Wheels & tires.
Updated July 14th 2002.

The wheels and tires of your car are not primarily cosmetical styling items as some seem to think. Tires and wheels are the one most important thing that will keep your car sticking to the ground, either when accelerating hard, braking or when going through turns. The suspension have about the same impact on roadholding as tires and wheels.

Therefore it is of vital importance that one pays close attention to which tires and wheels one chooses and that they fit your car. Especially on high-performance cars such as the Ford Escort RS Cosworth it is vital, since such cars can create much larger G-forces when accelerating and cornering than "normal" cars.

When choosing tires and wheels it is a number of things to keep track of; tire width, the tires rolling circumference, speedrating, wheel size (width and diameter), offset(ET)and bolt circle. I will list all the vital specs for the Escort RS Cosworth, and wheels and tires that will fit. And even though there are a lot of tire and wheel combinations that will fit, not all of them are allowed by the government. In Norway where I live there are two criteria that must be filled: 1. The tires rolling circumference must be within 5% of the original tire fitted to the car. 2. The tires must not extend outward beyond the bodywork (wheelarches) of the car. This limits the tire and wheel choices a bit, but I would never have used anything outside those limits anyway, because tires differing more than 5% will throw the speedometer out of adjustment and change the gearing too much.

Original tires for the Escort RS Cosworth is Pirelli P-Zero in dimension 225/45/16 so the rolling circumference of the new tires must be within 5% of that tire. Then: what is the rolling circumference of the Pirelli P-Zero 225/45/16 ? Either use my formula: here, to calculate it yourself, or go to Tirecalc to get the circumference the easy way. You did get 1913mm didn't you ? That's correct: so the maximum rolling circumference we would want is 1913mm x 1,05 = 2008,65mm. Then when you find a tire in a dimension you think might work just calculate the circumference and see if it's inside the 5 percents. Or go to my tirecalculations to get an Excel-file that I have made that shows "all" tirecombinations for the Escort RS Cosworth, or a screenshot of the same file.

For the width of the tire I think 245mm is the most you can get onto an Escort RS Cosworth without modifications, and then you would have to choose wheels with less inset than the original wheels witch have an inset of 25mm (ET25). Or else the tires won't clear the suspension. But don't change the inset more than you need to, because large changes in inset will change the steering characteristics of the car. Less inset will make the steering lighter and that I don't think is a good idea on an Escort RS Cosworth. From my point of view it is light enough already, especially if you drive on roads that are worn down where the tires go. So if it had been possible I'd gone with more inset for a bit heavier steering. But I think it might be a good idea to change the caster angle for a bigger self-centering effect. For that you need adjustable top-mounts.

When checking you will very soon find out that there are a limited number of tires available in the required dimensions with 18" wheels, I have found three tires to my liking:

Unfortunately the S02 PP has gone out of production and been replaced by the S03 PP which isn't the same quality as far as grip goes.
There are a number of other tires that you might use too. Among the highly rated ones are: When one goes for 17" wheels the choices are many, but the dimensions I'd go for are: 225/40/17 , 235/40/17 , 245/35/17 or 245/40/17 all inside the 5% difference in rolling circumference. My personal favorite is the Bridgestone S02 Pole Position in 235/40/17, off course, as I had them, in 18in though. Read some tests to find out how good they are. They are said to give extremely good grip in the wet and dry, but seems to need some driving before they reach their best.

Wheels.

Wheelchoices are a bit limited because of the 4x108mm boltcircle but there are still couple of good choices out there. Regarding wheel width I think one should stick to the original 8" or go to 7,5" or 8,5". 9" or wider are silly because you can't fit tires that are wide enough to cover the wheelsides well. 16" wheels are ok, but you can't fit the biggest brakes then. 17 inch wheels is probably the best combination between comfort and performance. 18 inch wheels may look better and I think they will give an increase in traction on asphalt as they are in fact used on rallycars on stages with asphalt and concrete. Many people use the weight of "bigger" wheels as an excuse for not having them, but I don't think the rallyteams would have used them if they weren't an advantage, as in making them go faster. And the weight isn't that different: I have found a weight table for some tires and I'm not too sad to say that the 225/35/18 and the 225/45/16 tires weighted exactly the same: 23lbs. or 10,44 kg. So the reality is that it's only the wheel that will weigh a bit more, but if one buys bigger wheels chances are that they are of higher quality and thus lighter, so the difference will be minimal. On the other hand some people might find them to be a bit on the harsh side for everyday driving.
Regarding the offset of the wheels the original offset i 25mm, but with 8" wide wheels anything between ET15 and ET25 can be used.
Wheels that people have used on Escort Cosworths and found good are:
- Compmotive MO - Available in whatever offfset you like in 16, 17 and 18. Very strong.
- Rondell 122 - 8,5x18. Probably the best lliked wheels for Escort Cosworths (looks good).
- Raceline RL7 & RL5 - Sizes as Compomotivee.
- OZ Superturismo - 8x16 and 8x18. Looks Goood.
- Speedline magnesium rallywheels. 8x18. Veery strong and light.

OZ Superturismo

Two good wheelchoices: Compomotive MO in 8x18 or OZ Superturismo in 8x16 or 8x18.

My own experiences.

When I bought my car it had original size (225/45/16) Dunlop SP7000 tires on the standard wheels. It followed cambers and lines in the road a lot and the traction was very poor for tires 225 mm wide. The car slid all over the place when taking turns on dry concrete a bit fast. So I suppose the Dunlop tires aren't that good.
Then when winter came it ditched the Dunlops and bought studded winter tires; Nokian Hakapelita 1, 205/55/16 on the original 8x16 wheels still. A completely different car to drive: No following cambers or lines in the road and a pretty quite and smooth ride, better grip too. Should be impossible but better it was. The car tends to rip out the studs though; if one doesn't take it easy with accelerations on dry non snowy roads.
When it was time for summer tires again I first bought the Compomotive MO wheels currently on my car, 8x18 ET25. Same width and same offset as the original wheels to retain the cars handling characteristics. Then there was tires: I has my mind set on the size: 225/35ZR18, but the brand I hadn't decided yet. Luckily I was able to get a good price on the Bridgestone Potenza S02 PP tires. And I am very happy with them too. The grip is nothing short of fantastic; I have not been able to loose grip on a single occasion in the wet. In the dry I have been very close, but there was still a bit left. The car follows cambers and lines in the road a bit more than the winter tires, but not even close to how much the Dunlops did. As for ridecomfort, I must admit that if the roads are very rough the ride becomes somewhat harsh, and I do feel every minor crack in the surface. But if the roads are good, then there's nothing like 'em. All in all I am very satisfied with them. For more info about the Bridgestone S02 PP tires go to Bridgestone-USA.


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