Suspension Geometry w +1 Rear Question

[CaligoneTx]

Ok... here we go...

I've been contemplating the plus 1 mod to raise the rear suspension.

Currently I have been running a 3/4" down in the front for a more positive caster and faster turn in without sacrificing stability. But I am dragging hard parts on the track and since the season for track riding is coming around soon I need to get some more ground clearance and get use to the set up on the street.

So, what effects on pivoting the suspension have you found in the geometry of the front rake. What angle does the front caster sit w +1 rear and at what sag? I want to stay around 105 in the front so I dont lose stability after turn in.


Motorcycles Unlimited offered to spec the whole suspension to my weight and riding style(not just a suspension adjustment, but wheel off set ups.) They are incredible people and set up many race bikes year round; but I'd like to have some general guidelines so we have a general baseline when we start.

Likely, without taking the baseline first, I may be looking at a +.50 for the rear but we wont know for sure until the baseline is made and we start modding it w weight.

Thanks ahead of time H.org!

 

[BA BUSA]

Have you upgraded your suspension ???

You will need stiffer springs and better valving first

 

[BigDiesel]

Have you upgraded your suspension ???

You will need stiffer springs and better valving first

+1 gotta get the suspension bits sorted if you are doin serious track-riding.
start at OEM height and then raise rear +1...from what friends have sed, going lower than .50" down in front is only used for drag racers n straightline-runners as it decreases ground clearance (which unfortunately you've already discovered-at least you learned now you can make adjustments)

good luck on the track n take some PICS!

 

[CaligoneTx]

Im 190, 5'11" so the stock springs/forks work fine for my weight/height.

I ride aggressive street and usually ride to the tracks/ride and return home(we have four within an hour each way from the homestead.)

Mainly, I dont want to shorten rake too much to prevent stability. Raking the suspension on a heavier bike will put more rider weight over the front providing a faster turn in. But when going real aggressive, a shortened caster rake(forks are more verticle and causes washout when over) is dangerous. I was just wondering if someone had the specifications of the rake angle w their plus 1 and what sag/spring rate they are set at. Regardless, I'll post up mine when I have it dialed in before I start modding it w rides/sprints; but a general baseline would be nice so I dont have to have to come back and remake dogbones. Thankfully trackarm pivot is least of the worries since the trailing arm is more parallel then most bikes. Im assuming there aren't problems w chains slapping the arms, correct?

Our decision is to bring the whole bike back to oem ride height/adjustment level remove the wheels and dial the bike. Then measure the rake/track. Then set sag/spring rates again w me on the bike. To check available pitch of the rear, we will start lifting the rear frame and continue to measure the front caster rake. Adjust dampening then ride and recheck after setting.

BTW, I run a 190/55 (for tighter turn in) on the rear so my front caster rake is already straighter.

These are from a session I did at TWS w TTD amongst a forest ride

 

[CaligoneTx]

(scrapes above 'motohouston' not the others on the fender... that was from being rear ended on a drag strip)

 

[BA BUSA]

Even if you weighed 150...you NEED stiffer springs and better valving for the track. The Hayabusa suspension is too soft.

 

[Commuta_Busa]

I think you want to focus on trail more than rake.

 

[CaligoneTx]

Front rake is effected by pivoting the rear.

W everyone doing this mod, no one has an idea at the actual numbers? We are starting it tomorrow and adjusting to 105 deg front rake. That will determine what we can raise the rear safely without sacrificing performance during hard lean angles.

 

[phierce]

Even if you weighed 150...you NEED stiffer springs and better valving for the track. The Hayabusa suspension is too soft.

I weight the same as you and after revalving/spring the fork and a new Penske the Busa was a completely different animal.
The stock suspension is way too soft, trust us.

 

[BA BUSA]

STIFFER springs and upgrade the valving...-1/4" on the front and +1" on the rear...120/70 front 190/55 rear

The stock suspension is TOO SOFT...and after a couple of MONTHS it's even worse

 

[megawatt]

Kinda too technical for me on asking the rake, caster, angle, etc. But when you said "But I am dragging hard parts on the track..." then I would suggest +1 in the rear and a 55 series tire on the back. That is the setup I run on trackdays and have never dragged hard parts yet.

You think the stock suspension works for your weight"...Im 190, 5'11" so the stock springs/forks work fine for my weight/height." I am not going to try to sound like I know about suspension so I will let the race tech guys website spell it out for you.

