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"Best 18 or 19 inch HPDE Tire for S197/S550 Mustang?"

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  • "Best 18 or 19 inch HPDE Tire for S197/S550 Mustang?"

    This was a reply I made on another forum when asked the question in the subject line. It was really hard to recommend the "best HPDE tire for 18 inch" when there are really a lot of other variables that the OP and others have thrown in:
    • The ability to daily drive AND do track days on the same tire (huge compromise)
    • The attractiveness of SUPER CHEAP pricing (for the "off" brands like Federal, Nexen, etc - which are cheap for a reason)
    • The ability to keep close to the stock tire diameter (which isn't a big deal, but some people get hung up on it.

    I stand by my previous recommendations: Right now the best "dual purpose" track and street tire options come from the Hankook RS-4 tire, and the RE-71R is the more dedicated street tire you can drive to the track on and GO FAST with, but is not really for daily driving. So to prove that I "practice what I preach" I have included our latest wide tire test - which we have done hundreds of times on our previous cars and customer cars...

    I bought a 2018 GT a few weeks ago and it came with 18x8" wheels and 235mm all seasons. Total crap. The 4 piston 14" brakes easily fit within an 18" wheel but we are moving to a 380mm brake (these S550 14" brakes aren't good), so that means we should only look at a 19" wheel....

    Our 11" wide wheel prices aren't much different in 18" vs 19", and because there are SO many more wide choices in 19", and we need the extra brake clearance, we went with a 19x11" wheel. We built them with offsets that allow them to bolt on without spacers, long wheel studs, etc. That seems to be a rarity right now, but we've been squeezing 11" wide wheels on Mustangs since our first set of Forgestars in 2012.

    For the track specific set tires we wanted to run a 305/30/19, which is 26.2" tall. As you can see it is shorter than the 27" tall stock tires, but that's not the end of the world. Width matters more... but going with a short 24.8" tall (285/30/18 size) or even a 25.5" tall (315/30/18 size) tire is a significant change. The car will .... look weird without lowering, and it will definitely lower ground clearance with either of those two 18" sizes.

    These S197 and S550 Mustangs are heavy cars and they need as much tire width as you can possibly fit under the fenders (and then some!) The 305mm tire will help deal with much of the added weight and heat generated in the tiny stock 235-255mm tires.

    As you can see these 11" wide wheels fit under the stock fenders with just camber on the S550 (S197 also needs adj panhard or watts). Its tight so you have to make every millimeter count.

    Our baseline lap was a 1:31 and change on the stock suspension and tires. I went back a week later and ran a 1:21 at the same track. It had a soft coilover setup and camber plates, but the majority of this TEN SECOND lap time drop was in the 305 Bridgestone RE-71R tires. Yes tires do make that much of a difference some times... this is why we preach GO WIDE when you upgrade.

    Now the bargain wheels are often only 10" wide and many times only 18". I get that - everyone has a budget - but if you are looking at lap times you cannot spend money in a more productive way than in getting the widest wheels and tires possible to fit your Mustang. And right now, for both the S197 and S550, there are more choices in 305/30R19. Don't take my word for it - look it up on TireRack.

    I have a set of 18x11" wheels on order to test a few other tires on this car, too. I will post up more about this in our S550 build thread - which is here on S197forum in our "Vorshlag" section. See my sig...

    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev

  • #2
    I am writing this update in September of 2022. By now you might know that we no longer market or sell wheels. It's a long story, but basically Forgestar / MW Wheels changed their business model and added a +$600 per set upcharge for the custom offsets and sizes we used to order, which made them impossible to sell in this market. But we still get questions about wheels all the time - because we created some of the earliest "wide fitments" for S197 and S550 Mustangs. Here are some tricks and tips to keep in mind for the S550 chassis.


    315 Hoosiers - especially the taller 19" versions - are a challenge to fit to the S550 chassis (2015-2023 models) under the factory fenders. Strangely the earlier S197 chassis has more tire room for Hoosier 315s than the S550, but it's a completely different chassis.

