Advice on Tire Size

[leadrsa729]

I lowered the ride height of my 72' 911 Targa on 205/60r15 tires. This was a difficult job done a good number of years ago. Adjusting the torsion bars to get the perfect ride height is a daunting task to say the least.

Its time to replace the tires as they are quite old, but I'm finding it difficult to find a modern high performance tire in the same size as I have now. The closest I can get is 205/55r15. 60% of 205mm is 123mm, so that's how tall my sidewalls are now. If I go to 55 that means the new sidewall height will be roughly 113mm, a difference of 10mm.

My question to all of you - is 10mm going to make a huge difference in fender gap with my ride height as it is? I really don't want to have to go through lowering the car again if possible but I can't use these tires any longer.

Thanks for the advice!

[Mr. Merk]

What size wheels do you have? Probably 6" wide

195/65R15 is a popular size because there are plenty of options (none of them particularly great), but like I always say; "How many tires are you going to run at once?" You only need one good option.

185/70R15 is the correct size for the car, would feel nicer on the 6" wide wheels and is available in a sticky but period-correct Pirelli CN36. I wouldn't be concerned they'd wear too fast or be too expensive if your current tires are expired by time. If these last you 10 years before they expire then it's money well spent.

Comparatively the 205/55 is .8" shorter than what you've been running and 1.3" shorter than standard. This would look pretty short but also feel like horsepower effectively lowering your gear ratio. Again, not any great tire options in performance or appearance.

In 1969, PIRELLI developed their low-profile tyre in conjunction with Porsche, the CINTURATO ™; CN36 which became the tyre of choice on these early 911s.
Porsche has recently been involved with PIRELLI producing and homologating the 185/70WR15 PIRELLI CINTURATO ™; CN36 N, which would be the tyre of choice. We would suggest that the Cinturato CN36 N tyres are the best.

[leadrsa729]

Thanks for the info and the tire calculator link! I'm definitely running the 6" wheels like you mentioned.

I've got some extra horsepower in this car as I'm running a 3.0L engine with a hot cam and larger intake/exhaust ports so I would like to stick with the 205 width to maximize my contact patch as much as possible. I think I'll just have to see what 10mm smaller looks like in the wheel wells. I might be readjusting the ride height after all.

[Matt Monson]

You don’t say how much you’ve lowered it, so nobody knows. Personally I’d be worried about driveways and what I might scrape now that the smaller tire puts me closer to the ground.

It’s a very common tire size and I’ve run it on multiple old 911/912 cars. I’ve also run the 195/65/15 as well. I like them both, from a driving standpoint.

[leadrsa729]

Hi Matt -

I'd have to check my notes to see how much I actually lowered the car, but hopefully these pictures come through that show how the car sits now on the 60 sidewall tires.

[Bill Verburg]

Originally Posted by leadrsa729

I lowered the ride height of my 72' 911 Targa on 205/60r15 tires. This was a difficult job done a good number of years ago. Adjusting the torsion bars to get the perfect ride height is a daunting task to say the least.

Its time to replace the tires as they are quite old, but I'm finding it difficult to find a modern high performance tire in the same size as I have now. The closest I can get is 205/55r15. 60% of 205mm is 123mm, so that's how tall my sidewalls are now. If I go to 55 that means the new sidewall height will be roughly 113mm, a difference of 10mm.

My question to all of you - is 10mm going to make a huge difference in fender gap with my ride height as it is? I really don't want to have to go through lowering the car again if possible but I can't use these tires any longer.

Thanks for the advice!

Most or all the 205/60x15 available today are all season
BFG Radial T/A are still available in that size w/ a UTQG 400 AB

if you go 205/55, yes they are ~.8" shorter but only 1/2 is on the top, the other half is somewhat squashed by the cars weight

for example Kumho ECSTA PS31 also available but in 205/50x15 w/ UTQG of 460AA
is ~23.9" OD and has a of ~11.9 the 205/60 x15 BFG is ~24.7" w/ an a of 12"

a is the height of the axle

if you go w/ the 1885/70 x15 CN336 OD is ~25.1" UTQG is unknown and a is


another option is 195/55 @~23.$" OD w/ a of ~11.3" sticky A052 and R1R are available in this size

[leadrsa729]

Thanks for the information Bill!

