Nick Woods Posted November 11, 2002 Share Posted November 11, 2002 My 1.6K supersport is being rebuilt after my crash a few weeks ago. As part of the rebuild I'm switching from 15" prisoners to 13" minotaurs with A021R's on. Cash is very tight and 185/70's are a good bit cheaper than 60's, so I was wondering will there be much difference btween the two for road use ? Nick P8MRA - The green one with red wings. Which is now bent ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ but is being fixed Link to comment Share on other sites More sharing options...
Sheds Moderator Posted November 11, 2002 Share Posted November 11, 2002 Not having tried it I would obviously be guessing, but I would say the difference would be modest. The sizes are very similar. Of course one man's "not much different" is another's "streets away" but there you are. I suspect you would notice the difference in ride quality, with slightly more springing from the tyre itself. Link to comment Share on other sites More sharing options...
Clay Head Posted November 11, 2002 Share Posted November 11, 2002 One thing that will probably change is the gearing will be longer than the 60's as the rolling circ will be bigger. The smaller 60's will warm up quicker and your car will be faster through the gears! Link to comment Share on other sites More sharing options...
scooby dooby doo Posted November 11, 2002 Share Posted November 11, 2002 the difference in squidgyness is apparentally noticeable. The gearing difference will also make a few% difference and a couple of cm in ride height. One more practical note - I think that there are no 185/60s available at the moment, or expected for a couple of weeks. HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
Sheds Moderator Posted November 11, 2002 Share Posted November 11, 2002 According to my arithmetic, +6.7% on gearing (so speedo 6.7% lower, bearing in mind they are usually around 5-10% optimistic) and +19mm ride height (assuming same "squidge" under load). Not being able to get 60s might force the issue, as I understand that the grip between ally and tarmac is VERY poor. Link to comment Share on other sites More sharing options...
Graham Sewell Posted November 12, 2002 Share Posted November 12, 2002 Then you have the cosmetics to think about. I think that the 70 porofile tyres look great underneath clamshells as the 60's start to look a little small. But this position is reversed for cycle wings. Although in your case, with 15" wheels, I assume that the cycle wings are larger than those used by people with 13" wheels. Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
Nick Woods Posted November 12, 2002 Author Share Posted November 12, 2002 Graham - The wings were larger until I damaged both of them by crashing the car but the current thinking is to go to the smaller wings as part of the rebuild. It has got me wondering if 70's will physically fit under the smaller wings though, if they do then 15" wheels ought to as well and then there wouldnt be a need for the bigger ones Re the speedo gearing, I didnt mention it in my original post because I didnt want to cloud the issue, but I'm aware that I'll need to get the speedo recalibrated, which adds to the cost (its one of the all-mechanical models and I've already asked about this elsewhere in tech talk) The cost of all the bits and pieces that I cant claim for on the insurance has turned out a lot higher than expected, hence the drive to cut costs wherever I can. I'm now seriously thinking of selling it when I get it back as I'm stuggling to afford to run it. Nick P8MRA - The green one with red wings. Which is now bent ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ but is being fixed Link to comment Share on other sites More sharing options...
Colin Grundy Posted November 12, 2002 Share Posted November 12, 2002 Nick I dont know whether this will be of help, but with 185x60 the circumference is 68.3" and with 185x70 this increases to 72.9. In addition the revs per minute goes from 928 (185x60) to 869 (185x70). Presumably this will effect the speedo reading. Link to comment Share on other sites More sharing options...
Jaseb Posted November 12, 2002 Share Posted November 12, 2002 I've just made the swap from prisoners to minitaurs with 185/70 21r's - the difference is awesome, the progressiveness from taller sidewalls is mentalist and I can guarantee you'll love it. Ultimately I think grip on the road is down just a touch (maybe it was just a dieselly roundabout) compared to my 15's with AVS but it's a load more fun and I wouldn't go back. I can't speak for the 60 profile tyres but I started on 70's to keep ground clearance and have not been disappointed - that and when they wear out you can always try the 60's as I probably will Like the ad says - just do it - you won't regret it 😬 PS Where are you? With a minimum of effort you could try my wheels and tyres before you commit Edited by - jaseb on 12 Nov 2002 09:46:32 Link to comment Share on other sites More sharing options...
Nick Woods Posted November 12, 2002 Author Share Posted November 12, 2002 Thanks for the offer Jase - I'm in Norwich, but my car is in a large pile of bits at the seven workshop so I cant try your wheels. I'm now thinking along the sames lines as you , ie go for 70's now to save money then switch to 60's in the future and recalibrate the speedo at the same time Nick P8MRA - The green one with red wings. Which is now bent ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ but is being fixed Link to comment Share on other sites More sharing options...
scooby dooby doo Posted November 12, 2002 Share Posted November 12, 2002 i wouldn't worry about the speedo - its going to be be a bit out whatever. Adding/subtacting a few percent is quite easy when you're driving anyway... HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
philwaters Posted November 12, 2002 Share Posted November 12, 2002 I had a chat to Goerge Polley at the Festival and this came up. He said that 70's actually give a bit more grip as the greater wall deflection means that a larger footprint is in contact with the road for longer. With a 60 the edge gets lifted off the road earlier. He quoted us £43.50 fitted for the 13"x185x70's which is darn good! I have not tried it so can't comment, but the theory sounds good to me. Phil Waters You mean you can drive these? I thought it was just there to polish 😬 Edited by - philwaters on 12 Nov 2002 13:08:46 Link to comment Share on other sites More sharing options...
