spring size and questions on shocks

[SEVEN]

hey guys, for a mountainbike shock with 6.5X1.5, what does the 1.5 mean? does it stand for the travel of the shock?

and what diamter of spring do you usually use (i mean the wire diameter of the spring)?

[SEVEN]

hey guys, for a mountainbike shock with 6.5X1.5, what does the 1.5 mean? does it stand for the travel of the shock?

and what diamter of spring do you usually use (i mean the wire diameter of the spring)?

[Bart Smith]

You need to do your homework on this one!!

You need a rough mass of the car for starters. Most of the mountain bike shock/spring units come with different poundage spring rates, you just have to do the maths!

The numbers you are mentioning are the travel, and distance from (usually) eye to eye. If in doubt ask the supplier.

[SEVEN]

thanks for the answer, i ve already calculated wheel rate and the spring rate. but dont have idea on what wire diameter of the spring should we use

[RonBurgundy01]

There is a formula somewhere in one of my design books that calculates wire diameter but i can not remember it to save myself. It should however be a pretty comon formula so if you looked at any book on mechanical design i'm sure you could find something similar. Just also keep in mind that you want to make sure that the wire diameter is not so large that you get binding of the spring before the damper reaches full compression.

Sorry i can't be of more assistance

Matt

[Bart Smith]

The equation is listed in heaps of places.
Try this:
"Fndamentals of Machine Component Design"
Juvinall & Marshek, 3rd ed Page 495

If you are still having dramas, give me a yell..

[SEVEN]

thanks, i ve got the spring size now.

I have another question on the travel of shocks:

the desired shock travel (not the wheel travel)of the car is about 1.3 inches, should I choose the shock with 1.5in travel for lighter weight or the one with 2.3in? (the wheel rate of the car is about 270 lb/in and spring rate is 250 lb/in)

[mtg]

The longer travel shock will give you more freedom to stack up bump rubbers or change the static eye-to-eye length to put the suspension in a different range of the motion ratio curve.

The shorter one will, as you said, be lighter, and also probably easier to package.

Ease of finding springs is another thing to look for- one shock size might have better spring availability.

Decisions, decisions.

[SEVEN]

if the desired travel of shock is 1.4in, will that be a problem if i choose a shock with travel of 1.5in?

[Mike Cook]

These guys will wind whatever spring you want for a very reasonable price.

http://www.kirk-habicht.com/


They also shot peen them and powder coat them.

Mike

[mario_rbr]

We shoot for a 80% of spring travel used, I mean that if the shock travel is 2", we shoot for 1,6" in normal conditions, this opens the door for 0,4" of travel for critical situations.
What % of total shock travel do you guys (fsae) use?

[Jersey Tom]

Your motion ratio is pretty close to 1.. and you only have 1.3" of shock travel? How many inches of wheel travel is that? How much is req'd by the rules?