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

[makenzie71]

1981 GS750E. As posted before, I'm running a 17X3 up front and a 17X3.5 in the back. 110/70 radial up front with a 130/70 bias-ply in the back.

Changing wheels I shaved 21lbs of rotating mass off (I'll post a full breakdown of weight to compare later). This is, by far, the BIGGEST thing you'll notice. Steering is completely effortless...I'm actually going to install a damper because she's so easy to throw around.

I was concerned about the narrow tire in the back but I am very happy with it. Not quite the tread pattern I want, but she's smooth and has plenty of grip all the way to the edge. I can tell you that if you have a 4-1, you can REALLY get the bike down...dangerously so. Just something to keep in mind when mixing modern stuff with old stuff...the capabilities of your modifications may exceed the abilities of your machine, despite the fact that they will replace the devil's counterpart, that angel who tells you to "cool it", with a damn demon that says "**** the devil, and take your hands off the bars while you do it."

Anyway...after 200 miles on the setup I've got to say I'm pretty pleased. The bike is nimbler, but it is commanding of respect and far more attention. Gearing, at 16/38, still isn't quite right for highway but she motors around town with ease and gusto.

All in all, it's very worth doing, just mind your road manners. Oh and I'd like to apologize for this post...I wrote most of it then got distracted by a movie and forgot where exactly I was going to go with it. I may remember, though...

 

[jwhelan65]

Have some pics??

 

[makenzie71]

There's some info here, including a pic that actually shows the wheels...I just haven't had a chance to get a better one up.

 

[Ogri]

Just imagine how much better it will handle when you have matching rubber front and rear.

 

[makenzie71]

The dangers of mixing bias ply and radial tires are mythical, brought about years ago by manufacturers' suggestions not to mix them as there was not sufficient data concerning the results of the combination. Where as, today, at least twenty models (that I'm aware of) come from the factory with radials and bias combinations.

While it's not exactly the tread pattern I want (my new tires are on hold at the moment), the combination is sound. I may have to change to a different setup, but it'll be because the handling characteristics between my GS750E and my old TL1000S are so drastically different...not because a radial/bias combo is unsafe.

 

[Ogri]

The dangers of mixing bias ply and radial tires are mythical, brought about years ago by manufacturers' suggestions not to mix them as there was not sufficient data concerning the results of the combination. Where as, today, at least twenty models (that I'm aware of) come from the factory with radials and bias combinations.

While it's not exactly the tread pattern I want (my new tires are on hold at the moment), the combination is sound. I may have to change to a different setup, but it'll be because the handling characteristics between my GS750E and my old TL1000S are so drastically different...not because a radial/bias combo is unsafe.

Please provide links that show the twenty models of motorcycles that come from the factory with radial and bias tire mixed. I'd be curious to know.

 

[makenzie71]

You can do your own research as well as I have. Look mostly toward European bikes...Beamers are big on it. Yamaha, Honda, and Harley also send several of their bikes out there door with such a configuration.

It does change handling. It does not make it dangerous...or not any more so than riding. Probably not something the inexperienced should experiment with.

 

[posplayr]

Myth or not

Myth or not

Back in college, drove a large 73 Impala with mixed tires. I think it was radials on the back and bias on the front. It did not feel too bad until I passed a car as about 60 mph+. The weaving of the rear very scary and I was very careful to slow down without unduly exciting the big a$$ rear end.
I'm not sure if the radial were on the rear as this was some 30 years ago, but with the increase rear side wall flex on the rear radial would have an uncontrolled feeling like that. If the radials would have been on front i suspect i could have compensated with the steering a little better but rear not so.
On a motorcycle the side wall flex of a rear radial could cause the rear to push out more possibly causing instability. Of course with a 180/55-17, that 5.5" rear rim is so wide that I doubt there is a whole lot of side wall flex. So this probably mainly applies to avoiding narrow radial ties on the rear.

