Need Help with Big Tires for a 2014 M6?

[chask]

I have searched the forum but not found much on this - I'll freely admit my search skills border on pathetic. So I'd appreciate some help with what will fit under the fenders with no rubbing.

The car currently has the stock Pirelli P Zero 265/35ZR20's in front and 295/30ZR20's in the rear. Looking at specs Tire Rack has online I'd like to go to Michelin Pilot Super Sport 275/35ZR20's in front (maybe a 285/30) and one of these in the rear: 305/30ZR20, 315/35ZR20, 325/25ZR20 or 335/30ZR20. SInce I do not plan to change rims the main thing is will these fit without hitting the fender or the suspension. The RIMSnTIRE calculator shows an increase of 5mm with the 305 (both sides on all these figures), 10 mm with the 315, 15 mm with the 325 and 20 mm with the 335. I think my preference would be the 335's (if possible), followed by the 315's. The 325's are shorter than the stock tires and I've already got a low reading speedo (about 3 mph - probably like everyone else from what I have read) and the 305 does not seem like much of an increase. I just feel like the car has nowhere near enough rubber on it for the power it's putting out and would like to have as much tire as possible to help this.

In front -
I lean towards the 275/35's because of all the bad weather around here - potholes are multiplying like rabbits but they are more the size of elephants. In addition, the Tire Rack specs don't show much of a gain in tread width going from a 275 to a 285.

In the rear -
In spite of my ineptness with searches, I did manage to find a thread here where someone had used a 20 mm spacer in the rear, seemingly without any trouble - (http://www.6post.com/forums/showthre...t=plus+1+tires). That gives me some hope for the 335's working. If the RIMSnTIRE calculator is correct, my only other worry with them would be on the inside. As it shows the 335's are only 12 mm taller (I assume from the wheel center) there should not be much of an issue with them contacting anything. It also looks like this would come awfully close to correcting the speedo error too.

I could almost guaranty without asking that the 315's would work except that they are 21mm taller than the stock tire (again, from the wheel center). I would like this as the 6.2% increase in actual speed over the current setup would definitely correct the speedo error I have.

Another consideration for me are the road conditions around here. The countless freeze-thaw cycles we went through this winter really tore up the roads like crazy. Having a bit more sidewall would be nice. That's made me think about going to a 295/35 in the rear if there is absolutely no room. It too would fix the speedo error, but I think it might also help with the pothole issue around here too. And according to the TR data it is almost half an inch improvement over the stock 295/30s. However, from looking at the car, online, and what little I have been able to find here it sure looks like there is space for almost another inch in width, assuming that the shift during hard cornering doesn't take a fender over into the sidewall.

If no one has any experience with this, any thoughts or comments would be greatly appreciated too. Thanks for looking and the assistance. Calculations can be helpful but there is nothing that substitutes for experience, especially with this stuff.

[M6-Coupe]

If you are planing to keep your OEM rims, the maximum width of tire you can go for front is 285 and for rear is 305.
Your OEM rims are 9.5" wide on front and 10.5" wide on rear

[brad850csi]

I'm personally most keen for 335/30/20 with a 275/35/20 up front. Quite a few people here are running 325/25/21 but none of them could tell me what offset they were running or how much room there was around the wheels. I suspect that 335/30/20 is possible without dropping the car and with just the right offset.

For what it is worth that thread you like to has winter wheels which are either 20x9" or 19x9" and have a 25mm offset and 255mm wide tyres. This would mean even with the 20mm spacer the stock summer wheels stick out 5mm further than the winters with a 20mm spacer.

I do recall seeing some people run a stock wheel with a 12mm spacer at the rear, unsure about any wider than that?

[brad850csi]

Just looked up other 6 series, the Alpina comes with 9.5" wheels with a 44mm offset and 285/35/20 tyres. Compared to the stock M6 wheels with a 19mm offset and 295/35/20 tyres, you would be able to go 20mm further inwards to have the same clearance.

So based on my post above of a 12mm spacer plus this 20mm inwards that is possible, this would take you to a 325 wide tyre again without any issues, just like the guys running 325/25/21. This would need an offset of about 25mm.

[gmd2003]

Originally Posted by brad850csi

Just looked up other 6 series, the Alpina comes with 9.5" wheels with a 44mm offset and 285/35/20 tyres. Compared to the stock M6 wheels with a 19mm offset and 295/35/20 tyres, you would be able to go 20mm further inwards to have the same clearance.

So based on my post above of a 12mm spacer plus this 20mm inwards that is possible, this would take you to a 325 wide tyre again without any issues, just like the guys running 325/25/21. This would need an offset of about 25mm.

