I've mostly heard that monotube dampers are better for performance than twin-tubes. However, I've never had a chance to study or ready up on damper technology, so I don't know why this is so. What are the pros and cons of each design? Which is better suited for performance driving? I ask this because some very well respected dampers (e.g. Racing Gear) still use a twin-tube design, while most others (Tein, Zeal, BC, etc.) use monotube. Thanks for any info and explanations you guys can provide.

 

mono tube:
big piston.
more oil can store in the shock

twin tube:
smaller piston(assume same OD of the shock)
less oil store in shock compare to mono


after all, mono is better IMO(for track driving).

 

I would say that if either is designed and built well - you won't be able to tell the difference.

The monotube and twin-tube designs differ in (of course) their internal anatomy. Many use oil only - others have oil and high pressure gas inside. They both function to restrict oscillation of the springs they are attached to.

Design becomes more critical when the amount of oscillation (or stroke) becomes shorter. Generally speaking for road going cars - the faster you go - the less travel of the suspension you will encounter. Thus the sensitivity of the damper (in terms of compression and rebound) becomes more critical. The movement of fluid inside the damper provides this "sensitivity" - most high-end or competition type dampers will use external reservoirs to maximize the amount of fluid capacity of the system (and hence the sensitivity).

Read more here:

http://www.turnfast.com/tech_handlin...g_shocks.lasso

and here:

http://www.rpmnet.com/techart/shocks.shtml

 

Thanks for the links Big Phat R! It would still seem that monotube would be better for the track, but still puzzles me that companies such as Racing Gear use twin-tubes.

In any case, I just have one other question: for shocks/dampers that do not have adjustable shock length (to keep spring preload the same), why do they feel stiffer the lower you go? Is it the shock's valve position (it now has more oil/gas on the other side of the piston) or is it the spring's preload? If it's the spring's preload, how does that change when the damper is compressed more to lower the car since the length of the spring has stayed constant? Anyone know? Thanks.

 

Bilstein has a patent on their monotube design but Showa makes monotubes as well.

If you go too low with a coilover - you are probably riding on the bumpstops more than you think - thus the stiff ride. Either that or the bumpstops were not trimmed enough to allow for the lower ride height.

A spring in general has a working range of motion. If you use a stock length spring on a lowered car the space between the coils of the spring will be less and thus the spring does not have a lot of ability to compress - because of this you usually have to use a shorter spring.

Can you explain what you mean by pre-load? And my "adjustable shock length" do you mean the spring perches??

This sentence "If it's the spring's preload, how does that change when the damper is compressed more to lower the car since the length of the spring has stayed constant?" makes no sense to me.

 

A good number of Japanese manufacturers have shocks that are height and preload independently adjustable. Mugen, JIC, Buddy Club, etc. I happen to like JIC since they have a shop in Cali, with an engineer. Hard to understand him at times though

Warren

 

Big Phat R: if you look at the JIC picture that Warren posted, there are 2 adjustable brackets. One is the lower spring seat, the other is the bottom bracket of the shock/damper. When you adjust the bottom bracket, you literally shorten the length of the damper to adjust height. Ppl say this "keeps the spring preload constant". However, in a coilover that does not have that bottom bracket adjustment, and you adjust the lower spring seat to lower the car, the spring's length seems to stay constant, so I'm not quite sure what ppl mean when they say "constant spring preload". If the spring's length is constant, the spring's energy should be the same.

Regarding the stiffer dampers when lowered, friends and I have tried this out and we know we weren't running on the bumpstops. There was still suspension travel, it just felt stiffer, like changing the damping setting from a low 1 to a higher setting, like 10 or something (just an example). Just wondering why dampers feel stiffer when they're compressed more statically (like when lowering a car via the lower spring seat...the damper's rest/static position is lower than optimal). Thanks.

 

Are you using linear or progessive rate springs on that car??

 

Monotube - the fluid and gas inside are highly pressurized and are separated with a movable piston.

Advantages:
1) It gives more fluid volume --- energy from spring oscillation is mainly being dissipated in a form of heat and absorbed by the fluid. So higher fluid volume equals higher heat capacity. Remote reservoir has almost double the fluid volume and the reservoirs can be located away from the heat source (ie. inside the driving compartment.)
2) Valve diameter is big. It gives the same amount of energy dissipation with shorter stroke. It performs well even with very little shock travel. So it is ideal for low ride height and stiff springs (1000 lbs+ springs).
3) Highly pressurized gas and fluid eliminate cavitation (air bubble in fluid) so performance is consistent.

