Opinions: 17" rims in front 18" rims in the rear - OZ Supperleggera

[c55m8o]

Opinions... The rims in the pic are 17"x8" all around. How do you think this will look with the 17"x8" rims only in the front and 18"x9" rims in the rear? Look Weird using a rim w/o a lip?

There's a few cars that come from the showroom floor with different sized rims front and rear. We all know with the right tire choice of a plus size rim the outer diameter will remain the same 25" needed on our cars so handling and such isn't a concern of mine. Really, just the 'look' is what I'm wondering about doing this with this kind of rim.
http://images17.fotki.com/v309/photos/2/296054/3608713/CIMG1605-vi.jpg
Why? Because
a) I want to use 255mm tires on the rear, and 255mm on a 8" wide rim will most likely have negative affect on handling as sidewalls are rounded and couuld flex more left to right easier, and the center of the tire will wear more as the tire's tread will be rounded too.
b) I bend -every- 18" rim I ever run in the fronts. Want to go back to 17" for my performance set (I'll still have a 18" show set).
c) I'm being cheap and don't want to by a whole set of 18" rims again. These 17" rims are running snows right now. I'll take two off and use them in the front with summer tires; and by another two in 18" for the rear.

At least that's what I'm thinking about doing. Might just overlook point "a" above and run the 17" with 255 tires anyway. If consensus is it'll look dopey and not dope that'll help my decision.

Edit: Nixed!

[jnolte]

why dont you just get your FIskes redone, already!

[c55m8o]

I am, but I'm not planning on ever doing 'hard' driving on them again; Will just bend again. Want a set of grippy everyday tires I can barrel down the road or AutoX with and not worry about bending. Plus being a few pounds lighter doesn't hurt either. ;)

edit: p.s. not Fiske, they're Kinesis K58

[knvs]

I say do the staggered setup. It would look good on those wheels.

[SLAMMED_C]

there wont be any issues with running 17's up front and 18's in back.. hell Ive seen 18's and 20's on a W208 CLK cabio before.. looked pretty sweet.. well the 20's did!.. the 18's just looked too small.. he shouls have done 19's up fornt and then it would have suited better.
but no problem with running 17 and 18 wheel set up.. just as long as overall rolling diameters are close to one another.
I think it would probably look good..

[c55m8o]

Thanx. I'd tend to think so too. But I also know there's a lot I don't know. For best handling, Luke from the Tire Rack was pretty adamant that I shouldn't do it ...

"that would upset the handling characteristics of your car pretty dramatically. Can you say extreme understeer... All of the tires will have the same overall diameter in order to not effect traction control ABS functions and such. That means that the front tire on a 17" wheel will have a 4.0" sidewall and the rear on an 18" wheel sidewall height would be 3.5". When cornering the front tires sidewall will have approximately 15% more deflection than the rear which will cause huge amounts of understeer.

Now, I know you have seen cars running 1" larger wheels in the back before and maybe that's what gave you the idea. The Corvette is the most glaring example of this theory but, not only is the rear wheel 1" larger but, the car is designed to run a rear tire which is also 1" taller which means the sidewall heights are the same"
So, just wanted to provide this other perspective on it discussing the importance of uniform tire sidewall height on handling.

[rman]

i love staggered diameters...especially on domestic muscle...

but i have thought of doing the same, maybe an 18/19 combo tho..

[Nitrogenbalance]

I think it would look good. It's so hard to say. It seems as if your drop tucks the top of the tire into the fender. I think that will help keep attention off of the different tire profiles and more focus on the wheels themselves.

I've personally grown tire of the huge lip thing. It looks sick but because every cheap wheel company is making 2 piece forged nock offs with gravity cast poo makes it less special. Same goes for every new car sport models offered with red calipers. Getting a little beat.

The DTM race look of OZ wheels and a few others like the SLK55 wheels and Carllsson UL's has me thinking of something on that lines for myself. I say go. Also, what about contacting oz for a custom 17"x9" rear. Maybe they could send you a blank 17x9 and you could have the bolt pattern matched and drilled at a machine shop.

