Dark Side


Brit Butt Tour Admin.
I am entered in the 2021 Euro Tour as I am sure many of you are.
Through lock down I have researched and practiced rally planning and farkled my bike to make the Tour as easy as possible. Now the the commute to and from the start / finish plus the tour it's self I estimate will be in the region of 8000 miles put I am working on 9k for safety. Now that is beyond the life of many tyres or the life of of what remain. I feel that PR4/5 will complete this mileage fine, but I for some stupid reason have entered the 2023 12day tour so tyre life will be an issue.

Whilst surfing the internet I came across a web site by Greg Rice,http://www.gregrice.com/index.htm l were he went into great detail about using a car tyre in place of the motorcycle rear tyre, i believe it is commonly called the DARK SIDE. It appears that there is little difference in handling but a major improvement in mileage. My question is has anyone done this mod in the UK, what problems did you encounter, were the problems out weighed by the extra mileage, increasing to 15 or 20k.


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Car tyres are flat and squared off to get maximum tread in contact
Bike tyres are rounded off for the same reason maximum tread in contact
is it worth the risk just to save a couple of quid?


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Pete west had one on his rocket 3. In USA riders send wheel/tyre to midway hotel to swap them. On the fazer and tiger the Michelin PR3/4 were good for 12,000 miles. I used to line up a change near the start
i've passed comment on this before it still does not make any sense in fitting a car tyre to a bike. I've done this but did fit it on a car rim to a sidecar so that negated the problems lean angle plus rim fit.. Even though car and bike rims have the same nominal rim size the dimensions are different, plus does cooler running mean not reaching operating temperature? watched the video that covered the mechanics of why they don't work,

there's no way i'll get 12000 out of a set of tyres 7000 or 8000 seems more realistic


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<...>My question is has anyone done this mod in the UK, what problems did you encounter, were the problems out weighed by the extra mileage, increasing to 15 or 20k.
First off, not in the UK, but I do have in excess of 100,000 miles of CT use on a GL1800 - take it for what it's worth.

Would strongly recommend having a few hundred miles on the tire *before* you get into rally mode. There is a difference in handling, but the ass-to-brain calibration is different for every rider. Personally, it took me about 350 miles the first time.

We are lucky here in the States; we do have certain tire shops that will mount one on a rim at minimal cost. Installing them on your bike? That's your job (liability and all of that...) to accomplish.

Speaking of which, I do suppose that bike would fail an MOT inspection in a heartbeat. Spare wheels are also recommended.

You'll get many, many naysayers on the topic. The *only* proper way to decide is to watch one in action personally. Videos are nice and all, but the tire I'll be changing shortly has roughly 17,000 miles on it. Picked up a cut somewhere which I found in the comfort of my garage. Sticky rope plug is allowing me to wring the last little bit of life out of it at this time.

Luck to you!


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I used a Toyo car tyre on the rear of my Rocket, as I was finding that a standard Avon or Michelin (the only two available) would last me about 3000 miles if I was lucky - sometimes only 1800 miles if I was too heavy on the throttle.
I would get around 18,000 to 20,000 from the Toyo. You have to run the tyre at a fairly low pressure, in order for it to flex. From memory, I ran mine at 22psi.
I can only speak for the Rocket, but you have to put much more counter steering effort into day to day riding, even keeping it in a straight line on a road with a camber.
Riding twisties takes a lot more effort.
I found that handling was perfectly good in that I still wore out the hero blobs under the footrests, even after raising them with rearsets.
Even at 20K there was still plenty of tread left on the sides, with the centre getting a bit low on tread.
It passed plenty of MOT tests without question.
I got plenty of criticism, but so what - it worked for me.
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In the UK and Europe I would be a bit more careful with putting on a car tyre, insurance and road regulations are more strict here I think than across the pond. Especially look up the small print in your bike, travel and health insurance; what could happen if police or other investigators find your bike fitted with an illegal (non motorcycle) tyre?


