Mismatched Tyres, Cornering is awful!

[LatencyXR]

So before we start with the tyre politics and the fact that mismatching is a stupid idea.

My front Tyre type is Adventure (100/90)
My rear tyre type is a Pilot street (120/80)

Riding in a straight line absolute dream, slight cornering again beautiful, but a corner that requires a lean, bike doesn't agree! Doesn't feel unstable but it's heavier to get out of the bend.

Again mismatched tyre yes but how many miles approximately does it take to break in tyres.

Thanks
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Honda CB300R - More 125's then the heart can handle!

[stinkwheel]

Modern michelin tyres with a silicone compound? Zero time to "break in", they are ready to go.

Are they the right size? What bike?

A lower profile on the front and/or higher profile on the rear that it's supposed to have can tighten the rake angle which makes turn-in faster but stability worse (kind of the same thing really). The other way round (ie a profile that raises the front/lowers the rear) tends to stabilise the bike when upright but they eventually flop over into corners and take a lot of countersteer to get back up again.
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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.

[LatencyXR]

Thanks for your reply!

Modern tyres so yes feels great .. to be honest to the profile of the tyres that confuses me, the bike is a modified 125 cafe racer type with modded cams, higher acceleration so needed a good rear tyre for stability, again stability I get untill I corner then the bike just feels like it's in a complete world of it own.
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Honda CB300R - More 125's then the heart can handle!

[stinkwheel]

Did it handle properly before the tyre change? What size wheels do you have?

Modded how? Does it have the original front and rear ride height, forks and shock? Wheel sizes? Frame altered? I know a lot of people who make those brat chopper type things slam the forks through the yoke. A 1/2" difference in front or rear ride height can radically alter the handling of the bike.

Although in fairness, what you described sounds like a bike with too much rake angle for its frame geometry (think old-school chops, they have really extreme rake angles but they also have chopped frames to make them handle with it, it's not just that they fitted longer forks). This would usually be caused by lowering the back end or raising the front end. If you start fiddling with ride height at one end, unless you did it for a specific reason, you either need to compensate with the other end or start altering frame geometry or handling will potentially suffer.

So likes of my trials bike, I fitted 2" over standard shocks to it, but I also went from a 19 to 21" front wheel. This still effectively dropped the front end by about 1". If I was riding it like a road bike, that would be a total liability, it would probably crash if leaned over too far, front end would tuck. But it's meant to be very manouverable at low speeds and it's all about keeping the bike as upright as possible so a very tight rake angle is actually useful in this setup.

TL;DR if you're going to modify a bike in such a way as it alters frame geometry or ride height, you need to know what effect that will have on the handling and either take steps to compensate for it or accept those changes and ride accordingly.
____________________
“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.

[LatencyXR]

My apologies on previous post for being short and the lack of information.

The engine is modified but has no weight gain and the center mass of the bike is unchanged. Front tyre is 19" and rear is 18", bike performance is optimal and maybe, just maybe the rear suspension needs looking at. this bike only really goes out during the summer months.

To be honest bike handles great but had an accident on other bike which broken many bones so maybe it's just me. We'll call it anxiety and presume it's not the bike!

Thanks for your informative reply
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Honda CB300R - More 125's then the heart can handle!

[stinkwheel]

Being a 125, it's probably not all that adjustable in terms of suspension but there are things you can check and do.

First is tyre pressures, make sure those are correct.

Check your wheel alignment is correct, if they aren't both pointing in the same direction, it doesn't help.

You can probably only adjust preload on the suspension. Have a read about measuring static sag. Set your preload so the static sag is as near to ideal as you can get it. Ignore rider sag unless you're going to get into altering spring rates and such. Most rear shocks are preload adjustable. On most 125s, you can only really adjust front preload by altering the size of the spacer on top of the spring by either fitting a different spacer or stacking repair washers on top of the spring. I'd probably only go to the effort of doing that if the sag is way out.

You could also carefully experiment with altering front ride height. Depending on the bike, you may be able to let the forks through the yokes slightly so they're sticking up through the top yoke. I'd do it in very small increments, maybe 1/4 to 1/2" at a time and go for a careful test ride after to see if it's any better. Remember it could potentially be worse so creep up on it.

Rear ride height is trickier to alter. On monoshock bikes, it usually involves fitting different dog-bone spacers, on twinshocks it would be fitting different shocks. I'd probably only bother if you are 100% convinced it's too low at the front and there's no fork left to raise up.
____________________
“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.

[doggone]

With mine tyre pressures even 5psi out can make it feel unpredictable cornering aggressively - just saying, because not being at the sweet spot probably has more effect than anything else you are thinking is involved.