Tyres are the most overlooked performance enhancement that can be made to any car and the Atom is no exception. In fact, due to the very light weight and high performance of the Atom, they are even more important. If you’ve never regarded them seriously, consider this – they are the only part of the car that is actually in contact with the road – and there isn’t that much of a contact patch to start with!
Some of the advice below will apply to other cars but not all, so think of this as a guide that is exclusive to the Atom, as opposed to a general tyre guide.
The main factors that determine how a tyre will work on a specific car and under certain conditions are as follows:
- Amount of tread – it’s a common misconception that the tread on the tyre is what gives it the grip. This isn’t the case. The tread blocks allow for the clearing away of water from the contact patch of the tyre (where it meets the road). In fact, as a rule (as you’ll see in the race tyres section later in this guide), the less tread, the more contact patch, so the better the grip.
- Rubber compound – the softness of the rubber used in the making of the main part or contact patch of the tyre. As a rule, the harder the compound the longer the tyre will last and the softer the compound the shorter the life but the better the grip. Again this isn’t always the case – as a tyre gets hotter the rubber can become overheated and grip will reduce. More on that later.
- Sidewall construction – the sidewalls of a tyre are the parts which make contact with the wheel, through the bead of the tyre, and have an enormous effect on how the tyre behaves. It’s a little understood area which we’ll attempt to delve into here. The sidewall behaves as part of the suspension of the car. Imagine it deforming and deflecting as it absorbs the loads between the car and the road. So with a very heavy car, with relatively soft suspension, a stiffer construction will help to mask any inherent flaws in the suspension under load by ‘propping up’ the car under heavy cornering, braking or acceleration. On a very light car with stiff suspension the opposite would be true because there would never be enough load to get the tyre working properly or up to its intended operating temperature.
- Tyre pressure – this is an extremely complex area and will be the subject of its very own Ariel Club guide. Pressure follows on from sidewall construction, in as much as air volume will determine how much deflection will be in the tyre. For the purposes of the guide below, if you have a tyre with too hard a sidewall construction you can remove some air pressure, which will have the same effect as softening the construction. On a tyre with a very soft construction you can add air pressure to ‘prop up’ the tyre, which would have a similiar effect to stiffening the construction of that tyre.
Atom tyres fall into three main categories:
- Pure road tyres
- Track day tyres
- Race tyres – slick/wet tyres
Road tyres
Road tyres are the most easily obtained and the cheapest tyres you can fit to your Atom. If you have a look at your day-to-day family saloon car this is what’ll be fitted. They vary in price from around £30 per tyre up to £180 per tyre depending on size and quality.
Road tyres are designed purely for road use – so they are destined to give higher mileages, work in all weathers, under nearly all road conditions and on a variety of different types of vehicles. Because of this, they are extremely compromised for track day use, particularly on an Atom.
Pros – a road tyre on an Atom will last a long time and will clear a lot of water away from the contact patch in torrential rain. For those who never track their cars and don’t drive fast on the road this type of tyre is fine.
Cons – a road tyre on an Atom will provide the least amount of outright grip under 99% of conditions, out of all the possible types of tyre.
In general terms, a road tyre will have a relatively hard rubber compound, to increase mileage between changes and to decrease rolling resistance so as to increase fuel economy. It will also have a large amount of tread, or rubber blocks. This is mainly to provide a good ability to clear water away from the contact patch to prevent aquaplaning in bad weather conditions. Sidewall contruction will vary widely across road tyres – a ‘high performance’ road tyre designed to work on a heavy car will have an incredibly stiff construction to ‘prop up’ the car under load, whereas a budget non-performance tyre can have quite a soft construction.
Unfortunately there is no such thing as a road tyre that has been designed with the Atom in mind. So all road tyres have too hard a compound and far too many tread blocks to truly work well on an Atom. This will result in very low grip levels in dry weather conditions and the number of tread blocks present mean that under spirited track driving conditions the rubber blocks themselves will deflect and move around a lot, causing the tyre to overheat and provide little or next to no grip. Some road tyres of a perfomance nature will have too hard a sidewall for a light car like the Atom, too, and won’t allow any deflection of the tyre when the suspension is under load, causing an unpleasant, skittish ride, as well as vastly reduced grip. Some budget tyres will have a very soft sidewall construction which will cause too much deflection and squirming of the tyre, which can feel very unpleasant for the driver. It will also mean that the tyre will very easily overheat on track – because as the tyre deflects more heat is created throughout the rubber.
