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2bims
Joined: 03 Apr 2010
Posts: 7289
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 Posted: Tue Oct 18, 2011 9:32 am Post subject: Re: More info |
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| robin wrote: |
Hi
All the experience of other bikes is fascinating, but I really want to know how a Mantra handles. Does anyone actually have one?
Robin |
Evidently if we were all stood around your bike we could help more and possibly target issues, if there were any, The set up you have is evidently different to what Bimota intended, but rake, suspension, wheelbase etc all similar to DB2/DB4, hence folk trying to tell you what their bikes are like. GeeKay has a Mantra and put on over 6000miles round Italy this year, and thats with back-packs/panniers over the rear wheel. Perhaps removing the front fairing section has taken away effect of planting the front end, who knows? Did you actually have the bike as a Mantra and ride it before it was changed about? i.e. were there any problems prior to the changes? |
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2bims
Joined: 03 Apr 2010
Posts: 7289
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| Posted: Tue Oct 18, 2011 1:06 pm Post subject: Re: More info |
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| robin wrote: |
Hi
. The tyres are 120/70 and 180/55 Dunlop qualifiers (original type). They are balanced and at the recommended pressure of 2.5 front 2.9 rear. These are the recommended sizes, yes?
Robin |
Tyre sizes and profiles are right, 120/70 and 180/55, same for Db2/3/4. I think DJT's point about your nose fairing being fitted to the forks could be most valid. The other Mantra special that GeeKay(+ others) posted a picture of at the Stafford show has a modified/aftermarket nose fairing fitted, but it does appear to be mounted to a separate subframe attached to the headstock, just like most bikes, leaving any buffeting that hits the nose fairing well away from the forks and hence the stability. My Db2 is far from comfortable under 50mph, but after that speed is reached, the increase in the wind resistance lifts your torso up and relieves the pressure on your forearms and wrists considerably, getting better and better with speed. Evidently you wont have this with your bar fitments and small nose fairing and I can only imagine that at 50mph+ the wind hitting your torso will only make the front lighter, combined with the nose fairing and forks its attached to taking a fair beating/buffeting. The other Mantra special also has clip-ons under the top yoke as opposed to handlebars. It could be that your mods just aren't going to work. Only way really is take off the front shroud in daylight and go f0r a blast |
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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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| Posted: Tue Oct 18, 2011 7:25 pm Post subject: Re: More info |
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| robin wrote: |
| Hi Some of you have asked questions that are answered in my original post - worth having a look. The tyres are 120/70 and 180/55 Dunlop qualifiers (original type). They are balanced and at the recommended pressure of 2.5 front 2.9 rear. These are the recommended sizes, yes? |
Still I find the tire pressures on the high side, I normally ride less pressurized, more like 2.1 front and 2.5 rear streetwise. On track it's 1.9 - 2.0 front and 1.7 to 1.8 rear. Tire manufacturers seem to raise the tire pressures for road use more and more and go lower than usual for track use.
| robin wrote: |
and discs are true and don't bind.
I've checked head bearings, they are fine.
I will try taking the fairing and mirrors off to eliminate these. |
I agree with other respondants that the fairing is the most likely cause of te instability, so better check that out and if it makes the difference make a subframe to the headstock and attach your fairing to that.
| robin wrote: |
| I have been given a handling manual that has some interesting points on sprung vs. unsprung weight. I've made the bike lighter, but the wheels and brakes are standard, meaning there's a lot of unsprung weight. I will try a single disc arrangement, as that's the only cheap way I can reduce the weight of the front wheel. |
Not my experience: I lightened my track db4 by taking most of the street wiring off, lights, switches, sidestand, horn, airbox, stock seat, engine lightened and fitted a titanium exhaust as a replacement for the heavy shotgun set. Kept the stock wheels except front rotors that are the later 320 mm lightweight Brembo's and the later Brembo P4 calipers. No problems in the handling department...
| robin wrote: |
| As I can't drop the front any more (forks have no preload, and no space to extend further through the yokes) I will also try raising the rear as much as possible. The shock has ride height adjustment, and I will increase the preload. Not sure if it will help, but I'll try it. |
As advised before: don't alter too much at the same time. Create a base setting and work from that.
| robin wrote: |
| All the experience of other bikes is fascinating, but I really want to know how a Mantra handles. Does anyone actually have one? |
Yes, I've ridden one and it felt like a db4 with raised bars with forward footrests and just a fraction less nimble. My point: a stock Mantra is an excellent handling motorcycle.
| robin wrote: |
| ps the bike is in London. I get to the Ace regularly, if anyone wants to have a look. |
Sorry mate, just a little too far from my home stretch, but I sure would like to visit the Ace. So maybe next season.
Cheers!
_________________
Track riding on a Bimota: FUN! |
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