Two-Up Travel on the 919 - Wrist Twisters
 3Likes
  • 3 Post By Nickr919
 
Thread Tools Display Modes
post #1 of 16 Old 11-12-2015, 12:18 PM Thread Starter
Tesserarius
 
CKutz_GO's Avatar
 
Join Date: Feb 2014
Location: Frederick
Posts: 607
Rep Power: 1
 
Two-Up Travel on the 919

Hey guys,

I wanted to see what recommendations people have setting up the niner for two-up travel, primarily tire pressures and suspension settings.

I did my first "2-up overnighter" last weekend and I think the bike squats so much it really slows down the steering. It was of course heavier and harder to turn but i think it squatted so much under the load that it really messed with the steering geometry. Airing up the tires to 34f/38r cold seemed to help a lot with making it a bit more nimble again and transition into turns better. I didn't adjust the preload, which is at the 3rd step from the top i think. I don't remember what it was at in the front but you can see where a zip tie is at on the fork tube (pic taken before setting out on the trip).
our combined weight is probably 300#lbs (we're both pretty short) + the luggage.
I'm sure "buy a new shock" will be suggested, but I don't think i'm getting the most out of the stock set up yet, also i wouldn't want to spend all that money for a shock sprung for two-up weight when that's probably 10% of riding.
Attached Images
File Type: jpg IMG_20151107_155345682[1].jpg (223.9 KB, 48 views)

CKutz_GO is offline  
Sponsored Links
Advertisement
 
post #2 of 16 Old 11-12-2015, 12:45 PM
...is a Nihonjin.
 
Shmoo's Avatar
 
Join Date: Feb 2011
Location: Virginia
Posts: 1,573
Rep Power: 1
 
I did a lot of miles two up, with a rear case. On most of my bikes, I lower the front a little bit for steering. I remember cranking the rear of the 919.
Also helps a lot if your passenger has some experience, especially your riding style. It took my wife and I a few thousand miles to get in sync on those hard twisties.
Also had one of those Triboseat grips, so she wouldn't slide into me.

Shmoo is offline  
post #3 of 16 Old 11-12-2015, 01:23 PM Thread Starter
Tesserarius
 
CKutz_GO's Avatar
 
Join Date: Feb 2014
Location: Frederick
Posts: 607
Rep Power: 1
 
Quote:
Originally Posted by Shmoo View Post
I did a lot of miles two up, with a rear case. On most of my bikes, I lower the front a little bit for steering. I remember cranking the rear of the 919.
Also helps a lot if your passenger has some experience, especially your riding style. It took my wife and I a few thousand miles to get in sync on those hard twisties.
Also had one of those Triboseat grips, so she wouldn't slide into me.
well that's a thought. it definitely felt a bit raked out in the front, and i was too hard on the throttle once when passing some cars and got an unexpected wheelie. i like the seat grip idea too because she does slide into me a bit. Takes a while to get used to the new braking distance needed.
I really liked the saddlebags for lower weight, but unfortunately they didn't let her move her legs out and if i was trying to move around on the bike through twisties it didn't work so well. so that made things interesting on the first few bits of twisties. this was sort of a shakedown ride to see how it went and how well we managed the cold. Honestly it took some enjoyment out of it because i had to focus a lot on handling the bike and worrying about how cold or comfortable she was. but the point of it was suppossed to be a learning experience so hopefully we can smooth things out for the next one.
We had our tent and sleeping bags in the top case, sleeping pads, clothes, odds n ends in the saddlebags.

CKutz_GO is offline  
post #4 of 16 Old 11-12-2015, 02:16 PM
Immune
 
Join Date: Dec 2010
Posts: 331
Rep Power: 1
 
I don't do two up anymore, but I do travel a lot with side cases and a duffle bag across the seat. I always cranked the preload a notch or two when I had the stock shock, depending on how much weight I had. The 919 is sprung really light so you need to adjust the preload... or just have the spring swapped out (cost about 100.00 when I looked into doing it) to one with a higher load rating.

jnich77 is offline  
post #5 of 16 Old 11-12-2015, 02:35 PM
LDH
Test Rider
 
LDH's Avatar
 
Join Date: Feb 2006
Location: by the ocean
Posts: 4,327
Rep Power: 1
 

Awards Showcase
Trackday Recognition Referral Award 
Total Awards: 2

You'll end up cranking the preload to max with 2 riders, but with that much weight on the back the front remains light at normal cruising speeds so basically leave the front alone.

If you do this A LOT then I recommend a 60 series front tire as it will offer a better geometry and turn-in when riding with a passenger.

