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Discussion Starter #1
How has it changed your car's handling?

I've got a stock 2014 sport MZ 3i and I will be upgrading my wheel and tire package soon. I've got 205/60 16 Conti Pure Contacts on it now. My tire preference after a lot of research here and on TireRack (and other sites) for late spring/summer/early fall is BFG G-Force Sport 2 A/S. I'm in southern Ontario so temps and weather conditions can really swing far in the spring and fall.

I'm leaning towards 215/45 17 with Konig Runilite 17" x 7.5 x 45mm O/S wheels. They are relatively light at ~19 lbs and will give me plenty of options for tire sizes. What I am unsure of is the change in scrub radius this combination of wheel and tires will do to my car's handling. This size will give me ~9 mm more positive SR, so it will very likely put me into positive SR territory.

I love the no torque steer and bump steer I get form the stock setup I have now. I can accept a bit of torque steer and other issues in exchange for more cornering grip and possibly less understeer, but I don't want to be sorry I made this change later.

So, if any of you have done a similar tire change and can shed some light on the performance changes you experienced I would love to hear about your experience.

Many thanks for any info anyone can pass on.
 

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Discussion Starter #2
Just realized I should add this info.

The 2 tire sizes I'm asking about are both about the same S/R difference from stock, about 9 mm more positive, which is why I am interested in your experiences with these sizes. I have tried to find out how much negative S/R we have in the stock setup and I just am not getting anything like a reliable number.
 

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If you want to go to a 17" wheel you should be looking more at a 215/50-17 (0.8% smaller than stock) or a 225/50-17 (0.8% larger than stock).

A 215/45-17 is 4.3% smaller than stock. That's a big difference.

Not sure what you mean by "SR"?
 

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How has it changed your car's handling?

I've got a stock 2014 sport MZ 3i and I will be upgrading my wheel and tire package soon. I've got 205/60 16 Conti Pure Contacts on it now. My tire preference after a lot of research here and on TireRack (and other sites) for late spring/summer/early fall is BFG G-Force Sport 2 A/S. I'm in southern Ontario so temps and weather conditions can really swing far in the spring and fall.

I'm leaning towards 215/45 17 with Konig Runilite 17" x 7.5 x 45mm O/S wheels. They are relatively light at ~19 lbs and will give me plenty of options for tire sizes. What I am unsure of is the change in scrub radius this combination of wheel and tires will do to my car's handling. This size will give me ~9 mm more positive SR, so it will very likely put me into positive SR territory.

I love the no torque steer and bump steer I get form the stock setup I have now. I can accept a bit of torque steer and other issues in exchange for more cornering grip and possibly less understeer, but I don't want to be sorry I made this change later.

So, if any of you have done a similar tire change and can shed some light on the performance changes you experienced I would love to hear about your experience.

Many thanks for any info anyone can pass on.
That rim size is only 5mm difference in offset from stock, nothing to worry about. 19 lbs is a bit heavy for good aftermarket 17" rims. Thats the same as the OEM 16" rims so you won't notice any difference there.
On those 17x7.5 rims, there are many tire options that will be better than 215/45. I have 205/50 Continental ECS on mine, they are about right as far as tread width and height for my car. Tires vary quite a bit in actual specification despite the numbers on the sidewall. Some are wider, some aren't. You need to compare tread width numbers and section width numbers (adjusted for rim width) with actual rim width. That will give you an idea of how the tire will look. Overall wheel height should be fairly close to OEM height too. If your car is at stock height, smaller tires will make the large wheel gap even larger. 225/50s are a good place to start. Size and height is about right for what you want.
The stacked tires are both 205s....




Just realized I should add this info.

The 2 tire sizes I'm asking about are both about the same S/R difference from stock, about 9 mm more positive, which is why I am interested in your experiences with these sizes. I have tried to find out how much negative S/R we have in the stock setup and I just am not getting anything like a reliable number.
Tire size has nothing to do with scrub radius. Rim offset does...You're worrying too much about inconsequential numbers here.
 

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Discussion Starter #5
If you want to go to a 17" wheel you should be looking more at a 215/50-17 (0.8% smaller than stock) or a 225/50-17 (0.8% larger than stock).

A 215/45-17 is 4.3% smaller than stock. That's a big difference.

Not sure what you mean by "SR"?
I would like to try a smaller tire diameter. SR is scrub radius.

