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Sure, but as you say it's complicated as you need to either remove or compress the spring, You use dial indicators and a flat plate bolted to the hub to measure the toe change wrt to suspension travel, I'v posted several of these over the years
Generally it's sufficient to measure the caster w/ the Motorsports Gauge but that depends on having a stock motorsports suspension setup. Of course most of us do except for the big variable of static ride height.
Bill, so the way Mirage told me is the way to do it or not? Im lost on this KT alignment
What he is saying is there is an easier way to do it when you have the factory control arms and when you go aftermarket there are other ways to achieve the same outcome with more effort, which is what you shared that Jae @Mirage does.
Bill, so the way Mirage told me is the way to do it or not? Im lost on this KT alignment
I like the sweep, it gives you information on your car the way it is set up.
The factory specs are fine for factory setup cars I run mine at ~Cup car height and so feel comfortable using Cup car specs, which is +3° to +3° 30' of rear caster.
The factory has other specs using other tools for the street height cars, including RS. If running at those heights use those specs, or experiment
Keep in mind that when you have a full monoball suspension, as you appear to have, there is no longer any KT, you just have the usual toe variation w/ suspension travel.
Toe variation is a powerful tool, that significantly affects how the car handles, yes, you need the same toe variation on both sides, but keep in mind that the less caster the car has the less toe variation and the faster the car will respond, so if I ran +3° instead of +3° 30' static rear caster the rear would react faster, when I was younger and more aggressive this might have been a good thing, but I'm older and slower so like the slower reactions. How do I know I like this? well I've spent the last 10yrs tracking the car trying all sorts of different configurations, I like the full monoball suspension at the ride height w/ the alignment, tires and aero that are dialed in now.
W/ a bump sweep curve you will still want to drive the car and see how you like it at the edge, if it's too twitchy slow whichever end of the car down to suit or vice versa. All good shops will have a feel for their customers and where the car ought to be set, but the proof is in the driving.
This info is about stock RoW 993 rear KT, the toe curve( aka bump sweep) is the result of a summation of the toe Δ caused by suspension travel + toe Δ from the elastic deformation of the bushes in arm 5 and arm 4, what is happening is that the rear wheel turns around the instant axis as the suspension moves up and down under load. When using all mono-***** the elastic deformation component is eliminated
If the toe curve is vertical(ie zero caster) that end of the car will lack directional stability and be nervous, as the curve flattens more and more directional stability is induced, the rear slows down. The curve shown is for stock spec on KT(rear caster), KT is changed by adjusting arm 4, lengthening arm 4 moves the hub down and forward, reducing caster, lengthening it does the opposite
Wheels are done. They were disassembled, polished and reassembled. Used a Ceramic coating on the lips and calipers to keep the shine and repel the brake dust.
The KT adjustment is really the same thing as "Caster Lead" in the front suspension. If caster lead in the front is not equal the chassis will pull to the side with the most caster lead.
In the rear of the 993 the caster lead determines the force driving the deformation of the bushings - the "Kinematic Effect". This causes a rear wheel steering effect where the outside wheel toes in and the inside wheel toes out thus steering the rear of the car toward corner decreasing oversteer. This is really passive 4 wheel steering and is now done actively in some of the latest 911s. The adjustment tooling Porsche supplies for Kinematic adjustment assumes a ride height and camber within their published specifications but for many ride height and camber are outside published Porsche specs.
Removing the suspension bushings by installing monoballs eliminates this effect but there still is a bump steer as the wheel moves up and down. The magnitude and direction of steer effect is influenced by ride height, caster, toe and camber settings.
What I believe Jae at Mirage does is a bump steer analysis using dial indicators to measure steering angle while the suspension is moved up and down with the spring removed at the particular ride height and camber chosen by the customer.
The goal is to get slight toe in in droop to stabilize the car under braking but still have no toe out in jounce to cause oversteer when the chassis is loaded in a corner. Personally, I like this method since it an outcome analysis of the caster setting not simply a dial in of a caster setting and hope for of what you want at your given ride height and camber settings.
Wheels are done. They were disassembled, polished and reassembled. Used a Ceramic coating on the lips and calipers to keep the shine and repel the brake dust.
wheels look great, did you sub the wheels out to a shop or DIY?
Originally Posted by DutchNy
Wheels are done. They were disassembled, polished and reassembled. Used a Ceramic coating on the lips and calipers to keep the shine and repel the brake dust.
Drove the car yesterday, everything felt great... then i hit a pole hole and it started making a noise and these two bolts fell out... no idea what they are from
01-17-2019, 10:07 PM
