Rear Wheel Clearance V Tyre Choice....Opinions Sought

[998gsb]

Following on from an earlier thread...

I discovered that the 190/55 tyre has been kissing the link section of the exhaust system on the 998 and has also just touched the hugger....neither rub is severe - but its only done 70 miles around the track - so prolonged use is likely to cause further damage.

By my reckoning a 180/55 tyre will be even taller by about 4.5mm....the bike is running stock 15/36 gearing.

At rest, the rear wheel has about 5mm-7mm clearance on the exhaust and about the same on the hugger.


Someone suggested taking the axle out and rotating the eccentric cam adjuster by 180 degrees.....now i've been thinking about this, and drawn it out on paper and as far as i can see this wont make any difference will it...? The cam rotates through a fixed axis and at the furthest point from the swing arm - the position of the axle will be same whichever way the cam is installed - the only difference would be the rotational direction of the cam to adjust the chain tension.

This must be a common problem on all the 748-998 range in terms of tyre choice - as there are actually very few / no 50 sticky track / race tyres - everything is 55 fitment.....

Is there a fix for this - or do you just accept that the tyre will kiss the exhaust through a certain part of the suspension travel.....

Would running 14/38 gearing give me any greater travel of the rear wheel in terms of distance between the axle and the pivot on the swing arm.

Talking to RodH who has a 916sps running this gearing with a 180/55 and he does'nt have the clearance problems that i seem to have....?

[ianm1982]

My 998 have had this problem in the past as when i got it the hugger has a small hole in it in the exhaust indent from either the termi's touching it or the tyre wearing through it not sure which as i just covered the small hole up for now with some black tape till i can buy a new hugger. Not sure what tyre is on my bike as i am in work but will update this later to let you know.

I have seen some threads where people just raise the hugger slightly using spacers under the hugger to lift it how mush that will do i dont know but if it is catching the link pipes that will only make it worse?

[Bungi]

Originally Posted by 998gsb

Following on from an earlier thread...

I discovered that the 190/55 tyre has been kissing the link section of the exhaust system on the 998 and has also just touched the hugger....neither rub is severe - but its only done 70 miles around the track - so prolonged use is likely to cause further damage.

By my reckoning a 180/55 tyre will be even taller by about 4.5mm....the bike is running stock 15/36 gearing.

At rest, the rear wheel has about 5mm-7mm clearance on the exhaust and about the same on the hugger.


Someone suggested taking the axle out and rotating the eccentric cam adjuster by 180 degrees.....now i've been thinking about this, and drawn it out on paper and as far as i can see this wont make any difference will it...? The cam rotates through a fixed axis and at the furthest point from the swing arm - the position of the axle will be same whichever way the cam is installed - the only difference would be the rotational direction of the cam to adjust the chain tension.

This must be a common problem on all the 748-998 range in terms of tyre choice - as there are actually very few / no 50 sticky track / race tyres - everything is 55 fitment.....

Is there a fix for this - or do you just accept that the tyre will kiss the exhaust through a certain part of the suspension travel.....

Would running 14/38 gearing give me any greater travel of the rear wheel in terms of distance between the axle and the pivot on the swing arm.

Talking to RodH who has a 916sps running this gearing with a 180/55 and he does'nt have the clearance problems that i seem to have....?

i had this problem running this tyre size on a track bike a few years ago, we changed the tyre size to get around the problem in the end if i recall correctly, but there are other options if you dont wish to do that .

firstly check your eccentric is operating in the lower semi circle, as if its in the top this will casue problems.

the exhaust size we were using at the time was a 54mm full system on a 996R , and when using a larger tyre it just wouldnt work when the tyre wrmed up an ballooned at speed it would smoke on the xhaust.

the other thing to do is move the wheel back in the eccentric toward the rear of the bike . this can be done by compromising you sproket sizes and chain length to get the gearing you want with the wheel in or near to the correct position, if the wheel is further back it will also give you a better geometry . especially if set up with the front, to move the central mass forward in the wheelbase .

[Denzil the Ducati]

Folks, as a track day virgin, is there that much difference (for us mortal road riders) using a good sports tyre in comparison with a track tyre for those 2 or 3 track visits in the year? Its just this seems a little OCD to me and the simple answer is to stick with a 190-50 or a 180-55 as standard for the bike, but what do I know. I have had tyre/hugger rubbing with a new 180-55 rosso at walking pace so faffing around with ratios where the rolling radius is going to get bigger is surely going to cause the rubbing problem - this cannot be a surprise. The solutions offered will inevitably alter the geometry which may then require height adjustments at either end to ensure the best set up. Is it not likely that the result of making the tyre fit will negate the benefits of the 'stickier' tyre in any case?

[DukeDesmo]

You can increase the wheel base by altering the combination by up to 12mm plus also raise the ride height should give you a few more mm of clearance.

According to Shazaam's chart 14/38 or better still 15/41 + longer chain would give you the longest available wheel base.

[Sorted]

Originally Posted by 998gsb

Following on from an earlier thread...

I discovered that the 190/55 tyre has been kissing the link section of the exhaust system on the 998 and has also just touched the hugger....neither rub is severe - but its only done 70 miles around the track - so prolonged use is likely to cause further damage.

By my reckoning a 180/55 tyre will be even taller by about 4.5mm....the bike is running stock 15/36 gearing.

At rest, the rear wheel has about 5mm-7mm clearance on the exhaust and about the same on the hugger.


