Rear End Sensitivity After Rear Tire Size Change

[jmp]

I had 215-40-17s on the front on 17x7.5 & 255-40-18's on 18x9.5's in the rear.

I replaced the rears today from 255-40-18 to 285-35-18's. The ride height difference is about 8/10ths which from what I had read should make the relative ride height of front to rear more proportional with what the NSX originally had on its 15/16 setup.

Here is the problem: I drove the vehicle home and noticed that from about 75 or 80 mph and up, the rear end became very light, sensitive and caused me to have little confidence in the car. Every time I would steer even mildly it felt like the car was about to spin and lose its rear end.

Four possibilities come to mind: (a) the change in relative front to rear height has created less downforce on the rear wing, (b) the weight transfer is causing a lighter and more sensitive rear, (d) something whacky is going on with the traction control, or (d) the tire tread depth needs to be worn and broken in.

Can anyone shed light on what might be happening?

 

[RP-Motorsports]

oem 15" = 586mm tall
yours = 603.8mm tall
17.8mm taller (just under 3/4")

oem 16" = 631.4mm tall
your old rear = 661.2mm tall
your new rear = 656.7mm tall
25.3mm taller (1 inch)

Should be TCS friendly


The two rears that you used are almost identical. Your floating comes from 1 of 2, or a combination of both issues.

1) new tires are slippery, and you will feel floating for about 500 miles or so, until scrubbed in.

2) your toe may be out of wack, and the wider tires will pull a bit harder when the suspension unloads a bit in the transition over bumps.

Stay under 100mph until the rubber is scrubbed in, then slowly increase speeds, and see if it gets any better. You may want to go in for an alignment now anyway to rule that out.

 

[jalnjr]

your ass hurts????????



nice evaluation rp.

 

[RP-Motorsports]

your ass hurts????????



QUOTE]

I thought I was going to read this...
http://www.aftenposten.no/english/local/article1148570.ece

or
http://www.thepittsburghchannel.com/news/5235856/detail.html


or this
http://news.yahoo.com/s/ap/20051103/ap_on_fe_st/toilet_seat_lawsuit

 

[jalnjr]

those are some mighty big tires!!!! :biggrin:
always hurts using larger wheels[ not from my experience...]


welcome aboard jmp, not everyone's a s*ithead like me.

 

[Jin1976]

Incorrect tire pressure?

 

[jmp]

Thanks RP.

 

[NSX-Racer]

It would be interesting to know not only the size but also the brand and type of the tires.

 

[jmp]

Toyo Proxy's.

 

[Onsoku]

1. New Toyo T1-S's need 250-500 miles of freeway driving. I had the same issue on my C320 SS...felt like I had a flat tire during turn-in...after break in; they stuck like glue!
2. Also check your pressures. What worked for you before will not work for you now. My guess is that you most likely need to go no higher than 34-36 psi initially. Keep in mind, that you will lose some of that razor sharp response due to a slightly taller tire.
3. 285's on a 9.5 may be a little much for that wheel. No problem if you were running a 10.

.02

 

[RON98]

New tires. They are only wearing on the inside tread so your getting less surface area. Your old ones where probably all worn down so your where getting close to full tread contact due to the extra ware from the cambers.

It is normal. I rotorated my tires from left side to right side and my car does not feel as solid due to a decreased in tire surface area. No worries. Once they wear in, it'll be all back to normal.

 

[jmp]

Ron98 & Onsoku,

Thanks. That is what I am hoping. Also, the tire pressure was way overboard 50 lbs. I have lowered it and between that and the wear-in, I should be good to go.

 

[CarCrazed4Life]

I would say find another NSX owner, or a shop that might have used tires or even ebay.

But find 215/40/17s for the front, and 255/35/18s for the rear instead of 255/40/18s. Or 285/30/18s versus 285/35/18s... But RP knows better...

 

[garthed]

I just put Toyo T1-r's on the back and feel the same thing. I'll check presure tomorrow.

 

[RON98]

i got 285/30RZ/18 on the back and

225/30or35RZ/17 on the front. Before i did the rotation the car was planted no trouble's what so ever.

Good luck.

 

[Onsoku]

i got 285/30RZ/18 on the back and

225/30or35RZ/17 on the front. Before i did the rotation the car was planted no trouble's what so ever.

Good luck.

On your X? What size wheel and what brand tire?

 

[Greybloke]

I had the very same sensation, having put Dunlop's on the rear ( it's all I could get quickly) It was dangerous. So placed an order for 4 new Toyo Proxies which were put on today. Straight out of the fitters they felt better, although still not perfect. from comments above It seams they need to wear in a bit, but also pressure can effect matters also.

Checked mine and they were 40psi all round, which I've adjusted to 33 front and 38 rear which has improved the "feel" and stability, but can anyone suggest any alternatives ( I have non standard 17" fronts with 205 x 40, and 17" 235 x 40 rears)

JMP hope your's is now sorted.

 

[garthed]

38 psi in my rear and hope they feel better soon. Have about 100 miles on them.

 

[sjones]

my nsx had a similiar feel to it after put new tires on the rear with the same size 17" yokohama es100. i could really notice it when changing lanes on the highway. Almost as if i would turn the wheel and a split second later the rear would follow.... everything felt back normal after about 500 miles on the new tires.

 

[Greybloke]

Probably done about 250 miles on them now, and they do feel much better. However have encountered another problem........ TCS sometimes kicks in?????

Did not have this before with the same size tyres / wheels, surely it can't be so sensitive to the extra depth of tread? Any ideas ( other than turn it off )

 

[jmp]

I now have about 500 miles on my Toyos. A combination of excessive tire pressure (50 lbs), break-in and alignment have changed the rear end problem. The rear-end digs in now like it used to.

 

[NSXDreamer2]

I now have about 500 miles on my Toyos. A combination of excessive tire pressure (50 lbs), break-in and alignment have changed the rear end problem. The rear-end digs in now like it used to.

did you mean 50psi?? You didn't mean you are running 50psi to eliminate the problem, right? Whoever suggested you that should get a shot on his/her head. Be careful riding that kind of tire pressure when you have long distance trip... I also thinks that the 50psi will effectively decrease your tire's contact patches, thus a more sensitive butt.....

 

[NSXAU]

how timely is this thread .
...I also have just had new tires, rims and Eibach springs put on and my first comment about the car to AU_NSX [Mike] was that it felt 'tailey' in the rear..tires are new Falken ze326s all round, Racing Hart rims are 7.5x17 and 18x9, tires 215/40x17 and 275/35x18s...alignment/toe was done, next I will check air pressure as I am sure the shop has put 40psi all round, and do some miles on them... :smile:

 

[ERICKGS3]

I have had my tires on for some time, about 2500 miles on them and when im driving it hard, on a straight, i also feel as if the rear tires feel "loose" for a split second. Ive noticed it more and more. kinda scary...