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Thread: Tire size question on stock wheels

  1. #11
    Gluon
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    Quote Originally Posted by Richard Buckingham View Post
    I've been running my SRA for >4 years and I've settled on 205/50-15 at the front and 275/35-15 at the rear running Hoosier R7s. For wheel size at the track you want to max out wheel for whatever tire you run so the tire sits right on the wheel and you get the max contact patch and even wear, so for the 275/35-15 I run a 15x11 wheel, for the 205/50-15 I hear you can go as large as a 15x9 (so the Miata guys tell me!) though I have not tried that large yet.

    For larger wheels for your SRA you probably can't do any better than to get the 949 Racing 6UL wheels, we share the same 4x100 bolt pattern as the Miata. For the Atom 3... I have no idea.

    TMI are correct that getting heat in bigger tires is harder... but not that hard at the rear on the Atom. Of course it depends how hard you drive the car but heavy braking and acceleration will put plenty of heat in the rears. For the fronts you just have to work them real hard on the brakes too, but on a cold track it just is not going to happen. Some people run A7s to compensate for that. Downforce at the front helps of course if you want to invest in some aero but its not really necessary in order to have a good time and a high performing car. Running lower pressures than you might think is right too. You want to monitor heat as soon as you get off track (probes are not cheap but best, cheaper IR gun can work) and monitor wear. Tune pressures, brake bias, dampers, toe & camber as you see fit for optimal lap times but you should just be able to have a single configuration for everything that at least works ok everywhere and is comfortable and balanced. The factory TMI set-up for the SRA is not bad, although I hear they ship spring rates as 400 front and 300 rear which is weird to me, I run very little toe but add a bit more camber to the back but you can get to those tweaks over time, also depends of course on what tire and dampers you run how you want to adjust those.
    Thank you for giving us an excellent starting point for tire sizes. Few questions
    - What wheel width are you running on front? It would seem that 8in would be perfect for 205 width - same as 11in for 275.
    - Do you feel that 205/275 widths are "optimal" - in other words you have tried larger/smaller sizes for front/rear and settled onto 205/275 or used some other approach to figure out if you are at optimal sizes? Or you are happy with your setup and don't feel need to experiment more even though there may be further performance gains?
    - Did you leave SRA suspension as is or changed it? Any other modifications from standard SRA that may have impacted your tire/suspension setup?

    I am in similar situation as other poster - have SRA that I only use for tracking and for my next set of tires I am considering going with size/type that will provide higher performance potential (though I am very aware of being the "weak link" on the track - not the car).

    Thank you
    Aleks

  2. #12
    Electron
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    I still have 7" fronts, I think an 8" or even a 9" if possible with a 205/50 would be the best combo (again the Miata guys say this is possible.) I don't know that I will pull the trigger on replacing my front wheels but if I were to buy wheels today I would go larger but keep the same 205 tire.

    Optimal... I think that depends on driving style and how much you push the car. A larger rear is definitely better; the car has a 35:65 weight ratio front to back so all things being equal the energy exerted on the tire contact patch should match that ratio per square inch for a balanced car, at least that's what an engineer would tell you. 205/275 sounds incredibly asymmetrical to most people but the Atom weight is incredibly asymmetrical and of course the rear is also trying to exert acceleration forces too. Take the Deltawing as an example of extreme asymmetry, it runs 4" up front and 12.5" at the rear on a 27:73 weight distribution.

    You want to get heat into the fronts so a smaller tire is better IMO (energy transfers through a smaller contact patch and dissipates over less rubber so it creates more heat in the tire) and the 205 with heat in it will turn the car just fine. So then the question is how much rear can you add to that. I haven't tried anything larger but MadMaxAtom runs a 15x10 and 15x14 wheel combo on his Atom for instance but you also are restricted by tire choice too (he uses FA slicks which mean you have to have such large wheels) I just think the 275/35-15 for me is a good stopping point based on price and availability as much as anything else.