But the stock wheel isn't nearly wide enough for a 325 . 275/35/20 front and 305/30/20 on the stock rims are the best options for performance and I have tracked the car with this setup no rubbing and excellent grip / feel . A 325 tire on a 10.5 wheel will add unnecessary weight , not increase contact patch significantly and will make the handling horrible due to sidewall flex .

[chask]

Originally Posted by M6-Coupe

If you are planing to keep your OEM rims, the maximum width of tire you can go for front is 285 and for rear is 305.
Your OEM rims are 9.5" wide on front and 10.5" wide on rear

First off - Thanks M6-Coupe for the help. I really appreciate it. The dealer is helping me with this as part of the transaction so I don't have much time to figure this out.

I have the 433 rims on mine (probably should have mentioned this too) like the ones in this link - http://www.6post.com/forums/showthre...&highlight=433. Sorry about not putting all the details in the original post. Do their offsets change any of that?

The way the car bites up front I am not sure it really needs much more tire for the way I drive. It's the back I worry about, and mostly because of all the power the car has. I have not gone full throttle yet during break in (not babying it either), but I remember some bad experiences from a previous car. I had a S65 that was really scary. When I would floor it to get out into a break in traffic the tires would invariably spin and traction control would literally just stop the car. Several times while I was trying to enter a 4 lane heavily trafficked road from a side street (left turn to get onto that street) the car would almost completely stop before it made it to the double yellow in the middle of the road.

I'll never forget the first time - I'd been sitting there for several minutes, waiting for traffic to clear. I saw a break and nailed it to get into traffic safely - nothing I had not done in all my years of driving. Everything was going as planned until the front of the car crossed the first lane divider and the tires started to lose traction. The traction control kicked in and quickly brought the car to a complete stop. You can imagine my surprise (and terrifying shock) when the car literally stopped moving just shy of the double yellow running down the middle of the road; well, technically it was still moving but at the pace it was moving I could have gotten out and walked faster, and I use 2 canes to get around. I've got 15-20 cars barreling down on me on my left and the ones approaching on the right are quickly cutting off my chances of getting out of the predicament in one piece. And I'm sitting there with my foot on the floor but going nowhere. It took me a while to adapt to the 'less is more' aspect of driving that car - another episode with a gravel truck about to T-bone me finally drove that concept home. Fortunately none of these incidents involved any damage to the car (no body work); just a couple of close calls that nearly gave me a heart attack. That car desperately needed more traction in the back, and a traction control that functioned correctly. Then again, perhaps the mfg's don't want that in order to keep their trannies and rear ends in one piece. This M6 feels pretty much the same way so far, maybe even more brutal in that regard. I have not nailed the M6 yet (so I don't know if the effect will be as bad as it was in the S65) but I have felt the traction control sneak in a couple of times and it has a similar feel under some close conditions. This is mostly what I am trying to "fix", or at least alleviate a little. But with all the hp in the M6 it's probably a futile effort.

I take it anything larger than a 305 in the back will hit the outside fender, the suspension and/or the top of the fender well. Since the guy in the link I posted put 20 mm spacers on the same rims (according to RIMSnTIRES, 10 mm more than the increase the 315/35 would have on the outside) it would seem that the outside fender is not the issue. There also is another guy here running a 325/25 x 21 setup. The 325/25 x 21 setup is 5 mm wider on both sides than the 315’s but 17 mm shorter (about 5/8"). It would seem that the suspension components aren’t the issue either. So I am guessing the problem with the 315's is the height, unless it is wheel offset. I can't tell about the height or the inside clearance for sure (can't get under the car like I used to) but it does look like there is a lot more room and I can feel a lot of space up above the tire too. Can anyone tell me what the problem is? .

Please understand, I am not questioning what you tell me, I am just trying to figure out which aspect of the setup is causing the trouble to see if there is any way around it (like maybe some slight inner fender work). I am an engineer type and like more knowledge - can't help it, it's just my nature. Since others here are using a similar width tires that have a same overall size (albeit with a taller rim and shorter sidewall) I am thinking this must have to do with rim offset or something I am just not seeing.

I might bite the bullet and get new rims too if they would allow the car to accommodate larger tires. My primary reason so far has been that I worry about the tires and rims lasting around here with the terrible roads; I like the looks of these 433's too. The other day I saw a hole that I could not see the bottom of - it was easily at least 4-5" deep and looked considerably deeper. I was on that road the day before and it wasn't there. I know for sure as it is right at a jog in the road where you have to pay really close attention to the lane markers to keep from hitting another car. And with the winter we've had they aren't going to get any better. At least for a while more and more are going to be appearing daily. I really hate to go to a bigger rim but I guess with the tire/wheel insurance it would just cost time.

