I've been digging through searches looking for a definitive answer- and came up empty handed...
I've gone and confused myself with the tire-size question. I'd like to go to a 17"x7" front (40-45mm offset), and a 17"x8" rear (45mm offset). I'll be installing a set of Koni Adjustables (Struts in back, not coilovers) and possibly lowering springs. I'd like to keep the stock ratio/diameter so I don't mess up my speedometer- So right now I've got 15"x7" (stock are 7" right?)Wheels all the way around, running 205/60/15 front & 215/60/15 rear. So If I switch to the above mentioned 17s, what tire size would I run?
According to the "Tire Size Calculator" I would use 245/40/17 (front) 255/40/17 (rear) to have less than 1% error in speedometer reading... Is this right? Or is it not taking into account a different tire width? Help! I'm lost.
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01:03 PM
PFF
System Bot
Alex4mula Member
Posts: 7405 From: Canton, MI US Registered: Dec 1999
You will get another hundred different answers and still feel empty handed. Is always the same with this topic. What you could do is compare what everybody is using and better yet look how it looks in their cars. I use 215-45-17 frt and 235-40-17 rear on 7" rims. If you want pics email me (sorry, can't post). Good luck.
------------------ Alex4mula :) Red-Original Owner & White-1/94 with PM (:
Rob, I believe 245 on a 7" rim is really pushing it. The 255 40 rear sounds like a good size. For front, I'd either go with a 215 45, or 225 45. The 215 will be closer to the stock front diameter. The 225 will be just a bit smaller diameter than your 255 40 on the rear. So from a side view of your car, the 225 45, 255 40 will look almost exactly the same height. If you want the front to be a little smaller, like the stock setup, then the 215 45 will work good. Did you follow me on that??
OK... I know I'm figuring something wrong here (Width =###/25.4=inches). A 245 tire is a little over 9.5 inches wide (A bit too wide for a 7" rim), then a 255 is a touch over 10 inches wide. So I'm seeing that my stock tires measure about 1-1.5" wider than the 7" rim. So a 235 (9.25" wide) would be OK on an 8" rim. and a 225 would fit OK on a 7.5" rim (but probably not a 7"). Does this sound right to anyone...? Or am I just rambling?
Okey-Dokey. Squoach- thanks (you posted while I was trying to sort what I was typing).
OK- 215/45-17 for the front is good (.3% fast). Still trying to figure if the 255/40-17 (.5% fast) is too wide for the back (without coilovers)? I guess a 235/45-17 would be about the same then... (.7% slow)? Argh... damn math.
Guess the question is down to: Will a 255/40-17 fit on a 17x8 rim without any rubbing on a stock 87 rear suspension?
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03:04 PM
Formula88 Member
Posts: 53788 From: Raleigh NC Registered: Jan 2001
Check this out: http://www.miata.net/garage/tirecalc.html Just plug in the original tire size, and your new tire size and it calculates the difference. One of the most useful tools I've found on the internet.
Also, check http://www.tirerack.com for tire specs. Each tire mfg. has a page listing the acceptable rim widths for their tires. Remember, as the aspect ratio gets lower, you need a wider rim - even if the tread width stays the same.
Using the Bridgestone Potenza RE730 as an example, the rim width ranges are:
The Measured Width is the standard rim width the manufacturer uses to measure their tire by - basically their recommended rim width.
Compared to a 215/60-15, the closest sizes in overall diameter are: 255/40-17 -0.5% speedo difference 235/45-17 -0.7% 225/45-17 +0.7%
Side note: The Dunlop SP8000 in 245/50-15 that many people say is too wide for a stock 15x7" rim is recommended for rim sizes 6.5" - 9.5" with a recommended (meas. width) of 7". Sounds like Dunlop says it will fit perfectly. However, it will cause your speedo to read 2.2% too fast (at a registered 60mph, you're doing 58.8mph) since it's 0.6" shorter in diameter than a 215/60-15.
[This message has been edited by Formula88 (edited 11-08-2001).]
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03:19 PM
Formula88 Member
Posts: 53788 From: Raleigh NC Registered: Jan 2001
Yes, you'd run 255/40-17's on a 9" wide rim in the back and 245/40-17's on a 8.5" wide rim in the front.
