R75/5 Front End Dive.

[Tom H Ca]

I have a '73 R75/5 SWB. The problem is that I think I have too much front end dive under "normal/light" braking, I rarely ever "get on" the brakes. The front end is also a bit stiff when going over rough pavement that my other bikes handle much better. Maybe that's just the way the bike is, or is there something I should work on?

I replaced the original springs a few years ago with IIRR Progressive springs with the recommended top spacer that came with them, the correct ones for my bike, at least per their list. The dive was "slightly" less, but the ride was much stiffer. IIRR I'm using 7wt fork oil. I can look up the spring model and oil weight if needed.

I think my goal is to soften up the ride of the front end a bit, but not add more dive. Any thoughts?

Thank you,
Tom

[gspd]

Try 5W fork oil, that should smooth it out a bit on rough pavement.
Not sure what other bikes you're used to riding, but these bikes have relatively long travel suspensions for their day, so the diving you are experiencing is possibly normal.

[Tom H Ca]

See my signature section.

The dive I get does not dive down to the stop as in bottoming out. It's just rather unnerving for it to move so much.

Wouldn't the lighter oil also add more dive?

Tom

[Seth]

Try adding more oil than the stock amount.
The reduced air volume will add "variable" spring rate.
It won't change the dampening rate.

The other option is a slightly stiffer spring
31 42 1 232 017 COMPRESSION SPRING REINFORCED

[Tom H Ca]

The springs are Progressive brand and the oil is 5wt with the amount in the manual.

Tom

[Zombie Master]

There are many different combinations of spring types and fork oil to get the balance you want. It's complicated. You have to know what you want. Comparing a progressive spring to a straight rate alone can change results. I use straight rate because I want consistent fork response when riding quickly. Progressive springs can give a soft ride at low speeds and firm up through the fork travel. Oil viscosity and volume changes effect the fork performance. Other than reliability, what could be more important than suspension, on a vehicle that has only two tires, and a small contact patch?

[Kurt in S.A.]

Then there are Race Tech Gold Valve emulators. Back in the day there were also anti bottom/dive springs sold by maybe San Jose?? Basically items to kick in once the fork moved too much.

Kurt in S.A.

[Tom H Ca]

Thanks for the replies. Maybe GSPD has the answer, I'm not used to the travel on this bike. My HD has a fair bit of travel under braking as well. Maybe I just don't notice it as much due to seating position. The R75 is the only bike I have closest to a lean forward riding position and maybe that's why I notice the dive more?

I think I was hoping that someone here has had the same issue and would say that some valve is clogged or the like. I have never torn the valving apart, but have pulled the lowers and cleaned the outside of the valving assy and the inside of the lowers. Neither were very dirty, I have seen much worse.

Maybe to get the softer ride, I need to play with the spring spacer length (per the manual that came with the springs to tune them) and oil amount and just not worry about the dive. Or maybe even go back to the original almost 50 year old springs and heavier/more oil? The originals were comfortable, but I felt had excessive dive.

I'm not a sport bike rider carving the twisties and need a million dollar suspension. I'm just looking for a comfortable and safe ride.

Thank you all so far!!
Tom

[Zombie Master]

Try it stock for a comfy ride on rough roads. BMW might just have had a clue!

[gspd]

I suggested 5W fork oil because you initially said you had used 7W.

Your springs and spacers are in the ballpark if the bike sags an inch or two (from full extension) when you take the bike off the stand AND if it bottoms out occasionally on the worst pothole or speed bump you ever expect to encounter.
If it never bottoms out on the real rough stuff, your not using your full suspension travel, your springs are too stiff.
It's normal to bottom out on real hard braking if the front brake is functioning properly.

You have to adapt to the bike, not vice-versa.
These bikes were always relatively totally 'mushy', both front and rear, but once you adapt your riding style to them, they'll carve along at a pace that will embarrass a lot of bikes that should blow them away, at least on paper.