    I run 300/400 springs (Front/Back). My 2012 SRA came with 400/500 but it was too stiff for the bumpy tracks here in SoCal. Factory ships SRA with 400/300 apparently which I find weird but maybe it works?

    Now that I have more power and downforce the experimentation starts all over again.

    And yes, much like buying new golf clubs the best gains are most definitely made by practicing not by buying more expensive stuff.

  3. #13
    Positron cvjoint's Avatar
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    With tires I think you have to know exactly what you want out of the car, there are many compromises. Do you want top speed, fuel efficiency, a balanced car, lowest lap times, an easy car to drive?

    Personally I want lowest lap times but I'm willing to compromise some quickness to get an easy to drive car. I just got the Atom so that is a good way to start for me. Eventually though I think most track cars run quickest on the widest tires front and rear and the stickiest compound. At least if you judge by quickest lap (time attack).

    If I were to throw a guess out there as to the fastest combination I'd say FA tires, or rear FA tires all around.

    If you need to stay road legal it's much harder. The Cup 2 Michelin tires require too much heat to work well. I'd say the Trofeo Rs and the Kumho ACR street tires are the softest compound street legal tire. Get the widest rears you can find. Front on this car may not work well if too wide, but in most cars wider front is better because it's so easy to cut time in the breaking zones.

  4. #14
    Up Quark
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    I took the plunge and ordered the 949 Racing 15x9's and 15x11's. The guys at 949 assure me they've has great results with the Hoosier 205/50's on the 15x9, and the 15x8 is on backorder nationwide, so I figured I'd take one for the team and try it out. Richard, did you need any spacers for your set up, or were you good to go out of the box?

  5. #15
    Electron
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    No spacers, I bought the hub centric rings though but they are not required. The 205/50 sits on the 9" tire really well (I bought 4 of them in the end), the 275/35 sits on the 11" really well, I think it's the perfect simple setup (larger FA slicks on a 15x12 most likely are better but complicated to source.)

  6. #16
    Fermion
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    Was researching tires for stock wheels and reading as many threads as I could and this one seemed the best one to resurrect. I've only tracked a car once and wanted to build my skills some with my AA2. I presently have Toyo R888 tires and know very little about the pro's/con's of street tires. First thought was buy a set of autocross tires that were meant to hold up better so was looking at Hoosier R7's.

    Talked to another member on the board and he recommend for a driver at my skill level another tire that talks to you more to help with the learning curve on the car. Also recommended I attend some local autocross events to learn more about handling which I'm down to do. Essentially whatever is going to teach me the most and the community would be good too.

    So if I could get some recommendations from others?

    I'd like to
    1. Keep the fenders on so it's easy to attend the events and also drive the car on the street.
    2. Have something that is beginner friendly.
    3. Try to maintain a ratio of a tire with more grip on the rear. I tried sizing a hoosier R7 and was concerend that the front tire has the same treat width as the smaller 205/45r16 rear, and that the 225/50r16 wouldn't fit under the fender.



    I'm open to other brands but haven't found one yet that'll work. I'm going to have another set of team dynamic wheels from 2/3's cobra cheap so having 2 sets is easy. Should I just use the Toyo's?

    Just for added info I was trying to find something that compared to the stock sizes and added them to this chart for anyone else interested.
    15-16 inch Hoosier R7_2.jpg
    Last edited by Bravo25; September 27, 2018 at 11:41 AM.

  7. #17
    Positron cvjoint's Avatar
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    Hoosier A7 would be the one to get. As far as fitment goes, it may or may not work, they do run wide. Rear fenders worked on the front stays from Skunkwurx so that's one way to getting past the limitation.

