carcass and cap differences H vs. V

[cltgto]

I'm new to the board and would like some informed guidance in selection of tires from folks who design them (and/or cars) for a living. The people at the retail/sales/customer service level just don't get it, especially when I'm deviating from the car's perceived expected usage...

First some background... the car is a 2005 GTO that is a daily driver, usage is 80+% interstate commuting, and typically driven lightly (cruise engaged) to moderately (weekend trips on two-lane rural roads where lateral forces might approach 0.7g). It's never been slid through a corner, drag raced, driven at sustained triple digit speeds or otherwise abused. Came from the factory with BFG KDWS 245/45-17 95W tires (it’s governed @ 158). A very good choice by GM in my opinion, as these tires offer excellent dry and wet grip and acceptable levels of ride quality and noise generation. Given the 400 treadwear rating, wear has been disappointing as I'm @ 20K miles and by 24k will be down to the wear bars (rotations every 5K, alignment optimal per factory specs).

So now my dilemma... I need to go from "acceptable" ride quality and noise control to "excellent" or "exceptional" without giving up dry or wet braking capacity. The car's suspension system is tuned appropriately... offers an excellent blend of comfort and control/feel. But the tires have always had a harshness to them (or, lack of sophistication) I find that detracts from the driving experience. Don't know if I'm getting too old or what, but NVH control is a major thing with me anymore. Given all of this, I've decided to change tire segments and drop speed ratings.

Based on my experience with these installed on my minivan (225/60-16 98H) I'm going with the Continental ContiProContact. On the Odyssey they are an excellent fitment... Same if not better NVH characteristics as the Michelin MXV4 Plus they replaced but with much better wet traction, equivalent steering response, and less expensive. They do seem to be wearing a bit faster than the Michelins did, so from a cost/mile perspective it might be a wash. So here is my primary question: do I go with a 99H or a 99V on the GTO?

My current tire (the BFG) has the following construction: 2 polyester carcass plies, tread 2 steel + 1 nylon.

The ProContact on the van has 1 poly carcass ply, tread 2 steel + 2 nylon. Right away I realized that going from a multi-ply carcass to a mono-ply probably explained the segment difference (UHPAS vs. GTAS)...

I checked out an Audi A6 where the 245/45-17 99H ProContact is OE and found the following: 1 rayon carcass ply, tread 2 steel + 2 nylon. According to Conti the OE 99H and replacement market tire are one and the same. The 99V is a new product for them (there's also a new 95H runflat in the same size I'm not considering) and I could not determine if it's intended for the replacement market or was designed for an OE fitment that hasn't been announced yet. Dimensionally the H and V are the same, but the V weighs 0.2kg more than the H, indicating some kind of construction difference. Customer service couldn't tell me what the differences are between the two, so they referred me to a product development engineer. Spoke with him yesterday... he was away from the desk and didn't have details at his fingertips but said it would be unusual for the carcass construction to be different between an H and V in the same size within the same line. Believes the difference between these two would solely be in the cap ply material and/or thickness.

Does this sound accurate? A tire maintaining its uniformity throughout its life is a priority for me, and I prefer the concept of a single rayon carcass ply vs. two polyester and will go with the H if there are differences there vs. the V. But if the only difference were in the cap, I'd rather go with the V as it more closely matches the capabilities of the car. In short, if I can go with the V with little to no difference in ride/noise quality vs. the H I will, but I'm also willing to sacrifice the ability to sustain speeds in the 130-149 range (theoretical in the US anyway) if the H provides noticeably more comfort vs. the V. Or, are there other factors I need to consider I haven't yet?

Thanks in advance for any guidance you can provide...

 

[cibachrome]

I will strongly recommend you stay with the BFG KD construction simply because of handling stablity reasons. This car has very little understeer (< 1. deg/g) and sure doesn't gain very much as you push it. On a compact spare tire in the rear you will REALLY have your hands full. Other tire brands and constructions will not have as much linear range understeer, much less any that stays positive above .25g.

This car probably would benefit very much from split tires and rims.

All other constructions and brands used during US version GTO development could generate loss of control at today's highway speeds with just low amplitude, quick pulse type steer inputs.

Don't recall why Yokohamas (OEM in AU ?) didn't come along to the Statees, either sourcing, durability, or safety issues. I can probably find out....

 

[CapriRacer]

CltGTO,

First, you can’t go from a “acceptable” to “excellent” in ride quality with a 45 series tire. The best you can hope for is “good”.

Second, OE tires are noted for good rolling resistance which is obtained by sacrificing wear and / or traction. So if you want better wear, you will probably give up RR.
Dropping speed rating is probably going to negatively affect the handling crispness – which is obtained by the use of a less stiff sidewall and therefore the better ride.
But it will also probably affect the grip negatively
BTW the difference between H and V rated tires is generally going to be the amount of nylon (or whatever) in the cap plies. This would be seen printed on the sidewall as:” Tread: 1 ply polyester, 2 plies steel, 2 plies nylon.”

So I am thinking you are going to want to use the H and gain ride quality and wear at the expense of RR, grip and steering response – all other things being equal.

 

[cltgto]

Thank you both for your input... after reading through your responses several times I'm definitely reconsidering switching segments and may end up putting the KDWS back on there.

I do like the way the car handles as it does now, and even though it's not driven aggressively, I don't want any surprises in an emergency. One trait about the car's dynamics I really appreciate is its neutral handling... no understeer, and measured/incremental oversteer through application of more power. Found this out one night coming home late from work... 6 lane interstate, low beams due to opposing traffic, cruise set 70+, center lane, and a deer materializes less than 200 ft directly ahead... I had to make a snap decision (reaction mainly, as I didn't think about it) and swerved to the rear of the animal into the right lane. Didn't tap the cruise off, didn't attempt to brake, just got over very quickly using a "low amplitude, quick pulse" steer input... about a mile down the road I realized how composed the car remained during all of that.

The point of my story is that I definitely don't want to do anything that will increase the amount of inherent oversteer or induce additional oversteer. It's fine as is.... and if I read cibachrome's comment correctly, the KDWS's construction lends an additional understeer component that balances the dynamics of the car. And I agree, it would've been nice if clearances in the rear and OE wheel availability permitted 9" wide wheels and 265s out back.

So it appears that too many other elements (handling, absolute grip, steering response, etc) would change in my quest for cush, and that would change too many things too much. I figured there would be some trade offs but I don't want to change the overall character of the car either just to get better isolation from road imperfections/irregularities.

Thanks again...

 

[cibachrome]

My personal choice for the car would be P225/55R16 GDY Eagle RSA front and P225/50R17 GDY Eagle RSA rear. Both at 30 psi. This combo will reduce the high speed steering gain to a more comfortable (and somewhat familiar) level and increase its lateral frequency bandwidth. It was the winner from a bunch of tire rides on the cars made during development. You can get these tires from a Cadillac dealer because they are the uplevel CTS meats. Spare tire issue, though.

 

[Xwheelguy]

That would also make his speedometer reading incorrect.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

Some people are like slinkies....they don't really have a purpose, but they still bring a smile to your face when you push them down the stairs.

 

[cibachrome]

My dog says your speed meter would read about 3.28% high with the splits @ 17" rear. Yikes! The GTO KDs are construction 74062 if you want to get REAL GTO tires. If you want steering a bit heavier (with its understeer baggage), a Michelin or Goodyear in this size will do the trick. BTW: these tires like rim width if you don't mind the rub up front. (That's what the rear drive is for anyways, eh?)