Suspension Recommendation ~$2,500

[TheLion]

So, last night I pulled onto a certain stretch of back road just shortly after getting off the highway with two slightly banked arching curves and a 1/4 mile stretch nestled between them. Nice little patch of "back country road race". No driveways or anything around them to pose danger. There was an Audi RS5 behind me. At first I thought it was a regular S5, so I punched it and he was right on my tail the entire time (after pulling up behind him at a stop sign much further down the road I realized it had a red RS5 badge on the back).

He never pulled on my GT's bumper, but never fell back either. So either he was limiting throttle or more likely (based on power to weight ratios, gearing and curb weights) I believe we where neck and neck in straight line acceleration. I kept on it through the first arc and slightly into the straight and hit the top of 3rd gear at 93 mph then just let the car slow down after bouncing off the rev limiter.

I didn't have confidence to continue pushing on the P Zeros into 4th gear. The Zeros are numb. They lack quite a bit of lateral grip that even my Pilot Sport AS3+ All Seasons have in corners and they don't really communicate what's going on between the car and road. They almost "glide" or "float" over the road. Ford chose these tires for their ride quality attributes, not their performance.

I've not liked them since switching out my worn out Pilot Sport AS3+'s on RTR Tech 7's for the stock PP wheels and P Zeros. They are more or less a summer grand touring tire in my opinion, but the rears were brand new and fronts had 3/4 of their tread still on them so I figured it was a waste not to burn them up. But I digress.

After I slowed to 80 mph the RS5 pulled out and around me and blew by and entered the second corner with surprising speed. He did get a little unsettled and I saw the tail lights come on, but he was going a good 10~15 mph better than I felt comfortable managing on the same turn (these are wide arching turns you can manage 80~90 mph on). He may have been a seasoned driver or just some idiot pushing the limits while relying on all the RS5's advanced electronic controls and hoping for the best so he can brag about beating mustang in a 1/2 mile quasi road / drag race that costs less than 1/2 of his RS5, but either way, it wasn't' worth getting in a wreck over, so I let off and let him go by.

I was impressed at the corner speed he managed however. Well above what I felt confident in. So out of curiosity I looked up the 2018 RS5 specs to see what it had. I figured it was pricey, fast and handled well. What surprised me though was that the RS5 weighs a whopping 300 lbs more, but it also has one heck of a suspension and he may have very well been a more experienced driver. Who knows.

I didn't feel confident in pushing the car in corners at higher speeds on these P Zeros and with my driving skills, so I'm definitely looking forward to starting HPDE sessions next summer to get some experience at higher speeds on a track and instruction as well as getting a decent set of track / street tires that allow me to exploit much more of the handling capabilities of the car as is. Right now it's very limited by my driving and tires. Maybe they called them P Zeros because that's about how well they grip the road....? But they do ride like a nice set of touring tires, so for daily I like them. For anything performance oriented (corner carving) I don't have confidence in them.

2018 Audi RS5 - Starting at $69,900 with a fully optioned variant topping out at around $85,000.

4050 lbs Curb Weight
2.9L TT V6 (Water to Air inter cooled)
444 hp at 6,700 RPM
443 ft-lb at 1,900 RPM (note with those torque and RPM numbers so far apart in the rev range, I'm betting this TT V6 has a REALLY broad power band, much broader than my 5.0's even if it makes 20 hp less peak)
8-Speed Auto with Electronic Paddle Shift
Active Suspension
Torque Vectoring AWD including front to rear biasing (about as good as you can get)
1/4 mile on C&D: 12.4

Power to Weight Ratio: 9.12 lbs / hp
My Power Pack 2 PP GT sit's at 8.1 lbs / hp

Obviously his broader power band and 8 speed auto more than makes up for the lower peak power output. But added weight keeps it's straight line performance about on par with a Power Pack 2 5.0, so it's all about handling, applying the available power (big advantage with the RS5's very advanced AWD system) and driver skill if these two cars ever match up again. But us lowly GT owners would have by far the most work cut out for us as the RS5's quite effective electronics package and AWD system is hard to compete against. It's an impressive car, but I think a very skilled GT driver with a good suspension could match it.

