What effect do tyre profiles have?

[Cath]

My bike is recommended to run a 120/65 tyre on the front. I know that this means it's 120mm wide and 65% of that high.

If I put a 120/70 on the front, what difference (theoretically) will that have on how the bike handles?

(I had some suspension changes done, and put a 120/70 on yesterday, stupidly - I should've made each change separately. Now I'm chasing handling problems and want to know what part the tyre profile could be playing, hence the question)

[robracer]

Should tip in faster Cath, being a taller profile, what's the new tyre?

[Cath]

BT-016's

[robracer]

Had no probs on the zeddy with the 016's profile except I only got 6K out of the rear can you go back on the suspension changes?

[Cath]

Maybe. But it will probably cost me

At the moment I can't decide what's going wrong. (Yeah, I know - I'll *never* be a development rider!) Mid-corner it feels like it's moving around a lot. Like the geometry / balance is all out of whack. And it also feels like the front and the back are fighting each other a little - almost as if the back and front have different turn-in input, though that doesn't make sense.
When I first got the bike, Dave lowered the back a little by taking out the spacer, and it feels similar to that. The spacer went straight back in and I learnt to tippy-toe instead. We tried lowering the front a little, lifting the forks through the triple clamp by 4mm, but it still feels that way. We'll probably just lift the forks a few mm more and see if that does the trick. If not, I'll throw a tanty, have a cry and a cup of tea with scones, demand the suspension goes back to how it originally was, erroneously blame everything on the BT016s and get some Pirellis back on her feet. Hopefully it does work, since I've already maxed out my tanty allowance for the month.

Anyway - just wanted to understand the effects of the higher tyre profile before I (or more accurately, my authorised garage biatch) make even more changes. Thanks for the response Rob

[hoffy]

discipline your head mechanic/pit biatch ! it is obviously his fault ..

[photomike666]

By increasing the front profile, you have infact done the equivalent of pulling the forks through the tripple clamp and raised the front ride height. Not only will this affect the from tip in rate, it also loads more weight on the rear completly altering the bikes balance.

Working out the ride height raise, you could simply lift the forks that much further through the tripple clamps. Then the only difference will be the suspension changes.

[Six Addict]

hey cath...

my understanding that your dear pit bitcch passed on to me was that the higher profile will slightly quicken the steering IF you keep the geometry the same, and of course it doesnt (larger circumfrence = larger radius)... it actually makes the geometry slightly more lazy which requires suspension adjustments...dave talked me through this when i put the 120/70 pilot powers on...

the walking feeling may just be down to the rubber compound and not the geometry of the bike... or maybe the weight distribution and therefore heat generated in the tyre...

maybe other aspects of the suspension need to be looked at... i dont know

its amazing how much of motorcycling is about personal preference and technique...

i'm going to be keen to see what the pirelli dragon supercorsa pros are like... and what changes i may need to make...

[brockzila]

mid to late 90s yamahas all had 60 profile fronts. one of the most commonly recomended things to do is to change to a 70 series tyre. the 60 series looked better but the 70 series was quicker on turn and lean.

[Strika]

Also remember Cath, that a 70 profile, having a higher and thus more flexible sidewall, can feel a little doughy compared to a 65 or 60. But, In essence, what others have said is pretty close. Lowering the front or raising the rear by about 3mm will compensate for the higher profile front tyre. Any other changes are unneccesary if you were happy with the set-up on the old tyres. It might just be a matter of getting used to that doughy feel??

[Cath]

It might just be the doughy-ness of the 70 profile then, as we did lower the front by 4mm... I'm not a fan of dough

Interesting explanations - thanks to all who responded

[Wattie]

woh woh woh...

after an in depth speaking with a Bridgestone tyre person.


each manufacturer measures their tyres from a slightly different point.

if my 190/50 is 190mm across the tread, is that 190 when its flat and squashed?
or is it 190mm while pumped up and on a 6inch rim? or 5.5 inch rim?

is the 50, a 50% of tat 190mm of the sidewall?? or is it the whole height of the tyre at the highest point down to the rim?

Bridgstone are selling an 195 section tyre, that has "the exact same external dimensions as Casey Stoners rear tyre"

ask the manufaturer for a decent expanation of their measurements if you want to know the exact science. or just chuck on a set and give em a go!

[the kid]

Cath .. you should always read their Profile and try to analyse what they are really saying .

for instance

"Hi , my name is Ben and I am looking for a really nice girl . I like travel , long walks along the beach at Sunrise and cuddling up on the couch"

Analysis

"Hi my name is Ben and I am looking for a root , my first coz I usually get told to fuck off and end up walking home by myself and spend the next day watching pornos on the couch "

Profiles are very important Cath .

Why you ever responded to "Hi I am Dave and I like to ride motorbikes wearing frilly knickers under my leathers " is truely beyond me

[*Slojo]

My bike is recommended to run a 120/65 tyre on the front. I know that this means it's 120mm wide and 65% of that high.

If I put a 120/70 on the front, what difference (theoretically) will that have on how the bike handles?

(I had some suspension changes done, and put a 120/70 on yesterday, stupidly - I should've made each change separately. Now I'm chasing handling problems and want to know what part the tyre profile could be playing, hence the question)

It was a common handling fix on the olders sixes. Put the 70 profile on and you'll lose the nervousness and that feeling like its going to tuck in on you. You won't regret it.

[Cath]

???

I've got an '06 ZX6, it's not that old! I already put the 70 profile on at the same time as I made suspension changes, hence the thread. And I don't have nervousness at all, and it doesn't feel like it's going to tuck in on me. I just don't like the handling since those changes were made. I wanted to know the effects of the non-standard profile, so I could try to sort out what was due to the suspension changes and what might be due to the tyre profile change.