abdon 

I luuuuuv early straight top tube lugged mountain bikes with lugged forks. It is such a crying shame that this trend only lasted a few years before everybody jumped into unicrown forks, then welded frames, and then in my opinion downhill from there. The early ones were exceedingly well built, then a lot of cheaper mass produced me-too's followed.

What I'm puzzled by is the geometry of these early frames. I just picked a Mt. Fuji and the measurements are just crazy. On the horizontal drops I can push the tires to pretty much 18 1/2" and it has a wheelbase of 42 1/2". This is pretty insane considering that this 18" frame with 26" wheels pretty much matches the numbers on my 21" Trek 720 touring bike. My daughter's Panasonic 7500 (converted to a touring bike) has similar long numbers.

Simply put, back then what was the rationale to build them this long and with such a steep fork trail? It is as if what they really wanted was to build was a touring bike with fat (for the time) 26" wheels and a flat bar. By the early 90's it looks like the long chainstays and fork trail began to shrink.

merziac

Always keep in mind that Klunkers begat MTB's.

abdon 

Yeah, but by the time they took proper form they crystalized into this. Then they evolved from there.

Trakhak

Early on, the sole objective was to bomb down California's longest off-road descents. Without suspension and on rough surfaces, long chainstays provided high-speed stability. Maneuverability on level ground and uphill was a secondary consideration at best.

Cannondale's short-chainstay geometry for the Beast of the East was quite an outlier ("the East" referred to the fact that the East Coast off-road trails that the bike was designed for had very few extended downhill sections and lots of twisty, rough-surfaced stretches).

Long chainstays? Take a look at Denise Mueller-Korenek's world land speed record bike.

Bianchi84

The space between rear tire and seat tube on my 1985 Cannondale looks very long compared to modern MTBs.

PhilFo 

Also look at the British 3 speed bikes, such as the Raleigh Sports (or any TI variant) as well for clues on where the geometry came from.
When I wanted to find a "modern" equivalent of my 1956 Rudge, I found that many early mountain bikes were nearly identical. I got my 1983 Univega Alpina Uno and sitting next to the Rudge, the geometry is very close. Those old British bikes were stable, very well seasoned designs that could go most places and do most things.

vespasianus

This. And they had really low bottom brackets as well, which made them a pain for us east coast people. With that said, gravel bikes with longer seat stays are really great!

Trakhak

Except, again, Cannondale's Beast of the East. Whenever I rode mine after mostly riding my road bikes, I felt as if I were a mile off the ground.

bikemig 

Agreed, vintage mountain bikes make great gravel bikes.

Smokinapankake

And vintage mountain bikes can make great touring bikes. I've got a 1985 Peugeot Canyon Express with 18" chainstays and a 69 degree head angle. Many early production mountain bikes were, essentially, a 26" wheeled touring bike. Mines got every braze-on a touring bike of the era had (3 bottle bosses, dual eyelets front and rear, seatstay and chainstay bridge fender mounts, and pump pegs at the top and bottom of the seat tube). Only thing missing is the mid fork lowrider braze on, but I may be remedying that soon. Maybe.

merziac

Exactly, they still thought they wanted the long wheelbase stability until they figured out it slowed them down as the whole thing took off and got very competitive very quickly.

bikingshearer 

From a handling standpoint, straight-line stability is pretty much the only criterion for that bike. I mean, I seriously doubt Ms. Mueller-Korenek gave one-millionth of a poop about how well it cornered.

abdon 

So basically Gary Fisher set the tone of the early market and once manufacturers saw it was not a fad but a bonafide boom they just replicated the recipe?

Is there an interview with Fisher that discusses his thought process in his early mountain bikes designs? What he was trying to accomplish?