https://www.caranddriver.com/reviews/2018-audi-rs5-first-drive-review

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[Eritas]

I'm really happy with my Continental extremecontact Sport tires. They ride better than the factory pzeros, have A LOT more wet grip, more dry grip, and overall are a far better tire. The only tire that's slightly better is the PS4S but it costs a lot more.

 

[TheLion]

Yah the P Zeros do not inspire confidence. Ford absolutely chose this tire for it's ride quality and noise characteristics. Lateral acceleration was an abysmal 0.85 g dry compared to the PS4S's 0.92 g. And the Continentals's achieved nearly the same cornering g force in the wet as the P Zero's did in the dry. Cornering stability was quite low on the Zero's compared to other top tier tires in that category on the Tire Rack tests. The RS5 would be running something pretty sticky, might even be running an "Ultra High Performance Tire" like the Sport Cup 2's.

I think there's a very substantial amount of handling I can exploit once I get a decent set of tires on it in a 4-square setup. I've been tempted to throw my nearly balled AS3's back on at times lol. But I don't want to waste the P Zeros, there's nothing wrong with them functionally, they just don't really have that great of handling characteristics. I even recall Ford Performance telling me at one point my tire sucked when I had asked a suspension question and they asked what tires I was running.

But I'm pretty dead set on PS4S's. Yes they are pricey and the Conti's are markedly cheaper, but I've never regretted buying a top tier product (other than the fact that I paid top dollar), but I've in many instances regretted buying the lower cost options. Same with the GT. I originally started with an Ecoboost even though I wanted a GT. I should have waited and just bought the GT from the get go.

Sure, the PP GT is lacking out of the box, it's not a bad car, but it's got some quirks / conservative aspects that are hidden. Power wise, Power Pack 2 really brings out the 2nd gen 5.0's potential without major modifications. It's more or less a CAI, throttle body and good tune.

For handling, it's a good set of springs, toe link bearings and cradle lockout with some tires. Those 4 things really change the nature of the car without getting a little more involved with a full set of new struts, springs and sway bars (which obviously can very substantially increase the handling capabilities, but I'm talking starting out on the cheap).

Throw in a short throw shifter and some BG SyncroShiftII fluid in the MT-82 to smooth it out and the car is a solid performer at it's price point and can compete against some higher tier German cars in outright performance. With a full suspension re-work I don't see why it wouldn't compete against something more than double it's cost like the RS5 I mentioned above. Power is there and I believe the chassis will also support that. The GT350R certainly was faster on the track than any RS5, but the RS5 out did a stock PP GT.

But none of the suspension work or power will really be usable without some really good tires to put it to the pavement. Tires are EVERYTHING in handling.

 

[BmacIL]

@TheLion tires certainly are everything. Try your car with some RE71Rs...

 

[TheLion]

I would, but I can't justify putting tires on for a mostly street car that I'll get maybe 5k to 7k miles out of. But yes, they stick like glue and I'll bet I could have maintained a similar corner speed to that RS5 if I was running a set of RE71R's. A co worker runs an S2000 in Auto x with them and he said there's just nothing quite as sticky that's road legal and their grip level just just in a league of it's own even compared to Max Performance Summer tires like the Pilot Sport 4S's. However it is my understanding they don't do well in HPDE due to being too soft. They are better suited to situations where you need extreme performance for a short time frame, like a quick back road run or Auto x run that 30 seconds to a minute or two.

