Ducati Sporting Club

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 21-Dec-2006, 07:59 PM
Jasper's Avatar
Jasper Jasper is offline
Registered Forum User
Ducati Corse
 
Posts: 3,701
Join Date: Jun 2002
What tyre sizes?

I have been lucky enough to get a new set of Marvic mag wheels.The rear is a 6.25",which means a switch to a 190/50 or 190/55 rear tyre.What size combinations are you guys using and why?

Can i retain the 120/70 Front or does that need to go?

I want turn in speed as opposed to stability.Oh,and i'll be sticking with Pirellis Diablo Corsas!!

Thanks in advance.

Jasper

Last edited by Jasper : 21-Dec-2006 at 08:09 PM.
Reply With Quote
  #2  
Old 21-Dec-2006, 09:04 PM
keefer's Avatar
keefer keefer is offline
Registered Forum User
Ducati Meccanica
 
Posts: 2,519
Join Date: Jul 2004
Mood: Found a CR250. Let the bone braking begin
190/55 with 120/70 front for me
I love it
didn't like the 190/50 it just didn't look steep enough for me.
Reply With Quote
  #3  
Old 21-Dec-2006, 09:09 PM
Shazaam!'s Avatar
DSC Member Shazaam! Shazaam! is offline
DSC Club Member
Big Twin
 
Posts: 1,167
Join Date: Nov 2001
A 65-series tyre isn’t the way to improve turn-in.

It’s generally true that a 65-series tyre is shorter, so it lowers the front end. However, even tyres having the same aspect ratios have different heights. For example, the Pirelli Dragon Evo front tyre is almost 30mm shorter than the same size-rated Michelin Pilot Race (H2). So you should check this dimension before you replace your current setup.

If you decrease the tyre height then you lower the front end, and consequently, you lower the center of gravity (CG) of the bike as well. This also increases the fork angle.

If you raise the rear end using the ride height adjuster, or go to a taller rear tyre, you raise the CG relative to it’s initial position. So, lowering the front ride height or raising the rear ride height are not equivalent adjustments.

In particular, the thought that lowering the front to improve turn-in response is incorrect.

Ducati Corse, in a 1996 memorandum*, recommended raising the front 10mm to increase “flickability" as in a chicane. Yes, I said RAISE, not lower. Raising the front end raises CG and a higher CG makes the bike go to the tyre edge quicker (according to the Ducati race engineers).

* Ths memo was previous available via the search engine at the old Ducati.com web site but lost when they put up the new site and no longer available.

The same advice is currently given in the factory race bike setup manual.

Take a look at the Mille SP. It has the capability to raise the engine in the frame to increase CG to improve flickability. Same effect. Even the Mille R has the engine higher in the frame to do the same.

It’s true that when you move from a 65-series to a 70-series tyre you’ll sense a slower steering. But, the slower steering you sense is the effect of the change in the tire section, not from the higher front ride height. The higher 70-profile tyre flexes more, reducing the severity of the loads transmitted to the wheel rim, suspension and handlebars. So the steering feels more vague with a higher profile tyre.

Your tyres are an integral part of your suspension, so when you go from a 65 to a less-stiff 70 profile, you’ll often see some benefit from increasing fork compression damping a little.

You can also increase rear ride height further to compensate.

Another effect from the taller tyre is an increased rake to the forks, so you can try compensating by using the steeper steering head position. This will also give you a 6mm shorter trail but will make the bike more prone to head-shake.

---------------------

But try it and see if you like it. It's really a question of handling preference, although there are some side issues.

Keep in mind is that (unlike the back tyre), the front tyre wears most quickly at it's edges. So over time, the profile gets progressively steeper and the steering gets more tippy; that is, it falls into the corner more readily. Starting with a 120/60 or a 120/65 section tyre reduces this wear-induced effect.

Further, a lower 60-ish profile tyre (often) has a shorter height so it doesn't flex as easily. This increases the severity of the loads transmitted to the wheel rim, suspension and handlebars. This in turn, increases the likelihood of alloy wheel damage, so a 70-series tyre will be kinder to magnesium wheels.

Also, an increase in the outside diameter of the tyre will cause your already inaccurately high-reading speedometer to read more accurately and will change your ride height so you may want to compensate by repositioning the front forks.

The 120/70 tyre is approximately (not all 120/70s are alike) 24mm larger in diameter than a 120/60, so to keep the identical chassis geometry, you'll need to raise the forks (drop the triple clamps) enough to compensate for the ~12mm higher axle. Take a front ride height reference dimension first.

-------------

That said, I personally like the 70-series tyre on a superbike.

Last edited by Shazaam! : 21-Dec-2006 at 09:20 PM.
Reply With Quote
  #4  
Old 21-Dec-2006, 10:24 PM
Jasper's Avatar
Jasper Jasper is offline
Registered Forum User
Ducati Corse
 
Posts: 3,701
Join Date: Jun 2002
Thanks Shazaam.I'm Happy to stay with a 120/70 on the front,i really like it.BUT what about the 190/55 against a 190/50?Which one to give me the same feel i have now with a 180/55?

Last edited by Jasper : 22-Dec-2006 at 09:46 AM.
Reply With Quote
  #5  
Old 22-Dec-2006, 07:37 PM
851neil 851neil is offline
Registered Forum User
500SD
 
Posts: 717
Join Date: Mar 2005
Mood: need a bike...
ahd just go for summat round an black jasp....infantile giggles...
Reply With Quote
  #6  
Old 22-Dec-2006, 08:01 PM
Jasper's Avatar
Jasper Jasper is offline
Registered Forum User
Ducati Corse
 
Posts: 3,701
Join Date: Jun 2002
But i lean my bike over neil,it's ok for you,you just put it on paddock stands and take pictures of it(for me!!).
Reply With Quote
  #7  
Old 23-Dec-2006, 05:07 PM
851neil 851neil is offline
Registered Forum User
500SD
 
Posts: 717
Join Date: Mar 2005
Mood: need a bike...
can't afford to run around on it, I just sit on it now and again and play a previously recorded 955 soundtrack...it's really good on tyres...
Reply With Quote
Reply
  
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes
Postbit Selector
Switch to Vertical postbit Use Vertical Postbit

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Recent Posts - Contact Us - DSC Home - Archive - Top
Powered by vBulletin 3.5.4 - Copyright © 2000 - 2017, Jelsoft Enterprises Ltd. - © Ducati Sporting Club - All times are GMT +1. The time now is 04:57 AM.