100mm susfork on a 80mm designed frame advice!?

[DocBraunson]

sup yall, this friend of mine has a frame he is building up and he believes that it is designed around a 80mm sus fork. He was curious if he can use a 100mm fork instead. this will undoubtedly slacken the headtube angle. If the SAG is increased on the longer travel fork could the changes to the frame geometry be mitigated? would the end result be something ride worthy? Has anyone done this it would be nice to have the extra travel but not at the expense of a quality ride. i believe the headtube angle is 71 degrees.

any advice is appreciated!


DOC

 

[dyna-ti]

I had a 100mm judy on my bike,it was meant for a 75mm fork
I swopped to a 75mm Z2 and it made a huge difference,mostly in the handling.before it felt like the front end was wanting to slide out when cornering.

 

[mikee]

doubt if he'll notice the differance

 

[SStumpjump]

Depending on which fork he is going to use, I don't see any problems with that. Thing is, a bike designed around an 80 mm fork would probably date the frame to the late nineties. And back then, fork sag was not as much as it is today. So fitting a properly setup modern 100 mm fork, should give you around 20% sag, which places it around the 80 mm length. And you will get around 20 mm of nice plush negative travel to soak up the holes.

The difference will only be a better riding bike in my opinion. Go for it!

 

[FairfaxPat]

I asked Joe Breeze how much the head angle changes when you put a one inch longer fork on and he said "about 1/3 degree". So that isn't much of a head angle change. I have set up several bikes with forks longer than they were designed for and the handling changes were slight, mostly a little slower steering feel, but more stable in the bumps at high speed.

 

[JamesM]

I allways thought it was approximately 1 degree per 20mm :?

I run 85mm forks on a frame that came with 63mm forks and the bike handles fine, as stated the real difference is probably 10 to 15mm due to the increased sag on the more modern 85mm fork.

 

[DocBraunson]

you guys are saying good things here... I figured if i was going suspension, it would be better to have more than less, within reason of course. and i wanted to be less afraid catching the occasional air or real rough patch. sounds like 100mm should be just fine. now i just need the money to buy said fork. if anyone has more input still for OR against, but sounds like not a bad idea. thanks all for your info so far!

oh yeah forgot to mention the "friend" of mine is actually just me ....


doc

 

[mikee]

on-ones 456 is designed to run 4",5" or 6" forks
if this dismisses/proves anything

 

[kaiser]

Another running a 100mm on an 80mm bike, no probs(modern salsa)

 

[messiah]

Somewhere on here are some pics of my Trek 8900 from 1998/9. This was designed for 80mm SIDS but I always ran it with 100mm Manitou X-verts... in fact... I still do :roll:

I have found that I need to have the saddle forward on the rails to keep the bike climbing good, If I let the saddle slip backwards which sometimes happens then I find the seat angle too slack for in the saddle steep rocky climbing manouvers

Try it - it's a bike, you will probably love it.