Bicycle Mechanics - How much pedal travel is normal when braking on coaster brake bmx bike??

Hi All!

My daughter has a 4 yr old kid's Dynacraft BMX coaster brake bike. I've noticed the pedal travel when braking seems to be a greater distance than what I remember. Can someone let me know what the pedal travel should be for a normal functioning coaster brake bike- if that doesn't vary by model. I know this cheaper bike could be the problem itself. Also can pedal travel be adjusted?? I tried to adjusting by turning the axle cone and the brakes start to grab the wheel right away when I start turning the axle cone, but the pedal travel doesn't decrease at all. (When I turn the axle cone in on the left side of the bike, opposite the brake arm, the wheel brakes start grabbing right away from freely spinning with very little turn of the cone, so I think this may indicate the brakes are okay. I thought this might decrease the pedal travel, but obviously it didn't.).

Appreciate any help!

Visser

I am not a bike mechanic by any means. But back long ago when I road my Huffy with a coaster brake I recall there was maybe 45 degrees of travel before the brake engaged.

Dynacraft BMX coaster brake bike
Q: who made the rear hub itself? is it a major brand?

That's about the amount of pedal travel this one has, so it's probably ok and I'm just not recalling there ever being that much in these types of bikes. It's been a long time since I've ridden anything without hand brakes, I couldn't remember. Thanks for the input!

Can anyone confirm if pedal travel is adjustable at all? Just for my sake of knowing, and learning.

Q: who made the rear hub itself? is it a major brand?

Good question, fietsbob. I don't see anything distinguishing on the hub itself, the brake arm has a stamp, "YCC" and the word "China", so I assume the whole bike was made in the same factory in China. It is one of those "Barbie" branded walmart bikes- my wife bought without me knowing. Not great quality at all, but its lasted 4 years and sustained the abuse of 2 kids now, haha. Thought it was okay to get them through the training wheel stages!! Thought it would be good to know about the braking stuff for when I start shopping for the next level bikes for them.

The pedal travel depends on the front sprocket/rear sprocket gear ratio.

Assume that the hub has a certain amount of free arc to engage the brake. If the front and rear sprockets are the same, you'll have the same dwell in the cranks. As the front gets larger the crank dwell is reduced, since less crank travel moves the hub through the same arc.

Children's bikes often (usually) have more pedal travel than adult bikes since they tend to have lower gear ratios, but in no case should the crank have more than about 45° of dwell, so the rider can keep the cranks in the horizontal sweet spot both when starting to brake and actually engaging. It would be a hardship for a child to have to begin, or achieve braking at the 6/12 o'clock crank position.


BTW- on some coaster brake hubs the engagement dwell is somewhat adjustable, so if the bike isn't working to your satisfaction it may be fixable.

A cone adjustment may have some effect. Scroll down to see how: http://sheldonbrown.com/coaster-brakes.html

My daughter has a 4 yr old kid's Dynacraft BMX coaster brake bike. I've noticed the pedal travel when braking seems to be a greater distance than what I remember.

Almost certainly due to a much lower gear ratio.

I'll look at the new versions of this bike on my next trip to Walmart to see if they are any different, hahahaha!!

Thanks to all for the great help!!

Visser

Almost certainly due to a much lower gear ratio.

Thanks for mentioning, Kimmo. This makes sense to me, especially since being brought up by someone with the experience to know.

I'll look at the new versions of this bike on my next trip to Walmart to see if they are any different, hahahaha!!

Sorry, all. This was only a partial message. I just checked back to the thread to find the first part of what I originally typed is missing. here's what I intended,a nd the line in bold will make more sense!! Sorry about that!

I actually followed the Sheldon Brown procedure that dsbrantjr linked me too before I posted. In adjusting the cone, Sheldon indicates that turning too much will result in the wheel binding, and too loose results in the wheel wobbling, and having a lot of pedal travel. This is one of the reasons that actually prompted me to dig a little deeper after I tried the procedure. As I tightened the cone, the wheel started to bind right away, (and the wheel seemed to have the right amount of free spin to begin with), and the pedal travel stayed as it was. So I was pretty sure there was no adjustment that could be made to decrease the pedal travel, but thought I'd ask those that know, and learn about what I should know about this already, lol! I really appreciate the help from knowledgeable people!

So it would seem that the pedal travel is probably certainly normal for this bike, (due to its quality, or type, or fact that it's a kids bike...). I'll look at the new versions of this bike on my next trip to Walmart to see if they are any different, hahahaha!!

Thanks to all for the great help!!