Nate Kern's R12S front spring issue
 

All:

What is going on with this R12S front spring? The point of the telelever is that it is has Anti-Dive geometry. It should not bottom out under braking...right?

Could the front shock be lengthened (raise the front) to increase the Anti-dive effect - no spring change necessary?

Or is the main problem that it lifts the back wheel?

Are we thinking about this as a "conventional" suspension rather than the unconventional design that it is?


For some reason this issue is really bothering me. Please chime in if you think you have figured this out...

Feeling like part of the team...! :)

best,

Dave
99 R11S

Thank you David, I know the Tele lever is a better design, and sometime I have to argue this with even previous BMW Boxer Cup front runners...

One massive strong front spring (shock) vs. conventional flimsy springs are awesome for real deep straightline braking. The fact that the spring rate is to soft is due to it being a street spring. The speed carried and the amount of brake force I use coming into a corner, prety much bottoms out this spring, lifting the rear and causing me not to have enough travel left to brake more efefectively (meaning I cant get her slwoed down soon enough).

I really hope that BMW can see and taste the # 1 plate for a National Championship this bikes first year out. I need some easy development done with Ohlins and walla, we have the right spring for the job and I can hopefully just check out on the field.

Im really happy though regardless how hard I have to ride with the new bike!

I rode my set up R11S with Thousands inot it, and the R12S went 2 seconds a lap faster, stock.

I LOVE my (NA's) R11S, IT IS THE PERFECT 50/50 BETWEEN SPROT AND TOURING!

I still think it look sbetter to but you didnt hear me tyoe that, lol

There is a new blo that was creatd for us by BMW.

PLEASE post your thoughts and support there, very accuratly monitored!

www.nate-kern.blogspot.com
Ok, Im going to go ride the R12S around a lake here and get the new ceramic clutch broken in.

N8!

While the telelever is very good at accomplishing its goals, it can't do everything for everyone. Meaning if you are very aggressive in the corners the front spring needs to be stiffened to prevent the bike from squatting as it takes the corners. The shock can be shimmed up for more ground clearance, but that does not make up for a soft spring and aggressive riding behavior. Therefore stiffening the front spring is recommended. I for instance have a very stiff front spring on my R11S which is the same stiff a$$ spring on Nate's thunderbike. The problem with the new R12S is that the shock body is shorter and makes it harder to find a spring that will work properly in a stiffer range. It looks like Nate was able to get the 85nm spring to fit on the front today and he is testing it out as we speak, I will have a go of it myself later in the day. The new R12S has what we call more leverage ratio on the front end as BMW has changed the rake and geometry slightly = longer wheel base and slower turn in. So consequently it may require even a stiffer spring in the front then the currently tuned R11S's have despite the R12S being a tad lighter. The standard Ohlins front spring for an R11S is 57nm and both Nate and I are running an 85nm (along with a few of our customers) and the R12S comes with a 62nm spring on the OEM Ohlins front. So,....it's apparent that even BMW and Ohlins agrees the new front Telelever found on the R12S needs a stiffer spring then the R11S even though the R12S is a lighter steed.

sounds like you guys have it sorted out then... I was going to offer the 85 nm spring that I have, but it seems moot. good luck, guys!

Hi N8 and all,

OK, obviously Nate could ride circles around me in my sleep, but I'll comment anyway.

I'm with DS on this one. Given the geometry, very little dive is happening due to brake forces alone, which means that an increase in spring rate can only have so much effect. (although it does stand to reason that IF this is the chosen method to tackle the front end issue, that you would indeed need a very large spring) That is not however w/o other handling consquences.

Is the problem truly dive proper, or is it the rear trying to rotate up and over the front, as I suspect it is???

Either way, until a spring that makes you happy can be found, you should be able to get some of the desired effect by raising the front a bit with either preload, or a spring spacer, or an upper shock mount spacer, or, worst case, a lower mounting weld job (top of telelever)

Similarly, a slight drop in rear height would help too. A bit more rebound out back would help further, as long as you're not already experiencing significant rear traction issues, or packing down. A bit more compression up front is worth considering too.

