LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently Sat Sep 24, 2016 11:43 pm

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 7 posts ] 
Author Message
 Post subject: Charlies RM8
PostPosted: Sun May 22, 2016 12:26 pm 
Offline

Joined: Tue Nov 30, 2010 4:38 am
Posts: 11
I am finally getting serious about finishing an RM8 part built kit that I bought a few years ago. A lot of things got in the way, I was building in a single car garage, I learnt to fly, I painted my house Blah blah blah....

I am now installed in my (very messy) workshop on Texada Island BC and am putting some time on the car (though I am also working and building a hangar and....)

I bought the car back in 2010, put a Miata motor and gearbox in, put in a pedal box and then really stalled on the rear end. The car came with a Sierra diff, and sandcast uprights but no drive shafts, brakes or shocks. The A arms were there, with a mix of rubber bushings and rose joints, but nothing fitted or lined up. After a lot of time messing around I decided to start from scratch and bought a 7.5" Ford rear end and am building a four link setup. I have that about done now, and am just about to tack on the shock mounts.

One question that I have is whether at ride height the shock should be fully extended, or should there be room for the axle to drop further? I have a pair of 12" shocks with 10" springs (I bought these for the old rear end, 10" would be plenty now).


Attachments:
File comment: I know I will get flack for the short panhard, but I think it will work for me.
Panhard.jpg
Panhard.jpg [ 1.4 MiB | Viewed 234 times ]
File comment: Four link, the top mount will get triangulated
Four link.jpg
Four link.jpg [ 1.95 MiB | Viewed 234 times ]
File comment: Old rear end
IRS rear end.jpg
IRS rear end.jpg [ 1.65 MiB | Viewed 234 times ]
File comment: What I bought
Side view, front fender is  removable.jpg
Side view, front fender is removable.jpg [ 55 KiB | Viewed 234 times ]
Top
 Profile  
 
 Post subject: Re: Charlies RM8
PostPosted: Sun May 22, 2016 1:14 pm 
Offline

Joined: Sat Feb 08, 2014 10:47 pm
Posts: 240
No the shock should not be fully extended at ride height.

Your suspension design should allow for some droop as well as compression or you will be banging against the shock extension limit in normal driving and it will pick up wheels in chassis roll.

I'm not sure what you should design for but 1-1.5 up and 2.5-3 down seem like reasonable numbers.

Maybe someone will chime in who has more experience in design.

Since your 4 link rods are short and not adjustable your ride height is fixed and working height will be somewhat limited.

Since your rods are parallel, before you finalize your rod placement do an instant center calculation.

I would add that you should make the panhard or watts link adjustable so you can fiddle with rear roll center.

_________________
Feels like I'm on the last train,
rolling on cracked wheels,
and Obama is the engineer!


Last edited by Bent Wrench on Sun May 22, 2016 1:22 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Charlies RM8
PostPosted: Sun May 22, 2016 1:18 pm 
Offline

Joined: Tue Nov 30, 2010 4:38 am
Posts: 11
Bent Wrench wrote:
No the shock should not be fully extended at ride height.

Your suspension design should allow for some droop as well as compression or you will be banging against the shock extension limit in normal driving and it will pick up wheels in chassis roll.

I'm not sure what you should design for but 1-1.5 up and 2.5-3 down seem like reasonable numbers.

Maybe someone will chime in who has more experience in design.

I would add that you should make the panhard or watts link adjustable so you can fiddle with rear roll center.


More down than up?


Top
 Profile  
 
 Post subject: Re: Charlies RM8
PostPosted: Sun May 22, 2016 1:24 pm 
Offline

Joined: Sat Feb 08, 2014 10:47 pm
Posts: 240
yes and there are other concerns see my edit.

_________________
Feels like I'm on the last train,
rolling on cracked wheels,
and Obama is the engineer!


Top
 Profile  
 
 Post subject: Re: Charlies RM8
PostPosted: Sun May 22, 2016 1:27 pm 
Offline
User avatar

Joined: Sat Mar 19, 2011 10:22 am
Posts: 788
Location: Holden, Alberta, Canada
Charles

Here is some good info on your question, I cut a pasted the shock mounting info from Alden's site. This is how I set up my cars.

Hope this helps.

http://aldanamerican.com/suspension-installation-guides/

The more vertical the shock, the firmer the ride; the less vertical, the softer the ride (but less support, especially on cornering). We recommend a mounting angle of 30 degrees from true vertical at ride height. Generally speaking, the weight of the car will collapse the shock 1-1/4 to 1-1/2 inches at ride height. Using this rule of thumb, you will achieve a 30 degree angle at ride height if the shock is mounted at 26 to 27 degrees when it is fully extended (Figure C). When designing your suspension mounting points, extend the shock to 2/3 at ride height; i.e., if stroke is 3 inches, set the car up so that at ride height, the shock as room for 2 inches compression and 1 inch rebound. Do not design your suspension with the shock fully extended and the car at rest–allow it to sag, otherwise damage from excessive rebound force may occur.

_________________
Perry

2 down, 2 to go, no 3 to go

'If man built it, man can fix it'

"No one ever told me I couldn't do it."

http://www.locostusa.com/forums/viewtopic.php?f=35&t=12234

http://www.locostusa.com/forums/viewtopic.php?f=35&t=14030


Top
 Profile  
 
 Post subject: Re: Charlies RM8
PostPosted: Sun May 22, 2016 5:07 pm 
Offline

Joined: Tue Nov 30, 2010 4:38 am
Posts: 11
Great, thanks for the replies.

I tacked on the shock mounts with enough travel up and down. The shocks are nearly vertical, and when I put the car down all seems good. I need to put the body back on to check wheel arch clearance before I weld everything finally.

My 4 links are not quite parallel, I read that they work better if they are not?

The panhard is short I know, but I did not want to beef up the rear subframe enough to mount to it, and I could not find a nice clean path for a full width rod in front of the axle without compromising ground clearance.

I'm afraid that I am of the opinion that pretty much anything will work, and am far from knowledgeable about all the technical stuff. These cars were pretty basic in the 50s and 60s, and were still a lot of fun. I think it is too easy to get all hung up with suspension theory.


Attachments:
File comment: With thumb:)
Shock mounts.jpg
Shock mounts.jpg [ 1.74 MiB | Viewed 194 times ]
Top
 Profile  
 
 Post subject: Re: Charlies RM8
PostPosted: Mon May 23, 2016 7:21 pm 
Offline
Always Moore!
User avatar

Joined: Fri Nov 09, 2007 3:40 pm
Posts: 3704
Location: Fort Worth, TX
Bent Wrench wrote:
I'm not sure what you should design for but 1-1.5 up and 2.5-3 down seem like reasonable numbers.


Are you saying 1-1.5" bump travel and 2.5-3" droop travel?

_________________
-Andrew
Build Log
Youtube


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot], Yahoo [Bot] and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
POWERED_BY