Problems with Running Slick Tyres

[Captain Ahab Jr]

Would be interested to know of peoples experiences using slicks on an early pre-73 car.

I'm building a trackday car and would like the ability to run with slicks but am concerned thet the extra tyre grip will cause problems to suspension, wheel bearing, wheel hub components due to the increased loads.

Might be worrying about nothing but thought it was worth asking.

[Flieger]

They run SC/Carreras with wide bodies and slicks in POC all the time. The only reinforcements they do are the roll cage (and rear anti-sway bar brackets probably) to my knowledge. Magnus runs Hoosiers on all his cars all the time. Not to mention the original RSRs used sticky tires.

[GaryR]

If you are an advanced driver use Hoosier R6's, if not stick with a tire like the Nitto 1 or 5, Kuomo ecsta, etc..

[ted]

Originally Posted by Captain Ahab Jr

I'm building a trackday car and would like the ability to run with slicks but am concerned thet the extra tyre grip will cause problems to suspension, wheel bearing, wheel hub components due to the increased loads.
Might be worrying about nothing but thought it was worth asking.

No bearing/hub life issues here with vry wide tires/rims.
If you keep rubber bushings,
might see cracking/require weld repair around your 4 spring plate cover studs.
If you track a lot consider the ERP spherical suspension.


Can't beat a set of 15x9 bias ply cantilevers with phone dials or cookie cutters.

[Quicksilver]

Slicks really aren't a big deal. The real detail to remember is the closer to the peak of performance pretty much anything is the more abrupt the transition when it falls off that peak. This is true with a lot more things besides tires...
When the tires let go it is with some real 'snap' so things happen in a hurry. The grip falls off abruptly with higher slip angles on a race tire too. When you walk on a tightrope falling off is very noticeable!

As GaryR mentioned: If you are still learning I highly recommend that you don't start with a really high grip tire. I know a few people who are plenty smart but because they started out with GT3s or Lotus Elises on gumballs, they have never learned to be smooth and they probably never will. They would be much better served by putting on a set of cheap Sears radials and feeling their way around on something that reacts slow enough that it can be comprehended and learned.
When we teach car control classes we do the most important ground work on a watered down skidpad. The police even have a training center in San Bernadino with a polished concrete pad with a sprinkler system on it. It is almost as slick as ice.

[Captain Ahab Jr]

I'm not really concerned how slicks perform as a tyre more how different parts of the car handle the extra loads put on them by slicks.

The one part I don't want to have to upgrade is the rear wheel bearing as this would be a major job for me to do.

[GaryR]

Originally Posted by Captain Ahab Jr

I'm not really concerned how slicks perform as a tyre more how different parts of the car handle the extra loads put on them by slicks.

The one part I don't want to have to upgrade is the rear wheel bearing as this would be a major job for me to do.

The stock Porsche 911 bearings and spindles are more than strong enough to handle the loads placed on them by sticky tires if they are in good condition. I'm racing a 33 year old car using all stock parts (as are most everyone else). If it was a 944 you were talking about then there are weaknesses you need to address.

You do understand that "Slicks" refer to treadless designs that are not DOT approved such as the Michelins, Dunlops, Yokos. etc. and a "DOT Racing Tire" has grooves and is substantially harder compound such as Hoosier R6 or BFG R1.. yes?

What I stated above is true for both types, but a "track day car" would be quite expensive to run on true "Slicks" and a total waste IMHO.. Personally I would replace the rear wheel bearings in an old car when I had it all apart to install new poly bushings/monoballs in the trailing arm (track prep), a shop can press them out/in and replace the seals no problem, then you know what you have....

[Captain Ahab Jr]

Originally Posted by GaryR

The stock Porsche 911 bearings and spindles are more than strong enough to handle the loads placed on them by sticky tires if they are in good condition. I'm racing a 33 year old car using all stock parts (as are most everyone else). If it was a 944 you were talking about then there are weaknesses you need to address.

You do understand that "Slicks" refer to treadless designs that are not DOT approved such as the Michelins, Dunlops, Yokos. etc. and a "DOT Racing Tire" has grooves and is substantially harder compound such as Hoosier R6 or BFG R1.. yes?

Thanks GaryR, my project is a bit different to the norm but I'm trying to use the lightest stock 911 parts I can find to keep weight to a minimum and am trying to find out how much abuse they can take before committing to one particular car type.

Yes, I'm familiar with what slicks are and do

[Jeff Higgins]

You'll only run into trouble if you continue to insist on calling them "tyres". Here in the states, they are known as "tires". What part o' Texas you from, boy?

[Captain Ahab Jr]

Originally Posted by Jeff Higgins

You'll only run into trouble if you continue to insist on calling them "tyres". Here in the states, they are known as "tires". What part o' Texas you from, boy?

Thanks for the expanding my vocabulary, please allow me to return the favour,

"Irony", the definition is,
You giving me a lesson on the English language

Never been to Texas but I think I'll like it there if they can read and write all proper like

[Jeff Higgins]

All kidding aside, like the others have pointed out, you will have no troubles whatsoever. The suspension components on these cars (I assume we are discussing torsion bar 911's, even if subsequently modified to coil over) have been so well vetted by so many people for so long that any additional stresses imposed by today's improved tires have proven to be a non-issue. Even with relatively stock suspensions on the very "stickiest" of slicks.

About the only issue folks run into is a somewhat vague feeling, or a lack of precise "feel" to the car, when the stock rubber bushings are kept. They kind of feel like they are wallowing a bit as the available grip overwhelms those poor rubber bushings, compressing them more than ever intended, and allowing the suspension points they are meant to control to move around too much. This is not really a wear issue, or a safety issue of any kind. Simply replace those "soft" points with the appropriate harder bushings or monoballs, retaining the stock components otherwise, and you will be fine.

About the only durability / safety issue I've seen arrises with the use of extremely heavy torsion and / or sway bars. While I have never seen an issue with the front suspension on any car, the rear torsion bar tubes do seem to be prone to twisting in the body. You'll see cracks developing around the four outboard mounting holes in the wheel wells. Rear torsion bar mounts are well know for tearing off as well. Please note neither of these conditions come about through the use of sticky tires, but rather substantially increased torsion and sway bar sizes.

[Captain Ahab Jr]

thanks Jeff, from the replies so far it looks like I shouldn't have any problems.

I plan to use the stock rear wheel hub, stub axle and bearing but in a custom machined or cast alumnium upright. There is a good weight saving to be had by going with the smaller version of bearing, at least 2lbs but could be more.

As a plan 'B' I will design in a little extra material thickness in case I have to machine out for a bigger bearing.

Won't run into any other problems with other stock rear suspension parts as I won't be using of these.

All wishbone joints will be mono balls (spherical bearings) so everthing should feel very stiff

[ted]

Originally Posted by Jeff Higgins

You'll only run into trouble if you continue to insist on calling them "tyres". Here in the states, they are known as "tires". What part o' Texas you from, boy?

in the south is it "tar"?
I got a chevy too.
Chase Rice "Country 'Til I'm Dead" 8-12-10 - YouTube

[Todd Simpson]

I have replaced the left rear bearing twice now in 12 years of track days.

I'd use the later, larger bearing from the Al trailing arms, but otherwise you will get years of use from the stock components.