Upsizing upsized tires?

See http://ferrarichat.com/forum/showpost.php?p=135427879&postcount=54 for my 328 on exactly that setup with Kumho Ecsta ASX tires.

You really have to watch the inner rear sidewall clearance, but I haven't had any issues. Note that my car is at stock height, so it still has some of that 4x4 look. Hopefully some paperweights will correct that soon

 

No issues at all. Had them for years, through 2 sets of Ecsta 712s and my current Ecsta ASX set. I have heard others complain about interference on the inner sidewall/spring, but I have not seen that on mine at all. Could be a Kumho vs other manufacturer thing, or just the normal variance between cars.

Speedo is MORE accurate after I changed to these sizes.

 

IMHO - You're going to make the steering heavier by upsizing the front. Unless you're in love with "meats look" I'd stay with the original sizes where were very well balanced with the car.

 

Are you saying that from personal experience? I didn't find that to be the case at all -- unless your car isn't moving!

 

I just did something a bit similar with the Mondial to achieve two goals, remembering that this is not a track car so ultimate grip was not as much an issue as having a good street GT.

1. Lighten steering and keep it precise. Previously had 225/50 Pilot A/S on 7.5" rims. Ordered a set of PS2 205/55 to reduce contact patch and have the widest rim for the same wall height as the previous 225/50. While I will lose the all wx capability I needed in DC, I don't need it here in San Antonio.

2. Functionally have a taller final drive. I had looked at different drop gerars and even ring/pinion, but figured out the easiest way to do it would be by upsizing the wall height on the rear tire. The previous 245/45 P A/S on a 8.5" rim had a height of 25.8 and rolling ratio of 811 revolutions per mile. By going to a newer technology higher grip tire in a PS2, am trying a 235/55 on the same rim, again the widest rim recommended for the tire. The new tire height is 26.6" with a rolling ratio of 777 revolutions per mile. Using tire sizes, I have functionally reduced my differential ratio by 4.3%, taking the original 4.06 ratio and funtionally making it more like a 3.86. This slightly reduces the cruise rpm from about 20 mph per 1000 rpm to about 21 or so. I do not worry about speedometer error as it is so wildly inaccurate to begin with, and if anything, this makes it closer.

I do have adjustable spring perches, so ride height adjustment is not as big an issue. I've heard that PS2's have a good ride and very good steering response with the newer technology rubber. Coincidentally, these are the same f/r tire sizes on a newer Porsche Boxster and have the N0 designation. I ordered the tires today, so I'm hopeful this will work out.

 

+1

 

Not on my own car. Just comparison between my own 328 and others that have been upsized.

A bigger contact patch is going to make for heavier steering at slow speeds (probably parking lot only given that it is only 20mm in this particular case).

Whether you find it objectionable or not is a different story, hence the IMHO.

I have upsized by Bora as I felt the additional tread was necessary for that car's girth. The original fronts (and rears for that matter) were 215/70-15 which is a difficult tire to find in a V+ rating. When I bought the car it had 205/60-15s on the front which was too far off in rotational size IMHO, so I purchased 16 rims and upsized to 245s all around. That did make the car's steering too heavy for my personal taste and I ended up with 225/55-16s on the front as a compromise. However, modern sidewall construction probably makes the steering close to what it might have originally been (still heavier than the 328).

It currently has 255s on the rear, which I'm not sure I like, but the Bora does have a very heavy looking rear-end which helps offset the tire width. It might have looked better IMHO with the 235s that were on the rear when I purchased the car, though the majority of my friends disagree.