JackJohn

Hi all,
Just mounted a pair of Shimano Tiagra BR-4700 calipers on a 28'' wheels road bike and was surprised of their poor performance in wet conditions. Under normal dry conditions, braking might seem acceptable, but compared to some entry-level V-brake calipers I have on a 26'' bike it seems like having an "ABS", i.e. wheels not quickly stopping but rather gradually. However, when weather conditions change to wet, braking takes a looong time, with the rim sliding for some time under the pads before stopping the bike. Official specs announce "30% greater braking power modulation with Linear brake operation" and "Better performance with Alloy rim under wet condition". Now I have no idea of what power modulation and linear brake mean. I can only say that I'm not that impressed about performance and that under wet conditions it gets dangerous. I checked the installation to see if that was the problem : cable is properly tensed, pads are close to the rim and follow its profile. Pads are also not perfectly parallel to the rim in order to leave 0.5mm more space on the back, as stated in the instructions.
Did any of you have an experience with these calipers or an idea where the problem might come from? Also, what does "power modulation" and "linear brake" mean?
Many thanks in advance.

delbiker1 

What brake levers are matched with the calipers? It could be you are using a set that has cable pull that does not match with the calipers.

JackJohn

I use the calipers with Shimano Tourney Dual Control Levers ST-A073
https://bike.shimano.com/fr-FR/produ...ST-A073-L.html
Is it possible to have compatibility issues? Didn’t think that cable pull could make such difference, especially within the same brand. Thanks.

delbiker1 

I have 5700 STI shift/brake levers and they do not work well with 4600 or 6600 calipers that I have. The 5700 are the hidden under tape cables and the 4600/5600 are exposed cables.

JackJohn

In my case, brake cables run under the handlebar tape but shift cables (those mentioned in the video to verify compatibilty) are exposed, the video suggesting that they should therefore not be compatible with slr calipers, is it corrrect?
Neverthless, I don't understand why. The lever pull feel is not "mushy" nor too firm.
Also, I still don't get the notion of power and modulation.
Help please...

smashndash

If it's a wet weather issue, it could be that the pads are too hard. Might be worth trying kool stop salmons.

It's also possible that the levers you have don't give you enough mechanical advantage. You actually WANT the brakes to feel squishy. Because they are. They're rubber pads strapped to long, skinny arms. If the brakes don't feel squishy at all, you don't have enough mechanical advantage.

If you don't understand why this is an issue, try bending a ruler while holding the 5 and 7cm. Then try bending it at 1 and 11cm. The same ruler now feels "squishier". You have to move your hands a greater distance to achieve the same amount of bending, but the bending itself is easier. With brakes, higher mechanical advantage means your pads sit closer to the rim and you have to use more lever travel, but you get more force at the rim.

smashndash

Shimano officially says your brake levers are not compatible with 4700 brakes:



https://productinfo.shimano.com/download/pdf/com/2.6/en

JackJohn

Ok thanks, I see what you mean. If I understand correctly, the “squishy” level comes from the lever, and the new slr callipers are not made to work for this type of pull, is that right? I naively thought that a pull was a pull, given that the physical movement is the same, does it mean that inside the lever there is a mechanism, varying for the different models, that applies a variable force after the initial mechanical pull ?

JackJohn

Thanks, very useful doc

smashndash

Yes. You are describing "pull ratio". It can be a big issue if you try to step outside of a perfectly matched groupset. https://www.bikeforums.net/bicycle-m...ll-ratios.html

I have 105 5800 levers with R7000 brakes and have plenty of power. You should not want for power on rim brakes.

shelbyfv

Thanks for the link! I see now the brakes are "new super SLR" and the levers are only "super SLR." Duh....

JackJohn

Thanks for the link. When you say power do you mean more mechanical advantage and therefore less braking efficiency? Is modulation the opposite of that?

Otherwise, according to the compatibility doc, 4700 calipers are ok with basically all integrated levers except exactly those I have . There’s no line linking the two groups, be it go for it, less than standard or never use, which is unclear on how to interpret it. In the drivetrain section, these Tourney levers would be compatible only with same Tourney groupset derailleurs, but I actually mixed them with a Sora FD and an Altus RD and it’s ok, so maybe I’m wrong, but my impression is that Shimano gets things a bit confused. The feedback from mixing brakes however confirms that braking is not very good, but the fact is that the only compatible calipers mentioned in the doc are not easily (or at all) available, Only the BR-R451 can be found somewhere and they’re not that cheap. Changing levers is not an option as the Tourney 3x7 are the only I can use. So I’m lacking ideas on this. According to the video posted, this combination should result in mushy levers but it was not particularly noticeable, so I tightened the pull cable to get pads even closer to the rims. Levers feeling is a bit harder now, but not too much, I’ll try to go for a ride and see what happens. In the meantime, any idea is welcome... thanks !

