My recently-bought Mk1 is intended pretty much only for trackdays … I have a great set of standard 14" alloys and P6000s for the little road use it gets, and for driving to/from the track, but I wondered if - instead of going bigger like everyone else - I could conceivably fit 13" wheels to my Eunos.
Anyone ever tried this, or does anyone know of (as opposed to just guess at) proven reasons why I shouldn’t? I know people regularly go 1, or 2, or even 3 inches up on standard 14s, but what about down?
My reasons for even considering this? There’s a few: the advantages to suspension and handling of lighter wheels on a track … most appealingly the the plethora of very cheap 13" slick and full wet tyres out there … plus the likely shift towards better acceleration from the lower diameter wheels.
Very interested to hear your views, people! In anticipation, cheers!
I wouldn’t say this is “common”. A club member in N.Ireland used to run 13" Opel Manta wheels on the track, but found, on his 1.6, unless his dust shields were removed, he would suffer bad brake fade. I would guess at a typical Autocross, the brakes are never getting hot enough for this to be an issue. For 1.8 brakes, many 13" won’t clear the calipers, and so you have to grind down the calipers, which might result in a MOT failure. There’s no chance 13" wheels will fit over Sport brakes.
This: Masraum - If the tire pressures are the same, then the contact patches will all be the same size, just a different shape.
Is totally wrong and the babblings of an idiot. Applying the same maths to flat tyres makes them infinitely large, which they aren’t. It is a massive simplification that doesn’t even work for balloons, never mind the highly complex engineering that goes on inside a tyre. It is just one step away from the “wider tyres doen’t give you more grip, because of friction” thing that makes me so angry I actually have to go to peoples’ houses and shout at them in person.
I’m still debating in my own tiny mind, tbh - I did a fair amount of sniffing around on US forums, and it does seem to be the case that it’s mainly autocross events that people are using 13s for. It’s the comment above suggesting that I might get brake fade that has me a bit concerned … I suppose running 13s on short events like autocross means it’s not an issue … on the road you’re never braking that hard, that often, and that consistently … and for drift events (forgive me, Captain M, if I’m about to betray my utter ignorance), I’d guess you’re not using the brakes too often anyway, but on track … I’ll be doing open pit-lane track days, so I think there’s a much greater risk of brake fade, which really ruins your day, so even though I’m running Redstuff front and rear, I’m keen to avoid that if it’s a genuine likelihood.
So … given the dearth of 14" slicks/semi-slicks knocking around, I think I’m going to have to dig a little deeper and get a set of 15" slicks for the ultra-light Enkeis I have in reserve. It’ll certainly be a little more expensive, but I’ve got another six weeks before the first event, so I’ll keep looking for that mythical set of part-worn Toyo R888s!
Let me know what you decide to do in case my brake fade fears prove unfounded!
I used to do track days in my CRX which had fantastically poor brakes. I ended up with a couple of pretty huge ducts going from the front of the car to the back of the discs, which combined with decent fluid and pads fixed the problem. I was using 185/60R14 Colway cut slicks, which I wouldn’t recommend.
Are the 13" wheels and tyres cheap enogh that you could try it and see?
Failing that: Toyo 888 and Yoko A021R and A048R are available in 185/60R14, Yoko A048Rs also come in 195/60R14, and Kumho do their track day V70A in 195/55R14 in medium and hard compounds. For lower gearing you can get A048Rs, the Kumhos (soft, medium and hard!) and Dunlop DZ02s in 185/55R14s. It might be worth investing in tyres to avoid having to buy 15 inch wheels.
Then what does dictate the size of the contact patch? I think you will find that the major factor is tyre pressure, modified of course by tyre stiffness. At very low tyre pressures the major factor becomes tyre stiffness coupled to the basic circular shape of the tyre, but at normal operating pressures the major factor is tyre pressure!
Tyre pressure is a factor, as is the construction of the steel banding, sidewall stiffness, tread block deflection and, obviously, vehicle weight. It is certainly not just tyre pressure - as can be shown by different tyre constructions having different optimum pressures, and that’s just with road tyres.
I regularly get to drive my car under safe, controlled conditions with tyre pressures ranging from 26 to 60psi. The effect of pressure on grip is certianly not linear (as is extremely obvious to anyone who has driven on a flat tyre or a tyre at 60psi). Grip is strongly related to the size of the contact patch.
If my other car has a “flat” tyre on the front tyre it will not actually flatten the bottom of the sidewall of the tyres fitted - the effect on the contact patch is small because the tyre construction is such that the effect of pressure is dwarfed by the effects of tyre construction and vehicle weight. This is with “normal” tyres, not run flats, and with a standard production car.
The “major” factor is tyre construction - you can tell this because the only shape for a volume under pressure with zero skin stiffness is a sphere. If pressure were the major factor tyres would become spherical at opreating pressures, which they don’t. Even with 60psi in them the unloaded tread of the tyre only moves a couple of mm.
Tyre pressure is however the only factor you can change by yourself, which is why people forget all the other factors and simplify the entire system to something unusable.
Bob - where are you based? I gave away a set of 14x6 wheels last month, and I have a pair of 14x6 you could have for twenty quid if you’re close enough to Norfolk to pick them up.
Years ago I used to have some random Yokohama 205/60/13’s on a Capri. The sidewalls were so thick that the pressure could get down to 15psi before you could even see that a tyre was soft !!!
Something else thats just sprung to mind, Air’s springy (Remember holding your finger over the end of a bicycle pump as a kid? If you pushed the plunger it felt like a progressive spring didn’t it). If you jump from 14" wheels to 18" you notice the the ride quality go to pot, This is partly because rubber band tyres have very little sidewall to flex over bumps, But also because theres physically less volume of air within the tyre (Like playing with a much shorter bicycle pump)…
If you increase the volume of air in the tyres by dropping to 13" wheels, You might find your car’s ride turns bouncy because you’d increased the tyres ability to work like an undamped spring (Or playing with a much longer bicycle pump)…
I hope this all makes at least some sense, I’m off work with back ache at the moment and I’m having a bit of a problem concentrating…
Captain M, just wanted to thank you for the ace list of track day tyres - genuinely really helpful.
My choice on which way to go - 13s, 14s or 15s - is led by the fact that I have a nice set of pretty light (like 5.5kg each light) 15" Enkei wheels sat there doing nothing and decent 15" slicks or semi-slicks seem to be more commonplace and cheaper than the equivalent 14" ones. If I were to go down the 13" route, that’d mean buying wheels and tyres, so I’m going to be led by my wallet and stick with 15s for the track.
Those Wedsports look the business, though … are they really so much lighter than the Enkeis I’ve got? Not that I have a spare £200 note burning a hole in my pocket exactly!
Not 200 quids worth of lighter! I can feel the difference between my wedsports and some huge heavy wheels I have, but I when it comes down to a kg or two I can’t tell just by driving on them (because my driving “feel” just isn’t that highly tuned). I just love owning some amazingly light wheels. Tragic really.
