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Wheel & Tire Question - 16" weight savings, or 17" lower profile

6K views 21 replies 8 participants last post by  STS-focus 
#1 ·
I drive my MK3 in the STF class (does pretty well by the way). I love it - gives me a great chance to really work on the driver-mod of my AutoX rather than dumping a bunch of money upfront.

I am looking to get some new wheels and tires however, the STF class limitations are: Wheel width <= 7.5in; Tire width <=225mm


Current setup:
Wheel:OEM Wheel 16x7" (19lbs)
Tire: 215/55-16 (118.25mm [4.65in] sidewall height)

Here's where I see my two options to upgrade my wheel setup.
OPTION 1.
Wheel: A 16x7.5" wheel with ~2-3lbs weight savings over current
Tire: 225/50-16 tire (112.5mm [4.49in] sidewall height)

OPTION 2
Wheel:A 17x7.5" wheel with negligible weight savings.
Tire: 225/45-17 tire (101.25mm [3.98in] sidewall height)

I'm wondering what you guys think will give more handling capability on the AutoX course. the 2-3lbs weight savings with minimal [.15in] decrease in sidewall hieght, or the more substantial [.65in] in sidewall height?

Thanks for your input guys!
 
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#3 ·
Are you looking for a autocross specific setup?

16x7.5 benefits are less unsprung weight acting on your suspension components, less weight to turn on acceleration and less weight to stop during braking. Wheels are cheaper.. tires are cheaper.. Only disadvantage are transitions like slaloms and quick movements. This can be overcome buy turning in split second sooner to overcome the extra flex of the sidewall. You would probably figure that out real quick.

17x7.5's.... the only advantage would be better turn in due to the smaller side wall.

I myself am excited to put 16x7's on my SVT next year in the new street classes. (If it goes through). With 225/45/16 Z2's
 
#4 ·
I don't know how I didn't think of going 225/45-16... The speedo difference will be 5.3% slower though (reads 60MPH when actual is 56.8MPH)

What's the usual guideline for changing diamater? What's the point where the gearing is significantly affected? 225/45-16 would be the best of both worlds - but I still want to DD on the wheels. Not looking to get just AutoX specific wheels.
 
#6 ·
The lack of tire support is a little off putting.

Top speed in 2nd at OEM setup is right about 60MPH.
 
#7 ·
I find that running a 225/45R16 is a good choice for an SVT, due to it's tall gearing, and is what I'm running right now for STF. But not that big of deal for other models. You can get a 17x7.5 wheel in about the 16-17 lbs range if you willing to look around or spend the cash. I'm thinking 5Zigen might be able to build you a nice light weight wheel for a good price. Then you could run any tire of your choice in a 225/45R17. It'll be a little taller, but once again, not that big of deal with a non-SVT car. If you did want to go with a 225/45R16, then your choices for a good light weight 16x7.5 is kinda slim. If you can find a set of old Kosei K1s, then your lucky, but they are hard to find, which is why I ended up with two sets :p.
 
#9 ·
Finding wheels for the SVT is a different story then MK3. 5x108 lug pattern is a real killer.

Is there a different website to look for wheels than Tire Rack that people use? Because in the 5x108 pattern at 17" there are very few wheels lighter than 19lbs.

Sent from my HTC One X using Tapatalk 2
 
#12 ·
I wouldn't worry about sidewall height when choosing autox tires. Overall diameter is more important.

Right now your tires are 25.3" Tall

the 225/50/16 is shorter 24.9"
the 225/45/17 is taller at 25"

If you want a tiny bit more gearing, get the 16's, if you want a tiny bit more speed at the top of 2nd gear, get the 17's.
 
#13 ·
So you're saying the difference in sidewall roll won't be substantial enough to notice?

If that's the case then the 16" would be a clear choice because with lighter weight and overall lower diameter (assuming the distance of the neutral axis isn't in a substantially different spot than the current setup) the overall reduction in weight and diameter would cause a rather large reduction in moment of inertia - making this the best setup.

Especially because I'm not really worried about a small change like that in the gearing, I've never even come close to the top of 2nd in an AutoX

Sent from my HTC One X using Tapatalk 2
 
#14 ·
Is there any way for this to be a dedicated set up?

I know you said you didn't really want that, but if you can swing it you can go with a 16 with a shorter tire and reap the benefits of gearing, weight, and stiffer sidewall.

I'll note it's hilarious to hear people complain about 5x108. I wish either of my cars had 5x108.
 
#15 · (Edited)
As I look at it more and more for why I would want to get it - the dedicated setup makes more and more sense. It's either miles coming off of my DD wheels, or miles off of these. And these will wear more during every day use. So the most cost effective and the highest gain is in the dedicated setup. But since 225/45/16 tires are few and far between it worries me that the manufacturers would drop the very few lines they have, or that I won't like the D2's...

Also brings out the interesting possibility. Why not 15" wheels if I'm going dedicated? Even less rotatating mass, gain more range in 2nd gear.
 
#18 ·
If I was planning on making another run at the championships in my Focus, which I am not, I would be looking for some 15" wheels that clear the SVT front calipers and running BFG Rivals in a 225/45r15 for STF. Otherwise, I love the gearing and grip of my Dunlop Z2's in the 225/45r16, that is until the temps go above 95*, then the Z2's are junk on concrete. If the BFG Rivals or the Bridgestone RE11a's were available in a 215/45r16 or a 225/45r16, that would be my first and second choices for 2014 if I were to continue competing in the Focus.
 
#19 ·
If I was planning on making another run at the championships in my Focus, which I am not,
Hate to hear that.

I would be looking for some 15" wheels that clear the SVT front calipers
Rota Slipstreams do fit the SVT rotors with a small spacer and as long as the tire guy mounts the weights away from the spokes.

and running BFG Rivals in a 225/45r15 for STF.
I wrestled with the 205 vs 225 Rival decision myself. I went with the 205 and am happy. The tires is VERY square on the 7.5" wheel and very responsive. My past experience with putting too much street tire on a wheel led me to mushy turn-in.

Otherwise, I love the gearing and grip of my Dunlop Z2's in the 225/45r16, that is until the temps go above 95*, then the Z2's are junk on concrete. If the BFG Rivals or the Bridgestone RE11a's were available in a 215/45r16 or a 225/45r16, that would be my first and second choices for 2014 if I were to continue competing in the Focus.
I have seen it written else where but there are no wrong choices, some tires are better in certain situation but nothing comes out on top 100% of the time.
 
#22 ·
Thanks ECUgrad! If anyone has questions about my setup or anything else autox Focus related, I would be more than willing to share, inbox me. Just as a footnote, I am looking at a C5 Corvette FRC for B-Street competition in 2014 amongst other ride offers.
 
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