I'm getting ready to replace my stock tires (195/55R16 Run Flats) with some new tires. I've been looking at the Yokohama S.Drives and trying to compare the sizes using assorted calculators online. My stock tires list at 825 rev/mile. The Yokohamas come in 205/50 and 205/55 and list at 865 and 836 rev/mile respectively on the Yokohama website. This is a good bit different from what the tire calculators say, but it is what Yokohama has on their own website. Should I trust that and go with the 205/55R16? Any other advice?

 

Howdy..I put 205-50-16' S Drives on my '05 MCS back in September, have about 1500 fun miles on them now and I could not be happier with the tires.They are very, very good in the rain too.

They are quiet, very grippy and give pretty good feedback in the twisties when you put your boot in it.I had planned to go with the 55 sidewall, but decided to go 50 to avoid any possible softness.I honestly like the ride and the turn in better, and with the 16" wheels I am not too concerned with harshness.

The speedo is probably lying to me, but not too much.Just a happy Yoko customer putting in my .02 cents.

Madgepetto

 

BRG: 205/50/16 is the size I'd go with too. If your speedometer over-reads mph as most do, that size should put it closer to your actual speed. I also prefer a slightly shorter than OEM tire to a slightly taller than OEM tire.

The RPMi of 825 stated for your 195/55/16 run-flats seems too low. I think it should be somewhere around 850 (between 844 and 856).

 

205/55/16 would over-read mph less than 205/50/16 or 195/55/16.

I'm running 205/50/16 for shorter sidewalls and better summer tire selections in that size compared to 205/55/16.

 

215 50 16 is also very close to stock size , but there is not a big selection in that range

 

I guess that makes five of us.

Speedo reads ~2 mph higher than actual speed but that is similar to what most experience with the stock set up.

I've run a set of S.drives for the past two years (less the four winter months). Experience has been similar to Madge's. They will become less quiet as they wear but if you are religious about rotating them between front and back every 3-4K miles or so you will significantly extend their performance lifetime. Of course, that's probably true for most tires.

 

cristo: By my calculations, the larger diameter 205/55/16 should over-read mph even more than the smaller diameter 195/55/16. Specifically, if the 195/55/16 is over-reading speed by 3 mph (reading about 63 mph at an actual 60 mph), the 205/55/16 should be over-reading by about 4 mph (reading about 64 mph at an actual 60 mph). The 205/50/16 that you have would still be over-reading by 2 mph (reading about 62 mph at an actual 60), but at least that would be a little closer to true speed.

I did the calculations by ratios, but math was my most worstest subject.

 

205X50X16 on mine -- I did it mostly to achieve a very slightly lower overall gear ratio, and I feel like it did exactly what I had hoped for. I'm over 10K int the change. My next set of tires will be the same size. I'm very happy with the results. As sort of a side comment, I really don't pay much atention to the Mini speedo. My Garmin has become a permanent fixture, and I use its speedo, almost exclusively. Its dead-on according to the local police radar. The Mini speedo seems to read 4 mph high after the change in tire size. It consistently read 2 mph over before the change.

Oddly, the one unexpected change in the car with 205X50s is that the car sits noticeably lower. Its really only about half an inch, but its noticeable.

 

Jim,
You are not doing the math correctly . Here is the breakdown.

195/55/16 will turn 825 revs in one mile - in an R56 at 3000 engine rpm in 6th gear that will give you 73.31 mph

205/50/16 will turn 838 revs per mile - again at 3000 engine rpm in 6th gear you will get 72.19 mph.

205/55/16 will only turn 811 revs per mile (largest diameter) - which gets you 74.61 mph in 6th at 3000 engine rpm.

All this means is that the speedo typically reads 5% high with the stock setup. With the 205/50's, because of the smaller diameter, you are not traveling as far for the same wheel revs. The speedometer doesn't know the wheel diameter, only the revs, so the speed will now read about 7% high (compared to a GPS). With the 205/55's, because the diameter is larger than stock, you are traveling farther for the same wheel revs. So now the speedo will only be about 3% high.

