GP2 newbie with tire info to share
 

Hello. I have lurked on NAM for while mostly in the marketplace and did not even know this forum existed. I will be catching up on all the posts I have missed this weekend :) Anyway, I have a unique? experience I would like to share with the community. I purchased my GP2 used with the OEM Kumhos but only had one or 2 drives before switching to some 45 series winter Michelins. These I drove for a few hundred miles and was really worried I needed to change the suspension! The car never really settled in on the highway and just jiggled around. I had intended to buy 45 series summer tires as there are many more options avail like Bridge SO4s etc. Given my winter experience I decided to put the worn out Kumhos back on the car before buying fresh summers. I am sure glad I did! The suspension is great - it was the 45 series tires! I understand this from an engineering perspective - a spring on top of a spring if not properly calibrated can have unintended consequences - but it is difficult to believe just how how bad this "real world" example was. Unless I read otherwise on this forum, I do not intend to take any chances and not only stick with 40 series but the OEM Kumhos specifically. As there are so few of these cars I thought others might like to know of my experience. best, david

Thanks for that insight. I'm on my 2nd pair of Kumhos and I love how they handle.

I took my stock wheels & Kumhos off at about 200 miles to save for the track and replaced them with NM engineering wheels and Nitto Neogens in the 215/40 size. The car rides and handles almost as well as the stock setup, no bad manners as you experienced. Just not the extreme grip the Kumhos have, but at less than $100 a tire and better wear, they are great street tires.

Bill

Hi,

It is more the tire than the aspect ratio that is causing this.

The kumhos (V70A/V700) are a semi-slick tire, designed for track days etc. They have an extremely stiff sidewall, as do most dedicated track tires. BMW / Mini tuned the suspension of the car for these particular tires.

Your 45 series michelins are a completely differently contructed tire. The difference in "spring rate" of the tire is much more due to the sidewall construction than the aspect ratio

I happen to have the stock kumhos 215/40/17, and I also have the exact same tire (kumho V70A/V700) in 215/45/17. The tires are identical in all respects except the aspect ratio. If you drive them back to back on the road or a racetrack you cannot perceive a difference in handling (there is a slight difference in gearing).

The take home message from this is the cars suspension was tuned to a specific tire. If you change to a different type of tire this will make a significant difference. Changing aspect ratio will theoretically make a difference, but this is less I believe.

@ robbo mcs - "yeah what he said" :) your description of my experience is much better, thank you

Your comparing winter tires to pure performance summer tires!!!!
By their nature, they are designed to be soft and pliable (tread and sidewall) to allow for better traction in cold snowy conditions. If you expected them to behave like your Kuhmos in the dry, then you need to give your head a shake...THEY ARE WINTER TIRES--no matter what aspect ratio.

@1qwkmini - I have dutifully shaken my head and stand by what I wrote. I am not comparing lap times, g-force, comfort or any or the like. I put winter wheels and tires on all my cars and typically go narrower and up a ratio. I have never had a suspension change its straight line highway cruising comfort in this way. Best way I can describe it is the car never quite stopped bouncing even on ruler flat pavement. I only thought others might want to know. By no means am I advocating anyone take action based upon my experience.

When I first bought the car the dealer gave me am extra set of stock GP2 wheels with winter tires. They were pirelli sottozero serie 2 240 in 205/45/17. For the first few hundred km they actually made highway driving straight line felt unstable. But after about 1000km they felt just fine. My guess is that the stock GP2 has too much camber and so it took longer for the tires to fully break in. So maybe this is that the thread opener is experiencing.