Tyres, tires, round rubber hoops

Why do companies spend loads of cash on researching which tyre sizes go best with which bikes?

Can anyone answer me truthfully.


Why do folk bother messing around trying to shoe on a bigger size? Is it a willy waving thing or what.


My reading of it was that if you try and stick on a 190 where a 180 was you not only decrease your contact patch and slow steering because you are forcing the tyre to be taller. would I be correct?

 

You are right. Someone on one of our forums went into great mathematical detail with diagrams on the changes in curvature and overall diameter on improper rims. With all the differences in performance between manufactures and compounds, changing the size will probably decrease performance.

 

I am a big believer in staying with the stock size unless you understand the effects of the possible change.

Case in point would be my 1986 VFR750 with 2.5 x 16 front and 3.5 x 18 rear rims. Stock size for these is 110/80 front and 130/80 rear, but at one stage I tried a 120 front, and a 160/60 rear. The 120 front made for a less stable ride as the wider tyre was more prone to kicking back on bumps and having more effect on steering. The 160 rear ended up with a weird curvature where the centre was flat but the sides were pulled in, which made for a tipping in feeling when leaning. There is an optimum tyre width for each rim width, and you are best to stay within the bike or tyre manufacturer's recommendations.

On my ST1100, the PO had fitted a 160/60 rear tyre in place of the stock 160/70. If you didn't already know, the height of the tyre is the width x the aspect ratio, so a 160/60 is 96mm high, and a 160/70 is 112mm high. 16mm difference in tyre height seriously affects steering geometry and gearing, and on a heavy old bus like an ST1100, it was hard work to lift onto the centre stand.

 

Think the st may be the fly in the ointment. The abs version had a different front tyre size compared to the STD.

120/70 abs to the 110/80 STD although the wheel was the same. Agree about the rear, mine was fitted with 160/60 when I bought it. Nearly gave mesel a hernia. Lol

 

Price and choice ?

Personally stick to OEM sizes though a mate when he had a BMW S1000rr HP4 researched replacing the OEM 200/55 with the standard rrs 190/55 due to price and wider tire choice though ended staying with the 200s as the dealer recommended also reflashing the HP4s ECU to take into account the tyre size change for the banking abs & traction control.

 

Yea there's a lot of experimenting. I have a feeling folks are willing to do whats necessary for the money. I stay with stock sizing, but look at how the tire acts in regards to compounds. Some of these new tires really push what you can get away with. The only hic up was with the 4th gen, that 170 in today's stickier compound is hard to come by, in this case I went to the 180 with no noticeable set backs.