23 Jul 2012

Continental GP4000 tyres

I thought I'd give an update of my experience with these tyres. I have covered 1800 miles on them so far. From the last day of May until the 23rd of July. Roughly eight weeks.

Brand new GP4000

After running for a short while at 80-85psi they were then inflated and held close to 90-92 psi for most of their active life. This pressure was chosen as the most comfortable and tolerably quiet while completely avoiding pinch flats. Buying a quality track pump aided the routine of applying the correct pressure prior to every day's ride. A couple of strokes of the pump handle was usually all that was required. The Topeak pump has a handy, red dial marker. Saving the spectacle wearer having to read the numerals. 

 GP4000 after a couple of hundred miles from new.

These Continental GP4000 road tyres have suffered their (unfair) share of off-road riding. On rough farm tracks for quite a few miles. A few hundred yards of nasty, granite cobbles are regular features of some rides. Mostly, though, they have been ridden on normal roads. With all that means in the way of poorly maintained surfaces, potholes, patches and mixed debris and detritus.

Many local roads have been resurfaced with larger (rougher) gravel than is remotely comfortable. This caused heavy vibration and much increased tyre noise. Had the tyres been ridden only on smooth roads I doubt they would have shown nearly as much wear and surface damage as they do now. (Little as it is) Our own access drive involves at least two rides of 200 yards, on very rough, loose gravel per day. It all takes its toll. After all, these are light, high performance, road racing tyres not MTB knobblies!

GP4000 rear left after 1800 triking miles.

Being used on a trike means that the tyres present only one (flat) face to the road surface. They do not lean on corners. Nor constantly weave to maintain the rider's balance. Nor suffer from asymmetrical camber wear. As they would on any bike. Which raises interesting questions about tyre pressure versus the width of the contact patch. Would higher or lower pressures wear them out more quickly? What would be the cost in comfort and rolling resistance? There must be an optimum pressure which minimises rolling resistance. I like 90psi on my trike without offering any scientific proof of this being an optimal pressure for all these variables. 

Initially, the darker contact stripe was very narrow. Only about 6mm wide at 90psi. This usually broadened on every ride to about 10mm on smooth surfaces. The "stripe" formed a darker, central ring on the blue tread of the tyre as it rolled along. Rougher gravels removed this darker stripe. Or spread it wider. Running on smooth surfaces the tyre would sometimes get its initially narrow stripe back again. For a while. Running over damp patches on the road showed that the central contact stripe was very real. The tyre would take on its narrow, darker stripe again until it dried off.

This all came as quite a shock to someone who has spent his entire life noticing how all tyres flattened themselves onto the road. The side walls of high pressure bicycle tyres still do look flattened at the bottom. It's just that the tread width in contact with the road remains very narrow. Much narrower than the tyre wall distortion near the ground would suggest.

 GP4000 rear right after 1800 triking miles.

I used to have a simple trick with the Bontrager Race Lites. I would look down at the outside of the rear tyres. Looking beyond the rim through the whirring spokes as I was riding along. If the tyres were hard enough I could not see the side-wall bulge. The tyre wall distortion would be masked by the rim at the particular angle I was viewing. This was a handy trick when changing road surfaces made it feel like yet another pinch flat had occurred. It saved stopping to press the tyre with an exploratory thumb. The trick was doubly handy when the tyres were wet or muddy! I cannot see the bulge of the GP4000 through the spokes either.  

It must be remembered that there is quite a lot of tyre scrub on corners on a trike. Pedalling hard out of corners can induce temporary wheelspin as the rider's weight shifts. Taking sharp corners with any degree of "over-enthusiasm" produces clear sounds of tyres scrubbing as the trike drifts smoothly outwards. The trike is also being steered "uphill" out of the verge due to more or less constant road camber. Though the problems of OWD (One Wheel Drive) are a thing of the past thanks to the Trykit 2WD freehub system. It is just that one is no longer aware of constantly having to steer gently away from the gutter.

