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Discussion Starter #1 (Edited)
I plan on opening a can of worms here, but, I am good at that so here goes. I was sharing brews with an engineer buddy I went to school with who doesn’t ride but is a smart fella who does some finite element modeling for his work. He is a huge sports car buff and tire freak and grease under the nails kind of guy. So we get to chatting about car tires on a bike and he almost blew beer out his nostrils. He made a few quick points that I found interesting in my reduced mental state from consuming hops.

1) My buddy thought the turn in and handling of the tires would suck and that alone would kill the deal. I said, nope try harder, I know several people doing this and all log high miles or they wouldn’t bother with a car tire. If the handling sucked, somebody would fess up. So we agreed, handling is a non issue – I have my doubts though.
2) Now here it gets a little better. Car tires are designed so that the contact patch forces (acceleration, braking, and side slip) for the most part are perpendicular (at a right angle) to the wheel and always act in the same plane. A moto tire must tilt, so the forces are not directed the same as a car tire and change with the angle of the lean. He went on to state that car tires have a softer sidewall since they don’t have these varying force directions to deal with. And on a bike, in a turn, the braking and side slip foces are at two different angles. My eyes started getting glassy and I was trying to change the subject now to hot women.
3) A continuation of 2) is his belief that a bike in a lot of turns will build up heat from this side wall loading and could over stress the radial tire internal cordage that provides the load carrying capacity. Then he gave back and commented that a car tire would be designed for a heavier wheel load and started talking in circles a little.
4) The sidewall of a car tire is thinner than a moto tire. I am not as sure of this as he was.
5) A moto tire has a softer and therefore higher grip compound. Thus reduced mileage potential. I bought that.
6) And the best one for me, and I just remembered so I edited, is that the contact patch size and shape on a moto tire should not change much with lean angle. With a car tire, this is not so and the patch gets smaller as you lean and the car tire shoulder starts to roll under the bike. This could be embarrasing if riding near the limits of traction and you start to turn tighter or need to brake.

He commented he would rather play with loaded guns than try it and asked what it was like to have a blow out on a bike (he is a non rider). I told him it scared the smelly solids out of me when mine blew out from valve stem failure.


Yawl be safe, I just orderd two new Tourance tires for my strom, it was painfully expensive.
 

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Uh, someone did it for a drag bike over on newninja.com (not sure if the forum is still alive), they said it deforemed a lot in the turns but on the straights it beat a bike tire for grip.


so for a 1\4 stretch go for it, if you're planning on using it for daily riding you'll probably end up chewing through the sidewall from all the deformation.
 

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Look at the darkside threads and you'll see that these theories hold no water. An engineer here at work runs a car tire (AKA Darkside) on his Goldwing and loves it.
 

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Discussion Starter #4
Larry, I have looked at these threads. Its why I bothered to inquire a little to satisfy my own curiosity and maybe debunk a myth or two.

There is a minority here who are happy with car tires also and have miles to show for it. And there is also majority (like me) who would never run a car tire but do not have a good arguement why.

No insult to your gold wing buddy...but most wingers are not pushing the handling envelope of their half ton machines.
 

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I run a C/T on my ST 1300 and love it,
I do mostly touring on this bike pulling a trailer,,
I would not install a C/T on my Hayabusa,,
but it works fine on the ST,,
 

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Discussion Starter #6
Iride,

So, why do you feel one way with the ST (my latest lust for bike BTW) and another for the busa?

Would some fancy extreme save your biscuits type of maneuvuring on your ST concern you? Like swervimng around a car or similar?

Would the car tire stand up better to the smoky burnouts of the busa?
 

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Aside from the lack of a speed rating over abotu 115mph I don't think I would like the idea of having a car tire lean that far over in the turns.... just my opinion tho.
 

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... an engineer buddy I went to school with who doesn’t ride but is a smart fella who does some finite element modeling...
Is he a 'tire' engineer?

Being a smart guy and performing FEA does not qualify him as a tire expert...

A heavy, loaded bike, pulling a trailer...
hmmm?

The 'darksiders' forums show way more blowouts on motorcycle tires than CTs.

Many folks that run CTs run ROFs (run on flats)...



