OEM Fork Spring Length

[AnnapolisAirhead]

I know I've seen this dimension but searches have eluded me.

Does anyone know the length of an OEM fork spring when new? 57cm?

[20774]

Would this have the information?

http://mysite.verizon.net/vze4dp63/b...ts/forks1.html

[AnnapolisAirhead]

Still reading, that's a lotta stuff in thar! It puts my bike in the 472-488mm (18.58 - 19.21inch) range. I thought I read it was 20 or 22"...hmm

I like this part: BMW R80GS ('83-'84) , R80RT, R80RS '83-'84, /7 "81-'84

Always thought an R80RS would be nice. Smooth powerplant and the best fairing...if only they made them for the US. Did they ever make them for non-US markets or is this a typo? I'd think they'l change the FD ratio like they did on the R80RT due to the fairing taxing the performance...then again, an RS is far from a barn door in the wind.

[20774]

Tony -

Checking my Haynes, it says that the '83 R100RT spring free length is 539-551 mm. Your original number of 57cm seems to be for the /5/6/7 up to 1980. The RS and RT up to 1980 is listed as about 55cm.

[AnnapolisAirhead]

Thanks Kurt, that helps.

I should clarify why I am asking about this. I'm trying to determine if a spring is worn out or not. While it is undoubtedly obvious to the seasoned rider, I've been hitting this hard but only for 2.5 years. So, short of an oingo-boingo gut feel, I was wondering what the specs are.

My OEM springs measure 552.5mm (longer than what you mentioned. Perhaps the PO put earlier model springs in?? he rode 2up with a trailer and he worked at Bob's so, may have had help) while the new Progressive springs measure just 520.75mm. That leaves a delta of 31.75mm (1.25 inches) to get to the same length as the OEM spring (assuming it has retained its length) and back to stock setting. So, then before the pre-load, I measured the thickness of my aluminum top clamp, minus the OEM top clamp thickness which comes to a tad under a 1/4". So that totals up to just shy of 1.5" without adding in any pre-load for riding preference (not sure how much I'd notice given my riding experience) and my weight, a bit heavier than a typical rider.

I've cut spacers from Schedule 40, 3/4" PVC to account for the all these differences and try things out. My first guess is to go with what adds up to the OEM length and accounts for the new top clamp, but not my weight. My reasoning is that the wire is thicker on the Progressives and they are new, so I'll start there as a baseline.

Clearly, I need more to ponder about.

[20774]

Tom Cutter offered some information on the Airheads list a number years ago...see stuff below the dashed line. Not sure which bike model he was talking about. Based upon these measurements, I think that's he's referring to bikes prior to 1981.

Haynes also lists spring diameters:

/5/6/7 to 1980 - 4mm
most bikes '85 and on - 4.3mm
R80GS and R100GS - 4.67mm
All others - 4.25mm

What's your diameter?

----------

BMW Standard spring #31 42 1 231 358 is 567 mm length (22.32") with wire
diameter 4.0 mm (0.1574")

BMW "Heavy-Duty" Spring #31 42 1 232 017 is 543 mm long (21.38") with wire
dia. 4.25 mm (0.163")

Sounds like the PO put in the BMW Heavy Duty springs. Measure the wire
diameter in a couple places to be sure.

When you get done, you want the forks to compress about 2-3/4 to 3" from
fully extended (wheel off the ground) when you are seated on the bike with your
customary riding load (fairing, tank bag, etc.) Have a friend make the
measurement. use you tippytoes to just balance the bike. Take several
measurements. If the fork binds at all, fix that before bothering to measure anything.

[CTellman]

I just rebuilt my front and rear suspension. The old progressive springs had a 1 inch piece of pvc as a spacer. My new springs were about 1 inch longer than Clymer's said so I did not reinstall the pvc. Check Clymer's advice and spring length.
Campbell Tellman II
'93 R100RT