[c55m8o]

Originally posted by Nitrogenbalance
Also, what about contacting oz for a custom 17"x9" rear. Maybe they could send you a blank 17x9 and you could have the bolt pattern matched and drilled at a machine shop.
Now that's an interesting idea. I'll have to check with them.

I've definitely given up on running 18" in the rear and 17" in the front, unless I hear Jeff [speedybenz] contradict what Luke explained for whatever reason.

[Nitrogenbalance]

A buddy of mine purchased a set of wheels for his porsche that way a couple years ago. It was the only way possible and the company had no problem selling him wheels with a blank hub.

I also think that luke is dead on. I didn't even think about that. Makes perfect sense.

[c55m8o]

Yup. Additionally, I just read/learned of another probably more important reason why, in a great book I have on handling. Slip Angle.

As you turn the centerline angle of the wheel becomes more then that of the tire. (tire "twists" on the wheel). That difference is known as slip angle. An example the book cited was a graph that showed grip in relation to the slip angle. It quickly rose to 7 degrees, then peaked as 8 degrees, dropped to the same level at 9 degrees as it was at 7 degrees, then quickly dropped off from there (where the tires would be breaking loose and you'd be in a slide).

The book explained a number of things:

1) balance of a car is ensuring the slip angle of the front tires are the same as the back tires (not an easy thing it says).

2) Maximum grip for that example tire is when slip angle is between 7 and 9 degrees. (duh)

3) The tire will have as much grip when the slip angle is 9 degrees as when it is 7 degrees, however the tire will be wearing much faster @ 9 degrees, as well as quickly overheating. Over that you're in a slide.

The important thing to this dicussion however is it immediately dawned on me when I read the point in "1" above that the slip angle, meaning the 'curve' of the grip to slip angle relationship, of a tire with a 4" sidewall as it react to a turn will simply -always- be different then a tire with a 3.5" sidewall. Without exhaustive explaination, simply, the car will always be a handful and either understeer or oversteer; with a 4" tire up front, more then likely always wanting to understeer.

This stuff is kewl... ;)

[Nitrogenbalance]

Could you tell me where you got that book, the name, and the author??

It's not often I get excited about books LOL.

[c55m8o]

Sorry, I keep forgetting to look when I get home! :o Cross your fingers for this weekend.

Edit: Until then, here, The Physics of Racing (http://www.miata.net/sport/Physics/index.html)
This is what I started with myself.

[c55m8o]

Nitrogenbalance,

Book Name: High Performance Handling Handbook
Author: Don Alexander
Book Series: Motorbooks Workshop
Publisher: Motorbooks International

Cost: $19.95 USD (softcover book)
www.motorbooks.com (http://www.motorbooks.com)

[Nitrogenbalance]

Originally posted by c55m8o
Nitrogenbalance,

Book Name: High Performance Handling Handbook
Author: Don Alexander
Book Series: Motorbooks Workshop
Publisher: Motorbooks International

Cost: $19.95 USD (softcover book)
www.motorbooks.com (http://www.motorbooks.com)

THANKS!!

You da man!!

That should burn up a good 40 hours next week LOL.

[speedybenz]

Steve,

You should be running 17X8.5 or 17X9 rims up front. The 8.5" wide wheels should have an ET of 35mm which will allow you to run 245/40/17 tires without rubbing problems. I have that size tire on the front of my stock C43/55 and they do not rub and the ride hts. look to be very similar. The 245 will really help you on the front grip issue. The 225's are just too narrow.

Jeff

[c55m8o]

Hey Jeff! Nice to see you back online. Hoping that life is returning to normal and the new house is greate and trouble free.

Surprised you get no rubbing though. It's amazing. Mine was rubbing so bad with the 235mm snow tires I was running. But then again, the car was sitting too low. (What spring rate are you using up front BTW?)

I actually couldn't wait anymore and had to get the snow tires off and use these 8" wide rims I had [while the others are repaired/rebuilt] , so bought a set of stock sided rubber. Yes, I'm unhappy. :(

Though I read, learned & realized 17" dia up fron and 18" dia rim in the rear wouldn't be good for slip/grip angle, what I didn't realize soon enough is running a rear tire at the minimum rim width and a front tire near the maximum recommended rim width would likewise affect slip/grip angle in a non-linear manner front and rear when turning near max grip of the tires.