If I choose to go with new and larger rims, what is the best setup in the back? In case I am not too fond of the style of the rims mentioned, what wheel offset do I need to make that tire size work in the back? So far I am seeing 325/25 x 21 but I also hear Michelin is no longer making those (read it in another thread or two here). I am pretty much set on Michelin Pilot Super Sport tires.

If the problem is wheel offset, it seems like the sizes I am considering would work. Again, thinking about tire/wheel damage and getting stuck some place I really don't want to be, I might get a 20" rim with a different offset to keep the larger aspect ratio tire. I know this will seem like a mortal sin to some of you guys (okay, I used to do this stuff for a living – it’ll probably seem much worse than that to about everyone here) but I'm getting on in years and don't like to ruff it like I used to.

I also think I should add that I stumbled across an error I made about the tires. I built a little spreadsheet so I could more easily compare various tire options and see the limitations and potential problems - yes, I truly are an engineer. I just noticed I had probably cut and pasted but failed to correct the recommended rim data on the 325 and 335 tires. Both require at least an 11.5" rim so they are out unless I go to different wheels. It's too bad because I thought the 335's might be kind of nice on the car. I might go for some different rims to make those work in back.

Ideally, I guess what I am looking for is more tread width in back (for better traction) and a little more sidewall all the way around (to prevent blow outs - wider tire with same aspect ratio => more sidewall). I just wish I had more time for this. The M6 was a surprise deal. My wife's lease on her X5 was coming to an end and we had to get her into a new one (I tried to convince her a X5 M would be better but no such luck - this time anyway ). The dealer had some incentives that made an early out work very nicely on hers ($$$$) and offered me something to get out of the B7 I was driving ($$). That they handed me some keys and said "take the M6 for the weekend" was the proverbial straw. I should have known better. Anyway, I am loving it so far. Normally I would have done the research and figured all this out before making the move on the M6. As it stands now I am kind of leaving this issue open with the dealer (who has been exceptionally good to me for most of the 30+ years I've driven Bimmers) and want to get this matter off their desk and mine.

[chask]

Just now am seeing all the other replies. Thanks guys. I appreciate it. Let me digest over dinner and I'll get back to you.

Mostly though, I'd love to find someone who has done this and can say it works.

I like the 305 but wish it had a 30 aspect ratio. Being nearly 4% shorter than the 295/30 it only adds to the speedo error - another thing I'd like to get rid of, but it's not that critical. Handling and noise (along with ride comfort) are the key issues to me.

[gmd2003]

Originally Posted by chask

Just now am seeing all the other replies. Thanks guys. I appreciate it. Let me digest over dinner and I'll get back to you.

Mostly though, I'd love to find someone who has done this and can say it works.

I like the 305 but wish it had a 30 aspect ratio. Being nearly 4% shorter than the 295/30 it only adds to the speedo error - another thing I'd like to get rid of, but it's not that critical. Handling and noise (along with ride comfort) are the key issues to me.

I have a 305/30/20 PSS slightly larger diameter as stock and is very close to the larger diameter 275/35/20 and 285/30/20 PSS options for maintained mdm function .

[M6-Coupe]

Originally Posted by chask

Just now am seeing all the other replies. Thanks guys. I appreciate it. Let me digest over dinner and I'll get back to you.

Mostly though, I'd love to find someone who has done this and can say it works.

I like the 305 but wish it had a 30 aspect ratio. Being nearly 4% shorter than the 295/30 it only adds to the speedo error - another thing I'd like to get rid of, but it's not that critical. Handling and noise (along with ride comfort) are the key issues to me.

I have 305/30/20 MPSS (rear) and most of the time am driving in MDM… traction is significantly better than stock tire. And yes, I drive the car the way M6 is supposed to be driven...

[chask]

Originally Posted by brad850csi

I'm personally most keen for 335/30/20 with a 275/35/20 up front. Quite a few people here are running 325/25/21 but none of them could tell me what offset they were running or how much room there was around the wheels. I suspect that 335/30/20 is possible without dropping the car and with just the right offset.

For what it is worth that thread you like to has winter wheels which are either 20x9" or 19x9" and have a 25mm offset and 255mm wide tyres. This would mean even with the 20mm spacer the stock summer wheels stick out 5mm further than the winters with a 20mm spacer.

I do recall seeing some people run a stock wheel with a 12mm spacer at the rear, unsure about any wider than that?

