Interesting article in Excellence. Olaf Manthey states, "if you use 19 inch wheels - the wider tires and stiffer, shorter sidewalls create more geometry problems then they solve on bumpy roads." He goes on to say, "I agree they look better, but we are all about performance and driving qualities here, not posing."

 

Preaching to the choir with me I'm not even sure I like the look of 19s and rubber band tires to be honest

 

Olaf Manthey

 

Interesting comment … however, it makes me wonder if he was speaking in Germany and something was lost in the translation. I understand the possibility of some scrub changes if the width is different but, if the O.D. of the tire is the same as an 18�, it will have absolutely ZERO effect on the suspensions “geometry.� There are unsprung weight issues and actual tire design issues but, other than that, that statement is no more than garble from someone trying to explain something they don’t technically understand. Car geometry refers to lines drawn to specific points at specific angles and specific lengths. The numbers could care less if the tire is a solid block of rubber or a 25� wheel with a rubber band around it as long as they are the same overall diameter … Sorry Olaf but, if that is a direct quote it’s incorrectly phrased

 

Cary,
Nice post...Will the sidewall height be of any issue?...I know you secretly hope to be the first one with the bling bling 20's on your car...

TTech

 

As I understand the cars that had 19" rims during the shootout suffered some blowouts. The sidewall on the 19s is just too small when we´re talking the 996 wheel sizes.

 

Well, I guess one more person who agrees with my theory on 19" wheels.

Cary, as much as you are the guru of all things suspension on this board, I would have to say that Olaf Manthey probably knows more about racing and tuning than all of us put together.

His racing experience makes all but Kevin Buckler look like backyard amateurs.

Even then, I'd say Manthey has a wider range of experience preparing Porsches than TRG. Look at their 996 Turbos that ran in 24H Nurburgring. The Alzen cars were fast, but the Manthey cars did better.

 

Well I wonder why Porsche is moving to 19" for the 997 and up.

 

Cary,

The article does go on to talk about unsprug weight. Manthey has come up with a new BBE Motosport wheel that weight just over 15 pounds each.

In addition he mentions that he sets up the front 5-8 mm lower than the rear. This would be a correction for understeer tendencies. He also uses 295's and 245's, again another understeer correction.

Overall, the article was very interesting. It helped validate many of the modifications performed on Killer Angel. The unsprung weight issue is what we are currently working on.

Before I go too far, the article is about an older GT3.

 

Tyson, All I was trying to say is the statement that rim size effects geometry is misleading and simply wrong. I was fairly surprised myself that he would make such an ignorant misleading statement. None of my cars have 19’s on them but it’s not because it changes geometry it’s because there isn’t a good wheel and tire combination available … yet. What are we all going to think when the proper combination comes out and we all like the ride and the stick better? Will it be because the cars geometry changed? Nope, I think it’ll be because the wheels and tires changed. Manthey’s car did win Nurburgring but only by default because the Pole setting Alzen car broke. Alzen car has won basically all the other racers over there since. I’m not saying anything against Manthey’s experience or ability to win races but that statement he made was just incorrect.

 

Cary, I am your biggest advocate on this board RE: your suspension knowledge. Do you think I would let just anyone drive my GT2?

When my GT2 is ready for suspension tuning, you will be the one to set it up and spec out parts, if you are willing.

As far as 19's, don't hold your breath. The sidewalls to keep the rolling diameter the same as stock is too thin, and I seriously doubt you will see the right tire carcass structure to be able to give you the vehicle dynamics you desire in a 25-series rear aspect ratio.

If you look at the tires for Stradale and CGT, their sidewalls are much higher. The rolling diameter is therefore much larger to begin with, and that's how the suspension geometry was designed.

19's on 996 is for looks, not performance. You and I both know that.

997 may move up to 19, but money says that the rolling diameter will differ than the 996, therefore, tire sizes will be different. People will see....

 

Tyson, I should have said "IF" they ever come out with a 19 that works. I still feel just because they don't have it now, doesn’t mean it's not possible someday. In the 70's who'd a thought we'd ever get a 30 series radial to work at all?

I just read the article and have a better idea of what he was saying now. Olaf was talk about all the different setups needed to get the best performance from same sized 18" tires by different manufactures. This was because the construction is so different from one to another he has to change the alignment setting and ride height for each tire in order to optimize their performance. While this does affect the geometry some, I think the word of choice should have been "alignment" and not "geometry." If you have metal burr in your finger and you have to dig it out ... while it's not pleasant, it’s not surgery.

What I believe he is trying to say is this; over bumpy roads the tire creates osolating input that the cars standard geometry can’t interpret regardless of the alignment. I buy that.

 

Cary -> would the 'effective' rolling diameter of a tire using 18" wheels be less than the 'effective' rolling diameter of a tire on 19" wheels during hard cornering? My assumption is that a similiar diameter tire on an 18" wheel will compress more during hard cornering than a 19" due to the taller, more flexable sidewall? Could this be where the Manathey guy is calculating different geometries. (They would in fact be different during cornering, although to what degree I'm not sure).

 

Zippy,

With the same spring rate in the sidewall construction the tires should maintain similar rolling diameters. I¡¦m sure they are not the same in this case making what you say a possibility. However, I think more of the problem is in the Slip Angles of the tires in which case your Instantaneous Turn Center will move to an undesirable location and that¡¦s one way the tires could ¡§create geometry problems.¡¨ So, now that looked into this deeper, hindsight tells me ¡K maybe I should left this one alone ƒº it¡¦s just that the issues of 19¡¨ always riel me up because most of the time logic tells us they won¡¦t work but the logic being used isn¡¦t necessarily the correct logic.

PS. Notice his one off custom BBS Motorsport wheels. Hmmmm where have we seen wheels like that? Only without the 5 lug holes and fake center lock cap. No comment

 

I just put a set of HRE 542s in 19" on my GT2 and I didn't feel many noticible reduction in ride quality or handling at all. I'm going to put Cups on the stock rims for the track for now. Those 15 lb Mantheys sound really worthwhile. That kind of weight reduction would make a difference. I think the whole issue of 18" vs. 19" is way over blown especially once the Michelins come out. 19" cups sound good too. I can only hope for now.