Anyone ever question why we have 305’s in the rear for a 355hp engined car??

My friends M5 with 500hp has 275’s in the rear and his car handles great.

I get the engine in the rear and rear weight biased needs. Couldn’t this be solved with taller tires? 305’s for a 355hp car more for just looks? Please enlighten me.

 

I never gave this much (if any) thought to be honest. First thing that comes to my mind is that a lot of these cars end up on a track sooner or later and I would imagine that 305's (or 325's) back there will enhance the grip over 275's. M5's no matter how many HP are less likely to be tracked so it's not really built/configured for that purpose. Maybe you could fit a wheel that would accommodate a 305 tire on it but I'm not sure it would be a good look or serve any useful purpose.

 

I assume it's for proper grip balance on the car to prevent the end swapping pendulum effect that used to plague 911s due to their rear weight bias. Also helps with traction out of corners, especially if traction conditions are less than ideal - wet, sandy, etc.

It's also possible that the M5 is under-tired rather than the 911 being over-tired.

I'm probably going to move to 245s on my 8.5" wide fronts and 315s on the 12" rears for my next set of tires.

 

Porsche designed the bias of the layout for all power levels. Weight distribution and balanced corner grip.
The Turbo has the same tire size.

This saves development costs, car layout cost for less HP engines since they were able to make one fits all.

My 325HP Carrera has 305's as well and this is way to much for straight performance but I love the corner grip of the PS4s and wouldn't go smaller just for that.

 

All good points. I do enjoy the cornering prowess of the 911. Just wondering if our 911’s would be faster with skinnier rear tires. I remember back in the days Supra twin turbos with double or even triple the hp of the 911 S models and 275’s in the rear was a big deal and those cars drove pretty nice on the track as well. Not the triple hp ones. Those were more straight line beasts.

 

Sorry for the hijack but I just bought a set of 4 for my GTS from Tire Rack. Plugged in my car and whatever else they asked for and the widest rear tire that came up for my car was 305 regardless of brand. I screwed up by going into "Shop by vehicle" instead of "Shop by size". Went back and shopped by size instead and there are 19" rear tires in both 315 and 325 available through that search.