BTW--I recently completed a 4300 mile trip on my GL1800A with a pillion and a trailer and the CT was GREAT!









p.s. I am also an engineer that performs FEA, but I am also, not a tire engineer...
.
 

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I think I'll stick with motorcycle tires designed for motorcycles by motorcycle tire engineers. :var_26:
 

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Discussion Starter #10
No henry, he is a civil engineer now but worked for aerospace previously before they downsized, designing rocket motors. So he is the proverbial rocket scientist...not tire engineer. He also is a car nut and common sense kinda of guy. I think if you give serious thought to some of his ideas they have merit.

I have a hard time believing the car tire would fail from the stresses of a bike...NOPE, not happening.

But I do have a concern with the handling characteristics on the "edge" of the riding envelope. This is the same reason I buy good/name brand/ and yes expensive radial tires. I care much less about looks, longevity or the price of a tire than I do about sliding on my ass down the road because I hit marginal traction of some sort. This is the reason why the goldwing or other heavy touring experience pulling a trailor or such is "almost" meaningless to me. The type of stresses and riding between a wing and trailor and my strom way over in a turn an loaded to the hilt also I believe are different.

henry, you are an engineer as you state, so am I. The physics around what is happening is not that difficult an engineering concept. What is unknown by you, me, and my rocket scientist beer drinking friend is the amount of factor of safety built in to a tire of any type.
 

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The most I can get out of a motorcycle tire on the ST is 5000 miles,,,
Pulling a trailer kills the mileage, You can not get a touring tire in the size for the ST,,,
If you want to run a C/T on a motor talk to the people that are doing it,,
Not the ones that have never done it,,,,
My C/T has better grip than any M/C that I have run,, That baby stops on a dime,,
I live in West Texas so the curves I have taken are fine, It takes a little to get used to..
Its been so hot here I have not been able to put a lot of miles on it,, I do have a big trip planed in Aug for Yellowstone...
Like I say talk to the ones that have done the C/T not the ones that scream
You will die, you will catch fire, you will slide down, and the C/T will blow up.
It will go flat, you will die,,
Oh yea, If I was just going to drag race my Busa I would install a C/T

Mike


Iride,

So, why do you feel one way with the ST (my latest lust for bike BTW) and another for the busa?

Would some fancy extreme save your biscuits type of maneuvuring on your ST concern you? Like swervimng around a car or similar?

Would the car tire stand up better to the smoky burnouts of the busa?
 

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Discussion Starter #12
"If you want to run a C/T on a motor talk to the people that are doing it,,
Not the ones that have never done it"

Iride...great advice, and the whole reason I even bothered to post this to the forum to begin with. If you read my posts on this, my mind is not as made up or closed as many about this issue.

I can see why a touring bike would go this route. I am less convinced on a bike that I plan to run the edges of the tire on a lot.

What I am hoping for is somebody to come out of the woodwork who has a non biased opinion of this...and the entire reason I asked my frined since I know no tire engineers and he had no bias since he stays on 4 wheels.

The point of this discussion is not me telling you or you me that we know nothing of what we discuss. The point was to cut through all the hype and maybe save myself some money in tires.
 

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My opinion means little being I am a new rider but I don't see any good reason to run a car tire on my V-strom (Other to say I have done it.)
On the darkside website, from what I read most riders run only a rear tire on their cruiser, not a dual sport or sport bike. This is because the rider understands the strength of the side walls on a motorcycle tire is stronger than a car tire side walls. Before the rider ended up riding on the side walls in a turn they would be scraping chrome so this issue would be avoided. (Makes sense to me.)
Tires are designed with certain jobs and performance expectations in mind so a motorcycle’s need would differ from a car/trucks needs. Plus what kind of rims would you use to mount a car tire to a motorcycle. If you are mounting them to the motorcycle rim, would the tires form be compromised? If you used a full car setup what mods would be needed to setup them up on the bike?
I can see increase traction using a car tire because a car tire is not rounded like a motorcycle tire but in turn more friction would mean less gas mileage and that also increases stress on other parts of the bike aka brake system and maybe frame?
If you do it, thats cool and I would love to see it live in person.
 

