So, I'm looking at a 1997 Mongoose Sycamore mtb.

Up until 1996 these bikes had Cr-mo frames.

Bikepedia describes the 1997 model as having "Mongoose CFA" tubing.

https://www.bikepedia.com/QuickBike/B...more&Type=bike

I have since worked out that CFA stands for "Complex Ferrous Array". One (unreliable) source described this as "4138 Cr-mo"

Can anybody tell me what this all means? Is it actually cro-mo tubing or is it really just a hi-ten boat anchor?

I know that the Sycamores were a low end bike to start with, so I'm not expecting the tubing to be anything special. I'm just looking at this thing as an upgrade from my existing hi-ten/cr-mo combo backup bike.

SAE/AISI 4138 is a 1.1% Cr, 0.25% Mo alloy, from the same family as the 4130 we're all used to in low to mid-range steel tubesets.
The first two digits in the AISI nomenclature refer to the alloy composition family, in this case the 4100 series, 1.1% Cr, 0.25% Mo, and the last two digits refer to the average carbon content in hundredths of a percent. In 4130, that's 0.30% C, and in reality usually falls between .28% and 0.32%. In 4138, that's 0.38% C, nominally identical to the better known 4140 alloy.

I'm not calling b*llsh*t one way or the other on the actuality of these forks being 4138, merely informing you of how the naming system works :-)

The only issue I see is that 4140 can't be cold-rolled into sheets and made into tubing. Parts made from it are typically cast or machined from cast billets. "Complex Ferrous Array" sounds like jargon-speak for pot-metal.

Yes, that's what I was thinking.

I think I'll give that one a miss. It's a shame, it's a good looking bike in very good condition.

I beg to differ. 4140 is used by Range Rover for tubular driveshafts, drawn and heat-treated. It's a bit more difficult to draw, but not impossible. 0.1% carbon doesn't make that much difference to its drawign behaviour, and certainly doesn't make it impossible, or 300M and 4340 wouldn't be available as drawn, tubular parts for aircraft undercarriage.

The main issue I have is whether Mongoose's term "Complex Ferrous Array", or CFA for short, even means Cr-mo, let alone 4138 Cr-mo. The seller of the bike believes that's what CFA means, I'm trying to verify it. It seems to be a Mongoose-only term, nobody else seems to use it.

The thing is, up until 1997 Mongoose claimed that these bikes had Cr-mo frames. For 1997 they changed the description to "CFA" and significantly changed the frame (e.g. went from 1" theadless to 1 1/8 threadless). It seems to me that if it was still a Cr-mo frame they wouldn't have changed the description to this mysterious "CFA" designation. As DannoXYZ says, it is likely that the steel is just hi-tens. Somebody out there will know....

Having explored Bikepedia a bit more, it seems that CFA might have been a form of Cr-mo after all.

For instance, looking at 1997, Mongoose produced a hybrid called a "Crossway" at various levels.

The Crossway 250 was the $249 base Altus/Tourney model and was described as having a Tange Cromoly frame.

Next up the totem pole came the Crossway 450 at $329. Along with its Acera-X/Altus components it also had a Tange Cromoly frame.

Next rung up was the Crossway 650 at $415. This Alivio/Acera-X variant is described as having the mysterious CFA tubing.

Top of this rather low tree was the Crossway 850. At $549 it picked up STX and Alivio bits and another unique-to-Mongoose-terminology frame called a C(a)2 frame, whatever that means. I think its aluminum.

So putting this together, and assuming that the more expensive bikes got the better tubing, and seeing as even the base model bike had some form of cr-mo tubing, crummy though it might have been, it seem reasonable to assume that the middle-of-the-range bikes might have got a better form of cr-mo.

Following this logic, I'm guessing that the Sycamore was somewhere in the middle of Mongoose's 1997 mtb range, and the frame tubing was at least one level from the bottom. Seeing as my current backup bike is hi-tens except for the cr-mo seatpost, I'm inclined to think the Mongoose might be a better ride.

If think that 1997 was about the time Mongoose started to go down the toilet. With stupid, brain-dead, ambiguous terminology like "CFA" and "C(a)2" that nobody can interpret, it's no wonder they crashed and burned.

[Edit] Yep, Mongoose 1997 mtb heirarchy from bottom to top was:

- Switchback (Tange Cr-mo)
- Sycamore (CFA)
- Hilltopper (CFA)
- Rockadile C(a)2

So it looks like CFA is probably a form of Cr-mo.

Wouldn't it make sense that they would ramp up the bafflegab at the same time they made the other changes in the frames youre refer to? If nothing else to distinguish the model years.