Slick tyre advice

[chops]

I have been running my modified SE in the club track day for a few years on 225/45/15 V70A which have been pretty good but think I want to at least try a full slick. Trailer should arrive next week and full cage in by the end of the year so thought I should go the whole hog and buy some good tyres but my knowledge in this area is limited. I am not going to register the car again and the intention is to run MX5 cup next year. Went to the MX5 Nationals meeting and saw a few combinations and probably should have paid more attention.

i currently run 15x8 949 wheels and am wondering if it is worth trying to use those or are they not wide enough? Am i kidding myself thinking i won't need to cut guards and put flares on it and just go that way from the start? my brakes fit inside 15's, is it worth going to 17's as that seemed to be a popular choice? I also don't know a great deal about brands/compounds of slicks

This is not my area of expertise and any help would be appreciated

[david_syd_au]

A couple of thoughts.

Switching to 17's will increase your overall gearing, and so might mean also changing your diff ratio to avoid loosing punch out of corners.

The MX-5 Cup classes are time based, so it isn't really necessary run with the front guys to have fun and score points in the championship.

FWIW, I plan to return to the MX-5 Cup next year, but don't have the budget, nor probably the skill, to be right at the front, so I plan to run my car as is likely slotting into the 1:09 to 1:12 (at WP) category.

[wasabi]

Not sure on what mods you've done, but I would assume you have a baffled sump as IMHO, it's something you would want to have if you were running slicks.

[david_syd_au]

Not sure on what mods you've done, but I would assume you have a baffled sump as IMHO, it's something you would want to have if you were running slicks.

Good point. Stronger wheel bearings would also be necessary. Standard bearings don't last with the extra loads from cornering on slicks.

[greenMachine]

Wheel bearings are a consumable and more so with slicks/turbo, especially the fronts, and I am not aware of any 'better' ones. This has been a subject of some discussion over at MTnet. Just have a spare set in the racebox, and the right socket in the toolbox, it is not a big job.

You also have to watch the hubs for cracking (again, it seems to mainly (but not only) the fronts), this is a known problem on high power high grip cars over there, don't read about it so much here so their tracks may be a contributor to the problem. Nevertheless, because the failure mode can be catastrophic, it would be something I would watch - bearings give lots of warning, hub, you just see the wheel come off ...

[chops]

have a spare set of genuine hubs on hand and have replaced them in the past and are checked regularly and do carry a spare set of bearings. I have better diff mounts to go in the car and a spare set of drive shafts. I get that maintenance/spend can only increase but i have run a turbo car for a long time and have got my head around that! I have spent a fair bit of time/effort/money on the car and have got down to 1.05.5 on V70A and want to see how quick it can go.

Trying to pick peoples brains about wheel and tyre sizing and also tyre options. I understand if much of this is guarded info but no harm in asking

[MattR]

Stay with the 15 inch wheels you are currently using, there are plenty of good size slicks available in a 205-225 width and around a 540 diameter that will keep the same overall gearing you have now.

I haven't played with 15" slicks, only 18", but they could probably do with a bit more camber and you put as much caster as possible in general terms for set up. Pressures start pretty low, on my car start pressures are around 22psi, but check with the tyre supplier, they should give you some assistance.

They do take a little to get used to, but once you have run on slicks you won't want to go back. They stick like the proverbial to the blanket, but with most slicks being radial, when they let go it is very quick and with little warning.

They also become sensitive to set up of the car and pressures, and may need to get the car realigned to suit what the slicks want.

Best bet maybe to chase up some second hand slicks for a couple of sets to have a play and see if that is the way you want to go. You don't want to spend a fair few dollars and then ruin one by flat spotting, or ruining all in a day with poor setup. Even a second hand slick will give you grip and you will get a good feel for what they are like to drive on.

Have a chat to those already running slicks and see what they are running, and then grab their old ones. Brands in 15" easily available would be dunlop, avon, I think Pirelli, maybe toyo and Khumho.

For my S14 I will be running 18" slicks as that was what I ran on my 240Z, brands I can source are Yokohama, Pirelli, Michelin and Achilles in a 240-250 wide 640-650 diameter tyre

[forcedfive]

If you go much faster chops you will have no one to race with....