38/34 is close enough for street tires and 300lbs

LDH is offline  
post #6 of 16 Old 11-18-2015, 06:02 AM Thread Starter
Tesserarius
 
CKutz_GO's Avatar
 
Join Date: Feb 2014
Location: Frederick
Posts: 607
Rep Power: 1
 
Quote:
Originally Posted by LDH View Post
You'll end up cranking the preload to max with 2 riders, but with that much weight on the back the front remains light at normal cruising speeds so basically leave the front alone.

If you do this A LOT then I recommend a 60 series front tire as it will offer a better geometry and turn-in when riding with a passenger.

38/34 is close enough for street tires and 300lbs
Thanks for the good info LDH.
by "cranking the preload to max" you mean compressing the spring the maximum amount? I'm getting all noob confused about preload terms. To me it seems 2 up i would want to increase the spring travel which would mean elongating the spring (removing preload). However i also have a bit of physics understanding, and the force exerted by the spring increases based on how much it is compressed..
from doing some googling, it sounds like compressing the spring let's that force lift the rear end of the bike more. did some reading sorta get it.

we took a 1 hr twisty ride last weekend, the rear damping was set to what was comfortable for just me on the street (slightly plush) preload was not changed from the 2nd or 3rd step from the top. fun ride, but a lot of pogoing, not as confident feeling as i'm used to. for the return trip i decided to Harden the rear damping one turn. this really seemed to reduce the pogoing and gave sharper response, granted we didn't take the same cowpath road home, but still did some twisties and it just felt much more planted.
I need to get a better spanner wrench so it's not so hard to adjust that damn preload. the handle on mine is so short, so annoying how the subframe gets in the way too.. I tried to move it a few weeks ago and it wouldn't budge. Is there a specific size that works well?

CKutz_GO is offline  
post #7 of 16 Old 11-18-2015, 07:51 AM
LDH
Test Rider
 
LDH's Avatar
 
Join Date: Feb 2006
Location: by the ocean
Posts: 4,327
Rep Power: 1
 

Awards Showcase
Trackday Recognition Referral Award 
Total Awards: 2

The more pressure a coil spring has on it the more progressive the rate becomes and the spring gets stiffer. You need more rate to hold up more weight.

LDH is offline  
post #8 of 16 Old 11-18-2015, 10:48 AM
Josh
 
Join Date: Aug 2014
Location: Greenfield
Posts: 226
Rep Power: 1
 
Garage
Quote:
Originally Posted by LDH View Post
The more pressure a coil spring has on it the more progressive the rate becomes and the spring gets stiffer. You need more rate to hold up more weight.
Come on LDH, you know that the rate of the spring has NOTHING to do with the amount that it is compressed from it's resting state. The rate of a straight-rate spring never changes, from rest to full bind.

This obviously changes with a progressive rate spring, but you said "a coil spring." Is the 919 shock fitted with a progressive rate spring from the factory?

jmdavis984 is offline  
post #9 of 16 Old 11-18-2015, 10:58 AM
Tesserarius
 
Nickr919's Avatar
 
Join Date: Oct 2013
Location: Corona
Posts: 734
Rep Power: 1
 
Shit where's my popcorn
jnich77, CKutz_GO and Sc0rch like this.

Nickr919 is offline  
post #10 of 16 Old 11-18-2015, 11:01 AM
LDH
Test Rider
 
LDH's Avatar
 
Join Date: Feb 2006
Location: by the ocean
Posts: 4,327
Rep Power: 1
 

Awards Showcase
Trackday Recognition Referral Award 
Total Awards: 2

No, even linear springs become progressive as the displacement increases.

This is an example of a typical linear coil spring and as you can see it still has a rising rate throughout the curve. This is also very similar to what a lot of OEM spring rates look like.



This is an example of a good linear coil spring like we would use on a racebike and it still goes progressive at the end



The more of the linear travel we use up with initial preload the quicker you get to the progressive area to add support for heavier weights. That is a trick a lot of the OEM manufacturers use like Ducati where they take a really soft spring and put a lot of initial preload on it making it harsh, but capable of supporting any weight rider.

LDH is offline  
post #11 of 16 Old 11-18-2015, 11:21 AM
Josh
 
Join Date: Aug 2014
Location: Greenfield
Posts: 226
Rep Power: 1
 
Garage
Ah, gotta love the good old impirical evidence dispelling the myth of theory. Most of my engineering background exists in the same world as frictionless planes and perfectly measurable quantities. A friction free world, where a linear spring has no degradation during compression. Thanks for letting me be wrong without beating me up over it.

