Braking effect, fork brace and placement of the caliper

[irishjohn]

We returned home tonight from an extended wkend ride through NC, TN and VA via various well known roads. While riding on 129 I really noticed a phenomenon when braking which prompts the following questions. Under heavy braking while setting a corner, the bike tries to stand itself upright, I know this is partly the function of physics. At the same time I feel what seems to be the forks flexing as the Ninjettes only have one front disc. These are not something I notice on our larger Ninjas, I assume partly because of the stiffer front forks and dual disc brakes.

My question is, does anyone make a fork brace for the 250, has anyone used one and found these to be beneficial?

Also, is there a reason that the caliper mounts behind the axis of the front wheel rather than in front? Behind the wheel seems to magnify the torquing of the forks under heavy brake load because of the direction of rotation of the front wheel. This in effect tries to pull the wheel up off the ground under braking. If the caliper mounted in front of the wheel axis, would that not transfer the brake force down toward the ground, increasing tire contact and reducing the torque transferred to the forks?

[backinthesaddleagain]

I've wondered whether there is any impact on caliper placement (relative to fork leg) as well. Google search returns this thread, LOL

[DaBlue1]

I rode the US 129 and some other roads in that area recently. I think the flexing you feel may be in the way the front springs and suspension are set up. A little firmer front spring or heavier oil and re-valving could fix the problem. They do make fork braces, but they mainly use them for dirt bikes because of they shock load they get. As far as the brakes calipers being mounted on the backside of the fork is probably because of the amount of force that is put on the mounting points. Force is being pushed into the (cheap) shock tower as opposed to being pulled away form it. The 250 is a simply designed yet very functional bike. Anything else would cost more money. Just my

[kkim]

there is already a "fork brace" under the front fender.

[DaBlue1]

Originally Posted by kkim

there is already a "fork brace" under the front fender.

That's a front fender brace assy. I think he means something like this. http://www.superbrace.com/simulation.html

[kkim]

I know, but they still perform the same function in tying the forks together.

[DaBlue1]

Originally Posted by kkim

I know, but they still perform the same function in tying the forks together.

True. But I'm wondering if it is as effective as the superbrace.

[kkim]

most likely not, but how stiff/solid do you want the front end? I haven't noticed front end flex in my riding for it to be a concern, have you?

[DaBlue1]

Originally Posted by kkim

most likely not, but how stiff/solid do you want the front end? I haven't noticed front end flex in my riding for it to be a concern, have you?

Nope. And if it did I didn't see it. I think it's just a matter of knowing how the bike handles and adjusting your riding style to it.

[backinthesaddleagain]

IrishJohn some cool older bikes - the Penton and the Bultaco

[tapdiggy]

Originally Posted by irishjohn

We returned home tonight from an extended wkend ride through NC, TN and VA via various well known roads. While riding on 129 I really noticed a phenomenon when braking which prompts the following questions. Under heavy braking while setting a corner, the bike tries to stand itself upright, I know this is partly the function of physics. At the same time I feel what seems to be the forks flexing as the Ninjettes only have one front disc. These are not something I notice on our larger Ninjas, I assume partly because of the stiffer front forks and dual disc brakes.

My question is, does anyone make a fork brace for the 250, has anyone used one and found these to be beneficial?

Do you think the problem could be with one fork's internals? Maybe what feels like flex is actually one fork compressing or rebounding at a different rate than the other. There are, it seems, far too many bikes functioning properly with one front brake rotor for this to be normal.

Also, braking hard enough to start a high-side might be too much speed to start with for setting up on a corner.

Originally Posted by irishjohn

Also, is there a reason that the caliper mounts behind the axis of the front wheel rather than in front? Behind the wheel seems to magnify the torquing of the forks under heavy brake load because of the direction of rotation of the front wheel. This in effect tries to pull the wheel up off the ground under braking. If the caliper mounted in front of the wheel axis, would that not transfer the brake force down toward the ground, increasing tire contact and reducing the torque transferred to the forks?

Brake calipers mounted to the back of the fork is almost a universal configuration.

[Alex]

The torque from the brake disk wouldn't change no matter where the caliper is mounted, it would still be slowing the disk in the same direction. The caliper is typically mounted toward the rear as it makes for better (more centralized) weight distribution, and also simplifies brake line routing (somewhat).

Many bikes stand up under braking, and it has more to do with the front tire profile and steering geometry, than the relative stiffness of the front fork placement. A stiffer brace wouldn't hurt, but as it hasn't been generally found necessary for riding this bike at its limits on the track, it's unlikely to significantly change things on the street.

[irishjohn]

I appreciate everyones comments. It does make sense that ROI would dictate using "lesser" components than on the 250's bigger brothers. The effect of the bike trying to stand up under brake load is an effect of physics. However, I have noticed a significant difference between how the 250 handles this effect than say my 650 ninja. Any suggestions on a different front tire which might have better performance. The bike only has 2800 miles on it so I am still running the OEM tires.

As for the placement of the caliper behind the axis, I have a noticed on some GP bikes the caliper is mounted forward. The purpose of this is reverse the dirction of the braking torque effect.

[HKr1]

Originally Posted by DaBlue1

That's a front fender brace assy. I think he means something like this. http://www.superbrace.com/simulation.html

Think its there for the forks. What the hell does it brace on the fender?

Telefix is a nice brace, dont think it would work with the 08 up fender thou.

[DaBlue1]

Originally Posted by HKr1

Think its there for the forks. What the hell does it brace on the fender?

The front fender is mounted to it by four bolts and it has has the speedo cable and brake hose retainers on it.

[FishaRneked]

My factory fender/fork brace is slighty warped, its soft steel, i bent it back, but im sure its not perfect...

Sooooo should i replace it with a potentially damaged used one off ebay? a brand new OVERPRICED OEM one? or one or something like this http://www.superbrace.com/simulation.html ?

[Motofool]

Originally Posted by irishjohn

As for the placement of the caliper behind the axis, I have a noticed on some GP bikes the caliper is mounted forward. The purpose of this is reverse the dirction of the braking torque effect.

Alex's explanation above is correct.
The radial point of pads' pressure application over the disc has no effect on the resulting torque or forces on the suspension.

The braking torque tends to bend one telescope assembly (center portion forward-tire and bearings aft), while the other one remains unloaded.
However, that asymmetrical bending is minimum and it would only twist the forks to the right an imperceptible amount.

If your problem shows up during right and left turns alike, then that is not the cause.
I believe that the increased inertia of the bigger bikes does make a difference.

Note that those GP bikes have inverted forks; hence, the caliper is anchored in a different way.