New tires for a 2005 Q45 - Current size is 245/45 18

[TorontoAndy]

Hi All,I need to replace the OEM Michelin Pilot HXMXM4 245/45 18 tires that came with my car when new. Can I put a slightly wider tire say a 255/40 18 on it or will it affect the spedometer?

Any suggestions on specific tire to choose. I travel a lot on highways and dont drive overly aggressively ie hitting corners at 100mph in the rain but I do enjoy a good winding road when it pops up. I have dedicated winter rims and tires but the new tires would be used when it was cold before the snow hits, so a "summer only" tire would not work for me.

All help is appreciated.

[seldomseen]

The width shouldn't interfere with your speedo, but you will want to ensure that it doesn't cause any rubbing on the inside. If you go wider try finding an application with a 45 series thickness so you to degrade ride quality just to have more contact patch. Tires that thick on the OEM 18's won't look pretty. lol The folks at tirerack really know their $h1t...hit them up.

[qship96]

Look at tireracks scores of high performance all season tires and pick the highest rated that just squeezes your budget.....hard to go wrong with Michelin pilot a/s, but they are not cheap in upfront price, but overall may provide lowest running costs and best ownership experience.

[mcrews]

welcome!go to the search button ...type in Kuhmo. select Q45 forum.

Search Results: Your search for kuhmo returned 15 results.

There are some very good threads on tires.I run 255/45/18 on an 02 sport. I also do lots of highway. the slightly larger tire is good for 1-2 more mpg on the freeway. I'm in northern CA Valley so no snow no rain. the Kuhmo is a great tire. Im on my fourth set w/180k on the kcar.here's the clearance in the front

tire is 10 inches fits the factory rim fine.

[Q45tech]

After using Michelins, every other brand will seem excessively noisey after 8,000 miles.

[Busbin]

I've been through several brands of tires lately - some came on cars I bought and some on wheel sets. First, I inhereted some high-end Bridegestone g-Force TA's - really unbelieveably noisey tires - the rumble was hard to talk over while driving. Then came a fairly new set of high-end Bridestone Potenza RE 070's on a set of 350Z wheels. They were somewhat more quiet, but became progressively noisier after about 10,000 miles. Lastly came a set of Kumho Ecsta ASX's on another set of 350z wheels, and while these tires cost much less than the Firestones and Bridgestones, they have been really great tires. After 20,000 miles they are almost to the wear bars and are still quiet and ride nice. I highly recommend them - especially for the price, and wear rating.

I have high-end Michelins on my other three cars and, and as others have noted, have always proven to be the best (although they cost more!)

[mcrews]

The OP is up in the north so I can,t speak to the characteristic of the Kuhmo in those conditions.But I needed to add that the 255 is going to thrw of the speedo about 3percent. but that is a very fair trade off for a little better hgwy mpg.

also, I don't push my Q so maybe another tire is better suited for agressive driving but the Ecsta asxworks very well for me

[Q45tech]

For most people wet panic braking is the most critical function of a tire.

Tire rack has analysed about 30 different tires from a 50mph panic stop distance perspective.Obviously the tire sizes used on the BMW mules are different but generally the difference between brand translate to larger sizes as long as you select the same speed rating.Intentionally buying a tire that is 20-25 feet worse in stopping than the best should be questioned.

[TorontoAndy]

Are you saying that a 255 tire will have worse stopping than a 245 or that I should just look at the braking review data and choose the best wet stopping tire I can get??

[Q45tech]

The stopping distance depends on how well the tire sheds the instant heat build up during the 1-3 seconds. Cold wet stopping has a critical temperature vs rubber compound component that is never tested in public reports.

Footprint is primarily a function of PSI inflation and weight on tire. +-1 size makes little difference in braking. A higher load index [carrying capacity] will improve braking just as it does handling.

Front tires [heaviest load points] wash out first as with handling so strongest tires should always be loacated on front

[elwesso]

i think tech is more/less saying you need to be conscious on what tire selecting, because cheaping out could result in reduced stopping distances...

Bottom line: All season tires= compromised performance for all seasons. if you really want to do things right, you would get a set of summer tires and a set of winter tires. If you drove your Q in the winter time with and without snow tires, you'd never go back to having a non-snow tire in the winter!

[Q45tech]

Here's an SAE article about how tires are braking tested between 60-80F.http://www.thefreelibrary.com/...55892

http://www.minigpx.com/enlarge...=1554h ... icle=25151

[TorontoAndy]

Are you saying that a 255 tire will have worse stopping than a 245 or that I should just look at the braking review data and choose the best wet stopping tire I can get??

[mcrews]

Footprint is primarily a function of PSI inflation and weight on tire. +-1 size makes little difference in braking. A higher load index [carrying capacity] will improve braking just as it does handling.

Are you saying that a 255 tire will have worse stopping than a 245 or that I should just look at the braking review data and choose the best wet stopping tire I can get??

my 'undergraduate' understandinf of what he meant.....is the the slightly larger footprint doesn't matter as much as the load index. I do believe that the 255/45/18 has a higher load rating than the 245/45/18.

Also, from personal experience, the 05 has a 'higher rear end ratio' ....goes faster off the line and runs at a higher RPM at a steady speed than the 02. If?when I replace my 02 w an 05 or 06 I personally will absolutely run the 255 on the stock rim. That will lower the rpm at highway speeds just a little but will also improve gas mileage