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Debate ... 70 Series Tires verses Low Profile Tires

noquarternoquarterMember
I was just thinking… What really looks old on my Longchamp and what everybody comments are the 15” wheels and 70 profile tires. Really yesteryear… But it handles great, how can it on those tires you could ask. That brings me to this line of thought, bear with me…

If I changed wheels to 18” and low profile, the car would be less comfortable and maybe at times not able to keep the tires on the ground. It would require softer springs/dampers, because some of the 70 profile flex has gone away. All agree so far?

Now, comparing the two alternatives that give the same damping:
1. 70 profiles and hard springs/dampers
2. Low profile and softer springs/dampers
Now it becomes interesting. Think about unsprung weight. In situation 2. the unsprung weight would be significantly higher, because the whole tire and rim and brakes and upright etc., with a hard short profile tire all that would be unsprung weight. But on a 70 profile tire, some of that weight becomes sprung weight to some degree, because of the flex in the high profile tire.

I also remember reading a few years back, that a Formula 1 team was asked why they didn’t have bigger rims and lower profile tires. I would have thought it was regulations, but the answer was that they preferred to have some flex in the tires so they could have firmer springs.

So is it F1 and my Longchamp that’ got it right, and all the cars on low profile tires, that’s only a fashion statement? Or am I way off the point?
Confused
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D detom (Guest)
IMHO, the ONLY reason one should go with larger diameter wheels is to accomodate larger diameter calipers. Having said that, there are such things a diminishing returns even for that. Given how heavy modern cars have become, the need for larger diameter calipers started a trend that has gone way too far. There is no reasons for the existance of dubs. I am sorry, but it is high time for them to go the way of the hula-hoop.
tbergtbergMember
I agree with your assessment. Several years ago, I bought a Jaguar XJ Sport that had very low profile tires on 18" rims, and the car was dangerously undrivable. It darted back and forth over the smallest of pavement irregularities like a pack of sardines with a shark coming toward them. I would not let anyone in my family drive it until I changed the tires to a higher, more traditional profile and the ride quality as well as handling significantly improved. Go with your instincts and have a comfortable ride.
jtpanterajtpanteraMember
I suspect if the Jag darted around it had poor alignment or worn suspension bushings verses the low profile tires. Although, I do not deny that the symtoms of these attributes would be more acute with low profile tires.

I have had a different experience. To add some credibility to my remarks, I raced open wheeled winged and non-wing Formula cars for many years and tracked my Pantera for over a decade, including autocrosses.

The single biggest improvement in both my wide body and L Panteras' handling and track performance was the transition to modern low profile tires. Specifically, Michelin Pilots. I did not percieve a meaningful difference ( as in degradation) in the ride quality over bumps due to the shorter sidewalls.

F1 tires are regulated and their width, aspect ratio and tread design were modified about a decade ago to reduce traction, improve tire wear, reduce costs to provide less advantage to richer teams, lower cornering speeds to enhance safety and place more emphasis on the driver. It is an apples to oranges comparison.

If the F1 tire manufactures could build the best tire, I'd bet the tires would have lower aspect ratios. The main reason is less flex means less heat build up and better ability to control the contact patch.

A few thoughts to stir the pot.
George PGeorge PAdmin.
The needs of a F1 car, a 30-40 year old luxury sport coupe, and a Pantera are three different applications.

The F1 car is very low, travels very fast, and has extremely high down-force glueing it to the asphalt. The high downforce requires very stiff springs, otherwise the downforce would fully compress the suspension on a smooth/fast section of track and leave nothing for the bumps. Throw in the tire regulations set by the FIA, and you have a situation that does not apply at all to the vehicles we drive.

Modern low profile tires have very low slip angles giving them razor sharp response to driver input; and low side wall deflection giving them incredible grip in corners. State of the art performance in keeping with the concept behind a sports car like the Pantera. Your statement that low profile tires are only a fashion statement is in error.

If I owned a Longchamp (I wish I did) I'd probably look into 50 or 55 series tires and modern gas shocks (Koni of course). I think that combination would give the car the compliance I would expect in a luxury sport coupe. I confess I like a well dampened ride and a sharp handling chassis.

However if you like the look and feel of the 70 series tires, and you're able to find modern 70 series rubber that gives you the performance you expect, you'll get no argument from me, rock and roll.

-G
Last edited by George P
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