That rim size is only 5mm difference in offset from stock, nothing to worry about. 19 lbs is a bit heavy for good aftermarket 17" rims. Thats the same as the OEM 16" rims so you won't notice any difference there.
I was tired last night and didn't explain myself well at all :no:. I'm going to try to be a little clearer now :)

The 5 mm less wheel offset plus the smaller tire diameter using 215/45 17's makes the scrub radius move ~9 mm in the positive direction. I believe that will move my scrub radius from the OEM slightly negative, to a bit more than slightly positive. A very similar SR result will be had from the 215/40 18 tires on a 45 mm offset wheel.

That SR change is about equal to using a 40 mm offset wheel with a tire that has close to the same diameter as OEM.

I'm wondering about the handling changes I will experience, specially torque steer, and anything else that may happen as a result.

I hear you on the 19 lbs and I agree I could get lighter wheels, but the cost goes up too.

I chose the smaller diameter tires on purpose to get a bit more torque at the wheels. 4.3% isn't much, but at least it's going in the right direction. I don't care about the increase in fender gap.

Man, I really blew my OP. Hopefully this is a bit clearer than mud now.

On those 17x7.5 rims, there are many tire options that will be better than 215/45. I have 205/50 Continental ECS on mine, they are about right as far as tread width and height for my car. Tires vary quite a bit in actual specification despite the numbers on the sidewall. Some are wider, some aren't. You need to compare tread width numbers and section width numbers (adjusted for rim width) with actual rim width.
That is something I never thought of. Thanks :)

Tire size has nothing to do with scrub radius. Rim offset does...You're worrying too much about inconsequential numbers here.
I am very likely overthinking this stuff, but I tend to do that.

The tire diameter does change the scrub radius because of the strut angle. It's not a factor if you chose a diameter close to OEM, but I'm not so I'm factoring that into my decision. It's still only a 9mm change, but I suspect that will large enough to feel and I would feel better going into the change if I had some real world feedback on the results.
 

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Discussion Starter #6
I have 205/50 Continental ECS on mine, they are about right as far as tread width and height for my car.
@arathol, are your wheels 17"? What wheel offset are you using with those tires and how is the handling? I know they are going to be gripier than mine, more interested in torque steer and anything else you can comment on.
 

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The tire diameter does change the scrub radius because of the strut angle. It's not a factor if you chose a diameter close to OEM, but I'm not so I'm factoring that into my decision. It's still only a 9mm change, but I suspect that will large enough to feel and I would feel better going into the change if I had some real world feedback on the results.
No way a small change in tire diameter will have enough effect on scrub radius to make a noticeable difference. Changing wheel offset is the primary concern.
I have Conti ECS 205/50-17s on my car. They have an OD of 25.1. OEM 16" tires are 25.6. My rims are TrakLite Gears, 17x7.5 +45, 15 lbs. I have not experienced any issues at all with bump steer, torque steer or anything else. In fact, my SIL drove my car to compare it to his new 2018 hatch, and said the steering felt tighter and more responsive than his.
In other words, don't worry about it. Get what you like, stay within the limitations of the body work (~+38 offset) and you'll be just fine.
 

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Discussion Starter #9
No way a small change in tire diameter will have enough effect on scrub radius to make a noticeable difference. Changing wheel offset is the primary concern.
I have Conti ECS 205/50-17s on my car. They have an OD of 25.1. OEM 16" tires are 25.6. My rims are TrakLite Gears, 17x7.5 +45, 15 lbs. I have not experienced any issues at all with bump steer, torque steer or anything else. In fact, my SIL drove my car to compare it to his new 2018 hatch, and said the steering felt tighter and more responsive than his.
In other words, don't worry about it. Get what you like, stay within the limitations of the body work (~+38 offset) and you'll be just fine.
That's exactly what I was hoping to hear, thanks!
 

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215/50 17x7 45 offset. 14.2lbs each, cheap summer tires and man, what a difference.
Looks good. I may switch to aftermarket rims once my Conti's wear down.

Shave off some weight..maybe go a little wider to 225/45-50/18-17.
CK
 

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Dammit, wrote a longer reply, but lost it from timing out.
In short, the shorter rolling diameter will affect gearing slightly, I think you may feel it a bit.

I'm in the same southern Ontario region and would steer you away from that BFG model towards either Michelin AS3+ or Continental DWS06. Both of which are markedly better in dry/rain/snow with the same or better tread life. AS3+ for dry/wet, DWS06 if you need to trade off dry/wet grip for a bit more compliant ride, prowess in snow, and tread life.

Wife is on 215/55R16 AS3+'s and the change in tire compound/model will have more appreciable effects than a change in rolling diameter/offset/rim weight.
 
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