running wider front tires than rear

B8 S4
#1

I wonder if this chassis would benefit from wider front tires than rear, so I’m seeking feedback from chassis guys. The RS3’s sport package option has a similar setup. I realize that cars in that Golf/TT family drive very differently (like a FWD). I think the S4 has a natural tendency to understeer, which is counteracted by the sports diff. The question is whether having better grip at the front end would benefit the car more than the differential in traction on the outside rear tire. A possible downside could be the car would not want to turn in as easily with a front that wide. Another unknown is whether this type of quattro system would break with a front tires 0.5" taller (I think the answer is no). I think the benefits are that the front tires are being asked to do A LOT of work - carry 60% of the static weight, heavy braking, and a lot of turning. My fronts wear faster than my rears. I don’t rotate wheels.

Anyway, for practical purposes I’d keep the 255/35ZR19 PSC2 with a 19x8.5 on the rear, and substitute a 275/35ZR19 PSC2 with a 19x9.5 in the front. I think I have front fender clearance with the high camber. I have no more clearance on the rear - the PSC2 runs quite wide and I suspect it could touch the fender (rear bumper cover edge) when the car is in motion. I can see it starting to peel back.

I’m not committed to this course of action, just seeking feedback.

#2

I will respond tmw. But the answer is not so cut and dry, and there are handling trade offs with such a setup. You will find more advantages with a more ideal alignment. A wider front tire is just a bandaid. OEM’s are not afraid of doing this BC the handling tradeoffs keep lawyers happy. Width is not everything.

#3

OK so now I have a keyboard.

Going with a wider tire front that rear as you mentioned, will introduce additional scrub - so there is a delayed steering response. Scrub is basically the tire needing to travel some distance before a direction change is initiated (even though the wheel is already turned). The greater the distance between the tire and the axis of the kingpin, the greater the scrub. So doing this type of setup will only make what this car is bad at even worse (corner entry).

Going to a wider front that rear also will alter the total dynamic load transfer of the front and rear axle–i am not saying the amount of load transfer suddenly changes, but the ratio will change. For example, if the original load transfer between the front and rear of the car was 50% in a corner (ie: 2000s lbs equally transferred from one side to another when the car is settled in a corner). With a wider front than rear, you are forcing the load transfer to happen more quickly in the front (which will make the loss of front end grip more sudden), but also having the rear of the car roll more due to the change in track width.

The real question is - what are you addressing with the desire for a wider front tire than rear?
You’re putting more unsprung weight up front, and really, if its handling balance you are after, you can do so with an alignment.

I am about to write a blog on this topic, but I’ve updated my alignment recently and my car can rotate on demand with ease - it now has lots of trailing throttle oversteer and corrections on entry/mid corner are very easy to execute. The car is much more nimble than before and actually has been the car that rotates more than any other car I have now owned. I have made the S4 neutral, and have the ability to oversteer as needed. It really no longer feels much like an awd car except on corner exit. I have taken a few guys from a race team for a spin and they are surprised that a street Audi was able to do the things it was doing–all this with 245 square rubber.

I got some guys who I pass that later tell me that they see the car rotate so much on entry that they think I’m about to lose it, but then see the car grip and continue on as usual. Not saying my setup is the be all end all–because it isn’t, and not everyone drives in this style. But my point is that if you’re looking to improve handling, an alignment is going to go further than an oddball tire setup that is full if compromises.

#4

Why do you not rotate wheels west? I swap front/rear at the end of day 1 and am considering cross rotating if it’s going to be dry day 2 (my tires are directional in the wet).

#5

^ yup curious to know the same.
I run direction tires and i take it even a step further - i dismount them and flip sides so that the outside shoulders ride on the inside and vice-versa after they are flipped.

i can get…5 track days total with Dunlop z2’s. Car is a pig on rubber.

#6

boro92, mind sharing the alignment settings you’re running now?

I’m going to increase my spring rate (bottomed out on the track) by 50lbs on all four corners and need an alignment after. Want to experiment with a few setups that seems to be working with the local guys and compare it with what you’re running.

