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      12-03-2018, 07:42 AM   #1
rowsdower
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Help with track wheel setup

I have a 128i with the sport package, which means a 7" wheel up front and 7.5" in the rear. I picked up a second set of the same wheels to make a track setup and a street setup, both square. I'm trying to decide which wheels I should use for the track and which for the street. I originally thought that wider wheels would be better for the track, though the second set of wheels that I bought have 235-section tires on the front and the rear. The fronts are just pinched a little to fit the narrower wheels. So I'm wondering if I should pinch the tires front and rear and keep the smaller wheels on for the track, since they should be a little lighter. The alternative is to run an even wider tire, maybe 245s, on the 7.5" wheels front and rear. They would be heavier but I'm thinking they might last longer before getting greasy. Just wondering if anyone has done this before and what the pros/cons are?

Obviously I'm making decisions based on the lighter of two heavy wheels, which is a silly, but I'm just trying to keep costs down. Someday I'll likely end up on light wheels, but not for the next track season.
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      12-03-2018, 07:50 AM   #2
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Your last sentence hit the nail on the head. Comparing a 7.5" wheel that is 25 pounds vs. a 7" wheel that is 24.5 pounds is a little meaningless......since there are many affordable 18-19 pound wheels out there.

You never really mentioned what track driving you are doing. Are we talking autocross or track days? What tires are you running? If we are talking all-season tires then it doesn't really matter.

It also depends on what you want. Purposefully putting on narrower tires can be really fun as it sets the limit a litter lower and helps for learning car control at the limit.

I run 245's on a 9" wheel (square, all around), so I think a 245 on a 7.5" is too much tire for that wheel. Too narrow of a wheel will leave the sidewalls less supported, which will lead to less feedback and feel. More tire will lead to more grip, but with less feedback. There is a point where you gain little contact area though since the tire is too pinched. The best rule of thumb is to run the same width wheels as the tread width of the tire. Tire Rack usually specifies tread width for every tire they sell, so you can go on their site and check what the tread width is for your tires.
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      12-03-2018, 09:36 AM   #3
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Quote:
Originally Posted by jcrane82 View Post
Your last sentence hit the nail on the head. Comparing a 7.5" wheel that is 25 pounds vs. a 7" wheel that is 24.5 pounds is a little meaningless......since there are many affordable 18-19 pound wheels out there.

You never really mentioned what track driving you are doing. Are we talking autocross or track days? What tires are you running? If we are talking all-season tires then it doesn't really matter.

It also depends on what you want. Purposefully putting on narrower tires can be really fun as it sets the limit a litter lower and helps for learning car control at the limit.

I run 245's on a 9" wheel (square, all around), so I think a 245 on a 7.5" is too much tire for that wheel. Too narrow of a wheel will leave the sidewalls less supported, which will lead to less feedback and feel. More tire will lead to more grip, but with less feedback. There is a point where you gain little contact area though since the tire is too pinched. The best rule of thumb is to run the same width wheels as the tread width of the tire. Tire Rack usually specifies tread width for every tire they sell, so you can go on their site and check what the tread width is for your tires.
Thanks, that's really helpful. I'm doing HPDEs and my goal is to learn the car, not necessarily be the fastest person out there. So perhaps a narrower track tire on the narrower wheels is the right move, not for weight savings but for better feel. The tires I have on now are Azenis RT615k+ 235/40R17, and they are awesome. Looks like narrower 215-section tires would save me about $25 per wheel, so that's a plus. Interesting that going to a 205-section tire, the prices actually go up.
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      12-03-2018, 10:13 AM   #4
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Quote:
Originally Posted by rowsdower View Post
So perhaps a narrower track tire on the narrower wheels is the right move, not for weight savings but for better feel.
I think you may have misunderstood. You will want the narrower tire, but on the wider wheel. The tire/wheel combo will determine the contact patch as well as how the sidewalls of the tire are supported. The wheel/tire is a system, and should be thought of as such.

