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karman1970

FWD wheel and tire dimensions

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Prior to now we have run hard, not sticky tires on our Civic.  Dunlop Direzza DZ102s.  460TW.  205/50(or 55)R15s.  Don't ask me why.  First was on some cheapo steelies, then we upgraded to a set of Integra "snowflakes".  Not bad wheels, about 15.5lbs, but kind of skinny.  But now we wanna go fast and some conversations on here recently now have the gears in my head turning - which is not always a good thing.

 

I found a couple of nice 15" wheels in the 10-12lbs range, but the wider ones (8-9") all really seem to mess with the offset - some of them move the center line as much as an inch out.  How much does reducing the factory negative scrub radius mess with the steering/handling/driveability of a FWD car?  Does adding power make those effects worse?  I'm really leaning toward welding the diff, but how does that play with a smaller negative scrub radius or even zero scrub?  Is there a point where front tires get so big or scrub radius changes enough that you might NOT want a welded diff?

 

Since we're also cheap and may keep our 15x6 wheels for the time-being, what would be the "best" tire size to run on that rim?  Narrower tire but "stretched" to fit that rim, the widest thing we can stuff under the fenders, or something in between?

 

Or am I trying to make too many changes at once?  Maybe stick with the Integra wheels, a decent 205 or 225 tire, and leave the diff open until we learn how to drive the 200TW tires and extra power?  I imagine more grip is suddenly going to change how it stops and turns compared to the harder rubber we've gotten used to.

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Go 205/50/15 unless you have a lot of HP. 150whp or less, you are good. As long as they fit and don't rub the struts or fenders for offset, you are good. And when you add in negative camber for better handling, it will give you more fender clearance.

 

Dunlop Direzza Zlll are very sticky, great in rain and wear well.

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53 minutes ago, djsteviec said:

Go 205/50/15 unless you have a lot of HP. 150whp or less, you are good. As long as they fit and don't rub the struts or fenders for offset, you are good. And when you add in negative camber for better handling, it will give you more fender clearance.

 

Dunlop Direzza Zlll are very sticky, great in rain and wear well.

 

Thanks. What if we're making 200-ish? Step up to 225 and a 7" rim?

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We always found it was easier for my group of drivers to go faster on the wider wheel tire setup 245’s on 8.5” rims as opposed to 225’s on 7” inchers. This was backed up by AIM data spread across multiple test sessions.

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1 hour ago, Mopar 4 Life said:

We always found it was easier for my group of drivers to go faster on the wider wheel tire setup 245’s on 8.5” rims as opposed to 225’s on 7” inchers. This was backed up by AIM data spread across multiple test sessions.

 

Were you able to maintain the factory offset/scrub radius? That's my main concern with the really wide wheels I've found so far - how will that change affect the handling?

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12 minutes ago, karman1970 said:

 

Were you able to maintain the factory offset/scrub radius? That's my main concern with the really wide wheels I've found so far - how will that change affect the handling?

It's a little more work in the steering but hardly noticeable on our Civic: 15x9s with 225/45-15s and spacers. Handling change is all but nonexistent, if you did a back to back you might feel the difference but I doubt it. 

 

We found the Z3s to be decent but not so good on a hot day. RE-71Rs or R-S4s are better. 

 

Do a 25 point transaxle swap to ITR with LSD.

Edited by mender

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13 minutes ago, karman1970 said:

 

Were you able to maintain the factory offset/scrub radius? That's my main concern with the really wide wheels I've found so far - how will that change affect the handling?

Nope, but data doesn’t lie

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1 hour ago, karman1970 said:

 

Were you able to maintain the factory offset/scrub radius? That's my main concern with the really wide wheels I've found so far - how will that change affect the handling?

 

I think you could be over thinking it. I did the same thing when looking at wider wheels and was worried from the technical type articles I read.  We added 17x9s to our Mazda 626 and had no issue.  I'd give the wide wheels a shot and suspect you will love them. 

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16 hours ago, karman1970 said:

 

Thanks. What if we're making 200-ish? Step up to 225 and a 7" rim?

