120/70 on a 620ie?

[Mr Gazza]

Could anyone please tell me or guess at what the effect of fitting a 120/70 front tyre on a 620ie would be?
It should have a 120/60. The rear is 160/60.

Could the extra height of the 120/70 be compensated for by fitting a different section tyre to the rear or do you reckon it would be okay anyway?

I imagine it will just make the steering a little slower?

Cheers

[slob]

You get a bit more lean before running off the edge of the tread ;-)

Many DD racers used that front with the stock 160/60 rear

[velosam]

This seems to be a common thing. My friend's 696 has a 120/70 and I didn't feel like it was a whale when I rode it, although that wasn't anything other than a pootle up the motorway on the way back from buying it and through town to her house.

Will be interesting to see what people say; 120/60 doesn't offer as much choice in terms of brand, I reckon I'd try and find one though when I need to replace the front on my 620ie.

[Stinger101]

Hi Gazza, You know I won't know about any clearance issues that are highly likely not to be there, but I can say that I don't think you'll feel any difference at all in normal road use. The difference in any ride height is negligible and shouldn't need any adjusting at the rear.

I say that because the original Yamaha R6 used to have a 120/60 but we all changed to 120/70 for track purposes and that's where speed of turn and feel are just as or more important maybe. We never felt anything other than supreme confidence as it always felt a lot better than any 120/60 item. Though that bike had a 180/55 rear already.
The 120/70 raised the front by about 5mm.
Well, that's my two penneth right there! :-)

As for slower steering, that's not an issue. The 120/60 has a flatter profile that the 70. The 70 will likely feel sharper as it happens.

[Dukedesmo]

Same sized wheel as other bikes so why not the tyre?

I recall back in the 916 and 748 days, the bikes used the same frame, suspension, wheels etc. yet 748s were fitted with a 60 profile front whilst 916 a 70 profile, similarly, at the rear 748 had a 180 width whilst 916 a 190 width.

It wasn't long before most adopted the 70 profile front and 180 width rear for both, my understanding was that they tried to sell the 748 as a more nimble bike (presumably to compensate for less power?) and fitting a lower profile front and narrower rear made it tip into a corner quicker but it soon became apparent that it ran out of front tyre/grip sooner due to the lower profile. The narrower rear, however was a good thing.

[Mr Gazza]

Thank you so much my friends that's all good news.

I have a good 120/70 that I'm giving to a mate and I didn't want to give him a tyre that would be likely to cause problems.

Would you stick with the 160/60 on the rear? I've never shopped for that size so I don't know what's available.
We need something to go well with the Angel ST front, I was going to suggest a Pirelli Diablo? Budget is an issue.

[velosam]

Might revise my earlier comment then if everyone's saying it's a better option!

[Dukedesmo]

If you really could feel the difference in front ride height that the 70 profile gives over a 60? then you could always compensate by dropping the front of the bike through the yokes but the difference is what, 5 or 6mm? - you probably get that much between different brands and from new to worn.

[Darkness]

Originally Posted by Dukedesmo

If you really could feel the difference in front ride height that the 70 profile gives over a 60? then you could always compensate by dropping the front of the bike through the yokes but the difference is what, 5 or 6mm? - you probably get that much between different brands and from new to worn.

In theory, (120*0.70)-(120*0.60) = 12mm increase in ride height, and the same reduction in clearance to the front mudguard. In practise, the change may be less, though I’d be surprised if it were as little as 5 or 6mm.

What rim width do you have on the rear of the bike? The 900 Monster has the 5.5” rear rim which was originally fitted with the scarce 170/60 size tyres. You can fit the 180/55 on those, but for 190 or 200 width tyres you really need a 6” rim.

If you’ve got the 4.5” rim you are probably already at the maximum rubber at 160.

[Zimbo]

120/70 is fine on the front, stick with the 160/60 on the rear.