For a 7" wide front rim, your size options are: 225/45-17 which is -1.2% off 215/45-17 which is +0.3% off
On an 8" wide rear rim, your options are: 235/45-17 which is -0.7% off 245/40-17 which is +1.8% off
This is why I want a minumum 7.5" wide front rim and 8" rear, and I'd prefer 8" wide front and 9" wide rear, but those are hard to find without paying a fortune.
There are other options, but these are the closest tire sizes you can get on the rim widths you mentioned.
Personally, I want to run 225/45-17's front and 255/40-17's rear. Just gotta find rims that fit, that I can afford, and that I like the looks of. And if I can get them under 25 pounds, even better. That's a tall order, and I've not had much luck yet.
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03:31 PM
Formula88 Member
Posts: 53788 From: Raleigh NC Registered: Jan 2001
One last thing. According to West Coast Fiero's FAQ, 255/45-17's will fit on a 17x9" rim with 45mm offset and not rub. Also, 245/40-17's will fit on a 17x8" rim with 45mm offset. Check their webpage's FAQ for the exact quote. The trick here is you can only run a 9" wide rim in 17", cuz a 16x9" rim will hit the suspension. So, while these sizes fit, you're pushing the envelope. If you've lowered your car, your mileage may vary.
Formula- Thanks! (The miata tire size calc is what I've been using- it's the link in my first post too ) You confirmed what I was hoping for. I too am planning to run 225/45-17's front and 255/40-17's rear. As to the rims themselves. I've got a quote request out to compomotive for their CX style rims (see photo) in 17x7 for front and 17x8 for the rear. If you're interested I'll pass along the info when I get it!
Originally posted by MinnGreenGT: I too am planning to run 225/45-17's front and 255/40-17's rear. As to the rims themselves. I've got a quote request out to compomotive for their CX style rims (see photo) in 17x7 for front and 17x8 for the rear. If you're interested I'll pass along the info when I get it!
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Yeah, get me the info, but make sure you check the specs on the tires you want to run. For the Bridgestone RE730 that I used as an examplet, the 255/40-17 will not fit on an 8" wide rim! You need a minimum 8.5" wide rim. I'd go with a 9" wide, if possible. For an 8" wide rim, I'd choose go with a 235/45-17.
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09:13 PM
PFF
System Bot
Rick 88 Member
Posts: 3914 From: El Paso, TX. Registered: Aug 2001
I could not find a 7/8 in wheel combo that I liked within my budget so I purchased 17x7.5 in .40 offset wheels all around. I am running a 215/45/17 front and 245/45/17 rear combo. Both these tires sizes fall within the acceptable range for a 7.5 in. rim width.
My speedo is only off by a little more than 1 mph. with the 245/45's on the back. Since my car is an 88, 215's seem about the largest that will not rub on the inside at full lock with this width wheel. 225's may be ok on pre 88's but it would be wise to mount a set and check. I really like this look on my 88, and get a lot of compliments on the rolling stock. Hope you are not too confused by now!
Rick 88
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10:07 PM
Nov 10th, 2001
artherd Member
Posts: 4159 From: Petaluma, CA. USA Registered: Apr 2001
Originally posted by Alex4mula: I use 215-45-17 frt and 235-40-17 rear on 7" rims.
Same here. 215-45-17 frt and 235-40-17 rear (on 7" rims front and back.)
Pic below, you be the judge
I wouldn't go any wider than 215 or so on the front, or the car will be hard to turn. 225 is ok.. (not much bigger.) Don't get any *higher* in profile (45 series) though, too much sidewall! Maybe go 225/40/17 in front? Fieros seem to like a slight size asymetry front-to-rear.
For your 8" wheels, go with 255/40/17s. They'll be *great!*
PS: My car loves it's 17s *so much* that I'm working on a set of 18s for the silver car, they're gonna be extreme
Best! Ben.
------------------ Ben Cannon 88 Formula, T-top, Metalic Red "Every Man Dies, not every man really Lives" 88 Formula, Northstar, Silver -Mel Gibson, "Braveheart"
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12:19 AM
skitime Member
Posts: 5765 From: Akron, PA, USA Registered: Aug 2000
I agree with artherd. I put 205/50/17s on the front since I have an 88 GT. I wanted to retain the great driving characteristics of the 88s which were retained. I put 235/45/17 on the rear.