Someone suggested taking the axle out and rotating the eccentric cam adjuster by 180 degrees.....now i've been thinking about this, and drawn it out on paper and as far as i can see this wont make any difference will it...? The cam rotates through a fixed axis and at the furthest point from the swing arm - the position of the axle will be same whichever way the cam is installed - the only difference would be the rotational direction of the cam to adjust the chain tension.

This must be a common problem on all the 748-998 range in terms of tyre choice - as there are actually very few / no 50 sticky track / race tyres - everything is 55 fitment.....

Is there a fix for this - or do you just accept that the tyre will kiss the exhaust through a certain part of the suspension travel.....

Would running 14/38 gearing give me any greater travel of the rear wheel in terms of distance between the axle and the pivot on the swing arm.

Talking to RodH who has a 916sps running this gearing with a 180/55 and he does'nt have the clearance problems that i seem to have....?

I use a 190/55 on my SPS track bike but don't use a hugger as I find them a hassle when fitting tyre warmers. The tyre was close to the exhaust and when on tickover/stationary for a while, that part of the tyre got VERY HOT (started smoking)!

I lengthened the chain by 2 links was already running 14/37 and it moved the tyre back about 10mm and lowered it by about the same (so you would end up with about 15mm clearance under the hugger)
Just make sure the stub axle centre line remains lower than the centre of the swingarm and if you don't want the rear to drop by that much use the ride height adjuster to put it back up by 10mm or so.

Metzeler Racetecs are a great track tyre and come in 190/50 K1 or K2 compund

[The Dieselinator]

Originally Posted by 998gsb

Following on from an earlier thread...
By my reckoning a 180/55 tyre will be even taller by about 4.5mm....the bike is running stock 15/36 gearing.

Why would a 180/55 profile tyre be taller? If it's 55% of 180 versus 190 is must surely be lower?

Or am I being dumb?

[998gsb]

Originally Posted by Denzil the Ducati

Folks, as a track day virgin, is there that much difference (for us mortal road riders) using a good sports tyre in comparison with a track tyre for those 2 or 3 track visits in the year? Its just this seems a little OCD to me and the simple answer is to stick with a 190-50 or a 180-55 as standard for the bike, but what do I know. I have had tyre/hugger rubbing with a new 180-55 rosso at walking pace so faffing around with ratios where the rolling radius is going to get bigger is surely going to cause the rubbing problem - this cannot be a surprise. The solutions offered will inevitably alter the geometry which may then require height adjustments at either end to ensure the best set up. Is it not likely that the result of making the tyre fit will negate the benefits of the 'stickier' tyre in any case?

I know what you are saying Denzil.....but after Pembrey on standard gearing I know i need to change the gearing anyway....one complex of bends the bike was reving out in second and hitting the limiter, but wouldn't pull in third...Rod who was running lower gearing was planted in third all the way through and just pulled away from me.....

Aside from that - The Supercorsa BSBs are road legal tyres and stick like nothing else i've ever tried so im a convert to them.....but they dont make them in 190/50 profile... and if you start looking 190/50 is actually a really odd size fitment and there isn't an awful lot of choice - switch to 180/55 or 190/55 and there is a vast amount of choice....


And.....i like finding solutions to problems, rather than just giving up and accepting lower spec...

Thanks for the advice guys...... have been mulling on this all morning and changing the gearing to 14/38 seems to be the obvious solution to try first as i wont have to chop the chain or add links.....

When measuring ride height - does it matter where you measure from as long as its a fixed point - and would you do this on the stands, or with the bike on the ground?

[DukeDesmo]

Originally Posted by 998gsb

When measuring ride height - does it matter where you measure from as long as its a fixed point - and would you do this on the stands, or with the bike on the ground?

Measure from axle to a fixed point on the subframe, obviously use the same point as you're only interested in the differences or there is an official Ducati ride height measuring tool.

You need to measure with the bike lifted ie with the rear wheel not on the ground - axle stands under the footrests work well.

[998gsb]

Originally Posted by DukeDesmo

Measure from axle to a fixed point on the subframe, obviously use the same point as you're only interested in the differences or there is an official Ducati ride height measuring tool.

You need to measure with the bike lifted ie with the rear wheel not on the ground - axle stands under the footrests work well.

Great - thanks DD

[Sorted]

Originally Posted by The Dieselinator

Why would a 180/55 profile tyre be taller? If it's 55% of 180 versus 190 is must surely be lower?

Or am I being dumb?

Nope you're right Pete its 99mm versus 104.5mm so it is lower by 5.5mm

[998gsb]

OOps! My mistake!

so if i changed the gearing to 14/38 and fitted 180/55s problem should be sorted...?

[DukeDesmo]

Originally Posted by 998gsb

OOps! My mistake!

so if i changed the gearing to 14/38 and fitted 180/55s problem should be sorted...?

If you fit 180/55 the problem should be sorted no matter what gearing you have.

[998gsb]

Originally Posted by DukeDesmo

If you fit 180/55 the problem should be sorted no matter what gearing you have.

Will do that next time...but buying a couple of renthals is cheaper at the mo as the 190s have only done 90 miles!

[Tobytyke]

Originally Posted by 998gsb

OOps! My mistake!

so if i changed the gearing to 14/38 and fitted 180/55s problem should be sorted...?

But are you running a standard 94 link chain? if so this'll reduce the clearance by 4mm because the eccentric will have to move forward so you'll still have a problem Gav. You need a longer chain mate