Luke Beaumont Posted November 12, 2002 Share Posted November 12, 2002 I agree with Hoopy, Nick. Get someone with a GPS to give you a true reading on the new tyres compared to the speedo before you go down the recalibration route. Link to comment Share on other sites More sharing options...
Colin Grundy Posted November 12, 2002 Share Posted November 12, 2002 Just for the record I purchased from George Polley a set of 185x70x13 complete with brand new Minators and still had change from £300, so if they difference is marginal you cant fault the price. Link to comment Share on other sites More sharing options...
Nick Woods Posted November 12, 2002 Author Share Posted November 12, 2002 Colin - do you have the big (ie 15") wings or the smaller ones ? If you have the smaller ones do the tyres fit ? Luke - good idea about the GPS / measured mile I'm still leaning towards 70's at the moment because of the costs, so providing they fit under the small front wings then they will be the ones I go for. Nick P8MRA - The green one with red wings. Which is now bent ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ but is being fixed Link to comment Share on other sites More sharing options...
Colin Grundy Posted November 12, 2002 Share Posted November 12, 2002 Nick I actually have the flared wings but wanted to go 13" wheels and that was the reason I went with the 70 profile, which looks ok IMO. The problem starts if you want to go to 7" wheels and want 205x70 tyres. Apparently they are like gold dust. Hope this helps. Link to comment Share on other sites More sharing options...
wonkey eyed barmaid Posted November 12, 2002 Share Posted November 12, 2002 this may turn out to be a stupid suggestion, for some reason im not aware of - but why not split the difference in this discussion and go with 185/65/13 - if they make them. best of both worlds? http://www.miata.net/garage/tirecalc.html is a handy site for checking rolling radius etc of different tyre sizes. Link to comment Share on other sites More sharing options...
scooby dooby doo Posted November 12, 2002 Share Posted November 12, 2002 they don't make them HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
Drumster Posted November 12, 2002 Share Posted November 12, 2002 Another convert to 185/70/13s. Changed from 15" Prisoners and Michelin 'Pile-ups' to Yoko 21Rs on 13 " wheels. Same ride height, same gearing and one hell of a lot more fun 😬 IMHO the 7o profiles fill the rear arches that bit better and also fit under the original 15" cycle wings Chris Alston 1800 Supersprint - Loud and Proud 😬 ...well it only sounds fast officer 😳 Brooklands aeroscreens for those........flies in the teeth moments Drive it like you stole it! Link to comment Share on other sites More sharing options...
Nick Woods Posted November 13, 2002 Author Share Posted November 13, 2002 Thanks everyone. No-one has put me off '70s (quite the opposite in fact) and as they are going to save me some money as well i'm going to go for them. Nick P8MRA - The green one with red wings. Which is now bent ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ 🙆🏻 ☹️ but is being fixed Link to comment Share on other sites More sharing options...
Fun to Drive Posted June 26, 2004 Share Posted June 26, 2004 NIck, My thoughts and experiences as I have often had similar dilemnas: design axiom for tyres is that high profile = low vertical stiffness, low conering stiffness, and low camber stiffness, and hence lower grip levels. Vertical stiffness is often highly dependent on pressure, camber stiffness less so, and cornering stiffness even less dependent on pressure. Another key difference between tyre profiles, for a given width tyre, the high profile tyre has a greater volume of air than a low profile tyre. The greater volume of air gives more control of the tyre stiffness characteristics, and hence playing around with the tyre pressures enables the car to be tuned to suit your taste more. I would not expect many tyres to be developed for cars as light as a 7, thus the vertical stiffness may be too high, and this is why having high profile tyre may best. High profile tyres tend to understeer more which I guess can be good or bad depending on what you want. They also tend to make the steering heavier at high speeds, although they may make the steering lighter depending on the tyre design. I have never thought about high profile tyres giving more grip due to the greater wall deflection giving a larger footprint. Although in my experience high profile tyres often do have grip near to that of low profile tyres. I find that rolling the tyre over onto the tyre shoulder wears the outer edge of the tyre a lot, and this can have quite a dramatic effect on turn-in response, particularly in the wet. High profile tyres for the road gets my vote every time - except if they look crap! Keep the revs up. Mark Link to comment Share on other sites More sharing options...
AMMO Posted June 26, 2004 Share Posted June 26, 2004 Nick I had the same dilemma a few years ago. I went for the 60 profile tyres on Pete McEwan's (Raceline) recommendation. Apparently the 60 profile is less squirmy than the 70. You also have a lower C of G. It's only a few quid extra for the 60's. If ground clearance or gearing are an issue (you prefer less rpm for a given speed in top gear) then go for the 70's. You will lose out a bit on acceleration. I also wouldn't bother with the speedo re-calibration. I just worked out how many miles per 1,000 rpm in top was and drive the car on the tacho. I have had my gearbox done and changed to 205/60/13 tyres on the rear. Whilst the gearbox was out I hade the speedo drive changed so the reading should be closer. I'll check the speedo with a GPS and drive accordingly once I know how close I am to reality. Personally I think the 70's look a bit high profile on the front. They do look right inside the rear wheel arch though. Has this helped? Probably just muddied the waters even further. Sorry 😬 AMMO Link to comment Share on other sites More sharing options...
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