[SAIG]

I'm building a 29er and live in a flat area, Austin and I'm recreational rider. Are the new XT 4 piston brakes overkill? I have 180mm rotors in front with XT 2 piston on my 26er and I feel they work well. When I had 160 in front I didn't think it was enough. Should I go with 4 piston or just with 200 front rotors?

 

[slapheadmofo]

You said what you have works fine, so no need to do anything different.

Bigger rotor will probably be a lot more noticeable than 4 pots though IME.

 

[biff55]

a 29" wheel with say a 2.6" tyre , will have a considerably greater rotational mass than a 26er with a 2.1 tyre -

so if you want to keep a similar level of braking feel / power you have now with the 26" wheel you'll prob need to upgrade something with your brakes , either rotor or caliper.

personally i'd go for the 4 piston caliper and keep the 180 rotor as 200mm rotors can sometimes be a pain in the ass to true and run quiet

your money your rig though......

 

[Lone Rager]

a 29" wheel with say a 2.6" tyre , will have a considerably greater rotational mass than a 26er with a 2.1 tyre -....

Put bike in stand, spin the wheel really fast, squeeze brake gently, and the wheel will stop nearly instantly. That'll give you a feel for how much rotational inertia contributes stopping distance. Nearly zero.

However, a larger diameter tire has more leverage over the brake so requires greater braking force to stop the same. A proportionally larger rotor will compensate perfectly for the difference.

 

[biff55]

Put bike in stand, spin the wheel really fast, squeeze brake gently, and the wheel will stop nearly instantly. That'll give you a feel for how much rotational inertia contributes stopping distance. Nearly zero.

but we dont ride the bike with it in a stand do we ?
so its hardly representing actual under load conditions.....

 

[scatterbrained]

I'm of the firm belief that all 29ers should come with 200mm rotors standard. Just sayin. 200mm rotors coupled with 4 pot up front and 2 pot in the rear works a treat.

 

[Harold]

but we dont ride the bike with it in a stand do we ?
so its hardly representing actual under load conditions.....

Lone Rager's workstand test isolates rotational inertia. Braking a bicycle while you're riding it involves more forces than JUST rotational inertia. As he also mentions, leverage of a larger diameter wheel ALSO plays a role.

I've ridden trails where I barely have to brake. 160/160 is fine there. Works well on my commuter bike, too. In other scenarios, 180/160 has worked well for me. I live in a place now where 203/180 is warranted. 2 pot calipers are usually fine, but I do encounter situations where I have to squeeze harder than I want to get the braking power I need. I have another bike with 4 piston calipers on 203/180 rotors. They are more powerful than I usually need, but what I like about that is that I can get the power I want with less hand effort. So I can focus more on controlling the bars than on braking.

I've ridden in Austin before. That's not a place that really warrants massive brakes. If you go places that do, then you'll be fine with them in Austin. But I wouldn't buy huge brakes specifically to ride there and only there.

 

[Tillers_Rule]

I've got XT 2-piston with 180 R, 203 F and both calipers leak. This is my 3rd rear and front just started. I live in the mountains though. Will try the Saint calipers next. They are a bit pricier than the XT 4-pots, but have larger pistons too.