Hi guys,

I have a mk4 built for serious track day use and at the moment I'm working with the suspension geometry to improve car handling so I can beat more sports cars. Pics: https://eero.kuvat.fi/kuvat/Ford+Escort/Escort+2020/



I have corrected my Roll center by lifting the TCA inner joint attaching points by 16mm. At the same time, I added apprx 1deg camber by moving the TCA 10mm to out. So I just drilled the new holes 16mm upper and 10mm outer than originally.

Roll center and camber before: 33mm LINK TO VSUSP 1

Roll center and camber after the change: 90mm VSUSP LINK 2

At the same time, this change did affect on bump steer. Even before the change my bump steer values were disaster:

Distance from hub to wheel arc and toe in / toe out value:
300mm / toe-IN 2,9mm
320mm / toe-IN 0,3mm
350mm / toe-OUT 5mm

So 50mm change in car height did cause apprx. 8mm difference from toe-in to toe-out. NOT GOOD! 50mm height change is not even far from the reality when braking and turning into a corner and then opening with full throttle. Lifting the TCA points might even increase this, so I really need to do something for it. I need to do more measurements, but now it's not about the current values but how to FIX this issue.

Possible actions to prevent this unwanted phenomenon:
1) changing the height of the steering rack (new attachment points or brackets needed)
2) changing the length of the steering rack (some spacers between the steering rack and tie rods so steering rack would be longer and tie rods shorter)
3) changing the attachment point of tie rod end to the hub (unlikely, tie rod end is attached from above, so only possible action is to open the hub and attach the tie rod end from below. this would be a very huge change, maybe +40mm.)
4) something else?

Have you guys made some actions for similar issue and can you share your thoughts about it?

 

If I’m not mistaken the Escort mk4 has the steering rack behind the front axle. So if you get toe in on compression I would think the steering ball joint would need to be mounted higher relative to the knuckle to get more neutral bump steer. So in that sense your correction of the roll center should have helped already with the bump steer as well.

But since the steering arm runs quite a bit higher than the TCA you will always get some bump steer over the full suspension travel. So you need to make it as neutral as possible close to the normal ride height.

 

Yes rack is behind and above the TCA:s. I have tried to visualize the geometry on paper and tested some changes but still won't get rid of this annoying bump steer issue. I mean current bumpsteer is way too much and should be reduced even by 70%. Next I might try some steering rack extension spacers but I would need like 75mm spacers and those would be pretty extreme for yearly inspection 😄

To be honest I'm very disappointed about the level of technical discussion there is. Most of the projects has some aluminium radiators and carbon roofs, forged Pistons etc. totally unnecessary parts and at the same time I'm the only one struggling with the geometry issues when actually using the power of a boosted engine. All show no go?

I think the real suspension masters arent sharing their thoughts for reason or another.

 

Still couldn't find a solution for this issue.

 

i have about 0.5mm over 2 inches
As you know mine is a little way off a standard car but it has taken a long time to get it where it currently is
do you use a bumpsteer gauge?

 

Yes nigel your car is on a totally another level compared to rest of us in this forum. It's impressive. I'm afraid of i can't ever get on the same level.

I made new fresh measurements yesterday. Pretty much camber & caster, roll center improved, steering parts stock.

I measured toe-OUT with different riding heights: from 573mm to 627mm floor-to-front-wing.

573mm --> toe-OUT 1mm
591mm --> toe-OUT 2mm
605mm --> toe-OUT 6mm
617mm --> toe-OUT 8mm
627mm --> toe-OUT 11mm

54mm change in car height and 10mm change in toe-out. I don't have a bump steer gauge so the accuracy might not be ideal.

All values are total toe-out with both wheels combined, so one corner value is splitted by 2. Seems that the steering rack should be dropped down and it might help, maybe the spacers to extend the rack length would also help. Don't know for sure.

I think the overall situation wouldn't be that bad if i try to prevent the suspension for moving that much. 54mm change from bump to droop is quite much. 573mm ride height will scratch the tyres for sure. Limiting the rear droop might help with the front bump and stiffer rear springs might help with the front droop.

Photos of the riding height:

https://eero.kuvat.fi/kuvat/Ford%20E...keus%20MAX.JPG
https://eero.kuvat.fi/kuvat/Ford%20E...keus%20MIN.JPG

 

only way to know for sure is use rosejointed steering arms and play with different height spacers eith underneath or on top of the steering arm
you will get different readings for each side of the car