Suspension travel limit - which bikes?

[supersenior 50]

Ross unfortunately it has become the norm on the forum for eligibility issues to turn into a bunfight, however this one has stayed relatively civilised. Your question is legitimate, and as Dave says put your query to MA.
With all rules, lines have to be drawn in the sand and they don't always suit everyone. The suspension travel limits have worked well I think and have helped to keep less advanced bikes in the game. I had my '74 Maico rear end limited and it was no biggie. If the limits are left open I think Geof's scenario is not that outlandish.
Kev you are a stickler for accuracy, and with that in view I am surprised you claim to have been the measurer at the 2012 Classic Nats.
Chief scrutineer was Kerry Marsh, assistant scrutineer Michael Vandenbroek, technical adviser Dave Tanner. Tanner did the measuring.
Sources are Sup regs, stewards report, C of C report, and my recollection as event co-ordinator. This is not a comment on your knowledge or expertise.

[LWC82PE]

Top out spring has no real bearing on usable suspension.

I would agree with this too, that's why i am curious as to what bikes are on the pre 78 'must be restricted list' only because of their advertised/over quoted brochure travel and if they actually have travel measured by MA scruitineer method they would/could quite possibly pass under the  9" limit. I have proven Suzukis don't match what the specs say unless you inc the added travel on rebound, but are other brands like this too?

[KTM47]

Don't rely on the specs stated. Check for yourself. Any measuring of bikes should be done by a licenced measurer.

[Rossvickicampbell]

"Anyway if you want to change it read the MOMS. It can't be changed until next years commission meeting. March 2016. Posting about it here is not going to change it."

Excuse me - who said anything about changing it before 2016 - who said anything about trying to change it before next years commission meeting.  I happen to be a 1/2 glass full person and thought I might do some homework before I even thought about putting in a submission!  No time frames entered into.  I think the forum - generally - is a place where I learn lots from - this happens to be the first time I have broached something from the MOMS/MA or whatever you would like to refer to.

I understand what the rules are and limit my YZB to suit and have done for years now - doesn't make me any slower  - however often wonder why we cannot simply ride them as they came out at the time - Geoff's thoughts taken into consideration here and honestly hope he is wrong.  But I am forced into restricting it or cannot ride it - can't go up a class or era.

I have written to the technical services - even if the email address you gave me Dave didn't work  - so will look through what I get and have a thought.

Just someone keen on the sport asking some questions - sorry Geoff if they have been asked before  but rather than debate it here was after info to question it the correct way.

[Momus]

Is Dave a MA licenced measured?  So the tape I borrowed from Michael Banford and still have wasn't used to measure suspension travel. Check your facts and then post your apology here. I wasn't measurer before the meeting, but apart from the Seward who can't do it I wasn't the only other one licenced to do it.

If you/MA are using  tapes, presumably printed,  for a precision measurement, that worries me.

Generally tape measures are for reference only.

I would like to think that certified scrutineers would at least be using an independently calibrated steel ruler or a set of certified Vernier calipers if there were a chance that things could go to the Steward or beyond.

When you say "... compress shock to bump rubber.  No need to try and compress bump rubber etc." that seems expedient.  The bump rubbers on my Pre 78 bike are urethane foam and about 35 mm long. They function as a rising rate auxillary spring with a little damping.

 I could have the legal 229 mm plus 50 mm in the stops allowing for the motion ratio.

Surely the test requirement should be a measurement with bump rubbers completely removed?

[skypig]

I'm sorry, I seemed to have wandered into parliamentary question time.

I'm looking for the site where adults (mainly like minded men, FFS!) talk about old motorbikes.

The dodgiest ruler I've seen in my life would be accurate to a mm (maybe 2) over 240mm

A "calibrated" ruler! "Vernier calipers".

Maybe if you think you came second in the world championships because the guy that beat you had 4mm extra travel.... Put your money down (in case it turns out to be legal, and you pay costs) remove the bump rubbers (not a 5 minute job, not a job that could be done at the track I'd suggest.) while waiting for the calibrated rule to be warmed/cooled to the correct temp.

Anyone know where I can get a radiator guard for an '81 RM125? Or suggest a mesh that doesn't inhibit the airflow too much.

 

[evo550]

Wouldn't you just put the bike on a stand with both wheels in the air and measure from top of the wheel to the underside of the guard. Shock shaft length would differ depending on it's position on the swingarm.

[KTM47]

If you/MA are using  tapes, presumably printed,  for a precision measurement, that worries me.

Generally tape measures are for reference only.
[/quote]

Tape measures are used by tradesman it depends on the tolerance needed.

[Iain Cameron]

I agree with Rosco , In all the travel bun fights that has been on here this one might just answer some of the questions . I race (wobble ) in pre 70 , 75 , 78 . Im building a YZb250 up but will not race her in the Nats . My  77 YZd's are great bikes all the go fast gear from the era White Bros swing arms and fork internals so they don't go to the Nats they are what I wanted in the day , I race my 76 yz'c for pre 78 in pre 75 I use MX'ers . When I do race its for fun but when I build I build to the best one could buy in the day as that was what I wanted back then .

[Nathan S]

KTM47, The point is that there's no defined way to measure the travel. Without it, EVERY conceivable method of measuring travel can be shot down.

[KTM47]

Not really.

I think if someone has an abnormally long bump stop I think that needs to be considered, but measuring travel without the bump stop is just not practical.

For rear wheel you are measuring rear wheel vertical travel. As I said the position of the wheel in the swingarm (chain adjustment) does have an affect. All the way forward less travel all the way back slightly more travel.

Either way a tolerance needs to be stated.

[JohnnyO]

Wouldn't you just put the bike on a stand with both wheels in the air and measure from top of the wheel to the underside of the guard. Shock shaft length would differ depending on it's position on the swingarm.

That's not accurate, many bikes bottom before they hit the guard. You can bolt longer shocks on with the same shaft travel and increase the gap between the tyre and guard but not increase the wheel travel..

[KTM47]

John. Who measured your suspension travel at QMP in 2012?

[Momus]

If you/MA are using  tapes, presumably printed,  for a precision measurement, that worries me.

Generally tape measures are for reference only.

Tape measures are used by tradesman it depends on the tolerance needed.
[/quote]

Mate, I am a tradesman and I sometimes make suspension parts for cars. 

For this type of work if you are going to measure 229 mm you reach for a steel ruler or calipers; the good old tape measure probably has a millimetre or more of slop in the hook rivet.

In your defense the tolerance is very generous but it also highlights the lack of precision and rigor in the whole exercise.

Not really.

I think if someone has an abnormally long bump stop I think that needs to be considered, but measuring travel without the bump stop is just not practical.

For rear wheel you are measuring rear wheel vertical travel. As I said the position of the wheel in the swingarm (chain adjustment) does have an affect. All the way forward less travel all the way back slightly more travel.

Either way a tolerance needs to be stated.

My bump rubber is off the shelf Ohlins.

Don't the AMA use 10% of the bump rubber's free length for their calculations?

Measurement logically should be in the mid point of the chain adjustment range.

[JohnnyO]

Like Wasp said, shock builders ignore the bump rubber when measuring travel. That's how Ohlins do it..