120/60 front tire

[freezer16801]

I mistakenly bought a 120/60 tire (Bstone BT16)for my track bike last year. I used it on that bike for a few track days before switching it out to BT003 120/70's.

I plan on running the tire the rest of the way out on the hyper, starting with two track days at the end of the month. What can I expect to change with handling? Should I make any geometry changes to compensate.

I plan on swapping the tires over a few days before the track days to test a bit on the street.

Any advise is helpful.

I have my rear link showing 5 threads and my forks flush with the triples.

[Decreasing Dave]

Without exact measurements I can only speculate, but I would drop the rear by one thread and leave the front alone, since you are flush anyway. The difference is noticable, but not dramatic, size-wise.

The issues with the 120/60s is that, while they will turn in a bit quicker, they have a shorter sidewall, so it's stiffer and lacks a bit of feel.

In my experience, they have had more of a tendancy to "Suprise!!" me more than the 120/70s.

YMMV

Dave

[freezer16801]

thanks dave, that is helpful. The front feels a bit slow to turn in now using the 120/70 with the forks being flush. I will measure the ride height before and after and go from there.

[Decreasing Dave]

Well, when I put my forks back into the trees after doing the springs, I left them sticking out to the first line, just as I got the bike originally. I found that it turned way better than before, both turn in and finishing the turn.

Maybe try it with the five threads and flush forks on the 120/60 and then raise the forks to the first line when you go back to the 120/70.

I would think that would give you a similar feel based on my limited knowledge. The bonus is that you would know for sure and be able to back me up (Think...Mythbusters) or call me a liar and mean it.

Dave

[Shazaam]

A 60-series tire isn’t the way to improve turn-in.

It’s generally true that a 60-series tire is shorter, so it lowers the front end. However, even tires having the same aspect ratios have different heights. For example, the Pirelli Dragon Evo front tire is almost 30mm shorter than the same size-rated Michelin Pilot Race (H2). So you should check this dimension before you replace the OEM tires that came with the bike.

If you decrease the tire height then you lower the front end, and consequently, you lower the center of gravity (C.G.) 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 tire, you raise the C.G. 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 C.G. and a higher C.G. makes the bike go to the tire edge quicker (as per 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 C.G. 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 60-series to a 70-series tire 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 tire 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 tire.

Your tires are an integral part of your suspension, so when you go from a 60 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 tire 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.

Changing from a 120/60 to a 120/70 Front Tire

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 tire), the front tire 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 tire reduces this wear-induced effect.

Further, a lower 60-ish profile tire (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 tire will be kinder to magnesium wheels.

Your tires are an integral part of your suspension so when you go from a 60 to a less-stiff 70 tire, the resultant handling change will probably benefit from front suspension setting modifications. Increased front compression damping may be in order to offset the less-stiff 70-series tire. Also, turn-in is slower with the 120/70 but this is easily compensated for by adjusting rear ride height

Also, an increase in the outside diameter of the tire 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 tire 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.

The decreased loads to the handlebars and increased sidewall flex combine to give you less (better?) feedback on the state of the front suspension and the traction condition at the front tire.

All this may better suit your riding style. Or not.

Some, like myself, find a less-nervous front end to be more appealing for the road so we run a 70-series tire. On the track, the better road surfaces make the benefits of a lower profile 60-series tire more obvious.

So, if you intend to convert to mag wheels, for the street a 120/60 is less able to handle rough pavement (less sidewall to cushion and flex for shock absorption) so wheel rim damage, especially to mag wheels, is an important consideration.

[johnnie27]

Originally Posted by Shazaam

A 60-series tire isn’t the way to improve turn-in.

It’s generally true that a 60-series tire is shorter, so it lowers the front end. However, even tires having the same aspect ratios have different heights. For example, the Pirelli Dragon Evo front tire is almost 30mm shorter than the same size-rated Michelin Pilot Race (H2). So you should check this dimension before you replace the OEM tires that came with the bike.

If you decrease the tire height then you lower the front end, and consequently, you lower the center of gravity (C.G.) 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 tire, you raise the C.G. 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 C.G. and a higher C.G. makes the bike go to the tire edge quicker (as per 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 C.G. 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 60-series to a 70-series tire 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 tire 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 tire.

Your tires are an integral part of your suspension, so when you go from a 60 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 tire 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.

Changing from a 120/60 to a 120/70 Front Tire

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 tire), the front tire 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 tire reduces this wear-induced effect.

Further, a lower 60-ish profile tire (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 tire will be kinder to magnesium wheels.

Your tires are an integral part of your suspension so when you go from a 60 to a less-stiff 70 tire, the resultant handling change will probably benefit from front suspension setting modifications. Increased front compression damping may be in order to offset the less-stiff 70-series tire. Also, turn-in is slower with the 120/70 but this is easily compensated for by adjusting rear ride height

Also, an increase in the outside diameter of the tire 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 tire 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.

The decreased loads to the handlebars and increased sidewall flex combine to give you less (better?) feedback on the state of the front suspension and the traction condition at the front tire.

All this may better suit your riding style. Or not.

Some, like myself, find a less-nervous front end to be more appealing for the road so we run a 70-series tire. On the track, the better road surfaces make the benefits of a lower profile 60-series tire more obvious.

So, if you intend to convert to mag wheels, for the street a 120/60 is less able to handle rough pavement (less sidewall to cushion and flex for shock absorption) so wheel rim damage, especially to mag wheels, is an important consideration.

what a great read, thanks for posting that good info mate