    The image above shows a 315/30R19 on our 19x11" wheels (with 5mm spacers) and they are not exactly "flush" with the fenders. They needed a little extra to clear the inside of the chassis. And if given a choice we would always choose the less costly, shorter, and easier to fit 315/30R18 Hoosier over the 19" version. Let's dig into the why and how...

    It comes down to the fact that not all "315" mm tires are the same width, and a 305mm tire really fits the stock fenders better (the GT350-GT500 have wider fenders, of course). Above is in image of our 19x11" S550 wheel (which has different offsets front to rear) with a 305/30R19 Bridgestone RE-71R. That 305mm street tire fits beautifully (without spacers - using two different wheel offsets) underneath stock fenders, which you can clearly see.

    That 305/30R19 size is the tire we built our 19x11s around but some of our competitors sold wheels back then (and still do) that have "poke" - more outboard offset that allows the tires to poke past the fenders. They simply use the wrong offsets, and we cannot explain why...

    If you go back and read our Forum Build Thread on this car you will notice most of the time we ran Hoosiers on this car we did so on these 18x11" Momo Heritage 6 wheels and used a 315/30R18 sized tire.

    We picked that 18" version of the Hoosier 315 because of several reasons. First, it was less costly than the 19" version - the prices above are from 2018 and have of course gone up, but that differences is still there. Second, the 18" wheel and tire weigh less than the 19" versions. Finally, the 18" version of the same 315mm Hoosier has a shorter overall tire diameter than the 19" version. That made it easier to fit under stock fenders, especially with a tiny bit of poke (from the 5mm spacers). We also show the 305/30R19 Bridgestone RE-71R above. Not only was that tire less costly than either Hoosier, with careful suspension choices we managed to get 7-9 weekends out of a set of these "200 treadwear" tires vs 2-4 weekends out of the Hoosiers. But they were 1-2 seconds a lap slower than the R7, too.

    In 2018 and 2019 NASA TT seasons we ran our 2018 Mustang GT on BOTH the 19" street tires and 18" Hoosiers, switching from street tires (on the 19x11s) on the Saturdays of NASA weekends to the Hoosiers on Sundays (on the 18x11s).

    We did this two tire swap to gather data for our own use as well as to share with NASA, in the (failed) hopes they would create a set of separate TT classes for 200TW tires. We definitely were NOT competitive in NASA TT on 200TW tires against our competition on Hoosiers!

    But early on in 2018 we only had the one set of 19x11" wheels, and we ran a handful of events on a 315/30R19 Hoosier A7 on these F14s, shown above.

    It was challenging and costly to swap from the street tires for Hoosiers on the same wheel set, so we only ran the Hoosiers on the 19" wheels for the one set of tires. After the got the 18x11 set we kept them for Hoosiers and went back to the 305/30R19 street tires on the 19x11s.

    Don't forget that swapping from 18" to 19" tires in the same width always changes tire height and circumference, which changes the effective rear gearing. Jason here at Vorshlag has a calculator he made to see these changes for every car we build. There are also great calculators online that you can find to plug in the tire heights to get your peak speed in each gear.


    There were a couple of tricks we used to make the very wide 315mm Hoosiers fit the S550 Mustang chassis.

    To make this VERY wide "315" fit with the taller 19" Hoosier version, we had to make some changes. Up front the wider Hoosiers rubbed the strut so we added a 5mm spacer up front. We also had to make sure to keep the strut-to-spindle junction biased for more tire room. Yes, there is always some "slop" in this junction and this effects ultimate camber AND tire room inboard.

    Out back we had to push the emergency brake cable inboard (it was rubbing the tire, as you can see above). I used a hammer to bend the bracket and that pushed it out of the way. AND we also added a 5mm spacer. When using spacers don't forget to make sure you have longer wheel studs. Ford Racing has hubs with 3" ARP studs for a great price.

    So that's it - to make the 315/30R19 Hoosier fit our 19x11" wheels on an S550 you need to watch for inboard tire rub and add a 3mm to 5mm spacer at each end. And likely do the e-brake cable mod (takes 2 minutes and has no compromises) shown above.

    Last edited by Fair!; 07-27-2023, 05:51 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev