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[TheSt|G]

Originally Posted by kafou

Not easy to make a choice, more members choose staggered (13vs9). But more comments about why choose square...

Probably because there is no valid reason to go staggered on the 128i besides style points. It is objectively worse in every way.

[kafou]

Originally Posted by TheSt|G

Probably because there is no valid reason to go staggered on the 128i besides style points. It is objectively worse in every way.

You're probably right

[jmcphillips1]

I just ordered a pair of PSS 225/45-17 for my fronts from Tirerack at the recommendation of Butch that works there. Very nice guy by the way. These will replace my stock 205/50-17 that came on the car. Mine is a 128 M-Sport wheel.

[kafou]

One thing I didn't mention is that my wheels are the 261m, so 7.5 inch front width and 8.5 inch rear width. By looking at the tires specs, maybe 225 on the rear will be a bit stretched...

[Black Flagged]

square it up

[cmcdonald]

I really think square vs staggered is like asking chocolate vs vanilla. Handling is a very subjective thing when it comes down to how much oversteer you like and are comfortable with. Most will say go square. Square will definitely give more oversteer. However, not everyone likes how the car feels like this. My car originally had a square setup, and I found it to be a bit twitchy on the highway. I went staggered, and I feel it is just a bit more planted in a straight line at speed now. Mind you I am switching from a previous car with an extremely long wheel base (Cadillac DTS), and I do not track my car, it is a daily driver. If you track your car, I would say square, if it is mostly a daily commuter, you may find staggered to be a bit more comfortable. Just my two cents after driving the car both square and staggered.

[kafou]

Is that understeer thing only when you drive at the limit of grip? On post about that, it always refer to more or less grip to the rear wheel to balance between oversteer and understeer. If as a daily driver, even on a spirited driving, I rarely push to the limit of losing grip, will I notice the difference between 225 or 245 at the rear wheel. A friend of mine test drive my car and even with the stock tires 205fr/225rr, he said that with that grip the car can handle 30-40hp more. It is my first RWD, and a feeling that I like is when I feel that the rear wheels are pushing me, If by going square I add to that feeling then that will be my choice. If I have to push to the limit to see a difference I will go staggered.

[John_01]

Originally Posted by kafou

Is that understeer thing only when you drive at the limit of grip? On post about that, it always refer to more or less grip to the rear wheel to balance between oversteer and understeer. If as a daily driver, even on a spirited driving, I rarely push to the limit of losing grip, will I notice the difference between 225 or 245 at the rear wheel. A friend of mine test drive my car and even with the stock tires 205fr/225rr, he said that with that grip the car can handle 30-40hp more. It is my first RWD, and a feeling that I like is when I feel that the rear wheels are pushing me, If by going square I add to that feeling then that will be my choice. If I have to push to the limit to see a difference I will go staggered.

Yes and no. The tire profile and grip will still have an effect on understeer if you are driving enthusiastically and not even close to the limits. So yes a square setup will be noticeable in daily driving, although not a very big difference IMO. The trouble I have with the 1 series coupe, is the rear suspension tends to wobble around very badly when the car is pushed hard. In normal driving the rear suspension still wobbles, but its manageable. By adopting non-staggered tyres you are not only reducing understeer but also reduce stability margin at the absolute limit. In combination with the wobbly rear suspension, it will make the car even less predictable when pushed to the limit. Due to this concern I wouldn't really recommend non-staggered tire setup unless you are very focussed on sport applications such as auto-x.

IMO, for a street driven car its better to keep the staggered tire setup and add a slight negative camber if you want to reduce understeer. For a street driven 1 series or 3 series, I found two modifications that work well: 1) Remove alignment pins in the top of the front strut mounts to add 0.4 degree negative camber per side. 2) Add a front stabiliser bar such as E92 M3 26.5mm bar. If you want to upgrade stability and handling further, then installing M3 rear subframe bushings is highly recommended. However that's quite an expensive job to get done.

[kafou]

Originally Posted by John_01

Yes and no. The tire profile and grip will still have an effect on understeer if you are driving enthusiastically and not even close to the limits. So yes a square setup will be noticeable in daily driving, although not a very big difference IMO. The trouble I have with the 1 series coupe, is the rear suspension tends to wobble around very badly when the car is pushed hard. In normal driving the rear suspension still wobbles, but its manageable. By adopting non-staggered tyres you are not only reducing understeer but also reduce stability margin at the absolute limit. In combination with the wobbly rear suspension, it will make the car even less predictable when pushed to the limit. Due to this concern I wouldn't really recommend non-staggered tire setup unless you are very focussed on sport applications such as auto-x.

IMO, for a street driven car its better to keep the staggered tire setup and add a slight negative camber if you want to reduce understeer. For a street driven 1 series or 3 series, I found two modifications that work well: 1) Remove alignment pins in the top of the front strut mounts to add 0.4 degree negative camber per side. 2) Add a front stabiliser bar such as E92 M3 26.5mm bar. If you want to upgrade stability and handling further, then installing M3 rear subframe bushings is highly recommended. However that's quite an expensive job to get done.

I will take a look at these mods.

Thanks

[kafou]

Hi,

Finally I decided to go staggered. My reasons are, better fit with my larger rear wheels, I won't do any track, look, better stability on highway and possible mods if I really need to reduce understeer.

For now my choice is 245 but I'm curious as why more peoples prefer 255 over 245?

What's your reason?

Thanks

Kafou

[kafou]

The others posts about square or staggered give some action to my poll

But there seem that there will be no winner!!!

[FactorX81]

I have 225 winters on my stock wheels and the backs have gotten tons of rock chips this winter I don't recommend 225s in the stock rears if you want them to stay in good condition.

[kafou]

I finally ordered 225/245 PSS. Not that much staggered and a better fit with my 261M rear wheels. Maybe If I change my wheels one day I will consider going square.

Thanks

Kafou

[kafou]

A few days since I installed my PSS. WOW!!! what a tire!!!! I always liked Michelin and again I like a lot this tire. Way better than the stock RFT. No chance to push a lot to date but I can feel that I had a lot of grip

[kobeballer96]

I'm running 225 square bfg rivals on 17s. Light and sticky for street and track, 128i doesn't need that much tire and weight!!!!!

[kafou]

Originally Posted by kobeballer96

I'm running 225 square bfg rivals on 17s. Light and sticky for street and track, 128i doesn't need that much tire and weight!!!!!

I take the 245 for the same reason, a little lighter than the 255 and don't go square because of the size of my wheels, so 245 is a good compromise.

[128Convertibleguy]

Can someone answer me this? It's a honest question, not an attempt to change people's mind. I'm more looking for the reasons to change mine.

If you're going to run 225s up front, regardless, why is going 245 (or even 255) on the back such a big (negative) deal?

The difference in weight/gear ratio/etc. is minimal. The car won't be any slower in a corner, or stopping, since the 225s up front are limiting that, anyway.

You'll just have a bit more rear grip, which could come in handy on damp pavement, or other low traction situations.

I've got the same decision. I'm leaning toward the 245/45-17 in the rear, because (in order of importance to me, most to least):

It will make my speedo and cruise control, which read the usual bit high, dead on. No more mental calculations to know how fast I'm really going.

I like the idea of turning 100 rpm less at cruise. When I accelerate the transmission compensates, this just changes the shift points (in mph) a bit.

That bit of more rear grip in reserve, just in case.

Slightly better ride.

Style.

So, to those advocates who say square is much better. Why? And why is that thing significant, as opposed to esthetic? I'll concede 245 may be unnecessary, although I've explained the reasons I prefer it.

But why is it bad?

[John_01]

I think the staggered setup causes understeer because of some physics related to the tire's "slip angle". Very generally, a wider rear tire generates more grip for the same slip angle, so it stabilises the car when lateral loading is applied. If you are accelerating, it can cause the rear slip angle to be higher, so the understeer due to staggered tires will be neutralized. Camber setting, toe angle and tire pressure also play into this, so it probably gets quite involved to properly analyse all the factors.

[128Convertibleguy]

Originally Posted by John_01

I think the staggered setup causes understeer

Agreed. So what's wrong with that? Either way, the limiting factor in how fast you can get around a corner will be the 225 fronts. And that only when you're at the very limit, which I don't deliberately do on the street. I might enter an autocross for fun, but I'll have mods (like M3 front arms) that will put me in a class where I'm uncompetitive, anyway.

[Solo_M_Tech]

I'm running 245/40R18 up front and 265/40R18 in the rears, with pilot super sport tires, and I have yet to experience any understeer, or oversteer. The car is hella planted, tracks straight into, and out of corners. The car feels very stable and planted at speed. I have no complaints. The tire size is alittle too big for my 261M wheels, but I haven't felt that squishy sidewall issue everyone had told me about. Once I install the KW coilovers and M3 bushings it should be extremely well planted.

[strati1]

Go square 225, I did and have been kicking myself for running 225f 245r for as long as I did. 245 will still promote the factory understeer quite a bit, I thought it would be more of a balance, but was incorrect. The 225 square feels much more balanced in general, especially at the edges of grip.

[chris82]

I have 215F, 245R

Seems to work very well. I don't track the car (yet).