Share a link to the 215 Azenis you are considering, I can then share my opinion as to what wheel width they should be installed on.

Here is a tech article from Tire Rack talking about wheel width. https://blog.tirerack.com/blog/roll-...-new-wheels-be

And here is another article that explains the tire tread width measurement in relation to wheel width. Usually the tire tread width increase 0.2" for every 0.5" of additional wheel width. https://www.tirerack.com/tires/tiret...jsp?techid=198
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      12-03-2018, 03:56 PM   #5
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Thanks for clarifying. I definitely understand the argument about the narrower tires possibly helping with learning car control, as you can reach the limit a little more quickly. So with that in mind, I think I'm going to try for the 7" wheels. According to the Falken website, 205 through 225 can be mounted on a 7" wheel. The only reason I would like to go with 215s instead of 205s is the cost - $126 per tire vs $148. Sounds like you would likely recommend the narrower tire to truly optimize the tire/wheel combo - correct?

http://www.falkentire.com/tires/pass...is-rt615k-tire
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      12-03-2018, 08:14 PM   #6
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The Azenis aren't available in a 205/50R17 tire, only a 205/40R17. That 205/40R17 will be too small in diameter. You need to maintain the stock outer diameter. A 215/45R17 is also a little small in diameter, but it will still work. The 215/45R17 also has a tread width of 8 inches, so for track use it really wants a 8" wheel. If you get those tires definately use them on the 7.5" wheels.

I have those Azenis on my E36 M3, in 255/40 on 17x9 square. They are a nice tire.
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      12-03-2018, 09:28 PM   #7
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Quote:
Originally Posted by jcrane82 View Post
The Azenis aren't available in a 205/50R17 tire, only a 205/40R17. That 205/40R17 will be too small in diameter. You need to maintain the stock outer diameter. A 215/45R17 is also a little small in diameter, but it will still work. The 215/45R17 also has a tread width of 8 inches, so for track use it really wants a 8" wheel. If you get those tires definately use them on the 7.5" wheels.

I have those Azenis on my E36 M3, in 255/40 on 17x9 square. They are a nice tire.
Why is a smaller diameter bad? The gearing would be slightly shorter, the odometer would creep up a bit faster, the speedo would read higher than actual speed, and the car would be lower than it is currently by 1/2 of the decrease in diameter. None of these seem like dealbreakers considering these would only be driven on the street to get to the track and back. But is there another reason why this should be avoided?
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      12-04-2018, 08:22 AM   #8
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Quote:
Originally Posted by rowsdower View Post
Why is a smaller diameter bad? The gearing would be slightly shorter, the odometer would creep up a bit faster, the speedo would read higher than actual speed, and the car would be lower than it is currently by 1/2 of the decrease in diameter. None of these seem like dealbreakers considering these would only be driven on the street to get to the track and back. But is there another reason why this should be avoided?
You are correct on all of the above. Many people run a slightly smaller diameter for a gearing advantage for autocross. I personally don't like doing this though, especially if your street tires will be stock diameter. I do track days so that I can learn car control on my daily driver so that I can safely and confidently do tail out antics on back road intersections and such. I think the car will behave quite differently though with a tire that is 1.5" smaller in diameter. And if you learn car control with a 23.5" tire, does that directly translate into having car control with a 25" tire......I guess I am not positive?

Either way your car will not explode with a 23.5" tire on it for track days, but that seems like a little too much gearing advantage in my opinion. Maybe others with experience running that small of a tire on track can chime in.

.......................

Edit: The 23.5" tire I am referencing is the 205/40R17. Rereading your post it looks like you are wanting to run the 215/45R17. That tire makes much more sense and is what I would suggest for your 7.5" wheels. You also said it is cheaper, so win win.