Probably not a bad idea, but you will need spacers, depending on the offset. I had a 38 offset and 205 was the biggest I could fit. You will also then need flares. Even with the 205s i needed flares.

 

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FWIW, 15x9's and 225s were made to fit on our Integra. 

 

Spacers and rolled fenders and you're good to go. 

 

All the "you need more hp for wider tires" thing is only very slightly true. I benchmarked 15x7.5 195's back to back with 15x9 and 225 on my 115whp Miata during a time trial weekend and lost precisely 2kph speed on the back straight. And went 1.5 seconds faster consistently.

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Thanks for all the feedback.  It's awful tempting to go with a big, wide setup. But with our finances being what they are and all the other changes we are making to the car this year, I'm thinking about sticking with the 6" wide wheels we already have and running some 195 or 205 Dunlops for 2019.  They are pretty inexpensive and going to be faster than our prior setups anyway simply due to the compound change.

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15 minutes ago, karman1970 said:

Thanks for all the feedback.  It's awful tempting to go with a big, wide setup. But with our finances being what they are and all the other changes we are making to the car this year, I'm thinking about sticking with the 6" wide wheels we already have and running some 195 or 205 Dunlops for 2019.  They are pretty inexpensive and going to be faster than our prior setups anyway simply due to the compound change.

True.  However, wider tires on the proper size rim last WAYYYYY longer.

 

If this is for a honda, can't you get cheap wide wheels for like free?

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I went to the 9" wheels and 225 R-S4 tires to reduce our tire budget over the 205 Dunlops we were running. Haven't been able to test that yet but pretty sure it'll pay for itself after the first weekend.

 

Hondas can use Miata wheels so good prices. Gotta work on using the Miata shocks now. ;)

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2 hours ago, wvumtnbkr said:

True.  However, wider tires on the proper size rim last WAYYYYY longer.

 

If this is for a honda, can't you get cheap wide wheels for like free?

 

43 minutes ago, mender said:

I went to the 9" wheels and 225 R-S4 tires to reduce our tire budget over the 205 Dunlops we were running. Haven't been able to test that yet but pretty sure it'll pay for itself after the first weekend.

 

Hondas can use Miata wheels so good prices. Gotta work on using the Miata shocks now. ;)

 

I dunno about free; maybe if I was a better scrounger, perhaps :)   Even a set of Bassetts would be about 275-300 bucks.  The 460TW 205s typically last a double 7 and then some, especially if we rotate them.  You think we'll wear down skinny 200TW tires quite a bit faster and not last a weekend?  Like I said, hopefully bigger changes for 2020, but we're likely only going to make one race for 2019 and will probably working some bugs out.

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15 minutes ago, karman1970 said:

 

 

I dunno about free; maybe if I was a better scrounger, perhaps :)   Even a set of Bassetts would be about 275-300 bucks.  The 460TW 205s typically last a double 7 and then some, especially if we rotate them.  You think we'll wear down skinny 200TW tires quite a bit faster and not last a weekend?  Like I said, hopefully bigger changes for 2020, but we're likely only going to make one race for 2019 and will probably working some bugs out.

I think the 200TW tires will wear longer than the 460 TW tires if "prepped" properly.

 

I also think a a 225 on an 8inch wide rim will last 50% longer than a 205 on a 6inch wide wheel.

 

In other words, if you can get 15 x 7 or 15 x 8 and run the RS4, you will be faster and probably have better wear than what you run today.

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The former owners of our Honda went through 205 RE-71Rs in about 6 hours. I expect to go as fast with the larger R-S4s while at least doubling the tire life. 

 

The choice was to either buy two sets of 205 RE-71Rs or one set of 225 R-S4s and a set of wheels. Pretty close to the same price but after the first weekend our tire budget for the R-S4s should drop to half that of the RE-71Rs.

 

Tried to prove that at ORP but when my first driver hit the pit wall 35 minutes in we had to use the Z3s that were new at Portland, where we ran the Z3s for about 6 hours before having to get into our spare tire pile when they started to cord from the heat (low 90s). We scrounged enough heat cycled tires after the ORP incident to last another 5 hours but there's not much left.

 

Got a new set of R-S4s though, just need another rim!