The tire I was considering is actually the Khumo Ecsta PS31 that you mentioned, but I am most likely going to go with the 55 not the 50. I see they have a 205/55r15 at Tire Rack in my area.

[Bill Verburg]

Originally Posted by leadrsa729

Thanks for the information Bill!

The tire I was considering is actually the Khumo Ecsta PS31 that you mentioned, but I am most likely going to go with the 55 not the 50. I see they have a 205/55r15 at Tire Rack in my area.

That was a typo, I meant 205/55. all the data was for that tire

my car came w/ 205/50 front P7s they are really short, and the car needs to be really low to look right

[HarryD]

I ran 205/55-15 tired on my 911 for a while. It was ok but I hated how much the Speedo was off.

I finally got a set of 6x16 Fuchs to improve my tire section and still keep a stockish look. I am currently running 205/55-16 Continental ExtremeContact Sports (if is my second set) and I don very happy with them.

FWIW, for fun I have, in the past, ran 205/50-15 Hoosier SM tires. Lots of fun but only in dry days!

[917_Langheck]

I had the ecsta31s on my car when I picked it up. They weren't old (only a year old), and drove terribly. Lots of tramlining, and weaving everytime near a big rig, for the 900 miles home. Used them for a performance driving school and one autocross. The only good thing about them, I was never going to get the back end around with how badly they pushed. Made it easy to throttle steer, however.

Now running BFG comp sport 2s (all seasons), which made a huge improve in feel and composure. 205/55/16 and 225/50/16.

[Mr. Merk]

Originally Posted by leadrsa729

I've got some extra horsepower in this car as I'm running a 3.0L engine with a hot cam and larger intake/exhaust ports so I would like to stick with the 205 width to maximize my contact patch as much as possible.

You're hung up on the width, assuming it'll automatically giving you more traction. The PS31 is a summer tire but still only a 460 treadwear rating, and you're near the bottom of the wheel width range of 5.5-7.5" and will be pinching the tire making the sidewalls feel squishy and loose.

Whereas the 185/70 is maxed out at 6" ideally giving you the least amount of sidewall roll. The CN36 doesn't have a treadwear rating but I'd estimate it less than 200.

If you're worried about wheel spin, I'd bet the taller and stickier compound 185/70 CN36 would have more grip in a straight line as well as feel more confident in the corners.

I calculated the contact patch area and the 205/55 on the same 6" wheel actually has slightly less than the 185/70 at 243.23 cm2 vs 245.97 cm2 respectively. This is due to the taller diameter and the 185 being stretched vs the 205 being pinched.

The 205 would be better suited for a 7" wheel where it would have a much larger contact patch than the 185 on a 6" wheel

[Cairo94507]

I ran 195x60x15 on my car with deep six wheels. I switched to 195x65x15 and they look so much better on the car. I am running a '95 3.6 in my car and I have no issues with the contact patch. I street drive my car and do not race it. Shorter sidewalls on our older cars just does not look correct to my eye.

[Bill Verburg]

Here's a comparison of CN36 and PS31, ignore the A052 in the tire section




I agree that for 6s the 185/70 is a better choice, 205/55 really want 7s

as was noted the narrower rim imparts a soft more flexible side wall, and the tire runs at a greater slip angle, all else being equal for performance you want the widest wheel spec'd for a given tire, for 185/70 that's a 6.5 and for 205/55 it's a 7.5

given that A052 are UTQG rated 200 I doubt that CN36 is close to that, but those #s are nebulous anyway. Certainly for street use das macht nichts.

[Mr. Merk]

Originally Posted by Bill Verburg

given that A052 are UTQG rated 200 I doubt that CN36 is close to that

I wouldn't have thought so either until observing that the P6000 is rated by Pirelli as a 180 treadwear. It's known to be less sticky than the CN36. Again, I'm estimating.

[Bill Verburg]

Originally Posted by Mr. Merk

I wouldn't have thought so either until observing that the P6000 is rated by Pirelli as a 180 treadwear. It's known to be less sticky than the CN36. Again, I'm estimating.

Back in the day my car came w/ P7s, at some point I put P6s on an they were nowhere near as grippy, track days were fun as he**, because the car was sideways half the time

as I said for street use it just doesn't matter

[leadrsa729]

Thanks for all the suggestions!

You're right it seems I am hung up on the width. Looks like I have a lot to think about!