Rake and Trail
Senior Member
MotoGP
Joined: Aug 2006
Posts: 2,934
From: altoona, pa
First of all, here's a better answer about 1st impressions:In order to model squat/antisquat and attitude under braking and acceleration you need to measure the center of gravity, which you can get by measuring the F/R weight distribution with the motorcycle horizontal and again with one wheel up on a pedestal.
Level surfaces, no brakes, and no weight on the bars of course.
Senior Member
SuperSport
Joined: Jul 2006
Posts: 655
From: Madison Wisconsin
Stumpy, if you can take all of those measurements - I can send you a sheet to fill out - we can look at the suspension rate and modify the rocker geometry for better track performance, based upon how the RC51 rear works.
This is assuming that you will never carry a passenger. The rising rate of the stock suspension rocker has increasing leverage at the top of travel, to prevent bottoming when riding 2-up. The modified racing linkage has more initial leverage and less rising rate.
This is assuming that you will never carry a passenger. The rising rate of the stock suspension rocker has increasing leverage at the top of travel, to prevent bottoming when riding 2-up. The modified racing linkage has more initial leverage and less rising rate.
Last edited by Stumpy; Nov 15, 2010 at 10:44 PM.
Senior Member
SuperBike
Joined: Dec 2005
Posts: 1,689
From: South Lake Tahoe, CA, USA
you will probably get a more accurate weigh if you roll you bike onto a board the approximate thickness of the weight laden scale(like a 2x6x6), then place the scale at either end of the board. For front weight, push the front wheel onto the scale and record the weight. Then move the scale to the rear and move the bike back onto it.
Level surfaces, no brakes, and no weight on the bars of course.
Level surfaces, no brakes, and no weight on the bars of course.
What I meant to say was that you need the center of mass of the bike and rider, both fore/aft and the vertical height. To get the vertical height, you need to find the change in the center of mass position, when you put the front (or rear) wheel on a pedestal, with the rider on it. The pedestal needs to be about 500 mm high. The bike needs to be free to roll, with no brake applied.
It sounds like a good way to drop your bike.
Senior Member
SuperSport
Joined: Nov 2009
Posts: 677
From: Rancho Cordova, California
Maybe we could chug on over to mamby pamby land where maybe we could find some self confidence for you!
Last edited by ranchomice; Jan 13, 2011 at 03:22 PM.
Member
Squid
Squid
Joined: Sep 2008
Posts: 48
From: NE Ohio
I had done a cbr 1000 (2007 forks) front end swap last year and spent the balance of the riding season sorting it out. Like many of the posts of other swappers I was never completely happy with my results. Over the winter I researched this forum, numerous Google searches and I purchased the Tony Foale software. I'm still gathering the required measurments, which may take some time. To get to the point there is a rake and trail calculator in the package which I used as a starting point. I also found an article in sport bike rider online which used an inclinometer on the triple tree to find the bikes rake. By using these tools, I used a digital protractor instead of the Craftsman inclinometer. I changed the bikes attitude via my Penske shock to restore the trail numbers to the stock 97mm, it had been as high as 106mm as I "sorted". I have not had much opportunity to ride it but my first impression was very good. In short my message is that with fairly inexpensive tool ($10 from Sears) and free rake and trail calculators RB Racing Rake and Trail Calculator, you can get in the "ballpark" and avoid some of the pit falls of unmeasured suspension modifications.
RUNLEVELZERO #99
SuperBike
Joined: Jan 2007
Posts: 2,218
From: Skokie
Rear Ride height?
Can someone tell me what OE rear ride height is as measured from center of OE bolt connecting the passenger foot peg brackets to the exhaust can hangers; or some other rearward fixed point (like the rearmost of the two bolts fastening the passenger foot peg brackets to the rear subframe)?
If someone can also provide front ride height, that would be nice too but I know what I’ve changed there (see below)
Heights normally are based on about 30 mm sag front and rear pumped and unloaded; i.e., without pilot static sag.
I’ve had a Penske for so long and played with ride height and lost the OE height.
I thought I was about +7 mm in shock overall length (using the adjuster) but the oil level marks on each side of the sight glass are not level with each other.
It appears I’m actually low in back even though the fork tubes are raised 6 mm in the OE top triple clamp with stock forks (massaged by Greg) with .90 RT springs, AllsBalls TRB & OE tire sizes.
When I’ve gone too high in back the side stand was too short but the opposite almost seems the case now. The Penske needs a rebuild but spring preload determines height in conjunction with overall shock eye-to-eye length given the OE linkage.
It’s been 14 years and 80k+ miles, so I’m a bit foggy with comparisons but steering does not seem slow or too quick. The Avon Ultra 2 Storm tires are pretty neutral steering though come to think of it with 11,500 miles on them its probably worn down 4 mm). But the oil sight glass marks were like that when these last set of Avons were new and just seem should be level left-to-right.
Maybe I’m seeing ghosts this close after Halloween.
If someone can also provide front ride height, that would be nice too but I know what I’ve changed there (see below)
Heights normally are based on about 30 mm sag front and rear pumped and unloaded; i.e., without pilot static sag.
I’ve had a Penske for so long and played with ride height and lost the OE height.
I thought I was about +7 mm in shock overall length (using the adjuster) but the oil level marks on each side of the sight glass are not level with each other.
It appears I’m actually low in back even though the fork tubes are raised 6 mm in the OE top triple clamp with stock forks (massaged by Greg) with .90 RT springs, AllsBalls TRB & OE tire sizes.
