TT Suspension Geometry Analysis: How Bad is Lowering for Handling?

I've always known that lowering cars past a point starts to impact handling...yes, for those of you unfamiliar with this logic, it seems counter intuitive. Lower car = lower center of gravity = better handling, right?

Problem is most cars' suspension geometry is not designed to sit low, hence when you lower a car, it can introduce things like bump steer or it can throw off static and dynamic camber.

Recently, I decided to look into the relationship between lowering and handling specifically in the case of the TT. I discovered this thread:
http://forums.vwvortex.com/zerothread?id=1363022

I must commend pyce on all the work he did to make those simulations...absolutely brilliant.

While it mostly deals with Mk4 VWs, the TT's front suspension is identical to a Mk4's, except for one critical component: the spindles (and matching control arms and ball joints to accommodate them)...more on that later.

Note: In that thread, "A4" refers to the Volkswagen A4 chassis which the Mk4 Golf/Jetta and also the Audi TT are built off of. It does not refer to the Audi A4 sedan.

The whole thread is a good read if you understand basic suspension concepts...I'll summarize my findings from that thread here.

First off, what's on everyone's mind: how can lowering hurt a car's handling? The TT uses a MacPherson strut design in which as the suspension starts to compress, the camber goes more negative (the top of the wheel tilts towards the inside of the car more). This is what you want for cornering to compensate for the large load being placed on the outer wheels to maintain as great a contact patch as possible. However, past a point, the camber starts to go more positive (bottom of the wheel tilts inwards towards the car), which is the opposite of what you want.

Lowering a car can often put its suspension geometry at the point where the camber is already more negative and as the car turns and the suspension compresses, the camber on the outer wheels goes more positive, which is opposite of what's desirable.

So just how much does lowering affect camber? Here's a graph based on a simulation pyce ran in the thread above:



(the graph is VERY close to true values...my car is lowered right around 2" (50mm) and its static camber is 1.3 deg)

Now you can see why anyone driving a lowered Mk4 VW is liable to complain about the handling. The stock Mk4 spindles lowered anywhere over about a half inch are in the region where suspension travel causes camber to become more positive...and very rapidly! At just over 3" of travel the suspension is back to zero camber.

The TT, due to its different spindle design, has a far better camber curve. TT suspension can travel about 2" before the camber starts to become more positive and even then it doesn't go anywhere near as positive as Mk4 suspension. Notice how within an inch of travel (from 55mm to 80mm), it only goes about .1 degrees more positive.

The third spindle is the H2Sport spindle for Mk4s. It has an even more optimized design, as you can see in the camber curve. The key to the TT's highly improved camber curve over the Mk4 is in the placement of the ball joint on the spindle:



giving it far better camber characteristics.


The above graph however is with the wheels pointing straight, which is obviously not going to be the case going around a turn. When you turn the wheels, the camber changes, thanks to the ~8 degrees of caster built into the system. Here's a graph of what happens with the camber at various steering angles:



As you can see, when the wheels are turned the camber goes even more negative with the TT...meanwhile the Mk4 is still sucking at life and at one point actually sees positive camber.

So now, the bottom line...how much worse are the camber characteristics of a lowered TT versus stock ride height, taking steering and now body roll into account?

Here's the graph:



As you can see, surprisingly the 60mm lowered TT actually has more negative camber (!!!) than stock ride height up to 4 degrees of body roll. As mentioned before, this is generally desirable in a turn. Past 4 degrees of body roll, the OEM ride height starts to have an advantage that at most (at 6 degrees body roll) is a half degree of camber.

So it looks like lowering doesn't impact the camber characteristics too badly. However, one thing that does change is the roll center. I won't go into detail with roll centers, but shifting the roll center can actually increase your car's tendency towards body roll. The roll center is positioned ideally right around stock ride height. The rule of thumb is that the roll center is optimized when the control arms are at or close to parallel with the ground. This is something to consider.

So what do I think?
From what the study shows, it is possible to have a reasonably low TT and not have it handle like crap. A lowered TT still maintains good dynamic camber characteristics, as shown in the graphs. At lesser degrees of body roll, the lowered TT's camber is actually more desirable than a TT at factory ride height.

