Tyres
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yres are arguably the most
important part of a car - any car. The
most powerful, luxurious, best-braked car is only as good as the tyres. Almost all driver input is eventually transmitted
to the road via the tyres. Of course,
this doesn’t mean that fitting excellent quality tyres transforms a poorly
handling car - sorry, but a Golf will always drive like a Golf, even with
Formula One tyres on it - but it can make a difference.
Generic Information
New
Tyres? Bed Them In...
When you replace a pair of tyres,
that end of the car should see an improvement in grip under most
circumstances. The temptation is,
therefore, to immediately go out and let rip with some gooning. However, a word of caution: new tyres come
with a coating that can take a few hundred miles to wear off. This coating is designed to protect the tyre
from the environment, so basically it’s water resistant - which can cause some
anxious moments in the wet! It’s
important to be a little patient with the tyres and slowly get used to their
behaviour, and perhaps adjust the tyre pressures since different tyres can
behave differently to tyre pressures.
The above is of special importance
if you’re replacing the factory fit tyres with another brand, since you may
find the replacement tyres have different levels of grip and traction under
different conditions compared to the factory fit originals.
It’s for this reason that I
recommend some research into the tyre replacements.
Winter
Tyres
Winter tyres are designed for cold
driving conditions through snow, ice and water.
They use tread patterns optimised for such conditions in conjunction
with different types of rubber compound.
Ordinary “all weather” or “summer” tyres become comparatively brittle in
cold weather whereas winter tyres are designed to stay soft and pliable, which
helps them grip the road surface.
Studded (winter) tyres are
illegal in the
In
Another reason to use winter
wheels and tyres is that using snow chains can damage wheels. Scratching a steel wheel isn’t as upsetting
as scratching an alloy wheel!
If you have fitted aftermarket
alloy wheels to your car you might want to consider keeping your original fit
wheels for winter use. Used standard
steel wheels are not worth much! If you
plan on driving a significant distance in wintry conditions, you could consider
getting deliberately narrow wheels for winter use. For the Ka driver, early mark three Fiestas
used 145/80 tyres on a 13” rim and many Fiesta drivers have replaced these
steel wheels with alloys.
The Ka
Kermit wore Continental CH90s from
the factory, in 165/60/14 size, and they go on to a wheel with a width of
5J. The original fit tyres have a speed
rating of H.
Picking Your
Ka’s Tyres
There are a great many brands of
tyre out there, and some manufacturers produce several compatible sizes.
It’s impossible for me to give you
a recommendation with any authority on tyres for the Ka for a few reasons. One is that I have only tried four tyres with the Ka - Continental CH90s,
Firestone Firehawk F700 “Fuel Savers,” a Wynstar tyre and the Falken ZE-502s.
The other reason is that different
people want different things from their tyres.
Some people want just the cheapest possible tyre for the purposes of
keeping their Ka legal. Some people
require longevity, or good ride comfort, ultimate grip in the dry, or grip in
the wet.
Although there are some tyres
designed to maximise performance in just one respect, almost all represent a
compromise.
Finding the right tyre for you and
your Ka will depend on what you want.
The information derived from the sidewall markings is of some use, but
not that much – see the FAKQ on
wheels and tyres for more information.
Dervy’s
Thoughts at 28,000 miles – Kermit needing two new rear tyres
From the factory, Kermit wore Continental CH90s. I’ve no reason to change from this tyre: with
the exception of the tracking being out, they’ve lasted reasonably well, and I
am quite hard on him on occasion.
However, the tracking had been out prior to rotating the tyres, so the
ones on the rear are, sadly, due for replacement.
They’re H-rated, which means the
tyre may be used on vehicles with a maximum speed of up to 130 mph - as
compared to T-rated tyres with a permitted maximum speed of 118 mph. Kermy’s tyres are all H-rated, and whilst
T-rated tyres should work without problems, it would mean mixing the two
ratings.
If I replace two, where should
these go? Putting them on the front
should reduce understeer, but may encourage oversteer. Putting them on the back may reduce oversteer
and encourage understeer. I think it
makes sense - strange I admit - to put them on the back! Unless I decide to replace all four (but
take a bigger financial hit).
For tyre consideration, well where
do you start? Although upon first
impression there are not many tyres offered in 165/60/14 size, after some
investigation, there is quite a bit of choice.
