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PostPosted: Tue Sep 15, 2020 7:59 pm 
Dirt Disciple

Joined: Thu May 08, 2008 2:30 pm
Posts: 62
Location: Flagstaff, AZ
The early 90's was a weird time for MTB geometry. Most bikes were still designed around rigid, 380mm a2c forks, but Turner's Rockshox RS1 started showing up in what, 1989?

What I find interesting is that if you look around at some of the early 90's catalogs, many "Teams" were running and marketing suspension forks as "options".

Whenever I mention running a longer fork on my 1990 Marin, I often get ridiculed for "messing up the geometry" and "ruining the purity of the non-suspension corrected handling", but these issues clearly didn't bother bike brands of the 90's, or racers.

Here's the Team Marin from the 1990 Catalog:
Image

And here's the Team Marin that Marin Bikes was showing off at 2015 "30th Anniversary" SeaOtter booth:
Image

The Mag21 pictured there would've been about a 405mm a2c, so not significantly higher than stock rigid forks, but also not so much that it made the bike unusable.

Were bikes during the transition period of front suspension being designed with front suspension in mind? As in, they could handle a little slacker head tube angles, a little slower steering, etc?


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PostPosted: Tue Sep 15, 2020 8:44 pm 
retrobike rider / Gold Trader
retrobike rider / Gold Trader
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Joined: Fri Feb 06, 2009 11:13 pm
Posts: 11759
Location: Skipton
I've found by playing with different options on my modern full suss that people over think geometry. My old bike that was designed for 120mm forks ran perfectly well with 140 or 150mm forks and my new frame, designed to use short offset forks works just as well with 51mm offset.

The range of changes modern bikes suck up suggest to me that the tiny difference between RS1's, RC35's, etc compared to the stock forks would make virtually no difference and certainly wouldn't ruin the ride. The % change in geometry would be slight at best.


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PostPosted: Tue Sep 15, 2020 11:55 pm 
Gold Trader
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Joined: Fri Jan 23, 2009 2:30 pm
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Location: Surrey
As above. Ive run 80mm or 100mm forks on frames designed for 60mm and if anything, rode better. Based an advice from the man above, I bolted on some 140mm travel forks on a frame designed around 120mm. I spent a lot of time over thinking before the advice, and after doing the deed, have a lovely riding and handling 29er.

As you say, a lot of replies to such threads about this start, as mine did with worrying about geometry changes. I'm a casual rider at best so probably wouldn't notice anyway, but as I didn't i can only assume all is well. You can do worse by fitting the wrong stem or stem at the wrong height.

Slack front ends are all the rage now, back then it was all arse high, front end low.

Back to your original point about older rigid frames being future proofed or built with suspension in mind, I'd guess some were, some weren't but many of us bolted suspension on to a frame that came with rigid forks and lived to tell the tale.


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PostPosted: Wed Sep 16, 2020 12:26 am 
MacRetro rider
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Joined: Fri Feb 09, 2007 4:16 pm
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If you fit a sus fork to an older frame but alter nothing else you will ruin the handling. If you alter the ride position by changes of components then you can get acceptable handling back. I had a Diamondback Topanga that was at best suited to 50mm travel forks. I fitted Manitou Six forks with 80mm travel. Further I used a zero lay back seat post with seat set forward and a long stem to put my weight forward and over the forks plus wide bars to slow the twitchy steering. In the new guise it served me well, giving me confidence on rougher terrain.


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PostPosted: Wed Sep 16, 2020 10:09 am 
retrobike rider
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Joined: Fri Aug 08, 2008 2:36 pm
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Location: Yorkshire, England
BITD, the suspension forks where designed to go on rigid frames, hence always trying to keep a2c short. mags doing the best job for the travel back then.
Zero rise stems then came.into fashion and inline seatposts to compensate. (or happened to compensate ;-)) for the slight rise in the from.

by 1993 most few where getting designed around 40/60 mm forks and some forks, like pace etc where longer for the travel.

so by mid 90s 60 was comfy on the frames...they then increased rigid fork length to compensate, pulled the stems shorter and this kept going in steps.


if you out a 100 mm fork on an Orange Elite, with short stems it.os the dogs bollocks... but I the all dangly wobbly and no idea where it is going

Do remember not all frames had the same geometry, for instance withing Rocky Mountain, each frame would be different for it intended use, they even changed with frame size within the same model.

Others like Kona only changed for bottom end, top end.
Marin similar.

You can't compare modern adjustments to old frame adjustments.

It was arse up/front down because the forks were shorter, it is now high front because the forks can't make it any lower.

iirc, 1" front was half a degree (or the other way around).

so you dropped the front end down a bit and maybe took 1cm of the stem length.

Forks where different back then to, sag wasn't really a thing until they could actually sag.

don't worry, try it out. see if you like it.

The main problem is the bottom bracket gets higher, loosing stability and the seat goes further back from the crank line.
then the front gets wobbly and flip floppy.


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 Post subject: Re:
PostPosted: Thu Sep 17, 2020 2:37 pm 
.o.T.M Triple Crown Winner
.o.T.M Triple Crown Winner
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Joined: Sun Dec 31, 2006 12:59 pm
Posts: 3615
Location: Sunny South of France
There were many school on frame geometries/suspension fork.
In 1991 catalog, Trek claimed that he adapted the 8900 composite frame geometry for the RS1. The 8700 got only a Tange BigFork. So, the frames have to be different. I got both in same size and… they are really the same !
Gary Fisher claimed the same thing with his 1991 Mt Tam specificaly designed for the RS1.

On other hand, Curtlo never cares about specific suspension geometries. He could be right if we consider taht a suspension fork hight is always changing (the SAG for example…)

Last case : the really first Bradbury's Manitou with a very low hight. But a vey little travel !


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