190/50 v190/55

[spamanglenn]

All along i was convinced the profile of a 55 series 190 was pointier than a 50 series.I,ve used 180/55,190/50,190/55,200/50.Well I WAS WRONG......I have a few tyres undr the house and looked at 190/50 next to a 190/55 and the only difference is the height of the sidewall,the crown of the tyre is the same.Don,t get me wrong, a 55 profile does tip in better as it raises the rear of the bike,but it has exactly the same contact patch as a 190/50 profile.So if a 190/55 is out of stock and a 50 profile is(cheaper too).if you can raise the rear ride height 5-10mm,it,ll have the same effect.Individual manufactures profiles have more effect on turning,eg michelin pilot powers are quite pointy compared to pirellis and bridgestones seem to be between the two.

[Driller]

G/day Glen I remember speaking to you about this at Jindy as i only have used the 55 series once on the track with a very noticeable difference about the same difference as when i put the raising links on and dropped the forks through In the shed I have a 190/60 and contact patch is the same as 190/55 these are dunlop gp 209s The 60 is going on next week for a run up the Oxley . My concern with raising rear more and changing the geometry how much will high speed stability be affected?Is a better steering damper the go! As far as the 55 are concerned wont be going back to a 50 anytime soon.


Cheers Mark

[spamanglenn]

I remember dad had a dunlop 60 series rear on at eastern creek once and it did head shake out of turn 5 a fair bit so yes it does affect stability.I,m all for raising the bike in preference to lowering the front,perhaps you can drop the forks in the clamps 5mm as well as putting the 60 series rear on.This gives a higher centre of mass at the front,better ground clearance,better tip in as the back will be 10mm or more higher,and your still tall enough to touch the ground,lol.Look at all the superbikes,they're all taller,as are there tyres and alot of them also have taller seats in them.Taller bikes stay on their sides and hold a line better.Having adjustable lowering links and fairly flat back tyres for the drags,with a low seat and converting that back to a stock seat,at full height with a 55 profile rear gives you a good comparison of the extremes of how the bike steers.

[spamanglenn]

if it headshakes,just take a bit of preload out of the rear spring so it will sit down a little more,if not,have fun.

[fastfreddygassit]

When I had my 00 busa I made up new dog bones that jacked the rear of the busa
sky high (figuratively speaking) in an attempt to quicken up steering.
The pic should give you an idea of how high the back was...



The bike was immediately better in all facets of cornering (ie. initial tip in, line changes etc)
but at high speeds would sometimes begin to gently shake its head. But we are talking velocities
that make my gixxer thou shake all over the place (with an ohlins dampener).
I don't believe that high speeds stability is compromised that much when compared to the better steering you get with a raised rear (from tyre profile or jacking up).

[Billy the kid]

Also try a 120/60 instead of 120/65 on the front tyre.Combined with a 55 rear it would be alot better!My own 60 rennsport front never gave me head shakes and bump absorption is almost the same..

[greenb5]

I'm on my second 190/55 rear and won't be going back to 50 as I prefer the way it corners. I also assumed it was "pointyer", so there you go.
Haven't noticed any stability issues at speed but I've only had it up to 260 or so.

[spamanglenn]

a taller tyre raises the axle higher off the ground so the rear wheels centre of gravity will be higher,hence more inclined to tip in.As the rear wheel also includes the sprocket and rotor and chain,thats a fair bit of mass thats higher off the ground.raising the rear suspension only,only lifts the rear of the bike and rider a bit further up with the heavy spinning wheel still quite low down.I,ll still stick with a higher profile rear as you don,t have to decrease the trail and rake as much for better turn in.

[Billy the kid]

a taller tyre raises the axle higher off the ground so the rear wheels centre of gravity will be higher,hence more inclined to tip in.As the rear wheel also includes the sprocket and rotor and chain,thats a fair bit of mass thats higher off the ground.raising the rear suspension only,only lifts the rear of the bike and rider a bit further up with the heavy spinning wheel still quite low down.I,ll still stick with a higher profile rear as you don,t have to decrease the trail and rake as much for better turn in.

When you say rasing the rear shock what do you mean??Fitting shorter dog bone or any other way?
In the case of shorter dog bones they definately raise the axle of the swing arm shorten the wheel base and make the rake and caster more aggressive.
I cannot remember any other way..
But as you say the cheapest,fastest,easiest way to get fast geometry is a 55 rear and 60 front!Take a few clicks off compression,add rebound and back off on the preload and you 'll see even major turn in abilities on the track!

[spamanglenn]

dog bones and adjustable length shocks were what i meant.

[Billy the kid]

dog bones and adjustable length shocks were what i meant.

Ok here's the set up.The link of the suspension connects the shock to the frame and the bones the swing arm to the link.
So fitting shorter bones makes the swing arm to come closer to the link so the swing arms has to be raised so the bones can be bolted..thus the axle of the swing arm is higher.Not only the tail.

Also fitting a shock that can alter it's lenght can do the same thing.A shorter shock will make the link to raise so it will pull the bones and the swing arm.
Basicaly i do not know a shock that can be shortened or lenghtened.Ohlins i suppose??

[spamanglenn]

Elka.the shock needs to be able to be lengthened.changing the dog bone length changes the ratio the how the shock/spring acts on the rear suspension .When i lengthen the dogbones for the drags it feels harder.

[Billy the kid]

Elka.the shock needs to be able to be lengthened.changing the dog bone length changes the ratio the how the shock/spring acts on the rear suspension .When i lengthen the dogbones for the drags it feels harder.

That is correct.Fitting longer bones positions the bottom of theshock even closer to the axle of the swing arm.It is harder to compress because the "leverage"(the distance between the turning point and where the force is applied) i shorter now so the torque applied to the shock is lesser.
I suppose it is a good thing to be harder for the drags right??

[humbussa]

Just had a rear fitted should have gone the 55....oh well they don't seem to last long anyway i'll go the 55 next time round!! sounds like a worth while change for sure.