Salt flats surface conditions, going fwd

[gschuld]

I realize this is a touchy subject, with lots of material to read from various sources from an array of points of view (I?ve done my share of reading up FWIW).

From the perspective of a new guy(salt wise) from the east coast US, it would be helpful to get an idea of the likelihood of having a quality salt surface going fwd.  Luckily I?m interested in the sub 200mph range for a vintage class with a shorter track requirement than the really fast classes out there.

It must be super disappointing to put in all the hard work in, the money spent, then schedule the time, make travel/lodging arrangements, only to find the salt conditions either totally unsuitable enough to cancel or just rough enough to make it far more dangerous and unlikely to be able to break a record on.

I get that this is part of the game. You can have fantastic salt depth, then it can rain like mad just before the event and leave a lovely salty lake surface.

I have to admit, a part of my drive to compete is the concern that we may be facing a worsening future regarding the race course conditions and I?ll have missed out and will regret it if I don?t do it while I can.  Is this overly pessimistic thinking?

Thanks in advance

George

[Stan Back]

It's not going to get any better by waiting -- nothing is happening to make it better.

And, indeed, you won't know heading there what the conditions will be.  We've driven to a World Finals meet, had the Driver's Meeting, and then had the meet cancelled 15 minutes later.

So you just have to take your chances.  Once you've been there, and run, you'll never regret it.

It's a crapshoot, and nothing's gonna change that.

[wobblywalrus]

Try to be at the BMST for the full event length.  Some days are better than others.

[bearingburner]

Come up to Loring ME. The surface is excellent and the tow is shorter. The course is only 1.5 mile.

[gschuld]

Bonneville is a unique place that draws me.  I?ve considered Loring as a shakedown opportunity however.  Others are currently involved at BMST that I?d very much like to join.

There is just something about the salt...

George

[kiwi belly tank]

You're right George, it's a special place so just do it while it's still there. There hasn't been "salt depth" there for a few years now, at best there is 1" of crust & the weather leading up to & during a meet dictates how it works.
  Sid.

[Happy Pappy]

3rd. year in land speed racing, 1st. year with my own build. Regrets none, concerns... Sure I considered the rapid decline of both venues, Bonneville & El Mirage.
Jim was right on target writing... "So you just have to take your chances.  Once you've been there, and run, you'll never regret it."
 Looking at your profile I suspect you have been interested for at least 8 years. Try not to wait another 8. 

[wobblywalrus]

As light an unsprung weight as possible.  That's the wheels, axles, brakes, swingarm, and fork lower tubes, rear sprocket, and anything else below the suspension springs.  Good suspension with separate settings for high and low speed damping.  That is the formula for just about any competition bike from road racers to dirt bikes running down the Baja peninsula.

Spring rate varies quite a bit based on rider and tuner preference with some opting for straight rate and others for progressive.  Straight rate has worked best for me at B'ville.

Suspension travel varies with longer travel for off road bikes and shorter for pavement racers.  About 4 to 6 inches travel at the axle seems best for the salt flats in my experience.

This is a set of guidelines for rough conditions that should not be a handicap if the track is smooth.  Specifics of damping, preload, and spring rates are different subjects.  Opinions vary on this topic with successful people doing different things.   

[gschuld]

Good points.

4-6 inches of front and rear suspension travel seems like a lot🤔. I was thinking 2-3 would be about right.

I realize the salt is fragile and unpredictable at this point.  I?m not driven enough to go to Bolivia for great salt...so I hope Bonneville holds up for the sub 200mph club anyway.

Yes, I?ve been curious for years.  I shifted other priorities in front of salt flats racing over the years. Easy to do since the time/money/travel efforts spent to track time ratio is truly tragic for this type of racing.  Hell I think it might be worse than ice boat racing(I have enough experience in that sport to know better)🙄

George

[wobblywalrus]

The guys that go faster than me in my class all have better suspension than I do.  There have been a few years when the salt has been rough or slushy and some folks managed to set records in the competitive higher speed classes.  The bikes they used tended to have modern sophisticated suspension.  An old rule of thumb is to get x number of inches of useful travel the actual travel would be an inch or two longer.  That allows for some heavy damping at both ends of the travel to prevent clattering when the suspension tops or bottoms out.  That travel near the ends is not considered to be useful travel.  It is only used in the more extreme circumstances.  The suspension travel of a Hayabusa might be a good starting point.  Those bikes go fast in all conditions.       

