Lowering Yokes V Raising The Rear Ride Height

[dhtmbowen@gmail.com]

I thought I knew the answers to these questions but I have recently come across people who are equally convinced that I am right and some that are convinced I am completely wrong.

Everyone seems to have an opinion but what are the FACTS?

What is actually effected by dropping the yokes down or raising them up the forks?

Rake? Trail? And how do they affect turn in, grip, stability and feel

Is changing the rear ride height the same?

What effect does raising and lowering the rear ride height do?

What is the effect of raising or lowering both by equal amounts? (answer to include, please, not just the effect of CoG on cornering speed v angle but what the effect is on braking and accelerating / pitching)

[spgtech]

Hi Dave,

 

I used to think that front and rear height adjustments accomplished the same thing as far as pitching the bike forward or back, and it does to a point but not entirely. So, what follows is probably an over simplification, but here we go...

 

 

Say you want to quicken handling; If you drop the front end (slide fork tubes up in clamps and make the triples closer to the ground), you reduce trail, steepen steering head, shorten wheelbase, reduce ground clearance and REDUCE swingarm angle.

 

So, in contrast, raising the rear to pitch the bike forward, the effects of steering head angle, and trail are the same, but you are raising ground clearance and INCREASING the swingarm angle.

 

With dropping the front, the swingarm angle changes are slight, but with raising the rear, they can be pronounced.

 

Swingarm angle is related to the anti squat tendencies of the bike and can have a pronounced effect on how well the bike finishes the corner (as does rake and trail)

 

So, if you know what handling changes you want with steering head angle and trail, you can decide which end to use based on desired swingarm angle (increase or decrease), and ground clearance (making the bike taller or shorter).

 

Hope this helps.

 

-Sean

[johnnyrod]

Very interesting, so which way give smore squat?

[spgtech]

Higher swingarm angle gives more anti-squat. In other words, the tail section of the motorcycle lifts when power is applied.

 

This ideally is roughly balanced by the rearward weight transfer, which helps keep the chassis stable, the suspension in it's sweet spot, and the rear tire firmly planted to the ground.

 

-Sean

[Balistic]

I agree with everything Sean has posted but agreement on this very limited. it's hard to find an AMA tuner that wants to raise the rear of a bike? Seems most like to raise the front to get the newer bikes to handle for the current crop of trail braking riders. IMHO it always comes down to the riders style which way you will go, a rider who is early to the gas after turning will like the rear up and a rider who runs it into the apex with the brakes on will like the front high.

 

Will

[ktk_ace]

http://www.sp125racing.com/RS125%20Technical%20suspension%20settings%20vol1.htm

 

 

 

 

I use this to tune my bike~ hope this helps ~ ^^

 

 

[spgtech]

I agree with Will that there are a lot of bikes where the forks are being lengthened for increased trail and feel based on the riding style (in his example trailing the brakes).

 

My example for lowering the back or the front were meant to compare the differences between ends of the bike. They will of course still hold true for raising one end or the other.

 

In addition, choosing to raise or lower the bike as a whole will change CG and the resulting turn and transition quickness and fore/aft pitch moment, as shown in the link from ktk-ace.

 

It all comes down to ballancing the effect you are looking for, with the other items which will be affected as a result of the change. There are very few settings on a motorcycle that act in isolation.

 

 

[psych0hans]

I'm actually planning on raising the rear of my 250r to sharpen the cornering a bit. I'll first be switching over to a GSXR 600 rear shock and then making custom linkages to increase the height by an inch or so...