I just purchased some Ruff racing wheels for my 06 350Z Roadster... Front 18/8.5 225/45 falcons back 18/9.5 245/45 Goodyear. I understand that I am going an inch wider than factory for front and back while keeping the size of the tires consistant with previous factory setup. If anything I figured that the tires would stretch out a little and give a little more solid grip. I went for a test drive today with my "fatass" new wheels. They are gorgeous. Couldn't pick a better looking wheel... don't care what planet you're from. Anyway, got on a back country road and started winding the RPM's and my car was dipping and bouncing all over the road. I don't understand what the problem is. I also had the shop I bought the tires from do an allignment to make sure everything was okay. I don't know what happened? The factory cornering on rails is gone. What happened??

larger heavier wheels take more power to turn, wider wheels make caster gain more noticable, larger diamter wheels with lower sidewalls offer less deflection, tire compounds and tread designs will determine your ultimate slip angle, not every falken or good year tire offers decent tration, it's generally a trade off, longlife and wet grip or dry traction and a short life

handeling on rails is an overused statement, a train is on rails and does not corner well, many peoole make the mistake of running too large of wheels, you need a certain amount of sidewall for deflection and roll, wwithout it you will slide or skip, many people do not think aobut it but the tires si the first part of your suspension, they flex and absorp some of the impact and trasition before ti gets to the mechanical parts of the suspension

Ruff Racing wheels are made by the same company that makes Nakayama wheels. I'm not trying to judge, but chances are the materials and manufacturing processes used aren't likely to produce the lightweight designs of higher quality wheels. Hard to say for certain as I don't see weights listed on their site, but from my own observations, manufacturers that build wheels with more reasonable to lighter weights tend to post the weights.

That said, based on what you are stating, it sounds like they are quite a bit heavier. Heavier wheels have more mass and therefore when they hit bumps, there will be more force applied against the suspension. If the spring and shock rates are not able to absorb this force adequately, the force gets transmitted to the chassis very quickly if the suspension goes to the bumpstops or allows a lot of excess wheel movement which could cause the wheel to momentarily lose contact with the ground (or just lose too much contact such that grips is lowered at the contact patch). Chances are the solution is to either get lighter wheels or change the spring and/or shocks to something that can handle the additional force. Frankly, lighter wheels would be the better choice as it would reduce both the unsprung mass and rotating mass. Not to mention the overall mass.

Also, if I read your post correctly, you're mixing tires (F: Falcons, R: Goodyear) ... even though the stock tires aren't the stickiest things on the market, I'm pretty sure you stepped down in tire performance, when you added the heavier wheels.

Well... I guess I am 1500.00 dols too late. I saw mentioned that some changing in the shocks may make a difference. I am pretty much stuck with these tires for a few thousand miles... and I like the wheels. So... I am wondering what the best adjustment is from here. If there is a change I can make with the shocks/suspension... ??What would be recommended to best benifit current and future suspension goals??

EROCK

EROCK777 wrote:Well... I guess I am 1500.00 dols too late. I saw mentioned that some changing in the shocks may make a difference. I am pretty much stuck with these tires for a few thousand miles... and I like the wheels. So... I am wondering what the best adjustment is from here. If there is a change I can make with the shocks/suspension... ??What would be recommended to best benifit current and future suspension goals??

EROCK

My assessment is really only speculation as it is a bit difficult to make such assessments over the internet. The first thing would be to confirm what the cause of the problems are. Then the solutions will make themselves more apparent.

As far as working with specific types of goals, we need to know what those goals are.

As for potential fixes, if you determine the wheels are heavier AND the cause of the handling problems, then the first component I'd look at is the shocks. Springs would be next, but most available springs or shock/spring combos are likely to sit your car lower. Not sure if that is something that is acceptable, not to mention what your budget is.

I'll mention that I can't be too specific about which products might be best as I have no experience with them on the 350Z. For options that are likely reasonably priced options I'd look towards adjustable (shock valving) units from Tokico, KYB, or Koni, if available.

Even if you just did struts (and not springs, too) you can adjust the rebound on Koni Yellows (single adjustable)

That should help the floating, particularly if you have 60K + miles on the car.

http://www.koni-na.com/cat_sea....y=10


Modified by HeavyDuty at 4:01 PM 9/14/2009

I recently swapped my rears out. I didn't change the fronts, the car felt all over the place. After 300-400 miles it got better. It wasn't back to stock since my fronts are worn, but it's way better than when I just got the tires installed. I hope your situation improves.

....at least you will drive a little bit slower, this way everyone can see your new wheels!

Hey... thanks for all of the imput from everyone. Sorry to drag this out.... but I think I found the problem. My wheels have the wrong offset. The ones on the back are 45 and on the front it is 35. Come to find out the wheels I bought off of craigs list (listed under 350z) are actually for a late model mustang.

Now my delima. Who has opinions on wheel spacers. Everyone I have been talking to in performance shops say sell em and don't go with the spacers. The wheels are half to an inch to far in on front and back. This allows the weight and force of the car more movement in bankiing.

I want to try them out because I really like the wheels. I just don't want it to be unsafe if I start cornering at 120 plus. Anyway... does anyone have any experience with spacers besides just an opinion.

And if an opinion, kul too. If the wheels are moved out about 20mm a piece the force will displace properly again. Or will it. Any imput on this would be helpful.

So the worst.... just have to sell the wheels and put the tires back on my factory wheels for now.

If you love the look and don't want to ditch it, spring for 4 decent tires (michelins come to mind). You would be back to square one with your handing.. tires make all the difference in the world.

This probaly ought to be moved to " technical"

EROCK777 wrote:Hey... thanks for all of the imput from everyone. Sorry to drag this out.... but I think I found the problem. My wheels have the wrong offset. The ones on the back are 45 and on the front it is 35. Come to find out the wheels I bought off of craigs list (listed under 350z) are actually for a late model mustang.

A 8.5 + 35 is a 1mm further out from stock, which isn't much. The rear is further out 1mm as well with the 9.5 +45.

Stock for the front 8 + 30 and the rear is 8.5 + 33. You do you less inner clearance but nothing that should effect your handling like you say. The difference that you see front to rear is due to the different widths your wheels have. As you see its the same idea from the factory.


Aaron