Flex and its role in slalom

[John Gilmour]

There are a few things going on in regards to flex.

Firstly in regards to the road we have several different kinds of things going on- in regards to flex in the system and maintaining the "correct suspension" ie road contact.

1. We have to absorb the larger surface imperfections in the road (cracks bumps etc.)

2. We must maintain contact with the road surface despite the surface abnormalities on the near micro scale.

3. We must adjust our suspension for differing g-forces through the turn and the effects on turning.

SO for "1" our "macro" suspension is our legs and we endeveor to absorb cracks in the pavement by "deweighting our decks". Since we don't have true shock absorbers and Independent suspension we must deweight the entire deck (not so good a way to deal with it) it would be like comparing how a regular car handles potholes and how a guy in a "hopping lowrider" might try to "pre hop" a pot hole ever so slightly to not bottom out his low ride.

Number "2" handles the courseness or "pebbleyness" of the road. This is optimized through durometer choice- and the thickness of the supported and unsupported uerthane on the wheel. Obviously the ground is not as smooth as glass so our traction patch is reduced. We want enough deformation into the surface to increase our traction patch, but not enough to mush in front of the wheel (Ie pushing a wavefront that is optimally too large relative to the diameter of the wheel) Such a overly deforming wheel would be slow. Go too hard in the wheel or too little supported and unsupported uerthane and you are only riding the "peaks of the pebbles" and with such a small contact patch you can "wax out" during a turn. Not to mention it is a hard ride.

Obviously the more level the asphalt is- the harder a durometer you can run- except to the point of running too hard a wheel which "deforms the pavement on a hot day" and pushes a "pavement wavefront" (yes its on a very micro scale- but sinec pavement is so much more viscous it doesn't take much of a wave height ot have a similar effect)in front of the wheel - also bad and slow.

In "3" we see how the cornering affects grip of the system. in a hard corner we exert more lateral force on the ground and urethane. In a ZERO flex deck the ability to "dole out" a smooth progressive increase in pressure that is perfect in regards to the arc of a turn is limited by the prowess of the rider. And for the harder and faster the run the harder it is to "modulate" the amount of force needed.

Most riders opt for having the FLEX deck do this by loading the deck and having the deck "remodulate" the force to the pavement. Also the deck may be able to assist in "remodulating" the force better than the rider can. For instance....we could all throw a spear, and certainly we could throw a spear the size of an arrow- but using a flexing bow helps to convert one aspect of our fitness into another. Ie we are converting Strength into Quickness- using the flexing bow for conversion.

How the bow accelerates the force is a function of the design of the bow/flexing skateboard and the duration of the speed is the "pop- period" of the deck. The shorter the "pop-period" the better the deck is suited to short turns of fewer degrees at high fequency (TS). The longer the "pop-Period" of the deck the better the deck is suited for drawn out turns that take a while to complete (GS).

Strangley enough....when the turns are very long and wide and drawn out- though small in degrees- we have a turn that is "Slow" enough in terms of building g-forces to react using our body. Such an example would be akin to using a servo controlled subwoofer because the waves are at a low enough frequency for a slow servo to be considered "fast acting" for such a system. Our legs can react fast enough at long drawn out turns in Super G and so long travel flex can become uneeded in these situations- especially where the deck could hit a resonant fequency. (look at how the rider lowers himself in a super g turn and how bent his legs are- he is "human suspension" and pavement changes in terms of very elongated waves are treatable using this riding style- extreme flex would be more a detriment than a help)

Lastly in "3" the wheelbase ELONGATES during high flex- the center of gravity LOWERS and the turning geometry of the trucks INCREASES. Hmmm sounds like we are making any deck more into a GS deck ie longer wheelbase, slightly increased turning geometry for both trucks, and lower camber. And indeed this is what happens.

We are making our board more suited for the longer turn by altering the boards characteristics while riding it- simultaneously increasing our traction by deforming the wheel with downforce (as opposed to overwhelming the wheel with lateral force)and by loading the wheel first in the downward direction we are taking up some of the slop which might otherwise be used to overwhelm the wheel in the lateral direction.

The shortest distance between two points is....a straight line.

