Rear tire width and handling?

[80GS1000]

What is the effect of rear tire width on a bike's handling?

All other things equal I would assume the tradeoff is like this:

A skinnier rear tire will cause the bike to have faster turn-in (flickability) and steering on corners, but sacrifice some cornering contact patch and stability at high lean angles.

A wider rear tire will cause the turn-in to be slower, but will be more stable and have more traction once leaned over due to the larger contact patch. A wider rear tire can be leaned over further than a skinnier tire as well (provided ground clearance isn't an issue), since there's more tire real estate to lean over on. Hence modern sportbikes have 180/190 section tires. And a wide rear tire also looks trick.

I'm looking to go with a 150 section radial for better handling and tire selection.

Are these assumptions correct?

[sharpy]

Wide wheels

Dont know about much about turn in and stuff but i know what handles on my bike (sort of) and thats a 140/80 x18 and on the street/track i have tyre wear all the way to the edges. Why oversize a bike just so it "looks good" when u have a spindley frame and swingarm that wont cope with a big tyre. Most people that see my bike think it "looks good" with this set up. Even with old 18in wheels. Come on boys correct me if im wrong LOL

[QuaiChangKane]

Mostly correct.....


A wider rear tire will somewhat slow the steering down, true - this can be a good thing on some bikes, as it lends a bit to stability.


But you can lean a bike over just as far with narrow tires as you can with wide tires. The difference is that you can handle greater speed at a given lean angle with a wider tire as there is a larger contact patch providing greater traction.

Racers were still scraping knee on the track with 130-section rear tires in the eighties. In fact, it is more difficult to scrub a narrow tire in edge-to-edge because it's got a drastically rounder profile than a wider tire (by "narrow" and "wide", think 130 vs 180). I have no chicken strips on my VFR which I ride at the same level as my GS - but the GS consistently has virgin rubber on the edges of its rear tire, although a few other things do come into play there, such as corner entry speed and weight shifting. The odd thing is that I can completely scrub the front on the GS with real estate to spare on the rear....

The stock rear on my VFR was a 170, but I run 180 Michelin Pilot Powers which actually have a more peaky profile than the 170 Metzeler that was on it when I bought it, so YMMV - no absolutes here, but I do have a number of riding partners that swapped their OEM 190's in favor of quicker-steering 180's on their newer liter-sports.


If you do go with a wider tire, experiment with different brands and models, as wider doesn't necessarily mean stickier, more stable, or better steering. Construction and shape can vary widely....


Just my .02



-Q!


(search the web for 125cc and 250cc GP bike photos and you'll see that the smaller bikes still use relatively narrow tires to keep from slowing the steering on an otherwise light bike, but they're capable of far greater speed and lean angle than most middleweight race replicas)

[Dink]

Another point to ponder, a wide tyre on a rim meant for a narrower tyre, will be distorted in it's profile. Leading to strange handling,i.e. a 150 tyre on a rim meant for a 130 will be "pinched" overly rounding the profile,also effecting shock absorbtion,and will drop off the centre of the tyre faster, BUT it will also make it drop off the edge of the tyre,due to the distorted profile. You will actually destroy the handlng of the bike, reduce traction when leant over, increase bump steer, and badly chew up the front tyre, due to push from the rear.

Dink

[80GS1000]

Thanks for the replies.

I definately agree that putting wider rubber on hardware that wasn't designed for it is a bad idea.

Wider tires on a GS1000 need to be part of a rear end swap, meaning a 4.5x17" Katana/GSXR rear rim, GS1100 swingarm, Katana/GSXR rear caliper and rotor, and a 530 chain conversion.

Another point to ponder, a wide tyre on a rim meant for a narrower tyre, will be distorted in it's profile. Leading to strange handling,i.e. a 150 tyre on a rim meant for a 130 will be "pinched" overly rounding the profile,also effecting shock absorbtion,and will drop off the centre of the tyre faster, BUT it will also make it drop off the edge of the tyre,due to the distorted profile. You will actually destroy the handlng of the bike, reduce traction when leant over, increase bump steer, and badly chew up the front tyre, due to push from the rear.

Dink

[sharpy]

real wheels

A 1988 GSXR1100 has a 4.5 x 18 inch rear which will give you a nice height as the 17inch will have lower profile tyres to suit and will sit a fraction lower. Jus a suggestion.

[denydog]

My last tire had a basic square profile! That is, after too many freeway miles wore the center flat.

Another point to ponder, a wide tyre on a rim meant for a narrower tyre, will be distorted in it's profile.

I sure tested that concept to the extreme! I just replaced a Metzler ME99 140/80V17 that I had mounted on my stock 2.50 rim #-o I could barely slip a piece of paper between the tire and the rear brake stay. I guess it rode OK. What do I know? I replaced it with a 130/90 section tire that is closer to stock. That's much more reasonable. I think the original tire was more like a 120 section, but I'm not sure.. It was listed as a 4.50".

I found out that marked tire width is not always what it says it is. Varies by brand, model, and rim width I think.

[Road_Clam]

What is the effect of rear tire width on a bike's handling?

All other things equal I would assume the tradeoff is like this:

A skinnier rear tire will cause the bike to have faster turn-in (flickability) and steering on corners, but sacrifice some cornering contact patch and stability at high lean angles.

A wider rear tire will cause the turn-in to be slower, but will be more stable and have more traction once leaned over due to the larger contact patch. A wider rear tire can be leaned over further than a skinnier tire as well (provided ground clearance isn't an issue), since there's more tire real estate to lean over on. Hence modern sportbikes have 180/190 section tires. And a wide rear tire also looks trick.

I'm looking to go with a 150 section radial for better handling and tire selection.

Are these assumptions correct?

Your thinking is pretty well stated. A few further facts, as the tires get fatter, the more pronounced leaned over "verticle return" you will feel. In other words, as you lay a bike into a graduall sweeping corner, fatter tires will want to force the bike back up to verticle. Fatter tires only offer more contact patch. But seriously ask yourself how far you really think you can lay over a 25 year old GS ??? (no matter how fat your rear tire is).

[earlfor]

Well.....since you asked, :-). You can lean until the footpegs fold up. Then you have to lift your feet to keep from scraping the sides of your boots. Holding your feet up and continuing to lean, you run outta lean when you start grinding the feet off the centerstand. Ask me how I found out. LOL

e.

[QUOTE=Road_Clam
But seriously ask yourself how far you really think you can lay over a 25 year old GS ??? (no matter how fat your rear tire is).[/QUOTE]

[80GS1000]

Earlfor - I'm totally with you on that.

Heheh, I ground off a nice little bit of the rear brake pedal the last time I was riding up in the canyons (time to look into installing rearsets). The bike with its current Pirelli Sport Demon 130 section rear tire will let you lean it over till metal starts sparking.

But you can't go very fast while leaned over that far - it starts feeling spooky and unstable. It'll be fun to do some track days and/or vintage roadracing on the new Miller Motorsports Park road racing track next season and maybe show up some of the newschool sportbikes with a hotrodded GS. \\/

Check out this guy dropping a knee in some club racing in the UK on his highly modded GS1000: