brake rotor and wheel rim questions

[Returnformer]

ok, so ive decided that im not gonna just live with the thump of my wheel that i smashed on a pothole, so the question now is what to replace it with. i could either contact the manufacturer and get an exact replacement, or find another higher quality rim. it would have to be the same size, though, i dont want to mess around with trying to figure out new spoke sizes etc. any suggestions on rims to look at and how to measure to make sure it fits? i just need to measure from the top of the rim to the bottom where the holes for the spokes are and make sure thats the same, right?


also, when i was putting this together, i ordered a 203 rotor to put on the rear wheel in place of the 160 that came with the bike. i figured the back could use the extra stopping power because of the heavy motor etc. when i went to put it on though, i realized that the chainstay is too close to the rotor, and theres no room for a larger rotor. so i was thinking about putting it on the front wheel instead since i alrady have it. dunno if i really need it, though, braking seems pretty good as is. im also a bit concerned about having too much braking power int he front and flipping if i stop too short. how concerned about that should i be? should i put the larger rotor inthe front or just stick with what ive got?

thanks.

 

[Balmorhea]

Remind us what kind of rim you dented, and what wheel size, so we can recommend one with a compatible effective rim diameter (ERD).

It won’t hurt to put the big rotor in front if it fits. The braking doesn’t feel that different with a big rotor; mostly it takes more braking to get it hot and faded. Big rotors warp more easily, if that matters to you.

 

[Returnformer]

from their website:

Recommended tire width: 1.75", 1.95", 2.125" (26")
Rim Width (Inner): 19mm
Rim Diameter (Outer): 572mm (26")
Rim Diameter (Inner): 522mm (26")
Spoke: 159mm (26") 12G Carbon Steel Copper Nipples



so the bigger rotor wont make it more likely to lock and flip? warping more easily could be an issue, but i can true it.

 

[Balmorhea]

The bigger rotor will increase braking torque by the difference in rotor diameter, which is +27%. Your fingers will get used to it.

Neither the rim OD nor the rim ID is relevant here. You need the ERD. Unlace the rim and have a bike shop use rim rods to measure the ERD at a few different (not dented) points. Average them, and then you'll have an ERD to compare to commercially available rims.

Tape the spokes together at their crossings if you don't want to relace everything from scratch.

If your spokes are fatter than 2.0mm/14ga, you're much better off replacing them with 14ga or 14-15ga spokes. Thick spokes reduce a wheel's ability to carry loads without disassembling itself.

 

[MadRhino]

You always put your best brake on the front. You don’t need braking power on the rear. That is because braking is unloading the rear and loading the front, thus you need the best braking power and control on the front.

Warping a rotor is common when you are using a caliper that is too small for the speed and terrain that you ride, or when you buy cheap rotors. Large rotors are really good when your caliper is big enough and your brake lever has good modulation. Brakes are working as an ensemble, improving one part can make another that is crap even worse.

 

[Balmorhea]

Warping a rotor is common when you are using a caliper that is too small for the speed and terrain that you ride, or when you buy cheap rotors.

On heavy pedicabs, 203mm rotors warp a lot more often than 160mm rotors of the same kind. I wouldn't have assumed that, but I have observed it firsthand.

 

[dogman dan]

I'm not sure how to measure it, but the ERD is the number you need to know to replace that rim. Then you buy a new rim with the same ERD. It will be in the specs for the new rim.

If you can find something on the rim that shows the brand and model, that might help you look up ERD. Sheldon Brown is the universal source for bike wheel info, so look for that. You should find a method to measure ERD there, or just google "how to measure ERD" to look for a you tube video or other source for how to get your old rims ERD.

Re the brakes, my gut reaction is to keep 160 rotor up front, because I believe in KISS. Sure, you can upgrade, but then you need adapters, or other calipers, etc. I say run what you got till it doesn't work. My heavier, and sometimes very fast cargo bike has done just fine with 160 rotors front and back. When loaded with a heavy trailer it goes slower, but its still a very heavy bike when set up for speed. Would bigger rotors be better? Likely, but the fact remains I stop fine with the simple 160 rotor, and cheaper calipers.

Re front brake too much, you do have to learn to watch for the usual hazards, sand, mud, water, leaves, to avoid locking up the front and going into a laydown. That's your real hazard. Its not too much brake, but sudden loss of tire traction while braking.

Actually going over the bars from too much front brake is fairly hard to do on level ground. When it happens on dirt, its usually more a matter of you are braking on steep downhill, and then something else puts the stop to your front wheel, like a log, a boulder, or burying the rim deep into a sand pit.

If you are panic braking because of a car in your path, actually, braking will make it worse. You will not stop in time, and hit the car either way. But it may be possible to turn in time, using back brake to start a turn, then throttle to finish it. Car turns left into your path, your only hope is to match that cars left turn with one of your own. Then, often as not, a just as quick right turn to stay off the cars that went straight at that intersection. Thread the needle and live.

 

[docw009]

ERD is difficult to measure on a built wheel. because you need a straight path from opposite faces, and the axle/motor gets in the way. You also have to twice add the extra length of the top of the nipple of the nipple from the edge of the rim. The latter is usually 2-3mm.

Probably best to always measure. I bought a rim, used the ERD given by the seller, and my spokes were still too long. But with double wall rims, you can have your spokes a few mm too long, and fix that with washers. They can be a little short too.

 

[Balmorhea]

ERD is usually the spoke nipple seat diameter plus 3mm. Rim rods take the extra 3mm into account.

Just the other day, I built wheels with a rim that had a manufacturer sticker on it that specified the ERD. Except the real ERD was about 4-5mm more. I had to unlace wheels that were fully laced, but not yet tightened. And I had to go to another shop to get the right length spokes.

Generally speaking, I find I can get away with spokes that are within 2mm under or over the ideal length.

 

[Returnformer]

Tape the spokes together at their crossings if you don't want to relace everything from scratch.

good idea. i did change a rim on a regular wheel once, and i used zip ties where the spokes cross to keep them in place. mostly worked, but some of them started to slip down.


finding the right size rim seems complicated, though. i dont want to have to unlace the rim before i get a new one. seems like the best easiest options is either get a new one of what it has from the company or take it to a shop and have them do it.