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Red 88 GT T-TOP
Red 86 GT
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08:26 AM
Formula88 Member
Posts: 53788 From: Raleigh NC Registered: Jan 2001
Originally posted by artherd: Same here. 215-45-17 frt and 235-40-17 rear (on 7" rims front and back.)
Well, the thing that concerns me here is, for the Bridgestone RE730's that I've been looking for, a 235/40-17 requires an 8" wide rim minimum and a 235/45-17 requires a 7.5" wide rim minimum. What brand are you running? I'd be concerned about running the tire on a rim narrower than the mfg. recommends. But if a 235/45-17 will work on a 17x7" I may use that on the rear. I want to increase the car's footprint, but maintain it's balance.
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03:09 PM
oneriskski Junior Member
Posts: 2 From: clearwater,florida,usa Registered: Nov 2001
i have a set of 17's now,with 205/40/17 on all 4's.setting my car up for racing and have 17x7 and 17x8 now.coing to run 215/40/17 up front and 255/45/17 rear.toyo tires has a tire to rim guide at team toyo or i can mail to you. my car is lowered 2" all around,with coilovers in rear right now. tires.com has great wheel prices! take a look at the konig tantrum,they were on sale for $160 each,your choice 7 or 8 wide! i know the 255's are wide and tall for an 8" rim,but the toyo guide approves it! the toyo proxes t1s is the same tire they race,just shave it down!the 245/45/17 is the best match for an 8" rim,but i have a 4.9 going in my car and need the bigger footprint,not too concerned with the speedo.
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06:23 PM
artherd Member
Posts: 4159 From: Petaluma, CA. USA Registered: Apr 2001
Good, stickyish tyres. And the sizes I posted do fit quite well, the front sidewall is FLAT as a board, and the rear has an almost imperceptable buldge.
The tyres are rock solid, seem to infact smooth out above 100mhp (they're a dream at 130. 'Don't speed on public roads', mmkay?
235 on an 8" rim? they're smoking things. And they should be giving you a tollerable rim width rante (ie, 7"-8" for 235/40, 7-7.5" for 225/40, or such.)
The car drives great (it's the T-top car in my sig) and the tyres are perfect for the stock engine. For an engine swap or boosted motor, they'd be inadequate in the rear however.
One thing is universally true though; you WILL be better off going with wider rear wheels though. Peroid.
All clear now? ;
Best! Ben
quote
Originally posted by Formula88: Well, the thing that concerns me here is, for the Bridgestone RE730's that I've been looking for, a 235/40-17 requires an 8" wide rim minimum and a 235/45-17 requires a 7.5" wide rim minimum. What brand are you running? I'd be concerned about running the tire on a rim narrower than the mfg. recommends. But if a 235/45-17 will work on a 17x7" I may use that on the rear. I want to increase the car's footprint, but maintain it's balance.
------------------ Ben Cannon 88 Formula, T-top, Metalic Red "Every Man Dies, not every man really Lives" 88 Formula, Northstar, Silver -Mel Gibson, "Braveheart"
Just one word of advice from someone who has had several size tires on his 17" wheels.
You don't need huge ass front tires , they will make the car understeer more.
255's are good , but make sure the sidewall is square to the rim. You want a 20mm difference between the front and rear tires , so 225's up front is a good start.
Now for those of you who caught it , Most 1990's 911 porsche's run 255's rear , and 225's front. It works perfectly on a Fiero or a porsche. There is such thing as a tire that is too big for the car. Big tires upfront suck ass to steer and contribute to understeer. (I had 235's up front and 255's rear for about 2 weeks , then I went back to 255/40's rear , 225/45's front. This worked perfectly.
IF you wanna save some cash you can pick up used 17's from Local PCA members cheap. I got a set of Pirelli P zero's 1/2 worn (255's rear , 225's front) for $100. The guy decided he wanted new tires... I picked up a set of 17" slicks from a 911 racer about 1/2 worn as well , for FREE!
JM
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08:07 PM
sjp777 Member
Posts: 613 From: San Francisco, CA Registered: Apr 2001
) You confirmed what I was hoping for. I too am planning to run 225/45-17's front and 255/40-17's rear. As to the rims themselves. I've got a quote request out to compomotive for their CX style rims (see photo) in 17x7 for front and 17x8 for the rear. If you're interested I'll pass along the info when I get it!