Lastly, do we have full desired spring dimensions? If so, there's always a chance someone might have something suitable, or that could be made suitable with a simple machined collar. If not one of us, then maybe somone at PPR or PPS or GPS or Dan Kyle, or if you can stand the abuse, Traxxion :)

Thoughts?

I wish I had even a 1/4 of Roger/Gigantic/Bobby (BMW ATL) brain power and still ride the way I do...

You guys are great and reading helps me with new perspectives.

I will say again, BMW Atlanta is a true BMW riders shop! I cannot thank them enough for their support and interest in the universal cause all of us BMW riders have! TO ENJOY LIFE THROUGH RIDING!

N8!

(Im smarter than I look, right Bobby?! LOL)

So apart from the shock ratio change, what I think this is telling me is that the front suspension could have less anti-dive (more dive) built in than the previous bike's geometry.

The more I think about it, it looks like the levels of braking in racing overcome the anti-dive in both old and new bikes - hence the move to stiffer springs.

What I'm wondering is: How could the hardware (geometry) be changed to dial in more (or less) anti-dive?

best,

Dave
99 R11S

Everything comes into play in that regard from the angle of the telelever at ride height to the length of the telelever and forks.

Computrak had to dial in 10mm of preload on that 85nm spring which is HEAVY to just install it on the shock at a minimum. So its looking like its on the too stiff side. I think Nate will go back to the stock spring, shim the shock up for ride height and dial a little more preload into the front and raise the rear back up as it has been lowered previously to balance out the front.

A shadetree way to stiffen up the spring you've got is to cut some coil length off of it; this is the hack way we usta do it at the track 'back in the day'. start with 1/2 a single coil length. Use an air-powered cutoff wheel in a die grinder and shoot a garden hose on it as you cut to keep the metal cool so you don't screw up the heattreat.
youo will have to fab a spacer to get the overall spring length back to stock; this is NOT preload. preload and spring stiffness are 2 different things, but often confused. I've gotten a spring 10% stiffer by doing this until I could get a proper replacement.

BTW, if they don't have a fuels test, 4OZ per gallon of price fuels max race (at www.pricefuels.com) is a tasty way to pull some HP. if you run brew, don't forget to yank the 02 sensor(s) so you don't poison them.
In the day, yosh used to always 'enhance' thier fuel with various nitromethane formulations:)

oops, here's the correct link:
http://www.pricechemical.com/max_race.htm

hehehehehehe:)

As Roger A. mentioned, is it possible Maxx at Traxxion Dynamics in Woodstock might help find a solution????????

The rest of the entire motorcycle world uses forks. They will not understand.

The knowledge to make real progress (OPEN the TUNING ENVELOPE) on these issues resides with BMW in Germany. They have already modeled many of these events to understand "limit handling". There is a development team that came up with the current geometry, modeled it, tested it, and can easily run the model again for racing applications...Can we drum up some support from them?

BMW are you listening??????

:)

best,

Dave
99 R11S

I was being a smartass listing Max/Traxx.
As DS mentions, they're not the right source for telelever bikes.

max is cranky under the most Ideal circumstances... down thataway, Thermosman is the only way to go, at least for regular bikes...

Hey N8

Some of us would gladly trade 1/4 of the brain power for 1/4 of the riding stuff. I'm pretty sure I'd be coming out ahead.

Also, for others, I just received some pix of myself at Barber.
Looking at my body positioning, they could serve well as counterexamples.


Grrrrrr

Thermosman is the Man! He has gotten so big that now he is not as obtainable as before :(

I know for a fact we need a 190mm spring regardless.

Nate

Not even close unfortunately, they do great service work on shocks and I live 6 miles from their shop. We send alot of our shocks up to them for service/rebuilds but not custom set up without our specifications. But for any custom tuning on a BMW telelever you're barking up the wrong tree.

Well Ok then....... I just thought they do a lot of set-up and do a lot of suspension/ shock work and tuning. Figured they might have a way to customize a spring or two for Ohlins or whatever........ There's a shock on the back and one on the front...... right??? Figured if Nate told them what he wanted they might be able to make it happen. And they are close to y'all. Just a thought. Hope it all works out.