#7

Yup - about to blog on this topic.

Camber: -3f, -2r
Caster: 5.5
Toe: -0.12f, 0.15r

All of the above is measured in degrees. FTG is 26f, 25.5r
I got some vids being uploaded from the track day over the weekend. Lots of rotation, never miss an apex again :slight_smile:
Front tires take much less of a beating–that’s for sure.

The above changes were so dramatic that I ended up running tire pressures in a FR style.
That is, 40f/34r hot pressures. Previous to this, i’d run 40f/44r to help with rotation. Now when I even run 40/40 it is too squirrely.

EDIT: Video here: https://www.youtube.com/watch?v=kyGIjeJQ1F8&t=103

Not my best lap by any means, but it’s a good view of what the rotation looks like. You may notice I’m diving into corners pretty hot. The back end will rotate on entry. Also will do it mid corner if I trail the throttle as needed (in double apex situations). i got other vids that show that more clearly, but dont want to bore you with videos.
OK wait, I lied: https://www.youtube.com/watch?v=kyGIjeJQ1F8&t=49

The clip above (49 seconds) is entering a double apex. See that I enter the first apex early, then swing wide to setup for the 2nd apex. It is here that you can see the trailing throttle rotation. The car can be throttled steered entirely.

#8

Blog post up!

http://dreamingin302ci.blogspot.ca/2015/08/how-to-make-your-understeering-s4-handle.html :smiley:

http://4.bp.blogspot.com/-rE-wZsNnFY4/VdKdLm9JhWI/AAAAAAAAA7g/Nu-oBQR2SL0/s500/11864790_1610054455923420_388123343400522060_o.jpg

#9

Wow, you run front toe out in the streets? I would think that would scrub your tires a lot during a normal work commute. Let us know how the long term tire wear works out for you.

#10

The amount of toe out that I run is less than the toe-in from factory. So i have less tire wear than what a factory alignment would otherwise offer. My rear toe is also significantly less than factory. More than anything, the factory #'s is what would kill tires (camber notwithstanding)

Also, because of how i use my car, i have greatly extended tire life. With a stock alignment, I got 2 track days before tires were dead (no joke–and that’s with rotations). I now have 4 on these tires (they have been dismounted and flipped once), and look like they have life for 2 more. 3x more tire life :slight_smile:

FWIW my tire wear from this past track day is even less than what it was on my old alignment. So it has only gotten better. With the car pushing less, the tires are not scrubbing their life away anymore.

#11

What bars are you running?

#12

Eurocode 32/25.5mm

#13

are you the stock endlinks? or theirs?

#14

Stock endlinks. Didn’t want the nvh of spherical.

#15

I would say the NVH of the spherical links is zero. The issue is they don’t wear well. Probably need to be rebuilt every 2-3 years. I’ve had mine through 2 winters and no noise or clunking. Knock on wood.

#16

Good to know! It’ll be zero until they begin to wear :slight_smile:
I’ve had spherical links before and the clanging (albiet this is after a few winters) is unbearable!
Though if one is ok with replacing them every so often, then it’s all good.

#17

West runs spherical lower control arms. EC also makes spherical upper SPC arms with the same bearing company. I would not run either of those on my car. But the links seem to have worn fine, even without a boot. YMMV I guess. I’ve read some not good cases and Jeff had his replaced after a year I believe.

#18

This is what concerns me, besides the ridiculous asking price they put on them

#19

I was fully expecting the lower sphericals to have to be replaced as it’s been 3 years, but they’re still tight as a drum. They do make noise but substantially less than if you had noisy brakes (I don’t). I’d say it’s only undesirable when you are pulling into a parking space or doing a low speed maneuver. You can “hear them working” but nothing is broken. I would say the effect on handling is over 10x greater than an Alu Kreuz. The car barely pitches under full braking force and the steering holds without adjustment no matter how much you load up one side of the car. This is the kind of thing that can give you an edge over a V8 R8, as crazy as that sounds.