Short forks and frame damage

[Si]

I've heard it said that if you put suspension forks of say, 100mm travel, onto an MTB that is not designed for suspension forks, not only will the handling be a bit funny but also, after a while, the extra stress on the steerer tube will damage the front end of the bike.

But what happens if you do it the other way around?  If you have a bike built for 100mm travel forks and you put a rigid fork on that is not suspension corrected.  I can live with the handling being faster - this is actually an advantage when taking a fairly neutral off-roader and converting it for use as a fast road bike, but will it risk damaging the frame?

[Chris N]

No.  If anything, it'll make it stronger.

[mzjo]

Do your sums before investing in the forks! While the effect on the front end will probably fine (even an improvement) a lot of MTB frames, particularly sus ones have seat tube angles a lot sharper than the head tube angle. I did this with a fork that was short (on a frame that was fine with a suspension-compensated rigid fork) and I finished with a seat angle that I calculated at 75°, which was unrideable for me. The steering was fine though. I have gone back to my sus-compensated rigid fork - heavier and slacker but at least I'm comfortable on the bike.

[LittleWheelsandBig]

Just use a seatpost with a heap of setback to compensate for a steep seat tube angle.

[zigzag]

Just use a seatpost with a heap of setback to compensate for a steep seat tube angle.

wondering why i'm getting numb fingers after 300km i measured seat tube angle on my hybrid and also found it to be 75deg(!). canyon seatpost with 33mm setback reduced the pressure on my wrists as well as added extra comfort.

[Si]

The seat tube is fine (I've already tried it when the fork went back to the maker for a fix and I only had a non-sus one to use until it came back) , indeed, the seat pin is an inline one so a normal set back one would make up for any change.
Thanks for the reassurance that the front of the bike won't fall off!  And yet another MTB finds that its days in the mud are over and it has a new life as a fast city bike / audax bike...

[mzjo]

Just use a seatpost with a heap of setback to compensate for a steep seat tube angle.

The most set-back post that I had was 27mm (measured) and it was about 15mm too far forward! I didn't mention the 150mm of head spacers that were needed to bring the bars up to something like level (with a fairly deep stem). The short forks (supposedly sus-compensated) were 390mm crown to axle, my usual rigid forks are 440mm and my Sugino sus forks 490mm fitted.