When I’ve gone too high in back the side stand was too short but the opposite almost seems the case now. The Penske needs a rebuild but spring preload determines height in conjunction with overall shock eye-to-eye length given the OE linkage.
It’s been 14 years and 80k+ miles, so I’m a bit foggy with comparisons but steering does not seem slow or too quick. The Avon Ultra 2 Storm tires are pretty neutral steering though come to think of it with 11,500 miles on them its probably worn down 4 mm). But the oil sight glass marks were like that when these last set of Avons were new and just seem should be level left-to-right.
Maybe I’m seeing ghosts this close after Halloween.
Junior Member
Squid
Joined: Dec 2013
Posts: 2
Very interesting article and well researched..
I've been studying and learning about racebike setup and have learned a fair amount so far and have a lot more to learn.
I have had hints that swingarm angle was a very important consideration, but have discovered that chassis setup pretty much begins there. So you start with the tire radius and set the swingarm pivot height, to give the desired angle. This defines the anti-squat behavior, for a given torque applied to the rear wheel and fina drive sprocket sizes. That sets the position of the rear suspension at maximum acceleration, when the front wheel is unloaded. I think, but I don't know for sure yet, that you want the loaded swingarm angle to be near the neutral point between squat and anti-squat, so that the rear suspension has good compliance.
From there you can work on rake and trail numbers - since not everything is adjustable, you are basically finidng the best compromise.
I purchased some software by Tony Foale (www.tonyfoale.com). It is available on ebay for $59. It is a beautiful piece of work. You can enter all of the geomtery info, including rear suspension linkage position and geometry and plot things like rear wheel force, vs. suspension position, rake a trail under full acceleration and full braking, etc.
As soon as my work table is finished, I'm going to compare stock rear suspension geometry, with the Moriwaki linkage and increased shock length, spring rate, etc.
If anyone wants to take measurements of the Super Hawk, I can provide a list of the necessary measurements and create a model of it. It may help to better define the necessary geometry for the rear suspension dogbone for stock and modified swingarms, as well as establishing a good baseline for people making modifications.
I will be happy to do the modeling. It will add to my understanding and hopefully increase the knowledge base of everyone who is interested.
I have had hints that swingarm angle was a very important consideration, but have discovered that chassis setup pretty much begins there. So you start with the tire radius and set the swingarm pivot height, to give the desired angle. This defines the anti-squat behavior, for a given torque applied to the rear wheel and fina drive sprocket sizes. That sets the position of the rear suspension at maximum acceleration, when the front wheel is unloaded. I think, but I don't know for sure yet, that you want the loaded swingarm angle to be near the neutral point between squat and anti-squat, so that the rear suspension has good compliance.
From there you can work on rake and trail numbers - since not everything is adjustable, you are basically finidng the best compromise.
I purchased some software by Tony Foale (www.tonyfoale.com). It is available on ebay for $59. It is a beautiful piece of work. You can enter all of the geomtery info, including rear suspension linkage position and geometry and plot things like rear wheel force, vs. suspension position, rake a trail under full acceleration and full braking, etc.
As soon as my work table is finished, I'm going to compare stock rear suspension geometry, with the Moriwaki linkage and increased shock length, spring rate, etc.
If anyone wants to take measurements of the Super Hawk, I can provide a list of the necessary measurements and create a model of it. It may help to better define the necessary geometry for the rear suspension dogbone for stock and modified swingarms, as well as establishing a good baseline for people making modifications.
I will be happy to do the modeling. It will add to my understanding and hopefully increase the knowledge base of everyone who is interested.
RUNLEVELZERO #99
SuperBike
Joined: Jan 2007
Posts: 2,218
From: Skokie
Why after over 2 years
did you reply to my post?
Attached is what I found in the mean time...
I have a Penski 2-way set at +7mm longer than OE shock length with a stiffer spring and about the shortest wheel base possible with 16F & 43R sprockets with the forks up in the TT +6mm (lowered head = -0.5 degrees steeper rake and slightly shorter trail). I find with a neutral turning tire I'm almost too quick / easy on tip-in and lost some high speed stability (especially with a Shad SH46 rear box ending over the tail light). I'm dropping the fork tubes back down to OE length to compensate. And that's with higher and more rear-set clip-ons, which has unloaded the front contact patch a bit! Squat in the rear under drive is good and bump absorption is balanced front-rear except on choppy pavement when hobby-horsing is a factor of the shorter wheel base.
My VTR is set up for sport touring not track use and is now serene at 75 ~ 85 mph but still hauls the mail in the twisties.
Attached is what I found in the mean time...
I have a Penski 2-way set at +7mm longer than OE shock length with a stiffer spring and about the shortest wheel base possible with 16F & 43R sprockets with the forks up in the TT +6mm (lowered head = -0.5 degrees steeper rake and slightly shorter trail). I find with a neutral turning tire I'm almost too quick / easy on tip-in and lost some high speed stability (especially with a Shad SH46 rear box ending over the tail light). I'm dropping the fork tubes back down to OE length to compensate. And that's with higher and more rear-set clip-ons, which has unloaded the front contact patch a bit! Squat in the rear under drive is good and bump absorption is balanced front-rear except on choppy pavement when hobby-horsing is a factor of the shorter wheel base.
My VTR is set up for sport touring not track use and is now serene at 75 ~ 85 mph but still hauls the mail in the twisties.
Last edited by skokievtr; Aug 15, 2014 at 03:35 PM.
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