Sag

[implovator]

Update: I put a much more detailed write-up on my blog. http://www.implovator.com/2013/03/suspension-setup-for-the-new-brammo-empulse-r/

I finally got around to measuring my static sag and rider sag tonight. The Empulse R is a bit of a heavy bike, and so I expected the static sag to be a little high. It wasn't too bad in the front at 30 mm for static and 40 mm with the rider. The rear was pretty soft at 28 mm static and 41 mm with the rider. I'm going to double check my measurements this weekend and try to bring the rear rider sag to 35 mm. I want to keep the suspension somewhat compliant for road use since I've been finding myself cranked way over and going through some pretty bumpy corners.

BTW, I came up with an interesting way to measure rear sag without help from a friend. I strapped a telescoping bolt retriever to the swingarm near the axle. Then I strapped a 1x6 board under the subframe directly above. To measure the full extension, I lifted the bike up while it was on the side-stand until the rear wheel came off of the ground and then I extended the bolt retriever and measured it. Then I took a measurement with the bike off of the stand with no rider on it (the difference is static sag). Then I hopped on the bike with gear and lightly leaned against a wall with my elbow. I carefully extended the bolt retriever again and then I hopped off and measured it (the difference from fully extended is rider sag).

Front sag is much easier if you just use a zip tie as the marker and repeat the same three measurements.

[ttxgpfan]

What is about the industry standard on sag for a Motorcycle? 

In the MTB world we use %.  XC 15-25%, trail 20-30%, and All Mountain 25-35%.  Although those are pretty generic settings.  I used to worry about mm when base lining a customer, but geometries have gotten so slack, and after talking to a suspension tuning company I have calmed down (my old '98 ProFlex is VERY sensitive to sag).  We chatted for a minute and I told him how I had learned some of what I know through the motorcycling community.  He shared that from what he knew of sport bikes racing mm tend to make a difference in sag.  But things we both figured that small differences get amplified at 180mph, much less 200mph.

[implovator]

What is about the industry standard on sag for a Motorcycle?

That's an interesting question. I ride bikes (dirt) a lot myself, and I'm stunned at how much information is out there for the MTB crowd. For instance, I've been trying to get some info on the Marzocchi forks on the Empulse. Most googlery turns up product info for their MTB products. Same goes for tutorials and what not. Perhaps this is because MTB suspension is still in its infancy and the equipment out there is highly varied. For instance, I've got bikes with front travel from 90mm all the way to 200+mm. Maybe it's because MTBers are geekier? Regardless, it's tough to find good info for motorcycles.

But back to the original question. I don't actually even know how much travel the Empulse has. So I don't even know what that magical middle third of travel on the front and rear is. Furthermore, I am rarely ever able to find sag recommendations for motorcycles given as percentages. It's almost always just mm figures. Does this mean that street bikes have all settled in on the same amount of travel?

Regardless of my quandary, I'm just sticking with Racetech's FAQ recommendations given here: http://racetech.com/page/id/30#3

I'm going to try and set my sag to 30 mm front and rear. I might end up with too much preload on the rear though, so I might try to get a stiffer spring down the road. I still don't know what to think about the excessive rear static sag (without rider). Racetech recommends 0-5mm (and their terminology is rear free sag). I don't know if this is due to the Empulse girth, rearward weight bias, or possibly light rear spring.

[Richard230]

The magazine articles that I have read have said that a sag of about 25% of the overall stroke of the suspension gets you in the ballpark for a sportbike.

Here is what the owner's manual for my 2012 Zero S has to say about setting the rear shock sag:

Rear Shock Adjustment
Spring Adjustment:
Obtaining the correct rear spring preload is critical for
proper handling. The spring preload must be set to
match the weight of the rider. The spring is preloaded
for an 82 kg (180 lb) rider. This puts the rear tire 1/3
of the way through its vertical travel. Heavier riders
require stiffer spring rates. A good approximation of
your rear spring requirements can be found by
measuring the rear suspension’s sag. This
measurement will quickly determine if your rear
spring is approximately correct for your weight. This
adjustment is a recommended guideline; personal
riding preference may vary from the specifications
given.
• Checking Sag
1. Support your motorcycle on a stand
with the rear wheel off the ground.
2. Measure vertically from the rear axle to
the rear fender. Mark this spot as it will
be used for other measurements.
3. Record this measurement, this will be
measurement M1.
4. Remove the motorcycle from the stand.
5. Wearing your normal riding apparel, sit
on the motorcycle.
6. Have an assistant hold the motorcycle
up, your feet should be on both pegs.
7. Bounce the suspension a couple of times.
8. Have a second assistant take a measurement
 using the same locations as in step 2.
9.  Record this measurement, this will be measurement M2.
10. Subtract the second measurement (M2) from the first measurement (M1).

