Suspension forks on old bikes

[QuikNZ]

Need some advice here and am interested in hearing opinions. I have a 1992 Zaskar LE with MAG21s in ok condition. I'm considering replacing the forks and wondering what length you can go to with these old frames without risking damage to the frame, reducing control of the bike and completely messing with the geometry.

These older frames are clearly designed for stiff or short travel forks (up to 60mm?) and anything longer is potentially impractical, silly and/or dangerous. I've been told that going up to a modern length 100ml plus steerer will slow your bike down and change the way it was intended on being ridden.

Anyway, keen to get people's thoughts on the best forks for this bike and the negative effects of a newer longer fork.

I'm looking at the possibility of a Judy SL 1997 or keeping the MAG21s. Just not sure how long they will last.

Also, at what year were frames designed for longer 100ml forks?

 

[mtbdave]

it would be a ridgid fork but you may get away with mag20's/21's otherwise gt bolonia lite/3d forks in black,original and very classy/sleek!

 

[IWish]

Frames from around 96-97 will take a 100mm fork. Basically when they started to reinforce the down tube and not the top tube. A good fork choice if you want bouncy is a rc35 but it would of been more common with a manitou/rockshox ma. The correct rigid fork model I can't remember but after market I'd say you can't go wrong with an rc30.

I would reccomend a 60mm fork for your bike. They will take 80 happily and 100 begrudgingly but the head angle becomes super slack.

 

[FluffyChicken]

Stick with the mag's. Do their job for me fine and many other people here. They are Retro of course.

Just give them a tune up, some fresh oil and a clean.

Gallery&Archive has the oil setting and pressure for your riding and weight. You can start them off there and tweak.

 

[We_are_Stevo]

...but if you do fancy trying a longer fork just get on and do it; see how it feels to you when you ride it and go from there (a shorter stem would counteract the slight change in geometry from the longer fork), bearing in mind that a longer fork has more sag so the difference will be less than you might imagine.

 

[QuikNZ]

Stick with the mag's. Do their job for me fine and many other people here. They are Retro of course.

Just give them a tune up, some fresh oil and a clean.

Gallery&Archive has the oil setting and pressure for your riding and weight. You can start them off there and tweak.

Thanks mate. I'm going to take it for a thrash about tomorrow to see how the forks respond. I'm a bit nervous about trying to service them because they are so old. They seem pretty good for their age and they feel pretty firm and have a decent rebound.

How should a MAG 21 feel at the proper pressure?

 

[FluffyChicken]

Feel, I don't know. er not as rigid as rigid forks
They shouldn't sag much when you sit on the bike and should be quite smooth in action. They'll take the sting out of tree routes and big stones but trail buzz will still be there a bit. A bit of Teflon lube like finish line wet chain oil works well to help the dust wipers slide, just drip a bit around the top.
Also do the same to the oil seal under the dust seal.

I assume you have the pump ? Just put some oil on it or fork grease and clean out the top area of the air valve/seals and gently push it in and set about 40PSI give or take a bit on your weight.

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

The forks original to the bike ? If so they'll be MAG20 not MAG21's

 

[Groundoggy]

My opinion - 60-80mm of travel is ideal and 100mm is the upper limit. More than that and you start to get into a choppery kind of slow and sluggish steering. That is probably what they are referring to rather than overall speed - a slow response (and general goofy look and feel to boot).

I have nothing against a fork upgrade though. Go big ($).

 

[We_are_Stevo]

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??

 

[QuikNZ]

Interesting, keep the comments coming.

No pump, just the bike. I bought it in rough condition a few weeks back and am in the process of doing her up.

The previous owner said the mag 21s were added later on and that the bike originally came with manitou forks, which doesn't sound right but I think it might have been a custom build.

Definitely mag 21s though.