Really considering downsizing to 17s from my current 18s.

I have ohlins DFV and find them a bit stiff / jarring over road imperfections. Very good on smooth roads. But the car has always felt that way regardless of suspension (always had these wheels)

With aggressive driving it "skips" around over cracks and small bumps which are all over the roads I drive on regularly. This makes the car feel unsettled and uncomfortable, the interior bangs and rattles a lot, especially in the back.

Have Pilot super sport tires, Ohlins DFV with 13k f and 9k r swift springs

Looking for feedback from people that have done the switch either way and their impressions on ride quality and handling.

 

That is odd, my Ohlins are *remarkably* smooove over any bumps or road imperfections. Almost magically so. What do you have the dampers set to, i.e., how many clicks out?

I'm running 13 kg front and 11 kg rear springs, and on the street I usually run 8 clicks out from full stiff. At the track, ~4-6 clicks out up front, 6-8 clicks in back.

Before I got the Ohlins I was ready to get rid of the car because of the jarring ride over potholes/etc. on the street with the Tein SS 9F/7R setup that was on the car. DFV's transformed the car's ride and handling. I've said it before and I'll say it again, with the Ohlins it's like riding on a gott-dam cloud.

At the track, I am able to keep my foot planted over pretty big curbing without upsetting the car.

FWIW I've run them with Pilot Super Sport, Nitto NT01, and B'Stone RE71R tires and the ride has been great with any of those.

Currently I'm on 235/40-17 front, 275/35-18 rear NT01s for street and track.

To tell the truth, my Pilot Super Sports were initially fine, but gave up all grip after 18 months to two years old and became *extremely* sketchy. I've never experienced such a loss of grip with age with street or track tires.

 

Thats great data ZDan,

I have my fronts 4 from full stiff, rears 5 from full stiff (seemed to ride better with it stiffer vs full soft and certainly handles better)

Car is a bit heavier than your standard rx7, 700hp 1jz up front, tr6060 six speed, braced stock diff

I have 94 rear sway bar and racing beat front bar

245s up front, 265s in the back on 18" SSR Intergals

All stock control arms (new pillow ***** going in this weekend, but I can't feel any looseness in them currently so doubting they are bad)

 

Pretty simple. If the car is too stiff, and "skipping" around you need softer springs and turn down the damping. What you are describing will not be fixed with more sidewall. Drop the front spring rate 100 - 150 lbs or 2-3k. If the back is bad too drop the rear rate 50 lbs or 1k, but start at the front first.

And Pilot Super Sports suck. They belong on a 300 HP BMW, not a 700 HP sports car... just saying.

 

My experience is that tires can result in this problem of "skipping" or "scrabbling" over rough pavement/small bumps.

On my stock base Mazda3 I went from stock 15" steelies and 195/65-15 to stock FD 16x8 w/ 205/50-16 Dunlop Direzza DZ101 (non Star Spec). Much lighter set-up.

The DZ101 sidewall and stock suspension frequency DID NOT JIVE.

I loved the turn in and grip on smooth pavement, but even just rough granulated pavement resulted in skipping/scrabbling with terrible traction.

I went back to the steelies with some $50 China tires and car is back to driving like a kitten over the rough stuff.

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You may be experiencing a similar problem.

Another 18" tire may significantly help. A 17" wheel/tire swap might help.

But... 17s only really go as wide as 255 for street tires/street-able race tires which is a downside for most.

255/40-17 all around wouldn't be bad for you though compared to what you have now.
Less understeer from a wider front tire and straight line traction is much more a function of tire construction than tire width as far as rear traction is concerned.

I also agree those Pilot Super Sports suck compared to a performance tire and the sidewall set-up for Euro barges probably isn't helping.

 

Another thing to think about is tire availability. I run 17x10 wheels and there really aren't that many choices for a tire wider than 245. There would be tons more options for me if I had 18s.

 

255/40/17s all over the place that will work.. Then you go to 275/40/17 which is a bit taller.

 

You have 17x10s too or did you just look it up on the internet? Put a set in your cart and try to actually buy them. You'll see what happens.

 

Should be able to get R1R, NT05, NT555R, R888, NT01 and RA1 in 275/40-17.

I forgot about that size though I used to run it.

Can't run it up front on an FD- too tall. Will work for rear.

 

a 13KG front and 9KG rear isn't a flat ride, that is probably one of your largest problems.

try a closer spring rate split.

11/9 or 10/9 and it will probably fix your issues.

 

I don't think 13/9 spring rate split is an issue.

It is the *wheel rate* that is important, and for a ~50/50 rwd sports car with a ton of power, you probably ultimately want front-biased wheel rates.

Given the FD's motion ratios (~0.61 front, ~0.69 rear) 13F/9R spring rates gives these wheel rates:
F = 13 x 0.61^2 = 4.84 kg/mm
R = 9 x 0.69^2 = 4.28 kg/mm

That's 53%F/47%R wheel rate bias.

I don't think you'd find a modern similar power/weight FR sports car with a more rearward wheel rate bias.

 

??

I run 275/35/17s on 17X10.5s or 255/40/17 on 17X9.5s

I can buy plenty of 255/40/17s today if I needed them.