Zero recommends 50 mm of sag for their “S” model, which has 140 mm of travel at the front forks and 149 mm of travel at the rear.

(Personally, that sounds too sag much to me.)

There is no sag recommendation for the front forks as their preload can not be adjusted without disassembling the forks and installing a different spring spacer - not an easy task on Fast Ace forks.

I wouldn't be at all surprised if the Ohlins website has detailed instructions for setting sag on a motorcycle, as this information comes with the owner's manual when you purchase one of their shock absorbers.

[implovator]

Holy smokes! I had no idea that the Empulse R was so under-sprung in the rear. I mean, I suspected it was when I took my initial measurements, but I had no idea that it would make such a difference. I finally got around to taking more accurate measurements and setting my sag today. I took it for a quick test ride and it was phenomenal!

Here's my factory setup. I'm using terms from Racetech where free sag is riderless and static sag is with the rider.

Factory:
Front Free Sag: 26.5mm
Front Static Sag: 38mm
Rear Free Sag: 28.5mm
Rear Static Sag: 51.5mm
Rear Threads Past Collar: 8mm

My goal was to get to the middle of Racetech's street recommendation which would would have been a front static sag of 32.5mm and a rear static sag of 32.5mm. This seemed pretty feasible for the front, but the back was going to have to come in by a lot. This is what I ended up with.

New:
Front Free Sag: 22.5mm
Front Static Sag: 33mm
Front Preload (turns from initial): 3
Rear Free Sag: 19mm
Rear Static Sag: 41.5mm
Rear Preload (threads past collar): 12mm

I ended up stopping way short on the rear end, since I felt uncomfortable adding so much preload. If I don't think it's perfect after doing a few rounds of dampening adjustments, then I might order a new spring for the rear. I think the springs for the front are just fine.

Riding Impressions:
When I first got the Empulse, I thought the back end felt harsh. I mean some of the bumps were bone-jarring. I'm not that heavy at 165 lbs and so I just figured the backend was really stiff. Well no it wasn't. The backend felt harsh because it was so deep in its travel that it was probably bottoming out. After making this adjustment, the big bumps are very distinct, but the rear end now works to suck them up. It feels like a sportbike should. A sportbike is not a touring bike and so it doesn't mask the bumps. It just makes them less catastrophic. I also found the backend to be way smoother over high speed highway bumps. Overall, it's just way more compliant.

My turn-in was affected a little. With the additional preload, it takes more rider input to get the weight bias forward when turning in. So now I just go in hotter and trail brake more.

I'm getting more squat mid-corner once I roll on the throttle and so I have to use my weight to keep the bike leaned over since the front end isn't pulling the bike in. This probably has something to do with the backend being a little soft still. I think I like this though. I feel a lot more of my weight being supported on my upper leg now as I'm pulling the bike down into the corner. In a sense, I'm adding rake to the front end. which is one of the first things that a decent chassis tuner will do in order to gain mid-corner stability and rear grip on exit.

The mid-corner stability is pretty phenomenal now. I have a 270 degree ramp that I take on commute home every day. I took it at about 5 mph faster today...and I haven't even touched the clickers yet.

Final Thoughts on the Rear:
I'm trying to figure out why the factory sag was so atypical for a sportbike.

Theory A - It matches the Triumph Street Triple at 50mm rear (according to some guy on Youtube).
Theory B - The Empulse R has a greater-than-normal weight bias to the rear. Anyone know the percentages?
Theory B - Sachs sells their shocks with a standard spring that's appropriate for ICEer like a Ducati Monster but not the somewhat heavy Empulse.

[7racer]

When I was listening to the webcast from ttxgpp both the riders mentioned that the suspension needed be changed due to the different weight distribution and higher weight.  So maybe that's why Brammo set this way out if the box?  Maybe we need a different algorithm for electric bikes?  Do people shock dyno and weight balance bikes like in cars?

[implovator]

When I was listening to the webcast from ttxgpp both the riders mentioned that the suspension needed be changed due to the different weight distribution and higher weight.  So maybe that's why Brammo set this way out if the box?  Maybe we need a different algorithm for electric bikes?  Do people shock dyno and weight balance bikes like in cars?

You can usually find information about weight bias on mainstream models. I think that most sportbikes are around 51% front. I was reading a review of the 2013 Street Triple that said they changed the weight bias to 52% front from 49% front. I doubt that any amateur or privateers adjust weight bias at all. The classes with weight restrictions might cause some factory pros to add ballast, but many privateers are probably too broke to lighten their bikes to need ballast in the first place.

I've never had a shock dyno'd, but I'm sure that some suspension shops offer it. Heck, I know of bicycle suspension shops that dyno their stuff. Crazy. I had a really good suspension/chassis shop when I lived in Florida, but he didn't have a dyno. He did have a Computrack system for chassis measuring and setup. It was pretty trick.

