Register now to get rid of these ads!

Technical What is the difference between front and rear shocks?

Discussion in 'The Hokey Ass Message Board' started by 57JoeFoMoPar, Feb 14, 2020.

  1. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 4,376

    57JoeFoMoPar
    Member

    So what's the difference between front and rear shocks?

    When I Google this question, it brings me to current issues of struts vs. tube shocks. Obviously that's not my inquiry. When talking the typical tube shocks, aside from manner of mounting, what is really the difference from front to rear? Is it a rate difference, of rebound and "soft vs hard"? Is it something more significant than just ride quality?

    My question stems from an issue I'm currently having with an air ride install on my 61 Olds. The factory shock must be relocated due to the bag going where the coil and shock used to be. No problem. In measuring my articulation, fully deflated vs fully inflated, I'm going to need a shock that has about 9" of stroke. Unfortunately, there don't seem to be many front shocks that have that much articulation. On the other hand, there are many common rear shocks that have a similar amount of stroke, and even have the grommet and through-bolt attachment at both ends, which will help with mounting and keeping the overall length as short as possible. Would using a shock intended for a rear suspension application be problematic in front suspension?

    Here is a mock up with no spring in place to determine travel.

    IMG_3518.jpg
     
  2. dana barlow
    Joined: May 30, 2006
    Posts: 3,712

    dana barlow
    Member
    from Miami Fla.

    Most shocks are valved to a car with in a given lbs. and front to back for most is only movement size. an stock is likely 60/40 valving. For street cars, but race cars is another can of worms all together. I hear off road big movement shocks work on air bag set ups,but there has got to be a lot of info about that on the net.
     
    Cosmo49 likes this.
  3. Warpspeed
    Joined: Nov 4, 2008
    Posts: 503

    Warpspeed
    Member

    You are right about the stroke. Front shocks are often mounted about roughly half way between the frame and the wheel, its a clearance issue. So the front shock travel is going to be a lot less than at the back, where the shock sees the full axle movement.

    Its not just the travel, the front shock valving has to be far more aggressive, because it has to damp a much stiffer spring with much less movement. At the back the shocks can be a bit more lazy, lots more fluid displacement, so the shocks can be valved softer and still damp perfectly well.

    If you really need nine inches of shock travel, its going to have to be a rear shock off something, a shock like that will be displacing a lot of fluid. As Dana above ^^says, if possible look for a shock of something that has a similar body mass and spring rate at the back. There should be far more choices for a rear shock from a softly sprung mid sized family car to a serious pickup truck or factory off road rear shock.
     
    Cosmo49 and dana barlow like this.
  4. gene-koning
    Joined: Oct 28, 2016
    Posts: 1,599

    gene-koning
    Member

    There are lots of 60s-90s trucks with long front shocks as well as the long rear shocks, especially when you get into 4x4s. Even then, I believe most of the trucks have different numbers for the front and the rear. The different numbers may be for the different mounting ends, but then again, maybe not.

    Not saying a rear shock won't work on the front, but if I could find a front shock with the needed travel, I think I would rather go that route. Gene
     
    Register now to get rid of these ads!

  5. Torana68
    Joined: Jan 28, 2008
    Posts: 1,132

    Torana68
    ALLIANCE MEMBER
    from Australia

    Springs keep your car off the ground, shocks control the springs, front of car , lots of weight so they are valved to work with the heavy front springs. Rear not so much weight not as heavy springs shocks valved to suit. That will be the issue , valving , but you have air so I have nfi about what you need but what I wrote is the basic difference.
     
  6. Bill Rinaldi
    Joined: Mar 23, 2006
    Posts: 1,725

    Bill Rinaldi
    ALLIANCE MEMBER

    I see your from the East coast, are there any reputable shops that install air ride set ups that you know of? Chances are these shops have had to deal with this problem, ask them what they do. Bill
     
    Cosmo49 likes this.
  7. jimmy six
    Joined: Mar 21, 2006
    Posts: 5,481

    jimmy six
    Member

    Air bags?......what's that?
     
  8. hudson48
    Joined: Oct 16, 2007
    Posts: 2,445

    hudson48
    Member

    From the beginning of the 20th Century(according to Wikapedia) but I have included here just from the 50's to show it should be HAMB friendly. Luckily technology has improved and now they are far more reliable.
    In the U.S., General Motors built on its World War II experience with air suspension for trucks and airplanes. It introduced air suspension as standard equipment on the new 1957 Cadillac Eldorado Brougham.[10] An "Air Dome" assembly at each wheel included sensors to compensate for uneven road surfaces and to automatically maintain the car's height.[11] For 1958 and 1959, the system continued on the Eldorado Brougham, and was offered as an extra cost option on other Cadillacs.[12][13]

    In 1958, Buick introduced an optional "Air-Poised Suspension" with four cylinders of air (instead of conventional coil springs) for automatic leveling, as well as a "Bootstrap" control on the dashboard to raise the car 5.5 inches (139.7 millimetres) for use on steep ramps or rutted country roads, as well as for facilitating tire changes or to clean the whitewall tires.[14] For 1959, Buick offered an optional "Air Ride" system on all models that combined "soft-rate" steel coil springs in the front with air springs in the rear.[15]

    An optional air suspension system was available on the 1958 and 1959 Rambler Ambassadors, as well as on all American Motors "Cross Country" station wagon models.[16][17] The "Air-Coil Ride" utilized an engine-driven compressor, reservoir, air bags within the coil springs, and a ride-height control, but the $99 optional system was not popular among buyers and American Motors (AMC) discontinued it for 1960.[16][18]

