Front tire size, performance, radial

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ericheath
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Front tire size, performance, radial

#1

Post by ericheath »

Not looking for any wars on tires or oil.

My 120/90/18 Continental front tire started getting some cracks in it so I shopped for a new tire. I needed a smaller size as it currently is too tight to the Magna fender and rubs at times. I ended up getting a Dunlop 120/70/18 radial for $54. I have the car tire radial on back so I figured, why not? The price was right. I had read that there isn’t a lot of difference on a bike between radials and bias. The 70 profile would give me clearance at the fender.

What kind of blows me away is how much more nimble the front end is now. It’s probably two inches shorter, but wow! What a difference. It cuts on a dime compared to the old tire.

I’m guessing it’s the size more than the radial aspect.

As to the car tire, I think I’ll ditch it next time. There are certain low speed maneuvers where it lurches a little unexpectedly. In a unforeseen emergency situation where you had to move in a direction of uneven road, it could be an issue. That’s just my opinion of it and bear in mind that mine is with the 1200 swing arm which keeps the tires in different planes by about half an inch. I’m sure that doesn’t help either. It does however make nice squealing sounds like car tires do when you smoke it.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
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Re: Front tire size, performance, radial

#2

Post by Whiskerfish »

Smaller on the front is a huge difference in the front end handling. Turn in seems to be much more controlled and stability through a corner is improved.
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Sidecar Bob
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Re: Front tire size, performance, radial

#3

Post by Sidecar Bob »

A 120/70 theoretically has a 24mm (almost an inch) smaller outside diameter than a 120/90 (assuming both are mounted on suitable rims) so the front end should only be about half an inch lower (the same effect as raising the forks in the clamps by half an inch).

From what read about radials several years ago, radial tires are designed to work with wider rims than similar sized bias ply tires would need. If that is true of the tire you have it is possible that you have mounted the tire on a rim that is too narrow to produce the intended cross sectional profile, which usually results in the tire having a significantly smaller contact patch, which usually will feel much more nimble.
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ericheath
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Re: Front tire size, performance, radial

#4

Post by ericheath »

It’s actually about 1.8” smaller. So front end dropped almost an inch and I can tell when side standing the bike. I just raised it about 3/4” in the trees. Haven’t had a chance to ride yet. Rain is close.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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Sidecar Bob
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Re: Front tire size, performance, radial

#5

Post by Sidecar Bob »

I would be very concerned about that.
Mr. Honda ('83 GL1100/Dnepr) summer How a motorcycle evolves thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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Re: Front tire size, performance, radial

#6

Post by pidjones »

Lowering the front also reduces trail. Keep a hand on the bars at all times to prevent wobble onset.
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ericheath
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Re: Front tire size, performance, radial

#7

Post by ericheath »

I have my front end raked, so I have ways to go before I reduce trail too much. I need to check my triple tree bearings but cannot find my tools for removing the Honda fasteners. I might have to make some more.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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