Increase rotor size to 220mm on 160mm posts

[Lectriceye]

I put a Shimano XT SM-RT86 203mm on the from forks and it fit and works grat. I put hte same Rotor on the rear and had nothing but problems. For some reason the offset of the rotor pushed the bladed out closer to the frame and it was rubbing. After looking at all the possibilites, washers installation, etc, I couldn't figure out why. The 180mm I took off the bike showed that increasing the size by 40mm should still have a clearance to any part of the frame by atleast 20mm. Looking for thoughts on this? I might take the easy way out and put on an SRAM..

 

[E-HP]

It’s not on backwards, is it?

 

[lnanek]

Just because a bike is designed to have a big front rotor doesn't mean the back is. Heck, I have bikes with disc brakes in front and no mounts for them in back. I use a roller brake back there.

The front is where most of the stopping power is anyway because as you brake the weight moves forward and on to the front wheel. Back wheel will just skid anyway.

 

[Lectriceye]

It’s not on backwards, is it?

Nope

 

[maiz]

Just because a bike is designed to have a big front rotor doesn't mean the back is. Heck, I have bikes with disc brakes in front and no mounts for them in back. I use a roller brake back there.

The front is where most of the stopping power is anyway because as you brake the weight moves forward and on to the front wheel. Back wheel will just skid anyway.

 

[lnanek]

Never heard of braking during a turn like that. In motorcycle safety school I was always taught to straighten the bike first if you have to, otherwise you lose traction and fall over. We even practiced it with the instructor randomly crossing his arms to tell us the brake in odd situations while on the course. Think that approach is much more safe than whatever that weirdo race guy is up to.

 

[E-HP]

Never heard of braking during a turn like that. In motorcycle safety school I was always taught to straighten the bike first if you have to, otherwise you lose traction and fall over.

He may be talking about off-road riding. Riding my bike off-road as a kid, with only a rear coaster brake, I’d “steer” with the rear brake all the time. The fastest racers, two wheel and four wheel, are the guys that started off-road, since sliding around is normal, as opposed to those who learned on pavement, where sliding isn’t familiar and causes overreaction.

 

[Lectriceye]

Get in the soft sand, like on the dunes where I live, and see what happens when you are going down hill and hit the front brake? You bury the front wheel and go askew, especially in a turn. Going down a hill with soft gravel isn't much different. Most of my riding is offroad with a lot of gravel and a lot of turns. The results are not so good when braking with the front in a turn, so you use the front and back coming to the turn and if needed in the turn use back only or you start to crab sideways, not good.

 

[maiz]

Never heard of braking during a turn like that. In motorcycle safety school I was always taught to straighten the bike first if you have to, otherwise you lose traction and fall over. We even practiced it with the instructor randomly crossing his arms to tell us the brake in odd situations while on the course. Think that approach is much more safe than whatever that weirdo race guy is up to.

What do you make of their comparison to motorbikes? Bikes are so much lighter and might need unique approaches.

 

[Lectriceye]

He may be talking about off-road riding. Riding my bike off-road as a kid, with only a rear coaster brake, I’d “steer” with the rear brake all the time. The fastest racers, two wheel and four wheel, are the guys that started off-road, since sliding around is normal, as opposed to those who learned on pavement, where sliding isn’t familiar and causes overreaction.

I can remember riding as a kid with coaster brakes that didn't work, we slowed down or stopped with our shoe in the front forks mashing on the front tire.

 

[Chalo]

I can remember riding as a kid with coaster brakes that didn't work, we slowed down or stopped with our shoe in the front forks mashing on the front tire.

Imagine how hopeless your brakes would have been if they're weren't coaster brakes. Kid maintenance is worse than abuse and neglect combined.

 

[hillslayer@]

I put a Shimano XT SM-RT86 203mm on the from forks and it fit and works grat. I put hte same Rotor on the rear and had nothing but problems. For some reason the offset of the rotor pushed the bladed out closer to the frame and it was rubbing. After looking at all the possibilites, washers installation, etc, I couldn't figure out why. The 180mm I took off the bike showed that increasing the size by 40mm should still have a clearance to any part of the frame by atleast 20mm. Looking for thoughts on this? I might take the easy way out and put on an SRAM..

All the rotors I use have no offset just AliExpress rotors and adapters never had a problem with them.

 

[Lectriceye]

I really appreciate all of the inputs on rotor sizing and fit. Now that I am done with that project (for the time being), here is what I ended up with: on the forks, I have a Shimano XT 86 203mm; on the rear, I have an SRAM HS2 200mm. Everything fits well and performs well, better than this machine ever has. Me, my bike with 2 motors, and 3 batteies @ 60ah, weighing in at about 330lbs, rode 40 miles in the hills, including one 4 mile 7% decent among several others, which were sometimes steeper but shorter. I don't ride for the thrill of going fast down hill, I mosey down safely, braking as necessary to check my speed. I never had a squeel, or a sense of brake fade, they were solid all the way. So, I guess I will mark this up as a very successful project. Thanks for your help.

Side note: I dont understand and probably never will, why the Shimano 203 wouldn't fit, but I am sure it has something to do with the offset of the rotor blade from the mounting plate.

 

[E-HP]

I really appreciate all of the inputs on rotor sizing and fit. Now that I am done with that project (for the time being), here is what I ended up with: on the forks, I have a Shimano XT 86 203mm; on the rear, I have an SRAM HS2 200mm. Everything fits well and performs well, better than this machine ever has. Me, my bike with 2 motors, and 3 batteies @ 60ah, weighing in at about 330lbs, rode 40 miles in the hills, including one 4 mile 7% decent among several others, which were sometimes steeper but shorter. I don't ride for the thrill of going fast down hill, I mosey down safely, braking as necessary to check my speed. I never had a squeel, or a sense of brake fade, they were solid all the way. So, I guess I will mark this up as a very successful project. Thanks for your help.

Side note: I dont understand and probably never will, why the Shimano 203 wouldn't fit, but I am sure it has something to do with the offset of the rotor blade from the mounting plate.

I’d pull off the pads and inspect them after 200 miles to ensure alignment and contact look good.

 

[lnanek]

Side note: I dont understand and probably never will, why the Shimano 203 wouldn't fit, but I am sure it has something to do with the offset of the rotor blade from the mounting plate.

I've definitely had two piece floating rotors that wouldn't fit places a solid rotor would. Annoying since the two piece ones supposedly cool better.

 

[ebike4healthandfitness]

Pictures save a lot of words

Is that a open drop out on the front with the opening facing downwards?