Aspect Ratios ~ how critical is a move one level in either direction

[Yukonica]

Looking to put a spare set of skins on the top shelf because, in stock sizes, the V7special has limited local availability.
However,  I'm seeing lots of near misses as clearance online or available stock in in the US (no shipping to Canada)
e.g., stock front is 100/90/18. Rear is 130/80/17
I can find Sport Demons in 100/80/18 (10% shorter sidewall)  or Pilot Activ (rear)  at 130/70/17
Any real world experience is welcomed.

[Yukonica]

Forgot to ask: has anyone used Pirelli Scorpion Trail's on their modern V7?
It is looking like a good tire for the roads up here.

[mtiberio]

do you drag any bits? are you short and could use a lower bike? the only thing to be careful about is lowering the front and not the rear if your bike has any tendency to headshake.

[Kev m]

I think MTib answered it for you.

I can't say personally on the V7, cause I went with a 130/80 Pilot Activ since I didn't want or need a lower bike.

However, IF memory serves, when I went with a thinner tire on the Jackal (a 130) I dropped 5mm or 10mm (I forget) on the diameter and I don't recall there being any problem. But maybe that's a bad example because over the years I lowered and raised it with various rear shocks depending on my mood at the time.

[redrider]

Many variables. The  size of any tire is not exact. All makers have a range of widths so a 180 could be anywhere between 170 and 190. My Avons are 180 but measure 188 and the stock was a 190. A different style from Avon listed at 180 measures 180. Then using the aspect ratio of whatever, the overall height will vary within the range as well. Confused yet? Generally, wider, low ratio tires slow the roll into and out of corners and on the front, increase the steering effort for the same lean. Going small may quicken the steering to the point of twitchiness and wobble. Critical? The Benelli handles better with the 180/55 vs. the stock 190/50 rear. Front 120/70 is standard. The Café Sport and Sport 1100 wear the recommended sizes. Michelins on the V11 were predictable but slow steering compared to the Avons. A size up or down should be OK but be prepared for a different feel, good or bad. The rim width also affects the final profile, especially for non-standard sizes that deviate greatly from stock.

[Kev m]

Red makes some good points.

And maybe we should also remind ourselves that IF you change the width AS WELL, then you change the significance of the aspect ratio.

I.E.

A 140/80 and a 130/90 are in theory only 5mm different in sidewall height, 10mm overall diameter.

While a 130/80 and a 130/90 are in theory 13mm different in sidewall height, 26mm overall diameter.

[lrutt]

I know I went down 1 level on AR on my Duc M900 and could really feel a difference in handling. I was surprised. Honestly, I liked it better before but will have to wear out this tire first.

Just seems to 'quicken' things up a bit. Not scary, but different.

[Yukonica]

Thanks all, I'm finding the supply of 'sets' of stock dimensions is pretty sketchy when looking for closeouts online here (Canada).

[Triple Jim]

Here's an interesting thing I'll add, that Redrider mentioned:  All the numbers that predict the width and height of a tire depend on the width of the rim that the manufacturer expects you to put it on.  My Mille had a 120/90 on the rear, and I tried a 130/80.  The book said the diameter should be very close, and I thought it would barely fit in the swing arm.  When I put it on, it was the same width that the 120/90 was, as measured with a caliper.  Checking Bridgestone's chart, although my 2.5" rim was within the allowable range, their numbers expected I'd put the 130/80 on a wider rim, so putting it on the same 2.5" rim made it narrower than their chart said, and probably a little taller too.  The result was mainly slightly more tread wrap than the 120/90.