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Wully. My experience with a CT on my 2016 Triumph Trophy started in November 2020. Since then I have travelled over 5,000 kilometres in all conditions. Saturday 13th. March I completed a FarRide to Bermagui on the South coast of New South Wales.
I had left my home in Trafalgar, Victoria at 03.30 am. and returned home at 6.45 pm. in time for the evening meal, total distance was 1082 kilometres. If you look on Google maps at the Pacific Hwy. passing through Eastern Victoria and on into New South Wales you will note the twisty nature of the road. Morning temperature starting was 18 degrees C dropping to 14 C then back up to 29 C at Bermagui. It reached a top of 35 C on the return ride.
At about Orbost the temperature started dropping with increasing strong winds. Rain had been forecast for the afternoon. Well that rain hit at Bruthen still three hours from home. It was possibly some of the heaviest rain I've ridden in for quite awhile, years in fact.
I have a Hancook 205/50 17 Ventus Prime fitted on the rear. I ride the bike normally like I would if a Michelin PR4 GT was fitted. I run the Hancook inflated to 33 PSI. Normally the Michelin would be at 44 PSI. The benefits of the CT over a MT are increased kilometres. Normally I'd expect about 12-14 thousand kilometres out of the Michelin. I'm looking at between 50-60 thousand kms. from the Hancook CT.
The other huge benefit is the increased traction in the wet. On white lines and what we call snake lines [liquid bitumen poured into cracks in the road surface] there is no loss of traction even with rapid speed increases.
My riding friend has a CT fitted to the rear of his BMW R1200RT and another has a Pirelli run flat on the rear of his Gold Wing. In fact this is his third Pirelli he has had fitted.
In answer to Ahamay's comment about cost saving, yes that is a factor. The Hancook cost $160 fitted/balanced to my Trophy rim compared to $400 for the Michelin fitted/balanced. I might also add that the most vocal/critical naysayers are those that have in fact never tried a CT on the rear of the motorcycle. I also agree that it would not be wise to fit a CT to certain bikes. I'm certainly not taking my Trophy to a racetrack for a ride day or am I out to break the time over my local twisty piece of bitumen. But saying that, maybe you should look at a You Tube of "Yellow Wolf at Deals Gap with friends", this might answer a lot of questions about handling of a Gold Wing fitted with a CT when ridden very fast by a very competent rider.
I know this has been a long drawn out reply to a much confused topic on many a Forum, but you won't see my Trophy fitted with a motorcycle tyre on the rear ever again. Finally remember that when motorcycles were first designed/made they were fitted with car tyres, there was no motorcycle tyres back then. Cheers, and all the best in motorcycling.
I forgot to add that from a policing point of view here in Australia all motor vehicles shall have roadworthy tyres fitted to them. It is not specified that a motorcycle shall have MT fitted. Insurance wise, the insurance company would need to prove that the crash/collision was caused by having a MT fitted to the motorcycle before making a payout on the policy. There is no evidence of this having ever happened. Until I'm questioned by a member of the constabulary re the fitment of the MT to the rear of my Trophy and if any charges are forthcoming then I'm not concerned. I hope this might have answered a "few" questions re going to the "DARK SIDE".
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You gotta love the bloke from FortNine , informed opinion.
I think the foot note says it all, “we are who we are” if it works for you it works for you.


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When I had the Toyo fitted to my Rocket (a period about 6 years) I informedly insurance company in writing about every non standard/extra on the bike, tyre included. They never questioned it. Should also add that at the time I was a serving police officer, albeit not in the traffic division. I did take the bike to a traffic officer I knew and asked him about it. All he was concerned with, after much scratching of head, was the depth and spread of the tread.
You have to keep in mind that insurance company's are looking for any excuse to avoid paying out on a claim the fact that you told them in writing might not help.


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Contract law. I had written proof of my extras and alterations, sent to them prior to being offered a contract. They accepted those extras and alterations and offered me a price based on them, which became firm once I'd paid. Pretty watertight.


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I didn't have an RTC during the time I was on the dark side, so as you say, didn't have to put it to the test. I just did what I could to mitigate any get out clauses that the insurance robbers might have tried.


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From the UK Motorcycle MOT manual


And then

If you're out on the road and get stopped.

From the roadside Prohibition Manual

Immediate prohibition on use if the examiner can justify the dangerously unstable.
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Looks like the regs have changed from when I was dark side, which would have been from about 2007 to 2013. I checked the MOT manual at the time and there was no mention. Shame - the choice seems to have been taken away. Hundreds of thousands of miles have been travelled by hundreds of bikers without the slightest problem. I'd love to know what accident statistics were used to outlaw the use.
As someone mentioned on this thread, the only people who are against it are the ones who have never tried it.
At least I had the good fortune to have tried it before it was outlawed.