Kapusta

You win the prize for being the only poster in this thread to actually answer the OP’s question.

Good work.

DrIsotope

Bigger rotors don't magically provide more braking force. If the caliper remains the same, the area where the pad contacts the rotor surface is exactly the same regardless of rotor size. Bigger rotors are for heat management, and nowhere did the OP mention routinely fading his brakes or bluing the rotors. More braking force comes from better brakes. For a 350+ pound rider, hydraulic brakes are absolutely appropriate.

Kapusta

No, it is not magic... it is physics. Bigger lever = more force.

It is also real-world application: Anyone who has ever up-sized a rotor and done nothing else knows this. I have done this several times myself.

If larger rotors did not provide more braking force, why would there be stated limits on rotor sizes for some forks?

DrIsotope

If you think that you can tell the difference in braking force by increasing the size of the lever arm by 9%, then good for you. The larger rotor gives better modulation, so it feels like the braking is more powerful.

I run 180/160 rotors because it evens out pad life. I felt absolutely no change in force going from the OEM 160 to the bigger rotor. I did however feel an enormous change going from single-piston mechanicals to 4-piston hydraulics.

Kapusta

Yes, apparently I can, and so can most other people who have done it. Go ask this question on any mountain bike forum.

And again, if the force is not greater, why the limit on size for some forks?

That's great...... Except that changing rotors is what the OP is actually asking about and will set him back about $60. 4-pot hydros requires a completely new brake-set, including new shifters in the OPs case.

Good God, how is this even a discussion? The OP is 370 lbs. That's two average sized men on a tandem. Even with hydros, 203mm are totally appropriate on a tandem MTB.

The only reason this should even be given a second thought is if the fork is not able to take a 203mm rotor.

base2 

+1 agree.

And to the above discussion: Yes larger rotors do indeed impart greater braking force because the disk is a larger lever. The trade-off is modulation. A rim brake is a 1:1 lever. A disk is about 5 or 8 to 1 or some such number. So your range of force input yields a much more fine output because it is multiplied/divided by some ratio.

Then there is the greater area for heat to sink to think about between rotor sizes, so larger equals more capacity. So even with the same pad/caliper a larger rotor (up to & including the rim) will last longer before fade or other failure.

203's are a smart move if, and only if, the fork is rated for the additional torque a larger rotor applies.

OP: I didn't catch if you were riding suspension forks or not, but I do know for a fact that RockShox Recon are rated for 203mm (but I don't know about their weight rating.) If you are riding rigid, Woundup Tandem Duo forks are rated for 203mm and up to a 450 pound tandem team use. (Which is different than being rated "up to" 450 pounds)

Also, in addition to the above forks I have personal experience with, I'd get rid of the Tektros. My experience with Tektro has been "problematic" at best. The Spyre/Spyke are a solid recommendation. As well as the compressionless housing.

Good luck.

Leebo

Bigger rotors on crappy brakes are not the solution. Keep the current rotors. Get some hydros, shimano deore, slx or such. Should be able to put the shifters on a separate clamp than the brakes. Check out problem solvers for ideas on that.

Kapusta

Come on, pay attention people. Stop recommending mountain bike brake systems. He’s using drop bars.

And please try to wrap your heads around the fact that this guy is 370 lbs. 203mm rotors make a lot of sense with whatever brake calipers he ends up using.

79pmooney

I'm jumping in with no experience with discs. I applaud the OP for recognizing he needs more brake before he really needs it. As an engineer I see heat as his biggest potential issue (assuming his fork/bike is strong enough to handle the brake forces). If larger discs can be mounted safely and appropriately, sounds like the right approach. More braking power on heat-dispelling-limited discs will only make the heat issue worse. Any means of squeezing the big enough discs' calipers hard enough to get the stopping power needed will work. (Aside re: braking power - I've "de-tuned" my rim brakes (my 3 mountain road worthy bikes have very effective dual-pivots or very good cantis - stoppers!) by using V-brake levers, probably close in effect to the OP wanting bigger discs but staying mechanical. I have to squeeze harder - a plus for hard slow-downs so I make that blind downhill corner without scraping a fix gear pedal. (Liked that experiment so much after coming down from McKenzie Pass that now my non-fixies sport the same levers.)