I’m only interested in known brands, and in specific properties; I’ve
had unbranded tyres before and they were appalling! To compound my decision, Continental CH90s
are no longer being made and are difficult to get hold of. Of course, sooner or later most tyre designs
are replaced, but this meant that I would not be able to put the same on.
After consideration, I elected to
stick to H-rated tyres. Although there
is a cost difference (they’re typically more expensive than T-rated), and that
the Ka’s maximum speed is only 96 mph so both are suitable, I don’t want to mix
ratings on the one vehicle. Furthermore,
the speed rating establishes the overall level of performance. The increase in power to take a car from 118
mph to 130 mph is considerable - H-rated tyres are designed for the
accelerations a 130 mph car is capable of.
Early on during my investigations, I decided that the
“low rolling resistance” tyres did, at least, merit closer attention. Ford used low rolling resistance tyres on all
2001 Kas anyway! Traditionally, low
rolling resistance tyres have sacrificed grip, stability and control for
longevity and energy efficiency, but advances in tyre tread design and material
technology has helped address these compromises. Of course, the same is true of all
tyres . . .
In the 165/60/14 size, I found
three tyres for potential use on Kermit.
Low rolling resistance tyres are
made possible by the use of silica in their construction. Without going into too much detail, mainly
because the science is a little bit beyond me, the harder the rubber compound
used in the tyre, the less energy they absorb - both in terms of bump
absorption and in rolling resistance.
Harder rubber compounds also last longer, too. Unfortunately, the harder the rubber
compound, the lower the level of grip - especially in the wet. This is where silica comes in: when used in
conjunction with rubber, it improves grip (especially in the wet). Basically, it absorbs energy at higher
frequencies, but not at lower frequencies.
The process of researching into
tyres can be quite long winded, and very little account is made of the
differences between vehicles. What works
well on one vehicle in one size does not always work well for another. With this in mind, I take all reviews with a
pinch of salt, and pay heed to personal experience and also with what
manufacturers fit their cars with as standard.
I’ve also talked with other Ka owners, and my usual Ford dealership over
what people tend to use, and go back to.
Michelin and Continental are
renowned manufacturers of energy efficient tyres. Michelin Energy TX1s are available in either
T or H rating, but it’s the H-rated ones I’m interested in. Prices for Michelin tyres varies, but with
one exception: they’re expensive!
Michelin Energy TX1s are original fit tyres for a number of cars on the
market these days.
During
my research, a number of themes cropped up for Energy TX1s. First off, they are hard wearing and offer
good ride comfort, and good grip in the dry.
Unfortunately, in the wet, it’s a different story and the Energy TX1s
are notable for being vulnerable to aquaplaning. They are also manufactured in
Continental also have two similar
low rolling resistant tyres for the different speed rating, but it’s the
H-rated EcoContact CP that I’m interested in.
From independent reports, the EcoContact CPs offer good grip in the dry,
mediocre grip in the wet and quite a high wear rate.
Finally, there is the Firestone
F700 Fuel Saver tyre, made by Bridgestone, and H-rated. Although the cheapest tyre of the trio, the
F700 Fuel Saver’s only notable weakness is in noise - it gets good marks for
both wet and dry grip. Furthermore,
Bridgestone are an American corporation, which is good news as far as the
DervMan household is concerned! So,
given the write-up, I’ve ordered two Firestone F700 Fuel Savers!
Overall, these “energy efficient”
tyres are regarded as being less grippy than standard tyres. The question remains as to how less
grippy they are! And that’s a question I
won’t be able to answer for a few thousand miles yet.
The
Firestone Firehawk F700 “Fuel Savers”
After a few thousand miles I was
able to discuss the performance of Kermit’s Firestone Firehawk 700 “Fuel Saver”
tyres over a variety of conditions.
In terms of noise, the Firehawks
are a little bit louder than the Continentals.
However, with Kermit’s Janspeed back box,
we sometimes don’t notice road noise as much as we used to!
As far as cornering grip goes, the
F700 “Fuel Savers” do not feel as grippy as the Continental CH90s, although as
they have matured, so they have become considerably less snappy than when new -
and less snappy than the Continental CH90s (not that I considered these to
be snappy). As you approach the
limits of adhesion, so the tyres “grumble” their protest, and this grumbling
continues if they start to slide.
For traction under acceleration,
I’ve no issues with the F700s, but then I don’t tend to launch off the line
with wheelspin in mind (quarter mile drag strips
excluded)! Moving off reasonably
smartly on a wet road, with four people in the car, doesn’t invoke wheelspin -
my suspicion is that they’re better than the Continental CH90s. This is just a suspicion that I’m not able to
confirm from drag strip figures, since I didn’t take the kid up the strip in
the wet.
