Suspension Travel....

[Highrev1]

This is the first "installment" of a series of tech articles that directly relate to you and your suspension design. These will be more informative and allow everyone on the site to gain knowledge in general suspension tuning. Alot of this information is quoted or taken from numerous people.

Our Mac-Strut front suspension, free-travel is the distance from the bottom of the bump stop to the top of the strut bearing (or camber plate). Most of use lowering springs to lower our cars. Its the easiest thing to use...There are pros and cons to this, but we will go over that in a later article

There are other ways to gain travel such as relocating the hub and spindles higher, Speed tourning cars do this, but I don't think there are too many on this site that will be doing this so we will discuss other options.

What are the disadvantages of lowering a car by shortening the springs?

The primary disadvantage of using shorter springs to lower a car is that the suspension travel is reduced.



This Stolen picture Shows what exactly happens when you lower your car on springs...Obviously this is a basic drawing, but works EXCELLENT for our purposes...The blue circle shows the suspension travel loss when you lower your car.

WHY? Well you reducing the distance between the upper mounting point and top of the Shock or damper. This is forcing the bump stop to be lower to the top of the shock, which in turn reduces travel between the two corelating points, Bump stop and top of the strut housing. The only way around this is to either use a shortened strut housing or to cut the bump stop. There is only one company I know of using shorter struts for our cars

The other alternative is to cut the bump stops..Cutting the bump stops may seem like a bad idea at first, and it really isn't an ideal situation if you are able to maintain the suspension travel through shortend shocks or relocated hubs. The stiffer the spring the less travel is needed since the suspension doesn't compress as much, but alot of our standard lowering springs are only SLIGHTLY higher rate, requiring a trim of the stop. The bump stop is a shock limiter/cushioner, if you have the time and ability you could determine the ideal bumps stop length and spring rate. Too long a bump stop and you add a stop to the travel causing you to ride on the stops and not the springs...Too short a bump stop and when you do fully compress the suspension it will make the change in your ashtray rattle Matching bumpstops to ride height is a key thing to do, this is done with testing an knowledge...Or just get shorter dampers

Comments? Questions? Concerns?

More too come

[Sirbelch]

Good Stuff

[Highrev1]

Moose I see you take it easy on me

[Izzy]

Rep 4 u.

I wonder who you're talking about when you're referring to a company who makes shorter strut housings, Greg.

[Highrev1]

I dunno... More Techie articles to come..

[aki]

Zomg I can actually rep you again.

There's one company in Japan that uses shorter strut housing in Japan, but their coilovers cost about $2k. I'll see if I can find it again.

I always wondered, why don't cars come stock with the shortest strut housing possible? Is there some downside that I don't know about?

There's another way to have a much lower car, with less suspension travel but greater handling: increasing the piston cross section and increasing fluid displacement. Motons use shorter fatter rods but have 2-3x more fluid displacement, meaning the suspension requires very little travel. The downside, of course, is that they're expensive puppies at $5-10k =)

[Sirbelch]

^^^ and fat dampers mean less clearence for other stuff like wheels.

[Moose]

Originally Posted by Highrev1

Moose I see you take it easy on me

HAHAHA ... I am not going to bust your balls ...yet

Looks good ... I see some ommisions (ie Shorter suspension travel and how it effects shock valving, or how shorter suspension travel requires higher spring rates to keep you off the bumpstops, and why running on the bumpstops is bad and how it wears out the shocks(very high rate springs)) ..BUT I figure they will be covered in future "installments" ... if not ...

Originally Posted by aki

I always wondered, why don't cars come stock with the shortest strut housing possible? Is there some downside that I don't know about?

Shock travel is designed to match spring travel with the bulk of the springs travel falling with in the "sweet spot" of the shocks valving range. So OE shocks and spring are matched ...Ie as short as they should be


Moose

[Highrev1]

Yeah, there will be some more detailed information to come...Camber and toe curves on the rear suspension may be next, not sure though as Math>Me I may just show why with the droop travel we have in this car a helper spring in the rear isn't a bad idea

[Moose]

HighRev ...I hope you do not mind ...I am going to add my thoughts to what you started ...