So in hitting the apex of the turn in a widely offset course - at slow speeds-sub 15mph (otherwise the wheels might be overwhelmed latterally) a board with significant flex and high camber would allow the turning arc to get much tighter resulting in a "Z" turn (note the shape of the letter Z) with increased steering "around the cones" and straighter steering "between the cones". Such a deck was ridden by Marus Stroble in Morro Bay 2001.

Add a lot of speed and the "Z" turn becomes useless (lateral forces build too quickly due to lateral g's which overwhelm the system) and a different line and board truck type should be used.

So board flex is part suspension, part truck geometry. The flex should match the rider's weight for the intended course and the riders ability to drive into the deck.

And of course we haven't touched on how important the first derivitave of flex ie the acceleration or progressiveness of the flex is.

[Shane McFarland]

i was out slaloming yesterday.the course we set up was the hardest for me so far,im fairly new to slalom.
ive been riding a black hill,i like it a lot.
but i was haveing problems getting down the course with out knocking over or blowing sections of the course.
the course was 6'center with sets of 4 then a set of 10 with 3 8'cones at the end,then a 4 cone off set to 4 8'center at a angle in a straight line to another angled set of 4.
then some more 8' to about 4 more 8' to a single cone across the road to 6 under 6'cones.
i had real problems with this course.
i got flusterd and went and got out the old G&S pro slalom.it has acs 651 trucks wedged,RoadRider Hester wheels and slow bearings.i made it .so i put my other wheels on,Abec stingers and Plesure tool bearings.
i hit some cones.but by the third run i was faster and just brushing cones.
the G&S flexs alot more than the Bahne,is alot narrower too.
so should i go to a board that has more flex,or should i go practice a lot more.

[Glenn S]

Shane,
Do you have your back trucks "de-wedged" on the Bahne? If so, you might want to try them flat.
I have found that turny'er back truck helps in making it easyier to get around the cones.
How do you have your Bahne set up?

[Shane McFarland]

Ive got them wedged Glen.
but ive noticed that some boards do have a flat riser on the back,so ill give it a shot.
the Bahne is set up with Tracker x/s wegded and Abec stinger 92 and 88.
but i was wondering about the flex tho.the old G&S felt slower and smoother,but i was just as fast if not faster on it.
plus the shape of the G&S is a double cut,both the nose and tail are narrow.
so being kind of new to this slalom stuff i was just wondering if board shape and flex plays a real big role in going a round the cones.
thanks for the info.

[Glenn S]

Shane,
By "wedged" which way is the small or big part of the wedge facing on both trucks? Is the small end facing forward on both trucks?

How much past flat does the Bahne flex, if at all, for you?

[Shane McFarland]

well glenn,
i had the skinny ends towards the front on both trucks,but i stopped by the skate shop and got some risers and took the wedge of the back truck and put the riser on it.i havent had a chance to try it out yet tho.looks like i wont get time till this week end.
if i stand on the Bahne it doesnt realy flatten out,i can bounce it a little below level tho.ill have to have my slalom partner look to see what it does the next time we run cones.
thanks for your help.

[Glenn S]

Report back your findings of riding the back truck with a flat riser. You might even try it wedged (not de-wedged) during the same session to see what that does for you too.

It is my understanding that conventional trucks like the Indy and Tracker are 40 degrees steering angle when flat.

Many of the pro riders that I've seen use a custom wedge up front, MUCH more angled than the store bought urethane wedge I am guessing you are using. I would guess that these custom wedges these guys are using make the front truck near 50 degrees or so.

And the back truck is usually either flat or de-wegded only slightly. My guess is about 3-5 degrees max.

Or a better way to describe it, I think, is to say if the front truck were flat on the deck you raised the back end of the truck baseplate up 5/8 to 11/16", for the front truck.

And the back truck flat to 3/8" max . Does that make sense?

So maybe you should also try more extreme wedge up front too.

[Shane McFarland]

well i took the back wedge out and put a 1/2" block in its place.
it works a lot better now,thank you.
ive seen the wedge that your talking about,i will see if i can get my hands on it.
i just got the cheap wedges,its the only ones the local skate shop carrys.
the course was almost the same as last time,but we put 3 cones on the other side of the road and then added a bunch of tight ones at the end.all together we had 61 cones out.but i made it threw all of them.even the tight ones at the end.my best run i hit 2 cones and that was at the start,i tend to do that alot when im going slow.so it is a big improvement from the last time.
i thank you for your help Glenn.
i'll try and keep you posted on the next session.