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SA 180x55 v's 190x55 and Ohlins rear ride height adjustment query

Discussion in 'Racing, Motorsports, and Track Days' started by lobe29, May 15, 2013.

  1. G'day,

    I've read alot regarding the 190x55 V's 180x55 tyre fitment on the standard 6" rim and understand the 180x55 , 190x50 190x55 scenario - profile, ride height, gearing etc.

    Bike (inc an 04 model) historically always set up professionally by reputable specialists for fast road with settings for track, using a 180x55 rear (Pirelli Supercorsa's from circa 06 - 09)

    Set up has been spot on & served well last 4 - 6 years.

    Cbr1000rr 07
    Ohlins Rear.
    Re valved front - quality oil etc.
    Good set up. Front end was lowered slightly during this set up 8-10mm i think from memory as i type this.

    I'm currently getting D211 GPA's from a mate - done a few practice laps. They are not shagged out ex trackday/race rubber. Rear is 190x55

    180x55 = 99mm height
    190x55 = 104.5mm

    Question - Is it a case of reducing the rear ride height by 5.5mm on the ohlins rear ride height adjuster (bike offground, supported under frame/footpegs, not a race stand etc), to return to the set up & handling as given by the specialists set up, when i was using/buying 180x55's ???

    Bike does feel like its loading the front up when riding accordingly inc the tighter twisty stuff if still dragging abit of front brake (hence ride height query). Not noticable when pottering around obviously.

  2. #2 RichiB, May 15, 2013
    Last edited: May 15, 2013
    So many variables I will make broad assumptions without evern mentioning them. Covered to death in race and track forums.

    2 schools of thought:
    1st - just try it with the new tyres. For 99 people out of 100 there is a chance riding the new tyres as is will provide useful feedback and possibly a setup that feels no different, or is even ‘better’ than before.And if not, you make informed decisions for the direction you would like to go in. Its also very easy. IMO unless your shop was on hand at the track and providing answers to you questions to dial things in and out, it is almost certainly a compromise off the shelf solution anyway. Besides, ideal setups are dynamic for rider skill and conditions, they def arent static.

    2nd one is you adjust the geometry to replicate the old. To do that you need 3 things: confidence your original setup was optimal and worth replicating, actual inflated diameter measurements of the tyres – both front and rear, and an understanding of what the changes to ride heights F & R mean to your geometry both rake/trail and swingarm angle. Adjust accordingly to preserve the angles. You might find going to GPAs raises the rear of the bike more than the front (think axle heights here), and that would mean the swingarm angle has reduced. So you would need to get it back, and it isnt by lowering the rear...

    Here’s a chart from Dunlop that might be helpful, don’t use tyre sizes and profiles to make decisions, it’s pointless. Disclaimer: all above is my opinion only. Just PM me for a copy if the pic doesnt work, I'll txt it to you. Dunlop chart.PNG
    • Informative Informative x 1
  3. I'd simply try it and see if you can feel the difference. I'd bet good money you wouldn't. It's probably only the difference in an extra big morning sh!t, or a bit more lunch in your backpack. Or a full or empty tank. Just rough examples, but you get the drift. Tyre compound, profile and tread pattern will most likely make a larger difference in the handling than a few mm of ride height.
  4. Simplistic theory sez.....

    Bigger back tyre should have the bike sitting higher at the rear, promoting quicker turn in (slightly).

    Bigger back tyre on the back should cause turn in to be (slightly) slower.

    "Loading up" the front, if you are still on the front brake in a corner is riding technique problem, not a different sized tyres problem.
  5. Erm ever heard of trail braking Cam? Seems to work for Jorge, Marc, Dani, Vale, Cal, Andrea, Nicky, Alvaro....
  6. I have heard of trail braking, Darren.

    These folk you mention, am I right in assuming they are famous heroes of MotoGP or possibly WSB? I dunno 'cos I ain't on first name terms with any of that crowd.:)
  7. Redo SAG, ride, make adjustments
  8. How much do you think curr sag will be upset with the new tyres? Ballpark.
  9. He could measure it now with the current tyres then with the 190's on and see. If its not a huge difference don't adjust it