If it'll handle a 12 mm spacer then the 315's ought to work. They are only supposed to add an additional 10 mm on the outside. I can't imagine there not being 10 mm more on the inside. The trouble for the 315 then becomes the height. That tire on a 20" rim is supposed to be 1.7" taller, or about 27/32" in radius (essentially 7/8"); that's 43.2 mm larger diameter or a 21.6 mm larger radius - RnT shows 21). It's hard for me to imagine there would not be that much room. But that is based on what little I can see and feel around the tire with it sitting in my drive. It also does not take into account any movement under driving conditions. And mounting it on a 10.5" rim probably isn't the ideal setup but it's supposed to work.

Originally Posted by brad850csi

Just looked up other 6 series, the Alpina comes with 9.5" wheels with a 44mm offset and 285/35/20 tyres. Compared to the stock M6 wheels with a 19mm offset and 295/35/20 tyres, you would be able to go 20mm further inwards to have the same clearance.

If this is accurate then the 315 should work on the inside as well. That leaves just the height as a potential problem.

Originally Posted by brad850csi

So based on my post above of a 12mm spacer plus this 20mm inwards that is possible, this would take you to a 325 wide tyre again without any issues, just like the guys running 325/25/21. This would need an offset of about 25mm.

I probably ought to get out a pen and paper and draw this up. Does anyone know what the offset of those 21" rims everyone is using to run the 325/25's?

Originally Posted by gmd2003

I have a 305/30/20 PSS slightly larger diameter as stock and is very close to the larger diameter 275/35/20 and 285/30/20 PSS options for maintained mdm function .

Originally Posted by M6-Coupe

I have 305/30/20 MPSS (rear) and most of the time am driving in MDM… traction is significantly better than stock tire. . . .

I am new to this forum but judging by your rank here I suspect you two are the guys who have been around and should be pretty much in the know.

Though I have not tried it yet I really like the idea of 'maintained mdm function'. I am having trouble understanding how the mdm would be affected by tire diameter, though I can see that it might be. Being a digital system it will make adjustments in steps. Some of the 'adjustment steps' it makes might not work as well for a taller tire. But the designers also have to take into account smaller tires too.

I would think the system would have to work in the winter too. After all, there is not snow or frozen stuff on the road all the time. I checked on some Michelin snow tires. There is a 255/45R19 snow tire that is 28.1" tall and a 275/40R19 that by RnT's calculator should be roughly 18 mm taller than stock, or about 28+". That brings the delta down to about 5/8".

On what do you base the mdm functionality to be compromised? I used to have several resources with BMW but I am sure they are long gone - it's been about 20 years since I last had contact with them.

I also am curious if you guys have actually tried the 315/35 or know anyone who has.

That said, I want to thank you two for the 305 recommendation. Knowing that it actually works makes it my definite fallback should I not be able to get the 315 to fit.

Boy it sure would be nice though to get some info on the M6 GC wheel well - like a technical drawing so offset and tire size could be checked. I'd bet somewhere there is a drawing that shows the tire/rim combination throughout its entire range of motion. I still have this feeling that with the right offset on a 20" x 11.5" rim this tire might work. Think about the traction the 335/30ZR20 would have on that.

Originally Posted by M6-Coupe

. . .
And yes, I drive the car the way M6 is supposed to be driven...

I've not been babying mine too much. All BMW's are made for the joy of driving. It's a driver's car for sure - good road feel and feedback. Like any athlete it needs 'exercise'. It also needs some warm up and proper conditioning too. Mine has been seeing some revs since I got behind the wheel (up to a reasonable RPM anyway), but no wide open throttle. Since I am getting close to the end of break in I started stretching mine's legs a bit on the way to dinner last night. Still no full throttle but definitely a little more spirited driving. What a ride this is! I've actually driven faster ones but what a package. This is one great car!. And I know this isn't even beginning to touch what this thing can do.

[M6-Coupe]

Originally Posted by chask

Though I have not tried it yet I really like the idea of 'maintained mdm function'. I am having trouble understanding how the mdm would be affected by tire diameter...

The driving Force that push your car can be calculated as:
F= F(on wheel) -Frr-Fd
Frr and Fd are air resistance force and drag (rolling resistance) force
F (on wheels ) = [Torque (at crank) * gear ratio * FD ratio * (1-drivetrain loss)]/wheel radius

So larger wheel means less driving force...you might expect less DSC interference "if is noticeable"...
make sense?