Using their spring rate calculator on racetech.com the busa front stock springs are .85kg/mm and using your 190 lbs for track riding the calculator suggest using a spring rate of 1.029kg/mm. That is a big difference of about 20% under strength you are using on your current setup.

I sent in my forks to lindemann engineering for springs and valving and lowered my track lap times by 4 seconds the first time back out. I have video of me with the stock suspension and the bike was diving hard on the brakes and was not stable in the corners. That is not a problem now, and even when I ride two up the ride is much better and more adjustable.

I wish you luck on your trackdays and have fun. Nice pics by the way.

 

[Big Red]

I wouldn't drop the front; raise the rear one inch.Get new front springs for your weight and re-valve front and rear. Set the sag.

 

[CaligoneTx]

We do have a heavier weight in the front forks to tighten it a bit. But still; I dont have significant issues with the front diving out or reason. Since I do more street riding rain/shine that is my focus. Track only happens on the weekends/invites. Ive had a 1k on backroads w a well tuned track suspension and it isn't a joyful ride after a few hours.

Update:
Patrick took it Saturday while I worked and found a 105 degree rake w the rear up 3/4inch(track within tolerance too.) So we are going to make dogbones for that to start with then reset sag.

 

[kml]

105 rake?
stock is 24.5

No wonder you got handling problems, you are riding the OCC firebike.

cheers
ken

 

[BA BUSA]

We do have a heavier weight in the front forks to tighten it a bit. But still; I dont have significant issues with the front diving out or reason. Since I do more street riding rain/shine that is my focus. Track only happens on the weekends/invites. Ive had a 1k on backroads w a well tuned track suspension and it isn't a joyful ride after a few hours.

Update:
Patrick took it Saturday while I worked and found a 105 degree rake w the rear up 3/4inch(track within tolerance too.) So we are going to make dogbones for that to start with then reset sag.

A 1k is OVER 100lbs lighter...AND a 3" shorter wheel base...that's why they ride
so rough. Do your homework...get the springs and valving done. You will not believe
the difference @ the track AND on the street

 

[BA BUSA]

Waiting for the 'troops'

 

[Commuta_Busa]

I still want to know about a bikes caster...???

 

[Devil Dog]

Dude.....do yourself a favor, stiffer springs and get the valving upgraded. I weigh 165lbs and do track days also.....Yes, I need mine done. I have scraped covers just like you. If you continue to drag hardparts like that.....You're going to crash! It's a fact: the Busa suspension is too soft for the aggressive riding that you are doing.

Good Luck w your upgrades

DD

 

[Tufbusa]

Dude, you are either a troll or you are lost when it comes to suspension. I'm not bashing you, but anyone who understands suspension and reads your post would have to agree you don't know much about suspension and how it functions.

With your front lowered, it doesn't take much to drag hard parts. I think you'll find your trackside suspension professional will raise the front back up to stock, raise the rear slightly, not to decrease trail for quicker tipin but to give your fat chick a little more ground clearance.

Apparently you have not mastered the art of braking yet or you would not be concerned about shortening your trail to quicken tipin. Take a couple or race classes and you'll learn how to brake properly, keeping your forks compressed, which decreases trail and speeds up tipin as you roll the big girl on her lips.

Let me suggest a very informative book you should read if you are indeed interested in learning how your suspension functions as well as what effects the different adjustments have on the bike. "Sportbike Suspension Tuning by Andrew Trevitt". Read it before you post up your next suspension thread so you don't look quite so, let's say, "Uninformed"!

 

[Wag]

If you're dragging hard parts, you need stiffer springs, both front and back. Gotta listen to what you're bike is telling you, man! Stock suspension on a Gen I is set up for a guy who weighs about 165. You get a little bit of room to play with adjustments but not enough to get it up to 190 lbs. As evidenced by your dragging parts.

There's not a whole lot wrong with a slightly steeper attack angle and it makes the ride feel more aggressive. Sometimes, it feels as if it's taking the turns a little better as it seems to "fall" in better. However, you don't want to overdo it, either, otherwise, it makes it too squirrely and less manageable with little or no added benefit beyond a certain point. If I were you, I'd leave the front at stock and add 1" (using dog bones) to the rear. See how that feels but I can guarantee you, you will eliminate the dragging parts, assuming you adjust the sag and comp/precomp and everything else correctly.

Whattaya think?

--Wag--