So in summary then, a tyre such as a Yokohama A539 or Toyo T1-R will be cheap to purchase, will last well (great for auto-tests or drift days) and will provide good water clearing in the worst rain conditions. If your Atom use is very much focussed on road driving in all weathers and outright performance isn’t a issue, these tyres will work for you. If you’re a dry weather only seasoned track day veteran, don’t waste your time with road tyres – you need to be looking at one of the following sections.
Examples of road tyres that Atom owners have used: Toyo T1-R, Yokohama A539 and AD08.
Track day tyres
Track day tyres represent the next step up in performance, but they do come with a higher price as well as much higher rates of wear. You might call these a ‘semi-slick’ tyre as they have far less tread than a conventional road tyre but are still E-marked and approved for road use. Expect to pay between £80 and £200 per tyre depending on size and manufacturer.
Track day tyres bridge the gap between a pure road tyre and a race tyre. They are designed to offer much more grip whilst retaining an ability to clear water and remaining legal for use on the road. The trade off here is greatly increased wear, so much fewer miles in between changes. Because of the extra grip they offer though, they are far more suited to use on cars like the Atom.
Pros – a track day tyre can be used on both road and track, in good or bad weather conditions and will offer far superior grip than a road tyre for 99% of weather conditions.
Cons – a track day tyre will cost more, wear much more quickly and provide less resistance to aquaplaning in the very worst weather conditions.
A track day tyre will have a lot less tread than a conventional road tyre. This gives a much bigger contact patch in the dry (thus increased grip) but with less ability to clear water in bad weather conditions. It seems to be the case with the Atom that in anything but torrential rain the track day tyre will still offer more grip than a road tyre. It’s only the 1% of days when dealing with torrential weather conditions that the track day tyre isn’t as reliable. Even then a track day tyre will be safe enough – you just need to drop your speed and drive much more carefully, looking out for large areas of standing water.
Quite often a track day tyre will have a choice of tyre compounds, so that you can decide which will work best for you. As a rule, the softer the compound the better the grip, but that isn’t always the case. A softer tyre will warm up and start to work quicker but under long hard use the softer compound can start to overheat, resulting in noticeable grip loss. So you may find that if you are doing long sessions in a car that a harder compound will work better for you. Testing of the Atom shows that a softer compound usually works best on the front tyres due to the lack of weight there, with a harder rear compound, because there is more weight at the back, and these are the driven wheels.
Sidewall constructions will again vary across this type of tyre. The Yokohama A048-R was designed around a Lotus Elise and has a relatively firm sidewall, but nothing that running a bit less air pressure won’t cure. The fact that it was designed for the Lotus is a bonus because an Elise shares a similar weight distribution to the Atom and is only slightly heavier and less powerful. The Toyo R888R tyre has been designed for a much broader range of cars so needs more optimisation in terms of suspension set-up, air pressure and compound choice to work, but when it does work, it works very well. The sidewall is softer, too, so benefits from running more air pressure than the Yokohama. Both of these tyres work well – the Yokohama warms up quicker and is better on the road and in all weathers but tends to overheat more quickly in the hands of an experienced driver at a circuit. The Toyo is far slower to warm up and indeed a less experienced driver will not get them up to the correct operating temperature at all, even over a 10 or 20 lap stint. It is also not as good in wet or cold conditions. However, when the tyre gets up to temperature (and we mean hot), the grip is exceptional and doesn’t tail off like the Yokohamas over a longer stint.
So in summary then, if you’re a dry weather fast road Atomer or are keen on your track days but still like to use the car on the road, the tyres in this section are for you. If you’re an inexperienced or not particularly fast circuit driver then the Yokohama A048-R tyre is perfect for your needs. But if you’re a die hard track day man or woman who spends time in the fast group lapping everyone in sight, you might find the Toyo R888R works best for you.
Examples of track days tyres that Atom owners have used: Yokohama A048-R, Yokohama A038-R, Toyo R888R, Dunlop Formula R.
Race tyres – slicks and wets
Race tyres provide the ultimate in grip and the fastest lap times at the circuit. Unfortunately as the name suggests they are not legal for use on the road, so you either need to trailer your Atom to the track or have a way of taking spare wheels with you. They are also expensive – you can expect to pay anywhere between £150 to £300 per tyre depending on brand and size.