Back to your point about weight bias, I wouldn't doubt that the Empulse R is rear-heavy so maybe some extra free/static sag is perfectly acceptable. Like I mentioned earlier, I'll definitely give the stock parts a solid chance and try to get a good setup since I don't like throwing money at my problems. I have a hunch that I will end up getting a new rear spring, but I don't want to order something until I get more information like weight bias, eye-to-eye extended/compressed shock length, and rear-end travel. Hopefully I can get the spring off without a compressor. I'll keep everyone posted. I've been taking pictures too, so maybe I'll do a writeup.

[ttxgpfan]

When I was listening to the webcast from ttxgpp both the riders mentioned that the suspension needed be changed due to the different weight distribution and higher weight.  So maybe that's why Brammo set this way out if the box?  Maybe we need a different algorithm for electric bikes?  Do people shock dyno and weight balance bikes like in cars?

Link?  thx

[7racer]

When I was listening to the webcast from ttxgpp both the riders mentioned that the suspension needed be changed due to the different weight distribution and higher weight.  So maybe that's why Brammo set this way out if the box?  Maybe we need a different algorithm for electric bikes?  Do people shock dyno and weight balance bikes like in cars?

Link?  thx

lol it was your webcast!!!  Sorry spelled your SN wrong
but I did actually listen to all 3 hours of that!
I think Shelina mentioned the suspension the most and the difference than an ice bike.  Am I wrong?  Did I miss interpret the convo?

http://brammoforum.com/index.php?topic=1952.0

[ttxgpfan]

Oh!  Haha.  I was wondering who the heck the TTXGP were putting out a competitor podcast.

Hmmm, no I think you are thinking about Eric and I talking about how different the chassis has to be.  And what we meant was more the frame and swing arm design and how the forces an electric motor places on the bike are different than an ICE motor does, and hence need to be designed differently.  The suspension is an important part of the chassis as I understand it, but in that sense the suspension itself wouldn't be that different.  I had heard from one racer that the weight of the elmotos were what was holding the bikes back from fast lap times, and I asked Eric directly, and that's what lead us down the chassis path.  Shelina and I did talk about it as well, but as it was conversation from 1-3am I don't recall much of it.

BTW, thank you for listening.  I'd appreciate a like on facebook or a follow on twitter if you do that sort of thing.  You can even sign up for e-mail alerts if you don't do either of those things and have any interest in following my blog and podcast.

[implovator]

I got a chance to get the Empulse on a shipping scale today .Brammo has given us a balanced 50/50 bike! Solid!

Front: 209.5 lbs.
Rear: 208.5 lbs.
Bias: 50.12% front

So much for one of those theories about the extra rear sag being due to rearward weight balance. This also means that I'll probably end up getting a new spring for the rear. I'm still going to wait until I'm done twiddling knobs.

[protomech]

418 pounds? Did you already wear 52 pounds off the tires?

Brammo still lists the Empulse at 470 pounds on their website fwiw. But specifications may not hold up in the real world..

[implovator]

418 pounds? Did you already wear 52 pounds off the tires?

Brammo still lists the Empulse at 470 pounds on their website fwiw. But specifications may not hold up in the real world..

LOL. Actually I think it has more to do with the fact that I didn't have a full tank at 59% SoC. O_o

I'm still mystified by the descrepency. I'm guessing the accuracy of the scale could be off.I do trust the precision, so I figure this is good enough to determine the bias but not the total weight. Maybe someone else can weigh theirs?

My procedure was to place one wheel on the scale and the other wheel on a stack of wood at an equal height. I took the reading and then flipped the bike around.

[flar]

418 pounds? Did you already wear 52 pounds off the tires?

Brammo still lists the Empulse at 470 pounds on their website fwiw. But specifications may not hold up in the real world..

We've also been given different motor torque numbers than are listed on the web site and the charge times listed in the provisional manual are different from the spec page.  [confused]

[implovator]

I dialed another 6mm of preload on the rear to bring the static sag to 35mm. Big hit response was greatly improved again. Bad bridge joints at 70 mph were a pleasure. It was absolutely planted in high speed corners. Low speed bump response in corners was sacrificed. That was to be expected, but I'm still going to try and work on it with damping. All in all, I'd say 35mm rear is perfect for aggressive street riding. 40mm might be better for folks more concerned with comfort with still good performance.

Now that I know what 35mm of static sag feels like, I'm going to go ahead and order a new spring since I am likely sacrificing travel. To choose a new spring, I think I'm going to take a bunch of measurements on the shock dimensions and swingarm geometry. Racetech has a couple of forms that you can fill in with your info and then they'll run the numbers and ship you a spring. If I can get my hands on a spring compressor, I'll pull this shock this weekend and get the measurements. I'm post up the numbers.