CO_Hoya 

You could ask Charlie Kelly - he's on this forum as Repack Rider

He may have covered all of this in his book, which I have not (yet) read:

jingy2

The early mountain bikes were 1930's Schwinn balloon tire cruisers with long chainstays and slack geo-68deg head 70deg seat tubes. This geo worked well for the riding they were doing-haul the bike in the back of a pickup to the top and bomb down(at least in Norcal).
The 1st custom MTB builders-Breeze, Ritchey etc copied this geo. The early production bikes copied the custom builders.
As the bikes grew in popularity and more people started riding them in more areas, the geo evolved-steeper and shorter for better climbing and all-around riding. Then racing got popular and NORBA geo took over.

merziac

Maybe, it really wasn't very cut and dried, lots of conflicting stories depending on who you are listening to.

You should probably get and read Charlie Kelly's Fat Tire Flyer.

There's plenty of speculation on a lot of this as all the players were jockeying for position as it took off.

Here's my 1982 Merz custom, one of only about a dozen according to Jim.

He was very early on this but gets very little recognition as he didn't capitalize for himself but went to Specialized and helped them far more than many know.

vespasianus

Yup, and the old EWR bikes, which had really high BB, short top tubes and short chain stays. Wheelie machines, but great to jump logs and stuff.

abdon 

You can still see that strong influence for a looong bike for size. It sounds that the downhill trail was first and foremost on the minds of early builders both on the length and the step seat tube so you can sit far back to avoid flying over the handlebars.

Heck if at first form followed function, sometimes it gains enough momentum that it becomes a standard in its own right. Take the down sloping quill stem, ubiquitous on road bikes even today. That was not a need, it was more a throwback from the quills of penny farthing bikes that needed to bring down the bars from the high mount on top of the giant wheels. But people got so used to stems angling that it became an evolutionary anachronism.

well they copied what worked that made them suitable for the task. They didn't copy things like coaster brakes that ended up smoking by the end of the run.

Out of curiosity I'm just trying to understand why they did what they did, which it seems to be fairly clear now.

Clang

Yes, but isn't that more because the rear wheel is only 24"?

chain_whipped

Quirky fun to see today but brings back a few memories. Acquired an SM500 back then with 24 / 26 mullet, roller cams, steel fork. Was a mistake. Poor handling, harsh ride, climbed like a dog on its last days. Wasn't even enjoyable on asphalt.
Sold it and got my first Ritchey, an XT equipped Ascent. Substantially better.

That said, I've had a number of C'dale road bikes and an early 700c hybrid that were greatly enjoyed.

Bianchi84

I'm pretty sure that the frame was designed for the 24"; the seat stays won't allow for a 26". BB Height is also kind of high at 11 - 3/4 inches even with the 24" wheel.
I built this back in '85 and love it!

abdon 

I'll post a picture later of my Mt. Fuji and my daughter Panasonic 7500, both 26" tires, both long chain stays, top tubes, and step angles. The Bridgestone MB4 I'm getting rid of has a much shorter geometry. It is lugged but with a unicorn fork so not that early but not that late.

Ironfish653

​​The Klunkers were kinda the Neanderthals of MTB evolution; they were there first, but they're a whole separate species; not really related to what came after them.

This here ^^^
The "Marin"- style ATBs of the early 1980s are what usually comes to mind when you mention Vintage MTBs. Upright, skinny-tube, triple crank, canti brakes; they share a lot of DNA with the touring bikes of the era. IMHO, they're pretty much touring bikes with the brake studs spaced for 26" wheels.
The early 1990s, particularly post-92 and the arrival of the first generation of suspension forks, saw the start of the constant, sometimes rapid, performance -oriented evolution that has characterized MTBs since.

I'd posit that my 89 KLEIN MTB has more similarities, geometry and hardware -wise to my 1976 Bridgestone tourer than it does with my 1996 Cannondale XC bike, despite being produced much closer together (and obviously being 26ers)

mechanicmatt

I think you got to rethink this slightly. Not so much downhill but uphill. I think it was for traction while climbing. Going up was just as important as going down.

Portlandjim

I built Gary's first MTB bike, he still has it! I have some information to add on this thread, if anyone is interested. Jim Merz