How come 17x7 +40 215/40 && 18x8 +45 225/35 both sit flush with fender?? - Honda Prelude Forum

99_SH · 05-01-2002, 06:53 PM

Just curious, I've been doing a search and seeing what size wheels rub and not. So far I have concluded the following:

17x7, 40mm offset, 215/40, no rubbing if rear tab is shaved
18x8, 45mm offset, 225/35, no rubbing, no need to roll fenders, just shave rear tab.

I punched these numbers in a wheel calculator and it gave me the following results. For the 17" wheel the wheel/tire is gonna stick out an additional 1.035 inches over stock. For the 18" wheel, the wheel/tire is gonna stick out 1.538 inches over stock.

People with the 17's and 18's both say that their wheels sit flush with their fenders. I dont understand this because if it sits flush with the 17's, then it must NOT sit flush with the 18s. The math says it all.

Could someone explain, am I missing something here

aklucsarits · 05-01-2002, 07:09 PM

This is as good an explaination as any...
http://prelude.vtec.net/gen5/faq/#wheels

Andrew

99_SH · 05-01-2002, 08:02 PM

That site is only good for calculations, which I already have. Now i'm just doing the analyzing part

aklucsarits · 05-01-2002, 08:09 PM

Quote:

Originally posted by 99_SH
That site is only good for calculations, which I already have. Now i'm just doing the analyzing part

The calculations you have for the position of the wheel vs stock appear to be incorrect. Use the formuals in the link I posted, and you'll see that the diffence between the position of the 2 wheels you described is only about 3/10"...

Andrew

99_SH · 05-01-2002, 08:49 PM

Actually both our calculations are correct. The thing is, the calculation shown on the vtec.net site only accounts for the wheel itself. My calculation accounts for the wheel AND tire. Because of the fact that tires stick out of the wheels, the numbers I have calculated are greater.

Here's the program I used to calculated the numbers:
http://www.tolan-hoechst.com/cars/tirecalc.htm

-Arax
~99SH

ludemaster · 05-01-2002, 10:34 PM

Hi fellows lude. I brought some wheels from a friend for cheap. The wheels size is 225zr40/18 with offset 40mm. I like drop my 2001 lude with H&R sport . Will it cause problems with rubbing or somethings else? Don't like coilover. thank

ShowSpeed · 05-01-2002, 10:47 PM

here's what i think...

if you think about it.. who can really tell if the rim pushes out 1/2 an inch more. it's hardly anything comparing to the width of the car. so when someone say.. "it sits flush".. it's only relative.

thats my .02

Man

SpanishRicer · 05-01-2002, 11:01 PM

You have to take the vehicles lowering and camber into account.
I used to have 18X8 wheels with 235 width tires and a 40mm offset that fit flush with my fenders. Why? Because my car was lowered 3 inches and the camber caused the wheels/tires to butterfly inward, allowing extra clearance. Now I still use 235 rubber, but with a 17X7.5 wheel with a 48mm offset and a fixed camber problem.

qboi · 05-01-2002, 11:08 PM

Quote:

Originally posted by SpanishRicer
You have to take the vehicles lowering and camber into account.
I used to have 18X8 wheels with 235 width tires and a 40mm offset that fit flush with my fenders. Why? Because my car was lowered 3 inches and the camber caused the wheels/tires to butterfly inward, allowing extra clearance. Now I still use 235 rubber, but with a 17X7.5 wheel with a 48mm offset and a fixed camber problem.

damn.. were those the verdicts?.. 235 is wide with only 40 offset..

SpanishRicer · 05-01-2002, 11:17 PM

Quote:

Originally posted by qboi

damn.. were those the verdicts?.. 235 is wide with only 40 offset..

No, it was my older Konig Villains. My father has them on his 3000GT now. And it was wide, too wide. My car looked like a RWD monster from the rear

lazilude909 · 05-02-2002, 02:04 AM

Man, I don't know what the hell you guys are talking about but I have a 48 offset 225/40/18 and the front is rubbing like a mofo. I have about a quarter finger gap in the front and it rubs when I go onto my driveway or make hard turns. I also noticed that when I tucked the tires it had bent my front fender. I suggest to be really careful! I'm going to buy me some 215 40 18 and hopefully solve this problem.