 

[TheLion]

Front to Rear spring rate ratio of SP080's: 0.229

Front to rear spring rate ratio of SP073's: 0.255

So the SP083's have more front anti-roll biasing due to the fronts being stiffer proportionally relative to the rear. SP080's would probably see even greater benefit from running a 34 mm front bar than SP083's. The car's moderate (intermediate) under-steer doesn't seem to have changed much with the SP080's / PP sway-bar combination and I wouldn't expect it to.

Sure, being a tad stiffer and a tad lower will reduce roll, but not much. But their linearity does seem better, I think that's due to higher quality spring material / process than OE. The PP bounce seems to have disappeared with the SP080's despite a similar rate. I'm guessing the factory PP spring rates were near a region of oscillation with the stock PP dampers. That would give them good dynamic response for very bumpy street roads, but might make them choppy and less stable on smoother higher speed roads.

I'm thinking a 34 mm front bar and 22.2 mm rear bar might be good even with the SP080's and PP struts until I'm ready to move up to the SP083's and FP Track Dampers as the SP080's have less inherent ant-roll relative to the rears when compared to the SP083's.

I think your right in that the car would be the easiest to drive if it has mild under-steer. Moderate > Mild on my scale. Mild is just barely where Moderate is more like intermediate. The stock 1SS exhibits mild under-steer as opposed to moderate of the PP GT, so the PP GT definitely under-steers more than the 1SS and I think it's a bit much stock. It is my guess they are trying to keep the track gap between a PP GT and a GT350 large enough to justify the cost of the GT350. Something Chevy completely screwed up with the new Camaro SS. Sure, the Vette is still the track champ, but the time gap is quite a bit smaller and it's a lot harder to justify the Corvette Grand Sport at it's price point over a SS 1LE that has much greater practicality.

@BmacIL, what are your thoughts on SP080's with a 34 mm front bar? I have a PP GT, so my rear bar should be 22.2mm or the same as the regular GT350. Struts are stock PP struts for now, I'll probably use them for a year or two before replacing them and get some experience, but I'm thinking what I have now + 34 mm front bar and some tires would be a really good starting setup to learn on and fairly easy to drive.

Also take into account that my performance wheel / tire setup will be a 4 square setup. Right now I'm running staggered PP stock wheels on stock P Zeros. My RTR Tech 7's (19x9.5) have an old set of Pilot Sport AS3+'s on them that are about shot, so I'm not using them right now but I will replace those tires with Pilot Sport 4S's. That will be my summer / HPDE setup.

Doesn't running wider front tire reduce under-steer typically? I'm wondering if adding bar and 275's up front would be too much or if it would still have mild under-steer.

 

[BmacIL]

Front to Rear spring rate ratio of SP080's: 0.229

Front to rear spring rate ratio of SP073's: 0.255

So the SP073's have more front anti-roll biasing due to the fronts being stiffer proportionally relative to the rear. SP080's would probably see even greater benefit from running a 34 mm front bar than SP073's. The car's moderate (intermediate) under-steer doesn't seem to have changed much with the SP080's / PP sway-bar combination and I wouldn't expect it to.

Sure, being a tad stiffer and a tad lower will reduce roll, but not much. But their linearity does seem better, I think that's due to higher quality spring material / process than OE. The PP bounce seems to have disappeared with the SP080's despite a similar rate. I'm guessing the factory PP spring rates were near a region of oscillation with the stock PP dampers. That would give them good dynamic response for very bumpy street roads, but might make them choppy and less stable on smoother higher speed roads.

I'm thinking a 34 mm front bar and 22.2 mm rear bar might be good even with the SP080's and PP struts until I'm ready to move up to the SP073's and FP Track Dampers as the SP080's have less inherent ant-roll relative to the rears when compared to the SP073's.

