tire sizing and load index (H Street)

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Eric Wong
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tire sizing and load index (H Street)

Postby Eric Wong » Wed Jan 31, 2018 8:42 pm

It's looking like I'll need new tires in March and maybe I should pre-order a set in case I destroy them sooner. I'll also be doing some autocrosses outside of Cal Club in February.

I'm still new at this and tend to over drive, so I don't think I'll be ready for expensive TW200 tires, yet.

The popular 215/45-R17 size doesn't seem recommended for the 6.5" wheels. I'm on 215/50-R17 now and it seems to roll onto the sidewalls unless I go to 45psi.

205/45-R17 tires are approved for 6.5" wheels and the Federal 595 (or 595 SS, not the RS-RR) looks like it could be a good choice (TW240). One problem is the highest load index available for that size seems to be only 88 (1235 lbs), whereas my current and past tires are all rated at 91 (1356 lbs).

My car is over 3700lb with me in it, weight distribution is 56.3/43.7 F/R, so I'm wondering if cornering forces would overwhelm a tire rated at only 1235 lbs.

Is 205/45-R17 worth a shot with a heavy car? Or should I stick to 215/50-R17, or maybe pinch a 215/45-R17 tire on?


Another option is to go down 1" in diameter as allowed by H Street rules to 16x6.5" Chevy Cruze wheels (39mm offset, cast aluminum). I can get those from junk yards at only $60 each and there's a lot more tires available at 205/55-R16 and 225/50-R16 with higher load indices. I don't know if a higher profile sidewall is a good idea, though.

Single-speed transmission tops out at 92mph, I won't have to worry about gearing for autocross. Not much suspension travel, either; so unlikely to scrape the metal battery shield.

Thanks in advance for any answers!

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Jayson Woodruff
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Re: tire sizing and load index (H Street)

Postby Jayson Woodruff » Fri Feb 02, 2018 2:48 pm

Get the better tires. Tires meant for what we do will actually last longer because they don't blister and chunk. This means the tires others are using, not something that 'claims' to be a racing street tire.

You can fudge a lot in weight ratings. That's more about cruising on the freeway and fatiguing an aged tire. We'll wear the tread out long before the sidewalls and belting starts to rot. Additionally the weight distribution doesn't really mean a whole lot to your rating calculations when you're pulling G-force.

I wouldn't worry about half an inch in the recommendations width. Stock guys commit much great sins.

Careful, most modern cars won't accept smaller rims due to clearances (especially brakes). Shortening up the gearing can do weird things, especially in the ABS department. I'd leave this option for a more experienced future Eric.

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Ed T
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Re: tire sizing and load index (H Street)

Postby Ed T » Fri Feb 02, 2018 11:39 pm

225 on 6" front wheels here :wave:
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Craig Naylor
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Re: tire sizing and load index (H Street)

Postby Craig Naylor » Mon Feb 05, 2018 9:55 pm

225/50/14's on 5" rims were all the rage on Civics/CRX's when Civics/CRX's were in ES.

I think 215's on 6.5" rims are completely doable. :thumbup:

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Re: tire sizing and load index (H Street)

Postby Eric Wong » Tue Feb 06, 2018 1:02 am

Thanks all for the responses. Most of my wear is coming from the shoulders so don't know if there's a way to solve that by putting better tires in a camber-challenged car. I've flipped one pair and will probably flip the other pair after this weekend. Will also try to drive more conservatively to extend my current tire life.

I know manufacturers approve 215 and 225 on 6.5" rims with a 50 aspect ratio, but they don't for 45 aspect ratio. I don't think there's any good 215/50-R17 or 225/50-R17 autocross tires, only 215/45-R17 and 225/45-R17.

The other thing is my car is way heavier than a MR2, Civic, or CRX; so I wonder what will happen when pinching for a heavy car like mine. I suppose I'll keep an eye out for used tires, first.

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Max Hayter
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Re: tire sizing and load index (H Street)

Postby Max Hayter » Tue Feb 06, 2018 8:34 am

I have a set of half used 225/45/17 Nexens I'll sell you for $75. Plenty of tread left. They paxed top 10 at the last event. I can bring this weekend or are available for pickup in Mission Viejo.

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Re: tire sizing and load index (H Street)

Postby Eric Wong » Tue Feb 06, 2018 9:56 am

Hey Max, $75 for the whole set? Wow, definitely worth the experiment and I'll be at Fontana both days this weekend.

I've had 225/50s on the car before but there was some rub under hard braking while turning at the same time; the smaller diameter of the 45s should clear it and I've learned to be a smoother driver in the meantime.

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Max Hayter
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Re: tire sizing and load index (H Street)

Postby Max Hayter » Tue Feb 06, 2018 10:04 am

Yup, $75 for the whole set. I'll bring them on Saturday and if nothing else, they will be a cheap experiment for you.

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Re: tire sizing and load index (H Street)

Postby Max Hayter » Wed Feb 07, 2018 10:35 am

Eric - this is what the tires look like. Please confirm you want them for $75 and I'll bring them on Saturday.

ImageNexen 225/45/17 by blkwrxwag, on Flickr

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Re: tire sizing and load index (H Street)

Postby Eric Wong » Wed Feb 07, 2018 10:50 am

Yup, looks like there's a good side I can use on them.
I'll be there both days if it's easier for you to split the transport, I will be with my Bolt and have plenty of carrying capacity :)
http://images.newcars.com/images/car-pi ... olt-ev.png

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Max Hayter
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Re: tire sizing and load index (H Street)

Postby Max Hayter » Wed Feb 07, 2018 10:56 am

Great - see you Saturday. I'll be the good looking fellow in the red SSC FRS.

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Re: tire sizing and load index (H Street)

Postby Eric Wong » Mon Mar 05, 2018 10:02 am

Thanks again Max! I had a nice improvement in consistency and the tires looked great after my competition runs on Sunday.

Unfortunately I sprayed too late into fun runs and my right front only has the center thread left. The left front isn't far behind, either. I'll be rotating for the next event and focus on lowering corner entry speeds to preserve tire life. Good thing I have a separate set of wheels and tires for daily driving.

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Max Hayter
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Re: tire sizing and load index (H Street)

Postby Max Hayter » Mon Mar 05, 2018 11:17 am

What front tire pressures were you running? Any difference between morning and afternoon?

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Re: tire sizing and load index (H Street)

Postby Eric Wong » Mon Mar 05, 2018 11:27 am

I kept them around 46psi throughout, lowering them after my 2nd or 3rd run.
The little triangles on the sidewall are all still visible, which is a first for me.
Maybe the pressure was too high and a little rollover is preferable to losing grip and sliding early?
But I think it's mainly a driver problem :)

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Max Hayter
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Re: tire sizing and load index (H Street)

Postby Max Hayter » Mon Mar 05, 2018 11:38 am

It depends. Anything over 40psi should be good. However, if you are pushing harder during your fun runs and understeering more, that will accelerate the wear.

The Nexens are pretty quiet, so it's not as easy to tell as some other tires when you are sliding too much. There's an expression... stick, slip, slide.

For optimal speed, you want to be "slipping".

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Re: tire sizing and load index (H Street)

Postby Eric Wong » Mon Mar 05, 2018 1:13 pm

Yes, I noticed the lack of constant tire squeal during my runs which I might have interpreted as a sign to drive harder. I suppose distinguishing "slip" from "slide" will be the next step for me.


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