Need input on rear tire width

[QikNip]

I'm sure somewhere in the history here it's been asked and answered, but I can't locate a thread that addresses tire width recommendation that address my situation, so here goes...

I'm building a ~2,400 pound Porsche 924 C/Pro 2.0 liter car that will have roughly 220 HP. I hope to reach 155 MPH. Since tires that are too wide pose an aero issue, and ones that are too skinny a traction issue, I need advice on how narrow a rear tire can I reasonably run? Is 4.5" anywhere in the ballpark?
Rick

[Seldom Seen Slim]

I'm a bike guy - and there are lots of car people here that'll give you good information, but here goes.

A skinnier tire will usually work better for you.  It's not plain traction that you need - at least not the kind of traction you get from having a large contact patch.  The salt is pretty danged slippery but hooking up can be done - by increasing the pounds per square inch pressing down on that contact patch.  Easiest way to do that - is to make the patch smaller than it is now.  Adding weight is also a good way, but you're asking about tires.  I could show you a zillion photos of cars with skinny tires - and some with wide tires, too.

As a real example of the increases available with more PSI on the contact patch, a bunch of years ago I was running our nitrous bike and getting wheelspin near the top end - say at a buck 70 and above.  I added about 60# of lead weights near the rear axle -- and picked up something like 6 or 7 mph with no other modifications of any kind.  Weight is good, skinny tires are (usually) good.  Your results might not be the same - but let's see what the other girls and boys have to say.

[fredvance]

 

[Stainless1]

buy a set of frontrunners for the front and back, they can be run well over 220 and are acceptable for salt and pavement.
You will be required to have race tires since the record in your class is 220,  your best bet may be 150 club with the USFRA, lot lower safety requirements and you can go 159.9999 legally.  Go to their website to read the club rules.

[QikNip]

Stainless:
Thanks for the input on tire width. Running drag fronts on 4" rims on both ends is the curent plan. BTW, Per the 2014 Rules and records book the G displacement Classic Production record is 138.8. I'm guessing that you're referring to the 5 liter C displacement class record?
Rick

[Stan Back]

You're not building a C/Pro car as you stated, I'd guess.

You're building a G/CPRO car.

Gotta get the slant in the right place.

You just misled Stainless (that's too easy).

[QikNip]

Stan:
You'd be right on the misplaced slash. But I'm guessing that Stainless is probably sharper than me anyhow! 
Rick

[Speed Limit 1000]

Stan:
You'd be right on the misplaced slash. But I'm guessing that Stainless is probably sharper than me anyhow! 
Rick

He may or may not be the sharpest pencil in the set
   

[Stainless1]

Yea, I guess I missed the 2.0 L part or I would have told you to bore and stroke the crap out of it to get to C.... 

[NathanStewart]

If only going 155 get treaded street tires.  No reason to waste money on LSR tire if not going >200.  Just get a narrow-ish tire that's the right height.  

[QikNip]

Thanks guys. I really appreciate the input. While I drag raced, Autocrossed, Motocrossed in my misspent youth and road raced for years, this LSR stuff is still all pretty new to me!
Rick

[racergeo]

   I've bought used Goodyear front runners at a swap meet for $20 a pair. Mounted them and trimmed the extra rubber off the outer corners, cut them round, balanced them and ran them over 270 MPH. FACT