Something like a 215/580 R15 I beleive are good for 8/9 inch rims so may be worth a try and you may only need little, if any, guardwork other than a roll. These are the same rolling diamter as your current tyres. Your car is obviously well set up on the 15's and personally I would be inclined to stay with 15's unless you are chasing bigger brakes rotors for more braking. 17's will probbaly also stress the bearings and hubs even more as you will have to run larger diameter by probably 30mm + along with teh extra grip.

Just my thoughts but I have no personal experience on slicks in my car.

[zossy1]

Stay with the 15 inch wheels you are currently using, there are plenty of good size slicks available in a 205-225 width and around a 540 diameter that will keep the same overall gearing you have now.
...
Have a chat to those already running slicks and see what they are running, and then grab their old ones. Brands in 15" easily available would be dunlop, avon, I think Pirelli, maybe toyo and Khumho.

Dunlop and Kumho, yes. Gary's Motorsport Tyres in Sydney do Dunlop, and Kumho Australia sell the s700 slick. But I have yet to see commercially available 15" Pirelli or Avon slicks in Australia, though I know they are made so its possible someone is importing them...

The lowest profile 15" slick you generally see is the 220/565R15 Dunlop. Most others are 580 profile. I've never seen a 540.

I am running Hoosiers. Max Dumnesy can get them but you need to order in advance and wait for them to arrive in the container. I personally import mine from the states and get takeoffs to save money - slicks are exxy.

My personal experience with slicks is that you get what you pay for. Kumhos are slow but consistent - they are quite hard from a durometer perspective and don't lose pace over the heat cycles like some of the others do, but they aren't that quick to begin with. They are, however, stiff in the sidewall and very responsive on turn in, which suited my driving style. YMMV.

Dunlops - well I was never able to make them work, but plenty of others have so don't hold that against them. They demand lots and lots of neg camber and have a soft, floppy sidewall that made my car feel like driving a hovercraft. I hated them - but even so they were faster than the Kumhos. They also have other quirks - they cycle out in 6-10 cycles, and they bleed lots of air through the sidewall. They are VERY soft as well, making them prone to flat spotting. Again, YMMV (though not with the air bleeding - they ALL do that).

Hoosiers - best of both worlds. For me, they have the same or more grip than the Dunlops, and the stiff sidewall of the Kumho. You can also run far less neg, making them stronger under braking. They do cycle out (all slicks do), but are generally on the pace for at least 15 cycles, and even after they go off, they will be as fast or faster than your V70As. As always, YMMV.

Budget $500-$600 per shoe for good slicks. Kumhos are much cheaper but i'd suggest there is a reason for that...

Moving to 17" rims will increase your choices in tyre. The NC and SP/SE crowd prefer Michelin, and from my observations, they are mighty quick.

[stuart1]

We have run Hankooks in semis and slicks for the last couple of years and I see no reason to change.

They have a very stiff sidewall and seem easy to set up.

I agree with the comments re the MX5 hubs...they are tiny and obviously suspect, especially with very high grip levels.

[zossy1]

We have run Hankooks in semis and slicks for the last couple of years and I see no reason to change.

They have a very stiff sidewall and seem easy to set up.

Any comparative data against the Dunlops? Kumhos? How about against semis like the A050, NT01 or V70A?

I wouldn't mind trying the Hankooks but the sizes they offer aren't ideal for me, so the tyre would need to be good...

[chops]

Thanks for all the input

George Vergotis who built my car has run Dunlop slicks and seemed to make them work for his car quite well and as he preps my car I am leaning that way. Can get 220/565/15 Dunlops from Gary's at 373 per corner which would work with my 8 inch wheels and he has stock. Might be a reasonable way to start with slicks without having the commitment of buying 17's, cutting guards/wheel arches. I haven't ruled that out but need to buy something as my semis are cactus

Thoughts?

[zossy1]

I can only repeat what I said about the Dunlops above and wish you good luck

[forcedfive]

If you can get 580 slicks in the Dunlop this will give you the same diameter as you 225 45 15 Kumho so gearing will be unchanged.