Tire questions

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Tire questions

Postby PhoenixyzF » Fri Feb 09, 2018 1:14 pm

My bike has 12 year-old tires on it, so they have to go.

Just wondering---does going to a 120/70/17 front adversely affect the steering/handling of the Cat? **Metzeler is my preferred brand, and they have 120/60 and 120/70 sizes available.

And I do believe that the rear wheel can take a 170....but I don't think that size is available any longer...


Thanks,

e.
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Re: Tire questions

Postby Riceburner » Fri Feb 09, 2018 3:31 pm

I've run 120/70 for almost as long as I've owned my Cats. Replaced the front the first season with 70 and it's been over a decade and 100k kms. Michelins rubbed the fender a little when it picked up pebbles. After that ran Pirelli for most of my time with it without any issues. Some drop the forks a bit to compensate. I tried it both ways and have left it stock since experimenting early on.

Always ran 160.
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Re: Tire questions

Postby Micah » Fri Feb 09, 2018 9:54 pm

I switched from 120/60 to 120/70 a couple years ago. I will not be switching back. I like how the bike tips in (note - I lowered the front to get close to the original front ride height, and I have an R6 shock, which raises the rear close to an inch). In addition, having a correct speedo is nice. The 60 series front caused the speedo to read optimistically.
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Re: Tire questions

Postby Micah » Fri Feb 09, 2018 9:59 pm

Oh... By the way, may I offer for your consideration a Q3+ from Dunlop? Mileage will be 3000 miles, so they wear quickly, but man oh man do they stick well. I needed more mileage on the YZF (and Falco) so I put Bridgestone BT-023 on so I can run around town or take the odd road trip. I like the Bridgestones, but the Q3 is my favorite.
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Re: Tire questions

Postby PhoenixyzF » Sat Feb 10, 2018 10:42 am

Thanks for the feedback and recommendations.

120/70 and 160 at the rear it will be.

**Micah, I never knew that the R6 shock and adapter changed rear ride height. I assumed that the stock shock was longer, hence the need for the adapter. Guess I'll be dropping the forks 1 inch, too. :)
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Re: Tire questions

Postby Riceburner » Sat Feb 10, 2018 12:04 pm

Come by if you want to compare to stock. My 04 is stock and low mileage. Thought my 96 with a worn out shock seems to sit at the same height...till I sit on it.
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Re: Tire questions

Postby Micah » Mon Feb 12, 2018 11:49 am

Mine's definitely taller. There were shock adapters made by Clyons and Captain Orange. Mine was made by Clyons, and it's more like 3/4 of an inch higher at the rear. The 120/70 raises the front up about 10 millimeters. I lowered my forks right about 8 millimeters. It's certainly more biased to the front (meaning less trail) than what was there originally. The whole bike is higher than stock, which puts me with my heels *just off* the ground at a stop given my height (5'8"). The bike handles beautifully with the R6 shock and the Race Tech springs. With this current geometry, it will track very neutrally. Where I live, there is an excellent sweeping interstate curve. I can set the throttle lock prior to getting to this curve, lean the bike in, and take the pressure of the bars, and it will not stand up or fall in - just holds the line. It is my definition of perfect (of course, everyone has their own opinions on what perfect handling looks like).

Measure your rear ride height prior to the installation. This way, if the adapter you have changes the ride height too much, you know where the bike needs to go in order to compensate. Also - you'll need to set your sag appropriately too, then move on to rebound and finally fine tune with compression. My YZF and Falco are street bikes, and I have set the sag to be a little more compliant on the street. My 996 - that is a stiff suspension. It is not set up for around town potholes and expansion joints. But oh boy I enjoy riding it when I do! :D Anyway, I digress... having good suspension is nice, getting it set up correctly is a game changer. Just my opinion, but a mediocre suspension, set up properly, would be better than an excellent suspension set up poorly.
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Re: Tire questions

Postby Pepperoni » Wed Feb 14, 2018 6:46 pm

Hey! STOP GUESSING at ride height changes and corrections to the steering geometry when you change tire models or tire brands! What follows is THE formula for making changes to a bike like the YZF that does NOT have a stock rear ride-height adjuster:

To maintain the SAME ride height, "the front ride height must be adjusted to maintain chassis attitude, making the equation:

Image

Here R is the rear wheel circumference, and F is the front. (...a positive number means you increase the ride height by sliding the triple clamp up the fork.)"


This is from motorcycle.com.

(Oddly, it is the exact opposite of the formula that I've been using from (the now late) Sport Rider magazine where the top terms are reversed and a positive number means sliding the triple clamps down the fork tubes but it works out exactly the same (feel free to do the math).)

Of course, if you are simply swapping on a new set of the SAME tire brand and tire model, you don't need this at all.

Note that you actually have to take a cloth/plastic tape measure or piece of string to measure the circumferences of the MOUNTED AND PROPERLY INFLATED tires. Don't just use the tire's nominal measurements (i.e. for a 120/60 - 17: do NOT use 431.8mm (17") x (120mm width x 0.60 x 2 for the tire height) x Pi) or you won't be using the right numbers because tire models of a particular size will vary in actual width and height from the marked size (i.e. 120/60 - 17).

Trust me, this really works.

BEFORE MAKING ANY CHANGES, go for a ride. You may find that just having the new tires makes everything feel great. Otherwise, go home and make the change. And if you think it still steers too quickly, then raise the triple clamps another 3mm to 5mm, or vice-versa if you think the steering is too slow.

And don't make RADICAL drops in ride height (like more than about 20mm) or you may end up with interference between the front tire and the radiator/headers/inner fairings that could lead to a crash.

Over my last 4 tire changes, I have seen a total 20 mm variance between new front tires and 28mm between rears (not necessarily in the same tire change) so there definitely are differences between tire models and the above formula will account for them.

This takes all of the guess work out of things.

If you have a ride height adjustable shock, it's:

(F.old - F.new) / (2 x Pi) and (R.old - R.new) / (2 x Pi)

For a positive number, raise the triple clamp on the front and increase rear ride height and vice-versa for negative numbers.

Note that you can "cheat" if it's easier to adjust the rear ride height (it usually is): for example, if the front is -3mm and the rear is +3mm, you can just raise the rear +6mm for the same effect. Also, if the numbers front and rear are the same (i.e. +3mm and +3mm), if you do nothing, the front and rear balance will be the same but you'll have raised the entire bike 3mm which you may or may not notice when you put your feet down at a stop.
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Re: Tire questions

Postby PhoenixyzF » Sat Feb 17, 2018 7:19 pm

Awesome info.~~!!!!! :) :) :) Thank-you. :)

*I was just going to ask the mechanic who will be installing the tires his opinion about maintaining the correct steering geometry, but these formulas are much more precise!

**My buddy who used to be a Honda mechanic just doesn't have the time to work on bikes anymore, leaving me to look for a good local mechanic/shop---which has turned out harder than I thought. The motorcycle [service] industry is seasonal up here, and has a hard time attracting and keeping talented mechanics/technicians, (-my friend went into steel detailing).


e.
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Re: Tire questions

Postby PhoenixyzF » Sat Feb 17, 2018 7:22 pm

Riceburner wrote:Come by if you want to compare to stock. My 04 is stock and low mileage. Thought my 96 with a worn out shock seems to sit at the same height...till I sit on it.


Thanks~~ for sure we should get together some time. :)

....eventually I'll be on the road, hehe.
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