Ok.

With 2mms on each side, things look better. I did the ton ad still alive . Though the problem is still not perished, just got better. I think i will try the 2.5mm/side. I dont care about tyres .

Oh yes, the car can be stabilised with left foot braking without stepping off the throttle. It is obviously something flexing/distorting in the rear suspension. i think this is the reason why GTM went on to revesrse A-arm...

Your Toe leg arrangement on the rear needs to be stiffer,


I had a simular problem with mine especially when I had some rubber bushes in the rear suspesnion and 180 hp, I replaced all rubber joints with Rod ends, and have strengthened the toe leg mounts alot based around the GTM setup, and have plans on a total redesign my new frame. I will once again plug Alan Brittons [rossa bitz] kit as it a simple bolt on kit which is a vast improvement over the mini steering arm/GTM style toe lock [like yours] and puts the bolts in double shear and gives zero bump steer, or can be shimmed to get the bump steer characteristics your looking for also the New steering arm is alot stiffer compared to a Mini Steering arm and you will be surprised how much one of those can flex.


The Reverse Arm setup is good but that also has issues.

Your test method is sensible, I did simular with a DTI clock on different parts of my rear toe lock setup to see which parts would make the biggest improvements.

I was running 2mm toe in to get stability before and im now down to 1mm due to the improvements I have made. I need to finish My new rear setup as that is a far better engineered solution to what I am currently running.

Neil

Flexing steering arm? I think this is ringing a bell. Especialy as i use longer Metro type arms - it was easier to get zero-bumpsteer with them.

Yes Fexing steering arms, In my High Speed Low Cost book, A Book about how to build a Low Cost single seater based on the Mini, It is mentioned in that book about how they found the steering arms flexed when they changed tyres for a high speed run. After reading this it confirmed my ideas and went to measure it for myself and currently have my thickest arms fitted.

Alans New arms are nice and thick and will be alot stiffer than the mini arms.

Neil

Are your steering arms the standard Mini or the Cooper S versions?

The 'S' versions (top) are much stronger.




I've just read your last post again.You are using Metro arms? I thought that they introduced bump steer?

I use Metro arms. I have repositioned the rack (now attached to the subframe) and also redesigned the rear steering rod pickup point (originaly it was realy dangerous).

I have corrected the front bumpsteer with sims under the steering arm, and the rear with a purpose-made pin connecting the steering arm and the rose joint. I used the merto arms on the front to correct the ackerman (I have also reduced the front track by cutting and revelding the front subframe).

Merto arms are stronger than normal mini arms - as I heard.

I feel totaly embrassed

I have found the main reason for my problem...

Hear and learn from my misstake.

I have checked the front suspension a couple of times, and found no free movement or play. I though its ok. I have checked it with the wheel on.

Yesterday I have attached a long bar to a steel rim and checked the rear suspension. After a full day of work and test of the rear suspension, I have made little improvement. At the end, I have decided to check the front also with this "device". Why not? I was shocked at the result

With the long bar, I could move the wheel a LOT with the steering wheel in position! After a closer look, the steering rack turned out to be able to move, if pushed HARD enough. A good reason why the problem came out at speed.

Now I have removed the u bolts and put anti-friction strips on and retorqued the rack. The improvement is marvelous. The 100mph is now easy.

Though the rear suspension is still flexing under load, the ride is "predictable".

Thanks everbody for Your input!

Good to hear you found the main cause of the problem.

Always worth checking everything when there is a problem. Enjoy the car

Neil

I had something similar with the 1970 GTM Coupe when sprinting & hillclimbing.
The car felt like it had very bad understeer.
It took a couple of events to realise that the rack was slipping sideways in the U bolt mounts