I do a lot of experimantal work in my day job, so I just naturally did the dame thing with my speedo and tires. I found that though the speedo is high the odometer is spot on to the GPS when running stock tires. With the smaller 205/50's you will be traveling less distance than the odometer thinks. This will seemingly give you better mileage if you calculate your gas mileage from the odometer readings at fillup. Conversely, the larger diameter 205/55's will have you traveling further than the odometer. I checked this on several interstate highway trips using the GPS. The tire diamer increase is 2% and so is the distance traveled (2 miles more for every 100 travels). This will make your calculated fuel mileage lower than it really is by the same 2%.

If one wants to get really ****, the typical tread depth is 10/32" on a new tire. By the time you wear it to 2/32" (tread wear indicators) you have lost 1/2 inch in tire diameter. That means the 205/55's are now about stock diameter (195/55) where the 205/50's are almost 1" less in diameter than new stock.

At the end of the day, all that doesn't mean much. Go with what you think looks best. The 205/50's have the effect of lowering the stance (but opening the gap between the tire and the fender. The 205/55's fill out the tire well more, but raise the car about 1/4".

I went with the bigger tires because I liked the way they looked.

Cheers,
Greg

 

NAProf: Thanks. You're absolutely correct! I see the error of my ways. I was thinking in the opposite direction; that a shorter tire would reduce speed over-read, and a taller tire would increase speed over-read. I must be lysdexic.

That might also change the tire size I intended to re-tire with. I was thinking about switching to 205/50/16 rather than 205/55/16, mainly because I thought .... well, you know what I thought.

This doesn't change anything, but the RPMi figures I got for the tire sizes at the Tire Rack site are all higher than the ones you cited. The RPMi figures I got by looking at four different brands/models of tires in each size are:

195/55/16 Diameter = 24.4" RPMi = 844-854 (midpoint about 849).
205/50/16 Diameter = 24.1" RPMi = 861-874 (midpoint about 867).
205/55/16 Diameter = 24.8" RPMi = 835-839 (midpoint about 837).

I don't know why those tires of the same diameter vary in RPMi, but the numbers you cited are 24 to 29 RPMi less than those I got at the Tire Rack site. Are you using another source for RPMi numbers?

 

Jim,
The numbers I used were simply the wheel&tire diameter calculated from the tire size and the wheel diameter (in my nifty Excel spreadsheet). I didn't account for the fact that the car weight flattens the tire a bit (and creates the contact patch) which effectively decreases the diameter a bit. Decreasing the diameter raises the number of revs/mile. A 1/2 inch decrease in radius due to flattening would increase the revs/mile by the amount you indicate. Also as the tire wears the number of revs/mile will change by the amount the Tire Rack site shows over its life.

The amount of tire flattening depends on lots of things, but mostly tire pressure, load per wheel, and tire construction. Tire manufacturers and car designers have a target tire contact patch size. That size affects controllability, performance, safety, and fuel mileage (i.e., "where the rubber meets the road", so to speak). The tire load rating is a way for the tire manufacturer to quantify these, for liability sake, in a form for the owner to understand. The load rating is the maximum amount of weight the tire can carry at the recommended tire pressure and still meet the performance and safety specs the manufacturer has stated the tire is capable of. You could carry more weight by increasing tire pressure, but then you would be putting more stress on the tire construction and decreasing the tire life (in terms of stiffness). At a typical autocross event folks typically play with tire pressure between runs to get the best contact patch for the days conditions(weather, temp, etc).

All of the above discussion is not based on detailed knowledge of the tire manufacturing business, but rather a lot of wikipeadia reading during my recent tire purchasing process and my many years as an engineer and a dynamics instructor. There are many other folks on NAM who know more about tires, but I am pretty sure that I have the above paragraph right.

Certainly Alex at Tire Rack (NAM poster) has better info than I do and Menihune (NAM poster from Hawaii) has shown in a lot of his posts some very extensive tire knowledge. They would be good folks to contact for more information.

