What size RE-71R is best for 16" wheels?

Discussion in 'Fiesta ST Autocross' started by AlanBDahl, Jul 3, 2015.

  1. AlanBDahl

    AlanBDahl Active Member

    I've decided to switch to the RE-71R for the upcoming Packwood NT as my Dunlops are getting a little long in the tooth. Unfortunately the specs on the Tire Rack site don't appear to be particularly accurate for the RE-71R. Which would be closest to the 225/45-16 size I run in the Dunlops? I want as much width as possible without running a risk of hitting the fenders. Any suggestions?
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  3. 205/50R16 : exact same width as the 225/45R16 (as posted multiple times before here ;) ), does NOT hit anything, and slightly taller (better gearing).
    Mightymango and Mr UFO like this.
  4. Mightymango

    Mightymango Active Member

    ^^^ This
  5. Izzy

    Izzy Member

    Yeah...but would they fit with Mountune springs?
  6. No idea...
  7. Izzy

    Izzy Member

    Do you think there's enough clearance for a 1in. drop and still no rubbing?
  8. Maybe. Only way to know is to try it...
  9. Phreak

    Phreak Guest

    So there are actually 2 sizes you can run for RE-71R's on 16" rims.... the 205/45R16 and the 205/50R16. I've run both on my car, and there are some pro's and cons to consider for both.

    Pro's for the 45 series were the lower center of gravity, the 2lb difference in each tire, and slightly quicker acceleration thanks to being shorter. I also found they slid easier than the 50 series coming around corners which helped with rotation sometimes, but can also lead to an increased risk of spinning if you upset the car. The lighter weight and smaller diameter really make the car feel light on it's feet when you stomp the pedal.

    The major pro for the 50 series tires was the cheaper price, like 30% cheaper than the 45 series. They are also nearly a half inch wider, when I stacked my 45's and 50's beside each other, the 50's were a good 2" higher. Not surprisingly I found they had better grip on hard corners (sidewall would also flex more and bite in rather than slide) and the taller tire gave me a slightly higher top end in each gear.

    So really the 50 series was the clear winner for me. The cost savings and the fact they return better times is all I needed to convince me of that.

    For both tires, the optimal tire pressure was between 47 and 50 in the front, and 44 to 47 in the rear. This does vary a bit depending on the venue, weather, and course speed. But generally if I was diligent about bleeding off the air after each run and keeping it somewhere in that optimal range, I found a sweet spot for traction there. I also found that the rear pressures are way more critical than the front... if I went to high or too low, the back end gets very waggy.

    Finally, in terms of wear.... for tread I average around 85 runs. Rainy or cool days will extend that life a bit too. That includes flipping them front to back, and inside to outside. One good thing is they also bite right down to the cords, so after I retire them from competition days I continue to run then right to the cords on practice days. I get another 20 to 40 runs on them doing that.
    Common Platypus likes this.
  10. Mightymango

    Mightymango Active Member

    Interesting on the low number of runs you get out of a set. Ed and I both get between 120-150 on a set and that pressure is WAY too high.

    Last season I ran 38/42 for pressures, after running out at crows and further talking to people I dropped to 36/38...at least for the cooler temp events. I know I not going to over 38/40 this season, even if I run the car at lincoln this year.
  11. Phreak

    Phreak Guest

    Hey, thanks for the reply. I haven't had a chance to talk to anybody who has run the Fiesta in Autocross events. Glad I signed up here!

    I think the low run numbers might have something to do with one of our regular venues. It is a 60's airport with high grade concrete. The concrete surface there is notorious for shredding tires when compared to other venues like parking lots. I also find when I retire them, if I continue to run them right to the cords on practice days I can get another 20-40 runs on them. So that would be about 105~125 runs in total right down to the cords.

    This isn't the first time I've heard that about tire pressures, and I am not 100% sure what the reason is. I try to control the roll over of my tires with the triangle indicator on the tire. I also find if I let the rear get under about 44psi, I might as well be driving with caster wheels on the back. It gets so loose it is hard to keep under control and my times for those runs are as much as 2-3 seconds slower on a 60 second course.

    I am really curios about your setup, are you guys running any sway bars or shocks? Mine is all stock for the moment.

    Below is a photo of all four tires with 2 days on them so far. The first day I had a co-driver (who won the event), but it was pouring rain so I didn't see much wear. The second day I put 4 competition runs and maybe 4 fun runs on them. I was running 49~50psi in the front, and 46.5psi in the rear.