[Stinger101]

Originally Posted by Darkness

In theory, (120*0.70)-(120*0.60) = 12mm increase in ride height, and the same reduction in clearance to the front mudguard. In practise, the change may be less, though I’d be surprised if it were as little as 5 or 6mm.

What rim width do you have on the rear of the bike? The 900 Monster has the 5.5” rear rim which was originally fitted with the scarce 170/60 size tyres. You can fit the 180/55 on those, but for 190 or 200 width tyres you really need a 6” rim.

If you’ve got the 4.5” rim you are probably already at the maximum rubber at 160.

ETRTO manufacturer parameters allow + or - 3.5% and it's very difficult to allow a fixed value into your calculation. In practice the ride height is an average 5 to 6mm.
I'm really boring on tyres as they've been my job for 34 years...

[Dukedesmo]

Originally Posted by Darkness

In theory, (120*0.70)-(120*0.60) = 12mm increase in ride height, and the same reduction in clearance to the front mudguard. In practise, the change may be less, though I’d be surprised if it were as little as 5 or 6mm.

Can't be bothered to try the maths now but, isn't 12mm the overall increase in size (diameter)?

If so then whilst the top of the tyre would be 12mm higher, the ride height is only 6mm higher as it comes from the axle in the centre (radius).

[Nickj]

Originally Posted by Dukedesmo

Same sized wheel as other bikes so why not the tyre?

I recall back in the 916 and 748 days, the bikes used the same frame, suspension, wheels etc. yet 748s were fitted with a 60 profile front whilst 916 a 70 profile, similarly, at the rear 748 had a 180 width whilst 916 a 190 width.

It wasn't long before most adopted the 70 profile front and 180 width rear for both, my understanding was that they tried to sell the 748 as a more nimble bike (presumably to compensate for less power?) and fitting a lower profile front and narrower rear made it tip into a corner quicker but it soon became apparent that it ran out of front tyre/grip sooner due to the lower profile. The narrower rear, however was a good thing.

I can confirm that the 748's, certainly the R's, are faster .. much faster.. into corners than 916's. Fitting the fatter rear profile trashes the handling. The power difference isn't that significant a good 916 has at best 9bhp at the limiter over my R. They're a much closer match than you'd imagine and that edge into corners and the insane corner speed they'll carry is a great leveler. The fast spin up of the 748 motor virtually compensates for the torque difference.
I like the 916's and the 748's, take the stickers off and you'd not know which was which without a close look.

[Darkness]

Originally Posted by Stinger101

ETRTO manufacturer parameters allow + or - 3.5% and it's very difficult to allow a fixed value into your calculation. In practice the ride height is an average 5 to 6mm.
I'm really boring on tyres as they've been my job for 34 years...

I based it on Pirelli’s explanation of motorcycle tyre sizings and sidewall markings:
https://www.pirelli.com/minisite/pir.../page-392.html

[Dukedesmo]

Originally Posted by Nickj

I can confirm that the 748's, certainly the R's, are faster .. much faster.. into corners than 916's. Fitting the fatter rear profile trashes the handling. The power difference isn't that significant a good 916 has at best 9bhp at the limiter over my R. They're a much closer match than you'd imagine and that edge into corners and the insane corner speed they'll carry is a great leveler. The fast spin up of the 748 motor virtually compensates for the torque difference.
I like the 916's and the 748's, take the stickers off and you'd not know which was which without a close look.

I would say it's all in the setup.

Tyres being equal and engine power aside what is the real difference between the bikes with regards to geometry and weight? because the chassis is the same, the engine is the same other than a few internal components and the weight difference is minimal (basically the weight of the missing oil cooler and 1/4L of oil on a standard 748).

Now a 748R will have better suspension components and some weight savings over a standard bike along with more power and the more rev-happy nature should make it easier to get on the power whilst the the larger engines have more torque - making it easier for the less race-focused.

But given that most people (that I've met) run the 180 rear/70 profile front combination regardless of model then any differences must be largely down to setup and, of course the size of your testicles...