Obsidian7 · 05-02-2002, 11:38 AM

When looking at tire calculations, the tire that you choose can make a *huge* difference. Not all 225 tires are 225mm wide.. it just doesn't work that way. The stock RE92 tires, for example, mounted on the stock 6.5" wide wheels are 213.36mm (8.4") at their widest point, but they are only 205s. My new tires are 225s.. but they are only 223.52mm (8.8") wide when mounted on 7" wide wheels.

223.52 - 213.36 ~= 10mm wider.. since everything "grows" from the centerline, that's only 5mm on both the inside and outside.

---

Here is how I compare my current setup to stock:

The stock setup is 213.36mm wide (at its widest point) with a 55mm offset.
My new setup is 223.52mm wide with a 45mm offset (225/45 S-03 tires on 16x7 Rota Slipstreams).

Since everything is figured from the centerline of the tire/wheel combo... the new setup will stick out (223.52 - 213.36)/2 + (55 - 45) = 15.08mm more than the stock setup.

On the inside, the difference will be (223.52 - 213.36)/2 - (55 - 45) = -4.92mm ... so the tire will actually be about 5mm further away from the suspension.

If you add everything together, it all adds up.
213.36(stock) + 15.08(outside) - 4.92(inside) = 223.52(new)

---

Another example with my old setup:

Stock 213.36 wide w/ 55mm offset
vs.
215.9mm wide w/ 47mm offset (215/40 Yoko A520 on 17x7 Team Loco 142)

Outside: (215.9 - 213.36)/2 + (55 - 47) = 9.27mm
Inside: (215.9 - 213.36)/2 - (55 - 47) = -6.73mm

Double-check: 213.36 + 9.27 - 6.73 = 215.9 check.

---

So now you're asking... where do I get these tire widths?
You can check on the tire manufacturer's sites, or on TireRack.com. If they show a tire has a 'section width' of 8.7" on a 7.5" wheel, and you're only using a 7" wide wheel, subtract 0.2" from the section width... mine that should get you pretty darn close to how wide the tire will actually be. On the flipside.. if they show their section width is measured on a 7" wide wheel and you have 7.5", add 0.2".

---

DO NOT BE FOOLED by people trying to add in the difference for BOTH wheel width AND tire width (Luke at TireRack does this, Eric does not. Eric is cool). That makes no sense, because the two 'overlap'. I've already taken the wheel's width into account because I measured the tire mounted on the wheel, and the tire is wider than the wheel anyway. Some idiot (Luke? :b) was trying to tell me that my new setup would stick out like this:

(223.52 - 213.36)/2 + (7" - 6.5")*25.4/2 + (55 - 45) = 21.43mm THIS IS WRONG.

---

FAQ?

On a side note: I *may* have to do some fender rolling in the rear with my new setup. I think I've only rubbed once since I put the new wheels on.

99_SH · 05-02-2002, 02:46 PM

Good info Obsidian7, I had completley forgotten about the different tire widths according to manufacturer:

Following the calcultions you did above, here is what I get for my setup, check if I did it right:

Stock:
205/50/16 RE92
treadwidth = 8.4" = 213.36mm
offset = 55mm

New setup:
225/35/18 S-03
treadwidth= 9.1" = 231.14mm
offset = 45mm

calculation:
outer side:
(231.14 -213.36)/2 + (55-45) = 18.89mm increase over stock

Here's the part I dont understand, lets ignore the tire for now, and just do a calculation on the wheel itself.
So, 25.4*(8 - 6.5)/2 + (55 - 45) = 29.05mm

This doesnt make sence with the above calculation. First we're saying that the wheel/tire is going to stick out 18.89mm, but with the second calculation with just the wheel we're saying the wheel by itself is going to stick out 29.05mm over stock. These two answers dont mix together

I hope you have a reasonable explanation for this.

thanks!
-Arax

Obsidian7 · 05-02-2002, 03:08 PM

Don't work with the treadwidth... you want the 'section width'. That is the widest width of the tire.

