Wheel size vs brake performance?

A couple days ago I posted on CDNSVX's topic how I was pleased with the brake performance on my X. Then I mounted up a 21" front wheel for off-roading and I feel like the front has taken a hit in the performance department. Before the switch a nice easy squeeze would bring me to a halt. After the switch I feel like I'm on my KLR again, really grabbing a handful to make a quick stop. Is there some physical reason why a larger diameter wheel would have worse performance with the same size rotor? To be clear it is the same rotor swapped over from my X wheelset, so there is no break-in issue or anything like that.

Jeremy

I've never swapped wheel sizes on a bike before and I'd never thought about it before, but your observations make sense. The 21" front wheel has a larger moment (torque) to apply against the moment caused by the brake/rotor.

I paid close attention to the brakes on the motard track last night and again today commuting. I think they could be better. I don't find them a problem because with the little bike I don't use them to scrub much speed (it's all about maintaining momentum) and they are adequate for emergency braking. I do think that in some situations the modulation could be a bit better yet though. A few times last night on the track (same spot each time) I noticed that I reached a point where there was an abrupt change between off and on. It's a little unsettling, but can be managed. I may try a steel line yet ...

Overall I still won't complain about the little bugger. Next to my Ducati it's the best 'out-of-the-box' bike I've been on.

I was thinking the size itself could make for a difference in feel/performance, but I'm not the physics type. I guess I'll just ride it for a while and see what happens. I just got another front disc to use on my X wheels, so maybe I'll switch back and see what that feels like.

Quote :

I think they could be better.

My problem is I am comparing the X's wimpy front brake to the full radial 4-pot system on my Aprilia which isn't a fair comparison but it is one I am subjected to all the time as I switch from bike to bike.