R65 rear spring rate?

[Allred]

I recently bought a set of vintage replacement shocks and springs from Bob's BMW, nice looking & rather pricey, but I thought my '83 R65 w/43k miles was riding too rough, and deserved them as part of the refurbishment project.

After installation, and now with about 1000 miles riding on them, I am convinced that they are no better than the old ones I removed!  Why???

Seems to me they are just VERY stiff!  Riding solo (wt 200lbs) even relatively minor urban road irregularities at moderate speeds generates a jolt to the butt which is very harsh.  It seriously detracts from the enjoyment of riding this otherwise very enjoyable around town bike.  I own four other beemers, and one lone Kawasaki, and all have a much more comfortable moderate speed supension.  Only the R65 stands out as a "punisher".  

I think either the springs are too stiff, or the shocks (non-adjustable) are, or both.

Does anyone have data on what the original spring rates (lbs compression per inch) should be for a stock '83 R65?  

I'm going to inquire with Bob's BMW if they can provide the specs on the new springs & shocks to compare.  Then decide whether or not I can find some alternates to try out, in attempting to get a more comfortable ride on my R65.

Any help or reference links would be greatly appreciated!  I'll share what I learn whether I am able to arrive at a comfortable ride, or not.  

Allred
Riverton, Utah

[Bob_Roller]

Do you have any pre-load adjustment on the springs ?

[Barry]

Allred

You can calculate the spring rates using this formula  Rate =(wire Dia to power 4 * 1470000)/(coil dia to power 3*no of coils)

Note:  use the mean coil diameter ie OD less wire diameter.

I admit it's not the easiest calculation. You really need to know the ballpark figure to be sure you did it right.

I've been unable to find front spring rates for R45/R65 so I did the calcs on my fork springs which came out as 26.87 lb/in soft rate and 34.1 hard rate.

What I learn't from this is that the rates are quite a bit stiffer than the early mainstream airheads and while I can understand stiffer springs were  a popular mod on those bikes I would think they are much less needed on a R45/R65.

I need to look - Somewhere I have a list of springs rates.

[Barry]

The only spring rate tables I have are for font forks and even then I have no values  for stock R65 springs.

I just measured my original BMW rear springs and did the calc which came out at 121lb/in.

Seems high compared to the fronts butt your sat right on em.

Tried to attach a spread  sheet which makes the calc easy but the system will not allow this file type. If you measure your springs I could run the calc for you.

[Barry]

Just realized I didn't allow for paint thickness when measuring the springs.  Don't laugh  measurement of the wire diameter is particularly critical    A mic or vernier caliper is essential.

I took .004" off the the wire diameter and spring diameter and the calc now comes out at 114.7 lb/in.  Quite a change for 2 thou of paint. I think maybe the paint is even thicker.

[weasel01]

I recently bought a set of vintage replacement shocks and springs from Bob's BMW, nice looking & rather pricey,

Are these Progressive brand?

[montmil]

I recently bought a set of vintage replacement shocks and springs from Bob's BMW, nice looking & rather pricey,

Are these Progressive brand?

I've seen them and if they are Progressives, it's a step backwards. No choice of springs, only three preload settings but they are rebuildable, according to Bob's advert. 1979-84 R65 is $299.00 pair. Other models are $339.00 pair.

The shocks look exactly like OEMs right down to the rubber handled adjustment lever. For a show bike, great. Mount up a pair on your daily rider and your buds will then rag on you for not replacing the "junker" factory shocks. You'll have some 'splaining to do, Lucy. I'd bet they're Pacific Rim.

Monte

[Allred]

Thanks for the formula, I'll carefully measure and see if I can calculate the result, will post finding.  Also will post what I hear back from Bob's BMW, if they reply with useful info,

and to answer Bob_Roller, yes there are three pre-load settings, and I have them set to the softest one.

More to follow...... [smiley=dankk2.gif]

[Bob_Roller]

I don't know if read this correctly or not, but you said that you bought shocks and springs from Bob's, did they arrive assembled, or did you have to install the springs on the shocks ?

Only reason I bring this up, is that if the springs are 'progressively' wound, the coils that are closer together should should be at the top .

[montmil]

...Only reason I bring this up, is that if the springs are 'progressively' wound, the coils that are closer together should should be at the top.

While researching for a photo -no joy- of the OEM replica shocks in Bob's catalog, I could not help but notice that the images for the Works and Ikon shocks have the tight, or closer together coils, at the bottom near the preload adjustment ring.

http://www.bobsbmw.com/catalog/2003_catalog/Suspension-Braking.pdf

Just an observation on my part.   Monte

[Bob_Roller]

I wasn't sure, as the progressive springs on the fork need to be installed with the close pitch coils at the top .

Just didn't know if it made a difference on not on the shocks .

I'm at work, so I can't check out both R65's in the garage .

[montmil]

...I'm at work, so I can't check out both R65's in the garage.

Well, D'oh.  I'm at home so went out and looked. Both my R65s are tighty toppie. Checked back and Bob's BMW pics have the tight ones at the bottom. I'm thinking it may not matter? Or do the fork lowers and the swingarm have less mass than... my head is starting to hurt.

Hey! It's Friday. Time for a B-double E-double R-UN.

[Bob_Roller]

I went out and checked the oilhead springs, and they are not progressive wound springs .

[weasel01]

I rode my R65 today and thought I'd have a look too my stock Boge are tighter at the top?

Beer run? count me in!!!!!!

[montmil]

Beer run? count me in!!!!!!

Check your fax machine... I just sent you a sixer. Now email me some eggs

Monte

Uh Oh. I'm falling off topic again. Yo! Bartender...