Motorcycle Consumer's News letter

[PJH]

Someone, I suspect it was someone from this board, sent a letter to MCN asking about the advisability of using a car tire on a motorcycle.  Valkyrie was specifically mentioned.  In short the response was don't do it.

Don't flame me.  I'm just reporting the letter and response are in this month's MCN.  I didn't write the letter, and I didn't write the response, nor do I have any emotion tied up in what kind of tire someone else uses.  Happy motoring.

[Valker]

Someone, I suspect it was someone from this board, sent a letter to MCN asking about the advisability of using a car tire on a motorcycle.  Valkyrie was specifically mentioned.  In short the response was don't do it.

Don't flame me.  I'm just reporting the letter and response are in this month's MCN.  I didn't write the letter, and I didn't write the response, nor do I have any emotion tied up in what kind of tire someone else uses.  Happy motoring.

They ran nearly the same thing several years ago. All the magazines will say the same thing or they will have folks take it as an endorsement of the practice. If you ask them about removing the turn signals from a bike, they'll advise against it also. Same for aftermarket exhaust. Anything they say that goes against a stock bike will be labeled off road or for track only since they can't legally advocate their readers breaking the law nor do things that might affect the running of the bike.

[mrflamewerks]

Couldn't find the letter you are refering to. Can you provide a link or say what data they based their opinion on?

It would be interesting to find information on this subject that provides information related to the negatives. So far all of the information I've found has been positive and provided by people who have actually done this kind of mod. In some cases they are on their third or forth tire and have nothing particularly negative to say. What little I've come across against doing it is from industry suits who sound like somebody singing a "company song" and working harder at covering their arses, rather than getting at the truth.

If there are truely problems with this mod, it would be interesting to hear about it. I'm about due for a new set of tires, and so far the information I've gathered tells me to save my money and put a car tire on the back wheel of my Valk.

[PJH]

The letter and response are on page 8 0f the May 2008 issue which I received today.  You may not have gotten it yet and are looking at the April issue since it's your latest.  The letter has the heading 'Car Tires Debate.' 

I can't find anyway to link to it because MCN does not post issues on the net.  MCN does not carry advertising. Their revenue stream is subscribers and it would be self defeating to provide the content free on the web. 

I don't want to be flip, but short of me retyping the letter and response here, there is no way for me to post it.  I have no inclination to do that.  I suggest that if you want a copy, buy the magazine. 

If you don't already get MCN, you should subscribe.  In short, it is the best motorcycle magazine - period.  It's worth every penny.  The website is mcnews.com  There is a button on there for subscriptions.  As I said, they don't take advertising so they're not trying to please the manufacturers or anyone else.  They're completely unbiased.

[Valker]

They're completely unbiased.

While this may be true of their bike evaluations and product reviews, they most certainly do have an editorial bias towards some issues. The most blatant example of which is their bias against the MSF program. It does carry to other areas though. That said, I have subscribed to Road Rider (MCN before they changed names) since 1971.

[mrflamewerks]

While I appreciate the suggestion about the magazine, I'm not the sort who buys an annual subscription for one article of interest.

Thus far the only contrary argument anybody seems to be able to offer appears to be based on a line of thinking that goes something like, “It’s a car tire of course you can’t use it on a motorcycle”. When I ask why not, the answer is invariably, “It’s unsafe”. When I ask why, the answer tends to be, “Because it’s a car tire, so it must be unsafe”. This strikes me as a circular argument and does nothing to convince me it isn’t a good idea. This is especially true when there are numerous examples of people running properly fitted auto tires for over 100,000 miles without any problems. And, in light of the fact that motorcycle tire technology is 25 years behind the curve when it comes to durability, at three or four time the cost of a car tire, it seems like a very good idea to at least give it a try myself.

[PJH]

Okay,  I'll key in the whole letter and response.  Remember that I wrote neither the letter nor response, and I take no responsibility/credit for either.  Save your flames.  Foregive me typos, I'm not a secretary.

Car Tires Debate
There's a debate raging online about the use of automobile tires on bikes, particularly heavy, powerful bikes like the Honda Valkyrie and the Triumph Rocket III.

While it doesn't seem to be a good idea to me, folks on this forum claim car tires handle corners as well as motorcycle-specific ones, plus they wear longer and give better braking performance, all while being significantly less expensive.

If I had one of these bikes, I wouldn't risk wadding in a corner when my rear contact patch disappeared to a knife edge on the square section of the tire.

I'd bet you'd agree, but what I lack is the definitive technological background and convincing language to make my point.

Tom Krise
chiefrider1953@hotmail.com

All I can say to this is NO!  The only application for car tires on motorcycles that I am aware of being even remotely reasonable is on a sidecar.  Some full-on sidecar conversions will use car tires but with different wheels or wheel modifications and/or a very specific tire size and model proven to be safe.  Car tires are not designed to lean or carry side loads as motorcycle tires are.  Traction and proper tire flex when leaning are factors, as you noted.  Straight line stability can even be a factor.  I have seen a few bikes with high-speed weave issues due to the rear rire wearing flat across, losing its proper round contour.

There are also potential bead sealing differences between a car tire and a motorcycle tire.  For more details on why car tires are wrong for motorcycles, you could contact the tech department At Dunlop, Bridgestone or Micheliin.  Each of these companies makes both bike and car tires.  They will have a list of issues and conflicts between the two applications.

[Valker]

Thanks for typing that in. I know it took a long time.
The letter and response are the typical ones most of the 'darkisders' have heard for years. At least they have calmed down from the 'horrible flaming death' posts that were rampant when this first came up.
Just to recap the responses I've posted here and elsewhere: Car tires do NOT lean on a bike. You don't get up on the sidewall, edge (corner), or very outside edge of  a car tire when the bike leans. About half of the normal, flat contact patch stays in contact with the road surface in even the sharpest turns. Car tire ARE designed for sidewall loads and flex. They stretch and flex MORE when mounted on cars than on bikes. There are some high speed weave issues with car tires as well as with some bike tires.
Most folks who think it is a bad idea have never tried it-same thought as "the people who best know how to raise kids are the ones without any of their own".
If you don't want to run a car tire on a bike....Don't! 8)

[dennisraz]

I'll never go back to a Over priced $200 motorcycle tire that lasts one season.
If they were so concerned about our safety,they would make the tires affordable.
They just want to sell over priced inferior tires.

My first dunlop lasted about 5000 miles.