Last edited by jcrane82; 12-04-2018 at 08:24 AM.. Reason: Edit........the 23.5" tire I am referencing is the 205/40
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      12-04-2018, 03:44 PM   #9
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Quote:
Originally Posted by jcrane82 View Post
You are correct on all of the above. Many people run a slightly smaller diameter for a gearing advantage for autocross. I personally don't like doing this though, especially if your street tires will be stock diameter. I do track days so that I can learn car control on my daily driver so that I can safely and confidently do tail out antics on back road intersections and such. I think the car will behave quite differently though with a tire that is 1.5" smaller in diameter. And if you learn car control with a 23.5" tire, does that directly translate into having car control with a 25" tire......I guess I am not positive?

Either way your car will not explode with a 23.5" tire on it for track days, but that seems like a little too much gearing advantage in my opinion. Maybe others with experience running that small of a tire on track can chime in.

.......................

Edit: The 23.5" tire I am referencing is the 205/40R17. Rereading your post it looks like you are wanting to run the 215/45R17. That tire makes much more sense and is what I would suggest for your 7.5" wheels. You also said it is cheaper, so win win.
Got it - thanks! Yeah I would probably go with the 215/45 since they're the cheapest and would have the least affect on rolling diameter, though also the heaviest and widest. The other option was the 215/40 which are quite a bit narrower and would fit the narrower wheel, but still be slightly taller than the 205/40. The 215/40s are also quite a bit lighter than the 215/45s so that would be my "lightweight" option. I have a little bit of time to make this decision, but appreciate all the feedback from you!
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      12-05-2018, 09:17 AM   #10
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Î like to buy wheels once, so i never have to get another set when i go wider.

For track days, im planning on 17x8.5 ET40 size all round, either Apex or OZ Alleggerita, still unsure, but that setup allows up to 255 all round (my goal is to use 235s all round then move up to 245s all round).

You can pick up some used 17x8 BMW OE wheels for a good price, and run 225s all round for now, and move up to 235s. The styling 32, 42, 47, 50, 89 and several others come in ET47 and weigh 10.3 kgs (20.6 lbs?) not bad for a factory wheel if you ask me.

Problem with used wheels, is checking for straightness and damage, does that sound like a viable option to you? a decent set of used wheels can run €300-€400 here (8x17 ET47 size).
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      12-05-2018, 10:42 AM   #11
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I got mine from a forum member who also tracks his car. The new set vibrates a little but I can’t tell if it’s an out of balance tire. After this next weekend, those tires should be shot so I’ll take a closer look at the wheels and have the next set balanced.

I would be skeptical of an aftermarket used set and would probably go with new Apex wheels.
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      12-05-2018, 11:14 AM   #12
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"The forum member" here

These wheels were only used on the track, so damage is unlikely, but the guys who mounted and balanced the tires, while decent mechanics, don't have A++ equipment, so I think they did have a little vibration to them when I got that set mounted. A shop with a newer balancing setup will probably get things right for you.

Also not to be pedantic, but I think there were 225s mounted on there, not 35s, no?
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      12-05-2018, 11:46 AM   #13
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Quote:
Originally Posted by Zombie_Head View Post
..... and weigh 10.3 kgs (20.6 lbs?) not bad for a factory wheel if you ask me.
1 kg = 2.2 lbs

10.3 kg would be 22.66 lbs.
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      12-05-2018, 12:27 PM   #14
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Quote:
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"The forum member" here

These wheels were only used on the track, so damage is unlikely, but the guys who mounted and balanced the tires, while decent mechanics, don't have A++ equipment, so I think they did have a little vibration to them when I got that set mounted. A shop with a newer balancing setup will probably get things right for you.

Also not to be pedantic, but I think there were 225s mounted on there, not 35s, no?
You're right - just checked and they are 225/45, not 235/40. Thanks for clarifying that. They are also RT615K tires, not RT615K+.

No worries about the balancing - the tires will be shot after this next weekend so I'll have the new set balanced.
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