As far as the roll center is concerned, while it tends to make the car more prone to body roll, there's all kinds of things you can do to inhibit body roll anyway:

-By lowering your car, you lower the center of gravity, which decreases the car's tendency to roll.
-Most coilover kits have stiffer springs than stock to help with body roll. Many of the springs are also progressive rate, meaning their spring rate gets higher (stiffer) the more they compress.
-Swaybars, the rear bar being an ever popular TT mod, also work to inhibit body roll.
-Tires can reduce body roll. Tires act like springs - when you apply a given force to them they give way somewhat based on how stiff the sidewall is and how large it is...just like the spring rate and length of a spring. Low profile tires with stiff sidewalls can work wonders in inhibiting body roll. A slight tire stretch can stiffen a sidewall even further. I used to run 19" wheels (which I don't suggest you do, they're too heavy) the fronts being 8.5" wide with a 225 series tire. It cut an amazing amount of body roll off of the stock suspension.

So there you have some brilliant research by pyce and my TT specific conclusions based on it. Hopefully this will shed some light on the TT's suspension to help you all choose your setups.

-Filip

Vmaxx coilovers review

Vmaxx coilovers are the subject of a good bit of debate between TT guys, VW guys and even BMW guys. Basic issue is that they're so cheap, they can't possibly be good no matter what anyone says, right?

Not in my book.

I had the opportunity to pick up a set of Vmaxx for an awesome price for my FWD TT, so I went ahead and took the plunge. Having ridden in/driven numerous cars with aftermarket suspension, I had a pretty good basis for evaluating the performance of my Vmaxx coils.

That said, here are my impressions.

Build quality/fitment/ease of installation:
Build quality seems solid, nothing blatantly cheap about it. Installation was the same as any coilover install, except for one issue; there's no provisions to clip the brake line to the strut. I ended up using zip ties to hold the brake line down and make sure it doesn't rub. No big deal.

They come with a two year warranty on them as well, so frankly, I'm not too concerned about them wearing out early or something like that because I can get replacement parts for the next two years.

Ride height:
Since a lot of other aspects of this review depend on the ride height, figure I'll mention it first. They go plenty low for me, with more room to go. The fronts still have 3/4 - 1" left to go down. The rears are all the way down with perches in. This picture isn't exactly on flat ground but it gives you a rough idea:

(if the pictures are cut off, right click and and click "view image" or "show image")






And one in the grass for better to look supar low! w3rd!



My height is set pretty low but still driveable. I don't subscribe to the "as low as you can go" school of thought. My subframe is close enough to the ground as it is, I'd rather it not be any closer. It doesn't rub at all daily driving either. Sometimes if I hit a bump/incline taking a turn real fast it'll rub up front a tad, but it's minimal. I'm running 8" wide ET35 wheels with 15/20mm spacers front and rear, respectively.

Technically it's too low for optimum handling right now, since the control arms are tilted upwards slightly, throwing off the roll center. When I hit the track this summer, I'll pick it up some, but for now I'll leave it this way for looks.


Ride quality:
The ride is great. It's obviously rougher than stock, but it's not uncomfortable by any means. It has not elicited complaints from any passenger's so far, including females.

I've actuallye ridden in cars that ride far, far worse. My car rides about the same as my buddy's Mk4 GTI on Koni coilovers. It's only rough enough to be slightly annoying when you're on really TERRIBLE roads, but what can you expect from a lowered car? I think the moral is that as long as you don't slam the crap out of them, they will ride fine. Then again what coilovers actually ride nicely when slammed to the ground? I doubt any do...

Handling:
Night and day over stock. Body roll is almost completely gone. What impressed me a lot however was that the car does not lurch forward and back anywhere near as much under braking/acceleration/corner lifting like it did with the stock suspension. This is excellent for braking stability and leaves some margin for error when going too fast into a turn (i.e. you can slow down and not lose the back end). They also don't bump steer or anything like that.