    It is close to the triangle, but does look like I am running them maybe 1-2 pounds too high.

    For my past tires, this is a sample what they look like near the end of their life running those pressures:


    Last edited by a moderator: May 23, 2016
  12. It has, well, been a while since I logged in :)

    Tire Pressures : I'll note Crows Landing is rougher on tires (VERY abrasive concrete) than anywhere else I've run. That includes Lincoln. Our other "main" local site is Marina CA airport...also concrete but a lot easier on tires.

    That said, try the lower pressures. I've experimented around a bit, and keep coming back to 35-36 in front and 37-38 in back. You're giving up a good bit of contact patch at mid/high 40s (as shown by your sidewall wear above). Arrrows on sidewall : note all those REALLY indicate are where the tire tread depth indicators are radially ;) . So even if you run "past" them a tiny bit, that is OK.

    Setup : Off-The-Shelf Koni singles all around, Base Fiesta (22mm) bar up front. In other words, nothing exotic. I've tried 3 different front bars so far (stock, this, Eibach) and found this as the "between" one on size is the best compromise between transition (bigger is better) and power out of corners (stock is better than the other 2). Also (very) briefly ran the stock front bar with the Eibach rear...yeah, don't do that. All it did was make it dog-leg worse :)

    Also played around some with 17s. I don't think it makes a huge difference on the clock either way, but the 17s do (as expected) feel crisper. True for both 205/45R17 and 215/45R17. Took a few runs with 245/40R17s...yeah, don't do that (mushy response city, and rubbed badly) :D . Nationals setup last year was 215/45R17 front and 205/50R16 rear, I expect to go on all 17s this year with 205/45R17 rear and "figure it out" between the 205 and 215s on the front.

    One other note on RE71R wear...I do pretty religiously rotate them and flip them (+1 for co-owning a tire mounting machine :D ) . What I'm finding is that while LATERAL grip is good pretty much to the cords, LONGITUDINAL grip (more noticable in acceleration, but some in braking) does appear to "go off" after a while. I'm not sure I'd give an exact run number they go off, but in the 50-75 run range sounds reasonably close. Lincoln plan is to get a set on the car a few weeks before, run a weekend out here at Crows to scrub them in, then take those to Lincoln.
  13. Phreak

    Phreak Guest

    Yeah a tire mounting and rotation machine would be awesome, so much money going towards that right now

    I swapped in some rear Koni's on my car last week, and then did a test & tune with it on the weekend. Great results, I ended up taking 1st place in pax, beating out the nearest competitor by 1.2 pax seconds (which never happens btw).

    For pressures, I started high and then dropped them 2psi for each run and noted the results. My ideal operating pressures ended up being 44psi in the front, and 39psi in the rear. I got way cooler running temperatures and there was a noticeable increase in traction. This venue however was not that high speed and in a paved lot. I am going to play around with pressures this upcoming weekend at race school (doing the Solo Pro school) which is at our airport venue.
    Impala SS AutocroSSer likes this.
  14. AlanBDahl

    AlanBDahl Active Member

    Is the RE-71R still the tire for the ST or are there better choices now?
  15. Still the best one. I suspect the Kumho V720 is close if you are sticking with 17s, but limited (for us) to just the 215/45R17 size. There have also been delamination issues on this tire with SOME cars/setups...not sure if we'd be one of the problem setups or not. I have my theories on it after talking extensively with a few folks...
  16. Nice results!

    I'd still urge you to try the mid/hi 30s range up front. I think it'll give up a little in response "feel" but be quicker.

    Put it this way, if I were looking for more time AND didn't care about tire lifetime, I'd go DOWN from my current front pressure settings!
  17. Phreak

    Phreak Guest

    Well it never hurts to try! Thanks for the advice!

    It has been a while since I've run them, but the thing I don't like about Kumho's is they perform awesome for the first one or two events, and then get really greasy. I don't know if they are still like that, but I just have never been that happy with them in the past.

    I'd say they are the most competitive tire right now for sure.

    The Dunlop Star Specs are also pretty good, they would be my pick for runner up. They last about twice as long and are way more livable on highways than the Bridgestones and also tend to have a crisper feel to them.
  18. peter3

    peter3 New Member

    Go to rnrwheels, their highly skilled staff will custom fit your wheels for a really smooth ride. Prices are really affordable and you can make your own payment plan, so there’s no need to delay!

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