I already was thinking about using the rear rubber on the front when I get my rims back from repair/rebuilding, where before I was toying with the idea I'd use them on my other car instead. I'm glad to hear about your success at those specs and appreciate the info very much.

I made mention of a custom set of Kinesis rims I'm having made they don't normally produce and sell to the public in another thread. They're using the center sections I already had with my 18" rims, but with a 17" diameter drum set in reverse lip (what I had before was a 18" stepped lip). Will be 8.5" wide in the front and 9.5" in the rear like before. And I think they are 35mm offset, but I'd better check again that they're not 30mm or something else; gotta get spacers otherwise.

Timing is perfect again with you just checked in. I just dropped the car off @ TKX Performance this very morning, to have them lift the car and re-align (and spec custom sway bars). The front springs had "walked" forward on me so that the front spring's pad is poking through the top spring perch, which resulted in the car dropping about an inch from when they gave it back to me in the winter.

I wanted to call you this past week but I've been like everyone it seems lately, really busy. I'm wondering if you completely made the top of your adjustable spring perch that holds and centers the spring; the section with the white nylon (or whatever material) cylinder and steel disc? I'm thinking what's needed is something like that on the top spring perch, with a bolt instead of circulating ball pointing up, then another large steel washer-like disc that gets bolted down to sandwich that unit as a spring centering unit, around the current stock upper spring perch. Would love to [actually, I "need to" ;) ] hear your thoughts. I doubt those units are something you bought but rather made; though I wanted to check.

....but, I digress off-topic on my own thread here... ;) What might be a good time to call you so you can give me a few minutes. Please PM or e-mail me.

All the best and hope the new home is treating you and the family great.

[Chupa]

c55m8o, you seem to have a good handle on your tire requirements/limitations now. I'm just throwing this out there as an idea but ... have you considered the effects of your wider tires on your suspension setup?

Front - the point that your steering axis of rotation crosses your contact patch changes the torque around the steering axis. This can negatively effect responses during freeway driving, cornering, AND ememgency braking with ABS.

Rear - the 202 has a 5-link rear which means it acts in a similar fashion to the front with variable toe-in, designed in for dynamic stability. Consequences (similar to the front) can be seen at the rear. Depending on suspension geometry, it is theoretically cause some toe-out in the rear which CAN cause instabilities ... much like pre-993 911s.

[c55m8o]

pardon the tardy response. Kept forgetting to respond to this thread. Thanx for your comments.

Chupa, if the offset of the wider setup is such that the extra width is spread equally between the inner and outer sides, does the situation you describe exist? Then am I correct in assuming with other suspension adjustments, one can counteract any negative influence of what you describe? Because Jeff's car was carving those canyons in Northern California like I never imagined with no negative effect with his super wide rubber; much better then mine was last week IMO when I was bombing the twisties of Northern Conneticut on my way to and from Limerock Racepark with my stock sized rubber.

Also, I was always wondering about what you are discussing with the 5-link setup and how toe change can actually help at times. Does the manner toe is affected by body lean in a turn actually work in favor of helping the car to turn, by creating a 'pseudo' 4-wheel steering effect? ...where on compression from static equilibrium (when going straight, no bumps) the outside rear tire toes out and on suspension lift from equilibrium the inside rear tire toes in?

Also, with the two sets of speedybenz adjustable arms, one used for camber arms and the other for the lower-link arm, I'm able to adjust toe and camber very well; running per speedybenz specs of 1/8" total toe in the rear and 1/16" total toe in the front. This 'little' benz turns very nicely. The thing that keeps me somewhat thentative then I'd like is definitely the 225mm rubber up front.

[speedybenz]

Steve,

I will come up with a fix and fixture to keep that spring centered,

Also did you add the rubber bump stops for the front shock or are waiting for me to send you some? Also what settings are running your shocks at and why.