Slick tyres are the way to extract the maximum from your Atom at the race track. Unfortunately, they are very expensive and have an extremely limited life span. Not only do they wear out quickly but after a certain number of heat cycles (this varies between tyres) they will also lose their grippiness. Wet tyres offer incredible levels of grip in the wet, as much almost as a track day tyre in the dry but if used in the dry they will immediately destroy the available tread – they need the wet conditions to keep them cool.
Pros – the ultimate in race track performance with the slick tyre and outstanding levels of wet grip with a wet tyre.
Cons – race tyres are not road legal and they have an extremely limited life span, they are also horrendously expensive. Also, suspension set-up needs to be optimised for these tyres to get the most out them them, rendering the car fairly unpleasant to drive on the road on a road legal tyre. They also need to be the correct type for a car like the Atom.
A slick tyre is exactly that – slick, with no tread whatsoever. This gives the maximum available contact patch and means that on a dry track, grip is second to none. A wet tyre has a large amount of tread and very soft compound to ensure the maximum possible water clearing capability and quick warm-up, the downside to this is that they are unusable in the dry and they will destroy themselves, ripping all the tread away from the carcass of the tyre.
You can usually get slicks in a range of compounds depending on what you plan to use the car/tyres for. For example, a hill climb race car that is only doing one run of under a minute will use the softest possible compound tyre to warm up as quickly as possible and extract the maximum amount of grip with longevity being a secondary requirement. If you tried to use a tyre this soft on a track day, running multiple laps, you would rip all of the rubber off the tyre in no time, because it is far too soft for anything other than short bursts. Hence, for track days you need to find a slick tyre that has a harder compund, maybe optimised for endurance racing so that you can get a decent amount of running from a set of tyres. Wet tyres are usually the softest possible slick which has had tread hand cut into it, hence the lack of life when used in anything other than wet conditions.
Sidewall constructions also vary greatly among race tyres. In fact this is one of the most important factors to be considered on a race tyre. A tyre which is designed for a heavy saloon car, a BMW M3 for example, will have a very stiff sidewall as well as a variety of compounds. Try putting an endurance compound slick like this on an Atom and you will see a sidewall construction that is far too stiff and a compound that is much too hard. So you won’t get any deflection or heat into the tyre whatsoever and you’d be better off in terms of grip with a track day tyre. Take the same construction of tyre but with a hill climb/qualifying soft compound and the stiff sidewall will again allow little or no deflection, hence no heat getting into the tyre and all it will do is tear off that super-soft compound from the carcass, with no grip to be had. Again, you’d be better off with a track day tyre.
So it’s not quite as simple as just buying any old slick and/or wet tyre for your Atom. Race tyres have a much narrower operating window, so you need to make sure that what you buy is optimised for use on a lightweight rear wheel drive car like the Atom. Not only that, but slicks generate such huge amounts of grip that you need to make sure the car is optimised for their use or again you will have something that is inherently compromised. Super stiff suspension, both springs and dampers, as well as more aggressive camber settings and the inevitable accelerated wear that these high loadings put on the car mean that if you’re going to run race tyres you’d better be serious about your track days! Most people who use race tyres will hit on a set-up they like and then find that their enjoyment of the car is vastly reduced on the road due to the extra camber and ultra stiff suspension you need to make the most of them. So the trailering to the track begins and you stop running the car as a fun Sunday morning blaster.
Wet tyres, however, have been used to good effect by Atom owners with standard suspension set-ups. Given that the car will generate no more grip with these tyres on in wet conditions than a track day tyre, the car is perfectly happy running a standard suspension set-up. So if you’ve got a spare set of wheels and a way of taking them to the track with you, wet tyres can be a good way to make the most of a winter track day.
So, in summary – if you want the ultimate in grip and lap times at the track, slick tyres could be for you. But, and this is a big but, you will find that the set-up you need to run to make the most of them will negate any road use with the car – so if you want to keep the car as a Sunday morning toy, it’s probably not a good idea. On the other hand, if you want to make the most of winter track days and know you’ll have plenty of grip whatever the weather, a set of wet tyres on some spare wheels could well be the way to go.
Examples of race tyres that Atom owners have used: Avon slick/wet, Dunlop slick/wet.
Written by Bruce Fielding in 2006.