I purchased an accelerometer and managed to pull just over 1 G on a highway on-ramp as well. Take that, domestics ;)

While they could be set a bit stiffer, I think if the setup was any stiffer it would start getting uncomfortable for daily use. Therefore I'm quite happy with how they're set up.

Overall I'm definitely impressed with how they handle.


So for me, Vmaxx is an excellent buy. I think most of the hate either comes from prejudice towards a cheap product or simply bad experiences with slammed cars, which don't ride or handle optimally (especially Mk4s, with their crappy spindle design...but that's another story).

Door sensor fix - DIY

I wasn't aware of how common this problem was until I experienced it - my door sensor stopped working i.e. the car wouldn't detect that my driver's door was open. This meant my window wouldn't do the slight roll down when I opened the door, the dome light wouldn't come on when I opened the door and most importantly the car wouldn't "bong" at me when I left my lights on...which lead to several instances of a dead battery.

Upon investigating it turns out this is a fairly common problem. There was some info I found in the AudiWorld FAQ but now it's FUBAR'd and I can't find it.

Here's how I went about fixing mine:

1. First I removed the door panel...probably the easiest thing to do on the whole car.

You have to first twist off the round metal cap at the base of the door handle (the thing that caps the metal cylinder where the window switches are). I believe you turn it counter clockwise. Once you have that off, there will be a lone torx screw in there...unscrew it and remove it. Then, grab the handle and lift up on the door card and you should feel it slide off the door.

Once you have access behind it, unhook the cable that attaches to the upper door release handle from the handle. Then, to get the card out of the way, just set it down on your door sill where it would normally sit when the door is closed...now it's conveniently out of your way.

2. Next you have to get the door latch assembly out; to do this you need to undo the two bolts on either side of the latch. You should use a 12 point bit to do this, and by "should" I mean "you can get away with using a torx bit carefully." However AutoZone and other parts stores do sell the 12 point bits, so I had a set to use.

Once you have it unbolted you have to disconnect the cable that ties the latch to the door handle. You have to turn the end of the cable the right way to let it slide off the lever that attaches it to the latch assembly. You can see the cable end here:



This was a bit tricky for me.

Next, just disconnect the wiring harness and the latch assembly should be free.

3. Now that you have the latch out, you can pop the sensor out (follow the blue and red wires, undo the clip and pull it out). Most likely you will see that it stopped working due to the rubber cap on the plunger getting worn off - it's no wonder. The design is crappy; you have rubber rubbing directly on another surface, it's BEGGING to wear out.

You can see here how it's worn the surface of the latch as well:

(door closed)


(door open)


In case you haven't figured it out, the worn part slides into contact with the plunger on the switch to close the circuit and let the car know that the door is open.

4. Apparently, there's a switch sold at Radio Shack that people use in place of the OEM switch, but I couldn't find any switch of this style at my local Radio Shack. So I resorted to a switch I had laying around, albeit much larger than the original piece:



So I ended up orienting the switch perpendicular to the OEM orientation to make it fit. I drilled a hole to attach it with a screw on one side and positioned the other side to sit against the body of the latch itself to prevent the switch from moving. Here's a picture of how it turned out:



So how you rig it depends on what switch you get a hold of, but that's how I did it.

5. Make sure you reassemble everything correctly. The paddle looking thing here:



Is what actuates your lock mechanism. Make sure it sits where it's supposed to in the latch assembly. Don't forget to reattach the cable for the handle as well.

Good luck!

Ultimate Timing Belt DIY

For those of you who need your timing belt done, some people have done it themselves. While you can get it done at independent shop (i.e. not a dealer) for $500-$700, you can also do it yourself with ~$250 of parts.

The best DIY I've seen for this is the one by BlueTTop:
http://forums.audiworld.com/showthread.php?t=1961739&highlight=bluettop

I have yet to see a more thorough and detailed writeup out there. Nice work :)

Suspension install DIY and tips.

DISCLAIMER: Follow these at your own risk. I'm not responsible for you damaging your car/injuring yourself/harming anything or anyone else. You shouldn't be touching suspension unless you have a good idea what you're doing.

