VMX suspension damper regs

[Michael Moore]

In AHRMA for pre-75 MX the rules say "Any shock absorber may be used, providing the technology and design was commercially available in 1974 or was supplied as OEM on any AHRMA-legal machine " but remote reservoirs are specifically prohibited.

I'd had the impression that external adjusters were frowned on, but I haven't been out to a race for quite a long time and that may not be the case now. There are certainly a lot more shim-stack valving dampers (like brand new Ohlins)in use now than there were in the pre-1975 period.

Koni had the steel body 8211 race car dampers with external adjustments in use in the 1960s, and the aluminum 8212 was introduced (per their website) in 1967 and both are still in production today. It would seem to follow that dampers with external rebound and compression adjustment are clearly period technology. Arnaco is the only damper targeted at the motorcycle industry that I can think of that had an external adjuster in the early 1970s. Koni bike dampers could be adjusted by pulling the spring and pushing the rod all the way to the bottom and then turning an internal valve with the rod. I think that moved both rebound and compression, but it has been a looong time since I learned about that so I'm not sure now.

What is the stance of the UK and other VMX organizations on what qualifies as a "period suitable" damper? Anything goes as long as you've got two of them, they have steel springs (no Fox AirShox) and you don't exceed the travel limits? If anyone knows how AHRMA is currently enforcing the rule I'd be interested in hearing about that too.

cheers,
Michael

[rhino]

Don't get me started

[Mark Cook]

LMAO

[Michael Moore]

I hadn't heard of Circa before, their attitude sounds similar to the US trials "twinshock" groups, where they aren't too sniffy about "did it come from the factory this way?" questions and in fact encourage specials.

All the vintage events available to me are run to AHRMA rules. Sometimes what the rules say depends on who is doing the interpreting, just as history is written by the winners. There's the letter of the rules and then there's the spirit of the rules. Occasionally a very blind eye is turned to people pointing out how the rules clearly ignore common practice during the period.

I don't have much interest in running a longer travel bike (which have much fewer suspension issues) as those mostly came after the time I was racing in the 1970s.

I found the AMCA rulebook and they leave things pretty open "27.7 Any make of suspension damper may be fitted, but external reservoir or air-sprung shocks are not permitted" as long as you meet the travel limits and no more than 35mm stanchion OD on teleforks (though I think Maico had 36mm and Rickman forks were much larger than that).

Spry is quite the craftsman, I've seen his bikes featured in CDB and VMX.

cheers,
Michael

[rhino]

If the rules are fairly applied, everything would be straightforward.

Like you say, 35mm stanchions, no leading axle forks, no reed valves.

All of these things were available in the '60's, 50's even, so why the embargo?

The AMCA's cut off date for pre-74 used to be 31/12/73 manufacture. Somebody then realised that 36mm stanchions, reed valves and leading axles were indeed available before the cut off date.

The AMCA's new cut off date is the 73 model year so no reeds, leading axles (unless AJS) or 36mm forks.

"in the spirit of the era" is the way forward.

I just want to ride me bike

[ampshire-og]

Hi Michael,
Have a look at classicmotorsport.org .
It's the ECMO (european classic moto cross organisation). They have a good website and a very good web page where you can calculate your rear wheel travel by entering a few dimension from your own bike. You can then print it off to prove your travel if you feel the need?
They have pretty much the same idea adout type of shocks but concentrate more on wheel travel at the spindle.
They do allow a bit more travel than us in the UK but personally i can't notice the difference.

They enforce the rules (certainly at each meeting i have attended in the last 4 years) at early meetings, they turned people away who infringe the rules. That said they will tell you what needs to be done and generally theres people aroung to help out. This year i didn't anyone being sent packing so i think the message has got across.

Thier classes are a bit differant and the newest bike allowed is a '72, so no radial finned CZ's or 4 valves CCM's. By having an ealier cut off date i been told this eliminates the argument about reeds and long travel suspension, but dont quote me as i'm no expert.

Like most people i just want to ride my bikes and aint that bothered about an extra 1/2" suspension movement, but i do appreciate there has to be some sort of rules and guide lines.