As far as braking goes, again I’ve
no issues. I have managed to activate
the ABS in the wet, with just the 
front wheels, but to be fair I was trying hard and
I’ve managed this with the CH90s too.
Indeed, in the wet, the Firehawks are more stable, and Kermit doesn’t
squirm over changes in road surface and friction as he did on the CH90s (a
good test of this behaviour involves firm braking down a steep hill, with
several road surface changes).
If the Firestones have a weakness,
it’s in cold weather. When the
temperature drops below approximately 5°C, the F700 “Fuel Savers” become more
and more “nervous.” Nervous isn’t quite
the right adjective to use, but essentially the tyres lose grip significantly
sooner when cold compared to when warm, especially when compared to the
Continentals the lad was wearing before these booties. Furthermore, when the temperature is at or
below freezing, especially when we’ve not used him for a few days, the tyre
compound feels rather hard. This gives
him a knobbly ride! After a few miles of
use, the ride softens up, but it is quite an unusual sensation!
As far as tyre wear goes, the
Firestones stood up well and were likely to cover 30,000 miles at the front and
close to twice that on the rear.
The XR2i Wheels - Wynstars
When we replaced Kermit’s wheels
with the XR2i rims, they came with four Wynstar tyres. Whilst I had heard of Wynstar, I’d never
experienced them, and following the last few months, I’ll not be buying Wynstar
again for any wheel of mine.
At first, we had the worn pair (down
to 3½ mm) on the front and the newer pair (at 7½ mm) on the
back. In the dry, I had no issues with
his handling. However in the wet, I was
getting understeer, torque steer and wheelspin under moderate load
situations. Almost as though the lower suspension
arms had unbundled.
A drag strip day took care of the front tyres, and I had
these replaced with Falken ZE502s, which I had put on the back and the existing
Wynstars moved to the front.
This is the preferred technique -
put the newer tyres on the back and the older, more worn booties on the
front. This is so that you get
understeer in preference to oversteer, which is easier for most drivers to
control. Unfortunately, with good
quality rubber on the back and the Wynstars on the front, the effect on
Kermit’s handling was... interesting.
At low speed, such as roundabouts,
it’s possible to get wheelspin in first, second and third gear under around
forty miles per hour. You can also get
torque steer or “power wiggles,” whereby the car squirms around as the tyre
struggles to put the power down.
Under braking, when the ABS works, it proved very easy to trigger
the unit under moderately firm braking.
However, Kermit’s ABS wasn’t functional for a chunk of the time (see here and here), so rather than triggering the ABS I would get
locking front wheels. That’s bad news.
Oh and it rained a lot, too. How much?
Seemingly almost every day between the ABS lamp illuminating and until
we changed the front tyres to Falkens!
Just a footnote on tyre pressures
- two of the valves used with the Wynstars were defective, so essentially
Kermit had a slow puncture during the weeks that we were using these
booties. Nevertheless, I found that
running all tyres at 34 PSI gave the best compromise between handling, ride,
composure (in the dry, in the wet it didn’t seem to matter) and
longevity.
Falken
ZE502s
Using these tyres is because of
the Ka Klub Klique and about the best thing I gained from the only Ka club in
the village.
The Falken ZE502s are quite an
attractive design, if you like the look of high performance tyres that is!
On the Ka, well when we were
running Wynstars on the front and Faklens on the back, in the wet the Falkens were
barely tickled by cornering or braking forces.
In the dry, the Falkens offer rather more grip than the Wynstars and
even quite abusive manoeuvres (hard on the power in second gear, plenty of
lock, lift off the power) simply made the front tuck in rather than the
back end swing out.
One thing I have noticed with the
Falkens is that they’re very vocal and literally howl their protest when you’re
nailing it.
The Falkens coped well with the
rigours of my commute and track time
and were probably going to last at least as well as the Firestone F700s if not
better. After ten thousand miles the
front tyres were down to six millimetres.
The rears (at fourteen thousand) still looked new, with close to
eight millimetres showing on my tread gauge.