The wear indicator dimples shown in the three images here suggest that there is still plenty of meat on all three tyres. Any "flattening" wear of the tread crown is minimal and subtle. I deliberately photographed the tyres with the sun sinking towards the horizon to one side of the trike. This was meant to exaggerate any uneven wear but failed to do so.

Three tyres spread the weight of this particular 12 stone, 168lb, 76kg rider (plus his occasional 20 lbs of shopping) rather better than only two. Though, as on a bicycle, the rear tyres of a trike carry more weight than the front.

GP4000 front tyre after 1800 triking miles.

My conclusions: These tyres wear well and evenly. They feel very light and "quick" in motion. They are fairly noisy at 90psi. Though this is surface and speed dependent. Going faster makes them much noisier. Often giving a sensation that a car is following when it isn't. I haven't tried them at higher pressures so cannot confirm that they really "sing" at the usually recommended 110psi. They "ping" on loose gravel well enough already. Anybody who has experienced the peloton passing by knows the roar road racing tyres make en masse.

Interestingly, the front tyre has a constant lower, metallic "ring" compared with the roar of the two rears. This reminds me (oddly enough) of butchers' bacon slicers from my childhood.

I would be very surprised if there isn't another 1000 miles in them before the dimples completely disappear. How long they last after this will be interesting and money saving.

The GP4000s are rather expensive at roughly £100 for three delivered. (At present Danish online prices) Assuming ~3000 miles per set probably means at least three sets per year. £300 is a not inconsiderable sum to lay out annually for a tricycling pensioner. Against that is the reduced cost of frequently replacing inner tubes with the Bontrager Race Lites. Plus the time wasted repairing tubes. Or replacing tubes at the side of the road when you'd much rather be moving fast. But you can get the Bontragers for £20 each or even less. Or (say) much less than £120 per year for a trike doing 10k miles.

Bontrager Race Lite after 6200 miles!
The visible debris is just dried leaves and grass.

I wish I had run the Bontrager Race Lites at 90psi. If only to have some valid comparisons to share. Buying the Topeak pressure gauge and track pump certainly proved that one cannot trust the (uncalibrated) MkI cyclist's thumb. No matter how many decades one has ridden a bike or trike!

The ping which hard tyres make when flicked with a finger nail is highly rim dependent! They sound much higher in pitch on Mavic's CXP22 than on the Shimano of very similar cross section. After two months of daily checking I still don't think I could hit 90psi consistently by feel alone. The tread deflection to a pressed thumbnail is far too subtle to judge accurately.

I haven't had a single pinch puncture thanks to the much higher pressures I'm now using. The Bontrager's were unfairly disadvantaged by being run at (probably) 70-75psi (max!) So almost inevitably suffered from pinch flats on farm and forest tracks. Which they might well have avoided at 90 psi on even the roughest of surfaces. The Bontragers had a hard central rubber strip which provided 5-6k miles each at 2/3rds the Continental prices. They did not feel as fast as the Continentals but that is hardly surprising given the large difference in inflation pressures.

I'm sure the Race Lites offered more grip than the GP4000s. But here again the lower pressures probably made all the difference. It's all about contact patch size even on a trike. The Bontrager Race Lites had a flatter 'top' as well as a bigger contact patch at lower pressures. They were also much more comfortable at those lower pressures.

You can't argue with physics. A harder tyre is not going to deform like a soft one. That really takes some getting used to! At lower pressures the GP4000s felt much more comfortable than the Bontragers! That was down to side-wall flexibility and suppleness of much higher thread counts per inch. (TPI) As soon as I pumped them up hard they became hard and uncomfortable on rough surfaces. On smooth roads they are worth every penny in energy saved and the exhilaration of being able to ride faster. The Continental GP4000s  are also very pretty in blue. Are they worth £6 per week in running costs compared with £2 for the Bontrager Race Lites? Only you (and time) can tell. I have heard that the GP4000 can usually manage 3000 miles without puncturing. They may do much better than this.

Click on any image for an enlargement.

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