[gschuld]

Your thoughts bring up a subject that has been on my mind.

Lightweight wheels, swingarms, brakes etc are very clearly beneficial to road racers and to a lesser extent, street bikes.

The salt is unique since light overall weight becomes a deterrent to speed at a certain point. Say ...200mph on up. All signs have pointed to needing to ballast the bike in an effort to force more traction into the rear tire.  I get that the difference between 700lb all up weight and 775lbs all up weight means next to nothing in top speed capability, it just won?t allow you to accelerate as quickly. But on the salt, accelerating quickly is impossible for obvious reasons.

What gets me is the weight in/on the swingarm.  The more weight on the swingarm, the less the rear suspension can dampen properly.  Rough salt surfaces would I?d think make a ballasted swingarm rear suspension run very harsh, close to a rigid rear perhaps.

I would think ballasting the frame near the rear tire and down low  (and fwd to balance if needed) and keeping the wheel/swingarm weight low would allow far better suspension action and improving both ride quality and traction as a result.

As ballast needs rise to counteract more and more engine power, I guess there is no other choice but to ballast the arm directly.

Most bikes up to the 150mph range don?t seem to use much (or any) ballast with a good F/R weight bias of around 50/50 or so.

It?s the 150 to 180mph range I am looking toward.  I?m assuming for a 50/50 or so F/R weight bias on a 63? wheelbase (M Classic class) and 110-115 RWHP N/A (Nitrous could add 30 to that for fuel) at sea level, needed ballast should be fairly minimal, and ideally any ballast would not be added to the swingarm but on the chassis so the suspension can work at its best.  High quality and adjustable rear shocks of the right spring rate, and top quality front forks are ideal.

Am I overthinking this?

George

[tortoise]

I would think ballasting the frame near the rear tire and down low  (and fwd to balance if needed) and keeping the wheel/swingarm weight low would allow far better suspension action and improving both ride quality and traction as a result.
George

Controllability on bikes (cars, too, actually) is improved by centralizing mass as nearly as possible to a point, reducing the polar moment of inertia. Ballast for traction should be placed at the C/G height of the existing bike/rider package. Putting it on the swingarm is pretty close to where you want it, heightwise. I agree with you that it should be sprung weight, though.

[mc2032]

This bike has about a 50/50 weight split and tips the scales at 800 lbs rider and bike.  We have about 50 lb of lead on the swing arm because 1). it was easy and 2). no real good place to hang it from the frame.  We have a gsxr 750/1000 front end set on the soft side of factory specs.  I put a ny tie on one of the fork tubes and slide it up to the seal before each run and try to remember to check it at the end of the run.  Driving thru the crunchies usually voids any real info but on the few runs I stayed on the smooth return roads, I saw 2 inches or so of travel at the front.  Pictures of the bike down track show the rear end squatted pretty good.  Data downloads show little if any tire spin and the rear tire did not show any evidence of spinning.

[Doc B.]

To save you guys a little Google time regarding the Busa here is something lifted from the hayabusa.org forum.-

"The Actual Suspension Travel Specs" for the Hayabusa are...

FRONT: 4.7" (120mm)

REAR: 5.5" (140mm)

[gschuld]

Thanks for the thoughts.  FWIW, my friends Cb750 is reportedly a bit front biased weight wise but with 80RWHP at sea level isn?t having too much in the was of traction problems other than in gears 1-4. Once in 5th it doesn?t seem to be a huge issue.

Classic class Modified.  Held CG, CF, MPS CG, and MPS-CF records until 2019 when he lost 3 of the 4 by 1-3 mph to a Triumph.

148 was top speed in MPS.  All motor, nothing spicy for fuel class.

George