Haynes Forums  

Go Back   Haynes Forums > Haynes Roadster Forums > Running gear
FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
  #11  
Old 7th October 2009, 08:24 AM
mr henderson mr henderson is offline
Senior Member
 
Join Date: May 2008
Location: Aylesbury
Posts: 364
Default

Springs cannot be define by rate alone, the unfitted length is also a big consideration. For suspension to work as well as it could, then both the rate and the length must be right.
Reply With Quote
  #12  
Old 7th October 2009, 08:34 AM
dogwood's Avatar
dogwood dogwood is offline
Senior Member
 
Join Date: Mar 2008
Posts: 899
Default

????
Explain, for dummies.

David
Reply With Quote
  #13  
Old 7th October 2009, 08:49 AM
mr henderson mr henderson is offline
Senior Member
 
Join Date: May 2008
Location: Aylesbury
Posts: 364
Default

Quote:
Originally Posted by dogwood View Post
????
Explain, for dummies.

David

Let's take a simplified example.

vertical spring damper with 400lbs of weight on it.

If the spring is a 200lb spring, then it will compress by 2 inches. If it started at 10 inches long, it will now be 8 inches.

If, on the other hand, it was a 400lb spring, then it would only compress 1 inch. If it started at 10 inches it will now be 9 inches long.

What I am getting at is that the two factors, rate and length are interdependant, and should both be chosen carefully to get the correct ride height and rate. Of course the adjustable spring base can be used to change the ride height, but people should be wary of using up the available suspension travel to compensate for having springs of the wrong length.
Reply With Quote
  #14  
Old 7th October 2009, 09:12 AM
Land Locked's Avatar
Land Locked Land Locked is offline
Senior Member
 
Join Date: Apr 2009
Location: Johannesburg, Sarf Efrika
Posts: 232
Default

Quote:
Originally Posted by dogwood View Post
I'm going to change to 250's on my rebuild.
I found it bottoms out quite easly, especialy 2 up.
Yea OK we are both lardy......

David

Anyone say we need 300's will get a slap!!!!
I'll probably need 300's

That said, Mr Henderson makes a good point. If I understand it right then for two up each around the 100Kg mark 250's that are a wee bit longer should do the trick then.
__________________
Regards (The mad Sarf Efriken)

Last edited by Land Locked : 7th October 2009 at 09:15 AM.
Reply With Quote
  #15  
Old 7th October 2009, 04:13 PM
mark mark is offline
Senior Member
 
Join Date: Mar 2009
Location: Billingham (north east)
Posts: 770
Default

Quote:
Originally Posted by londonsean69 View Post
What did they cost?
I just spoke to Dave at dampertech and it cost 340 delivered

He said i will have them on friday

Cant wait to take the the square box out thats been moonlighting as springs and dampers for the last few months since i got my chassis rolling
Reply With Quote
  #16  
Old 7th October 2009, 04:20 PM
londonsean69 londonsean69 is offline
Senior Member
 
Join Date: Nov 2008
Location: Surrey/South London Border
Posts: 453
Default

Quote:
Originally Posted by mark View Post
I just spoke to Dave at dampertech and it cost 340 delivered
Good to know, cheers
__________________
Sean
Reply With Quote
  #17  
Old 7th October 2009, 04:45 PM
dogwood's Avatar
dogwood dogwood is offline
Senior Member
 
Join Date: Mar 2008
Posts: 899
Default

Sorry Mr H.
I'm struggling with this one...
Wouldn't a longer spring wound up to make it stiffer (i.e. shorter)
have the same effect as a heavier one?

I'm happy with the ride height.
It's the bottoming out on humps and bumps I want to stop.

Sorry if I'm being thick.....

David
Reply With Quote
  #18  
Old 7th October 2009, 06:19 PM
mr henderson mr henderson is offline
Senior Member
 
Join Date: May 2008
Location: Aylesbury
Posts: 364
Default

Quote:
Originally Posted by dogwood View Post
Sorry Mr H.
I'm struggling with this one...
Wouldn't a longer spring wound up to make it stiffer (i.e. shorter)
have the same effect as a heavier one?

