"Weight on the wheels" - geometry discussion

[kuksul08]

I am constantly reading that if you raise the rear, or lower the front of your bike, you will consequently "put more weight on the front tire".

It seems to me that moving the fork up in the clamps by 3 to 5mm is not going to affect the weight distribution by any significant amount. Yet, this idea persists.

Can anyone explain?

-Has anyone actually put the bike on two scales and measured how much it changes?
-Does it have more to do with the how the rider tends to sit and therefore is not related to the bike's weight but the rider's weight?
-Is it all in our heads and 100% based on minor changes to trail?

Scientific discussion welcome :teeth

 

[afm199]

I am constantly reading that if you raise the rear, or lower the front of your bike, you will consequently "put more weight on the front tire".

It seems to me that moving the fork up in the clamps by 3 to 5mm is not going to affect the weight distribution by any significant amount. Yet, this idea persists.

Can anyone explain?

-Has anyone actually put the bike on two scales and measured how much it changes?
-Does it have more to do with the how the rider tends to sit and therefore is not related to the bike's weight but the rider's weight?
-Is it all in our heads and 100% based on minor changes to trail?

Scientific discussion welcome :teeth

It affects it enough that the increments in MotoGP might be a few millimeters. Moving the rear on bikes with links affect the rear close to 3x as much as the front. Yes, it makes a huge difference.

Particularly on the HP bikes, where you try find a happy medium between too much front weight ( bike will rotate on the headstock and easily lift the rear tire off the ground, and the rear will spin up super easily. The bike will be unstable on braking with the low front.

Spinning up the rear is an issue on most liter bikes, and 5 mm can affect it. In a race situation you're always on the edge of spinning up the rear on corner exit, and want to get power on as early as possible, which means for exits you want the front end higher and the rear lower. For entry the obverse may be true, so you look for a happy medium.

Yes, particularly on HP bikes, it makes a difference.

 

[kuksul08]

It affects it enough that the increments in MotoGP might be a few millimeters. Moving the rear on bikes with links affect the rear close to 3x as much as the front. Yes, it makes a huge difference.

Particularly on the HP bikes, where you try find a happy medium between too much front weight ( bike will rotate on the headstock and easily lift the rear tire off the ground, and the rear will spin up super easily. The bike will be unstable on braking with the low front.

Spinning up the rear is an issue on most liter bikes, and 5 mm can affect it. In a race situation you're always on the edge of spinning up the rear on corner exit, and want to get power on as early as possible, which means for exits you want the front end higher and the rear lower. For entry the obverse may be true, so you look for a happy medium.

Yes, particularly on HP bikes, it makes a difference.

But how, physically? Seems you're alluding to a dynamic weighting situation rather than the static one I defaulted to. Do you have any numbers or math to back it up?

 

[Busy Little Shop]

-Has anyone actually put the bike on two scales and measured how much it changes?

I actually employ a scale to track my bikes weight and balance...
There are a few steps an owner can take to gain a greater degree of
accuracy when weighting a bike with a single scale... first make sure
both wheels are equally raised above the ground... because with one
wheel raised on the scale and the other wheel on the ground more
weight is bias towards the lower wheel even though the total weight
adds up to be the same...

Mr.RC45 Front Weight 212 bias 52%

Mr.RC45 Rear Weight 195 bias 48%

I'm a graduate of Tony Foale's seminar and I recommend his book...

Tony is a good friend...

 

[89fj]

^^^carbon rotors, trick! :cool

 

[stangmx13]

"puts more weight on X end" is a summary of effects and resultant feelings, not a literal translation of what happened. small static changes produce similarly small changes in static weight. but riding a motorcycle is a dynamic action. there are countless dynamic effects that also affect what the rider is feeling. riders need to be able to communicate well with others, so we've got short phrases to summarize feelings.

dynamics is a rabbit hole. lets take one action - say increasing shock length. I wonder how many effects and sub-effects that would cause, or rather how many can I think of...
- decreases wheelbase
--- decreases lateral stability
- raises CG
--- decreases roll stability
--- increases dive
- moves CG forward
--- increases forward weight bias
----- affects both suspension positions
- increases swingarm angle
--- increases anti-squat
----- affects shock position
- reduces rake
--- reduces trail
----- reduces steering stability
----- reduces steering effectiveness

I think I got all of that right. there are tons more knock-on effects, but the formatting is already nuts. my point is that it all adds up to the rider actually feeling something different.

 

[RVFRick]

I am constantly reading that if you raise the rear, or lower the front of your bike, you will consequently "put more weight on the front tire".

It seems to me that moving the fork up in the clamps by 3 to 5mm is not going to affect the weight distribution by any significant amount. Yet, this idea persists.

Can anyone explain?

-Has anyone actually put the bike on two scales and measured how much it changes?
-Does it have more to do with the how the rider tends to sit and therefore is not related to the bike's weight but the rider's weight?
-Is it all in our heads and 100% based on minor changes to trail?

Scientific discussion welcome :teeth

Subbed.

I agree with OP, weight shift negligible. However, I do believe geometry change is the dominant effect. No math, just intuition. :x

 

[DannoXYZ]

As far as front/rear weight-bias changes, it's probably not enough to be significant in static or dynamic.

Typically lowering front-end by 12mm decreases rake-angle by ~3/4-degree (depends upon bike's specific geometry: wheelbase, fork-height, rake-angle, trail etc.). That's significant enough to notice. Many AFM Ninja-250 racers have recorded 1-1.5 sec/lap improvements with just this adjustment.

 

[kuksul08]

Oh yeah, I am not doubting that it greatly affects handling. Even raising the fork tubes by 3mm produces a noticeable change in handling such as quicker steering.