Those dyno graphs are actually pretty interesting. Do you know what bike the first spring came from? Is this the difference between a cheap spring and an expensive spring, the stability of the spring rate over full travel? My assumption has always been that a 90 Kg spring is a 90 Kg spring, whether it it come from Ohlins, Showa, or RaceTech.

jmdavis984 is offline  
post #12 of 16 Old 11-18-2015, 11:36 AM
LDH
Test Rider
 
LDH's Avatar
 
Join Date: Feb 2006
Location: by the ocean
Posts: 4,327
Rep Power: 1
 

Awards Showcase
Trackday Recognition Referral Award 
Total Awards: 2

Unfortunately that is merely the difference in manufacturing or luck of the draw in selecting a material to form into a coil etc.

That is why we like to rate all the springs that come in as you never really know which batch is going to be a good one, better than average or even in some cases poor. The good news is when we do find a good batch number then that level of quality is consistent for the entire batch & vice versa for the not so good springs so it's pretty easy to sort out which ones we want to keep etc.

There are also other alloys like Titanium and even carbon fiber coming into the realm now, but it is the same story with them. Manufacturing and material sourcing can cause huge variances in linearity. As a general rule once you get a linear Ti spring it is VERY linear, but the problem is most of them are NOT linear and I have even had one that had a hump in the middle of the graph like a camel. You should have felt what that shock was doing to me!!!

Some more visuals to enjoy

Steel spring 100n/mm vs. Ti spring 100n/mm


Then we add a thrust bearing to one end of the same linear spring and it becomes even more linear which goes back to your observation of friction.


LDH is offline  
post #13 of 16 Old 11-18-2015, 12:08 PM
Josh
 
Join Date: Aug 2014
Location: Greenfield
Posts: 226
Rep Power: 1
 
Garage
Quote:
Originally Posted by LDH View Post
We add a thrust bearing to one end of the same linear spring and it becomes even more linear which goes back to your observation of friction.
First off, Sorry to OP for de-railing your thread. Secondly, I gotta say thanks to LDH for educating me. This is fun.

Spring torque is another factor I failed to think about as well. It is something that airgun and firearm shooters have to deal with too, but on a much smaller/faster scale. Are polished spring seats/ends or bearings common for street bikes yet, or is that still a race only tuning trick for the most part?

That's interesting that you get inconsistent results from one batch to the next, even from the same manufacturer. That tells me they have steel suppliers who provide inconsistent materials.

jmdavis984 is offline  
post #14 of 16 Old 11-18-2015, 12:16 PM
LDH
Test Rider
 
LDH's Avatar
 
Join Date: Feb 2006
Location: by the ocean
Posts: 4,327
Rep Power: 1
 

Awards Showcase
Trackday Recognition Referral Award 
Total Awards: 2

Polishing spring seats is of negligible effect. You just cannot overcome the hundreds of pounds of pressure exerted.

The thrust bearings on the other hand are exceptionally well tasked for it, but they have their downsides too. I do not recommend them for street riders who do little to no maintenance on their bikes. Thrust bearings are steel and have to be greased to resist rust and wear. The grease attracts dirt, dust and debris when it is on there and if you wash it off and the oxidation of the needle bearings starts then you have not only another type of mess, but a bearing on its way to being defective. Racers and hardcore track guys service their shocks at more frequent intervals than street guys so the proper care can be given to the bearings


LDH is offline  
post #15 of 16 Old 11-20-2015, 07:35 PM
Left of Centre
 
K1w1Boy's Avatar
 
Join Date: May 2011
Location: Auckland, NZ
Posts: 3,471
Rep Power: 1
 
Quote:
Originally Posted by LDH View Post
The thrust bearings on the other hand are exceptionally well tasked for it, but they have their downsides too.
Very interesting!

I remember reading about those bearings [Torrington?] when I was riding off-road, wondering about whether their use would make any difference to the rear suspension of my bikes, but never got around to doing anything about it.

Doesn't sound like the off-road environment would suit them very well...

K1w1Boy is online now  
post #16 of 16 Old 11-25-2015, 06:42 AM Thread Starter
Tesserarius
 
CKutz_GO's Avatar
 
Join Date: Feb 2014
Location: Frederick
Posts: 607
Rep Power: 1
 
...just when you think you understand the physics

They throw friction in.

interesting derailment guys. The amount of work, variables, and calculations required to really set up high end race suspension blows my mind.

CKutz_GO is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Wrist Twisters forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome