Front Tire VS Rear Tire Grip

[The1970's]

Hi all, I have to admit this question stems from my Seca turbo but I figured the rules of physics still apply and the GS crowd would have an answer to my questions. Anyway I bought my 1982 Seca Turbo a few months ago and have gone through it pretty well fixing all the miscellaneous issues and neglect. I didn't put new tires on it but found that the date code on the Bridgestone Battleaxes to be just 2 years old and they have ~80% tread. Factory sizes where 3.25-19 on the front and 120/90/18 on the rear. Mine has 100/90/19 and a 130/80/18 respectively.

Like all my new bikes, now that I started riding it some more I wanted to find the limit of my comfort/riding ability before I hit the limit on accident trying to avoid traffic. I do this by finding some clean corners and seeing what the bike can do, starting slowly and picking up the pace until I no longer feel comfortable or reach the bikes limit (Which I've never done yet). So I take my Seca out and it feels rock solid going through the corners. I eventually got to a speed/lean angle that the bars started to go sort of numb and the steering got pretty light. I assumed this was getting pretty close to the limit of the front tire so I called it a day and rode home.

When I got home I took a look at the tires and it looked like the front had about a 1/4" chicken strip on either side and the rear had 3/4". Now in all my experience the edge of the rear tire seems to come before the front. I can't seem to think of why I would experience the opposite on the Seca. In addition, I really wasn't leaned over all that far. My GS750 will definitly lean further and they weigh about the same with the same size front tire. I'm wondering if maybe the larger rear tire plays a role in this or if I'm not on the power enough through the corners. Either way I've never been to a track with a motorcycle or really ridden any great canyons (Florida ) but I'm always willing to learn more from the guys that do. Discuss!

[Steve]

On most GSes (yes, I know you are talking about your Seca), the front tire is a 3.50. Doing the math, that is real close to a 90 in today's sizing. Many of us are running 100s with virtually no problems.

Your Seca came with a 3.25. Doing the math, that is 82.55mm, so if you up-size like we do, you should probably have a 90 on there, not a 100. Depending on the wheel width, the 100 might be getting pulled into a tighter radius, actually giving you a smaller contact patch.

On the rear, my bike came with a 4.50. Again, doing the math, that is 114.3, so should likely use a 120/90, but most of us use a 130/90.

You say your Seca came with a 120/90 on the rear and it now has a 130/80. That tire is wider AND shorter, which changes the profile on the rim. Depending on the width of the rim, it could be really distorted. The fact that it might be pulled into a tighter radius by a narrow rim would account for more of your tire not making contact with the road.

On top of all that, I would not worry about the difference in the width of the "chicken strips". The width of that strip will depend on your cornering angle, but if they happen to mold some tread all the way around the sidewall of the tire, you are going to have some HUGE chicken strips that you will not be able to get rid of. Your different widths are likely the result of different aspect ratios, too-large tires on too-narrow rims and simply a difference in tread design.

.

[Big T]

Steve is correct and, the 80 aspect of the back tire is responsible for the differences in the chicken strips

[greg78gs750]

As an aside, it's worth it to find a spot to do a track day, it is by far the best way to explore limits on a bike.

[Sandy]

Steve is correct and, the 80 aspect of the back tire is responsible for the differences in the chicken strips

Yes, the tire ends up being too round on the narrow rim. This is a 130/80 on my GS1000 and that's about as far up the tire as you're going to get. Except maybe on the track if you don't mind dragging parts. I went back to the 120/90 with no apparent difference in grip.



by soates50, on Flickr

[Steve]

If we are looking at chicken strips, here are the ones on my Wing. No sparks were generated in the process.

Front:


Rear:


.

[Burque73]

.......................chicken strips

............... chicken.................... Wing. ...........................
.

Man, I'm getting hungry reading this stuff!

[The1970's]

Hmm interesting. I had suspected the tire size was the cause but wanted to hear from someone who knew. Thanks for the info. I'll run these tires down then replace with the stock size. In reference to gregs post, this isn't something I typically do, I just like to know what sort of maneuvers I'm comfortable with as a relatively (2 years) new rider. I would love to head to a race track but I don't think my ancient machines combined with my skill would do anything but get in the way of all the 600 sport bike guys

[The1970's]

Man, I'm getting hungry reading this stuff!

Completely off topic here but your KLX in your signature has me intrigued. DRZ swap?

[Burque73]

Completely off topic here but your KLX in your signature has me intrigued. DRZ swap?

The KLX is made by Suzuki, it even says that on the frame tag. It's just a DRZ wearing green plastic.

Even further off topic, I sold it to Raygun, an inactive member here. Some great friendships have come from this forum.


I do find this discussion interesting, just don't have anything to add. If there was a like button I would hit it just to show my appreciation for the topic.

[TxGSrider]

The KLX is made by Suzuki, it even says that on the frame tag. It's just a DRZ wearing green plastic.

Even further off topic, I sold it to Raygun, an inactive member here. Some great friendships have come from this forum.


I do find this discussion interesting, just don't have anything to add. If there was a like button I would hit it just to show my appreciation for the topic.

They did the same thing for ATV's, I didn't know they did it for the bikes too. The Suzuki LTZ 400, KFX 400, and Arctic Cat DVX 400 were virtually the same machines with different body work and sometimes different shocks/springs.

[fbody_mike]

I have run 120-90-18 and 130-80-18 tires on my Seca Turbo. I'd usually revert to the skinnier tire when the 130 was not available. I can never tell the difference when riding which size tire it has on the back, but like others have said, most tire manufactures say the Seca rear rim is too narrow for a 130. After finding that out I will stick with 120.
By the way, I will go through three rear tires before I need to replace the front.

[The1970's]

The KLX is made by Suzuki, it even says that on the frame tag. It's just a DRZ wearing green plastic.

Even further off topic, I sold it to Raygun, an inactive member here. Some great friendships have come from this forum.

Hmm, didn't know that. I rode a DRZ 400 and loved it. I'm currently looking for some 70's era dual sport to do some trail riding with my friends so I was just curious.

[The1970's]

I have run 120-90-18 and 130-80-18 tires on my Seca Turbo. I'd usually revert to the skinnier tire when the 130 was not available. I can never tell the difference when riding which size tire it has on the back, but like others have said, most tire manufactures say the Seca rear rim is too narrow for a 130. After finding that out I will stick with 120.
By the way, I will go through three rear tires before I need to replace the front.

Mine had new tires on it when I bought it, but I am noticing the rear wears pretty fast. I weighed my bike in at about 530 lbs and I am currently running without the RH muffler and the lower fairings. Pretty heavy for a 120 rear. What tires do you like to run? Mine has battleaxes

[fbody_mike]

I use to run Avon, but they kept cracking and the life was very poor. Currently I am running the battelax too. Good tire so far, I think I have 3000 miles on it so far and I am just starting to be able to feel the center tread get a little square. Maybe it will last 6k miles. I want to try a Michelin next.