Would a width of 4.5 inches be within the acceptable range?

[AnthonyBobo]

I'm certain that the tire width recommendation I'm seeking has been discussed and answered somewhere in the previous conversations. However, I'm unable to find a specific thread that addresses my particular situation. Therefore, I'll go ahead and ask my question. I'm in the process of constructing a Porsche 924 C/Pro 2.0 liter car, which is estimated to weigh around 2,400 pounds and have approximately 220 HP. My goal is to achieve a top speed of 155 MPH. Considering that excessively wide tires can create aerodynamic challenges and overly narrow tires can result in traction issues, I need some guidance on the acceptable narrowness for the rear tire. Would a width of 4.5 inches be within the acceptable range? Thank you in advance for your assistance.

[Stainless1]

I think Frontrunners would be fine for your application on all 4.  Or if you are looking at tires in the VR or ZR rating then anything that puts 4-5.5 patch on the ground should be fine.  I think my 21 inch LSR tires have a 4 inch contact width.

[manta22]

I can see an advantage of running a narrow set of front tires but by he time the airflow gets to the rear tires my guess is that it is pretty turbulent so a somewhat wider tire could be used for traction without much of an aerodynamic penalty.

[kiwi belly tank]

LSR tires are narrow for both aero & traction reasons. Getting traction on the salt is more like getting traction in snow than on blacktop & the same reason a performance snow tire is narrow, more weight per contact patch area.
  Sid.

[Mr. Schimstock]

4.5" is a common front runner width.  Many heavier cars with more HP have run them successfully at speeds much higher than your target.

[jl222]

 
 Yeah...4.5 in would be good for your app,

 But if you want to feel like you're making a lot of HP put 80 lbs of air in the tires make the suspension ridged or not moving when pushed down and you should be spinnig the tires real good.

  Our 10in wide tires don't work very good for the 222 Camaro as we've only gone 280 mph in the 21/4 and 294 in the ist timed mile at Bville with 2 more miles to go.
 
 So our advice to our competitors, Run skinny tires.

  jl222

[Stan Back]

Be nice now, John. 

I admire your stick-to-it-yourself resolve over the years. 

Every time you post I remember having dinner at your table in the Nugget during my one and only time at the 200 Club Dinner.  Was nice meeting you and the rest of the family -- and I've been a fan ever sinse.

Stan

[jl222]

Be nice now, John. 

I admire your stick-to-it-yourself resolve over the years. 

Every time you post I remember having dinner at your table in the Nugget during my one and only time at the 200 Club Dinner.  Was nice meeting you and the rest of the family -- and I've been a fan ever sinse.

Stan

 And a Salty Dog to you 

[37 ROADSTER]

Just remember every door car over 300 has run skinny tires.

[jl222]

Just remember every door car over 300 has run skinny tires.
[/quote

 Yeah. in what mile and what fuel?

  we had an average of 294 in the 1st mile what do you think our speed was interring the 2nd mile?

     JL222

[Stainless1]

 Yeah...4.5 in would be good for your app,

 But if you want to feel like you're making a lot of HP put 80 lbs of air in the tires make the suspension ridged or not moving when pushed down and you should be spinning the tires real good.

 jl222

John, good advice on tires, I would not recommend non compliant suspension to any racer, although I doubt he will be spinning those at speed. 

  Our 10in wide tires don't work very good for the 222 Camaro as we've only gone 280 mph in the 21/4 and 294 in the ist timed mile at Bville with 2 more miles to go.
 
 So our advice to our competitors, Run skinny tires.

  jl222

I think your tires are doing well in your application... most people don't realize it is a 5 mile drag race... we are all hoping y'all get a couple of back to back 5 milers with the 222.
Good luck and salt this year 

[slowalex]

II'm in the process of constructing a Porsche 924 C/Pro 2.0 liter car, which is estimated to weigh around 2,400 pounds and have approximately 220 HP.

I'm assuming you are planning to run the 924 in the G/CPRO class a bit like this one.
https://flatsixes.com/cars/porsche-924/the-worlds-fastest-porsche-924-takes-another-land-speed-record-at-bonneville/

He appeared to have some problems with traction:

Rick recognized that the car was extremely light over the rear axle as the non-turbo 924 shell did not have a hatch-mounted rear spoiler, and several hundred pounds of lift were hampering forward progress. The rear wheels were struggling for traction above 140 miles per hour, resulting in nearly 20 miles per hour of wheelspin as the car ran over the slippery salt.

I'm not sure about how the rule book is interpreted in the /CPRO classes, so you might want to check the legality of different hatch options you have available.

Last winter the team lowered the car further until there was only about 2.5″ of clearance to the ground. The rear hatch was popped off and a be-spoilered unit from another Porsche, presumably a 944, was added. The team?s first run of the day on Saturday netted a 150.278 mph timed mile

Tend to agree with the comparison to snow and ice. Take a look at some of the snow tires used in rally events in extreme winter conditions such as Rally of Sweden. Rim: 4-5.5 inches.
https://pneu-sport.cz/en/rallye-tyres/snow-ice/

Some info on the engine used in the car that is G/CPRO record holder can be found in this thread:
https://rennlist.com/forums/924-and-931-forum/928555-old-school-924-2-0-engine.html

Porsche 924 board thread here:
http://www.924board.org/viewtopic.php?t=43428

[Stainless1]

Well as we all know "nothing difficult is ever easy" (OTC)

Wheel spin is partially a function of the right pedal... and vehicle design.  If you know your vehicle has lift in the rear at speed you add downforce... within the rules... learn from the experience of others
A good start is know the corner weights... and car balance... Ballast can be your friend...
good luck with your project...