200 miles on 17's...some things to keep in mind...

[Bad Kaw]

If you look at the size on the tire's sidewall and it has a R in it, it's a radial. Like 180/55ZR-17. The Z is the speed rating.

To throw a little fuel on the fire (), I still don't think it's a good idea to mix radials and bias ply tires on anything other than a cruiser or bike which spends most of its time going straight. Hence why you only see the factory-fitted mixes of radials and bias on cruisers and touring bikes.

If it were a good idea for cornering, you'd see that combo on sportbikes and on roadracing bikes. You don't.

Oh, and Mobil 1 is the best motor oil, chains are better than shafts, Michelin makes great street tires but their race tires suck.

Ha-haaaa! Nice post!
Going to have to jump on the "80GS1000" bandwagon on this one. Or, 'The Proof is in the Pudding'; I've done this on several occassions and found it to be substantially disturbing. Here are a couple experiences: Installed an inverted front clip on a bike and put the obligatory sticky Michelin on (b/c they make great street tires!) and experienced wierdness from the back end during hard cornering...the front would stick deep and hard (...easy!) and the rear liked to drift and slide and just plain step-out. Having experienced front-end problems caused by the rear, and rear-end problems caused by the front I was hesitant to lable the diagnosis early. But when I put the matching rear wheel/tire combo on everything calmed down and all things became composed once again.
Also, I have a Hawk that came with bias plys, and purchased a second one b/c they're so dang cool. The second one became my track weapon and I slapped some sticky Michelins on them (b/c they make good race tires!) and had a total gas on the track. My last set of track-day skins went to the wife's street Hawk after I got done with them and I installed the front first, leaving the 'like new' rear on the bike b/c I was considering selling it and wanted to save a tire. Again, cornering instability popped up and went away with the installation of the rear radial; and this is just 'spirited' street riding...lots of room to the edge.

So, respect rendered to all; I suppose a 'daily commuter' might be just fine, but I don't have a bike that I don't "push" from time to time. I've sampled this ride and I'm not gonna do it again.

-KR

 

[makenzie71]

For the record, I've done my own research into it and found combinations that work great for me. I am in no way suggesting anyone else do the tire thing.

 

[Guest]

They'll say "radial" or they have something like "tread 4 plies nylon, sidewall 2 plies nylon".

Bias-belted tires also have tread plies (the belts). As noted in another message, the "R" in the size designation indicates that the tire is a radial.

Based on my previously described experience as well as other reading and experiments, the lateral force on a car is directly associated with the angle between the tire tread and the wheel. The wheel turns further than the tire due to tire flex. A wider tire is stiffer and follows the rim better(smaller angle).
While motorcycle tires lean as the bike leans in turns, there is still a lateral component of centripetal acceleration (normal to the leaning rim)associated with the tire and therefore it must be twisted to some degree. Obviously 60 series tires don't twist as much as 90 series profiles.
So here is the issue that I saw with my rear mounted radials, the rear tires sidewalls would flex causing the rear to move around seemingly uncontrollably...

If your logic were correct, the rear sidewalls would also flex when the front is a radial.

I don't buy any of this without seeing some engineering studies. Way too many other variables are involved to reach these conclusions.

 

[makenzie71]

It should also be noted that with the sportier tires you don't really have much sidewall. I had to really push my TL...which had a 200mm tire at times on the rear...to really notice. When you're looking at bikes like the GS on the stock mags, you have almost as much sidewall as you do actually treat surface...the front wheel on my 79 actually has more sidewall.

Also, just to add...I'm selling my front end setup if anyone would like to pick one up already setup. 17X3 wheel, 4-piston Tokico calipers, fresh fluid in the forks...no fender, no brake lines...all for $170 shipped. I'll throw in a 250 mile michelin macadam for another $35.

 

[RobGS850L]

Ran a few combo's of mismatched tires. I found that the high sidewall tires seem to transmit a loose feel at low speeds on the rear and the front makes it feel non responsive, but at higher speeds though it wasn't all that noticeable. Mismatched types with low profiles don't seem to do this too bad. Actually running too large a tire (wide) gives you the same feel.

 

[white_2003]

one thing to be concerned with is harmonics a radial tire has steel belt and a bias is well bias plied that why you dont mix them on cars anyways, i have heard stories of tires destroying themselves if say placed next to eachother on a dually for example... could be an old wives tale like burning exhaust valves with a megaphone exhaust, but i like matching tires anyways looks like you planned on having the tire instead of just got a good deal kinda look

 

[posplayr]

themess

themess

I don't buy any of this without seeing some engineering studies. Way too many other variables are involved to reach these conclusions.

Here is a free engineering reference for you to read. There are less technical explanations around as well if you just google "tire slip angle".
See attached excerpt:


http://books.google.com/books?id=Kw0Xk9GmT0gC&pg=PA324&lpg=PA324&dq=tire+sideslip+angle&source=bl&ots=E433kV83Ej&sig=t7RiryvIv9mnOyz3HtzcKCrp7jc&hl=en&ei=Hg-vSbebIoSTngfR--G9Bg&sa=X&oi=book_result&resnum=4&ct=result#PPA324,M1

Based on my previously described experience as well as other reading and experiments,

I did not full elaborate on this simply provided the reason.

If your logic were correct,

This established theory; see above

the rear sidewalls would also flex when the front is a radial.

The rear tire does; that was the whole point of the explanation for not mixing. All things being equal (which they are generally not) a radial will have more side wall flex than a bias play. Lower profile tires twist less because of the general increased side wall stiffness because:
1.) shorter sidewall must have more force applied to get the same deflection as a longer side wall

2.) The wider tire will need more force to generate the same angular twist in the tread as compared to a higher profile tire. It is basically due to the moment arm of the tread at the longer offset (width).

