splinter conversation from the Unge' Tire Thread...
Quote from: mattyvas on February 12, 2012, 09:21:37 PM
I always ran a 120/70 on my 620, it gave better turn in feel from a rounder profile.
Yeah I've heard a couple of people suggest that the taller profile of a 120/70 should result in slightly quicker turn in and more contact with the ground when tipped over... was it really that noticeable Matty?
... anyone else on a 6xx? any thoughts on 120/60 v 120/70
I think it's a bit funny to be honest.... "the quicker turn in of the steeper edge tire".... hrm....
so, 120mm*(70%-60%) = 10mm ...
My ride height is 10mm higher now which should make my turn in slower, unless I pull my forks through my triples by 10mm, and I now need bar risers or clipons to make a direct comparison.
... suspension... it's chaos theory on wheels.
For me it was very noticeable the change in profile.
The profile of the tyre also make a difference, Pirelli and Conti's are generally quite round in shape.
Bridgestone's tend to be a bit squarer particularly with age, as do Michelin.
Can't really say about Dunlop haven't ever been on them.
Except for the tractor where the 606 is doing well.
Can I throw in my 2c worth.
AFAIK front tyres come in two basic profiles, a rounded profile and a triangulated profile.
Triangulated profile tyres like to spend their time on their side, that is the profile aides front end grip by placing a larger footprint on the ground and because of the profile when upright they by their very nature will have a smaller footprint, and might give less braking effect.
So the rounded profile will be opposite to the triangulated one, tyre manufactures try to come up with variations on these two themes by trying to get the best of both worlds, its called a compromise.
The sidewalls act as part of the suspension, so the higher the side wall the better the ride (all other things being equal) and really for street use I would go with the higher profile, I know on my mates monster he ran a low profile tyre and damaged his front rim.
I hope this helps or confuses you.
Mmick
Wellsy ... I am not sure if I quite understand where you are headed ... but to my amateur mind you may be confusing tyre profile (and height) with suspension geometry. Both may effect your turn-in but for different reasons and they are not necessarily comparable.
Your chosen tyre profile will remain predominantly unchanged but your suspension geometry will constantly change depending on the weighting on the front wheel. I can't see why you would need to change your steering (and/or suspension) geometry.
Am I close, an utter goose or both?
(posted before reading Mick's reply)
Quote from: Wells on February 12, 2012, 10:28:16 PM
My ride height is 10mm higher now which should make my turn in slower,
Actually, if your rear ride height is extended (I think thats what you mean) it will make your 'turn in' faster, as will dropping your forks.... er I mean lifting your forks up through your tripples.
Mmick
OK I'll try and get this right ... the Boss has always had the 60 series on the front of the little 'un. In changing from Michelin to Pirelli (last time around) she said it felt more sure footed on different road surfaces. This probably lends credence to Matty and Mick's combined knowledge of a more triangulated profile providing a greater cornering contact patch.
... but apparently it still takes more effort to 'hold it' in the corner than the big bike which has a higher profile despite (what I think) is the flatter Michelin profile. Of course the bikes are also slightly different in other areas (boingers, weight and power delivery) ... what isn't different is that they are both faster than me (but that's a pilot thing).
i igree with betty and told juls when i swiched to pirellis the do have a better rounded shoulder and also have wire on the beeds and hold up alot better when cranked right over but its when your on wet or gravel that when you will notice the real difference the 70 series put more contact patch down on the road to me thats a must [thumbsup] cheers bazz
There are different (and opposing) things happening. On the one hand, the shape of the 70 series tyre is steeper, which will make the bike turn in faster.
On the other hand, the taller tyre moves the front axle up, so if nothing else is done to the bike that'll mean the head angle is shallower, which will make for more stability and slower turn-in.
All else being equal, the 70 series tyre will be heavier, which will make for more stability and slower turn in by itself.
Of course if you pull the forks up through the triples, or otherwise change the geometry by raising the rear, then you remove the geometry change effect and you'll be left with the shape of the tyre carcass and weight.
Quote from: Betty on February 13, 2012, 01:26:23 AM
Wellsy ... I am not sure if I quite understand where you are headed ... but to my amateur mind you may be confusing tyre profile (and height) with suspension geometry. Both may effect your turn-in but for different reasons and they are not necessarily comparable.
Hey mate, not trying to confuse them, just saying that change in profile will have an effect on teh geometry which are opposing...
so, just clarifying...
Quote from: monstermick58 on February 13, 2012, 01:36:46 AM
Quote from: Wells on February 12, 2012, 10:28:16 PM
My ride height is 10mm higher now which should make my turn in slower,
Actually, if your rear ride height is extended (I think thats what you mean) it will make your 'turn in' faster, as will dropping your forks.... er I mean lifting your forks up through your tripples.
So what I actually meant was that the larger profile means the front is slightly higher .. as more eloquently stated by Suzy..
Quote from: suzyj on February 13, 2012, 01:06:16 PM
....the taller tyre moves the front axle up, so if nothing else is done to the bike that'll mean the head angle is shallower....
So it seems we're agreed.. in order to make a direct comparison between a 120/70 and 120/60, I'd need to adjust the geometry after the new tire is fitted.
Anyone else have any practical experience of going from 120/60 to 120/70?
HAHAHA.
I have no practical experience in those tyre sizes, nor am I a tyre expert, but do have a question.
Are we assuming the increase in profile is a combination of an increase in the 'round' shape and in the side wall height?
An increase in the 'round' shape of a cross section of the tyre (of the same width) is likely to give you a taller tyre with bigger contact areas on the sides as well as a larger circumference. This extra circumference needs to be covered (rolled over) to get on the side of the tyre. Only a small thing but not a good thing for fast turn in. If there is an increase in the side wall as well, assuming the side wall construction is the same as the comparison tyre, you will have more sideways movement, feeling squirmish but offering assistance to soak up those bumps.
Also if the tyre is bigger (larger diameter) and heavier (more rubber in it's construction), you will have more of the dreaded reciprocating unsprung mass that everybody is trying to minimise. Again negatively affecting turn in, acceleration and deceleration.
Now, I think all of these points are pretty petty because, at the end of the day, there are many other factors out there that will negate any small loss or gain achieved by the different profile of the tyre. These factors can only really be fully addressed by buying one of each and riding on your usual road on your usual bike in your usual way.
So, in conclusion, I have offered no helpful advise, probably repeated what others have already said, told you what you already know and wasted about 2 minutes of your time.
Hence my initial laugh.......