Rear Beam 205 - Toe Question

[andy0075 9 1 Cars]

The rear beam in my 205 race car has about 4mm toe in and the car is very unwilling to drive through tight bends.

 

I meassured that the "toe in" even increases in corners on the outside wheel instead of decreasing.

 

So I'am thinking of altering the toe setting to zero to improve cornering behaviour in tight bends.

 

Does anyone tried this? How is the behaviour of the car at high speeds on straights?

 

Andi

 

 

 

[j_turnell 136 3 Cars]

There are quite a few topics on this already so worth a quick search. It would be a good idea to speak to Allan at Bridgecraft engineering he can machine arms to whatever spec you want. The closest to zero toe off the shelf would be some ZX arms I believe which would help improve turn in. Although worth bearing in mind the toe will change depending on what ride height your running.

 

What's the rest of your spec? Spring rates? ARB thickness, track width etc?

[andy0075 9 1 Cars]

Rear : 25mm ARB, 23mm TB's

Front : No ARB, 100kg/cm springs, something about 2mm toe out, Camber ~1°

 

9x13, AVON Diagonal Slicks, ET 0

 

Turn in is not the problem, but the rear does not want to go round tight corners. The rear end

even starts to jump in very tight corners !

 

I think i will try 0 toe on the rear. But i read in another thread something about 3° camber!!!

This is for radial tyres and semis, isn't it?

Because AVON SLicks does not like that much camber. Maximum 1°.

 

Here is a video of me and my car : https://www.youtube.com/watch?v=skDYOJvVipE

 

Andi

[welshpug 1,655]

too low, looks like its sitting on the bump stops.

 

also probably not enough damping control

 

reverse rake not helpful to fwd also.

 

 

 

spring rates seem massive also, 560 lb/in front and circa 200 lb/in rear!!!

[allanallen 528 2 Cars]

Welshpug has summed up my thoughts also.

 

0 toe will help but I'd look elsewhere first.

 

For future reference we can machine rear arms to any geometry so -1 camber and 0 toe to suit your ride height isn't a problem.

[j_turnell 136 3 Cars]

As above, seems like the main issue is the balance front and rear. The rear dampers don't seem to be able to control the spring rate judging by the video either.

 

With your tyres, you may be able to get away with -1.25-1.5deg camber on the front assuming they are cross plys, I've managed that on Westfields, although they are a fair bit lighter..... Switching to radials may be a better option, and look at running -2.5-3deg.

[boldy205 75]

I know next to nothing about car set up, but id say that thing looks bloody quick! Sounds lovely too!

[andy0075 9 1 Cars]

Thanks for your answers. Could be true that the car is too low.

My rear arms are pointing a view degrees upward. Maybe this is too low and the rear

dampers do not have enough way to travel.

 

Suspension is a KW Competition V2 and match the springrates i use.

Do you really think that ~560lb/in is too stiff? I meassured the rear springrate on the wheel and it is about 250lb/in.

What do you guys use in your racecars? Like i said, i use no front ARB.

 

@boldi205 : THANKS A LOT

 

@allanallen : thanks for your offer, but i think shipping is very expensive from UK to Austria.

 

Andi

Edited January 4, 2016 by andy0075

[rallyeash 155]

I run 300lb springs but do have a front arb. 23mm rear bars and 27mm rear arb

[welshpug 1,655]

granted on a tarmac rally saxo, not a sprint car, but fairly close in corner weights to a 205.

 

from memory 250 lb front and 130 lb rear, no front arb, 24mm rear.

 

Its a Satchell front end setup, I think colin's own 205 is around that (no arbs at all) though its difficult to compare them in isolation as it's a complete chassis setup.

[petert 585]

I run 500lb springs with slicks, but -3 deg and 4mm toe out. Allan is current machining some rear arms for me, which will give 0mm toe and -3 deg to match the front. I too currently have 4mm toe in on back and it's so benign.

[welshpug 1,655]

what's your ride height though peter? bet you aren't on 13"s either!

[andy0075 9 1 Cars]

It is interesting that spring rates differs so much in nearly same cars (TB ~23mm, ARB ~25mm, slicks and carweight about 720-800kg)

 

I wonder how this can work

 

I mean it is a world between 250 and 550lb springs. A friend of mine drove a GroupeA 309GTI16V rallyecar and he used

350lb springs on the front on gravel/tarmac stages. The car was very fast and successful!

And i only drive sprint/hill races on very good tarmac surfaces. so i thought 550lb would be ok.

 

I would really be interested to test 300lb springs to have a direct comparement to mine.

But ~120.- Euro for 2 springs just for fun is a bit expensive.

Edited January 5, 2016 by andy0075

[welshpug 1,655]

I guess you have metric springs? imperial springs are much much cheaper, more like £50.

[petert 585]

what's your ride height though peter? bet you aren't on 13"s either!

If the ride height is compromisng the geometry then you need to fix it, in some way or another. But the numbers I quoted are typical for tarmac. Start by making sure there is 25mm of rake from back to front and increasing the front toe to +4mm. Dial in as much caster as you can. You'll need bigger than 23mm TB's in order to match 500lb+ springs on the front.

[andy0075 9 1 Cars]

Does 25mm rake mean that the front is 25mm lower then the rear?

I always thougth that the rear should be 10mm lower then the front.

 

What TB diameter do you suggest for my 560lb front springs?

 

I have metric springs. Unfortunately they cost a little bit more.

[welshpug 1,655]

springs are cheaper to change than torsion bars!

 

what I.d springs do you have?

 

reverse rake is a rwd thing, peugeots all come from the factory level or rear higher

[petert 585]

The back should be 25mm higher than the front. You really need 24mm TB's but as said, it will be expensive. If you want to get the best out of slicks that's what you have to do. Otherwise, go back to 350lb springs and be happy for what it is. I'm fairly sure your car will be understeering with the 560lb/23mm combination. That's all irrelevent if you don't have the geometry correct however.