[M6-Coupe]

OP,
I think Twitch Massacre is the one who can share his experience with you...
http://www.6post.com/forums/showthread.php?t=1008171

[brad850csi]

It didn't occur to me that stock wheels were going to be used. If so then 275/35/20 and 305/30/20 really is the biggest you'd want to go. The height difference is minimal.

[Twitch Massacre]

M6-Coupe you were right when you stated previously that the OP cannot run anything bigger than a 305 on his stock wheels. He also cannot run a 335 on his rear on any wheel setup with his M6. 325 is the max the m6 can clear and the widest wheel is a 12.5 with a VERY aggressive fitment.

[M6-Coupe]

Originally Posted by Twitch Massacre

M6-Coupe you were right when you stated previously that the OP cannot run anything bigger than a 305 on his stock wheels. He also cannot run a 335 on his rear on any wheel setup with his M6. 325 is the max the m6 can clear and the widest wheel is a 12.5 with a VERY aggressive fitment.

Buddy, thanks for your feedback...

[chask]

I can't tell you all how much I appreciate all this help. You guys are great! And everyone is so reasonable - even the arguments I have seen around here were kept pretty benign. I think I am really going to enjoy this place.

I still have one question though - Has anyone actually tried to put a 315/35ZR20 on a 433 rim (my factory stock rims) on a M6 GC?

m6beast tells me he is running 305/30 21's street and has a vehicle using Toyo 305/30/20's on stock rims. Two of you all are running that size on stock rims too. Others are running a 325 width on 21" rims. Those are supposedly 27.2" tall. I would swear I found some snow option that was about that height but can't find the size or brand now - way too many interruptions and too much going on.

There appears to be plenty of room in front, back and on both sides for a 315 width tire. The problem is the 28.7" height of the 315/35ZR20. I bolded the aspect ratio to make sure everyone catches it is a 35, not a 30. We are only talking about roughly a 1.5" increase over the 305/30's.

Unless I have this all wrong, it would seem like half the diameter increase is below the axle centerline, and that half will be taken up in raising the rear of the car. The rest of the height increase will be up in the fender well. It sure seems like there is that much room up there to me (just .75", maybe a bit less), but like I said I can't get a good look.

[devondragon]

Chask,

the issue you can't put a 315 (or anything wider than a 305) on a 10.5" wide rim without problems. With the stock rims, you shouldn't go wider than 305. Has nothing to do with clearance or spacers or rubbing, it's just a rim width to tire width thing.

[bshep604]

It would seem to me that a huge team of automotive engineers at one of the best car manufactures in the world would know what is the absolute best tire size configuration. These people have years and years of experience collectively. Millions of dollars invested in RnD. Years of testing before release. These tires that these cars are equipped with are the size they are for a long list of reasons. Altering the size of the tires in such a drastic way will surely be putting the car at risk for safety issues and not optimal handling characteristics. Just saying'

[M6-Coupe]

Originally Posted by chask

I can't tell you all how much I appreciate all this help. You guys are great! And everyone is so reasonable - even the arguments I have seen around here were kept pretty benign. I think I am really going to enjoy this place.

I still have one question though - Has anyone actually tried to put a 315/35ZR20 on a 433 rim (my factory stock rims) on a M6 GC?

m6beast tells me he is running 305/30 21's street and has a vehicle using Toyo 305/30/20's on stock rims. Two of you all are running that size on stock rims too. Others are running a 325 width on 21" rims. Those are supposedly 27.2" tall. I would swear I found some snow option that was about that height but can't find the size or brand now - way too many interruptions and too much going on.

There appears to be plenty of room in front, back and on both sides for a 315 width tire. The problem is the 28.7" height of the 315/35ZR20. I bolded the aspect ratio to make sure everyone catches it is a 35, not a 30. We are only talking about roughly a 1.5" increase over the 305/30's.

Unless I have this all wrong, it would seem like half the diameter increase is below the axle centerline, and that half will be taken up in raising the rear of the car. The rest of the height increase will be up in the fender well. It sure seems like there is that much room up there to me (just .75", maybe a bit less), but like I said I can't get a good look.

what we are discussing here is what you can do with no significant change to stock/standard specification; however you can install whatever you want. going out of manufacturer suggestion (ie 315 or 325 tire on 10.5" rim) is not suggested by manufacturer, but they are not here to arrest you if you do ... you just lose the right feeling of your car. Increasing 6% on wheel size (27" to 28.7") means you will have bigger wheel. It will definitely has some effects on driving experience and performance (ie handling)....for example the whole purpose of CF roof is to lower the weight as well as center of gravity and now you are increasing both of them... TBH, I do not do it to my car