suspension on a non sus frame

[dyna-ti]

I want to put a 3.5" fork on a non sus adjusted frame,
Ive heard over the years horror stories about it rips off the front end but nobody can say they've seen it happen ,Ive never seen it myself,except when a tree was added to the equation, possibly an old wives tale to make you buy a new frame
What i always thought it would do ,would be to really slacken up the steering,being a bit dicey on the corners but nothing much else and you could lessen that a little with a short stem
My reasoning is ,if it were the case that it, may damage the front,then the first drop off that you land on a sus frame ,it would bend,Like the big drop offs that went on in the early days of fork development..Ive seen some vids about guys in the states,from the nintys doing huge drops on early rockshox ,at this time there was no heavy gusseting or beefed up front ends on the frames
So whats the general consensus again

 

[rody]

I can say that I've never seen a front end "ripped off"... a few ovalized headtubes, maybe.

You are correct though, it will make the bike a slow speed wobbler with a penchance for wheel flop, raise the bb, and slacken the st angle.

Figure 3/4 degree of HT change for every 20mm of extra length as a rough guide...some more, some less dependant on rider weight with sag.

cheers,

rody

 

[hamster]

A 3.5" fork sounds like too much - something like a 63mm / 2.5" would be preferable.

You can also help somewhat by putting a really large tyre on the back and a smaller one on the front. But if your frame is old you may be unable to fit a 2.3" in the back.

 

[Andy R]

I've run 100mm forks on quite a few "non suspension corrected" frames, and while the handling changes are noticeable at first, you soon get used to it in my opinion.

Also it makes a big difference how far into their travel you run the forks - how much "static sag" you have. You would probably be running a pair of 100mm forks at about 25% sag anyway, so this is really the length you need to use to calculate angle changes, not the fully extended unloaded dimension.
There's nothing to stop you running a higher sag percentage though and this will reduce the effective geometry changes, with the added advantage of letting the front whell track well on stutter bumps and the like (cos' it can drop into the depressions).

Also to compensate for geometry changes you might want to run a lower stem and move the saddle forward on the rails 10mm or so to keep the same effective seat tube angle. Both these will help to stop that slack-angled wanderiness on steep on-the-nose-of-the-saddle climbs.