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My opinion means little being I am a new rider but I don't see any good reason to run a car tire on my V-strom (Other to say I have done it.)
superior milage, MC tires last 10-15k at most, more often only 6000 or 7500 miles. Car tires will deliver 25k, 40k, maybe 100k, saving thousands of $$ in tire cost

superior traction in low traction situations, gravel, snow, ice, wet


On the darkside website, from what I read most riders run only a rear tire on their cruiser, not a dual sport or sport bike.
cruisers usually have 15 or 16" rear wheels, car tires come in comparable sizes to the stock tires, sportbikes usually have 17" wheels, the selection of car tires becomes more limited and you usually have to settle for a car tire that is 40%-80% wider than the stock bike tire

This is because the rider understands the strength of the side walls on a motorcycle tire is stronger than a car tire side walls.
:confused: stock bike tire is 756lb load rating, car tire is 1465lb load rating and you think it has weaker sidewalls :green_lol: car tires are much stronger than bike tires all around

Before the rider ended up riding on the side walls in a turn they would be scraping chrome so this issue would be avoided. (Makes sense to me.)
radial tires are radial tires, the carcass flexes, you don't get up on the sidewall of a car tire anymore than you would a bike tire

Tires are designed with certain jobs and performance expectations in mind so a motorcycle’s need would differ from a car/trucks needs. Plus what kind of rims would you use to mount a car tire to a motorcycle. If you are mounting them to the motorcycle rim, would the tires form be compromised? If you used a full car setup what mods would be needed to setup them up on the bike?
I can see increase traction using a car tire because a car tire is not rounded like a motorcycle tire but in turn more friction would mean less gas mileage and that also increases stress on other parts of the bike aka brake system and maybe frame?
there is really no difference between how a radial car tire or radial bike tire rolls, yes, its a heavier tire which helps dramaticly in low traction situations, much easier to take off without wheels spin, I have not noticed ANY change in fuel economy, and rear brake is actually effective in stopping power
handling is no different than if you had a similar size bike tire

If you do it, thats cool and I would love to see it live in person.
8000 miles, no noticable wear, if yer primary riding is sport riding, a car tire is not for you any more than a 200/50 motorcycle tire is on a bike that normally runs a 150/70





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He went on to state that car tires have a softer sidewall
they may appear to have a softer sidewall, you would bulge a little more in the sidewalls if you were suppporting a 1½ton car instead of a 500lb bike
5) A moto tire has a softer and therefore higher grip compound. Thus reduced mileage potential. I bought that.
depends on what tires you compare a motorcycle racing tire will be softer than a 100,000 mile all season radial, on the other hand, I can guarantee you that my General Altimax Artic winter tire is softer compound than a sport touring bike tire

6) And the best one for me, and I just remembered so I edited, is that the contact patch size and shape on a moto tire should not change much with lean angle. With a car tire, this is not so and the patch gets smaller as you lean and the car tire shoulder starts to roll under the bike. .
with a bike tire, your contact patch is approx 40% of the tread width or less with a car tire your contact patch is 40% of the tread width at minimum, when yer going down the road straight its more like 90%, a car tire even at full lean scraping pegs is NEVER on the sidewall (infact, I have narrow chickenstrips on my car tire)



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Well said Randy
One thing I installed before the C/T was a Doran TPS, I call it a safety device
I can monitor my tire pressure while going down the road,,,
Even has a alarm that goes off and a red light that blinks if i Lose more then 10 % pressure,, I mounted the unit on my left handlebar and the red led alarm beside the gorilla, The price was a little steep, at 200 bucks
 

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Well said Randy
One thing I installed before the C/T was a Doran TPS, I call it a safety device
I can monitor my tire pressure while going down the road,,,
Even has a alarm that goes off and a red light that blinks if i Lose more then 10 % pressure,, I mounted the unit on my left handlebar and the red led alarm beside the gorilla, The price was a little steep, at 200 bucks
are you running a runflat? the tire store I bought my CT from recommended against running runflats unless you have a TPS, they say that's the only way you can tell it's flat



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No, Not running a run flat,
It seems the ST needs a very narrow 205/50/17 and the Hankook has the narrowest 17 inch tire,, I do not know of anyone that runs one on the ST,
Just do not think it will fit,,
Mike
 
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