Suspension forks on old bikes

[FluffyChicken]

The only drawback to a decent condition Mag 20/21 for anyone above 'a certain weight' is the inherent weakness of a rather flexy fork due to the very small overlap between stanchion/lower leg...

...probably the least of all the quality bouncy forks??

Well the overlaps probably longer between the bushings than a Bomber bushings total length can check.

All forks of that era are quite flexy. Modern large diameter hubs/contact points and good skewers help though.
The flex is down to having 1" diameter tubes and probably narrowing magnesium lower legs.
The Marzocchi and similar where all flexy as well.
But to be honest after a short while you get used to it. I rarely really notice it between them and my bomber Z2 Superflys to be honest.

Though I'm of average weight I think.

 

[We_are_Stevo]

If I remember rightly the overlap on the Mag's is only just over two inches, the rest are closer to three??

The fig's are in the 'Long Travel...' mod. you posted the links to that I use for my Manitous

 

[FMJ]

Oil change is relatively simple and requires only the top caps to come off, some oil and a measuring stick.

A STICK?!?! What are we, animals?

The flex is down to having 1" diameter tubes and probably narrowing magnesium lower legs.

Magnesium is actually very stiff, almost to the point of being brittle. The flex is from the stanctions and minimal bushing contact/overlap.

 

[hot chilli]

i know that at one point in time there was a long travel kit for the mag 21.

i also remember using posibly 3 sets of rock shox of different type to make up a hybrid fork, still have a fork crown and some rock shox boxes in the loft.

 

[SeeingisBelievingGTMuseum]

Can't begin to count the number of head tube, down tube failures I've seen posted here, mtbr and pinkbike because people stretched the travel and added stress to the frame that was not designed to be there in the first place. I'd error on the safe and known size, wouldn't go anywhere near a 100mm unless the fork is designed with a minimal axle to crown.

 

[We_are_Stevo]

Considering the minimal change in geometry evinced in fitting a slightly longer fork I suspect any damage was more than likely down to how the bikes were ridden just because they had the longer fork...

...beats me why podgy, middleaged blokes in inappropriate clothing seem to think they can ride an old bike as though they were Martyn Ashton just because they've hung a longer travel fork off it, then wonder why it breaks!

The frames in question were almost invariably intended for use as XC rides, long before the magazine led fashion for jumps and drop offs was ever thought of; used as intended, a stretched forked retro bike should be no more fragile than can be expected (I refer to steel of course, I wouldn't even want a retro alloy frame that only had an original life expectancy of 3 - 5 years in the first place!)...

...and, as posted elsewhere, if Dave Lloyd says you can retro-fit a 100mm fork to one of his frames without any problems I'm more inclined to go with the guy who built the damn thing!

 

[FairfaxPat]

As someone else previously stated-Try it, you might like it. I have Mag 21's on my '91 Funk, but that bike has slicks these days and is my road bike. The Mag 21 has a whopping 1.6 inches travel-not very much if you go anywhere rough. Longer travel forks will slacken the head angle, which results in slower steering-which can be a good thing if you are whipping it through a gnarly section----On tight U-turns or maneuvering in parking lots is where it will be slightly tougher. 100mm is not really all that much, but the benefits gained through bumpy stuff is well worth it.

 

[hamtaro145]

100mm on a '96 zaskar just doesn't sound right. mag 21's, 21SL and judy's were all the rage here on those frames, and with the judy DH being the longest travel at 73-80mm I would personally not go longer them 80mm on that frame.

My '96 rocky mountain Xs speed (their DH frame) is only rated for 80mm travel forks.

 

[FluffyChicken]

Oil change is relatively simple and requires only the top caps to come off, some oil and a measuring stick.

A STICK?!?! What are we, animals?

The flex is down to having 1" diameter tubes and probably narrowing magnesium lower legs.

Magnesium is actually very stiff, almost to the point of being brittle. The flex is from the stanctions and minimal bushing contact/overlap.

Looks like you bolted a hub spacer to some tubing
Might have to make myself one of them. I assume you lower it in at adjusted height an suck gently.

For MAG's I just use a digital micrometer stick and some funny angled light to see the surface tension alter. Probably far to accurate for what it's worth.


Thinking about it it was the Marz's that had the flexy bottom legs, especially with the holes. I know pure magnesium is stiff and brittle as i's easy to snap ribbon in the hands.
Though the brace could have been better as a one piece unit or wrap around as rotation of the legs is another area, a booster always helped out there. But hey I use a few sets all the time.