Return springs in Shimano SLR brake levers – purpose, etc.

[Samuel D]

Shimano introduced springs in their brake levers with the SLR (Shimano Linear Response) package of friction-reducing features nearly three decades ago. But what do they do?

Sheldon Brown says they reduce the needed strength of the spring at the calliper and also the total return spring(s) strength: with lower calliper spring strength, there is lower cable tension in the pad-clearance zone of lever travel, and therefore lower frictional losses in the cable there.

That sounds plausible although it seems to imply some pushing of the Bowden cable – inelegant but maybe pragmatic.

However, don’t small differences in cable friction due to calliper spring strength become irrelevant as soon as the pads hit the rim and the cable tension spikes?

Is the benefit then just a reduction in the work needed to get the brake on in the first place?

[Brucey]

it doesn't really infer 'pushing' per se necessarily because the lever would, if left to its own devices, not sit at rest but instead hang down at a different angle, without the spring. The spring in the lever alone is enough to stop the lever from rattling over most bumps, which means that the tension applied to the lever by the caliper can be very small.

The caliper spring can be reduced in force considerably because it only has to overcome what is in essence an almost slack cable; when releasing the brake there need be little or no work done by the caliper to help the lever back to the stop position.

However the levers and calipers are not well-differentiated for front or rear fitment (*) which means that both are fitted with springs that are strong enough to help in a typical rear brake cable run, which means they are both more than strong enough for a front fitment.

(*) the caliper springs on some models are adjustable; e.g. the spring sits in a plastic guide block, which may be fitted in one of two positions. It may work best with some cable runs if the rear brake is set with higher spring tension than the front.

In practice if your cables are in good shape you can use non-SLR levers (i.e. without springs) with SLR calipers, and it is also OK to use SLR levers with non-SLR calipers (although it can be more effort getting the brakes on). Occasionally the SLR spring will break in an SLR lever; if this happens, it is usually OK to fit the remaining good spring to the rear lever and omit it from the front lever.

An average setup might be slightly different, but the reality is that if your cables are in really good shape, you might struggle to notice whether you have an SLR system or not.

cheers

[Gattonero]

Shimano introduced springs in their brake levers with the SLR (Shimano Linear Response) package of friction-reducing features nearly three decades ago. But what do they do?
...

many quality levers do have a return spring. The thing they do, is to reduce a lot the chatter of the levers in case you are on very rough terrain, as the pulling force of the caliper may not be enough to compensate the mass of the lever blade moving on its own due to the bumps

[Mick F]

......many quality levers do have a return spring.

You include Campagnolo in this "quality"?

[Samuel D]

it doesn't really infer 'pushing' per se necessarily because the lever would, if left to its own devices, not sit at rest but instead hang down at a different angle, without the spring. The spring in the lever alone is enough to stop the lever from rattling over most bumps, which means that the tension applied to the lever by the caliper can be very small.

The thing they do, is to reduce a lot the chatter of the levers in case you are on very rough terrain, as the pulling force of the caliper may not be enough to compensate the mass of the lever blade moving on its own due to the bumps

I see. A single spring at the calliper would therefore need to be considerably stronger than for hypothetical smooth-ground cycling only. But even that strength wouldn’t be so strong as to problematically increase lever force during braking proper, would it?

Speaking of bumps, my Shimano BL-R400 levers came with a little plastic insert that rattled on rough ground, seen in someone else’s photo here. I wondered as I removed it if it was to allow the lever spring to push the cable, something Brucey’s comments here seem to cast doubt on. At any rate the brakes have worked fine without it.

Incidentally, the BL-R400 levers have a noticeably weaker return spring than the STI levers I’ve used, presumably because less force is needed to prevent the lighter levers from rattling over bumps.

If anyone’s interested, Frank Berto wrote this about lever return springs in Bicycling Magazine’s Complete Guide to Upgrading Your Bike (1988):

“When you apply the brakes, you first have to overcome the cable-casing friction, then you have to overcome the caliper return spring force, and finally you pull the pads against the rims. Lever return springs fight cable-casing friction. If the only return spring is the one located in the calipers, then that spring has to be made to overcome worst-case, cable-casing friction. With two light springs, one in the lever and one in the caliper, brake response becomes lighter.”

And Rob van der Plas, in Bicycle Technology (1991), wrote:

“On all caliper brakes, the brake arms must return to the unactivated position when the handle is released. This is done by means of one or more springs. As will be explained more fully under Brake Controls, these springs are not always powerful enough to overcome the friction in brake, cable and lever. This has something to do with the fact that some manufacturers use the method first introduced by Dia-Compe, integrating a spring in the lever as well. In this case, the spring in the brake need not do all of the work – but this brake must be used with the matching lever.”

Unfortunately nothing is “explained more fully under Brake Controls”; the existence of lever returns springs is merely mentioned again in even less detail.

These explanations are a bit casual for my taste.

I’d like to try some brakes that don’t have lever-return springs, just to see the effect for myself, but good ones (e.g. Campagnolo Record) are incredibly expensive on eBay, and most of them don’t use the recessed nuts my frame needs.

[Brucey]

you can remove the springs in SLR levers; just disassemble the pivot and once the lever is apart the springs can be removed.

If the cables are not in perfect condition, the levers may then not return fully with SLR calipers in use.

The friction in cables comprises two elements; sticking friction and dynamic friction. Expressions for both contain terms with are related to the cable tension; a lower cable tension means less friction, and SLR systems allow for a caliper with a weaker spring and lower cable tension.

They also allow for a lower force to initially actuate the brake, since the term for the force required to overcome the lever spring does not suffer any cable friction loss, unlike the terms required to overcome caliper spring and to apply the braking effort itself.

cheers

[Mick F]

I must say that the return springs in the only STIs I've had the "pleasure" to use seemed a bit odd. They didn't seem - to me at least - that they contributed to the brakes operation at all. In fact, I thought they were a disadvantage especially due to the long reach to the levers.

Why have STIs got them when other manufacturers don't have them?
You can mix and match brakes and levers between manufacturers (within reason) so it can't be anything to do with calliper springs.

[Brucey]

washing line type STIs are a different kettle of fish. They have much stronger springs in, merely in order to help with the mass-balance issue. There is so much weight ahead of the pivot that without the springs the brakes might come on every time you go over a bump.

cheers

[Mick F]

Ah, that explains it!
Thanks.

[Samuel D]

Do all Campagnolo Ergos have return springs in the brake lever?

[Brucey]

Do all Campagnolo Ergos have return springs in the brake lever?

-sort of; the downshift paddle is spring-loaded and this pushes on the brake lever.

cheers

[Mick F]

They don't have a return spring.
As Brucey suggests, the paddle pushes on the rear of the lever, but that's not in the design for a return spring. They don't need them.

Remove the brake cable and try it.
Floppy brake lever if you hold the paddle away.

The paddle spring is there to allow the paddle to move backward when you brake and to keep it behind the lever when you're not. That's all it's for.

[Mick F]

PS:
If I ever get rid of my Ergos, I'll try and get the Record brake levers. Not many about these days.
No return springs in any way with those.

https://www.condorcycles.com/products/c ... ake-levers

[Gattonero]

......many quality levers do have a return spring.

You include Campagnolo in this "quality"?

It's not the same design. And I just ride them without problems, simple as that!