So you should have:

New setup:
225/35/18 S-03
section width = 9.1" = 231.14mm
offset = 45mm

so..
Outside: (231.14 - 213.36)/2 + (55 - 45) = 18.89mm
Inside: (231.14- 213.36)/2 - (55 - 45) = -1.11mm

---

You calculation for the wheel is actually correct. The new wheel will stick out 29.05mm more than the stock wheel (not tire).

Also, for the inside:
25.4*(8 - 6.5) / 2 - (55 - 45) = 9.05mm

6.5" + 29.05mm + 9.05mm = 203.2mm = 8"

BUT, remember that the stock tire is wider than 8" by itself, so your wheel isn't gonna be rubbing anything. You need to worry about the tire choice. I would go with a 215/35-18.. it's closer to the stock diameter anyway. The Yokohama Parada Spec-2 in that size (8.5" + 0.2" wide) would stick out 13.81mm more than stock.

(8.7 - 8.4) * 25.4 / 2 + (55 - 45) = 13.81mm

[edit] You fixed your post

[/edit]

99_SH · 05-02-2002, 03:18 PM

I just realized that I used the tread width instead of the section width. I fixed those calculations. I already talked to two people using 225 width tire with a wheel size same as mine, and they have reported no rubbing issues. So i'm going to stick with the 225 setup.

The wheel and tire calculation i'm still unclear on. We calculated a tire increase of 18.89mm, and wheel increase of 29.05mm. So does this mean that the wheel is going to stick out an additonal 29.05mm over stock, and the tire is going to stick out 18.89mm relative to the new wheel?

So the edge of the tire its going to stick out a total of
29.05mm + 18.89mm=47.94mm

Is this correct?

Obsidian7 · 05-02-2002, 03:42 PM

nope... look at the part above where I say "THIS IS WRONG"

The way I figure things out takes into account the width of the whole setup (tire mounted on wheel). You don't need to add the difference of the wheel widths.. that's like adding it twice.

When we figure that it's going to stick out 18.89mm... that is 18.89mm more than the widest part of the stock tire. So look at your car, and imagine the sidewall at the top of the tire sticking out an extra 2cm.. and compare that with your fender.

99_SH · 05-02-2002, 06:45 PM

You're saying that the new wheels/tires are going to stick out 18.89mm relative to the widest part of the stock tires. But when we said earlier that the wheels themselves are going to stick out 29.05mm, thats contradicting with your earlier statement. Do you get what i'm saying?

how can the new setup stick out a total of only 18.89mm, while the wheel by-itself is sticking out 29.05mm.

-Arax

Obsidian7 · 05-02-2002, 08:33 PM

How is it contradictory when you're talking about different things?

The new tire/wheel combo doesn't have as much "bulge", that's all.

29.05mm(wheel outside) - 18.89mm(tire outside) = 10.16mm
9.05mm(wheel inside) - -1.11mm(tire inside) = 10.16mm

That's not a coincidence. That is how much the tire will be sticking out from the wheel on both the inside and outside.. 10.16mm.

BUT WAIT... you're thinking... 'the tire is 9.1" wide.. and the wheel is 8" wide... there's a 1.1" difference... that's 0.55" = 13.97mm .. that doesn't equal 10.16mm!!'

Well.. your 8" wheel probably doesn't measure exactly 8" wide either. It most likely measures closer to 8.3" (I'm guessing) from edge to edge.

This bad, bad picture may explain some things.

Blue = stock
Red = your new setup

99_SH · 05-02-2002, 10:10 PM

Ahhh,,, I think I see the picture now

While I was putting in all these values, I think all this makes sence,

Obsidian7 · 05-03-2002, 06:55 AM

Exactly!

Other things to think about:
Going along with the "not all tires are created equal" thing... some tires are more 'squared off' than others. So you may figure out that your tire sticks out a certain amount.. but you don't rub at all, while your friend has a setup that doesn't stick out as much, but he rubs like mad.

Maybe your friend's tires are more 'square' at the edges.. maybe you have a stiffer suspension.. maybe he's lowered more. The list can go on and on.

I can't stand it when people post things like:
'My 18" OZ wheels don't rub!'

OK.... how wide are they? What's the offset? What tire are you running? ..because the tire is what's going to rub, not the wheel. If the wheel itself rubs, you've got some other issues to worry about