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Discussion Starter #1
Hi,

I need to put new rubber on my 2006 910S. I see according to my manual I can fit tires with an aspect ratio of 50 or 55 on the rear.

I'm currently replacing the OEM Pirelli's which came with a rear aspect ratio of 50. I see all current model Brute's now come with 55 as stock. I believe I understand the technical definition of aspect ratio, but I have zero idea of what it will mean PRACTICALLY if I go from an aspect ratio of 50 to 55 in the rear performance wise. As far as I can tell right now it will make the rear end ever so slightly taller, correct?

Can anyone help enlighten me a bit?

Thanks much.

Rob
 

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So far, so good. Yes a taller tire will make the bike sit higher. It does not affect the factory specified ride height, but it certainly affects the ride height! (There was a long thread about this.)
 

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Discussion Starter #4
Thanks Cag. Any idea where that thread might be located? I've searched but have come up empty.
 

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I don't know about trade off but the way it just falls over and does all the work for me with just the slightest input is one of the best things about the bike. I'm staying with the 55.
 

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Do a search for "ride height tool" or look for posts by Hartley Hare. Hartley Hare, who is an electrical genius and a member whose opinion I respect, was making the case the if you measure the ride height using the factory ride height tool, you are not measuring the ride height of the bike. And he is correct. You are measuring the distance between the top of the rear axle and a fixed point on the bike. Maybe it was semantics, but he has a point.

I taller tire, 55 aspect ratio, will be "less round". There is a steeper pitch from the top of the tire to the side meaning that when you do lean the bike over, it will fall off the center "edge" quicker than on a 50 profile tire with its nice parabola. Because of this steeper angle, there is also more of the tire in contact with the ground when the bike is leaned over.

Disclaimer: I have not taken any actual measurements. There are a lot of guys on this forum a lot smarter than I am and they may have a different answer. If they do, ignore what I just posted and listen to them.
 

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I changed form a 50 to a 55 at the beginning of this season. I know that the 55 adds height, but feeling the difference is minimal at best. The turn in has improved exponentially, increasing "filckabilty" and allowing me to hold a line more easily in the turn. Go with the 55, you won't regret it.
 

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profiles.....

the rear 55s are 'triangular' which matches the front better than, for example the 190x50 which is very round in cross section
if when going to 55s, tip in seems a little fast, lower the forks 1/2 a line in the triple clamps, then try it

i just never felt comfortable on 190x50s.....then i went to 180x55, i love the difference

Noel-theknurl
 

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Discussion Starter #10
Wow thanks everyone, all opinions are solidly with the 55.

Interestingly enough, I had a conversation with Reg Pridmore (yes THAT Reg Pridmore) from CLASS motorcycle school. I will be riding with him and his instructors at VIR in July, he suggested staying with the 50, said he actually went from the 55's to the 50 as he felt the tip in was too fast and prefers the 50's. Thought I had my mind made up until I saw all the reply's from all you great folks all saying go 55!

Man am I torn!

Thanks again,

Rob
 

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50 vs 55

the 55s are taller than the 50s......so naturally tip in will be faster, its not the tire shape, its the diameter....rear tire shape has very little to do with tip in.....think about it
Yamahas used to use 120x65 fronts....then the riders would look around and see everybody else is using 120x70, they try them and their bike won't tip in because they 'raised' the front

triangular tires put more rubber on the ground when the bike is laid over.....but it also puts lots more torsional load into the chassis....the MV and Ducati have very stiff chassis, fully triangulated tubing vs the twin rail, beer can frames on a lot of other bikes
all this goes back to the early '70s and the TZ-700s, they had a POS 'featherbed' frame with rubber front engine mounts and a lot of horsepower...... thus the round tire profiles......Dunlop KR-83s would have broken the fames faster or pitched riders off

Noel-theknurl
 

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Discussion Starter #12
the 55s are taller than the 50s......so naturally tip in will be faster, its not the tire shape, its the diameter....rear tire shape has very little to do with tip in.....think about it
Yamahas used to use 120x65 fronts....then the riders would look around and see everybody else is using 120x70, they try them and their bike won't tip in because they 'raised' the front

triangular tires put more rubber on the ground when the bike is laid over.....but it also puts lots more torsional load into the chassis....the MV and Ducati have very stiff chassis, fully triangulated tubing vs the twin rail, beer can frames on a lot of other bikes
all this goes back to the early '70s and the TZ-700s, they had a POS 'featherbed' frame with rubber front engine mounts and a lot of horsepower...... thus the round tire profiles......Dunlop KR-83s would have broken the fames faster or pitched riders off

Noel-theknurl
Noel,

Excellent, excellent post! Thank you. At the end of the day, if I'm using these tires mostly for street and not for track and I'm looking for a lower ride that is less hard, then would you say the 50 is the way to go?

Also, at what point in terms of lean angle will the 55's extra sidewall contact patch become noticeable? I ask only because I'm not so sure I'll ever lean over on the street that far to take advantage of the 55's benefit here, possibly making that benefit a moot point for me. Would you agree?

Thanks again for the great post.

Rob
 

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The aspect ratio won't affect the firmness of the ride. That is a function of low speed damping. If you are getting bounced off the bike every time you go over a pebble in the road, back off on the high speed damping.

If your primary concern is ride height, by all means a 50 series tire is the way to go.
 

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my bike had 55 rear and 65 front (stock). i went with 50 rear and 60 front (michelin power pures), so both front and rear got lowered by (roughly) the same amount and handling is (roughly) unaffected. bike rides great with the 50/60 combo (well until i got a nail in the brand new rear, that is... lol)
 
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