Hard Tail Vs. Soft Tail? (and general questions)

[John Lawrence]

Hey Guys,

It seems like a majority of the land speed motorcycles I see primarily run a hard tail rear end. Can someone provide what the benefits are as opposed to a shock mounted swingarm (for the lack of a better term)? I am currently in the process of building a motorcycle that will be used only for land speed attempts, and was curious if it would be worth converting to a hard tail. The bike is a 1968 Honda CL175 (see build diary for more details).

I also see a lot of people running a lowered front end with limited travel. I understand that this will help keep the front end down, but on a bike with minimal power is it beneficial? Is it mainly to lower the bike?s CG and improve stability? Any other benefits?

Any insight is appreciated.

John

[donpearsall]

I don't think the majority of motorcycles are hardtails. Some are, but there is no advantage to a hardtail. For slow and low powered bikes, a hardtail would not make a difference but for the most traction, you want the rear tire to be in contact with the surface at all times. Since the salt and lake beds we race on are bumpy, you need a good rear suspension to do that. Likewise for the same reason you need a good fast rebounding front suspension.

I once made the mistake of putting the chin of my helmet on the gas tank while going well over 200 mph and the vibration from the salt scrambled my brains. The surface is nothing like pavement.

Don

[Dakin Engineering]

What Don said.
And there really was some effort in that suspension geometry.
Freshen up those bits.

Sam

[stay`tee]

you will find in the LandSpeed religion there are two "definite" trails of thought on this,,

everyone uses suspension on the front, but, on the rear, one camp advocates "Suspension" the other camp its "Hardtail",,

a lot of factors involved, engine size, weight, power, Speed, all contribute,,

I am in the "Hardtail" camp (+200mph bike), and when this subject comes up (usually over a few beers ) the first question I ask the Suspension folks is, "have you ran hardtail at all, or for more than one event ??", 95% of the time the answer is "always" no,,

"Your Call" 

[RansomT]

Lowered front end has to do with aero.  The lower, less frontal area.

[tortoise]

Some bikes put ballast on the swingarm. Seems funny to me.

[Dakin Engineering]

Hardtail, since 1991, KCIR.
Hardtail, since 2001, Bonneville.

You want suspension.

Sam

[jl222]

you will find in the LandSpeed religion there are two "definite" trails of thought on this,,

everyone uses suspension on the front, but, on the rear, one camp advocates "Suspension" the other camp its "Hardtail",,

a lot of factors involved, engine size, weight, power, Speed, all contribute,,

I am in the "Hardtail" camp (+200mph bike), and when this subject comes up (usually over a few beers ) the first question I ask the Suspension folks is, "have you ran hardtail at all, or for more than one event ??", 95% of the time the answer is "always" no,,

"Your Call" 

   And visa versa?

             JL222

[MAYOMAN]

When we ran the Honda Hawk in 1971, it was hard tail. The Interstate I80 construction debris washing onto the salt caused a slight waviness in the international course. With the hard tail that year, the waviness resulted in over revving the Honda 4s, resulting in some engine damage. That prevented the necessary return runs after 286.556mph one way.
Honda took over the project in 1972 and added rear suspension. The resulting pitching at high speeds caused the Honda Hawk to go airborne and crash. End of story.

[sabat]

I've ridden full suspension on asphalt, salt, and dirt. I once tried a hard tail on a naked NA Hayabusa at Loring (asphalt) and couldn't see straight after 185. I spent the day switching back to rear suspension and went 217 on the next pass. I think every bike, rider, and track is different, there is no one answer. Dean