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Old 05-03-2001, 08:21 PM   #1
beachbum
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Question Want to lower my final drive: Anybody use 205/45-16?

I posted this in the wheels/tires forum yesterday but got no response. In retrospect, it may have been better going here. Besides, I want some feedback.

When I had my AWD swapped over, we used a 3.90 tranny instead of a 4.11 (long story). As you can imagine, with 1.8L of raw horsepower pushing me down the road, I can't afford to have the final drive any taller. I spend 500+ miles a week on the Interstate at about 85 MPH, and now that it's getting hot enough where I'm starting to have to run the AC, even Nebraska's mild hills are making things interesting.
[edit] At an indicated 85 MPH, my engine's only turning at about 3375 RPM. LOTS of lugging going on here. I'm running stock 98 RS wheels and 205/55-16 Pirelli P7000SS right now which will need to be replaced soon.

Soooo... I want to run lower profile tires. Miata.net's tire size calculator shows that my final drive would be ~6.5% lower with the 205/45-16s which would be just about right. Anybody else run this tire size on the street? If so, have you had any problems with the low profile of the 45 series tires? Thanks for your input.

Josh Beach | <a href="http://www.lifeisbeachy.com" target="_blank">World's Slowest Impreza Project</a>

[This message has been edited by beachbum (edited May 03, 2001).]
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Old 05-03-2001, 08:30 PM   #2
IowaRS
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This subject probably should be in the tires forum.

You probably just caught everyone on an off day. Either that or a search might yield LOTS of talk about tires.

I run 215/40-16 Kumho 712's with no problems!!! Other than inaccurate speedo and odo, but I don't care. I want the handling they provide!
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Old 05-03-2001, 09:50 PM   #3
beachbum
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Well, I think this really is a drivetrain question as I'm not too concerned with the tires themselves, moreso with how it will affect the drivetrain. Anywho... That's not a typo, is it? 215/40-16? I guess if the 205/45-16s end up being not enough, I could always go that size. Have you had any problems with wheel damage?

Unless anyone has a good reason why I shouldn't, I think I'm going to do it. On another note, does anyone know the numbers to figure how this setup will relate to stock? Remember, my stock setup was a FWD 5 speed with 13" wheels.

Josh Beach | <a href="http://www.lifeisbeachy.com" target="_blank">World's Slowest Impreza Project</a>

[This message has been edited by beachbum (edited May 03, 2001).]
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Old 05-04-2001, 09:19 AM   #4
IowaRS
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I am constantly scanning the road ahead, and so tend to avoid anything that might damage the rim.
The streets here are decent, nothing spectacular, just decent.

Yes, 16"

Tires, are tires, obviously different sizes will effect your overall drive ratio though.

You don't have the stock tranny anymore do you? what speedo are you using?
I could give you the difference between the stock 13" and the 205/45-16's, but that's not the only difference from stock. correct?
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Old 05-04-2001, 10:41 AM   #5
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I have a bit of a Frankenstein car, you might say. I don't know what the ratios or final drive were on the original transaxle, but I do know the new final drive is a 3.90. The speedo and odo are the same ones I've always had in there. I'm almost thinking this change would take the overall ratio close to where it started at. You can look at my site for more details.

Josh Beach | <a href="http://www.lifeisbeachy.com" target="_blank">World's Slowest Impreza Project</a>
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Old 05-04-2001, 10:48 AM   #6
Midwayman
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Other than your speedo and odo being nowhere near accurate (heck, with the frankenstien parts it might get more accurate?) and the general danger of snakebites on low profile tires I cant see any reason not to do it.
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Old 05-04-2001, 11:12 AM   #7
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I'd try the 215/40-16, personally.
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Old 05-04-2001, 11:28 AM   #8
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Quote:
I'd try the 215/40-16, personally.
Why's that? I can only think of two reasons, one, it's even shorter, and two, it'd be wider to protect the wheels better. Am I right?

Josh
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Old 05-04-2001, 11:35 AM   #9
ColinL
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Because it's even shorter. I was guestimating your 5th gear RPM at reasonable speeds and it seemed like a better choice.
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Old 05-05-2001, 09:33 AM   #10
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Even shorter? Hmmm. I'm running on 205/45/16 and the car feels kickass. Like it pulls on all gears and any rpm. Take into account the lowering the car gets when you shave off almost two inches in diameter too!

Hmm 215/40/16, that sounds nice! Maybe for my next set of tires! It's a bit wider which is always good.
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Old 05-05-2001, 09:45 AM   #11
ColinL
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memnoch-- josh has a 1.8L thus the reason I suggested the 215/40-16. I would not recommend running even a 205/45-16 on an RS unless it's the Hoosier R compound for autocrossing...
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Old 05-05-2001, 10:04 AM   #12
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why would you not recomend lower profile tires for RS drivers? just out of curiousity.

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Old 05-05-2001, 11:02 AM   #13
Thug
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ive been running 215/40/16 Kumho 712's for about a week now with no problems. Obviously it tachs higher and my speedo is off, but other than it's great. My car is noticeably faster.
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Old 05-05-2001, 01:16 PM   #14
ColinL
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the RS already has plenty of gearing for an engine with such a low rev limit and a fair amount of low-end torque.

IMO 5th gear has such a huge jump it's to your advantage to have 4th gear do everything you need to about ~100MPH.

...there's also the issue of load rating and considerable speedo error.
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Old 05-05-2001, 06:46 PM   #15
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well IMO ive driven memnoch's car extensively with both the stockers and the 45 series and they seem to suit the gearing even better... the car feels like its always sending a lot more torque to the ground on all rpms in every gear...feels much stronger, you can feel the extra pull, and the thin hard sidewall is nice..

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Old 05-05-2001, 10:00 PM   #16
Kevin Thomas
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Don't quote me on this but I could've sworn I read somewhere that if you go to a smaller tire size 205/45-16 vs 205/55-16's, than your ride quality will be affected greatly. To reduce having an excessively hard ride, you'd have to keep the same amount of air volume within your tires. Thus, you would have to go with a wider tire (Hence 215's vs 205's) to keep the same ride quality as stock. This usually applies if you go to bigger rims.

I'm saying this to say that if you go to a smaller tire size, I think it may be a good idea to go with a wider tire to keep the same amount of air volume in your tires to keep the cushiness of your stock ride. Does this sound right? I must be getting old thinking about cushiness.

At any rate, good luck!
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