Reinforcements needed to use R-compound tires ?

Deschodt · 09:15 AM

Apologies if this is a silly question, but I've never run R-compound tires before and will next month at the track...

As the car will get a few safety goodies installed ahead of the next track day (new brake shoes, hoses, master cylinder, CV boots), while I'm there, I was wondering if there are any reinforcements that are a good idea to weld on an 83 SC chassis so that the extra grip of the R-rubber does not cause some other old part to break ? That or some parts to examine carefully and possibly replace before I proceed...

The car has been tracked many times in years past but on regular tires, has been just a driver the past 3 years, and it's got 185000 miles now, so if it's time, I'm open to spending a little more and do the right thing and avoid losing track time !

Thx !!

PS: It'll be repainted too ! In fact, it's painted now, just not reassembled!

Zeke · 07-21-2008, 09:47 AM

I think you are wise to consider the question. Older car subjected to new and higher stresses. I guess I'd look at the ball joints and other points of attachment before wondering about welding parts on the car. I see your lift, so I assume you go over the car carefully on a regular basis. What else can you do?

My only other thought(s) would be to examine the sway bars and see if they need some more support, especially if they are a lot bigger than stock. We all know of the problem of ripping out the rear mounts. Through-the-body fronts have ripped too. This should have nothing to do with the forces of the grippy tires, just routine. And, of course, the front pan has to be in excellent shape, no rust.

I haven't seen much evidence of welding gussets, etc., on a 911 until the coilovers start going on. Lastly, I think upgraded suspension bushings are in order and I don't know what you've done there.

I'm sure other track junkies have more, I'm more or less done out at the track. But, I've been there enough to know that these are pretty strong cars right up until they start to become radically modified. Then they can break.

KTL · 07-21-2008, 10:19 AM

The front underbody mounts (which I hate) are very solid and i've not heard of those breaking. Rear sway bar mounts are typically the worst offenders. Porsche applied a "butterfly" mount to the cars starting in '86 and even those can fail. Definitely check those rears.

That being said, a friend drives the crap out of his '87 Carrera with stock springs and a Weltmeister 22mm adj. rear bar. He's had one mount and one drop link re-welded in the past 4-5 years. He's been on R compounds all the time on the track, with notoriously "unorthodox" driving style and driving lines.

Other than that, you shouldn't have to worry about reinforcing anything to avoid breakage. These cars are pretty darn solid and R compounds are going to twist them into a pretzel. That's not saying chassis reinforcements aren't effective. But true reinforcement means safety cages and welded strut tower cross-bracing. I don't get the impression that's the intended use of your car- full-on track wheel to wheel race car.

Zeke · 07-21-2008, 10:34 AM

Oh yeah, what kind of strut tower brace do you use? I would think triangulated would be best. And, I'm sure you know about the stock upper strut bushing binding issue with '"certain" braces.

johndglynn · johndglynn's Garage

I have run Rs on my slightly stiffer Coupe for a while now (205/245 on 7 and 9x16)and nothing negative to report chassis-wise. Am sure you will love them, they work a treat with a bit of temperature.

JeremyD · JeremyD's Garage

Seems to me that the sway bar mounts are the weakest link going to r-compound tires. That and you'll do a better job at deforming all your suspension rubber goodies with R tires.

I found I really had to wait for the suspension to settle before going with the monoballs.

JeremyD · JeremyD's Garage

Seems to me that the sway bar mounts are the weakest link going to r-compound tires. That and you'll do a better job at deforming all your suspension rubber goodies with R tires.

I found I really had to wait for the suspension to settle before going with the monoballs.

Deschodt · 07-21-2008, 12:05 PM

Thanks guys, that was worth checking - The rear mounts were the #1 on my list, but if there is nothing else, I'll order the tires ! Then try to find a set of spare wheels too ;-)

JP911 · JP911's Garage

Good idea to do an all-around fastener check before, and check a few during the day. I had one of the front sway bar bolts (the big allen that also holds the belly pan in place) back out during a track day. I felt a "clunk" in the pedals and quickly pulled the car in to check things out. I'll be using blue loctite there in the future.