A trick I've been using for decades that I rarely heard mentioned for easing speed and keeping rims (discs) cool on long descents - I alternate between braking rather firmly with front only for a few seconds, then rear only for a few.

Ben edit: typing erroe

fietsbob

after 20 th posts replied, he, finally added that detail ,..

assumed we coul mind read before then..





my 1 disc brake bike wheel to disc ratio 3:1 20" wheel 160 discs ..
my use wet weather.. short demand caliper, long pull lever

straight bar Avid Speed Dial .. the Hy Rd has directions on
how to take all the cable slack out, with a short pull lever like that
using its barrel adjuster..

with the lever dialed back shorten its pull rariosome,
I still have useful slack in the cables, so the finger reach
is at its comfortable spot in the lever swing.. ..










.....

Kapusta

That detail was (and still is) utterly irrelevant to the question he was asking.

squirtdad

that is not a confirmed fact. the bike is hellga which per specialized is a flat bar bike with sram x10 trigger shifters, tektro aries disk brakes with organic pads https://www.specialized.com/us/en/hellga/p/118687

interesting, but not germane, is this model is women's specific model

I would be very surprised to see a drop bar fat tire bike.

the red herring was a mention of rival 10 what is needed is is for the OP to give the exact config of the bike

the op mentioned

Kapusta

No other info is needed from the OP. His question was answered correctly in post #4 .

If people read his follow up posts they will see he is running road calipers and integrated shifters.... not that it has any bearing on his actual question....

DarKris

So for the person asking to see a drop bar fat tire bike:




What I will say is that ATM I am retiring the drop bars and have gone back to flat bars for the sake of making this bike more trail oriented where before it was just my road bike for snow. What that means is that I do have more brake options now, however I do want to at least tackle the larger rotor situation. My plan is to contact Specialized and see if they say anything about if the fork can handle a 203mm rotor.

I did see that the 2018 Fatboy SE in it’s specs has 203/180mm and 180/160mm listed with the brakes, and it uses the same exact fork as the Hellga, so idk if that means anything (https://www.specialized.com/us/en/fatboy-se/p/128911). The other thing that I noticed was once I put my old flat bar brake levers back on my bike, I was getting quite a bit more power from my brakes, possibly due to the pull ratio of the levers. I will be doing more riding with this current setup however to hopefully better determine what I should look at if there are more improvements to be made.

squirtdad

that would have been me, thanks for posting, that is pretty wild It goes to prove that just because you can't see something, doesn't mean someone else can't or doesn't have a need that you don't (been a long time since I rode in snow and that was on a friend who made his own chains for his schwin cruiser BITD in montana)

base2 

Well...pull ratio! That was sitting right there the whole time? It's a wonder we didn't think of it.

Good thread!

DarKris

So update: I contacted Specialized about running a 203mm rotor on the 2018 Fatboy SE, which has the same exact fork as my Hellga. I got a response..... after I had already gone ahead with the upgrade.

203mm front, 180mm rear. Tested them out on a ramp near me and my descent felt very well controlled so I’m happy with the results so far.

base2 

Oh, HAPPY day!
That's awesome they were able to give you a difinitive answer.
Rock on!

Aaron

DrIsotope

How do you like those X-Tech hybrid calipers?

DarKris

They get the job done, definitely more suited to flat bars than drop bars I think, although they did work with drop bars and maybe I just sucked at dialing them in 😅

Pads seems to work fine albeit the rear pads squeaking quite a bit under hard braking. I swapped pads from front to rear and it started squeaking in the front but not the back, however over time they went back to squeaking in the back and not the front. That was with the 180/160 setup so I’m wondering if anything will change now with the different size rotors

fietsbob

I presume this is like Juin tech closed internal hydraulic system , manual pad wear compensation ..

You got them shipped direct from China? certainly are cheap/low cost..
only see sales links nothing about them otherwise, so you are on your own ..

the pads a unique type or copying a type you can find as 3rd party spares?

(My TRP use Shimano a type )





...

DarKris

I got these off Amazon and I think I posted the link to them a couple posts up. They were actually shipped via Prime so I’m guessing they had them stocked in the US. As for brake pads they use this style:

fietsbob

Guess if you don't like the stock pads you need other companies' offering of that kind of pad by name.. ..

short /road lever cable pull or long pull? any tech info not in Chinese?