    However, the carcass is too thin to be safe for driving on the road imo. So then you give up some stick and go with a street legal autocross tire. The Rival S 1.5 should do, it's a street legal autocross tire, a cheater one too:
    https://www.tirerack.com/tires/tires...ce+Rival+S+1.5

  8. #18
    Electron
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    Some general thoughts on tires:
    • 50 treadwear tires like Hoosier A7, R7, BFG RS1, Hankook C51, etc. are really great on an Atom. They are technically street legal but a poor choice for any sort of street driving. They don't wear out, they heat cycle out and every street drive can be considered a cycle. Also they aren't up to the rigors of street road hazards. So if you are thinking of these then you'd want to trailer them to track/ax and swap them (or trailer the whole car).
    • 100 treadwear tires, something like a Nitto NT-01 could be worth a look if they can be had in size you need. Comparable to R888. These are much more streetable and can take a lot more cycles.
    • 200 treadwear tires like the Rival are used in street tire classes in AX and are a common site on tin tops at track days. I have only used 50 treadwear on my SRA, so I'm no authority on this, but I suspect the 200 treadwear would not be a good choice for the Atom. I don't think you'd get enough heat in them and they'd be pretty slippy.


    Given what you've said, seems like the 100 tread wear class would be your best bet for now (good to learn on, can drive to event on).

  9. #19
    Gluon
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    Don't forget the Hankook TD (Z221), it has a treadwear rating of 80. They are great! I wear out the rears before they heat-cycle out--99% street driving. They come in soft, medium and hard compounds--I have always run the soft on the front and mediums on the rear. They are getting hard to find however.

  10. #20
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    Quote Originally Posted by argonaut View Post
    Some general thoughts on tires:
    • 50 treadwear tires like Hoosier A7, R7, BFG RS1, Hankook C51, etc. are really great on an Atom. They are technically street legal but a poor choice for any sort of street driving. They don't wear out, they heat cycle out and every street drive can be considered a cycle. Also they aren't up to the rigors of street road hazards. So if you are thinking of these then you'd want to trailer them to track/ax and swap them (or trailer the whole car).


    I haven't attended either track or autocross but in my mind I would always trailer the car to the track so I have my tools there with me and if a failure happened I wouldn't be stranded. The tracks I want to try are somewhat far away too so there's that. If I got a tire like the Hoosier I wouldn't really consider that a street tire either and I didn't even think about the street driving being considered a heat cycle which is a big consideration! I think for those tires I would definitely want them on a second set of wheels.



    As far as treadwear ratings and heat cycle capacity these are all new things to me. I'm doing reading on it so I'm glad I read on the forum a bit because I knew nothing about it. Thank you guys for the information. I'm going to attend an Autocross with my existing R888's and talk to some more people there to try and learn more about it before making a decision. Again, until chatting with people I didn't have a clue the R888 was a good tire to run.

    I checked some of the tires and it seems my biggest problem is they don't run in the sizes I think I need for the 16" rear wheels on the Atom keeping the fenders on.

    Hankook TD's looked interesting, but not made for 16" wheel.

    Hoosiers would work in a 205/45R16, but have the same width in front and rear at that size, which I think is a negative?

    The nitto's only come in 245/50ZR16 97V in 16". Too big.

    Rival S 1.5 comes in 215/45R16 86V. I think these would work. Still presents a negative the front are the same width as the rear. They do have a treadwear rating of 200 which was mentioned too which I don't think is good.

    Toyo R888's come in the stock sizes of 205/50R15 and 225/45R16 and they work well with the fenders. Slightly wider in the rear than the front and have a treadwear rating of 100 which is more in line with what people are saying the Atom needs. I guess the previous owner did his research because it seems to be an all around good tire for what is needed. I had no idea. Again, thank you for the suggestions. If anyone has any comments or critiques of my observations let me know, trying to learn!

    I feel comfortable with the Toyo R888's on street at this point and they seem they will work for me with track/autocross from what everyone is saying. Another good point Cobra2/3's had was to get comfortable with what I'm going to be driving most and learn the limits of them and what adjustments made will do with them, then go up from there.

    It's a shame I don't have more options at this point as I don't see alot of availability on the Toyo's and what I do see is much more expensive then some options above.

    I opted not to buy the stock 15/16" wheels considering all of what I have learned. I think what I will actually need in the future if I choose to continue to progress in this is to get another set of wheels that aren't 16" in the rear. That will allow me more options in tire selection.

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