    Only Cadillac continued to offer air suspension through the 1960 model year, where it was standard equipment on the Eldorado Seville, Biarritz, and Brougham.[19]
     
    Cosmo49 and anthony myrick like this.
  9. Mr48chev
    Joined: Dec 28, 2007
    Posts: 26,278

    Mr48chev
    ALLIANCE MEMBER

  10. jimmy six
    Joined: Mar 21, 2006
    Posts: 5,481

    jimmy six
    Member

    Thanks for your write up...I'm well of the 50-60's use of air suspension systems as I had a 58 Old's that had the factory set-up. The use of the systems today may not be as HAMB friendly as I interpret it or perhaps we would see more of it here. I do realize the subject is shock absorbers.
     
  11. Mimilan
    Joined: Jun 13, 2019
    Posts: 418

    Mimilan
    Member

    The answer is "Motion Ratios" so front and rear shocks will be rated differently [and have different travel]
    Most rear shocks are mounted directly off the rear axle [via spring pads etc] so 1" of travel = 1" of shock travel as long as the shock is vertical.
    Lay the shock over and the motion ratio changes. [see diagram attached]
    Shocks Motion Ratio.jpg

    On the front of most double A-Arm suspension the springs and shocks are moved inboard so the rating needs to be increased to counteract the leverage applied AND the distance moved. [hence the motion ratio squared formula because of 2 factors "distance and force"]

    There is a lot more involved [the above is basic]

    Motorcross bikes used to lay shocks down to reduce travel [and stiffen them as well]

    Formula cars go the other way with bellcranks to increase shock travel [a shock doesn't flow until the valve is bounced about 0.060" off the seat]
     
  12. RJP
    Joined: Oct 5, 2005
    Posts: 1,335

    RJP
    Member
    from PNW

    "Would using a shock intended for a rear suspension application be problematic in a front suspension?" On any forum other than the HAMB the answer would be a simple 'no'. Since your Olds won't be competing in F1, NASCAR, or LEMANS, the wealth of useless knowledge you'll be receiving in regards to your question here, will at best, do nothing more than confuse what started out as a simple question. MR. 48 has answered the relevant part of your question along with part numbers and pictures. Leaving it up to the HAMB experts you'll be building a coilover rocker arm system complete with custom machined parts using aerospace technology. It's a shock, it dampens bounce. It ain't rocket science.
     
  13. Mimilan
    Joined: Jun 13, 2019
    Posts: 418

    Mimilan
    Member

    Using you analogy , It is Rocket Science

    If you used a Front shock from a BB Camaro with 650 lb/in springs and 1.5:1 motion ratio on the back of an early mustang with 90 lb/in leaf springs the suspension would skip over the tops of bumps.

    Do it the other way around you would have the same effect as a shock that has totally worn out.

    This is the H.A.M.B where some people will build a P.O.S out of whats laying around
    and others will do things correctly.

    This forum is full of threads of suspension problems, brake problems, it goes on and on.
    The majority of these threads are caused by people that are using quality parts BUT are mismatched to the application
     
    5window and kevinrevin like this.
  14. uncle buck
    Joined: Feb 13, 2007
    Posts: 1,547

    uncle buck
    Member

    Using your example, I’m curious ... are the front shocks on a BB Camaro with air conditioning the same or different than a 6 cylinder plain Jane car?


    Sent from my iPhone using H.A.M.B.
     
    Gangrene likes this.
  15. Mimilan
    Joined: Jun 13, 2019
    Posts: 418

    Mimilan
    Member

    From the factory ....Yes. From an over the counter parts jockey [highly unlikely]

    The factory "poverty pack" Camaro only had 298 lb/in springs
    An Rpo L34 with AC and Auto trans is over 650 lb/in springs.


    These would require different rated shocks.

    Chevy had 23 different spring rates available in 1969 for Camaros
     
  16. Torana68
    Joined: Jan 28, 2008
    Posts: 1,132

    Torana68
    ALLIANCE MEMBER
    from Australia

    Uh oh you said the “S” word ......
     
  17. joedoh
    Joined: May 5, 2007
    Posts: 188

    joedoh
    Member
    from Wichita KS

    jump on craigslist and find someone selling original shocks from a jeep jk or rubicon, you should be able to pick up all 4 for under $50 in brand new take-off condition because there is a glut of them, the jeep guys upgrade the suspension immediately after buying. the jks are black and the rubicons are red, both are gas charged but the red ones are slightly stiffer, both have ~10 inch travel front and rear. the fronts are pin mount top and the eyelet bottom, the rears are eye/eye. I used these (red rubicons) on a 65 C10 with air ride, full travel and excellent ride. I dont think you could even get one monroe for $50.
     
  18. RJP
    Joined: Oct 5, 2005
    Posts: 1,335

    RJP
    Member
    from PNW

    In the OP's case, spring rates don't apply. He's using airbags. Coil spring motion has been taken out of the equation and is laying in the corner of the shop now. Hotrodding, by its very nature, is the act of using of mismatched parts for most applications.
     
  19. uncle buck
    Joined: Feb 13, 2007
    Posts: 1,547

    uncle buck
    Member

    Ok, so Chevy had 23 different spring rates. How many different shocks did they have to coincide with these 23 springs?


    Sent from my iPhone using H.A.M.B.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.