Can you explain the physics of...?

maxpr1

maxpr1

New Member
So here is the question:

What makes a bike push to the outside of the turn on exit?

Here is my scenario, I ride an 07 R6 in "B" and have been pretty comfortable with the way my bike has handled up until recently. Last season, I had a Race Tech Gold valve kit installed in my forks and kept the stock spring as I was told that it works for my weight. The bike has handled beautifully, and I can honestly say that I've been able to hold my lines with out a problem.

Recently I installed a set of Carrozeria Rims (found a great deal) and after havinge them installed I was told that because of the reduced weight (over 5.5 lbs less on the front plus an additional 5.5 lbs less in the rear) I should have my suspension dialed in. Well, I never did and the first thing I noticed was the bikes' tendency to drop effortlessy at the beginning of the corner and push way wide on the exit

Am I imagining this tendency the bike has to go wide? And if I am not imagining it, how do I correct it?

Please explain.....
 
betarace

betarace

Member
ejzsia.jpg
 
Steve

Steve

New Member
The dropping effortlessly into a corner can be explained by the weight loss. Each wheel acts like a gyro and tends to keep the bike going in a straight line, less weight = less gyroscopic force. Maybe the same is true for the exit :dunno: I would at least get the sag set and see if that helps.
 
maxpr1

maxpr1

New Member
Sag was set prior to the wheel swap. And Betarace, thanks for posting the flow chart I too will be printing it and keep it handy. So the rear is what may be causing this? I was under the impression that the forks would have been culpable
 
Gorecki

Gorecki

Member
That is a handy image Betadude!

I'm thinking the first line of the image is a big story teller. Your geometry changed! Get sag re-squared away before doing anything else and I wouldn't be shocked if that fixes it. Could be partially because it's that much lighter and that much easier to get it leaned over, it may seem like it takes unexpected leverage to keep it leaned over coming out of the turn because it wants to stand back up? (I making sense?)
 
ninjamansc

ninjamansc

THE Comstock
Control Rider
Ditto with Greg. Wheel/tire weight has NOTHING to do with sag. That's why it's called UNSPRUNG weight.

maxpr1, +1 what Steve said about the gyroscopic forces and turn-in.

With regard to the running wide on exit, some of it may be imaginary but some isn't. With the massive unsprung weight reduction, the same throttle application (with stock wheels) will provide more thrust, unloading the forks somewhat more, causing the going wide. Additionally, with the lighter wheels, steering input necessary to cause movement decreases significantly. Your handlebar pressure on exit could be causing the running wide. Next time you're out, be very conscious of it and see.
 
maxpr1

maxpr1

New Member
:dunno:

still in the dark about the whole geometry thing, as I said the only thing that I changed was the wheels (Sprokets and rotors as well)
 
Gorecki

Gorecki

Member
gkotlin;201742 wrote: How does reducing unsprung weight change your geometry?
Click to expand...
It's not the weight, it's the wheels. I wouldn't be shocked if they stand taller or smaller or thinner or wider? Maybe even ever so slightly changing the profile of the mounted tire? Something has to be different?
 
Dave561

Dave561

Control Rider
Rims are 17" in diameter. That can't change or the wheel won't mount. The conventional 600 rim is 3.5" wide up front and 5.5" in the rear. That is a standard. So there should be no difference in the size of the Rims. Did you change the type of tire you were running prior to the rim swap. Different brands and even different models within a brand will have different shapes even though the tire size is the same. This can have an effect on your geometry. If not than it could be a function of throttle application. Your pace and your application of throttle may have increased and allowed the rear to compress more and this raise the front as well. This crates an obvious geometry change and one that will cause the bike to go wide. Depending in your setup it may require more reload or compression. Without seeing the bike and the current setup I would advise you to seek the help of a suspension guru and specifically one that frequents the tracks you run on. There is a lot of good information to be found on the web, bit there is far more regurgitated false truths our there as well. If all else fails ill trade you a set of stock Rims for those obviously mis-performing Rims :D
 
maxpr1

maxpr1

New Member
Gorecki;201766 wrote: It's not the weight, it's the wheels. I wouldn't be shocked if they stand taller or smaller or thinner or wider? Maybe even ever so slightly changing the profile of the mounted tire? Something has to be different?
Click to expand...
The deal on the rims I got included a 6" rear. I mounted a 190/55 GP-A which falls in the Dunlop recomended range for rim size (5.5-6")
Obviously the stock was a 5.5"
 
Gorecki

Gorecki

Member
maxpr1;201781 wrote: The deal on the rims I got included a 6" rear. I mounted a 190/55 GP-A which falls in the Dunlop recomended range for rim size (5.5-6")
Obviously the stock was a 5.5"
Click to expand...
So what you're saying is something IS different?
 
Dave561

Dave561

Control Rider
maxpr1;201781 wrote: The deal on the rims I got included a 6" rear. I mounted a 190/55 GP-A which falls in the Dunlop recomended range for rim size (5.5-6")
Obviously the stock was a 5.5"
Click to expand...
That should have been in the first post. Yes you did change geometry and yes your rear is now lower
 
maxpr1

maxpr1

New Member
slow_honda;201773 wrote: ... If not than it could be a function of throttle application. Your pace and your application of throttle may have increased and allowed the rear to compress more and this raise the front as well. This crates an obvious geometry change and one that will cause the bike to go wide... If all else fails ill trade you a set of stock Rims for those obviously mis-performing Rims :D
Click to expand...
^^^:adore: ^^^ - The above sentence explains a lot, I do believe that the gearing change definitively effected my throttle application, Hence the same throttle input but a completely different outcome.
I think in the end I am simply ignorant and should have taken into account all of the possible outcomes for all of the changes that I made. I should have asked first; and by the way, if these rims continue to mis-perform, I will take you up on that swap!

Thanks to everyone for chipping in
 
maxpr1

maxpr1

New Member
slow_honda;201790 wrote: That should have been in the first post. Yes you did change geometry and yes your rear is now lower
Click to expand...
So do I then start out with adjusting the sag AGAIN?
 
Gorecki

Gorecki

Member
maxpr1;201796 wrote: Sorry I should have posted it earlier... Again I proclaim Ignorance
Click to expand...
Hey, I still think the wheel could be different SOME HOW. .5mm here, .7mm there. Ignorance is not asking at all. :cool:
 
Dave561

Dave561

Control Rider
No not really. Sag can affect ride height, but in this case you should increase the length of the shock. Since the bike has a stock shock you would need to add a shin to the top mount. You would do this by loosening the top post mount and added a washer or a body panel shin you could pick up at a auto parts store. 2-3 mm at a time since small increments can make a significant change.
 
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