Disadvantages:
1) Highly pressurized means higher construction cost.
2) More fluid means heavier unsprung weight (but still lighter than most twin tube dampers). So some monotube dampers are made with aluminum shell -- expensive.
3) Large diameter valve responses very well to transitional load (cornering, accelerating, braking) but responses very slow to bumps so it is not ideal for street use.

Twin Tube - A smaller tube is inside the outside shell and the valve is inside that smaller tube. Fluid and gas are in direct contact and are lowly pressurized.

Advantages:
1) Low construction cost and easy to rebuild.
2) Responses well to bumps and transitional load, but need longer shock travel.
3) Ideal for street and occasional track use.

Disadvantages:
1) Cavitation may occur under extreme use (track use) because of low pressure fluid inside.
2) Cannot handle high spring rates like the monotube.
3) Ride height needs to be set according to the amount of shock travel, usually means a bit higher ride height.

That's all I can think of now.

(Edited for better format)


[Modified by Wai, 2:00 PM 9/3/2002]

 

Big Phat R: The testing was done w/ A'pex N1 coilovers. They come w/ linear springs. We first lowered the car w/ the lower damper bracket, essentially shortening the length of the damper itself. Then, we raised it back to normal and lowered w/ the lower spring seat. We still had suspension travel, but the ride was harsh (it felt stiffer on the dampers 1 setting than it did on the damper's stiffest 13 setting when lowered via adjusting damper length).

I'm still also curious how the spring's preload is changed when lowered using the lower spring seat. I always thought of the adjustable length feature to be mostly for stroke retention.

Wai: Thanks for the info on the types of dampers!

 

What you are experiencing does not intuitively make sense.

Perhaps testing the spring portion of the coilover on a spring testing machine would give you better answers.

http://www.power-t.com/spring/pt-500.html

 

Eh, that's a lil pricey. This was more a curiosity thing to find out why the damper/coilover was behaving like that. Yeah, I don't get it either since the "stiffness" changes according to the speed that the piston moves, so I just wanted to understand why we were getting this. Oh well.

 

You have me completely confused - you talk about springs one moment, and then are talking about the dampers. And I still don't understand your original question.

 

I'm talking about an adjustable coilover assembly (damper + spring). The height on some coilovers, such as the JIC's Warren posted, can be adjusted 2 ways: 1. by adjusting the lower bracket that essentially shortens the length of the damper or 2. by adjusting the lower spring perch, thus reducing shock travel. When tried both ways on an A'pex N1 coilover, lowering using the lower spring perch created a stiffer ride, which doesn't make much sense to me since the "stiffness" of the damper is mostly dependent on the speed at which the piston moves and not the relative position of the piston in the damper. So, when I lowered by shortening the shock(damper), the ride was fine. When lowered by lowering the spring's position, the ride got stiffer. Just wondering why?

And, the second question dealt w/ spring preload. The adjustable lower bracket that shortens shock length is supposed to keep the "preload" on the spring constant. However, even when lowering via the lower spring perch (moving the spring downward relative to the shock), the spring's length remains the same. So, I don't understand how adjusting height via the lower spring perch changes "preload".

Hope I've made it a little clearer. Sorry if I haven't. Thanks.

 

1. The "stiffness of the damper" is dependent on fluid/gas movement - which in turn affects the piston. Maybe at the position where it feels more stiff there is less efficient fluid/gas movement in the body of the shock? Dunno.

2. What is the purpose of preload? THis is a mystery to me as well. As soon as you put the weight of the car on the springs - your need for preload is gone. Some types of dampers use "helper" springs for "preload" to keep the spring seated during rebound movements where the suspension has a great deal of travel - is that what you're talking about?? Since you are using N1 spec coilovers (which should have shorter springs and matched short stroke dampers) your potential wheel travel should be much less than OEM - so why do you need preload?

BPR - who thinks preload is a load

 

 

Warren...... im looking to get the SF-1's after i get the R. I havent heard much about them, what do you think for daily driving/occasional track & auto-x?
"Chris93Si" has Tein HA's on his prelude and they feel great. How do the SF-1's compare to the HA's?

Im open to all opinions.

 

SF1 and HA are the same design with twin tube( they both entry level suspension for the company). it should be around the same if the spring rate are close.......