Board logo

Do I have to add the 4" to my chassis?
rabiddog - 14/10/03 at 07:39 PM

See most folks who use sierras as donors end up adding 4" into the width of their chassis,I think this looks bulky so can I just use a book dimension chassis and increase the front and rear wishbones 2" each side or will this knacker my suspension geometry?

Thanks in advance
Craig

[Edited on 15/10/03 by rabiddog]

JoelP - 14/10/03 at 08:43 PM

it will change it, not necessarily knacker it. for instance, camber change in roll will be different with diff length arms and differrent angle wishbones.

provided the car has wheels at the right angle and not too much bump or roll steer, all should be well. I doubt any are perfect.

pbura - 14/10/03 at 10:17 PM

Anything that's not exactly book (chassis, uprights, wishbones, and tire diameter) is slightly knackered, unless someone has taken the trouble to work out new pivot points for the wishbones.

It's not too hard to get to get camber control, but there's a "sweet spot" for controlling the roll center, i.e., keeping it from moving laterally as you corner. The key to this is the location of the upper inboard pivots.

Go ahead and plan on using longer wishbones. No problem with that. All you need is a new (lower) location for your upper wishbone brackets.

You can work this out yourself with one of a few free programs, or maybe someone has done it already.

What do you have, Sierra uprights and book chassis?

rabiddog - 15/10/03 at 06:29 AM

quote:
Originally posted by pbura
What do you have, Sierra uprights and book chassis?


I plan on building a book chassis with rear irs and at the moment sierra uprights, was planning to start constructing the chassis and keeping my eye out for a set of the now rare cortina uprights to make life easier but if I get to a point where I need uprights before I find cortina items I will adapt the sierra items

Craig

westdown - 15/10/03 at 07:33 AM

The only reason to add 4" is if you have a large a** or long legs (like me)

Dave

pbura - 15/10/03 at 10:02 AM

Interesting -

I have a suspension program (wishbone.bas) with the setup for a book chassis and Cortina uprights. Just now I tried it with the wheel moved out 2" from center and it made very little difference in camber or RC location.

Well, I'm pleased to report that I was wrong! (LB needs a smiley for embarassment)

I've played around with this thing quite a lot, and can tell you that moving the pivots up and down, even by fractions of inches, has huge effects. However, lengthening the linkage a little bit didn't upset things at all.

So, go ahead and build, have a wonderful life, and all that If you go with Sierra uprights, you may still want to see if you need to change your pickup points.

BoL

Pete

James - 15/10/03 at 10:04 AM

quote:
Originally posted by rabiddog
See most folks who use sierras as donors end up adding 4" into the width of their chassis,I think this looks bulky so can I just use a book dimension chassis and increase the front and rear wishbones 2" each side or will this knacker my suspension geometry?

Thanks in advance
Craig

[Edited on 15/10/03 by rabiddog]



MK and Luego (Velocity) who use Sierra donors certainly don't increase the chassis width. Luego chop down the rear shafts and use standard front wishbones. MK extend the front wishbones.

Also, the 4" doesn't match up with the difference in track. The Sierra track is actually 7" wider than the MK2 Escort!
Therefore you need to extend the front wishbones by about 3.5" each. I stress about as I'm not sure of the exact figure.

If you go with a Sierra donor, you'll also need to mess around with the steering rack.

HTH,

James

JoelP - 15/10/03 at 11:05 AM

quote:
Originally posted by rabiddog
keeping my eye out for a set of the now rare cortina uprights to make life easier

Craig


http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=2437202906&category=40192

might point out that they need a few bob spending on ancilliaries, brakes etc. cheapish though.

craig1410 - 15/10/03 at 12:12 PM

James,
I'd have to disagree with the 7" figure quoted as it is only 5.8 inches as far as I am aware (I hope nobody reads this post before the previous posts... )

Escort track is 52", Sierra is 57.8" (Source www.carfolio.com)

Anyone else able to confirm?
Cheers,
Craig.

ned - 15/10/03 at 12:26 PM

i'm sure someone will poo poo this idea, but could you not just run different offsets wheels front and back to account for the difference in track?

ie et38 (ford sierra/focus) at the back to keep the wheels in and et19 (ford escort/cortina) at the front to push them out a bit. This would give 3/4" either side, that's 1 1/2" less to worry about, could go more extreme on the front offset if required eg et9, would add a further 3/4" off in total, leaving 2 1/2" total track difference front to back.

My understanding of track geometry affecting handling would be that the wider the back is in relation to the front (or narrower front is to back, same thing) is that you will get less understeer (more turn in) and more oversteer.
And vice-versa for wider track at front to that at the back. (ie less turn in, more rear end grip/less oversteer)

Other option is one sierra driveshaft is shorter than the other, so swap that to the other side and shorten only one drive shaft.

BTW, the new velocity Xt chassis uses full width sierra running gear, the earlier version uses narrower (book) track.

Ned.

James - 15/10/03 at 02:24 PM

quote:
Originally posted by craig1410
James,
I'd have to disagree with the 7" figure quoted as it is only 5.8 inches as far as I am aware (I hope nobody reads this post before the previous posts... )

Escort track is 52", Sierra is 57.8" (Source www.carfolio.com)

Anyone else able to confirm?
Cheers,
Craig.


quote:
Originally posted by James
Therefore you need to extend the front wishbones by about 3.5" each. I stress about as I'm not sure of the exact figure.


Hey, I did say I wasn't sure!!!

Anyway, those figures don't agree with TheConrodKid's data book, his says the Escort is 50" IIRC.

Cheers,

James

theconrodkid - 15/10/03 at 03:25 PM

acording to jeremy walton? the track goes from 49 to 52 depending on if its a shopping trolly or rip snorting BDA powered monster

JoelP - 15/10/03 at 03:39 PM

quote:
Originally posted by ned
i'm sure someone will poo poo this idea, but could you not just run different offsets wheels front and back to account for the difference in track?
Ned.


a good idea, but it would be another good idea to check how the scrub radius would be affected! might make stuff a bit heavy.

rabiddog - 15/10/03 at 10:14 PM

MK and Luego (Velocity) who use Sierra donors certainly don't increase the chassis width. Luego chop down the rear shafts and use standard front wishbones. MK extend the front wishbones
James


So how much hassle would it be to alter the length of my drive shafts? Would luego supply a cut down set to me and anyone got idea of cost?

Craig

rabiddog - 15/10/03 at 10:20 PM

quote:
Originally posted by ned
Other option is one sierra driveshaft is shorter than the other, so swap that to the other side and shorten only one drive shaft.

Ned.


Although I appreciate it still may be wider than the escort axle can't i use 2 short drive shafts to decrease the axle width slightly or is the diff offset for thrust reasons?

Craig

Ben_Copeland - 16/10/03 at 07:31 AM

Diff is offset i believe.

ned - 16/10/03 at 08:55 AM

the diff is mounted centrally, but is wider on one side (if that makes sense) so hence one drive shaft is longer than the other. I think luego can offer shortened shafts with new driveshaft gaitors for £70 or £40 just for the shaft (i think needs reassembling etc).

Ned.