I think your right in that the car would be the easiest to drive if it has mild under-steer. Moderate > Mild on my scale. Mild is just barely where Moderate is more like intermediate. The stock 1SS exhibits mild under-steer as opposed to moderate of the PP GT, so the PP GT definitely under-steers more than the 1SS and I think it's a bit much stock. It is my guess they are trying to keep the track gap between a PP GT and a GT350 large enough to justify the cost of the GT350. Something Chevy completely screwed up with the new Camaro SS. Sure, the Vette is still the track champ, but the time gap is quite a bit smaller and it's a lot harder to justify the Corvette Grand Sport at it's price point over a SS 1LE that has much greater practicality.

@BmacIL, what are your thoughts on SP080's with a 34 mm front bar? I have a PP GT, so my rear bar should be 22.2mm or the same as the regular GT350. Struts are stock PP struts for now, I'll probably use them for a year or two before replacing them and get some experience, but I'm thinking what I have now + 34 mm front bar and some tires would be a really good starting setup to learn on and fairly easy to drive.

Also take into account that my performance wheel / tire setup will be a 4 square setup. Right now I'm running staggered PP stock wheels on stock P Zeros. My RTR Tech 7's (19x9.5) have an old set of Pilot Sport AS3+'s on them that are about shot, so I'm not using them right now but I will replace those tires with Pilot Sport 4S's. That will be my summer / HPDE setup.

Doesn't running wider front tire reduce under-steer typically? I'm wondering if adding bar and 275's up front would be too much or if it would still have mild under-steer.

I think it'd work well. The stiffness balance from the springs F/R is very similar so the balance will work well, and the front is nowhere near as sensitive to stiffness changes in terms of ride.

Check this out:
https://www.mustang6g.com/forums/th...s-all-in-one-thread.44925/page-8#post-1637308

 

[TheLion]

I may just have to give it a try then. In fact I'm almost wondering if I should order both GT350R fronts and rears just to have tuning options. Since I have a PP GT I already have a 22.2mm rear. The factory GT350 bars are pretty darn cheap.

I don't think i'd need to add more rear bar, but I guess I wont' know 100% until I give the front a little more bar first and see if that slight increase is enough to remove some but not all of the under steer, especially once my 4 square tire setup goes back on next summer.

 

[Bull Run]

I didn't have confidence to continue pushing on the P Zeros into 4th gear. The Zeros are numb. They lack quite a bit of lateral grip that even my Pilot Sport AS3+ All Seasons have in corners and they don't really communicate what's going on between the car and road. They almost "glide" or "float" over the road. Ford chose these tires for their ride quality attributes, not their performance.

I think that you did very well considering that you were on those crappy P Zeros. I have serious traction issues accelerating with them from stop, slow roll, or turns even when I only had an intercooler and tune upgrades, so it's probably much worse on a GT.

 

[TheLion]

Agreed, they are far from what I would expect a Max Performance Summer tire to be. Mine may even be worse, I traded in my EB in December for the GT and had to drive home on the P Zeros in 20F weather....it was a very "white knuckle" experience, thankfully there was no snow, just a lot of salt on the roads. I took on ramps at 30 mph with flashers on lol. Car had 5,600 miles on it. So once I got home I swapped the PP Wheels / P Zeros out for my RTR Tech 7's with Pilot Sport AS3+'s as at least those were rated for cold weather use. Then put the P Zeros back on once it warmed up so I could burn them up this summer. Not sure if the cold temps damaged the compounds at all, but no cracking or anything like that so I"m guessing this is just how they are.

They do ride nice and smooth though. Problem is they give little feedback, it's almost like a touring tire with a stiffer side wall. They almost "glide" over bumps and "hide" them instead of transmitting some feedback. This is due to the structure of the tire and it's my guess that's their focus. It's almost like a summer "performance touring tire". Enough traction so you can have some fun with them, but their trying also give you a good ride quality.

I can see what Ford chose them as a base line summer tire as their focus is more on ride quality than grip / driver feed back. The Pilot Sport 4S's will be nice to have next summer to replace the worn out AS3+'s. I'll be throwing on some Geforce Comp 2 AS's on the PP wheels for winter as I no longer do much driving in the snow in the GT and they are enough to handle light snow / cold weather with some care. My other car has Ice X 3's on it for snow so that my daily / bad weather car.

