I have a 6MT on order to arrive in April. In the past I have installed slightly larger tires (within allowable margins) on my cars (most recently my wife's Mazda Tribute ESV6 to increase stability and replace the Firestone Wilderness ATs).

My question is for anyone knowledgeable about "plus-sizing" or otherwise adjusting from the standard sized tires:

What would be the effect of replacing the 45 profile 18" tires on the 6MT with a slightly higher profile tire (say 50-55) in order to put a little bit more air between the road and the rim? Would this achieve any reduction of harshness over less than smooth roads? Or would this alter the handling / balance characteristics of the car negatively?

P.S. Please don't urge me to buy a Buick if I want a numbed ride -- I am very much looking forward to owning this driver's car after passing down my Eclipse 5 speed to my son a few years back. I ask about this matter because I am 51 years old with occasional back pain and would love to achieve the "best of all worlds" with performance and a pain-free ride :-)

Thank you for any thoughtful replies and information in reply.

VW Clough
Diamond Graphite/Graphite interior 6MT on order

 

I would suggest going with 17" wheels if you want a higher profile...using the same wheels with 55 would throw off your odometer and speedometer too much I think...unless you go with narrower tires as well...and yes it will give you a more cushioned ride.

Red/Canadian

 

If you go too high, it will throw off your speedo and gearing. Just remember this... If the overall diameter is smaller than the OE, it will accelerate quicker and have a lower top end. The opposite is true for going larger than normal. You car will actually be less peppy than stock. If you aren't off that much, it's not a big deal.

I just reread your post. If you're concerned about back pain and ride quality, do not go with the 18" wheels. Jumping from a 45 series to a 55 series is a big jump and you'll ruin the performance of your car. You'll also throw off your speedo for sure.

I'd get the 17" wheels or if you wanted a 6MT, sell your original wheels and go with aftermarket 17's. Also, all tires aren't created equal when it comes to ride quality. Ultra High Performance tires like the Pilots are really stiff. A slower rated all season tire is going to give you a plusher ride, especially when the temps dip.

Any way you look at it, there is going to be a comprimise unfortunately.

Sal

 

Cranking through the math.....

Front:
OEM: 225/45 r18 (25.97" tall)
235/45 r18 (+1.36%)
215/50 r18 (+1.89%)

Rear:
OEM: 245/45 r18 (26.68" tall)
255/45 r18 (+1.33%)
235/50 r18 (+2.14%)


Whether the wider tires rub? My guess is no.

Have fun trying to find those sizes

 

I have 275 on my rear and 245 with no rubbing

marcel

6

 

I have 275 on my rear and 245 with out any rubbing

marcel

6

 

Thanks for all your comments and kind restraint.

I am especially intrigued by Sal's suggestion that the summer tires that come on the 6MT (Michelin Pilots) are of stiff construction, and that an all season tire may be made of softer composites and yield a bit more comfortable ride, although at the trade-off of some performance/handling (hopefully not much).

I have always enjoyed the TireRack website (and bought many tires there) and will begin looking for high performance all-season tires to fit the 6MT 18 rims. I have had good luck with Pirelli Supersport, Yokohama AVID and Bridgestones. It would be great if one of those makers comes out with 18" tires.

Meanwhile, if anyone else has any comments or ideas???

VW Clough
Diamond Graphite/Graphite interior 6MT on order

 

<blockquote><font class="small">In reply to:</font><hr>

I am especially intrigued by Sal's suggestion that the summer tires that come on the 6MT (Michelin Pilots) are of stiff construction, and that an all season tire may be made of softer composites and yield a bit more comfortable ride, although at the trade-off of some performance/handling (hopefully not much).

<hr></blockquote>
When I test drove the G35C, I drove a 5AT with 17" all season Goodyear GSA's and the 6MT with the 18" Michelin Pilots. I was SHOCKED at how different the ride quality was between the two cars and now that I think about it, I attribute most of that to the differences in types of tires and not the size difference.

I would certainly go with a softer riding all season tire in the 18" or even go down to the 17" aftermarket wheel that fits around the Brembo's than mess around with tires with different aspect ratios.

I would call someone at the Tire Rack for their recommendations on this. They know a lot more than I do or probably anyone else on this site about tires. They are trained well, most of them race and every salesman/woman gets to take cars out on their on-site test track and try different makes and types of tires in varying conditions.

Let us know what you end up doing?

Sal

PS.. Even with ultra high performance tires, you are going to get a variance in ride quality. I don't know how the Pilot's stack up, but I do know that I've driven on different brands of the same size 17" tire and they were all different. The more hard core tire is definitely going to give you a stiffer ride. I've heard that something like the Dunlop SP9000 is going to give you a much cushier ride than some of the others even though it's not an all season tire. Just some food for thought.

 

"In the past I have installed slightly larger tires (within allowable margins) on my cars (most recently my wife's Mazda Tribute ESV6 to increase stability and replace the Firestone Wilderness ATs). "


I don't think that installing slightly larger tires will increase the stability of an SUV - it will just raise the center of gravity (albeit by a small amount).

I'm not sure if the 18" rims are a very good idea if you have a bad back. I had the 18"'s on for one day only and have since been driving with 17"'s with snow tires. I can still feel every bump in the road with the 17's and the 18's were even better for road feel (and a little more harsh).

 

You may want to consider getting a Grand Touring tire instead of a Performance tire. They strike a balance between comfort and performance.

2003.5 G35 Sedan Desert Platinum/Graphite Premium/Sport/Aero/Nav/Winter

 

Here's a new twist on the topic- I read some tire reviews this weekend on the TireRack site, and one reviewer made the comment that ride quality and comfort can most easily be adjusted via tire pressure. That is, go to a lower tire pressure for a smoother ride.

However, I wonder with low profile tires such as the 45 series 18 Michelin Pilot Sports that are OEM on the G35, wouldn't one risk having too little air between the road and the rim to absorb bumps if the air pressure was reduced to say....28 PSI or thereabouts rather than the recommended 32-36 PSI ?

VW Clough
Diamond Graphite/Graphite interior 6MT on order

 

VW...do not reduced the pressure on the Pilot Sports! Lots of negative side affects will occur. Take the advice regarding getting 17" wheels and going with sport/touring tires vs. the high perf Michelins. You could sell the original 18"s here without too much hassle...or I would think so.

Good Luck!

 

From what I heard, your gas mileage will also get worse if you lower the tire pressure.


I've also heard that they're going to stop making the MICHELIN PILOT SPORT TIRES and their replacement is going to be called PILOT SPORT A/S. I have 18's and I will be getting these tires with 235/50/18 in the rear and 215/50/18 in the front. I drive through a lot of bumpy/crappy roads and the rough ride is starting to get to me.

 

LOL, this post is 2 years old man. How did you decide to respond to this out of the blue?