JackJohn

Ok, I talked to a couple of Shimano guys, after some initial confusing statement they ended up using the same compatibility doc posted here, so not much to say except “change your calipers”.
I gave a try with pads closer to the rim, seems having gained a little something in braking performance, but could not try in wet conditions yet. Let’s say that at approx. 10mph it takes between 1 and 2 seconds to stop.
What else can I do?
Also, does anyone knows if this thread should rather be in the mechanics section or is fine here?
thanks.

smashndash

more mechanical advantage = more power. I'm not sure what "braking efficiency" means.

SHIMANO R451 Caliper Bicycle Brake - BR-R451 https://www.amazon.com/dp/B005DTQ6UQ...ing=UTF8&psc=1

you only really need to swap your front caliper. Also pick up some kool stop pads while you're at it. Hopefully this works 😣

EDIT: It's also possible that you have so much mechanical advantage that your lever is bottoming out before you actually can get any power down. Is the lever bottoming out? That would explain why bringing the pads closer helped.

JackJohn

yes, maybe efficiency is not clear, what I meant was “doing the job in stopping the bike”.
Thanks for the link and the kool stop tip, many models available, is any of them ok? Why changing only the front caliper?

levers were not bottoming out before, now are a bit firmer and travel a little less than halfway to the bottom, maybe now they’re too hard.

One thing puzzling me, as I also compared some comments found searching the net, here’s a summary:

• Your quote: higher mechanical advantage means your pads sit closer to the rim and you have to use more lever travel, but you get more force at the rim.
• Sheldon Brown: A brake with high mechanical advantage will apply a lot of force to the brake shoe for a small amount of finger pressure on the lever […] the hand lever to move a long way to move the brake shoes a short distance toward the rim.
• Posted video above: The newer style shifters […] pull more brake cable per pull than the older levers […] the lever feel is very firm and lacks power and modulation. It isn’t as dangerous as an old lever with a new brake, but is obviously less than ideal.
• Blog Bikegremlin: […] less cable pulled, just 7 mm for a 20 degree lever rotation – providing higher mechanical advantage […] more cable pulled, 15 mm for a 20 degree lever rotation – thus providing lower mechanical advantage. (https://bike.bikegremlin.com/1419/bi...anical-brakes/)

please correct if I’m wrong: if more mechanical advantage equals more power (intended as force on the break shoe and rim) and implies more travel for the lever, then it needs more cable pulled, making levers squishy. Sheldon seems to confirm this. But the video above and the website explaining the issue seem to say the opposite.

So I can understand that different pull ratios can make some levers and calipers incompatible, that’s fine. But on the issue of mechanical advantage and cable pull, well that’s where I get confused...

smashndash

More mechanical advantage by the lever means more lever travel, less cable pull, more power. More cable pull = less mechanical advantage, less power. If a lever has a ton of cable pull, it's like trying to accelerate in your 50:11 gear. If you are incredibly strong, you can go very far with few pedal strokes. But most people will just stall and fall over.

Kool Stop Bicycle Brake Pads with X Pad (Dura-Ace/Ultegra) https://www.amazon.com/dp/B0014BRW6E...ing=UTF8&psc=1

These should work with the R451 calipers. Just don't let the hardware rust.

The reason I say just change the front is that you don't actually need much power in the rear. It's an unnecessary expense IMO

Iride01 

Probably why when the made the brakes they also made levers that they deemed compatible to use with them.

Are you just basing pull on the cables as what you see in lever travel between lever and bar? That will ignore things like where the pivot point on the lever is and any cam action that might be a part of them.

Also, not sure about what your method to determine stopping is for wet. Most everyone here knows that rim brakes initially feel like you will die for sure when squeezed that first time after getting wet. But that soon goes away if you aren't in rim deep water.

Psimet2001 

Don't mess with pull ratios. There's a reason Shimano has a compatibility matrix for everything. Don't try and outthink it. Abide by it.

After you go back to compatible brake calipers and levers and if you still are having problems with wet performance then swing on back for new ideas. Do not try and make these calipers work with the levers if they are called out by Shimano as being incompatible.

JackJohn

It’s rather empirical and as said based on previous experiences with v-brakes which gave a safer feeling. Not being able to stop quickly under light rain with rims sliding under pads at full braking was not reassuring. Makes me feel weird if “most everyone” knows differently, anyway I’ll try again to see if that poor braking goes away as you said.
Ok, that’s clear, thanks !