Pos

 

[makenzie71]

With my TL, that's why I went with a radial on the front and a bias on the rear. The rear didn't feel as stable with the taller radial in the back. It wasn't unstable, but sometimes you can feel your bike move a bit unexpectedly and it turns your stomach in a way...I'm sure you guys all know what I'm talking about.

The radial up front lightened the steering, but the tire was short and wide...there was no flex.

 

[Nessism]

I'm scratching my head trying to understand why mixing tires would cause a problem. As long as the relative grip is matched, it shouldn't matter what the construction method is.

 

[makenzie71]

That's what made me start experimenting, Nessism...amongst a few other things (mostly seeing bikes roll off the showroom floors with combos).

The tires are constructed differently and have different handling characteristics. Only a problem in the hands of the inexperienced or the unexpecting.

 

[jabberjoe87]

I can't beleive i'm asking this, but i don't know so thats why... is there a way to tell the difference between bias and radial by looking at the tire?

 

[makenzie71]

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

 

[posplayr]

Nessism

Nessism

Ed,
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. When you turn to the right the rear swings more to the left. If you need to go left you would need to swing the steering wheel right first to the rear to swing that way then return to the right turn. Kinda scary at 60+ mpg with a 4500 lbs beast.
Granted with stiff tires (wide profiles) there is probably little effect, and a flexing front tire is easier to deal with the flexing rear.
So basically if the tires flex differently and cause a different angle of attack, then the angle (in the horizontal plane) of the bike will change from normal stable ridding attitude. If it is the rear sliding out that is the most dangerous.
My most recent experience with excessive front tire flex was on my E350 full size 1 ton van (5700 lbs empty) . It had narrow factory tires on it when I bought it new. Going down a steep hill the first time at about 70 mph, I could feel the flex in the front tires in turns which gave it an uneasy feeling because it took a lot of wheel input to get the van to turn. Severe under steer. Later I put large mag wheels with 255/60-17 tires The handling improved dramatically .

Pos

 

[80GS1000]

I can't beleive i'm asking this, but i don't know so thats why... is there a way to tell the difference between bias and radial by looking at the tire?

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.

 

[Nessism]

Hey Jim (Pos),

As long as the radial tire sidewall is pulled tight, such as is the case when using an appropriately wide wheel, there shouldn't be any more slip angle when using a radial than with a bias ply tire.

Key thing is to make sure you have the right wheel width; using radial tires on narrow GS width wheels would make for a very dangerous handling machine.

As for not mixing tire types, I still don't think there would be any problems for a road going bike. Track riding, where tire matching is more crucial, might be a different story though.

 

[Billy Ricks]

Running a radial front with a bias rear has been done safely for years.
http://books.google.com/books?id=Ls...&hl=en&sa=X&oi=book_result&resnum=2&ct=result

 

[posplayr]

Note Quotes from the Source

Note Quotes from the Source

"In actual practice however, lots of people are having fine results putting either radial on the front, or radials on both ends of such bikes - provided the rims used are not narrower than the call-out for the radial tire(s) in question. "

and

"Particularly bad is putting radial on a narrow rear wheel".

As noted above and in prior posts a radial on the rear that has more flexible side walls than the front is bad. As can be imagined, it causes the rear to fishtail on the flexible sidewalls.

A flex front is less critical as it tends to cause under steer which is not as likely to cause stability issues.

I think makenzie71 has adhered to these guidelines so the phobia of mixing radials with bias tires is not routed in a myth, but is based in truth as the danger of the flexible walled rear tire warning. The truth however doesn't appear to be as restrictive as the phobia would suggest.

Billy,
Thanks I happen to have that book on my shelf


Pos

 

[Ludeykrus]

Thanks for the review Makenzie, what are the wheels off of?

 

[makenzie71]

They are from a Suzuki GS500E (or F works...all years I2 GS500's work).

I'll be switching to a YZF600 rear wheel sometime in the future...as soon as I can find a free tire for it, actually...haha...