kos11-12

Hi guys,
you may have red one of my old thread, saying I have fitted an ERP (& 993 inner tie rod) kit on a standard 964 upright use the small spacer at the upright, to see if it will work and improve steering feel.
https://rennlist.com/forums/964-foru...up-rights.html

Next step, I tried yesterday to measure the bump steer, by moving the wheel up and down by 2", here is a few pictures. Basically I used a plate, taped it level in the centre of the tire, the plate was graded it up and down 2" and 20 mm across, then I use a wire as a pointer, fixed by one of the inside plastic cover screw ..
I then lift the car & put a jack under the wheel, from normal ride height I let the wheel down 2" but only moved the wheel up 1" (my jack started to leak)
the last picture shows that the tire moved in by 10 mm in when compressed 1 "
and moved out 22 mm when realised 2 ", 11 mm realised down 1",
not so sure if this is the correct way to measure, surely I would like to know what happened at the ground where the wheel is in contact with the ground the tire is a 225 x 40 x 18 and has 638 mm diameter, but I am not sure what those measures tell me ...

anto1150

Kos,
AFAIK the main aim is to correct toe out when the suspensions are hardely compressed.
964's suspensions are designed to generate toe-in during compression, but this is true only from factoty height to RS-something (about 1 cm?). Below that, toe-in correction becomes neutral for about another 2 cm suspension travel, then you get toe-out... noone likes it!
When lowering the tie-rod connection point, you move that part of neutral behaviour at a lower suspension position, so you won't get toe-out during normal suspension compression.

Just my 2 cent contribution to make things clearer...

Ciao

kos11-12

Hi Anto,
Yes agreed, I will dig out my geo numbers, the ride heigh Is just a bit lower than RS .
from the measures I found it seam to my that I have some toe in when compressing rather than being equal amount when compress or rebound ...?!

panzerfaust

looks pretty darn good to me! typically on a drastically lowered car it will to in on compression and tow out on jounce.

from the few ERP cars ive driven (not on a 964 though) , these guys really know what they are doing !

regards

pf

PS so how does the car drive with this new kit?

alexjc4

That's a really clever setup but it seems like a huge amount of toe change, did you check if the steering remained centred? It may be that the way you jacked the wheel caused the steering to move.

kos11-12

Hi guys,

Yes Alex, it seams a lot, it's at the front of the tire as far as it could be red, so maybe that 's why, I suppose if the tire OD was bigger I would have been reading a greater number, tire OD is 638 mm, 225/40/18

the contact tire to the ground is where it affect the steering feel.... witch is perpendicular to the centre of the wheel,
I've checked if the steering was straight, maybe I will try another method, by putting all 4 wheels on thick blocks of wood (except the front right), so the car is level ...rather than lifting only one side of the car
then I will try to check the toe at the front, at the back of the wheel but also on the floor where the tire is in contact with the ground, by kind of sandwiching a plate underneath the front tire,
the other thing to consider is that the outer tie rod is attached to the upright further back from the centre of the wheel so there will always be a greater toe riding at the front of the tire than at the back...

I though if I have minor bump steer, I would have red more or less the same value, for the same amount of compression and rebound ...!?

my geo numbers are;

front;
camber -2.01°, caster 4.22°, toe 0 12°, total toe 0.25°

rear
camber - 2.15°, toe 0 12 ° total toe 0.22°

standard anti roll bars, ride height is RS, but lower at the front (still need to confirm numbers)

weight, car is LHD , front L 275/ R 286; rear L 390/ R 406 kg = total 1357 kg

alexjc4

I think the way the pros do it is to take the spring out of the suspension strut, so you can move the suspension through its range more easily. I guess you disconnected the anti-roll bar?

I read somewhere that toe when displayed in mm (on a printout from a geo machine) is actually as it would be measured on an imaginary 28inch wheel. So it might be easiest to compare to your static toe if you translate you mm measure into degrees with some simple trigonometry.

Are those weights with driver and fuel?

kos11-12

no driver, but with 1/2 tank of fuel, jack, tools, and a few others things, (no spare wheel, 7 kg battery)
one thing I should have done is disconnect the anti roll & realise shock spring, it was quite hard to compressed further than 1", but I thought best is to try and keep everything as it is when the car is on the road...

anto1150

IIRC 1mm = 7' = 0,12 degree

Talat

You can buy RCA kits for most Jap cars surely there must be something out there for 964's other than RS uprights ? Right I'm off to check my 964 HyerRev

panzerfaust

thats not the tow change u are looking at but the camber curve of the suspension movement i reckon. i see very little divergence from a smooth camber curve. bumpster will show a subtle sine wave (for lack of a better word) along this camber curve.

alexjc4

Yeah I think you're right, thinking about it its much more likely to be recording camber. You could setup the same measurement at the rear of the wheel arch and the difference between the two would be the change in toe i think

kos11-12

Hi Talat

The issue with the RS uprights is that a different disc is needed, the offset is 5 mm smaller (I think), the upright is also thicker where it bolts to the shock(that can be cut down) and so on,
if someone (re) build a car from scratch it maybe worth it, and if needed a greater camber than - 2°, like for race cars....witch for a road /track car it's already quite a lot...this is the reasons I am trying to see if I can use the ERP kit on the 64 upright, I may not be to far, but proper measuring is vital,
the only options I have; if it's toeing in to much when compressing is to reduce the top spacer or try and fit the outer tie rod above the arm, witch would give a radically different measure.

the steering feel very precise with great grip and no drifting at all , but a tad twitchy on bumpy roads following any road imperfections and I can't figure out what is the reasons; is it because of the toe setting, the excessive negative camber, or because the rose joint have made it to sharp for road use ( or for this setting) or is it because I have now to much toe in when compressing...

let us know what is your set up and what numbers are,

alexjc4

If you wanted to measure more on the compression side you could jack up the opposite rear corner (will have more of an effect if the ARB drop link is removed).

Really I think you are close to measuring the bump steer and I think the ERP link will make a positive difference. Just setup a similar board and indicator wire on the rear of the wheel and monitor the difference in the way the front and rear change with compression and droop.

kos11-12

I will try, , I think 2 " is well enough,