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I have seen bottoming springs for sale for post 70's forks. They are marketed to help with front end dive under hard braking and to help the overall ride. Has anyone ever had experience with these springs? The best solution is cartridge emulators but I wonder if these springs are of any real advantage?

The springs were used back in the day, I think that they replaced the big plastic/ rubber doughnut at thebottom of the fork slider. I think I might have used them , but can't remember if they worked. I would think three times before going down the emulator route and if you really want to use the emulator with stock springs reduced in length.

Hi Twist, I've no knowledge of these items, but two thoughts spring (sorry) to mind.
Diving under heavy braking, and "the overall ride" are poles apart -- these things help with both ...?
Also, I'm not a huge fan of heavy braking, it invariably means I've messed up one way or another, and buying a gadget to compensate for this failing would hardly help me to ride better.

Is there something about your bike's handling that you're unhappy with?

Sunbeem.

When I first disassembled my /7 fork I found these along w/ the remnants of the rubber bumpers. Not knowing anything @ anything, I installed both new bumpers & the helper springs-I like the ride though I'm unsure how much the anti-dives really contribute...

I've noticed a few sets for sale on e-bay recently; though I'd not purchase & install them unless I was already "in there".

However, as Sunbeem suggested,if you're having handling issues maybe you need to be in there...

twist wrote:I have seen bottoming springs for sale for post 70's forks. They are marketed to help with front end dive under hard braking and to help the overall ride. Has anyone ever had experience with these springs? The best solution is cartridge emulators but I wonder if these springs are of any real advantage?

They were popular in my day in the BMW Motorcycle business. Basically, it is a flawed concept. The BMW ride was soft and cushy. Mostly, riders wanted to keep the "cushy" and still reduce the dive on braking. If you have long travel and a soft ride, you are going to have a lot of dive under hard braking.

What made the bottoming springs hard to evaluate for most is that the industry had no clue about front end alignment. They made frequent changes to the front end and had no control over the stiction caused by poor alignment.

Add in another factor, when people make a decision to "buy something" is gets a good report. This is to confirm that the buyer made a good "decision" and needs to tell everybody.

It is no wonder that this spring got mixed reviews. For the average rider of the day, they were worthless and opened up the possibility of increasing stiction. That meant less stability.

This led to a firm coming out with aftermarket springs and they named it Progressive. All springs are progressive, so saying progressive springs is like saying spring springs.

I have a buddy with a '77 R100S with the bottoming springs in them. The advantage to them is they are larger (longer) than the bottom cushion, so they take affect sooner, making bottoming somewhat more gentle. But first, the primary spring must allow the fork slider move up the tube for this action to take affect, so you still get all of the brake dive, since the bottoming springs have a higher spring rate than the primary spring.

I disagree that all springs are progressive. When a coil spring compresses, is twists internally similar to a torsion bar. Straight rate coils have consistent windings, so every inch of compression provides the same number of # of pressure. Progressive springs have some coils far apart, and some coils close. Since they are generally made of the same material and thickness, the closer coils bind sooner, eliminating them from the spring process. Therefore each inch of compression after the binding of the close coils cause the further ones to compress faster, with less spring wire to take up that compression. This increases the spring rate.

Duane Ausherman wrote:. . . All springs are progressive, so saying progressive springs is like saying spring springs.

A true statement. The question is, progressive in what manner? As I expect you know, coil springs with the same spacing between coils operate in a linear manner, that is a certain amount of force results in a certain amount of compression. Doubling the force results in twice the compression. This constant continues until coil bind. I believe this is called the "K" of the spring.

A progressively wound spring means that the spacing between coils is not constant, and therefore the K of the spring is non-linear. So, conceptually, a motorcycle rider may enjoy a soft ride, but the ride becomes harder with a heavier bump.

A '78 R100S I bought years ago had those aftermarket springs installed. IIRC the coil spacing of the aftermarket spring was also uniform. So I guess that yields a spring with uniform deflection up to the point where the "helper" springs come into play, then the spring rate increases in a step fashion.

I wasn't impressed by the aftermarket springs, but I was a pup at the time and wasn't looking beyond what I thought I knew.

Many people don't recognize that there is another non-linear spring in the forks, and that would be the air above the oil in the springs. As long as the caps of the fork are air tight and as long as there is minimal escape of air from the fork seals, you have a decisively non linear spring. The implication is that the air spring can be tailored by raising or lowering the oil level in the fork legs.

I wasn't impressed by the air springs either.

A '78 R80/7 that I bought for parts had no springs in the front forks, and had a schrader (tire) valve in the top of the forks. I think there was also an air pressure gage fitted as well. The rear shocks also had no springs. Instead they too had an air spring with tubing attached to adjust the pressure.

I only rode the badly running bike for a block or so, so I formed no opinion.

In my motocrossing days, in the late 60's and 70's air springs became a fad. I remember postulating to my friend that if all MX bikes had air springs, a steel spring might be regarded as a great breakthrough in front suspension. With a minor amount of unsprung weight added to the forks one could achieve a great improvement in reliability. A blown seal, for example, might not cost you the race whereas a blown seal on an air spring would.



Ken

Duane has told us before of how the name "progressive springs" bothers him. If I remember correctly, even "progressive wound" doesn't work for him. The problem is: I don't know what they should have been called instead.

Progressive wound springs have a great advantage in their ability to handle a wider range of load on a motorcycle without bottoming, but still having acceptable compliance under lower loads. This is quite valuable for someone who rides with widely varying loads: such as sometimes solo and sometimes loaded with both luggage and passenger. For a solo rider with usually the same approximate load, the correct straight wound spring invariably gives superior performance.

BMW also made some improvements to the ATE forks whilst they were in production to improve their ride. This included changes to the damper rod and an improved rebound (?) damping valve which has much closer tolerances. It's called a damper nossle on the parts fiches and the improved version has a groove machined around the outside. I was able to pick up a set from my local dealers for a few quid. Back in the day we all fitted harder springs at the front and konis at the rear, as you really needed suspension which was a bit stiffer than stock, especially if the bike had done a few miles. (5000).

The big advantage to the springs over the rubber bumpers is that won't turn to goo at the bottom of your slider and contaminate your fork oil. That's why I got a set. Not sure why a new bumper wasn't made that was made of better stuff (maybe it has), but the original ones don't last long before they melt away.