Re: R75/5 Front End Dive.
Posted: Tue May 18, 2021 11:07 pm
I don't have the specific specs on the spring, either the BMW ones or the Progressive.
But in general, the "tight" (softer) windings of the progressive springs are softer than stock and the "wide" winding are stiffer.
When you pull on the brakes and the front end dives, the "tight" windings on the Progressive springs compress easier than the "wide" windings until they coil-bind. Then the softer spring rate is eliminated and you're working with the wider stiffer spring rate.
The point of this is that your front end dive is probably more accentuated because of the Progressive springs. Stock springs, which are straight-rate, will initially compress less than the Progressive ones.
If you add more spacer to the Progressive springs, you will compress the softer tight windings more than the stiffer area. Therefore you'll have less dive before the stiff area of the spring kicks in. It will also lift the front end, reducing the "sag". Note what GSPD says above about "an inch or two" when you take your bike off the stand. Still, this might be what you are looking for.
It should also be noted that the dive of the front end changes the geometry, which increases feel and stability as you get on the brakes. From what you've written, that doesn't seem to be important. This geometry change does not occur much on the newer BMWs with the Telelever front suspensions, as they don't dive. Not great for racing, but very comfortable for normal road use. I notice you have an interesting collection of bikes, mostly older, but you may be interested in riding a newer BMW. Considering the "standard" setup of your /5, you may want to try an R1100R, R1150R, or R1200R with the Telelever suspension plus the Paralever rear which eliminates the rear end jacking under acceleration. They have a nice compliant ride without dive. I find the riding position to be a bit tighter than the older bikes, though.
You might find this site interesting...
http://cycle-ergo.com/
You can compare your bike (the only /5 they show is an R60/5) to the newer Oil and Hexhead models. You can adjust your height and inseam to see they affect the angles of your body.
But in general, the "tight" (softer) windings of the progressive springs are softer than stock and the "wide" winding are stiffer.
When you pull on the brakes and the front end dives, the "tight" windings on the Progressive springs compress easier than the "wide" windings until they coil-bind. Then the softer spring rate is eliminated and you're working with the wider stiffer spring rate.
The point of this is that your front end dive is probably more accentuated because of the Progressive springs. Stock springs, which are straight-rate, will initially compress less than the Progressive ones.
If you add more spacer to the Progressive springs, you will compress the softer tight windings more than the stiffer area. Therefore you'll have less dive before the stiff area of the spring kicks in. It will also lift the front end, reducing the "sag". Note what GSPD says above about "an inch or two" when you take your bike off the stand. Still, this might be what you are looking for.
It should also be noted that the dive of the front end changes the geometry, which increases feel and stability as you get on the brakes. From what you've written, that doesn't seem to be important. This geometry change does not occur much on the newer BMWs with the Telelever front suspensions, as they don't dive. Not great for racing, but very comfortable for normal road use. I notice you have an interesting collection of bikes, mostly older, but you may be interested in riding a newer BMW. Considering the "standard" setup of your /5, you may want to try an R1100R, R1150R, or R1200R with the Telelever suspension plus the Paralever rear which eliminates the rear end jacking under acceleration. They have a nice compliant ride without dive. I find the riding position to be a bit tighter than the older bikes, though.
You might find this site interesting...
http://cycle-ergo.com/
You can compare your bike (the only /5 they show is an R60/5) to the newer Oil and Hexhead models. You can adjust your height and inseam to see they affect the angles of your body.