Good runnin' to Nate!! We rootin' for ye!

Is there any chance you could use RR's idea of cutting down a spring on the 210mm to make in an 85 Nm 190mm?

Is a spring rubber like NASCAR uses out of the question?

On geometry, consider the fork tubes as the hypontenous of a triangle. With springs in the tubes, they compress with both horizontal (braking) forces and vertical (weight = mass x acceleration) forces. The Telelever, Earles and Duolever transfer the horizontal forces to the frame without (much) spring compression (how "much" depends on how horizontal the arm is.) Vertical weight forces compress all designs, and remember that at head dragging speeds there's a lot of centrefical acceleration that to the spring makes the bike look heavier. (Note that I'm calling vertical reletive to the bike whether it's leaned over or not.)

And finally, since this is post #1 for me here, if you think passing "fast" modern sport bikes on a race track is fun on a new BMW (All oilheads are "new" to me), you should experience it on Vintage! So N8, I hear you're just a super nice guy, but if they're not faster than you and your gummy cow, they won't talk nice to you at the track.

i do not have access to my shop right now, i have two sets of ohlins for my 02 r1100sa, i believe that Ram Jet has the spring specs for both sets, one with Eibach springs one with official olies springs, i was diving the front end too far / hard on the street, have a similar problem to what is being described here,, increased F&R shock spring rates fixed that.
I will loan the spare shocks or springs if it is needed or is in time.
For the left coast, Lindeman and Kyle get it done right.
Kyle seems to have excellent access to spare springs, ohlie factory stuff.

Yeah, one would think and Max is too busy running the place to do it himself these days. Which means I spent 10 minutes yesterday trying to school one of his guys on BMW's and that the front shock actually has a 62nm rate spring to which his reply was front springs numbers have nothing to do with rate which is the case on fork springs,.........not Ohlins front SHOCK springs as found on the telelever.

Appreciate all the suggestions, however Ohlins doesnt do custom set up for BMW's, they only apply known good set ups and since their name isnt on the side of the bike there's too much cost for them to make a custom spring. Try calling Ohlins and asking for a stiffer spring on an R1100S Ohlins,...they will fight you to the end and not reccomend an 85nm front spring. Yet it's a known good set up for Nate, Myself and many others. However Kent at Computrack is much more willing and able to help and will be custom ordering a spring if the out of the box Ohlins spring turns out to be the wrong application on this new R12S. This new R12S front end is a bit different then the old. We can use some of the same tricks, but the geometry is different enough to have to relearn what to change. Between the newer gen Telelever and Paralever, its a challenge!

Already been considered, but would most likely make the front 85nm 200mm long spring we have swapped in too stiff. The other possible option is to lengthen the front shock internally to alleviate some of the pre-load in order to manipulate the telever/sag/leverage geometry. Second option is to shorten the stock front spring to stiffen it as there is some room on the threads to loose spring length and gain spring rate as a trade off. I think the ideal spring is going to be about 75-77nm in a 190mm length. That will have to be custom wound.

Ohlins doesnt make what we need. Not in the USA and not in Europe according to their charts. Everything in the rate we are looking for is too big of a diameter to safely fit on the shock body.

>
Which means I spent 10 minutes yesterday trying to school one of his guys on BMW's

BTDT. Funny, eh?

Again, if someone would get me the full dimensions, I might could come up wth the spring (custom). Nate's bike might need to run an extra sticker or two though.

So, k=76 N-m an l=190mm, right? I.D needed to fit spring seat properly (both top and bottom?) Max allowable O.D. to provide other needed clearances (both top and bottom) ??

Let me know. No guarantees, but...

Ya, know, I can't contribute squat to this thread, but I wanna say:

This has gotta be the most awesome thread I have ever seen on any BBS anywhere

Freakin' awesome! Go N8!

An interesting article about anti-dive can be found here:
http://www.tonyfoale.com/Articles/Dive/DIVE.htm
So if BMW changed the CoG position (and I think they have; doesn't the new S has more weight on the front?) then the anti-dive characteritic is already altered. Setting up a bike with a different front suspension then teles is difficult because the bike tends to react different to input parameters.

Hugo