So we can agree that "puts more weight on the front wheel" and equivalent phrases are complete bogus?

 

[295566]

Think of a teeter totter.

Start parallel to the ground. Lowering one side will require additional force (weight) from the other to level out again.

 

[Tom G]

That contradicts even high school physics. Remember about torque.

 

[295566]

That contradicts even high school physics. Remember about torque.

but the fulcrum isn't changing. What about scales, perhaps a better example?

 

[ontherearwheel]

The drawing is great for a see-saw but does not apply to a motorcycle. The reason is a motorcycle has contact with the ground at two points and those points being on each end of the motorcycle under the tires, not the middle.

When a motorcycle wheelies, it is rotating at the rear tire and stoppies, it is rotating at the front tire.......not in the middle.

There is in fact a weight change on the tires when raising or lowering the front or back. This is real. If you notice the change or not is another matter that depends on the motorcycle and how it is being used.

Lowering or raising either end of the bike is also changing the center of gravity of the motorcycle which does effect how it handles. Changing the center of gravity effects weight distribution under acceleration and deceleration and also in leaning the motorcycle.

Again, if you notice the changes or not is another matter.

Remember track and street are two different operating environments and you may not feel the changes on the street, but on the track where speeds are greater and handling and turn in and exit are far more important than on the street, you will.

 

[BillTuono]

There are very noticeable effects

Oh yeah, I am not doubting that it greatly affects handling. Even raising the fork tubes by 3mm produces a noticeable change in handling such as quicker steering.
So we can agree that "puts more weight on the front wheel" and equivalent phrases are complete bogus?

Nope we can't. Because even what seem like small changes produce noticable effects when riding. Most high peformance bikes now have very adjustable preload. If you increase the preload in the front you will see differences in sag, and actual weight distrubution. You can measure the difference on scales. Using 2 identical scales works best of course. Where I have noticed the greatest difference is in corners where you have rapid transitions left-right for instance. On my 600 race bike I saw a very noticeable change with a 1/4" preload adjustment. Of course YMMV, and rider weight makes a big difference too.
Bill

 

[kuksul08]

Nope we can't. Because even what seem like small changes produce noticable effects when riding. Most high peformance bikes now have very adjustable preload. If you increase the preload in the front you will see differences in sag, and actual weight distrubution. You can measure the difference on scales. Using 2 identical scales works best of course. Where I have noticed the greatest difference is in corners where you have rapid transitions left-right for instance. On my 600 race bike I saw a very noticeable change with a 1/4" preload adjustment. Of course YMMV, and rider weight makes a big difference too.
Bill

Have you done this experiment with two identical scales? How much weight shifts to the front wheel by raising the rear 1/4 inch?

 

[afm199]

But how, physically? Seems you're alluding to a dynamic weighting situation rather than the static one I defaulted to. Do you have any numbers or math to back it up?

Nope. Don't care. I know what works for me on the track.

 

[FreeRyde]

Nope. Don't care. I know what works for me on the track.

I am now unsure why you originally posted. I think the OP was looking for empirical data, from real world suspension tinker'ers. I'm glad you are super fast and experienced on the race track, but your contributions here have totaled to a negative net value thus far.

OP, while moving the forks around 3-5mm feels like a massive change to me... Can we throw in suspension fluid heights into the equation as well? I think it's impossible to just look at angles and ride height adjustments without acknowledging the internal fork fluid dynamics.

Hell, we might as well start discussing spring rates as well.

We are talking about a multifaceted, ever changing equation of motorcycle suspension and chassis dynamical changes.

 

[Busy Little Shop]

^^^carbon rotors, trick! :cool

Actually Mr.RC45 is equipped front and rear with Ceramic Matrix Composite rotors which are just as light and trick as carbon...

 

[afm199]

I am now unsure why you originally posted. I think the OP was looking for empirical data, from real world suspension tinker'ers. I'm glad you are super fast and experienced on the race track, but your contributions here have totaled to a negative net value thus far.

OP, while moving the forks around 3-5mm feels like a massive change to me... Can we throw in suspension fluid heights into the equation as well? I think it's impossible to just look at angles and ride height adjustments without acknowledging the internal fork fluid dynamics.

Hell, we might as well start discussing spring rates as well.

We are talking about a multifaceted, ever changing equation of motorcycle suspension and chassis dynamical changes.

I'm kinda lmao because there is no real accepted science of suspension, and set laws. There's just data and interpretation. There's no handbook, no tables, no charts, just data.

I agree with your analysis.

BTW, most of these changes won't even be felt by the average guy riding on the street, unless they are major. Lower the forks or raise them 8mm.? Most riders won't know the difference, that only becomes apparent when you're pushing hard.

Nor am I super fast. :rofl But what I do see, time after time, is fanatical interest in making suspension changes, multiple changes, and no apparent benefit. The suspension isn't making people slow, unless it's really off.

 

[stangmx13]

say your bike is kitted-out with every piece of data acquisition possible - suspension position, tire temp, IMU, strain gauges, etc. say you also pay a ridiculous amount of $$ to hire the best engineers in the world and to use the best pieces of software. do now have enough data, knowledge, and capabilities to fix or optimize every possible riding issue without guess and check? nope.

the problem is still indeterminate. you'll be able to optimize the majority of riding situations, but not all. you could probably input your bike, riding style, and track into a simulator and get a pretty damn good solution. but it won't be perfect.

how do I know? cuz MotoGP cant get it perfect. they show up to known track with a known bike on known tires with a known rider and still screw things up. sometimes they miss the setup so bad they go slower than previous years or previous tests.