Front tyre profile

[Sniper]

Hey all,

Im just curious to see if a claim made by a bike shop to sell me a tyre is true.

On my CBR, the front tyre is definetly a bigger profile than what it is meant to be. I can't check what it is now cause Im at work and the bikes not at home, but anyhoo. I know it is a bigger profile because I had to get a new front gaurd after the tyre kept picking up stones and using then to mash the front gaurd and put a few holes into it.

Anyway, the bike shop, who will stay un-named, said that with a bigger profile front, the bike will handle like shit. Now I think the handeling is pretty good at the moment, but will putting a smaller profile front (GPR70) make the bike handle a bit better?

Cheers

[limbimtimwim]

Anyway, the bike shop, who will stay un-named, said that with a bigger profile front, the bike will handle like shit. Now I think the handeling is pretty good at the moment, but will putting a smaller profile front (GPR70) make the bike handle a bit better?

You mean, let's pretend, it has a 120/70 on the front at the moment, and the manual says it should have a 120/60 on it?

My understanding is that it should tip in better with the taller tyre.

But tyres are weird. One make 120/70 will have a 'pointier' profile than another make. And different models of tyre of the same make will also have different shapes.

I if I remember correctly the profile tells you the tyres 'tallness' in proportion to it's width.

[Sniper]

yep, as in (I'll use a cage tyre) 175 70 R13
175 is the width across the tyre
75 is the height
and R13 is the diameter.

[DEATH_INC.]

A taller tyre may tip in easier,but it'll turn faster on the smaller one.A smaller diameter will turn faster than a big one for a given lean angle.Also you're stretching the front out by raising the height with the bigger tyre.And it'll be heavier too.

[Sniper]

Thats what I wanted to hear, thanks Death

[R1madness]

Hmm. A taller tyre will not tip in quicker (gyroscopic effect). It may tip in more (further over) for the same lean angle and will definitly feel worse. The correct width and profile will definitly help. The tyre guy seems to be on to it.

[riffer]

yep, as in (I'll use a cage tyre) 175 70 R13
175 is the width across the tyre
75 is the height
and R13 is the diameter.

Don't mean to be a pedant here, but I'm pretty sure the second figure (or the profile if you wish) is a percentage of the width, not physical dimension:

i.e. 175 is the width of the tyre
70 is the height (70% x 175)
13 is the diameter of the wheel.

[XTC]

You are right Riffer. Second number is what they call the aspect ratio. Percentage of width for height.

[Holy Roller]

Talking at our club BBQ last night the guys with R6 and SV650 remarked that a higher profile tyre gave them better handling
I guess its up to individual preferences and expectations or setups that the bike has.

[Sniper]

Thanks Holy Roller. Maybe I will try the GPR70 and then based on what its like, I may make a desition from there.

Riffer, you are right mate, my mistake.

[DEATH_INC.]

Hmm. A taller tyre will not tip in quicker (gyroscopic effect). It may tip in more (further over) for the same lean angle and will definitly feel worse.

What it does is very similar to using a smaller rear , it slows the turning down so the bike resists less when you lean it giving the effect of feeling like it handles better.....

[Swoop]

Just had the same on the vfr. The fitted front tyre was wider than the reccomended size for that rim. Now have correct size and scuffing-in. Handling has lightened up a bit!

[Sniper]

I think thats what Im after swoop. The handeling on my bike does feel a bit "Heavy" so Im hoping to change might lighten it and make it a bit more flickable.

[Drew]

Once you have said correct tyre fitted and scrubbed in, try to annalyze what the bike is doing and when.
I say this because a marked improvment can be obtained by putting a wider tyre on the back of most bikes. This is not a rule! Just an observation on my experience.
But a wider back tyre, means that when leaned over, the rear end effectively raises up, thereby reducing the rake. meaning more feel. Too much though and you have a constant feeling of the front washing out, even though you make round the bend.

[Sniper]

This is the front tyre Im talking about though.