What sort of issues are you having to disrupt your driving experience.

Better yet I will call you to discuss.

Jeff

[c55m8o]

Hey there Jeff!

I am using the stock bumpstops that came with the shocks. The gasket on the shaft shows me that the fronts never compress enough to hit. (tire used to hit the inner wheelwell before I raised the suspension a good deal). The rear does compress to max oddly enough (was wondering if I should use a stiffer spring, since I feel more comfortable with the spare tire in so I guess I'm riding with more weight then you). Also. I want to add washers between the top of the shock and wheelwell to give me perhaps a 1/2" more droop potential; just haven't gotten to it.

That's great to hear about the perch tops. Was the only thing that had me concerned since doing everything. I look forward to speaking to you about what can be done for it; and if you think it's something you'd fabricate or would spec it out to have me get fabricated. However I'll be away out of the country on vacation for the next two weeks, so I look forward to speaking to you towards the end of the month.

Taso of TKX also wanted me to ask you if you had any specs on the uprated anti-sway bars or have a contact for making the parts. But with the suspension raised to where it should have been to begin with right around where you were running your car (maybe a tad higher now) I'm not in as big a rush to do that anymore. The shocks seem to be operating in a "sweet spot" right now. Wow, what a difference in stiffness! :D Compression set on 4 or 5 as an example is what I'd expect now. ...niiiice! ;)

I'll speak to you later and thanx for everything again.

[Chupa]

Originally posted by c55m8o
pardon the tardy response. Kept forgetting to respond to this thread. Thanx for your comments.

Chupa, if the offset of the wider setup is such that the extra width is spread equally between the inner and outer sides, does the situation you describe exist? Then am I correct in assuming with other suspension adjustments, one can counteract any negative influence of what you describe? Because Jeff's car was carving those canyons in Northern California like I never imagined with no negative effect with his super wide rubber; much better then mine was last week IMO when I was bombing the twisties of Northern Conneticut on my way to and from Limerock Racepark with my stock sized rubber.

Also, I was always wondering about what you are discussing with the 5-link setup and how toe change can actually help at times. Does the manner toe is affected by body lean in a turn actually work in favor of helping the car to turn, by creating a 'pseudo' 4-wheel steering effect? ...where on compression from static equilibrium (when going straight, no bumps) the outside rear tire toes out and on suspension lift from equilibrium the inside rear tire toes in?

Also, with the two sets of speedybenz adjustable arms, one used for camber arms and the other for the lower-link arm, I'm able to adjust toe and camber very well; running per speedybenz specs of 1/8" total toe in the rear and 1/16" total toe in the front. This 'little' benz turns very nicely. The thing that keeps me somewhat thentative then I'd like is definitely the 225mm rubber up front.

Sorry but I've been away rewiring an electron beam welder (believe it or not). As for the front ... as long as you have grip on both tires, the torsion around the steering axes cancel each other out. The primary concern is perhaps braking during wet conditions, especially with ABS. Normally manufacturers design the tire WITH grip to naturally turn towards the center to conteract the lack of traction on the other side (before ABS, normally it was setup the opposite). With large front tires, this force CAN be large an overwhelming. Just check that you steering axis crosses through you contact patch at a similar distance to center as the stock setup.

As for the rear, variable toe-in is not really about 4 wheel steering. All things deflect under load. During braking and cornering, what you don't want are you rear suspension bushings to allow deflection such that you rears are toeing OUT. The multilink rears are based on the Weissach suspension pioneered on the 928 where the forces generated by your tires actually cause a small amount of toe-in, thus increasing stability a the rear end (the basis for your vehicles stability).

All I'm suggesting is that you should REALLY put you car through torture tests that involve limited traction braking and cornering and note how the car's behavior has changed since the stock setup. It's quite easy making a car grip with lots of rubber and good conditions. If that's all you were looking for you should have just bought a Corvette (just kidding). It's another matter entirely to create a car with stability (it's ability to maintain and recover from conditions not inteded by the driver).

I noticed you were interested in actually educating yourself, so I'm just throwing out some ideas for you to consider.