Tyre Sizes

Ericck · Scooby Slapper Joined: 21 Jul 2011 Karma :

Need new front tyre for 04 Bandit 600s. Currently has a PR 2 120/70/ZR17. Cant find PR 2s in stock anywhere so gonna go for a PR5 as I have a rear PR5 in garage when current rear needs changing.
Stock tyre for Bandit 04 600s is 120/60/ZR17. So going to go back to 120/60.
I have googled 70 versus 60 and read about aspect ratios and increased cornering stability etc. Is there really any difference in the real world and will I even notice it. If not why would someone change the size in the first place.
Anyway might be a stupid question.
If the bike feels alright to me I usually just put on what was there before.
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Current Bike: 2004 Suzuki Bandit 600S
Previous Bikes: Yamaha FS1E, Mobylette Moped Thingy, Suzuki GS125, Kawasaki Zephyr 550, Kawasaki Zephyr 750, Kawasaki ER500, Suzuki Bandit 600, Honda CBR600F, Triumph Street Triple 675, Suzuki V Strom 650, Suzuki Bandit 1200, Suzuki SV650N, Honda CB500F.

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

Usually tyre sizes that a manufacturer defines are done for a reason. The first R6 for example had a lower profile front than was usual and made the bike twitchy. This I assume was to ensure that it turned quickly, but lots of people reverted to the more usual size to get the stability back - and sometimes then got rubbing on the front mudguard too.

Personally I'd go with what the manufacturer says unless the size is not available. The difficulty being that if you don't like it, it's quite an expensive thing to buy yet another brand new tyre to swap over.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

120/70 means it's supposed to be 120mm wide and the height is 70% of the width, so 84mm high.

So a 120/60 is supposed to be 120mm wide and 72mm high.

You'll not I say "supposed to be" because they never are but in tyres of the same make, you should get a roughly 10% drop in profile when you go from a 70 to a 60 section.

What does this mean? Well, you'll drop the front end by 12mm. This will have an effect on the rake angle of the forks, making them marginally steeper. This tends to make the bike turn in a bit sharper but be a bit less stable. Effectively makes the steering quicker.

The cross section of the tread will be more oval/less circular. So it'll be closer to the edge of the tyre for the same angle of lean. Arguably, the contact patch should be slightly larger.

All these differences will be slight but I'd imagine if your bike is designed for a 60 section, you'll have quite a bit more unused tread on the edges of the front than on the rear.

All in all, you're probably looking at slightly more grip and slightly quicker steering response at the expense of slightly less stability.

I did it the other way for a long time (put a 60 section on a bike designed for a 70) and it did make the bike turn in noticeably quicker and get onto the grippier part of the tread sooner. I've since re-hashed my suspension setup (including altering the front ride height/rake angle) so it does effectively the same thing on the 70 section.

TL;DR. If it was designed for a 60 section, and is otherwise unaltered, I'd fit that. You may notice it corners a bit better. It may seem a little less stable.

EDIT: You probably wont notice any of this because going from a PR2 to a PR5 will be a huge step up in all round grip anyway. Enjoy.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

Ericck · Scooby Slapper Joined: 21 Jul 2011 Karma :

Thanks guys. I will revert back to the 120/60. I had a bandit 600 many years back and it ran 120/60. The steering on my current 600S does seem a little slower but that is probably more to do with me being older and dodderier. I had PR5s on my CB500F which is where the spare rear came from and that bike did ride well.
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Current Bike: 2004 Suzuki Bandit 600S
Previous Bikes: Yamaha FS1E, Mobylette Moped Thingy, Suzuki GS125, Kawasaki Zephyr 550, Kawasaki Zephyr 750, Kawasaki ER500, Suzuki Bandit 600, Honda CBR600F, Triumph Street Triple 675, Suzuki V Strom 650, Suzuki Bandit 1200, Suzuki SV650N, Honda CB500F.