I just got done installing coilovers and figured I'd share some of the things I picked up on while doing it. I went by this DIY for MkIV coilovers...they are almost identical up front (minus the swaybar links) and the rears are very similar to a FWD TT. http://www.nclh.org/car/coilover_howto/

Keep in mind, I have a FWD which is different in the rear...however even the quattro doesn't look that different.

Tip #1: Use air tools.
If you don't have air tools find someone who does. A lot of nuts in the suspension are nylon locknuts and an incredible pain to remove by hand. This way you also won't need special tools to remove nuts from the strut towers.

Tip #2: Make sure you have a spindle spreader tool and proper spring compressor.
You have to pry the front spindles apart to remove the front struts; there is a special tool for this. It's just a little socket tool with an oval shaped bit that's used to pry the spindle apart. It's available on ECSTuning for about $25 if I recall.

Also, if you rent spring compressors from AutoZone ($50 when you rent them, you get the $50 back when you return them) make sure you ask for STRUT SPRING COMPRESSORS. Initially I rented a pair of "spring compressors" and they were not the correct parts. You need "strut compressors" or "strut spring compressors" even though most people and DIYs just call them "spring compressors."

Tip #3: Replace your front strut bushings/bearings.
Not only is this good for refreshing your suspension, it also saves you from needing to take apart your OEM struts to retreive the bushings/bearings.

Tip #4: Use loctite blue.
Suspension components are constantly exposed to vibration and force...you don't want the bolts working themselves loose. Get a tube of loctite blue and put it on all the bolts you install...a lot of the nuts are locknuts but I still used loctite anyway.

Tip #5: Removing the front struts.
The front driver's side comes right out. You can get the control arm plenty low enough to just take the strut right out and put the new one right in.

However the passenger's side, for whatever reason, does not go down anywhere near as low. This makes it a bit of a pain to get the strut out.

At first I tried to compress the spring far enough to get some clearance to remove the strut....I hit the damn thing with four spring compressors and it still wouldn't come out. Point behind using more than two was that compressing several of the coils would give me access to the other coils then I'd compress those with the other pair...but this still wasn't working. I was doing this at a friend's garage and he didn't have a socket to remove the upper strut nut (deep 21mm)...so I couldn't get the bushing out. If I could have gotten the bushing out I MAY have had enough clearance to remove it.

There is BARELY ANY clearance to even get spring compressors in there...even the spring coils themselves are hard to get the spring compressors onto. Here's what I'm talking about:



What I ended up doing was disonnecting the tie rod from the spindle and removing the ball joints. This allowed me to move the spindle enough to get the strut out. Here's a pic of it removed...notice how I had four spring compressors on it by this point:



I'm not sure if spring compressors would have been necessary to remove it this way, I'm going to guess that they wouldn't have.

Make sure you put the ball joints back where they were or at least both in the same position. They are usually the whole way to the inside of the control arm. They should pretty much sit themselves in this position when you go to reassemble anyway. If you move them it adjusts your camber.

The part of the tie rod end that bolts into the spindle doesn't have any adjustment, so you shouldn't throw off your toe just by removing it. You'll need an alignment for the rears anyhow if you're quattro so you might as well get an alignement for good measure.

Tip #6: Removing rear springs.
Since my car is FWD, its rear suspension is a torsion beam setup. The torsion beam is pretty robust, however the quattro fully independent suspension might not be so robust.

That said the way I removed the rear springs on my FWD involved two people. I jacked up one corner, put it on stands and removed the wheel (obviously) then had my buddy stand on the rear brake caliper while I snatched the rear spring out. Again this might not be a good idea with rear control arms in the quattro (or in general) but it worked for me. Worst comes to worst you would just use a spring compressor to compress the spring and then remove it. However using my method you can have the spring out in notime.

Tip #7: Removing rear shock mounts.
You'll notice if you just try and unscrew the shock mount off the shock the shock will just spin. Have a vice grip or a pair of channel locks and a rag (to not damage the old/new one) ready to clamp down the shock so you can remove the nut that holds the mount.