Cheers,
Greg

 

Before obsessing about speedometer error, consider that MINI speedometers come in only one version; that there is variation in revolutions per mile (RPMi) among the stock tire sizes available on the MINI (15", 16", and 17"); and there is variation among different tire brands for a single size. It would be interesting to know what RPMi MINI considers 'standard.'

 

You guys are making my head (spin)!! If you already know how much +/- RPMi vs. Speedo your MINI is off, then why not use www.miata.net/garage/tirecalc.html!! All calculations are already done for you!!

 

If you look at the specs of 15, 16, 17, and 18 inch oem size tires at tire rack, and ignore the few numbers that appear to be in error,
theRPMile varies from 847 to 872.

 

Thanks for the informative posts/discussion on tire rev/mile options.

In this case, basically you have a non cooper S with Summer or All season tires on stock 16" wheels. Summer tires ok if mostly warm climates or switch in winter to snow tires is usual.

So 205/50-16 is where to start unless the tire you want only comes in 205/55-16. Example Michelin Pilot Exalto PE2. $133 each, 240 treadwear

Besides Yokohama S.Drive which is OK as a reference point,
300 treadwear 21 lbs, $77 each
Test results-
http://www.tirerack.com/tires/tests/...y.jsp?ttid=104

You can also consider:

Bridgestone Potenza RE760 Sport
(Good handling, higher price)
340 treadwear 21 lbs, $102 each

General Exclaim UHP
(softer riding, lower priced)
380 treadwear 19 lbs, $80 each

If same size but UHP All season tire then-
(Long wear, good comfort and any weather)
Continental ExtremeContact DWS (great snow tire)
540 Treadwear 19 lbs, $101 each

Also in same size but High Performance All Season tire then:
Sumitomo HTR A/S P01
360 treadwear 21 lbs, $84 each H speed rated
Or
Yokohama AVID ENVigor
560 treadwear 21 lbs, $96 each V speed rated
Tire test
http://www.tirerack.com/tires/tests/...y.jsp?ttid=129


Or in 205/55-16 but Grand Touring All Season
(longer wear and more comfort, less noise)
Michelin Primacy MXV4
620 treadwear, 23 lbs, $141 each H speed rated

Anytime you move to a longer wearing tire you get a harder rubber which gives up some grip. If you move away from Summer tires you can get a softer sidewall which improves comfort but reduces handling crispness.

Grand Touring tires can be used with the MINI if comfort and commuting are of highest priority. They will wear longer but don't expect tires to last forever.

 

Thanks to all who responded. I ordered a set of Yoko AVID ENVigors today in 205/50-16. I thought about going with the 205/55-16s, but decided I'd rather have the handling than the speedo correction (since my speedo is already about 2-3% high - now it will be 4-5%).

 

I think you will be well pleased with your decision. We've been very happy with them on ours. I had always before tried to go with what I saw as major manufacturers, i.e., Michelin, Goodyear, Pirelli, Bridgestone, etc. I wondered about Yokohoma. but I did as much homework as I could and found few, if any, disatisfied Yoko customers. I decided to gived them a try. Very happy so far. We've been talking about perhaps trading our Justa for a new "S" model, and one of my wife's first requirements from the dealership is that we get to take our Yokos off and trade them with whatever comes on the new car.

For a girl who never before even knew a tire brand, that speaks volumes.

 

Oh, I have a long history on Yokohama tires. I went through several sets of tires on different cars (Dunlop, Michelin, Goodyear, Bridgestone, et cetera) and have never had a bad experience with a set of Yokohama tires. I even had a dealer switch a set of wheels around to get a Yokohama set instead of another OEM tire before I would agree to take my last Miata off of the lot. I had a set of Yoko A008R tires (that carried me to a 2nd place regional ranking in my rookie year of SCCA Solo 2 autocrossing) that it broke my heart to get rid of.

Yokohama is definitely on my short list of preferred tire manufacturers.