The only difference between the motorcycle and a car with regard to side slip angle is that only a portion of the lateral force on the tire is parallel to the tread. Draw a vector diagram (in the wheel frame) to decompose the centripetal force in a turn to see why this is true.

Here is a reference if you want more of the Gory details specific to a motorcycle.

http://books.google.com/books?id=rJ...X&oi=book_result&resnum=3&ct=result#PPA124,M1


Pos

 

[Guest]

Here is a free engineering reference for you to read. There are less technical explanations around as well if you just google "tire slip angle".
See attached excerpt:


http://books.google.com/books?id=Kw0Xk9GmT0gC&pg=PA324&lpg=PA324&dq=tire+sideslip+angle&source=bl&ots=E433kV83Ej&sig=t7RiryvIv9mnOyz3HtzcKCrp7jc&hl=en&ei=Hg-vSbebIoSTngfR--G9Bg&sa=X&oi=book_result&resnum=4&ct=result#PPA324,M1



I did not full elaborate on this simply provided the reason.



This established theory; see above



The rear tire does; that was the whole point of the explanation for not mixing. All things being equal (which they are generally not) a radial will have more side wall flex than a bias play. Lower profile tires twist less because of the general increased side wall stiffness because:
1.) shorter sidewall must have more force applied to get the same deflection as a longer side wall

2.) The wider tire will need more force to generate the same angular twist in the tread as compared to a higher profile tire. It is basically due to the moment arm of the tread at the longer offset (width).

The only difference between the motorcycle and a car with regard to side slip angle is that only a portion of the lateral force on the tire is parallel to the tread. Draw a vector diagram (in the wheel frame) to decompose the centripetal force in a turn to see why this is true.

Here is a reference if you want more of the Gory details specific to a motorcycle.

http://books.google.com/books?id=rJ...X&oi=book_result&resnum=3&ct=result#PPA124,M1


Pos

I'll look through it. I'm not sure that it's on-point, and I can't jump into the center of an engineering argument without knowing premises that were defined far earlier in the text. But I'll look at it.

 

[posplayr]

themess

themess

I don't buy any of this without seeing some engineering studies.

I thought you were asking for an engineering reference.

I'm not sure that it's on-point,

The topic was on the subject of mixing radial and bias tires.

The practical experience is that it is OK to put bias plys on rear with radial in front but not the other way around esspecially if the radial is a higher profile (i.e. less side wall rigidity).

Side wall rigidity is intimately related to side slip angle (I described this). Some tires are stiffer than other depending upon profile and construction.

The reference describes mathematically the physics of what happens when you change the relative stiffness of the tires.

Section 4.6.2 represents the case where a radial would be mounted on the rear.

Section 4.6.3 represents the case where a radial would be mounted on the front.

Pos

 

[Billy Ricks]

As long as the radial goes up front things are fine. If it goes on the rear of a mismatched set the rear can overpower the traction up front.

 

[Guest]

I don't question the importance of slip angle, which is the topic of your first reference. I do question the other assumptions, mostly about tire stiffness. Radial and bias ply tire sidewall stiffness can be very similar. While the center of a radial tire sidewall is usually less stiff than that of a bias ply tire, the bead package of a radial tire is usually stiffened more, and the upper sidewall is also usually stiffer, to protect the edges of the tread and to keep the tread flatter.

It seems to me that wider tires change the contact patch enough that the slight difference in stiffness may no longer be relevant.

I'll look at the second reference, since it specifically addresses tire stiffness.

I've usually seen the better handling of radial tires attributed to maintaining a flatter tread contact patch, with less squirm.

 

[Guest]

The motorcycle dynamics book diagrams show the front tire turning in the same direction as the turn, instead of countersteering!

 

[posplayr]

themess

themess

A 180/55-17 tire on a 5.5" rim is not going to have much side wall flex, so there is not much danger in mixing this with a bias ply tire.

I'm pretty sure that was the qualification of the rear radial tire warning statement; i.e. it is a tall radial.

Pos

 

[76FJ55]

Of course the front tire is turned into the turn. The whole counter steering issue is widely miss under stood and an unknow concept to some. The counter steer is merely used to initiate the turn, then the front wheel is turned into the corner. Basically it works like this. Initially you are riding along ballanced, you now want to make a right turn. you willinitially turn the bars/wheel slightly left this upsets the balance of the motorcycle by causing the contact path to move to the left as the bike moves forward. now with the contact patch left of the cg the bike will start to fall right. you now transition from counter steer to turning into the corner. this is done to balance the force of gravity wnting to make the bike fall over with the centripetal acceleration force generated by the tires driving the bike into the corner. when held at static equalibrium you will maintain a continuous rate of turn. now when you have reached your new desired heading you will again upset the equalibrium by turning the bars/wheel into the corner further than required to maintain the arc you are traveling. this will cause a greater amount of cornering force than can ge counteracted by gravity causing the bike to move back towards the upright position....
Actually this is a continuous unconsious action being performed to balance and control direction. this is ofcourse aided by the geometry of the bike which in a sense acan be self stabilizing (usually mostly effected by trail), but these movements must be made in order to control direction.

 

[pkbjamn]

I've often tried to explain this phenomenon to non-riders (and riders alike!) using much of the terminology in your response, but not all of it. This very much helps to qualify the explanation of counter-steering. Thank you for increasing my knowledge and ability to propagate it.