Suspension Travel

When you lower a car via lowering springs you are doing a number of things

Shorten the suspension travel (As above) … less travel means the suspension has less movement to absorb the changes in the road surface …ie potholes … you are much more likely to bottom out and hit something important (like an oil-pan).

You MUST have higher spring rates to keep the car within the new suspension travel range. Why … Well the OE springs are designed with a specific spring rates and a specific spring compression (travel) Remember that spring rates are a measure of a springs length compressed by the amount of force(weight) … ie 200 lb/in springs will compress 1” for every 200# applied to them.

If the Stock suspension has for example 6” of total travel, and you lower the car by 2” you have reduced the overall travel by 33% to 4”. So what you say, well the weight of the car has not changed … and if the spring rates are similar to stock, the car will NEED the same amount of suspension travel as OE (6”) but you are only giving it 4” (lowering springs) …so now you will be using all the springs travel AND the car suspension will be spending a lot of time on the bump-stops rather then being supported by the Springs. Related to this, when you shorten the travel you also shorten the distance the shock has to damp the oscillations, so it has to work “harder” with an shorter distance and time.


Bump Stops
-Bump stops are springs … when the suspension runs out of travel it compresses to the point where the car is actually running on the bump stops. Since the bump-stops are actually elastomer springs with a high spring rate, your car “suddenly” goes from one spring rates (springs) to a much higher spring rate (bump-stops) causing the handling to become inconsistent and difficult to control. You car can and will suddenly go from under-steer to over-steer (or vis-versa) mid-corner as you load the suspension up and compresses the springs to the point where you are sitting on the bump-stops. Related to this, you shocks valveing are designed (hopefully) to properly damp or control the oscillations of the springs (based on the spring rate) … when you are running on the much higher rate bump-stops the shock have NO chance in damping them, adding to the instability of the suspension system at the limit (where you need the most stability)


Changing the frequency of the system
-As you increase the spring rates you also increase the frequency at which the suspension operates … The definition of frequency is “cycles per second”. Low spring rates provide long slow motions, high spring rates provide shorter, faster motions. This increase in speed and frequency obviously increases the “work” the shock has to do to damp the motions of the springs. When the car is riding on the bump-stops, the spring rates go up HUGE, thus the work the shock has to do is substantially increased. The Valving of the shock is not only designed for the specific spring rates but also the frequency that the suspension operates at … the valves and orifices are designed to flow a specific volume of fluid at a specific rate … the high frequency motion is beyond the high-speed damping ability of the shock, and as a result it cannot damp these higher rates and the highly increased flow rates wear out the shock WAY faster than normal.

It is my theory that the average lowering spring wears out shocks because it spends so much time on the (high-rate)bump-stops thus speeding up the wear on the shock.


Bottom line … lowering springs do not work well and actually negatively effect suspension performance for the following reasons

-Decrease suspension travel without compensating (with increased spring rates) for this loss in travel

-Allow the suspension to spend WAY more time then it should on the bump-stops … causing instability and wear

-Run beyond the shocks ability to damp the springs rates and motion frequency, and increase the wear on the shocks.


Any changes to the suspension must be systematic ... you need to create a complementary series of components that work well together.

-Spring rates matched to the ride-height and weight transfer charateristic you require
-Bump-stop travel and rates matched to the above
-Shock valving and travel matched to the above

Moose

[Highrev1]

Great Moose, thanks for the addition.

[Highrev1]

BUMP....Next article Coming soon... Maybee later tonight..

[brazilianguy]

great info
subscribed

[Xtreme Thunder]

Originally Posted by Highrev1

There is only one company I know of using shorter struts for our cars

Honda HFP?!?!

[fg2!kid]

man all this great info makes me just want to leave the suspension stock so i dont mess any thing up hahaha

[Sirbelch]

Bump for Sticky status?

[2.0si007]

i know u dont have to do all that.

[Highrev1]

Originally Posted by 2.0si007

i know u dont have to do all that.

Do all what? Compensate for lowering?

[2.0si007]

bump stop i will never cut it and will be on my new lower springs = adjustable struts or shocks like tokico done. i like the term half ass for that use! sorry

[Highrev1]

Why wouldn't you cut the bump stop?