120/70 front tyre, hmmm.....

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Rural Rat
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120/70 front tyre, hmmm.....

Post by Rural Rat » Wed Mar 07, 2007 9:33 am

Just changed to 120/70 front tyre as appears to be the consensus here. Not real impressed. Steering is now very heavy and extremely slow, not confidence inspiring at all. Tyre is Metzeler M1 and rear is Michelin Pilot Road. Forks are still at original height.
Any suggestions as to how far to drop yokes without causing too much excitement? :?

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Post by twolfe » Wed Mar 07, 2007 10:12 am

10 to 12 mm should account for the extra diameter of the tyre. I've had the 120/70 fitted for a while with no problems at all. I think I went 10mm lower.
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Doyle171
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Post by Doyle171 » Wed Mar 07, 2007 10:44 am

I have a 120 / 70 on mine and the change of direction is quicker but i will be going back to a 60 as the front end feels vague in fast sweepers. :cry:
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H1
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Post by H1 » Wed Mar 07, 2007 10:50 am

Hi !

Can´t understand your problems. But eventually it depends that you´re using different tires in front and rear? Did you use the right pressure? Normal road i go with 2,5 bar in front and 2,8 rear.

I´m using Maxxis Supermax in front and rear or Michelin Pilot Power in front and rear... everything works fantastic and easy!!!

Hope u get it fine!

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Heinz
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burty
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Post by burty » Wed Mar 07, 2007 11:27 am

I've just fitted a 120/70 on the front of mine. I've not ridden it yet then.

WRT the difference in diameter. I know that the difference is not always the same as theory, but I make the theoretical difference in 'tyre height' to be 12 mm.

That is:

120 x 60/100 = 72

or 120 x 70/100 = 84

Actually that is a lot more than I expected - just in my mind.

I guess that makes 10mm a reasonable adjustment on the forks.


BTW, has anyone changed the rear for a 70 profile too?

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Post by Shifty » Wed Mar 07, 2007 11:34 am

I have both front and rear MP sport.
Front 120/70
Rear a 170

Didnt change the forks tho, cant say theres much difference.
I dont think I can coz the forks will hit the steeringbar in my case. (SBK mod)

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Post by Max » Wed Mar 07, 2007 11:44 am

Increments of 5mm is my usual practice before I fine tune. Saves time and yes, a couple mm make a difference.

First make sure your sag and spring rates are set. I never recommend running two different models, let alone brands of tire on a bike. They are designed to work together.

Mine with Pirelli Dragon Super Corsa Pros on the track and on the street (120/70, 180/? with a 5.5" wheel) flip flop through direction changes like the bike weighs half of its actual weight. I'll be going with the Diablo range later as I don't see any track time in the near future.

You need to set it up. I had to spend a couple sessions of track time to reset mine when they went to the "Pro" version. It was a taller yet rounder tire and I was dragging stuff while pushing the front. Ended up raising the rear. On the road, this won't be a problem, but the geometry issues still matter.
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Greg
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Post by Greg » Wed Mar 07, 2007 11:54 am

Different brands front and rear might have a huuuuge effect...

As far as I'm aware, manufacturers match their profiles front and rear, so that the tyres at each end do the same thing at the same time - contact patch aspect, angles of incidence etc... Imagine a really peaky front (I've got some Pirellis that appear to be almost triangular in shape!) matched to a squat fat rear... If both tyres have the same relative profiles then they'll do the same thing at the same time, if the front is significantly different to the rear, like I've described above then it will behave completely differently with the front wanting to fall off the edge while the rear kinda rolls over its profile..

Just my five eggs...

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phuk72
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Post by phuk72 » Wed Mar 07, 2007 12:42 pm

120 / 70 is the way to go. The 60 profile was only put on there to satisfy the Japanese obsession for low profile tyres and also found it's way onto the early r6 - Yamaha soon changed its mind!

I would suggest that any problems are due to suspension set up, tyre mis matching or wrong PSI not the tyre.
Doyle171 wrote:I have a 120 / 70 on mine and the change of direction is quicker but i will be going back to a 60 as the front end feels vague in fast sweepers.
Strange - 70 profile should give a greater contact patch when cranked over and give more confidence
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burty
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Post by burty » Wed Mar 07, 2007 1:42 pm

Greg wrote:Different brands front and rear might have a huuuuge effect...

As far as I'm aware, manufacturers match their profiles front and rear, so that the tyres at each end do the same thing at the same time - contact patch aspect, angles of incidence etc... Imagine a really peaky front (I've got some Pirellis that appear to be almost triangular in shape!) matched to a squat fat rear... If both tyres have the same relative profiles then they'll do the same thing at the same time, if the front is significantly different to the rear, like I've described above then it will behave completely differently with the front wanting to fall off the edge while the rear kinda rolls over its profile..

Just my five eggs...

G
YZF750, FZR1000, R6 all have a 120/70 front and a 180/55 rear

R1 has 120/70 front and a 180/50 rear

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Post by Doyle171 » Wed Mar 07, 2007 3:52 pm

Phuk that's the very reason behind why i put a 70 on. :?
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Rural Rat
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Post by Rural Rat » Thu Mar 08, 2007 7:43 am

Thanks for the replies.
Spring rates and ride height were fine prior to changing and pressures are as recommended.Think I will match the rear tyre before touching too much.
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Post by dfh » Fri Mar 23, 2007 5:10 am

Doyle171 wrote:I have a 120 / 70 on mine and the change of direction is quicker but i will be going back to a 60 as the front end feels vague in fast sweepers. :cry:
Like Phuk says the 70 series will enhance stability and feel, and without changing the front ride height the 70 will slow down the steering not speed it up....... your problem lies elseware in the chassis.

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Doyle171
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Post by Doyle171 » Fri Mar 23, 2007 10:28 am

Yeah i though that too, so i put my wheel in my mates TRX and the problem was still the same, it might just be the tyre it's self. Maybe not up to temp or the road surface etc.
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Post by Wombat » Fri Mar 23, 2007 10:54 am

:shock: Well, I must be the odd one out then, 'cos I lurve the 60 profile. I 've tried the 70 and didn't like it. And when you come from a bike with a 120/80V16 to the TRX, its a revelation. A 65 profile might be a different kettle of fish, though?

Bob
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