My front roll center/bump steer solution
#47
Nordschleife Master
It is an awesome build. I'm curious to know why they would go to the trouble of producing a fiberglass us spec rear bumper when they had a lighter row rear bumper in the stock room. Class rules?
#48
Race Car
#50
Burning Brakes
That's a beautiful summary of the situation - thanks very much. My feeling is that this is a worthy endeavor for folks who are very far up the curve in terms of their driving skill and experience. I think I need to focus on my driving for awhile until I get to that level - to be honest, I couldn't even tell you if my car is front- or back-end limited in terms of grip. It feels pretty well balanced to me, and the instructors at the track have said the same thing. The most glaring issue with my car (other than the loose nut behind the wheel) is the fact that the suspension and brakes are so capable that the tires aren't keeping up, and this is the primary car-related item I'm currently working on addressing.
#51
Burning Brakes
Thanks for posting, Michael! That is certainly the "better" way of doing what we are discussing, as it eliminates any kind of drop pin or longer ball joint.
It would be simple enough to take some measurements and relocate the forward inner control arm mounts by drilling new holes in the crossmember. The rear mounting points would be more difficult as there is no room to raise these, but from the first pic it looks like they actually moved the caster blocks to mount on the inboard side of the chassis rails . . . . . quite trick! I would be interested to know what this would do to the caster setting, as the forward mounting points are also further inboard . . . . but this would also reduce the track width at the hubs, unless wider control arms were used.
It would be simple enough to take some measurements and relocate the forward inner control arm mounts by drilling new holes in the crossmember. The rear mounting points would be more difficult as there is no room to raise these, but from the first pic it looks like they actually moved the caster blocks to mount on the inboard side of the chassis rails . . . . . quite trick! I would be interested to know what this would do to the caster setting, as the forward mounting points are also further inboard . . . . but this would also reduce the track width at the hubs, unless wider control arms were used.
#52
Burning Brakes
The main mod I see in the rear suspension in terms of roll center geometry, is the inner pivot appears to be raised slightly with a plate. Is it really that simple? Can we just move the inner pivot up slightly to reduce roll?
#53
Rennlist Member
I did look at replacing the stock spindles with some custom ones down here. Not cheap but advantageous on many levels. One, you can design all these improvements into a one piece billet design. Two, you can utilise a much larger bearing than the stock ones which are pretty small compared to a lot of other cars. Especially with a lot of downforce cars exerting higher levels of Gs into these parts than they were ever designed for. We have decided to just change the front bearings after every meet. Lastly, these parts are old. I doubt many of us are crack testing their spindles?
#54
The 924 2.0s used cast iron.
Front is the same way. Either dictated by rules or not, likely to maintain the US appearance as the car was designed for SCCA.
Front is the same way. Either dictated by rules or not, likely to maintain the US appearance as the car was designed for SCCA.
#55
Rennlist Member
The rear has no torsion bars; coil-overs only.
Thanks for posting, Michael! That is certainly the "better" way of doing what we are discussing, as it eliminates any kind of drop pin or longer ball joint.
It would be simple enough to take some measurements and relocate the forward inner control arm mounts by drilling new holes in the crossmember. The rear mounting points would be more difficult as there is no room to raise these, but from the first pic it looks like they actually moved the caster blocks to mount on the inboard side of the chassis rails . . . . . quite trick! I would be interested to know what this would do to the caster setting, as the forward mounting points are also further inboard . . . . but this would also reduce the track width at the hubs, unless wider control arms were used. I would be interested to know more about this setup.
Also, I'm not sure there's enough room under the 944 sump to move the steering rack that far up, but I'd have to double-check that . . . .
It would be simple enough to take some measurements and relocate the forward inner control arm mounts by drilling new holes in the crossmember. The rear mounting points would be more difficult as there is no room to raise these, but from the first pic it looks like they actually moved the caster blocks to mount on the inboard side of the chassis rails . . . . . quite trick! I would be interested to know what this would do to the caster setting, as the forward mounting points are also further inboard . . . . but this would also reduce the track width at the hubs, unless wider control arms were used. I would be interested to know more about this setup.
Also, I'm not sure there's enough room under the 944 sump to move the steering rack that far up, but I'd have to double-check that . . . .
It was mine years ago. It seems that Friesinger has (almost) all of the original configuration cars and he now controls the value. Apparently BIG money now. I never measured the motion ratios, but did pay attention to the front roll center and realized I was running my car too low (I had another 933 with a 944 engine). On these 933 cars, Porsche had the suspension geometry figured out.
#57
Three Wheelin'
Thread Starter
That's a beautiful summary of the situation - thanks very much. My feeling is that this is a worthy endeavor for folks who are very far up the curve in terms of their driving skill and experience. I think I need to focus on my driving for awhile until I get to that level - to be honest, I couldn't even tell you if my car is front- or back-end limited in terms of grip. It feels pretty well balanced to me, and the instructors at the track have said the same thing. The most glaring issue with my car (other than the loose nut behind the wheel) is the fact that the suspension and brakes are so capable that the tires aren't keeping up, and this is the primary car-related item I'm currently working on addressing.
#58
Burning Brakes
I agree. However, I also think that if and when I level my front control arms, and thereby raise the roll center, I should do the same at the rear, and this is a much harder task than the mods to the front suspension discussed in this thread. The guy who made and sold several modified torsion tube carriers with the raised trailing arm mounting points says he isn't planning to make any more after the parts he has on hand to make a few more are gone, and Kokeln hasn't made theirs for years.
#59
I just received mine from Bruce a couple of weeks ago. It is the "extra beefy" design and though I am by no means any kind of engineer it certainly does seem like a strong unit. I am slowly assembling all the pieces to upgrade from the 85.5 suspension parts to late ABS parts. I will wait to do the entire rear in one go when I am ready to add ABS and everything. That won't be for a while so that won't stop me from upgrading just the front end earlier. I just don't like the angle of the control arm pin with the stock arm as low as I have the car.
#60
Burning Brakes
I just received mine from Bruce a couple of weeks ago. It is the "extra beefy" design and though I am by no means any kind of engineer it certainly does seem like a strong unit. I am slowly assembling all the pieces to upgrade from the 85.5 suspension parts to late ABS parts. I will wait to do the entire rear in one go when I am ready to add ABS and everything. That won't be for a while so that won't stop me from upgrading just the front end earlier. I just don't like the angle of the control arm pin with the stock arm as low as I have the car.