I'm happy with the ride height.
It's the bottoming out on humps and bumps I want to stop.

Sorry if I'm being thick.....

David

The stiffness is set by the spring rate alone. The length of the spring controls the ride height. Let's ignore the adjustable spring platform for the time being.

Let's continue the example from before- vertical spring with 400lbs sitting on it. The bottom of the spring is fixed to the wheel, and the top to the chassis. Let's suppose that the desire ride height is 5 inches. Let's suppose that it is found that if the spring is compressed to 8 inches then the ride height will be correct.

So the target is to get the spring length to 8 inches. If a 9 inch 400 lb spring is fitted then that will produce the correct height (in this example). If a 10 inch 200lb spring is fitted it will also produce the correct ride height (because it has been compressed by 400lbs, so it is compressed 2 inches).

Now the thing to consider is what hapens if some EXTRA load is imposed, suddenly, such as a bump in the road making the wheel want to go upwards. If that bump was to procude a force of 800lbs (extreme example to make the point), then the 400 lbs sppring would be compressed by 2 inches, but the 200lb spring would be compressed by 4 inches.

From that example we can see that the 400lb spring is indeed stiffer than the 200lb spring. If the ride height is changed using the adjuster then all that is changed is the ride height, the spring itself cannot be made stiffer. It won't even be made shorter, as the car will simply rise as the adjuster is wound upwards (until the shock runs out of travel).

The above example ignore the change in the corner weight that would happen on a car, in other words the weight on that corner would increase as the ajuster is wound up, but as both rear corners are being considered, that's ok.

It's a complicated subject, but the basic principles of springs are straightforward. Mike Capon, who contributes to locostbuilders from time to time, has written a spreadsheet that will enable the determination of the correct spring rate and length if one enters the variables such as the angles dimension and weights. Sorry, I don't have a link to it.
Reply With Quote
  #19  
Old 7th October 2009, 07:30 PM
spud69's Avatar
spud69 spud69 is offline
Senior Member
 
Join Date: Jul 2008
Location: Hartlepool
Posts: 1,678
Default

Quote:
Originally Posted by mark View Post
I just spoke to Dave at dampertech and it cost 340 delivered

He said i will have them on friday

Cant wait to take the the square box out thats been moonlighting as springs and dampers for the last few months since i got my chassis rolling
That's a very good price Mark, did you get Gaz or Protech for that price?

Just looked at my invoice and paid 458 delivered from ProtechShocks. Think i'll be going to Dampertech next time.

Also just looked at my SVA brake test and Axle 1 weight with driver is 272kg and Axle 2 weight with driver is 298kg so i think the 250 or 300lb/in springs would be more suitable.

AndyH
Reply With Quote
  #20  
Old 7th October 2009, 07:47 PM
mark mark is offline
Senior Member
 
Join Date: Mar 2009
Location: Billingham (north east)
Posts: 770
Default

Quote:
Originally Posted by spud69 View Post
That's a very good price Mark, did you get Gaz or Protech for that price?

Just looked at my invoice and paid 458 delivered from ProtechShocks. Think i'll be going to Dampertech next time.

Also just looked at my SVA brake test and Axle 1 weight with driver is 272kg and Axle 2 weight with driver is 298kg so i think the 250 or 300lb/in springs would be more suitable.

AndyH
They are GAZ ones and i went with the 250 rear springs

Ash said to mention his name from CKC and speak to Dave to tell him he should give me a good deal

Not sure if this had any reflection on the price, but i was pleased when he said 340 delivered it is a very good price.

He also said if i find the 250 rear springs a little too much, a set of 225 or 200lb springs are only 44 if i want to change them.
Reply With Quote
Reply


Thread Tools
Display Modes

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

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT +1. The time now is 12:11 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.