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We are having this same discussion on our team.

we run FWD and 205/50/15s, here’s a couple of thoughts...

 

go on YouTube, search for fwd Honda at Toronto.

they have some great info bout running 15s and 17s in mostly stock car.

then they talk to a guy racing a highly boosted Honda - like 600ish hp.

summary?

     - stock’ish hp, there was very little diff in lap times between 205/15s and 245/17s

     - with big hp gains over stock, yes, more rubber on ground improves lap times

 

one other take-away, for the racer on budget (we are)... reverse stagger for fwd cars.

put spacers or wider tires up front, but leave thinner rears. Does two things:

     - keeps costs down, only need the wider/more expensive tires up front

     - less rear grip helps get our under-steering fwd cars to rotate into corners better

that second point is where we have really concentrated.  Lap times are coming down 😉

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9 hours ago, Rick.Cook23@yahoo.com said:

We are having this same discussion on our team.

we run FWD and 205/50/15s, here’s a couple of thoughts...

 

go on YouTube, search for fwd Honda at Toronto.

they have some great info bout running 15s and 17s in mostly stock car.

then they talk to a guy racing a highly boosted Honda - like 600ish hp.

summary?

     - stock’ish hp, there was very little diff in lap times between 205/15s and 245/17s

     - with big hp gains over stock, yes, more rubber on ground improves lap times

 

one other take-away, for the racer on budget (we are)... reverse stagger for fwd cars.

put spacers or wider tires up front, but leave thinner rears. Does two things:

     - keeps costs down, only need the wider/more expensive tires up front

     - less rear grip helps get our under-steering fwd cars to rotate into corners better

that second point is where we have really concentrated.  Lap times are coming down 😉

Bigger tires may not help laptime.  They will help heat management and tire life.

 

Running a non square setup is a pain in the butt in regards to endurance racing.

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If fwd....i ran staggered sizes on my fwd car for years. Your tire wear will be so asymmetric rotation might not matter, and you can just run 2 races per rear set. 

 

On the rwd car i did staggered, i sort of wish i didn't. Wear on those was close enough enough i wasn't going to make 2x times the races on one end of the car, so rotating would have made more sense.

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You should be able to find Miata wheels and tires all over craigslist and FB. Spec miata wheel take offs are normally 15x7 and LIGHT. I run 949 6ULs on my daily Miata that weigh 12lbs in a 15x9, less in a 15x7 obviously and cheeeeeeeeap used. Go straight to a 225 RS4 and never look back, most likely two full race weekends per set definitely justifies the tire cost. Square setup for sure and take the points on a big rear sway bar if you want that much rotation. 

 

Buying new wheels for endurance wheel to wheel racing makes 0 sense to me, first contact and you'll cry at the lost wheel. The 17x9s I run on the Supra, I've picked up for $75 a set.

 

Stock Miata wheel weight and size chart for what to look for. https://www.miata.net/faq/wheel_weights.html

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On December 12, 2018 at 8:06 AM, IPF Racing said:

You should be able to find Miata wheels and tires all over craigslist and FB. Spec miata wheel take offs are normally 15x7 and LIGHT. I run 949 6ULs on my daily Miata that weigh 12lbs in a 15x9, less in a 15x7 obviously and cheeeeeeeeap used. Go straight to a 225 RS4 and never look back, most likely two full race weekends per set definitely justifies the tire cost. Square setup for sure and take the points on a big rear sway bar if you want that much rotation. 

 

Buying new wheels for endurance wheel to wheel racing makes 0 sense to me, first contact and you'll cry at the lost wheel. The 17x9s I run on the Supra, I've picked up for $75 a set.

 

Where does one find these super cheap used wheels? Apparently West Texas is not exactly a hot-bed of Miata racing.

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1 minute ago, karman1970 said:

 

Where does one find these super cheap used wheels? Apparently West Texas is not exactly a hot-bed of Miata racing.

 

I just saw a couple sets of 6uls with tires in Michigan for less than $500 on Facebook, but I've definitely seen cheaper. Maybe west Texas isn't if there aren't spec Miata races close by. Wasnt trying to lead you astray, but it might be worth finding some spec Miata people near you for leads on deals. 

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