I’d just put a 4 piston caliper up front. At least you’ll have a more reliably blead rear.

4 pots all the way, way more modulation than the 2 pots and a bit more power, though less than you might think.

They do take frequent bleeding to offset wandering bite points though.

You prefer the feel of 2 pot SLX over MT7’s at 90kg riding steep and techy terrain predominantly?!?!

This does not compute…

MT7’s are one of the most powerful brakes on the market, Vs a mid priced XC brake…

Whatever you do, at your size and riding the terrain you do, it is false economy to scrimp on braking power… So if you must go with Shimano, just get the 4 pots…

But don’t say we didn’t warn you about the wandering bite point!

Just put sinilar brakes on my bike and they are great even if they might not last the warranty period.

Always a shimano fan but since trying guide re and then codes I prefer the reliability and power of sram brakes. Guide res you can usually get 50-60 an end

What price do you have for the slx 4 pot?

Merlin have XT 4 pot for £200

https://www.merlincycles.com/shimano-xt-m8120-front-and-rear-disc-brake-set-179622.html

I’ve got 4 pot XTs on my new bike, vs Guide RSC on the old one. Can’t say there is a great deal of difference – both have good power and modulation. If anything the Guides are a bit more powerful but the new ones may still be bedding in a bit. Plus I prefer the Uberbike Race Matrix pads on the Guides to the supplied pads so will likely get a set of these when I change pads.

I went from deore 2 pots to deore 4pots

The 2 pots were fine but the 4 pots just do everything better, they still stop me fine but at 90kg after a day riding on the 4 pots my hands are less fatigued.

Recently upgraded from XT 2 pot to XT 4 pot. They’re fine, but I think I was expecting more of a night/day difference. They’re not anchors, but maybe have a bit more modulation. TBF, I was also running soft bitey pads on the 2 pots, and the standard Shimano pads aren’t as on/off.

I’m not particularly heavy, but do ride long, steep, techy stuff.

If it were me, I’d buy a set of 4-pots and put one 4-pot caliper on the front of each bike, with a 2-pot on the back.

They do take frequent bleeding to offset wandering bite points though.

It’s not the frequency of bleeding that is the issue, it’s whether they are thoroughly bled and you’ve got all the air out of the reservoir. If there’s air in the reservoir, there won’t be enough fluid to take up the piston travel when the pads wear. When that happens, air will get into the master cylinder if you lay the bike on its side. You’ll get excessive lever travel, but then it will correct itself once you’ve had the bike upright for a while and the air bubble pops back up to the reservoir. They are fiddly bastards to bleed, but if you get all the air out of the reservoir, you won’t have problems with wandering bite point.

^ True, show me a more powerful and better modulated brake than the o.g Gustav 2 piston brake!

TBH most of this stuff has nothing to do with the number of pistons. You need to get up to really big pistons in a 4-pot, stuff like Maven, before you’re doing something that can’t be duplicated with 4-pot.

AFAIK, Shimano 2-pots use 22 mm pistons, the 4-pots use a 16 mm and an 18 mm piston each side. That gives about 20% more piston area, so 20% more braking power for the same clamping force at the lever. The different sized pistons allow better control of the pressure across the pad. However, they will also be more prone to a spongy lever feel if they aren’t properly bled. 4-pots use a longer pad with more surface area (and weight), so the pads will last longer and be more resistant to fade on fast descents. 2-pots are a bit lighter and perfectly fine for most riding, but 4-pots are more powerful and resistant to overheating if you are doing long, fast descents.

Is it possible to replace a 2 pot Shimano SLX caliper with a 4 pot? No need to change the lever?

imnotamused
Free Member
Is it possible to replace a 2 pot Shimano SLX caliper with a 4 pot? No need to change the lever?

Yes, same levers

Once you live with the Shimano wandering bite point for long enough, your brain recalibrates to the bite point being random and it’s a non issue.

(insert laughing emoji)

TBF I’m surprised we’ve not done what motorbikes did and gone directly onto pointless 6 pots

I remember Hope did a 6-pot a LONG time ago

TBF I’m surprised we’ve not done what motorbikes did and gone directly onto pointless 6 pots

And then pulled back and worked out how to get 4-pots working properly.

I had the Yamaha R1 4-pots after various 6-pots.

thols2
Full Member

AFAIK, Shimano 2-pots use 22 mm pistons, the 4-pots use a 16 mm and an 18 mm piston each side. That gives about 20% more piston area, so 20% more braking power for the same clamping force at the lever. The different sized pistons allow better control of the pressure across the pad. However, they will also be more prone to a spongy lever feel if they aren’t properly bled. 4-pots use a longer pad with more surface area

So this is exactly my point, these aren’t 2 pot vs 4 pot issues. To replicate the 16/18 piston setup you just need a 26mm piston, that’s big but within scope for 2-pots. It’s just that Shimano have chosen a smaller than maximum sized piston for the 2 pots, it’s not a restriction but a choice. Presumably they think there are benefits to that smaller piston- but a skeptic might think that a key benefit is being able to say “these 4 pots are more powerful” in your marketing fluff. (I reckon you can <probably> replicate the 16/18 duals with a 22mm piston and the correct changes at the lever end,but that’s getting complicated)

And likewise the longer pad is a design choice- their 2 pot pad could easily be longer, many are. Especially with a larger piston. So if long pads are an advantage, rather than a side effect of the piston layout, you’ve got to ask why it’s not always maximised.

(quite a common thing, this- i’m always skeptical when a new thing is supposed to bring with it specific advantages, but when that same thing wasn’t maximised in the old. See also: boost hubs)

In this example the different size piston thing is the only bit that might actually be an unreplicatable benefit but like I mentioned Formula went with equal size and it seems to work just as well. Magura too. It does make sense on paper though. (my own suspicion is that it basically goes out the window once you’re actually applying braking force, and the whole thing just functions as a unit, but I could be wrong)

So if long pads are an advantage, rather than a side effect of the piston layout, you’ve got to ask why it’s not always maximised.

My guess is that they would suffer from uneven pad wear, plus they would tend to flex. At some point, it becomes better to have two pistons per pad, that’s why F1 cars use multi-piston setups (they are extremely weight conscious so a lighter 2-pot caliper would be the first thing they’d use if it could be made as effective).

 (I reckon you can <probably> replicate the 16/18 duals with a 22mm piston and the correct changes at the lever end,but that’s getting complicated)

That would increase the hydraulic pressure of the system. There’s a limit to how much pressure the system can handle without needing heavier hoses and fittings and changes to the seals that would probably cause more drag and make the lever feel worse. Also, increasing the hydraulic pressure of the system will make it more susceptible to air in the system so bleeding it will become increasingly critical, plus expansion of the hoses will tend to make it more spongy. The lever feel will suffer if you increase the hydraulic pressure too much.

Formula 2 pot brakes use a 24mm piston so are theoretically almost as powerful as a Shimano 4 pot.

That will depend on the diameter of the master cylinder piston. The hydraulic leverage is the ratio of the wheel cylinder piston area divided by the master cylinder piston area. If the Formulas have a larger diameter master cylinder, they won’t have the same hydraulic leverage. On top of that, there’s also the mechanical leverage of the lever, which is sometimes adjustable.