I hear the Pilot Sport 4S's ride nice, but also provide exceptional grip with good linear response and feedback. I've heard the 2018's are much "tighter handling" than the 2015-2017 GT's of the same trim. Yet Ford didn't change the basic suspension setups. Still the same. But they now come on Pilot Sport 4S's...it's an awesome street / light track tire.

 

[3er]

I hear the Pilot Sport 4S's ride nice, but also provide exceptional grip with good linear response and feedback. I've heard the 2018's are much "tighter handling" than the 2015-2017 GT's of the same trim. Yet Ford didn't change the basic suspension setups. Still the same. But they now come on Pilot Sport 4S's...it's an awesome street / light track tire.

For a daily-friendly (treadwear, rain compliance, etc.), performance-oriented (grip for days, communicative, etc.) street tire, it doesn't get better than PS4S'. Michelin really owns in this space. My car isn't a daily and won't see as many miles, so I'll likely go with PSC2's when I upgrade my wheels, which offer another level of grip when warm (not so great in the wet). IMO, don't even bother with other options.

 

[NightmareMoon]

IDK you should be able to get about 10k miles out of a set of RE71Rs if you run them primarily on the street. The only downside of them being a little soft for track use is that they will wear a little fast if that's all you're using them for, but if you heat cycle them driving on the street, that helps their longevity. I ran a set for a few months on the street and have kept wear records for my last 4 sets of RE71Rs (I'm on set #5). I've never driven on a tire that communicates as well and is as forgiving to drive as the RE71R, its pretty cool.

MP4S are a great choice tho. On grippy road surfaces they're quite good when heated up for spirited back roads driving. Usually that kind of driving won't overheat them. At the track its another story.

 

[BmacIL]

IDK you should be able to get about 10k miles out of a set of RE71Rs if you run them primarily on the street. The only downside of them being a little soft for track use is that they will wear a little fast if that's all you're using them for, but if you heat cycle them driving on the street, that helps their longevity. I ran a set for a few months on the street and have kept wear records for my last 4 sets of RE71Rs (I'm on set #5). I've never driven on a tire that communicates as well and is as forgiving to drive as the RE71R, its pretty cool.

MP4S are a great choice tho. On grippy road surfaces they're quite good when heated up for spirited back roads driving. Usually that kind of driving won't overheat them. At the track its another story.

I have a little bit of a sad moment every time I take my RE71R-shod wheels off and put my regular street wheels on. The RE71Rs are so nice to drive. They are noisy AF though.

 

[Bluemustang]

@TheLion


Have you considered the Firestone Indy 500s? They’re a great street tire IMO. I’m on my 2nd set now. From what I’ve read the they have 95% the grip of the MPSS. I’d expect the Contis and MP4S to be a bigger step above but the Indys are a lot cheaper and the grip is very good IMO. Probably not what you’d want for the track but more than good enough for the street I’d say. Just a suggestion for you. They also work very well in the rain with good anti-hydroplaning properties.

 

[Eritas]

@TheLion


Have you considered the Firestone Indy 500s? They’re a great street tire IMO. I’m on my 2nd set now. From what I’ve read the they have 95% the grip of the MPSS. I’d expect the Contis and MP4S to be a bigger step above but the Indys are a lot cheaper and the grip is very good IMO. Probably not what you’d want for the track but more than good enough for the street I’d say. Just a suggestion for you. They also work very well in the rain with good anti-hydroplaning properties.

500s are not that much cheaper than Conti Sports, and they SUCK in the rain. All 3 are pretty similar in the dry, but it's hugely erroneous to say they are even remotely close to a PSS in the wet, let alone a Conti Sport or PS4S.

BmacIL - 71s are great on autox or in cold weather, but on hot tracks, in 90* weather, they don't hold up very well.

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