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Has anyone put a Boxxer on a dyno?

nybike1971

Chimp
Nov 16, 2006
67
0
Niskayuna, NY
I would like to know how well tuned my ReStackor model for the compression base valve of a Boxxer 35mm is. If anyone has a dyno run of a Boxxer 35mm in any recorded setting that they can share (I seem to remember SteveM mentioning these measurements) I would appreciate it.

Cheers!
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,915
1,200


Unfortunately I think you'll find that given the cost of dyno ownership, most people that own one won't be willing to publish their findings online for all to see.
 

atrokz

Turbo Monkey
Mar 14, 2002
1,552
77
teedotohdot
11 horsepower.

The stickers on the WC add an additional .5 HP.

Also, I'm sure someone has tested one on a dyno, but I doubt we'll see the results any time soon.
 

Vrock

Linkage Design Blog
Aug 13, 2005
276
59
Spain
The funny thing is that if you like sport cars or motorbikes you can find Dyno plots of most shocks on-line and a lot of good discussions in their forums, If you like MTB you are only going to find marketing stuff, nothing useful.
 

nybike1971

Chimp
Nov 16, 2006
67
0
Niskayuna, NY
Darren that would be awesome! Basically, I have measured the shim stack, compression base valve geometry, and taper of the needle to model the compression damper in ShimRestackor. I am trying to have a more quantitative approach to reshimming and tuning of this fork and suspension in general.

The fork I have is a 2010 Boxxer Team. ShimRestackor struggles with the modeling of the preload on the high-speed shimstack but it's not hard to account for that by hand (I have measured the spring constant of the preload spring and the displacement per HSC click).

Ideally, what I would like to see are a few runs of this sort:

---LSC--------HSC---
1 turns out 0 clicks in
2 turns out 0 clicks in
3 turns out 0 clicks in
1 turns out 4 clicks in
2 turns out 4 clicks in
3 turns out 4 clicks in
1 turns out 8 clicks in
2 turns out 8 clicks in
3 turns out 8 clicks in

any subset of that would be incredibly useful and educational for me.

I built a suspension data logging system last season and did some measurements on this fork with a few shim stack configurations and peak speeds I was recording where in the 3 to 4m/s range (logging speed set at 800Hz). I don't know how fast your dyno can go. If you can see the transition from low-speed to high-speed that would be perfect.

By the way, I am working on the second version of the data logging box right now, it should be more compact, a bit faster (up to 1kHz), and with USB output so it's easier to use in the field. I'll be happy to send you more details if you are interested. This is all for personal use, just playing around for fun and learning something about suspension tuning. Dave Weagle pointed me to Active Sensors, where I bought the linear position sensors.

Thanks again!

Luca
 
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ocelot

Monkey
Mar 8, 2009
395
10
Canadastan
WTFUXORZ

I doubt a DH bike's ride frequency is even in the double digits. Why are you using 800hz?

You should do a complete adjustment sweep in divisions of HSC and HSR.
For example, 1 HSC/1 LSC, 1 HSC/2 LSC, 1 HSC/3 LSC, etc.

If you possess the skill and knowledge, you can build a model of your bike in matlab or some similar program, and play around with the suspension settings off the track :)
 
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mtg

Green with Envy
Sep 21, 2009
1,862
1,604
Denver, CO
WTFUXORZ

I doubt a DH bike's ride frequency is even in the double digits. Why are you using 800hz?
Ever heard of aliasing?

When I used to do data logging on race car suspensions, we logged the linear pots at 2000 Hz to get good data. And, while a typical race car has higher ride frequencies than a DH bike, they are still in the same ballpark. If you want to capture a decent representation of a dynamic system, you need to log at least 10x faster than the highest frequency you want accurately represented, which is going to be far higher than the primary ride frequency.
 

mtg

Green with Envy
Sep 21, 2009
1,862
1,604
Denver, CO
Ha ha, woops. I wondered how somebody would understand ride frequencies but not anti-aliasing.

800 Hz natural frequency would make for a bumpy ride!
 

nybike1971

Chimp
Nov 16, 2006
67
0
Niskayuna, NY
I know what you are saying, I just didn't want to ask for too much from Darren. Any one of those measurements will give me the information I am looking for to make sure that the valve measurements I took are in the right ballpark. The taper of the low-speed compression needle is particularly tricky to measure in the mission control damper.

This is the damping profile I get with the stock 2010 shim stack, HSC full open, and LSC 1 turn from closed (diamonds) and 3 turns from closed (yellow line):

Screen shot 2012-03-26 at 7.40.13 PM.png

If I were to guess, the forces seem a bit on the low side, but not by a factor of 10. I am looking for a dyno run with the same setup to calibrate this model.

Also, as far as the data logging setup is concerned, yes 800Hz is the sampling frequency. It's pretty simple to estimate the sampling rate necessary to have the resolution to measure big events and it's in the kHz range (for example a high speed impact that displaces the fork by 2in at 4m/s will require a sampling rate of 800Hz if you want to acquire 10 points over the course of the event).

Here is an example of an acquisition displayed in phase-space (position/velocity space as a function of time, I wrote the data analysis software in MATLAB):

phase_space13.jpg

You can see the temporal resolution of the measurements starts becoming limited close to highest-speed events.

These are the position and velocity traces for the same run:

pos_vel13.jpg
 
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