change the head angle between 0.5 and 1 degree slacker. Starting with a 71 degree oldskool hardtail you'd end up between 70 and 70.5 head angle, very useable. But do watch the fork rake for the compounded effect.
A longer stem will have an effect also. I found that a shorter stem will give more direct steering and helps to compensate for a slacker head angle. I have fitted 90mm Pace forks to my Mongoose desinged around 65mm.
Note you can run the longer forks with more sag to tune your ride height, that's what I do with my Pace. So depending on what fork you can pump up the negative spring, fit shorter springs, remove spacers etc. etc. and tune it to your liking. Fork rake is fixed though, and I'm sure others here wil chip in their experiences.
What frame/forks are you thinking of?
Enjoy!!
If memory serves me right you'll change the head angle between 0.5 and 1 degree slacker. Starting with a 71 degree oldskool hardtail you'd end up between 70 and 70.5 head angle, very useable. But do watch the fork rake for the compounded effect.
A longer stem will have an effect also. I found that a shorter stem will give more direct steering and helps to compensate for a slacker head angle. I have fitted 90mm Pace forks to my Mongoose desinged around 65mm.
Note you can run the longer forks with more sag to tune your ride height, that's what I do with my Pace. So depending on what fork you can pump up the negative spring, fit shorter springs, remove spacers etc. etc. and tune it to your liking. Fork rake is fixed though, and I'm sure others here wil chip in their experiences.
What frame/forks are you thinking of?
Enjoy!!
BikePimp
Retro Guru
Depending on the bike frame, it's also easier to crack the head tube right on the joint between the head tube and down tube.
It won't handle that well on the turns, and you'll have to lean more...
You might go better down the hills, but why risk cracking the head tube?...or getting injured?
It won't handle that well on the turns, and you'll have to lean more...
You might go better down the hills, but why risk cracking the head tube?...or getting injured?
I was thinking of putting a pair of Fox forks on a Ibis Mojo and was wondering how much they would mess up the handling, I would just like a bit more downhill uprightness 
, and not feel like I am pitched to much over the front end.. currently running a 120 stem on it which feels ok, with Rock Shox Judy DHs 80mm .. did think about risers but...... mmm... its an IBIS MOJO so want to try and keep the nice looks any suggestions ? :? 
, and not feel like I am pitched to much over the front end.. currently running a 120 stem on it which feels ok, with Rock Shox Judy DHs 80mm .. did think about risers but...... mmm... its an IBIS MOJO so want to try and keep the nice looks any suggestions ? :? 
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My Porkpie Pro Image was designed to run with a 60mm travel fork, I ran it with an 80mm travel 98 Judy XC without any problems at all. You can afford to run the fork softer than normal as the sag corrects the bikes geometry.
