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Car versus motorcycle rear tire
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2004ret
Posted 2/25/2016 1:13 PM (#88024)
Subject: Car versus motorcycle rear tire


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I recently took delivery of a ST1300 with Hannigan Astro Sport sidecar. The ST1300 has the steer lite fitted with a 120 70 ZR 18 motorcycle tire up front, and a Hankook 205 50 ZR 17 car tire installed on a stock rear motorcycle wheel, (which takes a 170 60 ZR 17 tire.) The rig tracks beautifully blasting straight line on the highway, but can be a handful through curves at modest speeds. This is my second rig, the first being a '85 GL1200 with an EML Tour T full package fitted.

Does fitting the oversize car tire in the rear slow down steering as compared to fitting the stock rear motorcycle tire? Should I consider fitting the stock rear motorcycle tire to reduce steering effort and improve steering responsiveness?

Thanks for you inputs.

Jim
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DRONE
Posted 2/26/2016 12:15 PM (#88033 - in reply to #88024)
Subject: Re: Car versus motorcycle rear tire



Veteran

Posts: 238
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Location: Tacoma, WA, USA
No, that's not it. As long as it's tracking straight as you say, I'd grab my compressor and bump the front up to 36 lbs, the rear to 32 lbs, and I don't know what those Astro tires take but I'd probably make sure it was at least 30 lbs. Then go out and try it. If it still feels sluggish, you might want to look at a different front tire. You said your tire was a 120/70-ZR18. Well, the "R" means radial, and radials tend to be squirmy up front. I'd prefer to see you with a bias belted tire, or even a bias ply tire up front but I'm not aware of any in your size. So that leaves you with the Metzeler ME880 which is about the stiffest radial front tire that you'll find. Added benefit is that the ME880 is long-wearing.

There's another approach. See how much room there is between your tire and the front fender. If there is a decent gap, you could switch to a 130/70-B18 (where the "B" stands for "bias") tire, maybe even a REAR tire for a flatter profile. Take for instance the Bridgestone BT45 rear tire which is a bias ply tire and much beloved by the trike crowd as a front tire. It's 1/2 centimeter wider on each side that your stock tire--do you have more than a 5mm gap between your tire and your fender? It might work. But it'll also be 7mm taller on the top (14mm larger overall diameter), so you'd need to check that gap as well.

Maybe there are some ST1300 guys on here who could chime in with what has worked best for them?
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2004ret
Posted 2/26/2016 2:27 PM (#88035 - in reply to #88033)
Subject: Re: Car versus motorcycle rear tire


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Posts: 4
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Thanks for the input - haven't considered a bias tire solution. I will check the clearances and tire availability.

Front tire is currently a Pilot Road 2, rather worn, and the chair tire is Hannigan's standard car tire fitment. The rear 205/50 ZR 17 fills all the available space inside the swing arm, so only choice there is to go smaller. Seller recommended air pressures 42 lb front and rear, with 32 in the chair, which I have been running. My issue may be resolved by fitting a new front tire, but before selecting one, I first wanted to confirm that the oversize rear tire is not compromising the handling. I need to replace both front and rear tires, due to front wear and a spike puncture in the just installed rear tire.

Thanks again,

Jim
Lakes High School '66
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Al Olme
Posted 2/26/2016 4:02 PM (#88037 - in reply to #88035)
Subject: Re: Car versus motorcycle rear tire


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Location: Minneapolis, Minnesota
Chances are that you are going to get several opinions on this... remember, these are opinions, so use good sense in what you decide to to. OK, here's my opinion... The car tire in the rear is not an issue. Many of us run car tires, some both front and rear. I believe that your tire pressures are too high. Remember, that car tire is built to carry MUCH more weight. When I tried running a car tire at full pressure it didn't grip and it I got bounced all over the road. With that much pressure, the tires are rock hard and both grip and ride comfort are degraded. I agree with Drone about running a radial front tire, I'm in favor of bias. Good luck.
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DRONE
Posted 2/26/2016 8:33 PM (#88038 - in reply to #88024)
Subject: Re: Car versus motorcycle rear tire



Veteran

Posts: 238
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Location: Tacoma, WA, USA

Whoa! 42 in a Pilot Road 2 front? That's a lot of air! So I guess we can rule out underinflation. Wink LOL   But seriously, 36-38 should be all you need up front.

In the car tire, 42 lbs would be more like what you'd use if they were mounted on a large SUV.  For a rig like yours, 30-34 should be more than enough.  The reason guys use the 205/50 is because there are lots of different tires available in that size from lots of different tire companies. There are NO 17" tires that are close to 25" diameter, which is what you're looking for, in a 195, 185, 175 or 165.  Fellow members correct me if I'm wrong about that.

 

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2004ret
Posted 2/27/2016 11:38 AM (#88044 - in reply to #88038)
Subject: Re: Car versus motorcycle rear tire


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Have ordered a BT45 130/70 18 rear tire to mount on the front wheel, and a Hankook Ventus 205/50 17 for the rear wheel. After mounting, will provide feedback on handling improvements. Will try different air pressures as suggested. Drone and Al, thanks for the comments and suggestions.

Jim
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DirtyDR
Posted 2/27/2016 2:23 PM (#88049 - in reply to #88024)
Subject: Re: Car versus motorcycle rear tire



Veteran

Posts: 254
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Location: Edwards, CO
Just so you know the Metzler ME888 is a better tire than the 880 and either is available in either Bias or radial in your size. I have run both 880 and 888 and the 888 is much better. I also run the bias ply Metzler on the front of mine.
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DRONE
Posted 2/27/2016 7:55 PM (#88051 - in reply to #88024)
Subject: Re: Car versus motorcycle rear tire



Veteran

Posts: 238
10010025
Location: Tacoma, WA, USA
Dana is right--the Metzeler ME888 Marathon Ultra does come in a 130/70-18 both "B" and "R" and it's an outstanding tire. Both for grip and longevity. I overlooked it when I was composing Post #2 above. I'd definitely choose it over the ME880 (which is still an excellent tire.) But both the ME880 and the ME888 are front tires, which means in terms of steering "feel" it would probably be pretty close to the Pilot Road front tire you have on there now. If it turns out that the BT45 is not to your liking, the ME888 would be an excellent next choice in your search for the perfect fit.
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2004ret
Posted 3/23/2016 7:05 PM (#88417 - in reply to #88024)
Subject: Re: Car versus motorcycle rear tire


New User

Posts: 4
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An update - Have mounted the BT45 130/70 x 18 rear tire on the front wheel and the new Hankook 205/50 x 17 on the rear. Handling did not change as expected, still a handful thru the turns, particularly turning right . So back to basics, ie check the alignment - found toe in set at 2 1/2 inches, looks like last person to set the toe in ran a line off the front and rear wheels combined, versus just a straight line touching the rear tire. Realigned the toe in, sidecar frame level and adjusted to slight lean out, and issue now solved - handling now as it should be, and front end remains stable both turning left and right. Now I am looking forward to wearing the new tires out! Thanks all for your perspectives and recommendations.

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DRONE
Posted 3/28/2016 2:18 PM (#88468 - in reply to #88024)
Subject: Re: Car versus motorcycle rear tire



Veteran

Posts: 238
10010025
Location: Tacoma, WA, USA
YaY!

(2-1/2 inches! OMG.)
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