How Much Bump Travel Does Rear Need? - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Suspension - Brakes - Steering
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 07-12-2006, 08:57 AM
Member
 
Last photo:
Join Date: Jun 2004
Location: TN
Posts: 425
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
How Much Bump Travel Does Rear Need?

I can use 12 inch springs on my rear coil-over. To select a spring rate, how much bump travel should I allow after the car is fully loaded with four passengers, fuel, and a couple hundred pounds in trunk?

And, how much can a linear 12 inch spring compress before binding occurs?

John

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 07-12-2006, 11:00 AM
xntrik's Avatar
Save a horse, Ride a Cowboy.
 
Last photo:
Join Date: Jul 2005
Location: Arkansas
Posts: 5,131
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
I'd say 3 inches at the solid rear axle bump stops.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-12-2006, 11:19 AM
Member
 
Join Date: Nov 2002
Location: Beverly Hills
Posts: 442
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
I'm guessing but I think 3" is not enough, particularly on Michigan roads! For the occasional sharp bump, 3" seems to be enough, but when the road becomes a washboard surface with highs and lows at the pavement joints, the car will go into a rise/fall motion that when fully loaded might bottom out at 3" of travel. I think if you can get an extra inch it would be a good thing. Don't forget to check your shock to match the travel distance of the spring.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-12-2006, 03:30 PM
Member
 
Last photo:
Join Date: Jun 2004
Location: TN
Posts: 425
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Whoaa!

If 3 inches or more is needed after fully loaded, I am in trouble and I don't see how most street rods handle life on the road.

Twelve inch springs can only compress about 5.5 inches total, right. So to maintain 3 inches of travel after fully loading the car (probably 1600 lbs on rear springs), the spring rate would have to be about 300 lb/in -- extremely stiff I think.

Most street rods I see on the road appear to have 10-12 inch rear springs -- do they just not load the cars down in order to still run reasonable comfortable springs?

Lightly loaded, weight on my rear springs with two people in the car (it is a 4 door car though) and a half tank of gas is about 1200 lbs. So even using fairly stiff 200 lb springs would result in a compression of 3 inches with remaining bump travel of only 2.5 inches.

Am I missing something, or is that the penalty I pay for using coil overs on a street passenger car?

John
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-14-2006, 04:54 AM
staleg's Avatar
Registered User
 

Last journal entry: Hand brake
Last photo:
Join Date: Dec 2005
Location: Norway - Europe
Age: 47
Posts: 782
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Remember that the coilovers rarely stand straight upward.
If it leans 25 degrees a 5" travel on the coilover means 6.09" travel on the axle (divide with 0,82)
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-14-2006, 10:17 AM
xntrik's Avatar
Save a horse, Ride a Cowboy.
 
Last photo:
Join Date: Jul 2005
Location: Arkansas
Posts: 5,131
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
I started this 3" thing.

As I stated:
Factory leaf spring cars when loaded have about 3 inches of axle travel remaining to the frame bump stop. Load one and look at it. That probably gives you 4" of tire travel with bump under one tire only.

That is LOADED, as he asked.

How many cars need more than 3-4 inches of suspension travel when running loaded on reasonable roads. That is a lot of axle movement. Look at the fender lip/tire relationship..... do you need more than another 3 inches when LOADED? If you do, you might consider air ride.

Also consider that if you hit a 1" bump that half that instant rise is compensated for by the tire compression. If you hit an instantaneous 3" vertical rise, you hit a mountain and you probably just ruined a tire.

As far as travel and the bump stops are concerned, ask yourselves this..... Am I building a baja buggy or a street rod?

Last edited by xntrik; 07-14-2006 at 10:26 AM.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 07-14-2006, 12:52 PM
Member
 
Last wiki edit: Vacuum brake bleeder set up
Join Date: Nov 2003
Location: So Cal
Posts: 1,245
Wiki Edits: 8

Thanks: 0
Thanked 0 Times in 0 Posts
Go here to find the actual block height of the springs.
http://eibach.com/cgi-bin/htmlos.exe...61812100002608

One other point is that using good polyurethane foam bump stops is a very good idea to keep the car off the ground and still provide a good ride. If you look most new factory bump stops are made out of this material rather than the hard rubber of old. The poly foam bump stops are very soft. Because of that you can have the car ride on those bump stops when fully loaded (as long as that isn't too often).

As for pot holes - they require droop travel; not bump travel.
Reply With Quote Quick reply to this message

Recent Suspension - Brakes - Steering posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
8.8 Ford rear end in my 79 G body Malibu 79 Malibu327 Transmission - Rearend 4 05-20-2007 02:26 PM
63 biscayne rear differential problems biscuit63 Transmission - Rearend 8 07-29-2005 04:37 PM
Universal 3-link kit pigman Suspension - Brakes - Steering 32 07-13-2005 03:43 PM
Best ways to straighten a twisted repro door? Ripped Body - Exterior 13 07-04-2005 07:29 AM
Rear end swap problems datsun dale Transmission - Rearend 1 12-17-2002 10:50 PM


All times are GMT -6. The time now is 10:59 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.