The XR2i wheel and Falken tyre combination is slightly lighter
than the original Ford alloy wheel and Firestone tyre so if anything it should
improve matters slightly. It’s too
similar for me to be able to tell anything although from some of my engine
efficiency work, matters have improved running on 185/60/13s rather than
165/60/14s. Using the smaller rims the
contact patch is slightly larger owing to the wheels using 185 width rubber
compared to 165 width. The tyre has a
higher performance design and is biased towards driving dynamics rather than
fuel efficiency, which isn’t good news for fuel consumption.
There has been no discernable difference in fuel consumption, probably
because the lower unsprung weight makes up for the higher friction.
For the more interesting and
exciting stuff, the Falkens are a higher performance tyre compared to my
previous choices but there are far gripper 185/60/13 alternatives. Grip in the dry is adequate but not
outstanding. In the wet they also offer
plenty of grip: you have to be trying hard to unstick either end. They produce a rumbling noise when you’re
approaching the limit of adhesion. If
the tyre pressure is at or below 30 PSI you can suffer from some sidewall
deformation, whereby the tyre starts to slip on the rim and can cause all sorts
of problems. Keeping the pressures at or
above 31 PSI solves this. In the wet
they also perform well but adhesion limits are understandably lower. Even so, you still have to be consciously
doing something borderline stupid to get them to unstick.
Their weakness is in low temperatures, specifically
when the road temperature is close to freezing point. They’re nervous when cold, more so than the
Firestones.
As the tyres wore their behaviour
changed a little. The compromise between
sidewall deflection and tyre pressure became significantly more focussed. With the fronts down to four millimetres,
keeping the pressure above 30 PSI became of paramount importance.
Writing about sidewall deflection
first, I’ve written about it in this Ka Diary
entry. When the tyres were newer the
pressure had to be over 30 PSI to avoid tyre wall deflection but as the tyres
age, so they require a more careful check on pressures. The difference between “just right” and
“slightly too low a pressure” has become more and more obvious.
As for outright grip, if I
increase the pressure to compensate for the sidewall deflection the tyre
produces less grip. It’s not such a big
issue at the front but at the back, if the rear tyre pressures are just a
little bit away from 32 PSI I have a real problem getting Kermit’s corning
attitude balanced how I like it. Run the
pressure below 29 PSI and I have known a great big snap of hedge-finding oversteer caused by sidewall
deflection to punt me towards the nearest hedge.
On The Track
Track days stress your tyres. The best way to judge how hard you’re
cornering the Ka is if the front wheels are squealing, you’re giving it too
much power. If the rear wheels are
squealing you need to give it some more power.
If all four wheels are squealing, that’s about right. If none of the wheels are squealing, you can
go faster.
On the track, I run Kermy at
slightly higher pressures. I typically
use 36 / 34 but the important thing is to balance out the pressures. Running 34 PSI at the front and say 40 PSI at
the back is asking for trouble of the oversteery type! The disadvantage of running higher pressures
is less grip but the advantages are that you run a significantly lower chance
of ripping a tyre off a rim, which will really ruin your day.
These two images show the full
sidewall deflection at the back when running the rear tyres at 34 PSI.
The Falkens have three main points for track day
use. The first is that they are a hard
wearing tyre and don’t wear out in one or two sessions. The second is that they offer a progressive
breakaway from ordinary control such that the kid doesn’t snap into understeer
or oversteer. And finally, whilst the
overall levels of grip are mediocre, they’re better than the previous 165/60
tyres on a 14” 5J alloy that I used. The
chassis and suspension are more capable than the tyres.
As I know I’ve written at length
in the past, this really isn’t an issue since of the twenty five thousand miles
I’ll cover a year we won’t even use half a tank on the track (probably).
When we picked Chef up he was
wearing a mix of brands. We had a Bridgestone
here, a Michelin there, a Dunlop over there and an unknown brand right over
there. All 195/60/15 V-rated, as they
should be. All four corners were at 4mm
tread, so two thirds worn at least. A
puncture (see here)
meant I had the opportunity to replace the tyres... but with what?
Actually the decision wasn’t all that
hard really. I bought the Saab for
motorway driving. My commute consisted
of leaving home, hacking it through part of the city, reaching the dual
carriageway, switching cruise control on... and
waking up at the other end. I wanted a
tyre that would be quiet, long-lived and if it benefited from low rolling
resistance, so much the better.
Michelin Energy E3As, then. Michelins wear very well (in other words they last an age), but
Michelin Energy booties are not the best for the most enthusiastic driver
because they don’t deliver the ultimate in grip, control or feel. For my purposes, though, I figured they’d be
absolutely fine.