JackJohn

Great, many thanks for the link and suggestions.

I went back “a few” years to go over some physics basics in order to link leverage principles with brake levers. I better understand what you say, only just one commentary: let’s have two type of levers. Levers 1 have more mechanical advantage, more power and more lever travel, we agree, the pivot (fulcrum) is closer to the cable anchor, but that doesn’t mean less total cable pulled. Maybe what you mean, is that when measuring equal lever travels in degrees, Levers 1 with closer pivot and shorter radius pull less cable compared with some Levers 2 having more distant pivot, longer radius, less mechanical advantage and more cable pull on the same travel distance. However, if we work in reverse and say that you need for the sake of an example 3mm to tighten calipers on the rim, both levers will pull the same cable distance, with Levers 1 travelling more and then pulling a little more given the higher leverage and power with that squishy feeling, while Levers 2 will feel harder but won’t be able to pull more given the lower leverage.
Does all this make sense?

shelbyfv

Have you been able to locate any of the calipers that will work with your levers?

JackJohn

on my local Amazon they’re not available, but I found a couple of websites selling the R451 at around 55-60$ the pair. The other models seem more difficult to find. I’ll give a few more tries with current calipers, if I don’t reach a security feeling then go for R451 calipers change, either just the front one as smashndash said or maybe both.
These calipers have a 57mm max reach and I need 51, normally minimum reach should be low enough to keep it in the range (I suppose it is 47) but couldn’t find on Shimano official specs.

Psimet2001 

I guess I am not getting what you're not sure on. There are quite a few different pull setups across all sorts of road and linear pull calipers not to mention mechanical disc. The calipers are designed with a pull ratio of the lever in mind. Not using the right pull ratio is a bad idea. As seemingly covered above in great detail you won't have enough power - which means you won't be able to provide enough force through the lever to be able to brake effectively (stop). Sometimes that's because the lever bottoms out (pulling too much cable), Sometimes it's because of the design of the caliper. Calipers, especially modern ones, have a dual pivot design and many times have a roller cam worked in that effectively changes the whole physics of the setup of the caliper as it is applied. Fast travel of the pads under low braking force to working its way up to high braking force with low travel as the cam engages. Sometimes it's a cam, sometimes it's the design of the pivots on the caliper that set the action.

In general you used to be super safe just putting a road lever with a road caliper. That isn't always the case anymore. Different component manufacturers sometimes didn't work great together (campy/shimano mix) or someone would get a bright idea to try something new...leading to strange outliers like your situation where certain levers just won't work with certain calipers safely. Brakes are the one thing that everyone will get sued over because it's the one thing that will assuredly kill people when they mess them up.

So I am not sure what's still being discussed I guess. If you're, as it seems, trying to figure out a way to make levers that change pull ratios so that they can be used with different calipers - it's been done. Shimano through the late 90's used to do linear pull levers that could switch pivot points to go between their road pull and LP pull ratios (Linear pull calipers). This was because at the dawn of the mtb movement a lot of people were repurposing road bikes and doing flat bar conversions...in addition to them updating mtbs from cantilever brakes to linear pulls. They stopped doing this. They now provide LP levers that have different pull setups depending on the application and caliper used.

So apologies if I was short earlier but it was my way of saying there's a helluva lot more to it than just pull ratios, you're not going to figure something out that all of the OEM companies that have been designing and mass producing brakes for bicycles haven't already considered or figured out, and if you're trying to somehow modify what you have, which is incompatible, that you're more likely to get yourself ded than discover something new *** and right then I had a stream of customers so I have no idea what I was writing but know there was some good stuff in there so I am posting it anyway. Fair warning I usually revise to pull out anything that could be interpreted as snotty so apologies if anything comes off that way. Sorry shop is busy.********

JackJohn

Thanks Psimet2001 for your thoughts. Just to reassure you, I’m not on an epic quest for a revolutionary solution Maybe it was not that clear, but after the useful replies received I practically accepted the idea of getting new calipers. The rest of the discussion was to me a more general talk to better understand the principles of pull ratios and the terminology around it I was unfamiliar with. And don’t worry, no snotty feeling here, only interesting stuff...

Iride01 

If you do, then make sure it's what is recommended by the manufacturer as compatible with your brake levers or STI's. So likely your brakes and levers need to be from the same manufacturer. When you go off and do your own thing mixing and matching, then you are experimenting. It might work well or it might not.